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  Subjects -> WATER RESOURCES (Total: 148 journals)
Showing 1 - 47 of 47 Journals sorted alphabetically
Acque Sotterranee - Italian Journal of Groundwater     Open Access   (Followers: 1)
Acta Limnologica Brasiliensia     Open Access   (Followers: 3)
Advances in Oceanography and Limnology     Open Access   (Followers: 11)
Advances in Water Resource and Protection     Open Access   (Followers: 10)
Advances in Water Resources     Hybrid Journal   (Followers: 39)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Agricultural Water Management     Hybrid Journal   (Followers: 35)
American Journal of Water Resources     Open Access   (Followers: 6)
American Water Works Association     Hybrid Journal   (Followers: 19)
Anales de Hidrología Médica     Open Access   (Followers: 1)
Annals of Warsaw University of Life Sciences - SGGW. Land Reclamation     Open Access  
Annual Review of Marine Science     Full-text available via subscription   (Followers: 11)
Applied Water Science     Open Access   (Followers: 6)
Aquacultural Engineering     Hybrid Journal   (Followers: 6)
Aquaculture     Hybrid Journal   (Followers: 31)
Aquaculture Environment Interactions     Open Access   (Followers: 2)
Aquaculture Research     Hybrid Journal   (Followers: 31)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 34)
Aquatic Geochemistry     Hybrid Journal   (Followers: 3)
Aquatic Living Resources     Hybrid Journal   (Followers: 11)
Aquatic Procedia     Open Access   (Followers: 2)
Aquatic Science and Technology     Open Access   (Followers: 3)
Aquatic Sciences     Hybrid Journal   (Followers: 12)
Asian Journal of Rural Development     Open Access   (Followers: 7)
Australian Journal of Water Resources     Full-text available via subscription   (Followers: 6)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 21)
Civil and Environmental Research     Open Access   (Followers: 17)
CLEAN - Soil, Air, Water     Hybrid Journal   (Followers: 19)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 4)
Cost Effectiveness and Resource Allocation     Open Access   (Followers: 5)
Desalination     Hybrid Journal   (Followers: 6)
Desalination and Water Treatment     Hybrid Journal   (Followers: 10)
Developments in Water Science     Full-text available via subscription   (Followers: 8)
Ecological Chemistry and Engineering S     Open Access   (Followers: 3)
Environmental Science : Water Research & Technology     Full-text available via subscription   (Followers: 4)
Environmental Toxicology     Hybrid Journal   (Followers: 7)
EQA - International Journal of Environmental Quality     Open Access   (Followers: 1)
European journal of water quality - Journal européen d'hydrologie     Full-text available via subscription   (Followers: 5)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 17)
Groundwater for Sustainable Development     Full-text available via subscription  
Grundwasser     Hybrid Journal  
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (Followers: 4)
Hydrology Research     Partially Free   (Followers: 12)
Hydrology: Current Research     Open Access   (Followers: 11)
IDA Journal of Desalination and Water Reuse     Hybrid Journal   (Followers: 1)
Ingeniería del agua     Open Access  
International Journal of Climatology     Hybrid Journal   (Followers: 24)
International Journal of Hydrology Science and Technology     Hybrid Journal   (Followers: 5)
International Journal of Nuclear Desalination     Hybrid Journal  
International Journal of River Basin Management     Hybrid Journal   (Followers: 1)
International Journal of Salt Lake Research     Hybrid Journal   (Followers: 2)
International Journal of Waste Resources     Open Access   (Followers: 4)
International Journal of Water     Hybrid Journal   (Followers: 14)
International Journal of Water Resources and Environmental Engineering     Open Access   (Followers: 9)
International Journal of Water Resources Development     Hybrid Journal   (Followers: 22)
International Soil and Water Conservation Research     Open Access  
Irrigation and Drainage     Hybrid Journal   (Followers: 12)
Irrigation Science     Hybrid Journal   (Followers: 4)
Journal of Aquatic Sciences     Full-text available via subscription   (Followers: 2)
Journal of Contemporary Water Resource & Education     Hybrid Journal   (Followers: 3)
Journal of Environmental Health Science & Engineering     Open Access   (Followers: 1)
Journal of Fisheries and Aquatic Science     Open Access   (Followers: 6)
Journal of Geophysical Research : Oceans     Partially Free   (Followers: 48)
Journal of Hydro-environment Research     Full-text available via subscription   (Followers: 9)
Journal of Hydroinformatics     Full-text available via subscription   (Followers: 2)
Journal of Hydrology (New Zealand)     Full-text available via subscription   (Followers: 1)
Journal of Hydrology and Hydromechanics     Open Access   (Followers: 2)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 6)
Journal of Limnology     Open Access   (Followers: 6)
Journal of the American Water Resources Association     Hybrid Journal   (Followers: 28)
Journal of Water and Climate Change     Partially Free   (Followers: 37)
Journal of Water and Health     Partially Free   (Followers: 3)
Journal of Water Chemistry and Technology     Hybrid Journal   (Followers: 9)
Journal of Water Process Engineering     Full-text available via subscription   (Followers: 4)
Journal of Water Resource and Hydraulic Engineering     Open Access   (Followers: 9)
Journal of Water Resource and Protection     Open Access   (Followers: 9)
Journal of Water Resource Engineering and Management     Full-text available via subscription   (Followers: 3)
Journal of Water Resources Planning and Management     Full-text available via subscription   (Followers: 46)
Journal of Water Reuse and Desalination     Partially Free   (Followers: 6)
Journal of Water Science & Environment Technologies     Open Access   (Followers: 2)
Journal of Water Security     Open Access   (Followers: 1)
Journal of Water Supply : Research and Technology - AQUA     Partially Free   (Followers: 7)
Journal of Water, Sanitation and Hygiene for Development     Open Access   (Followers: 4)
La Houille Blanche     Full-text available via subscription   (Followers: 1)
Lake and Reservoir Management     Hybrid Journal   (Followers: 6)
Lakes & Reservoirs Research & Management     Hybrid Journal   (Followers: 13)
Large Marine Ecosystems     Full-text available via subscription  
Liquid Waste Recovery     Open Access  
Mangroves and Salt Marshes     Hybrid Journal   (Followers: 2)
Marine and Freshwater Behaviour and Physiology     Hybrid Journal   (Followers: 1)
Marine Ecology Progress Series MEPS     Hybrid Journal   (Followers: 23)
Marine Ecosystem Stressor Response     Open Access  
Methods in Oceanography : An International Journal     Hybrid Journal   (Followers: 4)
New Zealand Journal of Marine and Freshwater Research     Hybrid Journal   (Followers: 6)
Open Journal of Modern Hydrology     Open Access   (Followers: 4)
Osterreichische Wasser- und Abfallwirtschaft     Hybrid Journal  
Ozone Science & Engineering     Hybrid Journal   (Followers: 1)
Paddy and Water Environment     Hybrid Journal   (Followers: 8)
Research Journal of Environmental Toxicology     Open Access   (Followers: 2)
Reviews in Aquaculture     Hybrid Journal   (Followers: 10)
Revue des sciences de l'eau / Journal of Water Science     Full-text available via subscription   (Followers: 2)
RIBAGUA - Revista Iberoamericana del Agua     Open Access  
Riparian Ecology and Conservation     Open Access   (Followers: 6)
River Research and Applications     Hybrid Journal   (Followers: 16)
River Systems     Full-text available via subscription   (Followers: 3)
SA Irrigation = SA Besproeiing     Full-text available via subscription   (Followers: 1)
SABI Magazine - Tydskrif     Full-text available via subscription  
San Francisco Estuary and Watershed Science     Open Access   (Followers: 1)
Sciences Eaux & Territoires : la Revue du Cemagref     Open Access  
Scientia Marina     Open Access   (Followers: 2)
Society & Natural Resources: An International Journal     Hybrid Journal   (Followers: 16)
Sri Lanka Journal of Aquatic Sciences     Open Access   (Followers: 1)
Sustainability of Water Quality and Ecology     Hybrid Journal   (Followers: 2)
Sustainable Technologies, Systems & Policies     Open Access   (Followers: 8)
Tecnología y Ciencias del Agua     Open Access  
Texas Water Journal     Open Access   (Followers: 2)
Urban Water Journal     Hybrid Journal   (Followers: 12)
Waste Technology     Open Access   (Followers: 3)
Water     Open Access   (Followers: 6)
Water & Sanitation Africa     Full-text available via subscription   (Followers: 3)
Water and Environment Journal     Hybrid Journal   (Followers: 19)
Water Environment and Technology     Full-text available via subscription   (Followers: 15)
Water Environment Research     Full-text available via subscription   (Followers: 40)
Water International     Hybrid Journal   (Followers: 13)
Water Policy     Partially Free   (Followers: 7)
Water Practice     Full-text available via subscription   (Followers: 3)
Water Practice and Technology     Full-text available via subscription   (Followers: 13)
Water Quality Research Journal of Canada     Full-text available via subscription   (Followers: 5)
Water Research     Hybrid Journal   (Followers: 51)
Water Resources     Hybrid Journal   (Followers: 18)
Water Resources and Economics     Hybrid Journal   (Followers: 3)
Water Resources and Industry     Open Access   (Followers: 3)
Water Resources and Rural Development     Hybrid Journal   (Followers: 2)
Water Resources Management     Hybrid Journal   (Followers: 32)
Water Resources Research     Full-text available via subscription   (Followers: 77)
Water SA     Open Access  
Water Science & Technology     Partially Free   (Followers: 25)
Water Science : The National Water Research Center Journal     Open Access   (Followers: 5)
Water Science and Engineering     Open Access   (Followers: 8)
Water Science and Technology : Water Supply     Partially Free   (Followers: 22)
Water Wheel     Open Access   (Followers: 2)
Water, Air, & Soil Pollution     Hybrid Journal   (Followers: 22)
Water21     Full-text available via subscription   (Followers: 1)
Waterlines     Full-text available via subscription   (Followers: 2)
Western Indian Ocean Journal of Marine Science     Open Access   (Followers: 1)
Wetlands Ecology and Management     Hybrid Journal   (Followers: 21)
Wiley Interdisciplinary Reviews : Water     Hybrid Journal  
WMU Journal of Maritime Affairs     Hybrid Journal   (Followers: 3)

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Journal Cover Water Resources Research
  [SJR: 2.661]   [H-I: 144]   [77 followers]  Follow
   Full-text available via subscription Subscription journal  (Not entitled to full-text)
   ISSN (Print) 0043-1397 - ISSN (Online) 1944-7973
   Published by AGU Homepage  [17 journals]
  • Mixing as a driver of temporal variations in river hydrochemistry. Part 2:
           Major and trace element concentration dynamics in the Andes-Amazon
    • Authors: J. Jotautas Baronas; Mark A. Torres, Kathryn E. Clark, A. Joshua West
      Abstract: Variations in riverine solute chemistry with changing runoff are used to interrogate catchment hydrology and to investigate chemical reactions in Earth's critical zone. This approach requires some understanding of how spatial and temporal averaging of solute-generating reactions affect the dissolved load of rivers and streams. In this study, we investigate the concentration-runoff (C-Q) dynamics of a suite of major (Na, Mg, Ca, Si, K, and SO4) and trace (Al, Ba, Cd, Co, Cr, Cu, Fe, Ge, Li, Mn, Mo, Nd, Ni, Rb, Sr, U, V, and Zn) elements in nested catchments of variable size, spanning the geomorphic gradient from the Andes mountains to the Amazon foreland-floodplain. The major elements exhibit various degrees of dilution with increasing runoff at all sites, whereas the concentrations of most trace elements either increase or show no relationship with increasing runoff in the three larger catchments (160 to 28 000 km2 area). We show that the observed mainstem C-Q dynamics are influenced by variable mixing of tributaries with distinct C-Q relationships. Trace element C-Q relationships are more variable among tributaries relative to major elements, which could be the result of variations in geomorphology, lithology, and hydrology of the sub-catchments. Certain trace metals are also lost from solution during in-channel processes (possibly related to colloidal size-partitioning), which may exert an additional control on C-Q dynamics. Overall, we suggest that aggregation effects should be assessed in heterogeneous catchments before C-Q or ratio-Q relationships can be interpreted as reflecting catchment-wide solute generation processes and their relationship to hydrology. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:15:39.992386-05:
      DOI: 10.1002/2016WR019729
  • Mixing as a driver of temporal variations in river hydrochemistry. Part 1:
           Insights from conservative tracers in the Andes-Amazon transition
    • Authors: Mark A. Torres; J. Jotautas Baronas, Kathryn E. Clark, Sarah J. Feakins, A. Joshua West
      Abstract: The response of hillslope processes to changes in precipitation may drive the observed changes in the solute geochemistry of rivers with discharge. This conjecture is most robust when variations in the key environmental factors that affect hillslope processes (e.g., lithology, erosion rate, and climate) are minimal across a river's catchment area. For rivers with heterogenous catchments, temporal variations in the relative contributions of different tributary sub-catchments may modulate variations in solute geochemistry with runoff. In the absence of a dense network of hydrologic gauging stations, alternative approaches are required to distinguish between the different drivers of temporal variability in river solute concentrations. In this contribution, we apportion the water and solute fluxes of a reach of the Madre de Dios River (Peru) between its four major tributary sub-catchments during two sampling campaigns (wet and dry seasons) using spatial variations in conservative tracers. Guided by the results of a mixing model, we identify temporal variations in solute concentrations of the mainstem Madre de Dios that are due to changes in the relative contributions of each tributary. Our results suggest that variations in tributary mixing are, in part, responsible for the observed concentration-discharge (C-Q) relationships. The implications of these results are further explored by re-analyzing previously published C-Q data from this region, developing a theoretical model of tributary mixing, and, in a companion paper, comparing the C-Q behavior of a suite of major and trace elements in the Madre de Dios River system. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:15:31.304506-05:
      DOI: 10.1002/2016WR019733
  • Posterior population expansion for solving inverse problems
    • Authors: C. Jäggli; J. Straubhaar, P. Renard
      Abstract: Solving inverse problems in a complex, geologically realistic, and discrete model space and from a sparse set of observations is a very challenging task. Extensive exploration by Markov chain Monte Carlo (McMC) methods often results in considerable computational efforts. Most optimization methods, on the other hand, are limited to linear (continuous) model spaces and the minimization of an objective function, what often proves to be insufficient. To overcome these problems, we propose a new ensemble based exploration scheme for geostatistical prior models generated by a multiple-point statistics (MPS) tool. The principle of our method is to expand an existing set of models by using posterior facies information for conditioning new MPS realizations. The algorithm is independent of the physical parametrization. It is tested on a simple synthetic inverse problem. When compared to two existing McMC methods (Iterative Spatial Resampling (ISR) and Interrupted Markov chain Monte Carlo (IMcMC)) the required number of forward model runs was divided by a factor of 8-12. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:05:45.239707-05:
      DOI: 10.1002/2016WR019550
  • The impact of sedimentary anisotropy on solute mixing in stacked
           scour-pool structures
    • Authors: Jeremy P. Bennett; Claus P. Haslauer, Olaf A. Cirpka
      Abstract: The spatial variability of hydraulic conductivity is known to have a strong impact on solute spreading and mixing. In most investigations, its local anisotropy has been neglected. Recent studies have shown that spatially varying orientation in sedimentary anisotropy can lead to twisting flow enhancing transverse mixing, but most of these studies used geologically implausible geometries. We use an object-based approach to generate stacked scour-pool structures with either isotropic or anisotropic filling which are typically reported in glacial outwash deposits. We analyze how spatially variable isotropic conductivity and variation of internal anisotropy in these features impacts transverse plume deformation and both longitudinal and transverse spreading and mixing. In five test cases either the scalar values of conductivity or the spatial orientation of its anisotropy is varied between the scour- pool structures. Based on 100 random configurations, we compare the variability of velocity components, stretching and folding metrics, advective travel-time distributions, one- and two-particle statistics in advective-dispersive transport, and the flux-related dilution indices for steady-state advective-dispersive transport among the five test cases. Variation in the orientation of internal anisotropy causes strong variability in the lateral velocity components, which leads to deformation in transverse directions and enhances transverse mixing, whereas it hardly affects the variability of the longitudinal velocity component and thus longitudinal spreading and mixing. The latter is controlled by the spatial variability in the scalar values of hydraulic conductivity. Our results demonstrate that sedimentary anisotropy is important for transverse mixing, whereas it may be neglected when considering longitudinal spreading and mixing. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:05:42.990487-05:
      DOI: 10.1002/2016WR019665
  • Modeling complex flow structures and drag around a submerged plant of
           varied posture
    • Authors: Richard J. Boothroyd; Richard J. Hardy, Jeff Warburton, Timothy I. Marjoribanks
      Abstract: Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple, and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time-averaged plant posture, collected through Terrestrial Laser Scanning, into a Computational Fluid Dynamics model to predict flow around a submerged riparian plant. For three depth-limited flow conditions (Reynolds number = 65 000 – 110 000), plant dynamics were recorded through high-definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin–Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in-stream drag, and allows a physically determined, species-dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:05:38.986329-05:
      DOI: 10.1002/2016WR020186
  • Representative point-integrated suspended sediment sampling in rivers
    • Authors: A.B. Gitto; J.G. Venditti, R. Kostaschuk, M. Church
      Abstract: The vast majority of continental sediment delivered to the world's oceans moves by suspension in rivers. Depth- or point-integrated bottle sampling are the traditional methods used to determine the mean concentration of suspended sediment in rivers. While there has been some investigation of the error associated with depth-integrated sampling, the representativeness of a point-integrated bottle sample has not been addressed in the literature. Here, we analyze continuous hour-long measurements of suspended sediment and grain size fractions collected using a LISST-SL in the sand-bed portion of the Fraser River, British Columbia to determine an appropriate sampling time. The 2σ uncertainty range of individual 30 s samples varied from ±3% to ±33% about the observed mean, with a systematic increase toward the streambed. Mean concentrations for suspended sediment and grain size fractions were computed over increasing time periods and compared with a long duration mean concentration to determine when a sample becomes representative. A cumulative probability distribution was generated from multiple iterations of this process. All suspended sediment load and grain size fractions bear a low probability of representing the actual mean concentration over standard bottle sample durations. A probability >90% of representing the mean concentration and grain-size of various fractions requires ∼570 seconds (9.5 minutes) of sampling. Sampling for a shorter period of 264 seconds (4.4 minutes) can yield a sample with 73% probability of representing the mean concentration. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-17T19:05:34.457019-05:
      DOI: 10.1002/2016WR019187
  • Impact of eliminating fracture intersection nodes in multiphase
           compositional flow simulation
    • Authors: Kenneth M. Walton; Andre J. A. Unger, Marios A. Ioannidis, Beth L. Parker
      Abstract: Algebraic elimination of nodes at discrete fracture intersections via the star-delta technique has proven to be a valuable tool for making multiphase numerical simulations more tractable and efficient. This study examines the assumptions of the star-delta technique and exposes its effects in a 3D, multiphase context for advective and dispersive/diffusive fluxes. Key issues of relative permeability-saturation-capillary pressure (kr-S-Pc) and capillary barriers at fracture-fracture intersections are discussed. This study uses a multiphase compositional, finite difference numerical model in discrete fracture network (DFN) and discrete fracture-matrix (DFM) modes. It verifies that the numerical model replicates analytical solutions and performs adequately in convergence exercises (conservative and decaying tracer, one- and two-phase flow, DFM and DFN domains). The study culminates in simulations of a two-phase laboratory experiment in which a fluid invades a simple fracture intersection. The experiment and simulations evoke different invading fluid flow paths by varying fracture apertures as oil invades water-filled fractures and as water invades air-filled fractures. Results indicate that the node elimination technique as implemented in numerical model correctly reproduces the long-term flow path of the invading fluid, but that short-term temporal effects of the capillary traps and barriers arising from the intersection node are lost. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T11:06:43.076938-05:
      DOI: 10.1002/2016WR020088
  • A method for preferential selection of dates in the Schaake shuffle
           approach to constructing spatiotemporal forecast fields of temperature and
    • Authors: Michael Scheuerer; Thomas M. Hamill, Brett Whitin, Minxue He, Arthur Henkel
      Abstract: Hydrological forecasts strongly rely on predictions of precipitation amounts and temperature as meteorological forcings for hydrological models. Ensemble weather predictions provide a number of different scenarios that reflect the uncertainty about these meteorological inputs, but these are often biased and under-dispersive, and therefore require statistical post-processing. In addition to correcting the marginal distributions of the two weather variables, post-processing methods must reconstruct their spatial, temporal, and inter-variable dependence in order to generate physically realistic forecast trajectories that can be used as forcings of hydrological streamflow forecast models.For many years, a sample reordering method referred to as “Schaake shuffle” has been used successfully to address this multivariate aspect of forecast distributions by using historical observation trajectories as multivariate “dependence templates”. This paper proposes a variant of the Schaake shuffle, in which the historical dates are selected such that the marginal distributions of the corresponding observation trajectories are similar to the forecast marginal distributions, thus making it more likely that spatial and temporal gradients are preserved during the reordering procedure. This new approach is demonstrated with temperature and precipitation forecasts over four river basins in California, and it is shown to improve upon the standard Schaake shuffle both with respect to verification metrics applied to the forcings, and verification metrics applied to the resulting streamflow predictions. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T11:01:05.425418-05:
      DOI: 10.1002/2016WR020133
  • Hyphenated hydrology: Interdisciplinary evolution of water resource
    • Authors: K.L. McCurley; J.W. Jawitz
      Abstract: Hydrology has advanced considerably as a scientific discipline since its recognized inception in the mid-20th century. Modern water resource related questions have forced adaptation from exclusively physical or engineering science viewpoints toward a deliberate interdisciplinary context. Over the past few decades, many of the eventual manifestations of this evolution were foreseen by prominent expert hydrologists. However, their narrative descriptions have lacked substantial quantification. This study addressed that gap by measuring the prevalence of and analyzing the relationships between the terms most frequently used by hydrologists to define and describe their research. We analyzed 16,591 journal article titles from 1965-2015 in Water Resources Research, through which the scientific dialogue and its time-sensitive progression emerged. Our word frequency and term co-occurrence network results revealed the dynamic timing of the lateral movement of hydrology across multiple disciplines as well as the deepening of scientific discourse with respect to traditional hydrologic questions. The conversation among water resource scientists surrounding the hydrologic sub-disciplines of catchment-hydrology, hydro-meteorology, socio-hydrology, hydro-climatology and eco-hydrology all gained statistically significant momentum in the analyzed time period, while hydro-geology and contaminant-hydrology experienced periods of increase followed by significant decline. This study concludes that formerly exotic disciplines can potentially modify hydrology, prompting new insights and inspiring unconventional perspectives on old questions that may have otherwise become obsolete. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T11:00:46.099892-05:
      DOI: 10.1002/2016WR019835
  • Multiscale temporal variability and regional patterns in 555 years of
           conterminous U.S. streamflow
    • Authors: Michelle Ho; Upmanu Lall, Xun Sun, Edward R. Cook
      Abstract: The development of paleoclimate streamflow reconstructions in the conterminous United States (CONUS) has provided water resource managers with improved insights into multi-decadal and centennial scale variability that cannot be reliably detected using shorter instrumental records. Paleoclimate streamflow reconstructions have largely focused on individual catchments limiting the ability to quantify variability across the CONUS. The Living Blended Drought Atlas (LBDA), a spatially and temporally complete 555-year-long paleoclimate record of summer drought across the CONUS, provides an opportunity to reconstruct and characterize streamflow variability at a continental scale. We explore the validity of the first paleo reconstructions of streamflow that span the CONUS informed by the LBDA targeting a set of US Geological Survey streamflow sites. The reconstructions are skillful under cross validation across most of the country, but the variance explained is generally low. Spatial and temporal structures of streamflow variability are analyzed using hierarchical clustering, principal component analysis, and wavelet analyses. Nine spatially coherent clusters are identified. The reconstructions show signals of contemporary droughts such as the Dust Bowl (1930s) and 1950s droughts. Decadal-scale variability was detected in the late 1900s in the western US, however, similar modes of temporal variability were rarely present prior to the 1950s. The 20th century featured longer wet spells and shorter dry spells compared with the preceding 450 years. Streamflow in the Pacific Northwest and Northeast are negatively correlated with the central US suggesting the potential to mitigate some drought impacts by balancing economic activities and insurance pools across these regions during major droughts. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T10:51:44.057466-05:
      DOI: 10.1002/2016WR019632
  • Theoretical analysis of non-Gaussian heterogeneity effects on subsurface
           flow and transport
    • Authors: Monica Riva; Alberto Guadagnini, Shlomo P. Neuman
      Abstract: Much of the stochastic groundwater literature is devoted to the analysis of flow and transport in Gaussian or multi-Gaussian log hydraulic conductivity (or transmissivity) fields, Y(x) =ln K(x) (x being a position vector), characterized by one or (less frequently) a multiplicity of spatial correlation scales. Yet Y, as well as many other variables and their (spatial or temporal) increments, ΔY, are known to be generally non-Gaussian. One common manifestation of non-Gaussianity is that whereas frequency distributions of Y often exhibit mild peaks and light tails, those of increments ΔY are generally symmetric with peaks that grow sharper, and tails that become heavier, as separation scale or lag between pairs of Y values decreases. A statistical model that captures these disparate, scale-dependent distributions of Y and ΔY in a unified and consistent manner has been recently proposed by us. This new “generalized sub-Gaussian (GSG)” model has the form Y(x) = U(x) G(x) where G(x) is (generally, but not necessarily) a multi-scale Gaussian random field and U(x) is a non-negative subordinator independent of G. The purpose of this paper is to explore analytically, in an elementary manner, lead-order effects that non-Gaussian heterogeneity described by the GSG model have on the stochastic description of flow and transport. Recognizing that perturbation expansion of hydraulic conductivity K = eY diverges when Y is sub-Gaussian, we render the expansion convergent by truncating Y's domain of definition. We then demonstrate theoretically and illustrate by way of numerical examples that, as the domain of truncation expands, (a) the variance of truncated Y (denoted by Yt) approaches that of Y, (b) the pdf (and thereby moments) of Yt increments approach those of Y increments and, as a consequence, the variogram of Yt approaches that of Y. This in turn guarantees that perturbing Kt=eYt to second order in σYt (the standard deviation of Yt) yields results which approach those we obtain upon perturbing K = eY to second order in σY even as the corresponding series diverges. Our analysis is rendered mathematically tractable by considering mean uniform steady state flow in an unbounded, two-dimensional domain of mildly heterogeneous Y with a single-scale function G having an isotropic exponential covariance. Results consist of expressions for (a) lead order autocovariance and cross-covariance functions of hydraulic head, velocity and advective particle displacement and (b) analogues of preasymptotic as well as asymptotic Fickian dispersion coefficients. We compare these theoretically and graphically with corresponding expressions developed in the literature for Gaussian Y. We find the former to differ from the latter by a factor k = 〈 U2 〉/〈 U 〉2 (〈〉 denoting ensemble expectation) and the GSG covariance of longitudinal velocity to contain an additional nugget term depending on this same factor. In the limit as Y becomes Gaussian k reduces to one and the nugget term drops out. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T10:51:26.779809-05:
      DOI: 10.1002/2016WR019353
  • Peaks over threshold (POT): A methodology for automatic threshold
           estimation using goodness-of-fit p-value
    • Authors: Sebastián Solari; Marta Egüen, María José Polo, Miguel A. Losada
      Abstract: Threshold estimation in the Peaks Over Threshold (POT) method, and the impact of the estimation method on the calculation of high return period quantiles and their uncertainty (or confidence intervals) are issues that are still unresolved. In the past, methods based on goodness-of-fit tests and EDF-statistics have yielded satisfactory results, but their use has not yet been systematized.This paper proposes a methodology for automatic threshold estimation, based on the Anderson-Darling EDF-statistic and goodness-of-fit test. When combined with bootstrapping techniques, this methodology can be used to quantify both the uncertainty of threshold estimation and its impact on the uncertainty of high return period quantiles.This methodology was applied to several simulated series and to four precipitation/riverflow data series. The results obtained confirmed its robustness. For the measured series, the estimated thresholds corresponded to those obtained by non-automatic methods. Moreover, even though the uncertainty of the threshold estimation was high, this did not have a significant effect on the width of the confidence intervals of high return period quantiles. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T10:51:06.215081-05:
      DOI: 10.1002/2016WR019426
  • Biofuel as an integrated farm drainage management crop: A bio-economic
    • Authors: L.R. Levers; K.A. Schwabe
      Abstract: Irrigated agricultural lands in arid regions often suffer from soil salinization and lack of drainage, which affect environmental quality and productivity. Integrated Farm Drainage Management (IFDM) systems, where drainage water generated from higher-valued crops grown on high quality soils are used to irrigate salt tolerant crops grown on marginal soils, is one possible strategy for managing salinity and drainage problems. If the IFDM crop were a biofuel crop, both environmental and private benefits may be generated; however, little is known about this possibility. As such, we develop a bio-economic programming model of irrigated agricultural production to examine the role salt-tolerant biofuel crops might play within an IFDM system. Our results, generated by optimizing profits over land, water, and crop choice decisions subject to resource constraints, suggest that based on the private profits alone, biofuel crops can be a competitive alternative to the common practices of land retirement and non-biofuel crop production under both low to high drainage water salinity. Yet, IFDM biofuel crop production generates 30 to 35 percent fewer GHG emissions than the other strategies. The private market competitiveness coupled with the public good benefits may justify policy changes encouraging the growth of IFDM biofuel crops in arid agricultural areas globally. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T10:50:46.605161-05:
      DOI: 10.1002/2016WR019773
  • A regional and non-stationary model for Partial Duration Series of extreme
    • Authors: Ida Bülow Gregersen; Henrik Madsen, Dan Rosbjerg, Karsten Arnbjerg-Nielsen
      Abstract: Regional extreme value models for estimation of extreme rainfall intensities are widely applied, but their underlying assumption of stationarity is challenged. Many recent studies show that the rainfall extremes worldwide exhibit a non-stationary behavior. This paper presents a spatio-temporal model of extreme rainfall. The framework is built on a Partial Duration Series approach with a non-stationary, regional threshold value. The model is based on Generalized Linear Regression solved by Generalized Estimation Equations. It allows a spatial correlation between the stations in the network and accounts furthermore for variable observation periods at each station and in each year. Marginal regional and temporal regression models solved by Generalized Least Squares are used to validate and discuss the results of the full spatio-temporal model.The model is applied on data from a large Danish rain gauge network for four durations ranging from 10 minutes to 24 hours. The observation period differs between stations, and the number of stations with more than 10 years of observations has increased over the years. A spatio-temporal model for the threshold is suggested, applying the Mean Annual Precipitation and time as the explanatory variables in the regional and temporal domain, respectively. Further analysis of Partial Duration Series with non-stationary and regional thresholds shows that the mean exceedances also exhibit a significant variation in space and time for some rainfall durations, while the shape parameter is found to be constant. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-16T05:40:54.624446-05:
      DOI: 10.1002/2016WR019554
  • The Future of Evapotranspiration: Global requirements for ecosystem
           functioning, carbon and climate feedbacks, agricultural management, and
           water resources
    • Authors: Joshua B. Fisher; Forrest Melton, Elizabeth Middleton, Christopher Hain, Martha Anderson, Richard Allen, Matthew McCabe, Simon Hook, Dennis Baldocchi, Philip A. Townsend, Ayse Kilic, Kevin Tu, Diego Miralles, Johan Perret, Jean-Pierre Lagouarde, Duane Waliser, Adam J. Purdy, Andrew French, David Schimel, James S. Famiglietti, Graeme Stephens, Eric F. Wood
      Abstract: The fate of the terrestrial biosphere is highly uncertain given recent and projected changes in climate. This is especially acute for impacts associated with changes in drought frequency and intensity on the distribution and timing of water availability. The development of effective adaptation strategies for these emerging threats to food and water security are compromised by limitations in our understanding of how natural and managed ecosystems are responding to changing hydrological and climatological regimes. This information gap is exacerbated by insufficient monitoring capabilities from local to global scales. Here, we describe how evapotranspiration (ET) represents the key variable in linking ecosystem functioning, carbon and climate feedbacks, agricultural management, and water resources, and highlight both the outstanding science and applications questions and the actions, especially from a space-based perspective, necessary to advance them. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-11T03:50:29.505917-05:
      DOI: 10.1002/2016WR020175
  • A new model for predicting the drag exerted by vegetation canopies
    • Authors: Vahid Etminan; Ryan J. Lowe, Marco Ghisalberti
      Abstract: The influence of vegetation canopies on the flow structure in streams, rivers and floodplains is heavily dependent on the cumulative drag forces exerted by the vegetation. The drag coefficient of vegetation elements within a canopy has been shown to be significantly different to well-established values for a single element in isolation. This study investigates the mechanisms that determine canopy flow resistance and proposes a new model for predicting canopy drag coefficients. Large Eddy Simulations were used to investigate the fine-scale hydrodynamics within emergent canopies with solid area fractions (λ) ranging from 0.016 to 0.25. The influence of three mechanisms in modifying canopy drag, namely blockage, sheltering and delayed separation, were investigated. While the effects of sheltering and delayed separation were found to slightly reduce the drag of very sparse canopies, the blockage effect significantly increased the drag of denser canopies (λ ≳ 0.04). Furthermore, an analogy drawn between canopy flow and wall-confined flow around bluff bodies is used to propose an alternative reference velocity to the conventional spatially-averaged velocity, namely the constricted cross-section velocity (Uc), to redefine the canopy drag coefficient. Through comparison with both prior experimental data and the present numerical simulations, typical formulations for the drag coefficient of a single cylinder are shown to accurately predict the drag coefficient of staggered emergent canopies when Uc is used as the reference velocity. Finally, it is shown that this new model can be extended to predict the bulk drag coefficient of randomly-arranged vegetation canopies. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-11T03:45:32.914639-05:
      DOI: 10.1002/2016WR020090
  • Validation of SMAP soil moisture for the SMAPVEX15 field campaign using a
           hyper-resolution model
    • Authors: Xitian Cai; Ming Pan, Nathaniel W. Chaney, Andreas Colliander, Sidharth Misra, Michael H. Cosh, Wade T. Crow, Thomas J. Jackson, Eric F. Wood
      Abstract: Accurate global mapping of soil moisture is the goal of the Soil Moisture Active Passive (SMAP) mission, which is expected to improve the estimation of water, energy, and carbon exchanges between the land and the atmosphere. Like other satellite products, the SMAP soil moisture retrievals need to be validated, with the validation relying heavily on in situ measurements. However, a one-to-one comparison is ill-advised due to the spatial mismatch of the large SMAP footprint (∼40 km) and the point scale in situ measurements. This study uses a recently developed hyper-resolution land surface model—HydroBlocks—as a tool to upscale in situ soil moisture measurements for the SMAPVEX15 (SMAP Validation Experiment 2015) field campaign during August 2-18, 2015. Calibrated against in situ observation, HydroBlocks shows a satisfactory Kling-Gupta efficiency (KGE) of 0.817 and RMSE of 0.019 m3/m3 for the calibration period. These results indicate that HydroBlocks can be used to upscale in situ measurements for this site. Different from previous studies, here in situ measurements are upscaled using a land surface model without bias correction. The upscaled soil moisture is then used to evaluate SMAP (passive) soil moisture products. The comparison of the upscaled network to SMAP shows that the retrievals are generally able to capture the areal-averaged soil moisture temporal variations. However, SMAP appears to be over sensitive to summer precipitation. We expect these findings can be used to improve the SMAP soil moisture product and thus facilitate its usage in studying the water, energy, and carbon cycles. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-11T03:45:25.661585-05:
      DOI: 10.1002/2016WR019967
  • Development of a Water and Enthalpy Budget-based Glacier mass balance
           Model (WEB-GM) and its preliminary validation
    • Authors: Baohong Ding; Kun Yang, Wei Yang, Xiaobo He, Yingying Chen, Zhu La, Xiaofeng Guo, Lei Wang, Hui Wu, Tandong Yao
      Abstract: This paper presents a new water and energy budget-based glacier mass balance model. Enthalpy, rather than temperature, is used in the energy balance equations to simplify the computation of the energy transfers through the water phase change and the movement of liquid water in the snow. A new parameterization for albedo estimation and state-of-the-art parameterization schemes for rainfall/snowfall type identification and surface turbulent heat flux calculations are implemented in the model. This model was driven with meteorological data and evaluated using mass balance and turbulent flux data collected during a field experiment implemented in the ablation zone of the Parlung No. 4 Glacier on the Southeast Tibetan Plateau during 2009 and 2015–2016. The evaluation shows that the model can reproduce the observed glacier ablation depth, surface albedo, surface temperature, sensible heat flux, and latent heat flux with high accuracy. Comparing with a traditional energy budget-based glacier mass balance model, this enthalpy-based model shows a superior capacity in simulation accuracy. Therefore, this model can reasonably simulate the energy budget and mass balance of glacier melting in this region and be used as a component of land surface models and hydrological models. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T19:07:11.799814-05:
      DOI: 10.1002/2016WR018865
  • Potential effects of landscape change on water supplies in the presence of
           reservoir storage
    • Authors: Andrew J. Guswa; Perrine Hamel, P. James Dennedy-Frank
      Abstract: This work presents a set of methods to evaluate the potential effects of landscape changes on water supplies. Potential impacts are a function of the seasonality of precipitation, losses of water to evapotranspiration and deep recharge, the flow-regulating ability of watersheds, and the availability of reservoir storage. For a given reservoir capacity, simple reservoir simulations with daily precipitation and streamflow enable the determination of the maximum steady supply of water for both the existing watershed and a hypothetical counter-factual that has neither flow-regulating benefits nor any losses. These two supply values, representing land-use end-members, create an envelope that defines the water supply-service and bounds the effect of landscape change on water supply. These bounds can be used to discriminate between water supplies that may be vulnerable to landscape change and those that are unlikely to be affected. Two indices of the water-supply service exhibit substantial variability across 593 watersheds in the continental United States. Rcross, the reservoir capacity at which landscape change is unlikely to have any detrimental effect on water supply has an interquartile range of 0.14% to 4% of mean-annual-streamflow. Steep, forested watersheds with seasonal climates tend to have greater service values, and the indices of water-supply service are positively correlated with runoff ratios during the months with lowest flows. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T19:07:10.027457-05:
      DOI: 10.1002/2016WR019691
  • The mechanistic basis for storage-dependent age distributions of water
           discharged from an experimental hillslope
    • Authors: Luke A. Pangle; Minseok Kim, Charlene Cardoso, Marco Lora, Antonio A. Meira Neto, Till H.M. Volkmann, Yadi Wang, Peter A Troch, Ciaran J. Harman
      Abstract: Distributions of water transit times (TTDs), and related storage-selection (SAS) distributions, are spatially-integrated metrics of hydrological transport within landscapes. Recent works confirm that the form of TTDs and SAS distributions should be considered time-variant—possibly depending, in predictable ways, on the dynamic storage of water within the landscape. We report on a 28-day periodic-steady-state-tracer experiment performed on a model hillslope contained within a 1-m3 sloping lysimeter. Using experimental data, we calibrate physically-based, spatially-distributed flow and transport models, and use the calibrated models to generate time-variable SAS distributions, which are subsequently compared to those directly observed from the actual experiment. The objective is to use the spatially-distributed estimates of storage and flux from the model to characterize how temporal variation in water storage influences temporal variation in flow-path configurations, and resulting SAS distributions. The simulated SAS distributions mimicked well the shape of observed distributions, once the model domain reflected the spatial heterogeneity of the lysimeter soil. The spatially-distributed flux vectors illustrate how the magnitude and directionality of water flux changes as the water-table surface rises and falls, yielding greater contributions of younger water when the water-table surface rises nearer to the soil surface. The illustrated mechanism is compliant with conclusions drawn from other recent studies, and supports the notion of an inverse-storage effect, whereby the probability of younger water exiting the system increases with storage. This mechanism may be prevalent in hillslopes and headwater catchments where discharge dynamics are controlled by vertical fluctuations in the water-table surface of an unconfined aquifer. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T19:01:39.992075-05:
      DOI: 10.1002/2016WR019901
  • Incorporating geologic information into hydraulic tomography: A general
           framework based on geostatistical approach
    • Authors: Yuanyuan Zha; Tian-Chyi J. Yeh, Walter A. Illman, Hironori Onoe, Chin Man, W. Mok, Jet-Chau Wen, Shao-Yang Huang, Wenke Wang
      Abstract: Hydraulic tomography (HT) has become a mature aquifer test technology over the last two decades. It collects non-redundant information of aquifer heterogeneity by sequentially stressing the aquifer at different wells and collecting aquifer responses at other wells during each stress. The collected information is then interpreted by inverse models. Among these models, the geostatistical approaches, built upon the Bayesian framework, first conceptualize hydraulic properties to be estimated as random fields, which are characterized by means and covariance functions. They then use the spatial statistics as prior information with the aquifer response data to estimate the spatial distribution of the hydraulic properties at a site. Since the spatial statistics describe the generic spatial structures of the geologic media at the site rather than site-specific ones (e.g., known spatial distributions of facies, faults, or paleochannels), the estimates are often not optimal. To improve the estimates, we introduce a general statistical framework, which allows the inclusion of site-specific spatial patterns of geologic features. Subsequently, we test this approach with synthetic numerical experiments. Results show that this approach, using conditional mean and covariance that reflect site-specific large-scale geologic features, indeed improves the HT estimates. Afterward, this approach is applied to HT surveys at a kilometer-scale fractured granite field site with a distinct fault zone. We find that by including fault information from outcrops and boreholes for HT analysis, the estimated hydraulic properties are improved. The improved estimates subsequently lead to better prediction of flow during a different pumping test at the site. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T19:01:37.525087-05:
      DOI: 10.1002/2016WR019185
  • Gas bubble size estimation in peat soils from EM wave scattering observed
           with ground penetrating radar
    • Authors: Neil Terry; Lee Slater
      Abstract: The size of biogenic gas bubbles in peatlands is believed to regulate ebullition of carbon gases to the atmosphere. The measurement of electromagnetic (EM) wave travel times using ground penetrating radar (GPR) is a proven field-scale method for indirect estimation of volumetric gas content. However, there is also the possibility that information on the size of the gas bubbles can be determined from the analysis of the spectral content of GPR signals as scattering attenuation possesses a frequency dependence for bubbles smaller than the EM wavelength (Rayleigh type scattering). Theoretical modeling shows that GPR data acquired with typical antenna frequencies are likely to be affected by bubble size in peat soils. Analysis of GPR data from two recent studies on peat monoliths where biogenic gas production was documented produced results consistent with the model predictions. Using the approach, zero offset cross borehole GPR data in a northern peatland suggest that large bubble clusters (i.e., 0.05 m radius) occur in peat. These findings broaden the utility of GPR for providing information on biogenic gas dynamics in peatlands. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T19:01:34.954598-05:
      DOI: 10.1002/2016WR019783
  • Developing reservoir monthly inflow forecasts using Artificial
           Intelligence and Climate Phenomenon Information
    • Authors: Tiantian Yang; Ata Akbari Asanjan, Edwin Welles, Xiaogang Gao, Soroosh Sorooshian, Xiaomang Liu
      Abstract: Reservoirs are fundamental human-built infrastructures that collect, store, and deliver fresh surface water in a timely manner for many purposes. Efficient reservoir operation requires policy makers and operators to understand how reservoir inflows are changing under different hydrological and climatic conditions to enable forecast-informed operations. Over the last decade, the uses of Artificial Intelligence and Data Mining (AI & DM) techniques in assisting reservoir streamflow sub-seasonal to seasonal forecasts have been increasing. In this study, Random Forest (RF), Artificial Neural Network (ANN) and Support Vector Regression (SVR), are employed and compared with respect to their capabilities for predicting one-month-ahead reservoir inflows for two headwater reservoirs in USA and China, respectively. Both current and lagged hydrological information and 17 known climate phenomenon indices, i.e. PDO and ENSO, etc., are selected as predictors for simulating reservoir inflows. Results show (1) three methods are capable of providing monthly reservoir inflows with satisfactory statistics; (2) the results obtained by Random Forest have the best statistical performances compared with the other two methods; (3) another advantage of Random Forest algorithm is its capability of interpreting raw model inputs; (4) climate phenomenon indices are useful in assisting monthly or seasonal forecasts of reservoir inflow; and (5) different climate conditions are auto-correlated with up to several months, and the climatic information and their lags are cross-correlated with local hydrological conditions in our case studies. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T18:57:09.89364-05:0
      DOI: 10.1002/2017WR020482
  • Tropical river suspended sediment and solute dynamics in storms during an
           extreme drought
    • Authors: Kathryn E. Clark; James B. Shanley, Martha A. Scholl, Nicolas Perdrial, Julia N. Perdrial, Alain F. Plante, William H. McDowell
      Abstract: Droughts, which can strongly affect both hydrologic and biogeochemical systems, are projected to become more prevalent in the tropics in the future. We assessed the effects of an extreme drought during 2015 on stream water composition in the Luquillo Mountains of Puerto Rico. We demonstrated that drought baseflow in the months leading up to the study was sourced from trade-wind orographic rainfall, suggesting a resistance to the effects of an otherwise extreme drought. In two catchments (Mameyes and Icacos), we sampled a series of four rewetting events that partially alleviated the drought. We collected and analyzed dissolved constituents (major cations and anions, organic carbon and nitrogen) and suspended sediment [inorganic and organic matter (particulate organic carbon and particulate nitrogen)]. The rivers appeared to be resistant to extreme drought, recovering quickly upon rewetting, as 1) the concentration - discharge (C-Q) relationships deviated little from the long-term patterns; 2) “new water” dominated streamflow during the latter events; 3) suspended sediment sources had accumulated in the channel during the drought flushed out during the initial events; and 4) the severity of the drought, as measured by the US drought monitor, was reduced dramatically after the rewetting events. Through this interdisciplinary study we were able to investigate the impact of extreme drought through rewetting events on the river biogeochemistry. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T18:57:06.989544-05:
      DOI: 10.1002/2016WR019737
  • Space-time duality for the fractional advection dispersion equation
    • Authors: James F. Kelly; Mark M. Meerschaert
      Abstract: The fractional advection dispersion equation replaces the second spatial derivative in the usual advection dispersion equation with a fractional derivative in the spatial variable. It was first applied to tracer tests in underground aquifers, and later to tracer tests in rivers. An alternative model replaces the first time derivative with a fractional derivative in time. Previous work has shown that both models provide a reasonable fit to breakthrough curves in rivers, which has led to a controversy regarding the physically appropriate fractional model. This paper shows that the relevant space fractional model is mathematically equivalent to the corresponding time-fractional model, thus resolving the controversy. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T18:57:04.757229-05:
      DOI: 10.1002/2016WR019668
  • Debates - Hypothesis testing in hydrology: A subsurface perspective
    • Authors: Insa Neuweiler; Rainer Helmig
      Abstract: Models for flow in environmental systems are subject to uncertainty. Models can thus be interpreted as hypotheses on the validity of the underlying model assumptions. One important source of uncertainty in models for flow and transport processes in the subsurface is the model concept. While uncertain model parameters or forcing terms can be captured as random processes and random fields, this type of uncertainty cannot be included into a model in a straightforward manner. This is particularly true if established model descriptions of a given process are not known or are still being debated. In this contribution, we outline several examples of subsurface flow and transport modeling where uncertainty of the model concept plays an important role. We discuss the need for the development of methods and standards to deal with this type of uncertainty in model hypothesis testing. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-09T18:51:31.223998-05:
      DOI: 10.1002/2016WR020047
  • Quantifying spatial groundwater dependence in peatlands through a
           distributed isotope mass balance approach
    • Authors: Elina Isokangas; Pekka M. Rossi, Anna-Kaisa Ronkanen, Hannu Marttila, Kazimierz Rozanski, Bjørn Kløve
      Abstract: The unique biodiversity and plant composition of peatlands rely on a mix of different water sources: precipitation, runoff and groundwater (GW). Methods used to delineate areas of ecosystem groundwater dependence, such as vegetation mapping and solute tracer studies, are indirect and lack the potential to assess temporal changes in hydrology, information needed in GW management. This paper outlines a new methodology for mapping groundwater-dependent areas (GDAs) in peatlands using a 2H and 18O isotope mass balance method. The approach reconstructs the initial isotopic composition of the peat pore water in the uppermost peat layer before its modification by evaporation. It was assumed that pore water in this layer subject to evaporation is a two-component mixture consisting of GW and precipitation input from the month preceding the sampling period. A Bayesian Monte Carlo isotope mixing model was applied to calculate the proportions of GW and rainwater in the sampled pore water and to assess uncertainties. The approach revealed large spatial variability in the contribution of GW to the pore water present in the top layer of peatland, covering the range from approximately 0 to 100%. Results show that the current GW protection zones determined by Finnish legislation do not cover the GDAs in peatlands and highlight a need for better classification of groundwater-dependent ecosystems and conceptualisation of aquifer-ecosystem interactions. Our approach offers an efficient tool for mapping GDAs and quantifying the contribution of GW to peatland pore water. However, more studies are needed to test the method for different peatland types. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T19:45:42.223532-05:
      DOI: 10.1002/2016WR019661
  • Improved modeling of snow and glacier melting by a progressive two-stage
           calibration strategy with GRACE and multi-source data: How snow and
           glacier meltwater contributes to the runoff of the Upper Brahmaputra River
    • Authors: Xi Chen; Di Long, Yang Hong, Chao Zeng, Denghua Yan
      Abstract: Snow and glacier melting and accumulation are important processes of the hydrological cycle in the cryosphere, e.g., high-mountain areas. Glaciers and snow cover respond to climate change notably over the Tibetan Plateau (TP) as the Earth's Third Pole where complex topography and lack of ground-based observations result in knowledge gaps in hydrological processes and large uncertainties in model output. This study develops a snow and glacier melt model for a distributed hydrological model (Coupled Routing and Excess Storage model, CREST) using the Upper Brahmaputra River (UBR) basin in the TP as a case study. Satellite and ground-based precipitation and land surface temperature are jointly used as model forcing. A progressive two-stage calibration strategy is developed to derive model parameters, i.e., (1) snow melting processes (stage I) and (2) glacier melting and runoff generation and routing using multi-source data (stage II). Stage-I calibration is performed using the MODIS snow cover area (SCA) product and a blending snow water equivalent (SWE) product combined with partial in situ measurements. Stage-II calibration is based on Gravity Recovery and Climate Experiment (GRACE) satellite-derived total water storage (TWS) changes and streamflow observed at a gauging station of the lower reach of the UBR. Results indicate that the developed two-stage calibration method provides more reliable streamflow, snow (both SCA and SWE), and TWS change simulations against corresponding observations than commonly used methods based on streamflow and/or SCA performance. The simulated TWS time series shows high consistency with GRACE counterparts for the study period 2003-2014, and overestimated melting rates and contributions of glacier meltwater to runoff in previous studies are improved to some degree by the developed model and calibration strategy. Snow and glacier runoff contributed 10.6% and 9.9% to the total runoff, and the depletion rate of glacier mass was ∼ -10 mm/a (∼ -2.4 Gt/a, Gt/a is gigaton (km3 of water) per year) over the UBR basin during the study period. This study is valuable in examining the impacts of climate change on hydrological processes of cryospheric regions and providing an improved approach for simulating more reliable hydrological variables over the UBR basin and potentially similar regions globally. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T19:45:37.816426-05:
      DOI: 10.1002/2016WR019656
  • Quantifying local rainfall dynamics and uncertain boundary conditions into
           a nested regional-local flood modelling system
    • Authors: Maria Bermudez; Jeffrey C. Neal, Paul D. Bates, Gemma Coxon, Jim E. Freer, Luis Cea, Jeronimo Puertas
      Abstract: Inflow discharge and outflow stage estimates for hydraulic flood models are generally derived from river gauge data. Uncertainties in the measured inflow data and the neglect of rainfall-runoff contributions to the modelled domain downstream of the gauging locations can have a significant impact on these estimated ‘whole reach' inflows and consequently on flood predictions. In this study, a method to incorporate rating curve uncertainty and local rainfall-runoff dynamics into the predictions of a reach-scale flood model is proposed. The methodology is applied to the July 2007 floods of the River Severn in the UK. Discharge uncertainty bounds are generated applying a non-parametric local weighted regression approach to stage-discharge measurements for two gauging stations. Measured rainfall downstream from these locations is used as input to a series of sub-catchment regional hydrological model to quantify additional local inflows along the main channel. A regional simplified-physics hydraulic model is then applied to combine these contributions and generate an ensemble of discharge and water elevation time series at the boundaries of a local-scale high complexity hydraulic model. Finally, the effect of these rainfall dynamics and uncertain boundary conditions are evaluated on the local-scale model. Accurate prediction of the flood peak was obtained with the proposed method, which was only possible by resolving the additional complexity of the extreme rainfall contributions over the modelled area. The findings highlight the importance of estimating boundary condition uncertainty and local rainfall contributions for accurate prediction of river flows and inundation at regional scales. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T19:45:30.482429-05:
      DOI: 10.1002/2016WR019903
  • A new drought index that considers the joint effects of climate and land
           surface change
    • Authors: Meixian Liu; Xianli Xu, Chaohao Xu, Alexander Y. Sun, Kelin Wang, Bridget R. Scanlon, Lu Zhang
      Abstract: This study proposes a hydrological drought index, the standardized wetness index (SWI), by combining the structure of the Standardized Precipitation-Evapotranspiration Index and actual-evaporation-based residual water-energy ratio, in which actual evaporation is estimated using the Budyko hypothesis. The SWI requires three parameters, precipitation, potential evaporation, and parameter n of a Budyko-type formulae. Based on different types of n (fixed or dynamic), SWI can be used to estimate the dryness/wetness resulting from climate change (variability) solely, and from the joint effects of climate and land surface change (variability). Performance of SWI is evaluated using historical droughts and by comparing to the self-calibrated Palmer Drought Severity Index. Results show that SWI effectively captures global droughts. Furthermore, a case study in two catchments with significant land surface modification, indicates that the joint effects of climate and land surface have greater impacts on dryness/wetness in the water-limited Wuding catchment than in the energy-limited Poyang catchment. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T19:45:27.468069-05:
      DOI: 10.1002/2016WR020178
  • Reply to comment by Hutton et al. on “Most computational hydrology is
           not reproducible, so is it really science?”
    • Authors: Christopher Hutton; Thorsten Wagener, Jim Freer, Dawei Han, Chris Duffy, Berit Arheimer
      Abstract: In this article we reply to a comment made on our previous commentary (Hutton et al [2016]) regarding reproducibility in computational hydrology. Software licensing and version control of code are important technical aspects of making code and workflows of scientific experiments open and reproducible. However, in our view it is the cultural change that is the greatest challenge to overcome to achieve reproducible scientific research in computational hydrology. We believe that from changing the culture and attitude among hydrological scientists, details will evolve to cover more (technical) aspects over time. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T03:35:26.275986-05:
      DOI: 10.1002/2017WR020480
  • Comment on ‘Most computational hydrology is not reproducible, so is it
           really science?’ by Hutton et al.
    • Authors: J. A. Añel
      PubDate: 2017-03-07T03:30:43.183012-05:
      DOI: 10.1002/2016WR020190
  • FracFit: A robust parameter estimation tool for fractional calculus models
    • Authors: James F. Kelly; Diogo Bolster, Mark M. Meerschaert, Jennifer D. Drummond, Aaron I. Packman
      Abstract: Anomalous transport cannot be adequately described with classical Fickian advection-dispersion equations (ADE) with constant coefficients. Rather, fractional calculus models may be used, which capture salient features of anomalous transport (e.g. skewness and power-law tails). FracFit is a parameter estimation tool based on space- and time-fractional models used by the hydrology community. Currently, four fractional models are supported: 1) space fractional advection-dispersion equation (sFADE), 2) time-fractional dispersion equation with drift (TFDE), 3) fractional mobile-immobile (FMIM) equation, and 4) temporally tempered Lévy motion (TTLM). Model solutions using pulse initial conditions and continuous injections are evaluated using stable distributions or subordination integrals. Parameter estimates are extracted from measured breakthrough curves (BTCs) using a weighted nonlinear least squares (WNLS) algorithm. Optimal weights for BTCs for pulse initial conditions and continuous injections are presented. Two sample applications are analyzed: 1)pulse injection BTCs in the Selke river and 2) continuous injection laboratory experiments using natural organic matter. Model parameters are compared across models and goodness-of-fit metrics are presented, facilitating model evaluation. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-07T03:30:25.809987-05:
      DOI: 10.1002/2016WR019748
  • Comment on “Most computational hydrology is not reproducible, so is it
           really science?”
    • Authors: Lieke A. Melsen; Paul J.J.F Torfs, Remko Uijlenhoet, Adriaan J. Teuling
      PubDate: 2017-03-07T03:26:01.913149-05:
      DOI: 10.1002/2016WR020208
  • Hydroeconomic modeling of sustainable groundwater management
    • Authors: Duncan MacEwan; Mesut Cayar Water, Ali Taghavi, David Mitchell, Steve Hatchett, Richard Howitt
      Abstract: In 2014 California passed legislation requiring the sustainable management of critically overdrafted groundwater basins, located primarily in the Central Valley agricultural region. Hydroeconomic modeling of the agricultural economy, groundwater, and surface water systems is critically important to simulate potential transition paths to sustainable management of the basins. The requirement for sustainable groundwater use by 2040 is mandated specifically for overdrafted groundwater basins that are decoupled from environmental and river flow effects. We argue that, for such cases, a modeling approach that integrates a biophysical response function from a hydrologic model into an economic model of groundwater use is preferable to embedding an economic response function in a complex hydrologic model as is more commonly done. Using this preferred approach, we develop a dynamic hydroeconomic model for the Kings and Tulare Lake sub-basins of California and evaluate three groundwater management institutions–open access, perfect foresight, and managed pumping. We quantify the costs and benefits of sustainable groundwater management, including energy pumping savings, drought reserve values, and avoided capital costs. Our analysis finds that, for basins that are severely depleted, losses in crop net revenue are offset by the benefits of energy savings, drought reserve value, and avoided capital costs. This finding provides an empirical counter-example to the Gisser and Sanchez Effect. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-06T11:45:29.744213-05:
      DOI: 10.1002/2016WR019639
  • A decomposition-integration risk analysis method for real-time operation
           of a complex flood control system
    • Authors: Juan Chen; Ping-An Zhong, Yu Zhang, David Navar, William W.-G. Yeh
      Abstract: Risk analysis plays an important role in decision making for real-time flood control operation of complex flood control systems. A typical flood control system consists of reservoirs, river channels, and downstream control points. The system generally is characterized by nonlinearity and large scale. Additionally, the input variables are mostly stochastic. Because of the dimensionality problem, generally, it would not be possible to carry out risk analysis without decomposition. In this paper, we propose a decomposition-integration approach whereby the original complex flood control system is decomposed into a number of independent subsystems. We conduct risk analysis for each subsystem and then integrate the results by means of combination theory of stochastic processes. We evaluate the propagation of uncertainties through the complex flood control system and calculate the risk of reservoir overtopping, as well as the risk of flooding at selected downstream control points. We apply the proposed methodology to a flood control system in the middle reaches of the Huaihe River basin in China. The results show that the proposed method is practical and provides a way to estimate the risks in real-time flood control operation of a complex flood control system. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-06T11:35:25.213669-05:
      DOI: 10.1002/2016WR019842
  • Hydrodynamics of steep streams with planar coarse-grained beds:
           Turbulence, flow resistance, and implications for sediment transport
    • Authors: Michael P. Lamb; Fanny Brun, Brian M. Fuller
      Abstract: The hydraulics of steep mountain streams differ from lower gradient rivers due to shallow and rough flows, energetic subsurface flow, and macro-scale form drag from immobile boulders and channel- and bed-forms. Heightened flow resistance and reduced sediment transport rates in steep streams are commonly attributed to macro-scale form drag; however, little work has explored steep river hydrodynamics in the absence of complex bed geometries. Here we present theory for the vertical structure of flow velocity in steep streams with planar, rough beds that couples surface and subsurface flow. We test it against flume experiments using a bed of fixed cobbles over a wide range of bed slopes (0.4 – 30%). Experimental flows have a nearly logarithmic velocity profile far above the bed; flow velocity decreases less than logarithmically towards the bed and is non-zero at the bed surface. Velocity profiles match theory derived using a hybrid eddy-viscosity model, in which the mixing length is a function of height above the bed and bed roughness. Subsurface flow velocities are large (> 1 m/s) and follow a modified Darcy-Brinkman-Forchheimer relation that accounts for channel slope and shear from overlying surface flow. Near-bed turbulent fluctuations decrease for shallow, rough flows and scale with the depth-averaged flow velocity rather than bed shear velocity. Flow resistance for rough, planar beds closely matches observations in natural steep streams despite the lack of bed- or channel-forms in the experiments, suggesting that macro-scale form drag is smaller than commonly assumed in stress partitioning models for sediment transport. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-03T08:15:31.074016-05:
      DOI: 10.1002/2016WR019579
  • Flow resistance and hydraulic geometry in contrasting reaches of a bedrock
    • Authors: R. I. Ferguson; B. P. Sharma, R. J. Hardy, R. A. Hodge, J. Warburton
      Abstract: Assumptions about flow resistance in bedrock channels have to be made for mechanistic modeling of river incision, paleoflood estimation, flood routing, and river engineering. Field data on bedrock flow resistance are very limited and calculations generally use standard alluvial-river assumptions such as a fixed value of Manning's n. To help inform future work we measured how depth, velocity and flow resistance vary with discharge in four short reaches of a small bedrock channel, one with an entirely rock bed and the others with 20%-70% sediment cover, and in the alluvial channel immediately upstream. As discharge and submergence increase in each of the partly or fully alluvial reaches there is a rapid increase in velocity and a strong decline in both n and the Darcy-Weisbach friction factor f. The bare-rock reach follows a similar trend from low to medium discharge but has increasing resistance at higher discharges because of the macro-roughness of its rock walls. Flow resistance at a given discharge differs considerably between reaches and is highest where the partial sediment cover is coarsest and most extensive. Apart from the effect of rough rock walls, the flow resistance trends are qualitatively consistent with logarithmic and variable-power equations and with non-dimensional hydraulic geometry, but quantitative agreement using sediment D84 as the roughness height is imperfect. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:51.530607-05:
      DOI: 10.1002/2016WR020233
  • Snowmelt controls on concentration-discharge relationships and the balance
           of oxidative and acid-base weathering fluxes in an alpine catchment, East
           River, Colorado
    • Authors: Matthew J. Winnick; Rosemary Carroll, Kenneth Williams, Reed Maxwell, Wenming Dong, Kate Maher
      Abstract: Although important for riverine solute and nutrient fluxes, the connections between biogeochemical processes and subsurface hydrology remain poorly characterized. We investigate these couplings in the East River, CO, a high-elevation shale-dominated catchment in the Rocky Mountains, using concentration-discharge (C-Q) relationships for major cations, anions, and organic carbon. Dissolved organic carbon (DOC) displays a positive C-Q relationship with clockwise hysteresis, indicating mobilization and depletion of DOC in the upper soil horizons and emphasizing the importance of shallow flowpaths during snowmelt. Cation and anion concentrations demonstrate that carbonate weathering, which dominates solute fluxes, is promoted by both sulfuric acid derived from pyrite oxidation in the shale bedrock and carbonic acid derived from subsurface respiration. Sulfuric acid weathering dominates during baseflow conditions when waters infiltrate below the inferred pyrite oxidation front, whereas carbonic acid weathering plays a dominant role during snowmelt as a result of shallow flowpaths. Differential C-Q relationships between solutes suggest that infiltrating waters approach calcite saturation before reaching the pyrite oxidation front, after which sulfuric acid reduces carbonate alkalinity. This reduction in alkalinity results in CO2 outgassing when waters equilibrate to surface conditions, and reduces the riverine export of carbon and alkalinity by roughly 33% annually. Future changes in snowmelt dynamics that control the balance of carbonic and sulfuric acid weathering may substantially alter carbon cycling in the East River. Ultimately, we demonstrate that differential C-Q relationships between major solutes can provide unique insights into the complex subsurface flow and biogeochemical dynamics that operate at catchment scales. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:50.337478-05:
      DOI: 10.1002/2016WR019724
  • Field estimates of groundwater circulation depths in two mountainous
           watersheds in the western U.S. and the effect of deep circulation on
           solute concentrations in streamflow
    • Authors: Marty D. Frisbee; Douglas G. Tolley, John L. Wilson
      Abstract: Estimates of groundwater circulation depths based on field data are lacking. These data are critical to inform and refine hydrogeologic models of mountainous watersheds, and to quantify depth- and time-dependencies of weathering processes in watersheds. Here we test two competing hypotheses on the role of geology and geologic setting in deep groundwater circulation and the role of deep groundwater in the geochemical evolution of streams and springs. We test these hypotheses in two mountainous watersheds that have distinctly different geologic settings (one crystalline, metamorphic bedrock and the other volcanic bedrock). Estimated circulation depths for springs in both watersheds range from 0.6 to 1.6 km and may be as great as 2.5 km. These estimated groundwater circulation depths are much deeper than commonly modeled depths suggesting that we may be forcing groundwater flowpaths too shallow in models. In addition, the spatial relationships of groundwater circulation depths are different between the two watersheds. Groundwater circulation depths in the crystalline bedrock watershed increase with decreasing elevation indicative of topography-driven groundwater flow. This relationship is not present in the volcanic bedrock watershed suggesting that both the source of fracturing (tectonic versus volcanic) and increased primary porosity in the volcanic bedrock play a role in deep groundwater circulation. The results from the crystalline bedrock watershed also indicate that relatively deep groundwater circulation can occur at local-scales in headwater drainages less than 9.0 km2 and at larger fractions than commonly perceived. Deep groundwater is a primary control on streamflow processes and solute concentrations in both watersheds. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:48.980498-05:
      DOI: 10.1002/2016WR019553
  • Reply to Comment on ‘Most computational hydrology is not reproducible,
           so is it really science?’
    • Authors: Christopher Hutton; Thorsten Wagener, Jim Freer, Dawei Han, Chris Duffy, Berit Arheimer
      Abstract: In this article we reply to a comment made on our previous commentary (Hutton et al [2016]) regarding reproducibility in computational hydrology. Re-executing someone else's code and workflow to derive a set of published results does not by itself constitute reproducibility. However, it forms a key part of the process: it demonstrates that all the degrees of freedom and choices made by the scientist in running the experiment are contained within that code and workflow. This does not only allow us to build and extend directly from the original work, but with full knowledge of decisions made in the original experimental setup, we can then focus our attention to the degrees of freedom of interest: those that occur in hydrological systems, that are ultimately our subject of study. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:43.35919-05:0
      DOI: 10.1002/2017WR020476
  • Steady-state fractionation of heavy noble gas isotopes in a deep
           unsaturated zone
    • Authors: Alan M. Seltzer; Jeffrey P. Severinghaus, Brian J. Andraski, David A. Stonestrom
      Abstract: To explore steady-state fractionation processes in the unsaturated zone (UZ), we measured argon, krypton and xenon isotope ratios throughout a ∼110-m deep UZ at the United States Geological Survey (USGS) Amargosa Desert Research Site (ADRS) in Nevada, USA. Prior work has suggested that gravitational settling should create a nearly linear increase in heavy-to-light isotope ratios toward the bottom of stagnant air columns in porous media. Our high-precision measurements revealed a binary mixture between 1) expected steady-state isotopic compositions, and 2) unfractionated atmospheric air. We hypothesize that the presence of an unsealed pipe connecting the surface to the water table allowed for direct inflow of surface air in response to extensive UZ gas sampling prior to our first (2015) measurements. Observed isotopic resettling in deep UZ samples collected a year later, after sealing the pipe, supports this interpretation. Data and modeling each suggest that the strong influence of gravitational settling and weaker influences of thermal diffusion and fluxes of CO2 and water vapor accurately describe steady-state isotopic fractionation of argon, krypton and xenon within the UZ. The data confirm that heavy noble gas isotopes are sensitive indicators of UZ depth. Based on this finding, we outline a potential inverse approach to quantify past water-table depths from noble gas isotope measurements in paleogroundwater, after accounting for fractionation during dissolution of UZ air and bubbles. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:37.464846-05:
      DOI: 10.1002/2016WR019655
  • Reducing uncertainty with flood frequency analysis: the contribution of
           palaeo- and historical flood information
    • Authors: Daryl Lam; Chris Thompson, Jacky Croke, Ashneel Sharma, Mark Macklin
      Abstract: Using a combination of stream gauge, historical and palaeoflood records to extend extreme flood records has proven to be useful in improving flood frequency analysis (FFA). The approach has typically been applied in localities with long historical records and/or suitable river settings for palaeoflood reconstruction from slackwater deposits (SWDs). However, many regions around the world have neither extensive historical information nor bedrock gorges suitable for SWDs preservation and palaeoflood reconstruction. This study from subtropical Australia demonstrates that confined, semi-alluvial channels such as macrochannels provide relatively stable boundaries over the 1000-2000 year time period and the preserved SWDs enabled palaeoflood reconstruction and their incorporation into FFA. FFA for three sites in subtropical Australia with the integration of historical and palaeoflood data using Bayesian Inference methods showed a significant reduction in uncertainty associated with the estimated discharge of a flood quantile. Uncertainty associated with estimated discharge for the 1% Annual Exceedance Probability (AEP) flood is reduced by over 50%. In addition, sensitivity analysis of possible within-channel boundary changes shows that FFA is not significantly affected by any associated changes in channel capacity. Therefore, a greater range of channel types may be used for reliable palaeoflood reconstruction by evaluating the stability of inset alluvial units, thereby increasing the quantity of temporal data available for FFA. The reduction in uncertainty, particularly in the prediction of the ≤ 1% AEP design flood, will improve flood risk planning and management in regions with limited temporal flood data. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:33.738167-05:
      DOI: 10.1002/2016WR019959
  • Glacier melt buffers river runoff in the Pamir Mountains
    • Authors: Eric Pohl; Richard Gloaguen, Christoff Andermann, Malte Knoche
      Abstract: Newly developed approaches based on satellite altimetry and gravity measurements provide promising results on glacier dynamics in the Pamir-Himalaya but cannot resolve short-term natural variability at regional and finer scale. We contribute to the ongoing debate by upscaling a hydrological model that we calibrated for the central Pamir. The model resolves the spatiotemporal variability in runoff over the entire catchment domain with high efficiency. We provide relevant information about individual components of the hydrological cycle and quantify short term hydrological variability. For validation we compare the modelled total water storages (TWS) with GRACE (Gravity Recovery and Climate Experiment) data with a very good agreement where GRACE uncertainties are low. The approach exemplifies the potential of GRACE for validating even regional scale hydrological applications in remote and hard to access mountain regions. We use modelled time-series of individual hydrological components to characterise the effect of climate variability on the hydrological cycle. We demonstrate that glaciers play a two-fold role by providing roughly 35% of the annual runoff of the Panj River basin and by effectively buffering runoff both during very wet and very dry years. The modelled glacier mass balance (GMB) of -0.52 m w.e. yr−1 (2002 to 2013) for the entire catchment suggests significant reduction of most Pamiri glaciers by the end of this century. The loss of glaciers and their buffer functionality in wet and dry years could not only result in reduced water availability and increase the regional instability, but also increase flood and drought hazards. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:30.870585-05:
      DOI: 10.1002/2016WR019431
  • Groundwater similarity across a watershed derived from time-warped and
           flow-corrected time series
    • Authors: M. Rinderer; B. L. McGlynn, H.J. van Meerveld
      Abstract: Information about catchment-scale groundwater dynamics is necessary to understand how catchments store and release water and why water quantity and quality varies in streams. However, groundwater level monitoring is often restricted to a limited number of sites. Knowledge of the factors that determine similarity between monitoring sites can be used to predict catchment-scale groundwater storage and connectivity of different runoff source areas. We used distance-based and correlation-based similarity measures to quantify the spatial and temporal differences in shallow groundwater similarity for 51 monitoring sites in a Swiss pre-alpine catchment. The 41 months long time series were pre-processed using dynamic time-warping and a flow-corrected time transformation to account for small timing differences and bias towards low-flow periods. The mean distance-based groundwater similarity was correlated to topographic indices, such as upslope contributing area, Topographic Wetness Index and local slope. Correlation-based similarity was less related to landscape position but instead revealed differences between seasons. Analysis of Variance and Partial Mantel tests showed that landscape position, represented by the Topographic Wetness Index, explained 52% of the variability in mean distance-based groundwater similarity, while spatial distance, represented by the Euclidean distance, explained only 5%. The variability in distance-based similarity and correlation-based similarity between groundwater and streamflow time series was significantly larger for midslope locations than for other landscape positions. This suggests, that groundwater dynamics at these midslope sites, which are important in order to understand runoff source areas and hydrological connectivity at the catchment-scale, are most difficult to predict. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T12:30:25.364245-05:
      DOI: 10.1002/2016WR019856
  • Preferences for policy attributes and willingness to pay for water quality
           improvements under uncertainty
    • Authors: Jeffrey D. Mullen; Kayla C. Calhoun, Gregory J. Colson
      Abstract: When exploring environmental policy options, sometimes neither the current state of the environmental good being analyzed nor the effectiveness of the proposed policy is known with certainty. This is the case with privately-owned, residential, onsite wastewater treatment systems (septic systems) – there is ample evidence that they can contribute to water quality impairment, but their contribution is generally stochastic in nature and the efficacy of technological solutions is uncertain. Furthermore, the benefits of ameliorating water quality impairments are public in nature. Septic system owners are legally responsible for maintaining their systems, but requiring them to upgrade otherwise properly functioning tanks is outside the scope of water quality regulations. An incentive structure is necessary to induce private homeowners to invest in septic upgrades that deliver both private benefits in addition to the positive externality for the wider public and environment. The question for policy makers is how these private incentives should be financed, and whether public support can be garnered. Results of a choice experiment in Gwinnett County, Georgia, accounting for both sources of uncertainty – the current state of water quality and the efficacy of the intervention – in the design of water quality policy are presented. We find baseline water quality conditions and policy efficacy significantly affect public support for a policy transferring public funds to private homeowners, in terms of both sentiment and willingness to pay. The manner in which costs are shared across stakeholders also affects the selection of a policy option, but not willingness to pay for it. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T08:45:34.486994-05:
      DOI: 10.1002/2016WR019397
  • A probabilistic approach to quantifying hydrologic thresholds regulating
           migration of adult Atlantic salmon into spawning streams
    • Authors: G. Lazzaro; C. Soulsby, D. Tetzlaff, G. Botter
      Abstract: Atlantic salmon is an economically and ecologically important fish species, whose survival is dependent on successful spawning in headwater rivers. Streamflow dynamics often have a strong control on spawning because fish require sufficiently high discharges to move upriver and enter spawning streams. However, these streamflow effects are modulated by biological factors such as the number and the timing of returning fish in relation to the annual spawning window in the fall/winter. In this paper we develop and apply a novel probabilistic approach to quantify these interactions using a parsimonious outflux-influx model linking the number of female salmon emigrating (i.e. outflux) and returning (i.e. influx) to a spawning stream in Scotland. The model explicitly accounts for the inter-annual variability of the hydrologic regime and the hydrological connectivity of spawning streams to main rivers. Model results are evaluated against a detailed long-term (40 years) hydro-ecological dataset that includes annual fluxes of salmon, allowing us to explicitly assess the role of discharge variability. The satisfactory model results show quantitatively that hydrologic variability contributes to the observed dynamics of salmon returns, with a good correlation between the positive (negative) peaks in the immigration dataset and the exceedance (non-exceedance) probability of a threshold flow (0.3 m\textsuperscript{3}/s). Importantly, model performance deteriorates when the inter-annual variability of flow regime is disregarded. The analysis suggests that flow thresholds and hydrological connectivity for spawning return represent a quantifiable and predictable feature of salmon rivers, which may be helpful in decision making where flow regimes are altered by water abstractions. This article is protected by copyright. All rights reserved.
      PubDate: 2017-03-02T08:45:30.611359-05:
      DOI: 10.1002/2016WR019244
  • Debates—Hypothesis testing in hydrology: Pursuing certainty versus
           pursuing uberty
    • Authors: Victor R. Baker
      Abstract: Modern hydrology places nearly all its emphasis on science-as-knowledge, the hypotheses of which are increasingly expressed as physical models, whose predictions are tested by correspondence to quantitative data sets. Though arguably appropriate for applications of theory to engineering and applied science, the associated emphases on truth and degrees of certainty are not optimal for the productive and creative processes that facilitate the fundamental advancement of science as a process of discovery. The latter requires an investigative approach, where the goal is uberty, a kind of fruitfulness of inquiry, in which the abductive mode of inference adds to the much more commonly acknowledged modes of deduction and induction. The resulting world-directed approach to hydrology provides a valuable complement to the prevailing hypothesis- (theory-) directed paradigm. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:50:22.23931-05:0
      DOI: 10.1002/2016WR020078
  • Debates—Hypothesis testing in hydrology: A view from the field: The
           value of hydrologic hypotheses in designing field studies and interpreting
           the results to advance hydrology
    • Authors: Diane M. McKnight
      Abstract: Advances in hydrology are greatly needed and approaches that employ hypotheses to guide research have the potential to contribute to future advances. In this context, hypotheses can serve a range of purposes. Overarching hypotheses can provide a common integrating framework for collaborative research and can be revised as research progresses over time. Hypotheses that attempt to explain unexpected field observations or experimental results can provide a guide for designing further field studies. Focused testable hypotheses can facilitate effective presentation of proposed research, and clarify alternative hypotheses. Finally, the value of employing a hypothesis-based approach depends upon the research environment, which can act as an “environmental filter” in determining successful research outcomes. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:45:37.593268-05:
      DOI: 10.1002/2016WR020050
  • Debates—Hypothesis testing in hydrology: Introduction
    • Authors: Günter Blöschl
      Abstract: This paper introduces the papers in the “Debates - Hypothesis testing in hydrology” series. The four articles in the series discuss whether and how the process of testing hypotheses leads to progress in hydrology. Repeated experiments with controlled boundary conditions are rarely feasible in hydrology. Research is therefore not easily aligned with the classical scientific method of testing hypotheses. Hypotheses in hydrology are often enshrined in computer models which are tested against observed data. Testability may be limited due to model complexity and data uncertainty. All four articles suggest that hypothesis testing has contributed to progress in hydrology and is needed in the future. However, the procedure is usually not as systematic as the philosophy of science suggests. A greater emphasis on a creative reasoning process on the basis of clues and explorative analyses is therefore needed. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:45:35.056559-05:
      DOI: 10.1002/2017WR020584
  • Debate—Hypothesis testing in hydrology: Theory and practice
    • Authors: Laurent Pfister; James W. Kirchner
      Abstract: The basic structure of the scientific method – at least in its idealized form – is widely championed as a recipe for scientific progress, but the day-to-day practice may be different. Here, we explore the spectrum of current practice in hypothesis formulation and testing in hydrology, based on a random sample of recent research papers. This analysis suggests that in hydrology, as in other fields, hypothesis formulation and testing rarely correspond to the idealized model of the scientific method. Practices such as “p-hacking “or “HARKing “(Hypothesizing After the Results are Known) are major obstacles to more rigorous hypothesis testing in hydrology, along with the well-known problem of confirmation bias – the tendency to value and trust confirmations more than refutations – among both researchers and reviewers. Nonetheless, as several examples illustrate, hypothesis tests have played an essential role in spurring major advances in hydrological theory. Hypothesis testing is not the only recipe for scientific progress, however. Exploratory research, driven by innovations in measurement and observation, has also underlain many key advances. Further improvements in observation and measurement will be vital to both exploratory research and hypothesis testing, and thus to advancing the science of hydrology. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:45:32.432022-05:
      DOI: 10.1002/2016WR020116
  • Colloidal transport in the Gordon Gulch catchment of the Boulder Creek CZO
           and its effect on C-Q relationships for silicon
    • Authors: Arnulfo A. Aguirre; Louis A. Derry, Taylor J. Mills, Suzanne P. Anderson
      Abstract: The near constant Si concentration under varying discharge observed in Gordon Gulch of the Boulder Critical Zone Observatory (CZO) indicates that the silica fluxes are strongly controlled by discharge. To identify the mechanisms supplying increased Si at high discharge (Q) we examine Si-Al-Fe-Ge in soils, streams and ground waters. We identify bedrock weathering in groundwater and colloidal transport as the two end-members that supply Si to the system. During baseflow, stream flow is derived from groundwater, and weathering of feldspar is the main source of Si with a Ge/Si ratio 0.2-0.5 µmol/mol and low dissolved Al and Fe. The groundwater data are consistent with incongruent weathering of feldspar as the main source of dissolved Si. As discharge increases, Si-Al-Fe bearing colloids are mobilized, and the Ge/Si ratio of the stream rises to 3.0 µmol/mol. Mineralogical analysis using XRD identified Al-Si phases including kaolinite, illite and quartz in the colloidal size fraction (< 0.45 µm). The Ge/Si ratio of stream and soil colloids ≈ 3.8 µmol/mol. The mechanism of colloidal transport with increasing discharge can account for the concentration-discharge (C-Q) patterns of Si, Al and Fe with near-zero or positive power law slopes observed in the Gordon Gulch catchment. Anomalously high Ge/Si ratios also identified a third end-member resulting from coal fly ash deposition during the winter and spring. Wind trajectories during 2012, correlation between Ge/Si and SO42-, and comparison to atmospheric deposition data imply contamination from nearby coal fired power plant operations. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:45:30.431911-05:
      DOI: 10.1002/2016WR019730
  • The influence of the length of the calibration period and observation
           frequency on predictive uncertainty in time series modeling of groundwater
    • Authors: Joanne van der Spek; Mark Bakker
      Abstract: The influence of the length of the calibration period and observation frequency on the predictive uncertainty in time series modeling of groundwater dynamics is investigated. Studied series are from deltaic regions with predominantly shallow groundwater tables in a temperate maritime climate where heads vary due to precipitation and evaporation. Response times vary over a wide range from ∼60 days to ∼1200 days. A Transfer Function-Noise model is calibrated with the Markov Chain Monte Carlo method to both synthetic series and measured series of heads. The model fit and uncertainty are evaluated for various calibration periods and observation frequencies. It is often assumed that the required length of the calibration period is related to the response time of the system. In this study, no strong relationship was observed. Results indicate, however, that the required length of the calibration period is related to the decay time of the noise. Furthermore, the length of the calibration period was much more important than the total number of observations. For the measured series, the credible intervals could commonly be reduced to ∼10% of the measured head range and the prediction intervals to ∼50% of the measured head range with calibration periods of 20 years with ∼2 observations per month. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:45:26.743279-05:
      DOI: 10.1002/2016WR019704
  • Changes in cold region flood regimes inferred from long record reference
           gauging stations
    • Authors: Donald H. Burn; Paul H. Whitfield
      Abstract: Variability and nonstationarity in flood regimes of cold regions are examined using data from hydrometric reference streamflow gauging stations from 27 natural watersheds in Canada and adjacent areas of the United States. Choosing stations from reference networks with nearly 100 years of data allows for the investigation of changes that span several phases of some of the atmospheric drivers that may influence flood behaviour. The reference hydrologic networks include only stations considered to have good quality data and were screened to avoid the influences of regulation, diversions, or land use change. Changes and variations in flood regimes are complex and require a multifaceted approach to properly characterize the types of changes that have occurred and are likely to occur in the future. Peaks over threshold (POT) data are extracted from daily flow data for each watershed and changes to the magnitude, timing, frequency, volume and duration of threshold exceedences are investigated. Seasonal statistics are used to explore changes in the nature of the flood regime based on changes in the timing of flood threshold exceedences. A variety of measures are developed to infer flood regime shifts including from a nival regime to a mixed regime and a mixed regime to a more pluvial-dominated regime. The flood regime at many of the watersheds demonstrates increased prominence of rainfall floods and decreased prevalence of snowmelt contributions to flood responses. While some individual stations show a relationship between flood variables and climate indices, these relationships are generally weak. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-27T10:40:24.145035-05:
      DOI: 10.1002/2016WR020108
  • Rapid processing of 85Kr/Kr ratios using Atom Trap Trace Analysis
    • Authors: J. C. Zappala; K. Bailey, P. Mueller, T. P. O'Connor, R. Purtschert
      Abstract: We report a methodology for measuring 85Kr/Kr isotopic abundances using Atom Trap Trace Analysis (ATTA) that increases sample measurement throughput by over an order of magnitude to 6 samples per 24 hours. The noble gas isotope 85Kr (half-life = 10.7 yr) is a useful tracer for young groundwater in the age range of 5-50 years. ATTA, an efficient and selective laser-based atom counting method, has recently been applied to 85Kr/Kr isotopic abundance measurements, requiring 5-10 μL of krypton gas at STP extracted from 50-100 L of water. Previously a single such measurement required 48 hours. Our new method demonstrates that we can measure 85Kr/Kr ratios with 3-5% relative uncertainty every 4 hours, on average, with the same sample requirements. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-23T07:15:48.9571-05:00
      DOI: 10.1002/2016WR020082
  • Effect of volcanic dykes on coastal groundwater flow and saltwater
           intrusion: A field-scale multiphysics approach and parameter evaluation
    • Authors: J.C. Comte; C. Wilson, U. Ofterdinger, A. González-Quirós
      Abstract: Volcanic dykes are common discrete heterogeneities in aquifers; however there is a lack of field examples of, and methodologies for, comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport. We have applied an integrated multi-physics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer. The approach involved ground geophysical imaging (passive magnetics and electrical resistivity tomography), well hydraulic testing and tidal propagation analysis, which provided constraints on the geometry of the dyke network, the subsurface saltwater distribution, and the sandstone hydrodynamic properties and connectivity. A three-dimensional variable-density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations. A good agreement of model simulations with tide-induced head fluctuations, geophysically-derived pore water salinities and measured apparent resistivities was obtained when dykes' hydraulic conductivity, storativity and effective porosity are respectively about three, one, and one orders of magnitude lower than the host aquifer. The presence of the dykes results in barrier-like alterations of groundwater flow and saltwater intrusion. Preferential flowpaths occur parallel to observed dyke orientations. Freshwater inflows from upland recharge areas concentrate on the land-facing side of the dykes and saltwater penetration is higher on their sea-facing side. This has major implications for managing groundwater resources in dyke-intruded aquifers, including in coastal and island regions, but also provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-23T07:15:46.697261-05:
      DOI: 10.1002/2016WR019480
  • Estimating the permanent loss of groundwater storage in the southern San
           Joaquin Valley, California
    • Authors: R.G. Smith; R. Knight, J. Chen, J.A. Reeves, H.A. Zebker, T. Farr, Z. Liu
      Abstract: In the San Joaquin Valley, California, recent droughts starting in 2007 have increased the pumping of groundwater, leading to widespread subsidence. In the southern portion of the San Joaquin Valley, vertical subsidence as high as 85 cm has been observed between June 2007 and December 2010 using Interferometric Synthetic Aperture Radar (InSAR). This study seeks to map regions where inelastic (not recoverable) deformation occurred during the study period, resulting in permanent compaction and loss of groundwater storage. We estimated the amount of permanent compaction by incorporating multiple datasets: the total deformation derived from InSAR, estimated skeletal specific storage and hydraulic parameters, geologic information, and measured water levels during our study period. We used two approaches, one that we consider to provide an estimate of the lowest possible amount of inelastic deformation, and one that provides a more reasonable estimate. These two approaches resulted in a spatial distribution of values for the percentage of the total deformation that was inelastic, with the former estimating a spatially averaged value of 54%, and the latter a spatially averaged value of 98%. The former corresponds to the permanent loss of 4.14 × 108 m3 of groundwater storage, or roughly 5% of the volume of groundwater used over the study time period; the latter corresponds to the loss of 7.48 × 108 m3 of groundwater storage, or roughly 9% of the volume of groundwater used. This study demonstrates that a data-driven approach can be used effectively to estimate the permanent loss of groundwater storage. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-23T07:15:43.262653-05:
      DOI: 10.1002/2016WR019861
  • Use and misuse of large density asymptotics in the reaction-infiltration
    • Authors: Anthony J. C. Ladd; Piotr Szymczak
      Abstract: Analyzing the dissolution of rocks and other porous materials is simplified by the large disparity between mineral and reactant concentrations. In essence, the porosity remains frozen on the time scale of the reactant transport, which can then be treated as a quasi-stationary process. This conceptual idea can be derived mathematically using asymptotic methods, which show that the length scales in the system are, to a first approximation, independent of the ratio of reactant and mineral concentrations. Nevertheless, in a growing number of papers on dissolutional instabilities, the reactant-mineral concentration ratio has been incorrectly linked to the thickness of the dissolution front. In this paper we critically review the application of asymptotic methods to the reaction-infiltration instability. In particular we discuss the limited validity of the thin-front or “Stefan” limit, where the interface between dissolved and undissolved mineral is sharp. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-23T07:10:29.348614-05:
      DOI: 10.1002/2016WR019263
  • Optimizing multiple reliable forward contracts for reservoir allocation
           using multitime scale streamflow forecasts
    • Authors: Mengqian Lu; Upmanu Lall, Andrew Robertson, Edward Cook
      Abstract: Streamflow forecasts at multiple time scales provide a new opportunity for reservoir management to address competing objectives. Market instruments such as forward contracts with specified reliability are considered as a tool that may help address the perceived risk associated with the use of such forecasts in lieu of traditional operation and allocation strategies. A water allocation process that enables multiple contracts for water supply and hydropower production with different durations, while maintaining a prescribed level of flood risk reduction, is presented. The allocation process is supported by an optimization model that considers multi-time scale ensemble forecasts of monthly streamflow and flood volume over the upcoming season and year, the desired reliability and pricing of proposed contracts for hydropower and water supply. It solves for the size of contracts at each reliability level that can be allocated for each future period, while meeting target end of period reservoir storage with a prescribed reliability. The contracts may be insurable, given that their reliability is verified through retrospective modelling. The process can allow reservoir operators to overcome their concerns as to the appropriate skill of probabilistic forecasts, while providing water users with short and long-term guarantees as to how much water or energy they may be allocated. An application of the optimization model to the Bhakra Dam, India provides an illustration of the process. The issues of forecast skill and contract performance are examined. A field engagement of the idea is useful to develop a real-world perspective, and needs a suitable institutional environment. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-21T03:30:26.235674-05:
      DOI: 10.1002/2016WR019552
  • Evaluating financial risk management strategies under climate change for
           hydropower producers on the Great Lakes
    • Authors: Eliot S. Meyer; Gregory W. Characklis, Casey Brown
      Abstract: Hydropower on the Great Lakes makes up a substantial fraction of regional electricity generation capacity. Hydropower producers on the Niagara River (flowing between lakes Erie and Ontario) operate as run-of-river, and changing lake levels alter interlake flows reducing both generation and revenues. Index-based insurance contracts, wherein contract payouts are linked to lake levels, offer a tool for mitigating this risk. While a potentially useful tool, pricing of financial insurance is typically based on historical behavior of the index. However, uncertainty with respect to the impacts of climate change on lake level behavior and how this might translate to increased (or decreased) risk for those selling or buying the insurance remains unexplored. Portfolios of binary index-insurance contracts are developed for hydropower producers on the Niagara River, and their performance is evaluated under a range of climate scenarios. Climate Informed Decision Analysis is used to inform the sensitivity of these portfolios to potential shifts in long term, climatological variations in water level behavior. Under historical conditions, hydropower producers can use portfolios costing 0.5% of mean revenues to increase their minimum revenue threshold by approximately 18%. However, a one standard deviation decrease in the fifty year mean water level potentially doubles the frequency with which these portfolios would underperform from the perspective of a potential insurer. Tradeoffs between portfolio cost and the frequency of underperformance are investigated over a range of climate futures. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-20T07:10:26.003183-05:
      DOI: 10.1002/2016WR019889
  • A tale of two riffles: Using multidimensional, multifractional,
           time-varying sediment transport to assess self-maintenance in pool-riffle
    • Authors: Esmaeel Bayat; José F. Rodríguez, Patricia M. Saco, Gustavo A.M. de Almeida, Elham Vahidi, Marcelo H. García
      Abstract: Pool-riffle sequences play a central role in providing habitat diversity conditions both in terms of flow and substrate in gravel bed streams. Understanding their capacity to self-maintain has been the focus of research for many years, starting with the velocity reversal hypothesis. This hypothesis relied only on cross sectional averaged flow information, but its limited success prompted extensions of the hypothesis and alternative explanations for self-maintenance. Significant advances beyond the velocity reversal hypothesis have been achieved by incorporating more information either on flow or sediment transport characteristics. However, this has been done in a compartmentalised way, with studies either focusing on one or the other aspect.This work bridges the gap between these two aspects by using an approximate methodology that combines observed characteristic stage-dependent 3-D flow patterns with time-varying cross sectional information on bed shear stresses, sediment distribution and sediment bed changes during a one-year record of continuous discharges from a real stream. This methodology allows us to track the behaviour of different sediment size fractions along flow streamlines over time and identify self-maintenance conditions due to the combined effect of both flow multi-dimensionality and sediment transport.We apply this approximate methodology to two contiguous pools and riffles and demonstrate that, unexpectedly, they may rely on different mechanisms for self-maintenance due to differences in geometry and sediment size distribution. We also demonstrate that our methodology is potentially overarching and integrative of previous partial approaches based on flow multidimensionality or sediment transport, which tend to underestimate the occurrence of self-maintenance. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-18T03:30:31.843555-05:
      DOI: 10.1002/2016WR019464
  • GALAXY: A new hybrid MOEA for the optimal design of water distribution
    • Authors: Q. Wang; D. A. Savić, Z. Kapelan
      Abstract: A new hybrid optimizer, called genetically adaptive leaping algorithm for approximation and diversity (GALAXY), is proposed for dealing with the discrete, combinatorial, multi-objective design of Water Distribution Systems (WDSs), which is NP-hard and computationally intensive. The merit of GALAXY is its ability to alleviate to a great extent the parameterization issue and the high computational overhead. It follows the generational framework of multi-objective evolutionary algorithms (MOEAs) and includes six search operators and several important strategies. These operators are selected based on their leaping ability in the objective space from the global and local search perspectives. These strategies steer the optimization and balance the exploration and exploitation aspects simultaneously. A highlighted feature of GALAXY lies in the fact that it eliminates majority of parameters, thus being robust and easy-to-use. The comparative studies between GALAXY and three representative MOEAs on five benchmark WDS design problems confirm its competitiveness. GALAXY can identify better converged and distributed boundary solutions efficiently and consistently, indicating a much more balanced capability between the global and local search. Moreover, its advantages over other MOEAs become more substantial as the complexity of the design problem increases. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-18T03:30:27.853019-05:
      DOI: 10.1002/2016WR019854
  • Hydrological mediated denitrification in groundwater below a seasonal
           flooded restored riparian zone
    • Authors: Jannick Kolbjørn Jensen; Peter Engesgaard, Anders R. Johnsen, Vicens Marti, Bertel Nilsson
      Abstract: A restored riparian zone was characterized to understand the effects of flooding on subsurface hydrological flow paths and nitrate removal in groundwater. Field and laboratory investigations were combined with numerical modeling of dynamic flow and reactive nitrate transport. Flooding enhances nitrate removal in groundwater primarily by two mechanisms. First, by creating a stagnant flow zone beneath the flooded area thereby increasing the residence time and leaving more time for nitrate removal. Secondly, nitrate removal is increased by enhancing upward flow into the highly reactive organic-rich top layers. Flooding therefore contributes to nitrate removal in “hot spots”, where nitrate is transported to the peat and during “hot moments”, when flow is stagnant. The permeability of the capping peat layer relative to the aquifer is important as it controls both mechanisms. The model shows that the deep-seated nitrate removal is greater than projected from the laboratory nitrate reduction experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-18T03:30:24.184772-05:
      DOI: 10.1002/2016WR019581
  • The 21st century Colorado River hot drought and implications for the
    • Authors: Bradley Udall; Jonathan Overpeck
      Abstract: Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906-1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9°C above the 1906-99 average), confirming model-based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend towards greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively -20% by mid-century and -35% by end–century, with support for losses exceeding -30% at mid-century and -55% at end-century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-17T11:45:24.540598-05:
      DOI: 10.1002/2016WR019638
  • A cellular automata-based deterministic inversion algorithm for the
           characterization of linear structural heterogeneities
    • Authors: P. Fischer; A. Jardani, N. Lecoq
      Abstract: Inverse problem permits to map the subsurface properties from a few observed data. The inverse problem can be physically constrained by a priori information on the property distribution in order to limit the non-uniqueness of the solution. The geostatistical information are often chosen as a priori information, however when the field properties present a spatial locally-distributed high variability the geostatistical approach becomes inefficient.Therefore, we propose a new method adapted for fields presenting linear structures (such as a fractured field). The Cellular Automata-based Deterministic Inversion (CADI) method is, as far as we know when this paper is produced, the first inversion method which permits a deterministic inversion based on a Bayesian approach and using a dynamic optimization to generate different linear structures iteratively. The model is partitioned in cellular automaton subspaces, each one controlling a different zone of the model. A cellular automata subspace structures the properties of the model in two units (‘structure' and ‘background') and control their dispensing direction and their values. The partitioning of the model in subspaces permits to monitor a large-scale structural model with only a few pilot-parameters and to generate linear structures with local direction changes. Thereby, the algorithm can easily handle with large-scale structures, and a sensitivity analysis is possible on these structural pilot-parameters, which permits to considerably accelerate the optimization process in order to find the best structural geometry. The algorithm has been successfully tested on simple, to more complex, theoretical models with different inversion techniques by using seismic and hydraulic data. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T10:50:42.408559-05:
      DOI: 10.1002/2016WR019572
  • Understanding watershed hydrogeochemistry: 2. Synchronized hydrological
           and geochemical processes drive stream chemostatic behavior
    • Authors: Li Li; Chen Bao, Pamela L. Sullivan, Susan Brantley, Yuning Shi, Chris Duffy
      Abstract: Why do solute concentrations in streams remain largely constant while discharge varies by orders of magnitude? We used a new hydrological land surface and reactive transport code, RT-Flux-PIHM, to understand this long-standing puzzle. We focus on the non-reactive chloride (Cl) and reactive magnesium (Mg) in the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO). Simulation results show that stream discharge comes from surface runoff (Qs), soil lateral flow (QL), and deeper groundwater (QG), with QL contributing >70%. In the summer when high evapotranspiration dries up and disconnects most of the watershed from the stream, Cl is trapped along planar hillslopes. Successive rainfalls connect the watershed and mobilize trapped Cl, which counteracts dilution effects brought about by high water storage (Vw) and maintains chemostasis. Similarly, the synchronous response of clay dissolution rates (Mg source) to hydrological conditions, maintained largely by a relatively constant ratio between wetted mineral surface area Aw and Vw, controls Mg chemostatic behavior. Sensitivity analysis indicates that cation exchange plays a secondary role in determining chemostasis compared to clay dissolution, although it does store an order-of-magnitude more Mg on exchange sites than soil water. Model simulations indicate that dilution (concentration decrease with increasing discharge) occurs only when mass influxes from soil lateral flow are negligible (e.g., via having low clay surface area) so that stream discharge is dominated by mass fluxes such as deep groundwater influxes that are relatively constant and unresponsive to surface hydrological processes. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T10:50:37.041497-05:
      DOI: 10.1002/2016WR018935
  • Efficient evaluation of small failure probability in high-dimensional
           groundwater contaminant transport modeling via a two-stage Monte Carlo
    • Authors: Jiangjiang Zhang; Weixuan Li, Guang Lin, Lingzao Zeng, Laosheng Wu
      Abstract: In decision-making for groundwater management and contamination remediation, it is important to accurately evaluate the probability of the occurrence of a failure event. For small failure probability analysis, a large number of model evaluations are needed in the Monte Carlo (MC) simulation, which is impractical for CPU-demanding models. One approach to alleviate the computational cost caused by the model evaluations is to construct a computationally inexpensive surrogate model instead. However, using a surrogate approximation can cause an extra error in the failure probability analysis. Moreover, constructing accurate surrogates is challenging for high-dimensional models, i.e., models containing many uncertain input parameters. To address these issues, we propose an efficient two-stage MC approach for small failure probability analysis in high-dimensional groundwater contaminant transport modeling. In the first stage, a low-dimensional representation of the original high-dimensional model is sought with Karhunen-Loève expansion and sliced inverse regression jointly, which allows for the easy construction of a surrogate with polynomial chaos expansion. Then a surrogate-based MC simulation is implemented. In the second stage, the small number of samples that are close to the failure boundary are re-evaluated with the original model, which corrects the bias introduced by the surrogate approximation. The proposed approach is tested with a numerical case study and is shown to be 100 times faster than the traditional MC approach in achieving the same level of estimation accuracy. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T10:50:31.716244-05:
      DOI: 10.1002/2016WR019518
  • Multiobjective hedging rules for flood water conservation
    • Authors: Wei Ding; Chi Zhang, Ximing Cai, Yu Li, Huicheng Zhou
      Abstract: Flood water conservation can be beneficial for water uses especially in areas with water stress but also can pose additional flood risk. The potential of flood water conservation is affected by many factors, especially decision makers' preference for water conservation and reservoir inflow forecast uncertainty. This paper discusses the individual and joint effects of these two factors on the tradeoff between flood control and water conservation, using a multi-objective, two-stage reservoir optimal operation model. It is shown that hedging between current water conservation and future flood control exists only when forecast uncertainty or decision makers' preference is within a certain range, beyond which, hedging is trivial and the multi-objective optimization problem is reduced to a single objective problem with either flood control or water conservation. Different types of hedging rules are identified with different levels of flood water conservation preference, forecast uncertainties, acceptable flood risk, and reservoir storage capacity. Critical values of decision preference (represented by a weight) and inflow forecast uncertainty (represented by standard deviation) are identified. These inform reservoir managers with a feasible range of their preference to water conservation and thresholds of forecast uncertainty, specifying possible water conservation within the thresholds. The analysis also provides inputs for setting up an optimization model by providing the range of objective weights and the choice of hedging rule types. A case study is conducted to illustrate the concepts and analyses. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T10:50:26.487381-05:
      DOI: 10.1002/2016WR019452
  • Understanding watershed hydrogeochemistry: 1. Development of RT-Flux-PIHM
    • Authors: Chen Bao; Li Li, Yuning Shi, Christopher Duffy
      Abstract: Model development in hydrology and geochemistry has been advancing separately with limited integration. We developed a watershed hydrogeochemical code RT-Flux-PIHM to understand complex interactions between hydrological processes (PIHM), land-surface processes (FLUX – Noah Land Surface Model), and multi-component subsurface reactive transport (RT). The RT module simulates geochemical processes including aqueous complexation, surface complexation, mineral dissolution and precipitation, and cation exchange. The RT module is verified against the widely-used reactive transport code CrunchFlow. The code uses semi-discrete finite volume methods and irregular gridding, and offers data harvesting capabilities from national databases. The application of RT-Flux-PIHM is demonstrated by applying the model in the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO). We aim to understand key processes that govern hydrogeochemical dynamics of the non-reactive chloride and reactive magnesium. Simulation results indicate that watershed characteristics, in particular topography, dictate the spatial distributions of water content and soil dissolution rates. Ion exchange provides buffering capacities and leads to a hysteresis loop of concentration and discharge relationship of magnesium, which differs from the open hysteresis of chloride. RT-Flux-PIHM offers physics-based modeling capabilities to integrate the vast amount of water and chemistry data that have now become available, to perform virtual experiments under “what if” scenarios, to differentiate the relative importance of individual processes, and to test hypotheses at the interface of hydrology and geochemistry. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T10:45:38.213919-05:
      DOI: 10.1002/2016WR018934
  • Analytical solution for tension-saturated and unsaturated flow from
           wicking porous pipes in subsurface irrigation: The Kornev-Philip legacies
    • Authors: A.R. Kacimov; Yu.V. Obnosov
      Abstract: The Russian engineer Kornev in his 1935 book raised perspectives of subsurface “negative pressure” irrigation, which have been overlooked in modern soil science. Kornev's auto-irrigation utilizes wicking of a vacuumed water from a porous pipe into a dry adjacent soil. We link Kornev's technology with a slightly modified J.R.Philip's (1984) analytical solutions for unsaturated flow from a 2D cylindrical pipe in an infinite domain. Two Darcian flows are considered and connected through continuity of pressure along the pipe-soil contact. The first fragment is a thin porous pipe wall in which water seeps at tension saturation, the hydraulic head is a harmonic function varying purely radially across the wall. The Thiem solution in this fragment gives the boundary condition for azimuthally varying suction pressure in the second fragment, ambient soil, making the exterior of the pipe. The constant head, rather than Philip's isobaricity boundary condition, along the external wall slightly modifies Philip's formulae for the Kirchhoff potential and pressure head in the soil fragment. Flow characteristics (magnitudes of the Darcian velocity, total flow rate and flow net) are explicitly expressed through series of Macdonald's functions. For a given pipe's external diameter, wall thickness, position of the pipe above a free water datum in the supply tank, saturated conductivities of the wall and soil, as well as soil's sorptive number, a nonlinear equation with respect to the total discharge from the pipe is obtained and solved by a computer algebra routine. Efficiency of irrigation is evaluated by computation of the moisture content within selected zones surrounding the porous pipe. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T03:20:55.713615-05:
      DOI: 10.1002/2016WR019919
  • Modeling sediment mobilization using a distributed hydrological model
           coupled with a bank stability model
    • Authors: J. Stryker; B. Wemple, A. Bomblies
      Abstract: In addition to surface erosion, streambank erosion and failure contributes significant sediment and sediment-bound nutrients to receiving waters during high flow events. However, distributed and mechanistic simulation of stream bank sediment contribution to sediment loads in a watershed has not been achieved. Here, we present a full coupling of existing distributed watershed and bank stability models, and apply the resulting model to the Mad River in central Vermont. We fully coupled the Bank Stability and Toe Erosion Model (BSTEM) with the Distributed Hydrology Soil Vegetation Model (DHSVM) to allow the simulation of streambank erosion and potential failure in a spatially explicit environment. We demonstrate the model's ability to simulate the impacts of unstable streams on sediment mobilization and transport within a watershed, and discuss the model's capability to simulate watershed sediment loading under climate change. The calibrated model simulates total suspended sediment loads and reproduces variability in suspended sediment concentrations at watershed and subbasin outlets. In addition, characteristics such as land use and road-to-stream ratio of subbasins are shown to impact the relative proportions of sediment mobilized by overland erosion, erosion of roads, and streambank erosion and failure in the subbasins and watershed. This coupled model will advance mechanistic simulation of suspended sediment mobilization and transport from watersheds, which will be particularly valuable for investigating the potential impacts of climate and land use changes, as well as extreme events. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-15T03:15:32.850678-05:
      DOI: 10.1002/2016WR019143
  • Process connectivity in a naturally prograding river delta
    • Authors: Alicia Sendrowski; Paola Passalacqua
      Abstract: River deltas are lowland systems that can display high hydrological connectivity. This connectivity can be structural (morphological connections), functional (control of fluxes), and process connectivity (information flow from system drivers to sinks). In this work, we quantify hydrological process connectivity in Wax Lake Delta, coastal Louisiana, by analyzing couplings among external drivers (discharge, tides, and wind) and water levels recorded at five islands and one channel over summer 2014. We quantify process connections with information theory, a branch of mathematics concerned with the communication of information. We represent process connections as a network; variables serve as network nodes and couplings as network links describing the strength, direction, and timescale of information flow. Comparing process connections at long (105-days) and short (10-days) timescales, we show that tides exhibit daily synchronization with water level, with decreasing strength from downstream to upstream, and that tides transfer information as tides transition from spring to neap. Discharge synchronizes with water level and the timescale of its information transfer compares well to physical travel times through the system, computed with a hydrodynamic model. Information transfer and physical transport show similar spatial patterns, although information transfer timescales are larger than physical travel times. Wind events associated with water level set-up lead to increased process connectivity with highly variable information transfer timescales. We discuss the information theory results in the context of the hydrologic behavior of the delta, the role of vegetation as a connector/dis-connector on islands, and the applicability of process networks as tools for delta modeling results. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-11T03:25:32.413087-05:
      DOI: 10.1002/2016WR019768
  • Using SAS functions and high resolution isotope data to unravel travel
           time distributions in headwater catchments
    • Authors: Paolo Benettin; Chris Soulsby, Christian Birkel, Doerthe Tetzlaff, Gianluca Botter4, Andrea Rinaldo
      Abstract: We use high resolution tracer data from an experimental site to test theoretical approaches that integrate catchment-scale flow and transport processes in a unified framework centered on selective age sampling by streamflow and evapotranspiration fluxes. Transport processes operating at the catchment scale are reflected in the evolving residence time distribution of the catchment water storage and in the age-selection operated by out-fluxes. Such processes are described here through StorAge Selection (SAS) functions parametrized as power laws of the normalized rank storage. Such functions are computed through appropriate solution of the master equation defining formally the evolution of residence and travel times. By representing the way in which catchment storage generates outflows composed by water of different ages, the main mechanism regulating the tracer composition of runoff is clearly identified and detailed comparison with empirical data sets are possible. Properly calibrated numerical tools provide simulations that convincingly reproduce complex measured signals of daily deuterium content in stream waters during wet and dry periods. Results for the catchment under consideration are consistent with other recent studies indicating a tendency for natural catchments to preferentially release younger available water. The study shows that power-law SAS functions prove a powerful tool to explain catchment-scale transport processes that also has potential in less intensively monitored sites. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-11T03:20:29.602217-05:
      DOI: 10.1002/2016WR020117
  • Experimental Investigation of clogging dynamics in homogeneous porous
    • Authors: Jikang Shen; Rui Ni
      Abstract: A 3D refractive-index matching Lagrangian particle tracking (3D-RIM-LPT) system was developed to study the filtration and clogging process inside a homogeneous porous medium. A small subset of particles flowing through the porous medium was dyed and tracked. As this subset was randomly chosen, its dynamics is representative of all the rest. The statistics of particle locations, number, and velocity vectors were obtained as functions of different volumetric concentrations. It is found that, in our system, the clogging time decays with particle concentration following a power law relationship. As the concentration increases, there is a transition from depth filtration to cake filtration. At high concentration, more clogged pores lead to frequent flow redirections and more transverse migrations of particles. In addition, the velocity distribution of the transverse direction is symmetrical around zero, and it is slightly more intermittent than the random Gaussian curve due to particle-particle interactions and particle-grain interactions. In contrast, as clogging develops, the longitudinal velocity of particles along the main flow direction has peak near zero because of those trapped particles. But at the same time, the remaining open pores will experience larger pressure and, as a result, particles through those pores will have a larger longitudinal velocity. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-11T03:20:27.937535-05:
      DOI: 10.1002/2016WR019421
  • The effects of spatial resolution and dimensionality on modeling
           regional-scale hydraulics in a multichannel river
    • Authors: Elizabeth H. Altenau; Tamlin M. Pavelsky, Paul D. Bates, Jeffrey C. Neal
      Abstract: As modeling capabilities at regional and global scales improve, questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics. This study uses the hydrodynamic model LISFLOOD-FP to simulate patterns of water surface elevation (WSE), depth, and inundation extent across a ∼90 km, anabranching reach of the Tanana River, Alaska. To provide boundary conditions, we collected field observations of bathymetry and WSE during a two-week field campaign in summer 2013. For the first time at this scale, we test a simple, raster-based model's capabilities to simulate 2D, in-channel patterns of WSE and inundation extent. Additionally, we compare finer resolution (≤ 25 m) 2D models to four other models of lower dimensionality and coarser resolution (100–500 m) to determine the effects of simplifying process representation. Results indicate that simple, raster-based models can accurately simulate 2D, in-channel hydraulics in the Tanana. Also, the fine-resolution, 2D models produce lower errors in spatiotemporal outputs of WSE and inundation extent compared to coarse-resolution, 1D models: 22.6 cm vs. 56.4 cm RMSE for WSE, and 90% vs. 41% Critical Success Index values for simulating inundation extent. Incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers RMSE in spatially distributed WSE by at least 16%. As a result, better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global scale models. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-09T10:51:16.905953-05:
      DOI: 10.1002/2016WR019396
  • Hydro-geomorphic perturbations on the soil-atmosphere CO2 exchange: How
           (un)certain are our balances?
    • Authors: Yannis G. Dialynas; Rafael L. Bras, Daniel deB. Richter
      Abstract: Attempts to estimate the influence of erosion on the carbon (C) cycle are limited by difficulties in accounting for the fate of mobilized organic material and for the uncertainty associated with land management practices. This study proposes a method to quantify the uncertainty introduced by the influence of land management on soil organic C (SOC) generation and decomposition at eroding soils. The framework is implemented in tRIBS-ECO (Triangulated Irregular Network-based Real-time Integrated Basin Simulator-Erosion and Carbon Oxidation). tRIBS-ECO is a spatially- and depth-explicit model of C dynamics coupled with a process-based hydro-geomorphic model. We assess the impact of soil erosion on the net soil-atmosphere CO2 exchange at the Calhoun Critical Zone Observatory, one of the most severely agriculturally eroded regions in the U.S. Measurements of SOC storage are used from different catena positions. We demonstrate that the spatio-temporal variations of land management practices introduce significant uncertainty in estimates of the erosion-induced CO2 exchange with the atmosphere. Observations and simulations suggest that a substantial portion of eroded organic material is buried in alluvial sediments at the study site. According to results, recent reforestation led to a partial decline in soil and SOC erosion rates. It is suggested that the representation of the fine spatio-temporal variability of the dynamics of eroded C is important in the computation of C budgets in regional and global scales. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-09T10:50:30.054548-05:
      DOI: 10.1002/2016WR019411
  • Permeability, porosity, and mineral surface area changes in basalt cores
           induced by reactive transport of CO2-rich brine
    • Authors: Andrew J. Luhmann; Benjamin M. Tutolo, Brian C. Bagley, David F.R. Mildner, William E. Seyfried, Martin O. Saar
      Abstract: Four reactive flow-through laboratory experiments (two each at 0.1 ml/min and 0.01 ml/min flow rates) at 150°C and 150 bar (15 MPa) are conducted on intact basalt cores to assess changes in porosity, permeability, and surface area caused by CO2-rich fluid-rock interaction. Permeability decreases slightly during the lower flow rate experiments and increases during the higher flow rate experiments. At the higher flow rate, core permeability increases by more than one order of magnitude in one experiment and less than a factor of two in the other due to differences in preexisting flow path structure. X-ray computed tomography (XRCT) scans of pre- and post-experiment cores identify both mineral dissolution and secondary mineralization, with a net decrease in XRCT porosity of ∼0.7% – 0.8% for all four cores. (Ultra) small-angle neutron scattering ((U)SANS) datasets indicate an increase in both (U)SANS porosity and specific surface area (SSA) over the ∼ 1 nm- to 10 µm-scale range in post-experiment basalt samples, with differences due to flow rate and reaction time. Net porosity increases from summing XRCT and (U)SANS analyses are consistent with core mass decreases. (U)SANS data suggest an overall preservation of the pore structure with no change in mineral surface roughness from reaction, and the pore structure is unique in comparison to previously published basalt analyses. Together, these datasets illustrate changes in physical parameters that arise due to fluid-basalt interaction in relatively low pH environments with elevated CO2 concentration, with significant implications for flow, transport, and reaction through geologic formations. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-07T11:30:34.27663-05:0
      DOI: 10.1002/2016WR019216
  • Pore-scale modelling of wettability alteration during primary drainage
    • Authors: W. Kallel; M.I.J. van Dijke, K.S. Sorbie, Rachel Wood
      Abstract: While carbonate reservoirs are recognized to be weakly-to-moderately oil-wet at the core-scale, pore-scale wettability distributions remain poorly understood. In particular, the wetting state of micropores (pores
      PubDate: 2017-02-07T03:20:49.524675-05:
      DOI: 10.1002/2016WR018703
  • Improving probabilistic prediction of daily streamflow by identifying
           Pareto optimal approaches for modeling heteroscedastic residual errors
    • Authors: David McInerney; Mark Thyer, Dmitri Kavetski, Julien Lerat, George Kuczera
      Abstract: Reliable and precise probabilistic prediction of daily catchment-scale streamflow requires statistical characterization of residual errors of hydrological models. This study focuses on approaches for representing error heteroscedasticity with respect to simulated streamflow, i.e., the pattern of larger errors in higher streamflow predictions. We evaluate 8 common residual error schemes, including standard and weighted least squares, the Box-Cox transformation (with fixed and calibrated power parameter λ) and the log-sinh transformation. Case studies include 17 perennial and 6 ephemeral catchments in Australia and USA, and two lumped hydrological models. Performance is quantified using predictive reliability, precision and volumetric bias metrics. We find the choice of heteroscedastic error modelling approach significantly impacts on predictive performance, though no single scheme simultaneously optimizes all performance metrics. The set of Pareto optimal schemes, reflecting performance trade-offs, comprises Box-Cox schemes with λ of 0.2 and 0.5, and the log scheme (λ=0, perennial catchments only). These schemes significantly outperform even the average-performing remaining schemes (e.g., across ephemeral catchments, median precision tightens from 105% to 40% of observed streamflow, and median biases decrease from 25% to 4%). Theoretical interpretations of empirical results highlight the importance of capturing the skew/kurtosis of raw residuals and reproducing zero flows. Paradoxically, calibration of λ is often counterproductive: in perennial catchments, it tends to overfit low flows at the expense of abysmal precision in high flows. The log-sinh transformation is dominated by the simpler Pareto optimal schemes listed above. Recommendations for researchers and practitioners seeking robust residual error schemes for practical work are provided. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-03T20:00:33.888941-05:
      DOI: 10.1002/2016WR019168
  • An estimation of the main wetting branch of the soil water retention curve
           based on its main drying branch using the machine learning method
    • Authors: Krzysztof Lamorski; Jiří Šimůnek, Cezary Sławiński, Joanna Lamorska
      Abstract: In this paper, we estimated using the machine learning methodology the main wetting branch of the soil water retention curve based on the knowledge of the main drying branch and other, optional, basic soil characteristics (particle size distribution, bulk density, organic matter content, or soil specific surface). The support vector machine algorithm, was used for the models' development. The data needed by this algorithm for model training and validation consisted of 104 different undisturbed soil core samples collected from the topsoil layer (A horizon) of different soil profiles in Poland. The main wetting and drying branches of SWRC, as well as other basic soil physical characteristics, were determined for all soil samples. Models relying on different sets of input parameters were developed and validated. The analysis showed that taking into account other input parameters (i.e., particle size distribution, bulk density, organic matter content, or soil specific surface) than information about the drying branch of the SWRC has essentially no impact on the models' estimations. Developed models are validated and compared with well-known models that can be used for the same purpose, such as the Mualem [1977] (M77) and Kool and Parker [1987] (KP87) models. The developed models estimate the main wetting SWRC branch with estimation errors (RMSE=0.018 m3/m3) that are significantly lower than those for the M77 (RMSE=0.025 m3/m3) or KP87 (RMSE=0. 047 m3/m3) models. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-03T19:55:42.871699-05:
      DOI: 10.1002/2016WR019533
  • An Eulerian equation for snow accumulation downstream of an object
    • Authors: Noriaki Ohara
      Abstract: This study investigated the form of the governing equation for the particle distribution by focusing on the particle motion processes rather than flow regime and particle characteristics. A linear erosion term for a fetch-eddy effect was introduced to the advection dispersion equation. The equation formulated in this paper described most of the particle deposit patterns behind an object including porous and solid snow fences, and a tree. This theory may enable us to estimate particle motion parameters, such as diffusion, drift, and erosion coefficients, from field observed particle distributions. Snow stratigraphy observed by ground penetrating radar (GPR) was used verify to result of the modeled theoretical snow redistribution. These analyses confirmed the effectiveness of the linear erosion term at explaining the particle deposition patterns due to eddys around a porous snow fence. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-03T19:55:37.414334-05:
      DOI: 10.1002/2016WR019673
  • A parametric approach for simultaneous bias correction and high-resolution
           downscaling of climate model rainfall
    • Authors: Antonios Mamalakis; Andreas Langousis, Roberto Deidda, Marino Marrocu
      Abstract: Distribution mapping has been identified as the most efficient approach to bias correct climate model rainfall, while reproducing its statistics at spatial and temporal resolutions suitable to run hydrologic models. Yet, its implementation based on empirical distributions derived from control samples (referred to as non-parametric distribution mapping), makes the method's performance sensitive to sample length variations, the presence of outliers, the spatial resolution of climate model results, and may lead to biases, especially in extreme rainfall estimation. To address these shortcomings, we propose a methodology for simultaneous bias correction and high resolution downscaling of climate model rainfall products that uses: a) a two component theoretical distribution model (i.e. a generalized Pareto (GP) model for rainfall intensities above a specified threshold u*, and an exponential model for lower rainrates), and b) proper interpolation of the corresponding distribution parameters on a user-defined high-resolution grid, using kriging for uncertain data. We assess the performance of the suggested parametric approach relative to the non-parametric one, using daily raingauge measurements from a dense network in the island of Sardinia (Italy), and rainfall data from 4 GCM/RCM model chains of the ENSEMBLES project. The obtained results shed light on the competitive advantages of the parametric approach, which is proved more accurate and considerably less sensitive to the characteristics of the calibration period, independent of the GCM/RCM combination used. This is especially the case for extreme rainfall estimation, where the GP assumption allows for more accurate and robust estimates, also beyond the range of the available data. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-03T19:55:34.836689-05:
      DOI: 10.1002/2016WR019578
  • Estimating bed shear stress from remotely measured surface turbulent
           dissipation fields in open channel flows
    • Authors: E. D. Johnson; E. A. Cowen
      Abstract: Synoptic information on bed shear stress is necessary in predicting the transport of sediments and environmental contaminants in rivers and open channels. Existing methods of estimating bed shear stress typically involve measuring vertical profiles of streamwise velocity or Reynolds stress and taking advantage of the logarithmic or the constant stress region, respectively, to determine friction velocity and subsequently, bed shear stress. While effective, these methods yield local measurements of bed shear stress only. Direct measurements of bed shear stress can also be obtained through measurements with a drag plate. However, this method yields average shear stress information over the area of the plate and is impractical for large-scale implementation in the field.Here we present a method capable of providing continuous synoptic measurements of bed shear stress over a large field-of-view. A series of Large-Scale Particle Image Velocimetry (LSPIV) and Acoustic Doppler Velocimetry (ADV) measurements were made in a variety of flows generated in a wide-open channel facility. Turbulent dissipation is calculated on the free-surface from the 2-D LSPIV results and is correlated with near surface ADV measurements of turbulent dissipation in the water column. The ADV results are consistent with the Nezu [1977] established relationship for the vertical variation of turbulent dissipation in the water column. Knowledge of the correlation between free-surface and near-surface dissipation values coupled with Nezu's [1977] relationship allow a robust and accurate estimate of friction velocity to be made and subsequently, shear stress at the bed can be estimated. This article is protected by copyright. All rights reserved.
      PubDate: 2017-02-03T19:55:29.945479-05:
      DOI: 10.1002/2016WR018898
  • Heat and water transport in soils and across the soil-atmosphere
           interface: 2. Numerical analysis
    • Authors: Thomas Fetzer; Jan Vanderborght, Klaus Mosthaf, Kathleen M. Smits, Rainer Helmig
      Abstract: In an accompanying paper, we presented an overview of a wide variety of modeling concepts, varying in complexity, used to describe evaporation from soil. Using theoretical analyses, we explained the simplifications and parameterizations in the different approaches. In this paper, we numerically evaluate the consequences of these simplifications and parameterizations. Two sets of simulations were performed. The first set investigates lateral variations in vertical fluxes, which emerge from both homogeneous and heterogeneous porous media, and their importance to capturing evaporation behavior. When evaporation decreases from parts of the heterogeneous soil surface, lateral flow and transport processes in the free flow and in the porous medium generate feedbacks that enhance evaporation from wet surface areas. In the second set of simulations, we assume that the vertical fluxes do not vary considerably in the simulation domain and represent the system using one-dimensional models which also consider dynamic forcing of the evaporation process, for example, due to diurnal variations in net radiation. Simulated evaporation fluxes subjected to dynamic forcing differed considerably between model concepts depending on how vapor transport in the air phase and the interaction at the interface between the free flow and porous medium were represented or parameterized. However, simulated cumulative evaporation losses from initially wet soil profiles were very similar between model concepts and mainly controlled by the desorptivity, Sevap, of the porous medium, which depends mainly on the liquid flow properties of the porous medium.
      PubDate: 2017-02-03T10:25:43.277283-05:
      DOI: 10.1002/2016WR019983
  • Heat and water transport in soils and across the soil-atmosphere
           interface: 1. Theory and different model concepts
    • Authors: Jan Vanderborght; Thomas Fetzer, Klaus Mosthaf, Kathleen M. Smits, Rainer Helmig
      Abstract: Evaporation is an important component of the soil water balance. It is composed of water flow and transport processes in a porous medium that are coupled with heat fluxes and free air flow. This work provides a comprehensive review of model concepts used in different research fields to describe evaporation. Concepts range from nonisothermal two-phase flow, two-component transport in the porous medium that is coupled with one-phase flow, two-component transport in the free air flow to isothermal liquid water flow in the porous medium with upper boundary conditions defined by a potential evaporation flux when available energy and transfer to the free airflow are limiting or by a critical threshold water pressure when soil water availability is limiting. The latter approach corresponds with the classical Richards equation with mixed boundary conditions. We compare the different approaches on a theoretical level by identifying the underlying simplifications that are made for the different compartments of the system: porous medium, free flow and their interface, and by discussing how processes not explicitly considered are parameterized. Simplifications can be grouped into three sets depending on whether lateral variations in vertical fluxes are considered, whether flow and transport in the air phase in the porous medium are considered, and depending on how the interaction at the interface between the free flow and the porous medium is represented. The consequences of the simplifications are illustrated by numerical simulations in an accompanying paper.
      PubDate: 2017-02-03T10:25:28.575528-05:
      DOI: 10.1002/2016WR019982
  • Improved water balance component estimates through Joint Assimilation of
           GRACE water storage and SMOS soil moisture retrievals
    • Authors: Siyuan Tian; Paul Tregoning, Luigi J. Renzullo, Albert I.J.M. van Dijk, Jeffrey P. Walker, Valentijn R.N. Pauwels, Sébastien Allgeyer
      Abstract: The accuracy of global water balance estimates is limited by the lack of observations at large scale, and the uncertainties of model simulations. Global retrievals of terrestrial water storage (TWS) change and soil moisture (SM) from satellites provide an opportunity to improve model estimates through data assimilation. However, combining these two data sets is challenging due to the disparity in temporal and spatial resolution at both vertical and horizontal scale. For the first time, TWS observations from the Gravity Recovery and Climate Experiment (GRACE) and near-surface SM observations from the Soil Moisture and Ocean Salinity (SMOS) were jointly assimilated into a water balance model using the Ensemble Kalman Smoother from January 2010 to December 2013 for the Australian continent. The performance of joint assimilation was assessed against open-loop model simulations and the assimilation of either GRACE TWS anomalies or SMOS SM alone. The SMOS-only assimilation improved SM estimates but reduced the accuracy of groundwater and TWS estimates. The GRACE-only assimilation improved groundwater estimates but did not always produce accurate estimates of SM. The joint assimilation typically led to more accurate water storage profile estimates with improved surface SM, root-zone SM, and groundwater estimates against in-situ observations. The assimilation successfully downscaled GRACE-derived integrated water storage horizontally and vertically into individual water stores at the same spatial scale as the model and SMOS, and partitioned monthly-averaged TWS into daily estimates. These results demonstrate that satellite TWS and SM measurements can be jointly assimilated to produce improved water balance component estimates. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-31T18:55:50.492522-05:
      DOI: 10.1002/2016WR019641
  • Assessment of uncertainties in global land cover products for hydroclimate
           modeling in India
    • Authors: C. G. Madhusoodhanan; K. G. Sreeja, T. I. Eldho
      Abstract: Earth's land cover (LC) has significant influence on land-atmospheric processes and affects the climate at multiple scales. There are multiple Global LC (GLC) datasets which are yet to be evaluated for uncertainties and their propagation into the simulation of land surface fluxes (LSFs) in land surface/climate modeling. The present study assesses the uncertainties in seven GLC products with reference to a regional dataset for the simulation of LSFs in India using a macro-scale land surface model. There is considerable overestimation of the extent of croplands in most of the GLCs. The uncertainties in LCs exert significant bias in the simulation of the LSFs of actual evapotranspiration (ETa), latent heat (LE) and sensible heat (H) fluxes. Error propagation in LSFs is proportional to the bias in cropping intensity under rainfed condition. The high under-representation of cropland area in the UMd dataset results in highest bias in LSFs whereas the least cropland bias in Globland30 leads to least bias. Irrigation has higher potential to alter the LSFs than uncertainties related to LC especially in regions with large area under irrigation like India. The changes in LSFs are higher in arid/semi-arid regions with medium irrigation intensity than in sub-humid regions with high irrigation intensity. This has significant implications for the country's future irrigation expansion plans in the arid/semi-arid regions. The study also emphasizes the need for focused efforts to quantify the uncertainties from varying irrigation intensities in the next generation CMIP6 experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-31T18:40:33.448367-05:
      DOI: 10.1002/2016WR020193
  • An index for drought induced financial risk in the mining industry
    • Authors: L. Bonnafous; U. Lall, J. Siegel
      Abstract: Water scarcity has emerged as a potential risk for mining operations. High capital spending for desalination and water conflicts leading to asset stranding have recently occurred. Investors in mining companies are interested in the exposure to such risks across portfolios of mining assets (whether the practical at-site consequences are foregone production, higher OPEX and CAPEX and ensuing lost revenues, or asset-stranding). In this paper, an index of the potential financial exposure of a portfolio is developed and its application is illustrated. Since the likely loss at each mine is hard to estimate a priori, one needs a proxy for potential loss. The index considers drought duration, severity and frequency (defined by a return-level in years) at each mining asset, and provides a measure of financial exposure through weighing of production or Net Asset Value. Changes in human needs are not considered, but are relevant, and could be incorporated if global data on mine and other water use were available at the appropriate resolution. Potential for contemporaneous drought incidence across sites in a portfolio is considered specifically. Through an appropriate choice of drought thresholds, an analyst can customize a scenario to assess potential losses in production value or profits, or whether conflicts could emerge that would lead to stranded assets or capital expenditure to secure alternate water supplies. Global climate data sets that allow a customized development of such an index are identified, and selected mining company portfolios are scored as to the risk associated with one publicly available drought index. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-31T18:35:41.919173-05:
      DOI: 10.1002/2016WR019866
  • The pulse of driftwood export from a very large forested river basin over
           multiple timescales, Slave River, Canada
    • Authors: Natalie Kramer; Ellen Wohl, Brooke Hess-Homeier, Stephen Leisz
      Abstract: This study presents a case study of large wood transport on the great Slave River in northern Canada with the objective to better understand the processes of and variability in pulsed wood fluxes from large forested catchments. We use a varied approach, integrating field characterization of wood, historical anecdotes, repeat aerial imagery of stored wood, and time-lapse imagery of moving wood, for a robust analysis and synthesis of processes behind pulsed wood flux, from yearly uncongested export to rare congested wood floods. Repeat monitoring of known sites of temporary storage with new or historic imagery proved to be a very useful tool for constraining wood flux histories. Pulsed wood export on the Slave River is not an artefact of episodic recruitment from major up-basin disturbances, but rather reflects decadal- to half-century-scale discharge patterns that re-distribute wood recruited from channel migration and bank slumping. We suggest that the multi-year flow history is of paramount importance for estimating wood flux magnitude, followed in declining importance by the yearly sequence of peaks and the magnitude and characteristics of the rising limb of individual floods. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-30T05:16:40.888271-05:
      DOI: 10.1002/2016WR019260
  • Tracer-based characterization of hyporheic exchange and benthic biolayers
           in streams
    • Authors: Julia L.A. Knapp; Ricardo González-Pinzón, Jennifer D. Drummond, Laurel G. Larsen, Olaf A. Cirpka, Judson W. Harvey
      Abstract: Shallow benthic biolayers at the top of the streambed are believed to be places of enhanced biogeochemical turnover within the hyporheic zone. They can be investigated by reactive stream tracer tests with tracer recordings in the streambed and in the stream channel. Common in-stream measurements of such reactive tracers cannot localize where the processing primarily takes place, whereas isolated vertical depth profiles of solutes within the hyporheic zone are usually not representative of the entire stream. We present results of a tracer test where we injected the conservative tracer bromide together with the reactive tracer resazurin into a third-order stream and combined the recording of in-stream breakthrough curves with multi-depth sampling of the hyporheic zone at several locations. The transformation of resazurin was used as an indicator of metabolism, and high-reactivity zones were identified from depth profiles. The results from our subsurface analysis indicate that the potential for tracer transformation (i.e., the reaction rate constant) varied with depth in the hyporheic zone. This highlights the importance of the benthic biolayer, which we found to be on average 2 cm thick in this study, which ranged from one third to one half of the full depth of the hyporheic zone. The reach-scale approach integrated the effects of processes along the reach length, isolating hyporheic processes relevant for whole-stream chemistry and estimating effective reaction rates. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-28T03:15:41.02738-05:0
      DOI: 10.1002/2016WR019393
  • The influence of NaCl concentration on salt precipitation in heterogeneous
           porous media
    • Authors: Mina Bergstad; Dani Or, P.J. Withers, Nima Shokri
      Abstract: Evaporation of saline solutions from porous media is governed by the complex interactions between the transport properties of the porous media, the evaporating solution and the external boundary conditions. In the present study, we have investigated the effects of salt concentration on the evaporation process from porous media in the presence of a sharp textural discontinuity; a common heterogeneity in natural porous media formed due to the weathering or formation of soil horizons, wind deposition and erosion. We have conducted a comprehensive series of macro- and micro-scale experiments to delineate how the precipitation pattern is modified as salt concentration varies from relatively low values to a concentration close to the solubility limit. For concentrations much less than the solubility limit, the precipitation begins at the coarse-textured part of the heterogeneous porous media (which is a counter-intuitive result considering the preferential evaporation of water from the fine-textured part of the heterogeneous surface). However, when the concentration is close to the solubility limit, precipitation initiates preferentially at the fine-textured part of the heterogeneous porous surface. This behaviour results from the interaction between the transport properties of the porous media and the properties of the evaporating solution which must be considered. Additionally, using pore-scale images obtained by X-ray micro-computed tomography (CT), we have visualized the dynamics of precipitation in the presence of heterogeneity at high spatial and temporal resolution. The pore-scale results corroborate the mechanisms controlling the precipitation patterns in the presence of textural discontinuities inferred from the macro-scale experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-28T03:15:39.369613-05:
      DOI: 10.1002/2016WR020060
  • Characterizing the spatial correlation of daily streamflows
    • Authors: A. Betterle; M. Schirmer, G. Botter
      Abstract: In this study we propose an analytical framework to estimate the spatial correlation of daily flows in two arbitrary locations within a given hydrologic district or river basin. The method builds on the description of the coupled streamflow dynamics at the outlet of two catchments, which are represented as correlated shot noises forced by Poisson rainfall. Novel analytical expressions for the spatial correlation of discharge are derived using a limited number of parameters that encapsulate effective precipitation regime and catchment drainage rates. The method is suited to describe how heterogeneity of climate and landscape features impact the spatial and temporal variability of flow regimes along river systems. The analysis suggests that frequency and intensity of synchronous effective rainfall events in the relevant contributing catchments are the main driver of the spatial correlation of daily discharge, unless the drainage rates of the two catchments differ by almost one order of magnitude. The method also portrays how the topological arrangement of the two outlets along the river network influences the underlying streamflow correlation, and shows how nested catchments tend to maximize the spatial correlation of flow regimes. To demonstrate the potential of the tool, the model is tested on a set of sixteen catchments belonging to a 120,000 km2 region of the United States. The application evidences satisfactory performance (RMSE 
      PubDate: 2017-01-28T03:15:32.110113-05:
      DOI: 10.1002/2016WR019195
  • Controls on solute concentration-discharge relationships revealed by
           simultaneous hydrochemistry observations of hillslope runoff and stream
           flow: The importance of critical zone structure
    • Authors: Hyojin Kim; William E. Dietrich, Benjamin M. Thurnhoffer, Jim K. B. Bishop, Inez Y. Fung
      Abstract: We investigated controls on concentration-discharge relationships of a catchment underlain by argillite by monitoring both groundwater along a hillslope transect and stream chemistry. Samples were collected at 1-3-day intervals over four years (2009-2013) in Elder Creek in the Eel River Critical Zone Observatory in California. Runoff at our study hillslope is driven by vadose zone flux through deeply weathered argillite (5-25 m thick) to a perched, seasonally dynamic groundwater that then drains to Elder Creek. Low flow derives from the slowly draining deepest perched groundwater that reaches equilibrium between primary and secondary minerals and saturation with calcite under high subsurface pCO2. Arriving winter rains pass through the thick vadose zone, where they rapidly acquire solutes via cation exchange reactions (driven by high pCO2), and then recharge the groundwater that delivers runoff to the stream. These new waters displayed lower solute concentrations than the deep groundwater by less than a factor of 5 (except for Ca). Up to 74% of the total annual solute flux is derived from the vadose zone. The deep groundwater's Ca concentration decreased as it exfiltrates to the stream due to CO2 degassing and this Ca loss is equivalent of 30% of the total chemical weathering flux of Elder Creek. The thick vadose zone in weathered bedrock and the perched groundwater on underlying fresh bedrock result in two distinct processes that lead to the relatively invariant (chemostatic) concentration-discharge behavior. The processes controlling solute chemistry are not evident from stream chemistry and runoff analysis alone. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-27T10:50:43.586544-05:
      DOI: 10.1002/2016WR019722
  • Impacts of precipitation and potential evapotranspiration patterns on
           downscaling soil moisture in regions with large topographic relief
    • Authors: Garret S. Cowley; Jeffrey D. Niemann, Timothy R. Green, Mark S. Seyfried, Andrew S. Jones, Peter J. Grazaitis
      Abstract: Soil moisture can be estimated at coarse resolutions (>1 km) using satellite remote sensing, but that resolution is poorly suited for many applications. The Equilibrium Moisture from Topography, Vegetation, and Soil (EMT+VS) model downscales coarse-resolution soil moisture using fine-resolution topographic, vegetation, and soil data to produce fine-resolution (10-30 m) estimates of soil moisture. The EMT+VS model performs well at catchments with low topographic relief (≤124 m), but it has not been applied to regions with larger ranges of elevation. Large relief can produce substantial variations in precipitation and potential evapotranspiration (PET), which might affect the fine-resolution patterns of soil moisture. In this research, simple methods to downscale temporal average precipitation and PET are developed and included in the EMT+VS model, and the effects of spatial variations in these variables on the surface soil moisture estimates are investigated. The methods are tested against ground truth data at the 239 km2 Reynolds Creek watershed in southern Idaho, which has 1145 m of relief. The precipitation and PET downscaling methods are able to capture the main features in the spatial patterns of both variables. The space-time Nash-Sutcliffe coefficients of efficiency of the fine-resolution soil moisture estimates improve from 0.33 to 0.36 and 0.41 when the precipitation and PET downscaling methods are included, respectively. PET downscaling provides a larger improvement in the soil moisture estimates than precipitation downscaling likely because the PET pattern is more persistent through time, and thus more predictable, than the precipitation pattern. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-27T10:44:20.838346-05:
      DOI: 10.1002/2016WR019907
  • Quantifying streambed advection and conduction heat fluxes
    • Authors: Daniel Caissie; Charles H. Luce
      Abstract: Groundwater and accompanying heat fluxes are particularly relevant for aquatic habitats as they influence living conditions both within the river and streambed. This study focuses on the theory and the development of new equations to estimate conduction and advection heat fluxes into and out of the bed, correcting some earlier misunderstandings and adding parameterizations that extend our understanding of timing of heat fluxes. The new heat flux equations are illustrated using Catamaran Brook (New Brunswick, Canada) stream/streambed temperature data. We show important relationships between fluxes when the surface water temperature 1) follows a sinusoidal function superimposed on a steady-state condition (constant deep streambed temperature) and 2) when sinusoidal variations in stream temperature at two frequencies (annual and diel) are superimposed. When the stream temperature is used as a prescribed boundary condition, the contribution of bed fluid fluxes to stream temperature occurs through the effects of conductive thermal gradients, not through direct contribution/mixing of cold/warm water. Boundary conditions can be modified however to account for direct contribution of cold/warm water (e.g., localised upwelling) and consequences for the conduction heat flux. Equations developed allow for prediction of conductive fluxes to the bed during summer driven by diel and annual temperature fluctuations of the stream water and good agreement was observed between analytic solutions and field data. Results from this study provide a better insight into groundwater and heat fluxes which will ultimately result in better stream temperature models and a better management of fisheries resources. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:10:28.317478-05:
      DOI: 10.1002/2016WR019813
  • An interdisciplinary framework for participatory modeling design and
           evaluation What makes models effective participatory decision tools?
    • Authors: Stefanie M. Falconi; Richard N. Palmer
      Abstract: Increased requirements for public involvement in water resources management (WRM) over the past century have stimulated the development of more collaborative decision-making methods. Participatory modeling (PM) uses computer models to inform and engage stakeholders in the planning process in order to influence collaborative decisions in WRM. Past evaluations of participatory models focused on process and final outcomes, yet, were hindered by diversity of purpose and inconsistent documentation. This paper presents a two-stage framework for evaluating PM based on mechanisms for improving model effectiveness as participatory tools. The five dimensions characterize the ‘who, when, how, and why' of each participatory effort (stage 1). Models are evaluated as “boundary objects,” a concept used to describe tools that bridge understanding and translate different bodies of knowledge to improve credibility, salience, and legitimacy (stage 2). This evaluation framework is applied to five existing case studies from the literature. Though the goals of participation can be diverse, the novel contribution of the two-stage proposed framework is the flexibility it has to evaluate a wide range of cases that differ in scope, modeling approach, and participatory context. Also, the evaluation criteria provide a structured vocabulary based on clear mechanisms that extend beyond previous process- and outcome-based evaluations. Effective models are those that take advantage of mechanisms that facilitate dialogue and resolution and improve the accessibility and applicability of technical knowledge. Furthermore, the framework can help build more complete records and systematic documentation of evidence to help standardize the field of PM. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:47.006491-05:
      DOI: 10.1002/2016WR019373
  • Nonmonotonic and spatial-temporal dynamic slope effects on soil erosion
           during rainfall-runoff processes
    • Authors: Songbai Wu; Minghui Yu, Li Chen
      Abstract: The slope effect on flow erosivity and soil erosion still remains a controversial issue. This theoretical framework explained and quantified the direct slope effect by coupling the modified Green-Ampt equation accounting for slope effect on infiltration, 1D kinematic wave overland flow routing model, and WEPP soil erosion model. The flow velocity, runoff rate, shear stress, interrill, and rill erosion were calculated on 0°-60° isotropic slopes with equal horizontal projective length. The results show that, for short duration rainfall events, the flow erosivity and erosion amounts exhibit a bell-shaped trend which first increase with slope gradient, and then decrease after a critical slope angle. The critical slope angles increase significantly or even vanish with increasing rainfall duration but are nearly independent of the slope projective length. The soil critical shear stress, rainfall intensity and temporal patterns have great influences on the slope effect trend, while the other soil erosion parameters, soil type, hydraulic conductivity, and antecedent soil moisture have minor impacts. Neglecting the slope effect on infiltration would generate smaller erosion and reduce critical slope angles. The relative slope effect on soil erosion in physically-based model WEPP was compared to those in the empirical models USLE and RUSLE. The trends of relative slope effect were found quite different, but the difference may diminish with increasing rainfall duration. Finally, relatively smaller critical slope angles could be obtained with the equal slope length and the range of variation provides a possible explanation for the different critical slope angles reported in previous studies. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:42.929378-05:
      DOI: 10.1002/2016WR019254
  • Subgrid parameterization for snow depth over mountainous terrain from flat
           field snow depth
    • Authors: N. Helbig; A. van Herwijnen
      Abstract: Snow depth is an important variable for a variety of models including land-surface, meteorological and climate models. Various measurement networks were therefore developed to measure snow depth on the ground. Measurement stations are generally located in gentle terrain (flat field measurements) most often at lower or mid elevation. While these sites have provided a wealth of information, various studies have questioned the representativity of such flat field measurements for the surrounding topography, especially in alpine regions. Using highly-resolved snow depth maps at the peak of winter from two distinct climatic regions in Switzerland and in the Spanish Pyrenees, we developed two parameterizations to estimate domain-averaged snow depth in coarse-scale model applications over complex topography using easy to derive topographic parameters. The first parameterization uses a commonly applied linear lapse rate. Removing the dominant elevation gradient in mean snow depth revealed remaining underlying correlations with other topographic parameters, in particular the sky view factor. The second parameterization combines a power law elevation trend scaled with the subgrid parameterized sky view factor. Using a variety of statistic measures showed that the more complex parameterization performs better when using mean high-resolution flat field snow depth. The performances slightly decreased when formulating the parameterizations for a single flat field snow depth measurement. Nevertheless, the more complex parameterization still outperformed the linear lapse rate model. As the parameterization was developed independently of a specific geographic region we suggest it could be used to assimilate flat field snow depth or snowfall into coarse-scale snow model frameworks. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:40.861575-05:
      DOI: 10.1002/2016WR019872
  • A new geophone device for understanding environmental impacts caused by
           gravel bedload during artificial floods
    • Authors: Ryota Tsubaki; Yoshihisa Kawahara, Xin-Hua Zhang, Kentaro Tsuboshita
      Abstract: Here, to assess the contribution of gravel bedload on the removal of attached-algae and aquatic plants from a cobble-bed river during small floods, we propose a geophone type method for measuring the local bedload of non-uniform sized gravel. Due to limited peak discharge for focused events during our study, a large fraction of bed material (here cobbles) was immobile and only a small fraction of bed material (sand and gravel) was expected to be transported during the flushing flows we analyzed. The device we developed has a size equivalent to immobile bed material and a shape similar to bed material (rounded cobbles) at the site. The instrument's design allows avoidance of disturbances in river bed micro-topography during installation and local bedload transport during floods. A flume experiment was conducted in order to establish an empirical algorithm for estimating the diameter of impacted gravel and, here, discuss uncertainty related to diameter estimations. The proposed method was utilized to quantify gravel bedload in a cobble-bed river during flushing flows. In the text, we also discuss the contribution of measured gravel bedload during flushing flows on the removal of attached-algae (up to a 37% reduction in chlorophyll-a density) and aquatic plants (a reduction of 38% in dry mass per area). Based on time variation for the measured gravel bedload, we also suggest the propagation of a bed-form composed of the fine sediment fraction migrating on immobile larger sediment and implications for the propagation of the fine sediment wave for attached-algae removal. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:39.745078-05:
      DOI: 10.1002/2016WR019726
  • Impact of saturation on dispersion and mixing in porous media:
           Photo-bleaching pulse injection experiments and shear-enhanced mixing
    • Authors: Joaquín Jiménez-Martínez; Tanguy Le Borgne, Hervé Tabuteau, Yves Méheust
      Abstract: The dynamics of solute dispersion and mixing in unsaturated flows is analyzed from photo-bleaching experiments in two-dimensional porous micro-models. This technique allows producing pulse line (delta-Dirac) injections of a conservative tracer by bleaching a finite volume of fluorescent without disturbing the flow field. The temporal evolution of the concentration field and the spatial distribution of the air and water phases can be monitored at pore scale. We study the dispersion and mixing of a line of tracer under different water saturations. While dispersion in saturated porous media follows an approximately Fickian scaling, a shift to ballistic scaling is observed as soon as saturation is lowered. Hence, at the time scale of observation, dispersion in our unsaturated flows is dominated by the ballistic separation of tracer blobs within the water phase, between trapped clusters and preferential flow paths. While diffusion plays a minor role in the longitudinal dispersion during the time scale of the experiments, its interplay with fluid deformation is apparent in the dynamics of mixing. The scalar dissipation rates show an initial stretching regime, during which mixing is enhanced by fluid deformation, followed by a dissipation regime, during which diffusion overcomes compression induced by stretching. The transition between these two regimes occurs at the mixing time, when concentration gradients are maximum. We propose a predictive analytical model, based on shear-enhanced diffusion, that captures the dynamics of mixing from basic unsaturated porous media parameters, suggesting that this type of model may be a useful framework at larger scales. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:32.743271-05:
      DOI: 10.1002/2016WR019849
  • Water quality data for national-scale aquatic research: The Water Quality
    • Authors: Emily K. Read; Lindsay Carr, Laura De Cicco, Hilary A. Dugan, Paul C. Hanson, Julia A. Hart, James Kreft, Jordan S. Read, Luke A. Winslow
      Abstract: Aquatic systems are critical to food, security, and society. But, water data are collected by hundreds of research groups and organizations, many of which use non-standard or inconsistent data description and dissemination, and disparities across different types of water observation systems represent a major challenge for freshwater research. In response to this, the Water Quality Portal (WQP) was developed by the U.S. Environmental Protection Agency, the U.S. Geological Survey, and the National Water Quality Monitoring Council to be a single point of access for water quality data dating back more than a century. The WQP is the largest standardized water quality data set available at the time of this writing, with more than 290 million records from more than 2.7 million sites in groundwater, inland, and coastal waters. The number of data contributors, data consumers, and third-party application developers making use of the WQP are rapidly growing. Here, we introduce the WQP, including an overview of data, the standardized data model, and data access and services; and we describe challenges and opportunities associated with using WQP data. We also demonstrate the value of the WQP data by characterizing seasonal variation in lake water clarity for regions of the continental U.S. The code used to access, download, analyze, and display this WQP data as shown in the figures is included as Supplemental Materials. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:29.949812-05:
      DOI: 10.1002/2016WR019993
  • The future role of dams in the United States of America
    • Authors: Michelle Ho; Upmanu Lall, Maura Allaire, Naresh Devineni, Hyun Han Kwon, Indrani Pal, David Raff, Dave Wegner
      Abstract: Storage and controlled distribution of water have been key elements of a human strategy to overcome the space and time variability of water, which have been marked by catastrophic droughts and floods throughout the course of civilization. In the United States the peak of dam building occurred in the mid-20th century with knowledge limited to the scientific understanding and hydrologic records of the time. Ecological impacts were considered differently than current legislative and regulatory controls would potentially dictate. Additionally, future costs such as maintenance or removal beyond the economic design life were not fully considered. The converging risks associated with aging water storage infrastructure and uncertainty in climate in addition to the continuing need for water storage, flood protection, and hydropower result in a pressing need to address the state of dam infrastructure across the nation. Decisions regarding the future of dams in the United States may, in turn, influence regional water futures through groundwater outcomes, economic productivity, migration, and urban growth. We advocate for a comprehensive national water assessment and a formal analysis of the role dams play in our water future. We emphasize the urgent need for environmentally and economically sound strategies to integrate surface and groundwater storage infrastructure in local, regional, and national water planning considerations. A research agenda is proposed to assess dam failure impacts and the design, operation, and need for dams considering both paleo and future climate, utilization of groundwater resources, and the changing societal values towards the environment. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:05:26.903507-05:
      DOI: 10.1002/2016WR019905
  • Examination of the seepage face boundary condition in subsurface and
           coupled surface/subsurface hydrological models
    • Authors: C. Scudeler; C. Paniconi, D. Pasetto, M. Putti
      Abstract: A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-24T12:00:47.093619-05:
      DOI: 10.1002/2016WR019277
  • Elemental properties, hydrology, and biology interact to shape
           concentration-discharge curves for carbon, nutrients, sediment, and major
    • Authors: F. Moatar; B.W. Abbott, M. Minaudo, F. Curie, G. Pinay
      Abstract: To investigate the prevalence and cause of concentration-discharge (C-Q) relationships for carbon, nutrients, major ions, and particulates, we analyzed 40 years of water quality data from 293 monitoring stations in France. Catchments drained diverse landscapes and ranged from 50 to 110,000 km2, together covering nearly half of France. To test for differences during low and high flows, we calculated independent C-Q slopes above and below the median discharge. We found that 84% of all catchment-element combinations were chemodynamic for at least half of the hydrograph and 60% of combinations showed non-linear C-Q curves. Only two or three of the nine possible C-Q modalities were manifest for each parameter, and these modalities were stable through time, suggesting that intrinsic and extrinsic elemental properties (e.g. solubility, reactivity, and source dynamics) set basic C-Q templates for each parameter, which are secondarily influenced by biological activity during low flows, and the interaction between hydrology and catchment characteristics at high flows. Several patterns challenged current C-Q views, including low-flow chemostasis for TSS in 66% of catchments, low-flow biological mediation of NO3- in 71% of catchments, and positive C-Q for dissolved organic carbon independent of catchment size in 80% of catchments. Efforts to reduce nutrient loading decreased phosphorus concentration and altered C-Q curves, but NO3- continued to increase. While C-Q segmentation requires more data than a single analysis, the prevalence of non-linear C-Q slopes demonstrates the potential information loss associated with linear or monotonic analysis of C-Q relationships, and conversely, the value of long-term monitoring. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-20T05:01:25.664545-05:
      DOI: 10.1002/2016WR019635
  • Impact of mountain permafrost on flow path and runoff response in a high
           alpine catchment
    • Authors: M. Rogger; G.B. Chirico, H. Hausmann, K. Krainer, E. Brückl, P. Stadler, G. Blöschl
      Abstract: Permafrost in high alpine catchments is expected to disappear in future warmer climates, but the hydrological impact of such changes is poorly understood. This paper investigates the flow paths and the hydrological response in a 5 km2 high alpine catchment in the Ötztal Alps, Austria, and their changes resulting from a loss of permafrost. Spatial permafrost distribution, depth to the permafrost table and depth to the bedrock were mapped by geophysical methods. Catchment runoff and meteorological variables were monitored from June 2008 to December 2011. These data were used along with field experience to infer conceptual schemes of the dominant flow paths in four types of hillslopes that differ in terms of their unconsolidated sediment characteristics and the presence of permafrost. The four types are: talus fans, rock glaciers, Little Ice Age (LIA) till and Pre-LIA till. Permafrost tends to occur in the first three types, but is absent from Pre-LIA till. Based on these flow path concepts, runoff was simulated for present conditions and for future conditions when permafrost has completely disappeared. The simulations indicate that complete disappearance of permafrost will reduce flood peaks by up to 17% and increase runoff during recession by up to 19%. It is argued that change modeling needs to account for flow path types and their changes based on geophysical surveys and field investigations. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-20T04:50:40.617776-05:
      DOI: 10.1002/2016WR019341
  • Probabilistic inversion with graph cuts: Application to the Boise
           hydrogeophysical research site
    • Authors: Guillaume Pirot; Niklas Linde, Grégoire Mariethoz, John Bradford
      Abstract: Inversion methods that build on multiple-point statistics tools offer the possibility to obtain model realizations that are not only in agreement with field data, but also with conceptual geological models that are represented by training images. A recent inversion approach based on patch-based geostatistical resimulation using graph cuts outperforms state-of-the-art multiple point statistics methods when applied to synthetic inversion examples featuring continuous and discontinuous property fields. Applications of multiple-point statistics tools to field data are challenging due to inevitable discrepancies between actual subsurface structure and the assumptions made in deriving the training image. We introduce several amendments to the original graph cut inversion algorithm and present a first-ever field application by addressing porosity estimation at the Boise Hydrogeophysical Research Site, Boise, Idaho. We consider both a classical multi-Gaussian and an outcrop-based prior model (training image) that are in agreement with available porosity data. When conditioning to available crosshole ground-penetrating radar data using Markov chain Monte Carlo, we find that the posterior realizations honor overall both the characteristics of the prior models and the geophysical data. The porosity field is inverted jointly with the measurement error and the petrophysical parameters that link dielectric permittivity to porosity. Even though the multi-Gaussian prior model leads to posterior realizations with higher likelihoods, the outcrop-based prior model shows better convergence. In addition, it offers geologically more realistic posterior realizations and it better preserves the full porosity range of the prior. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:50:59.691739-05:
      DOI: 10.1002/2016WR019347
  • Experimental investigation of the impact of compound-specific dispersion
           and electrostatic interactions on transient transport and solute
    • Authors: Muhammad Muniruzzaman; Massimo Rolle
      Abstract: This study investigates the effects of compound-specific diffusion/dispersion and electrochemical migration on transient solute transport in saturated porous media. We conducted laboratory bench-scale experiments, under advection-dominated regimes (seepage velocity: 0.5, 5, 25 m/day), in a quasi two-dimensional flow-through setup using pulse injection of multiple tracers (both uncharged and ionic species). Extensive sampling and measurement of solutes' concentrations (∼1500 samples; >3000 measurements) were performed at the outlet of the flow-through setup, at high spatial and temporal resolution. The experimental results show that compound-specific effects and charge-induced Coulombic interactions are important not only at low velocities and/or for steady-state plumes but also for transient transport under high flow velocities. Such effects can lead to a remarkably different behavior of measured breakthrough curves also at very high Péclet numbers. To quantitatively interpret the experimental results, we used four modeling approaches: classical advection-dispersion equation (ADE), continuous time random walk (CTRW), dual domain mass transfer model (DDMT), and a multicomponent ionic dispersion model. The latter is based on the multicomponent formulation of coupled diffusive/dispersive fluxes and was used to describe and explain the electrostatic effects of charged species. Furthermore, we determined experimentally the temporal profiles of the flux-related dilution index. This metric of mixing, used in connection with the traditional solute breakthrough curves, proved to be useful to correctly distinguish between plume spreading and mixing, particularly for the cases in which the sole analysis of integrated concentration breakthrough curves may lead to erroneous interpretation of plume dilution. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:50:53.593126-05:
      DOI: 10.1002/2016WR019727
  • Modeling multidecadal surface water inundation dynamics and key drivers on
           large river basin scale using multiple time series of Earth observation
           and river flow data
    • Authors: V. Heimhuber; M. G. Tulbure, M. Broich
      Abstract: Periodically inundated floodplain areas are hotspots of biodiversity and provide a broad range of ecosystem services but have suffered alarming declines in recent history. Despite their importance, their long-term surface water (SW) dynamics and hydro-climatic drivers remain poorly quantified on continental scales. In this study, we used a 26-year time series of Landsat-derived SW maps in combination with river flow data from 68 gauges and spatial time series of rainfall, evapotranspiration and soil moisture to statistically model SW dynamics as a function of key drivers across Australia's Murray-Darling Basin (∼1 million km2). We fitted generalized additive models for 18,521 individual modeling units made up of 10x10 km grid cells, each split into floodplain, floodplain-lake and non-floodplain area. Average goodness of fit of models was high across floodplains and floodplain-lakes (r2 > 0.65), which were primarily driven by river flow, and was lower for non-floodplain areas (r2 > 0.24), which were primarily driven by rainfall. Local climate conditions were more relevant for SW dynamics in the northern compared to the southern basin and had the highest influence in the least regulated and most extended floodplains. We further applied the models of two contrasting floodplain areas to predict SW extents of cloud-affected time steps in the Landsat series during the large 2010 floods with high validated accuracy (r2 > 0.97). Our framework is applicable to other complex river basins across the world and enables a more detailed quantification of large floods and drivers of SW dynamics compared to existing methods. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:50:49.2744-05:00
      DOI: 10.1002/2016WR019858
  • Analytical solutions for aquifer thermal energy storage
    • Authors: Jan Martin Nordbotten
      Abstract: The concept of aquifer thermal energy storage involves injection of water at elevated temperature, and possibly non-ambient salinity, into a host aquifer. We consider axisymmetric injection, wherein both the composition and temperature of the injected fluid differs from the fluid in the target aquifer. In this setting, we derive the governing equations within a vertically integrated framework, and show their self-similar structure. We subsequently derive explicit approximate solutions to the self-similar equations for parameter ranges of relevance to thermal energy storage (small density and viscosity differences), we derive explicit approximate solutions to the self-similar equations.The analysis is supported by numerical validation, covering the relevant parameter regime. The resulting comparisons demonstrate the mathematical qualities of the analytical approximations. A study based on field data from analogue sites, justifies the assertions regarding the magnitude of the dimensionless parameters used in the analysis. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:50:44.194583-05:
      DOI: 10.1002/2016WR019524
  • Measurement and simulation of heat exchange in fractured bedrock using
           inert and thermally degrading tracers
    • Authors: Adam. J. Hawkins; Don. B. Fox, Matthew. W. Becker, Jefferson. W. Tester
      Abstract: Multi-component groundwater tracer tests were conducted in a well-characterized field site in Altona, NY using inert carbon-cored nanoparticles and a thermally degrading phenolic compound. Experiments were conducted in a meso-scale reservoir consisting of a single sub-horizontal bedding plane fracture located 7.6 m below ground surface contained between two wells separated by 14.1 m. The reservoir rock, initially at 11.7°C, was heated using 74°C water. During the heating process, a series of tracer tests using thermally degrading tracers were used to characterize the progressive in-situ heating of the fracture. Fiber-Optic Distributed Temperature Sensing (FODTS) was used to measure temperature rise orthogonal to the fracture surface at ten locations. Recovery of the thermally degrading tracer's product was increased as the reservoir was progressively heated indicating that the advancement of the thermal front was proportional to the mass fraction of the thermally degrading tracer recovered. Both GPR imaging and FODTS measurements reveal that flow was reduced to a narrow channel which directly connected the two wells and led to rapid thermal breakthrough. Computational modeling of inert tracer and heat transport in a two-dimensional discrete fracture demonstrate that subsurface characterization using inert tracers alone could not uniquely characterize the Altona field site. However, the inclusion of a thermally degrading tracer may permit accurate subsurface temperature monitoring. At the Altona field site, however, fluid-rock interactions appear to have increased reaction rates relative to lab-based measurements made in the absence of rock surfaces. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:50:35.397818-05:
      DOI: 10.1002/2016WR019617
  • Incorporating institutions and collective action into a socio-hydrological
           model of flood resilience
    • Authors: David J. Yu; Nikhil Sangwan, Kyungmin Sung, Xi Chen, Venkatesh Merwade
      Abstract: Stylized socio-hydrological models have mainly used social memory aspects such as community awareness or sensitivity to connect hydrologic change and social response. However, social memory alone does not satisfactorily capture the details of how human behavior is translated into collective action for water resources governance. Nor is it the only social mechanism by which the two-way feedbacks of socio-hydrology can be operationalized. This study contributes towards bridging of this gap by developing a socio-hydrological model of a flood resilience that includes two additional components: (1) institutions for collective action, and (2) connections to an external economic system. Motivated by the case of community-managed flood protection systems (polders) in coastal Bangladesh, we use the model to understand critical general features that affect long-term resilience of human-flood systems. Our findings suggest that occasional adversity can enhance long-term resilience. Allowing some hydrological variability to enter into the polder can increase its adaptive capacity for resilience through the preservation of social norm for collective action. Further, there are potential trade-offs associated with optimization of flood resistance through structural measures. By reducing sensitivity to floods, the system may become more fragile under the double impact of floods and economic change. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-13T10:45:36.965622-05:
      DOI: 10.1002/2016WR019746
  • Differences in behavior and distribution of permafrost-related lakes in
           Central Yakutia and their response to climatic drivers
    • Authors: M. Ulrich; H. Matthes, L. Schirrmeister, J. Schütze, H. Park, Y. Iijima, A.N. Fedorov
      Abstract: The Central Yakutian permafrost landscape is rapidly being modified by land use and global warming, but small-scale thermokarst process variability and hydrological conditions are poorly understood. We analyze lake-area changes and thaw subsidence of young thermokarst lakes on ice-complex deposits (yedoma lakes) in comparison to residual lakes in alas basins during the last 70 years for a local study site and we record regional lake size and distribution on different ice-rich permafrost terraces using satellite and historical airborne imagery. Statistical analysis of climatic and ground-temperature data identified driving factors of yedoma- and alas-lake changes. Overall, lake area is larger today than in 1944 but alas-lake levels have oscillated greatly over 70 years, with a mean alas-lake-radius change rate of 1.6 ± 3.0 m/yr. Anthropogenic disturbance and forest degradation initiated, and climate forced rapid, continuous yedoma-lake growth. The mean yedoma lake-radius change rate equals 1.2 ± 1.0 m/yr over the whole observation period. Mean thaw subsidence below yedoma lakes is 6.2 ± 1.4 cm/yr. Multiple regression analysis suggests that winter precipitation, winter temperature, and active-layer properties are primary controllers of area changes in both lake types; summer weather and permafrost conditions additionally influence yedoma-lake growth rates. The main controlling factors of alas-lake changes are unclear due to larger catchment areas and subsurface hydrological conditions. Increasing thermokarst activity is currently linked to older terraces with higher ground-ice contents, but thermokarst activity will likely stay high and wet conditions will persist within the near future in Central Yakutian alas basins.
      PubDate: 2017-01-10T17:50:29.146694-05:
      DOI: 10.1002/2016WR019267
  • Insights into hydrologic and hydrochemical processes based on
           concentration-discharge and endmember mixing analyses in the mid-Merced
           River Basin, Sierra Nevada, California
    • Authors: Fengjing Liu; Martha H. Conklin, Glenn D. Shaw
      Abstract: Both concentration-discharge relation and endmember mixing analysis were explored to elucidate the connectivity of hydrologic and hydrochemical processes using chemical data collected during 2006-2008 at Happy Isles (468 km2), Pohono Bridge (833 km2), and Briceburg (1,873 km2) in the snowmelt-fed mid Merced River basin, augmented by chemical data collected by the USGS during 1990-2014 at Happy Isles. Concentration-discharge (C-Q) in streamflow was dominated by a well-defined power-law relation, with the magnitude of exponent (0.02-0.6) and R2 values (p
      PubDate: 2017-01-09T03:31:48.726042-05:
      DOI: 10.1002/2016WR019437
  • Transverse and longitudinal mixing in real emergent vegetation at low
    • Authors: F. Sonnenwald; J. R. Hart, P. West, V. R. Stovin, I. Guymer
      Abstract: Understanding solute mixing within real vegetation is critical to predicting and evaluating the performance of engineered natural systems such as stormwater ponds. For the first time, mixing has been quantified through simultaneous laboratory measurements of transverse and longitudinal dispersion within artificial and real emergent vegetation. Dispersion coefficients derived from a routing solution to the 2D Advection Dispersion Equation (ADE) are presented that compare the effects of vegetation type (artificial, Typha latifolia or Carex acutiformis) and growth season (winter or summer). The new experimental dispersion coefficients are plotted with the experimental values from other studies and used to review existing mixing models for emergent vegetation. The existing mixing models fail to predict the observed mixing within natural vegetation, particularly for transverse dispersion, reflecting the complexity of processes associated with the heterogeneous nature of real vegetation. Observed stem diameter distributions are utilized to highlight the sensitivity of existing models to this key length-scale descriptor, leading to a recommendation that future models intended for application to real vegetation should be based on probabilistic descriptions of both stem diameters and stem spacings. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-08T22:35:26.637157-05:
      DOI: 10.1002/2016WR019937
  • Labyrinths in large reservoirs: An invisible barrier to fish migration and
           the solution through reservoir operation
    • Authors: Zhihao Xu; Xinan Yin, Tao Sun, Yanpeng Cai, Yu Ding, Wei Yang, Zhifeng Yang
      Abstract: Reservoir construction changes a river's natural flows and temperature, thereby threatening fish migration. Researchers have tried to restore fish migration passages by ensuring environmental flows in downstream river channels. However, reservoir impoundment changes upstream environments from lotic to lentic and thereby hinders fish migration by eliminating migration cues, which has been rarely considered. This study characterized the invisible barriers that large reservoirs create for migratory fish. Water currents are the primary orientation cues for migration due to fish's natural rheotactic tendency. Fish also require suitable temperatures during migration. We built a quasi-3D model to simulate hydrodynamic and temperature conditions in large reservoirs and tested whether these conditions met the velocity and temperature requirements of fish. Due to the strong effects of operation on reservoir conditions, we proposed an eco-friendly technical operating solution to restore migration passages. We added an ecological constraint (i.e., creating a suitable velocity field for fish migration) to reservoir operation model and applied multi-objective optimization to simultaneously protect reservoir benefits. As a case, we applied our approach to China's Danjiangkou Reservoir. We found that velocities in more than half of the zones along the potential fish migration route through the reservoir were lower than the fish requirement and could not offer orientation cues for migration. The eco-friendly operating scheme effectively restored a fish migration passage by managing reservoir releases during key migration periods, slightly reducing the reservoir's socio-economic benefits by 1.67%∼5.03%. This study provides a new perspective on biodiversity and fisheries protection in global regulated rivers. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-04T03:30:36.874186-05:
      DOI: 10.1002/2016WR019485
  • Comparison of soil wetness from multiple models over Australia with
    • Authors: Vinod Kumar; I. Dharssi, J. Bally, P. Steinle, D. McJannet, J. Walker
      Abstract: The McArthur Forest Fire Danger Index used in Australia for operational fire warnings has a component representing fuel availability called the Drought Factor (DF). The DF is partly based on soil moisture deficit, calculated as either the Keetch-Byram Drought Index (KBDI) or Mount's Soil Dryness Index (MSDI). The KBDI and MSDI are simplified water balance models driven by observation based daily rainfall and temperature. In this work, gridded KBDI and MSDI analyses are computed at a horizontal resolution of 5 km and are verified against in-situ soil moisture observations. Also verified is another simple model called the Antecedent Precipitation Index (API). Soil moisture analyses from the Australian Community Climate and Earth System Simulator (ACCESS) global Numerical Weather Prediction (NWP) system as well as remotely sensed soil wetness retrievals from the Advanced Scatterometer (ASCAT) are also verified. The verification shows that the NWP soil wetness analyses have greater skill and smaller biases than the KBDI, MSDI and API analyses. This is despite the NWP system having a coarse horizontal resolution and not using observed precipitation. The average temporal correlations (root mean square difference) between cosmic ray soil moisture monitoring facility observations and modelled or remotely sensed soil wetness are 0.82 (0.15±0.02), 0.66 (0.33±0.07), 0.77 (0.20±0.03), 0.74 (0.22±0.03) and 0.83 (0.18±0.04) for NWP, KBDI, MSDI, API and ASCAT. The results from this study suggests that analyses of soil moisture can be greatly improved by using physically based land surface models, remote sensing measurements and data assimilation. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-04T03:30:34.565663-05:
      DOI: 10.1002/2015WR017738
  • Soil moisture background error covariance and data assimilation in a
           coupled land-atmosphere model
    • Authors: Liao-Fan Lin; Ardeshir M. Ebtehaj, Jingfeng Wang, Rafael L. Bras
      Abstract: This study characterizes the space-time structure of soil moisture background error covariance and paves the way for the development of a soil moisture variational data assimilation system for the Noah land surface model coupled to the Weather Research and Forecasting (WRF) model. The soil moisture background error covariance over the contiguous United States exhibits strong seasonal and regional variability with the largest values occurring in the uppermost soil layer during the summer. Large background error biases were identified, particularly over the Southeastern United States, caused mainly by the discrepancy between the WRF-Noah simulations and the initial conditions derived from the used operational global analysis dataset. The assimilation of the Soil Moisture and Ocean Salinity (SMOS) soil moisture data notably reduces the error of soil moisture simulations. On average, data assimilation with space-time varying background error covariance results in 33% and 35% reduction in the root-mean-square error and the mean absolute error, respectively, in the simulation of hourly top 10-cm soil moisture, mainly due to implicit reductions in soil moisture biases. In terms of correlation, the improvement in soil moisture simulations is also observed but less notable, indicating the limitation of coarse-scale soil moisture data assimilation in capturing fine-scale soil moisture variation. In addition, soil moisture data assimilation improves the simulations of latent heat fluxes but shows a marginal impact on the simulations of sensible latent heat fluxes and precipitation. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-04T03:30:28.614903-05:
      DOI: 10.1002/2015WR017548
  • Stochastic estimation of hydraulic transmissivity fields using flow
           connectivity indicator data
    • Authors: G. Freixas; D. Fernàndez-Garcia, X. Sanchez-Vila
      Abstract: Most methods for hydraulic test interpretation rely on a number of simplified assumptions regarding the homogeneity and isotropy of the underlying porous media. This way, the actual heterogeneity of any natural parameter, such as transmissivity (), is transferred to the corresponding estimates in a way heavily dependent on the interpretation method used. An example is a long-term pumping test interpreted by means of the Cooper-Jacob method, which implicitly assumes a homogeneous isotropic confined aquifer. The estimates obtained from this method are not local values, but still have a clear physical meaning; the estimated represents a regional-scale effective value, while the log-ratio of the normalized estimated storage coefficient, indicated by , is an indicator of flow connectivity, representative of the scale given by the distance between the pumping and the observation wells. In this work we propose a methodology to use , together with sampled local measurements of transmissivity at selected points, to map the expected value of local values using a technique based on cokriging. Since the interpolation involves two variables measured at different support scales, a critical point is the estimation of the covariance and crosscovariance matrices. The method is applied to a synthetic field displaying statistical anisotropy, showing that the inclusion of connectivity indicators in the estimation method provide maps that effectively display preferential flow pathways, with direct consequences in solute transport. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-03T03:05:47.165044-05:
      DOI: 10.1002/2015WR018507
  • Evaluating waterpoint sustainability and access implications of revenue
           collection approaches in rural Kenya
    • Authors: T. Foster; R. Hope
      Abstract: Water policies in many sub-Saharan African countries stipulate that rural communities are responsible for self-financing their waterpoint's operation and maintenance. In the absence of policy consensus or evidence on optimal payment models, rural communities adopt a diversity of approaches. This study empirically assesses waterpoint sustainability and access outcomes associated with different revenue collection approaches on the south coast of Kenya. The analysis draws on a unique data set comprising financial records spanning 27 years and 100 communities, operational performance indicators for 200 waterpoints, and water source choices for more than 2,000 households. Results suggest communities collecting pay-as-you-fetch fees on a volumetric basis generate higher levels of income and experience improved operational performance compared with communities charging flat fees. In both cases, financial flows mirror seasonal rainfall peaks and troughs. These outcomes are tempered by evidence that households are more likely to opt for an unimproved drinking water source when a pay-as-you-fetch system is in place. The findings illuminate a possible tension between financial sustainability and universal access. If the Sustainable Development Goal of 'safe water for all' is to become a reality, policymakers and practitioners will need to address this issue and ensure rural water services are both sustainable and inclusive. This article is protected by copyright. All rights reserved.
      PubDate: 2017-01-03T03:05:39.527029-05:
      DOI: 10.1002/2016WR019634
  • Issue Information
    • Pages: 1 - 4
      PubDate: 2017-02-22T02:23:11.327972-05:
      DOI: 10.1002/wrcr.22248
  • What is the “active layer”?
    • Authors: M. Church; J. K. Haschenburger
      Pages: 5 - 10
      Abstract: We note the presence in the literature of two different concepts of the term “active layer” in relation to fluvial sediment transport. It has been used to represent the current dynamically active streambed surface, or to represent the depth of event-scale scour and fill. These concepts involve distinct length and time scales. We propose that, when the distinction is important, the concepts be distinguished as either a “dynamical active layer” or an “event active layer.”
      PubDate: 2017-01-17T11:45:35.271206-05:
      DOI: 10.1002/2016WR019675
  • Estimation of three-phase relative permeability by simulating fluid
           dynamics directly on rock-microstructure images
    • Authors: F. Jiang; T. Tsuji
      Pages: 11 - 32
      Abstract: Given the world's growing demand for energy, a combination of geological CO2 sequestration and enhanced oil recovery (EOR) technologies is currently regarded as a promising solution, as it would provide a means of reducing carbon emissions into the atmosphere while also leading to the economic benefit of simultaneously recovering oil. The optimization of injection strategies to maximize CO2 storage and increase the oil recovery factors requires complicated pore-scale flow information within a reservoir system consisting of coexisting oil, water, and CO2 phases. In this study, an immiscible three-phase lattice-Boltzmann (LB) model was developed to investigate the complicated flow state with interaction between water, oil, and CO2 systems in porous media. The two main mechanisms of oil remobilization, namely, double-drainage and film flow, can be captured by our model. The estimation of three-phase relative permeability is proposed using the digital rock physics (DRP) simulations. The results indicate that the relative permeability of CO2 as calculated using our steady state method is not sensitive to the initial oil fraction if the oil distribution is originally uniform. Baker's (1988) empirical model was tested and found to be able to provide a good prediction of the three-phase relative permeability data. Our numerical method provides a new tool for accurately predicting three-phase relative permeability data directly based on micro-CT rock images.
      PubDate: 2017-01-05T05:45:34.846338-05:
      DOI: 10.1002/2016WR019098
  • The integral suspension pressure method (ISP) for precise particle-size
           analysis by gravitational sedimentation
    • Authors: Wolfgang Durner; Sascha C. Iden, Georg von Unold
      Pages: 33 - 48
      Abstract: The particle-size distribution (PSD) of a soil expresses the mass fractions of various sizes of mineral particles which constitute the soil material. It is a fundamental soil property, closely related to most physical and chemical soil properties and it affects almost any soil function. The experimental determination of soil texture, i.e., the relative amounts of sand, silt, and clay-sized particles, is done in the laboratory by a combination of sieving (sand) and gravitational sedimentation (silt and clay). In the latter, Stokes' law is applied to derive the particle size from the settling velocity in an aqueous suspension. Traditionally, there are two methodologies for particle-size analysis from sedimentation experiments: the pipette method and the hydrometer method. Both techniques rely on measuring the temporal change of the particle concentration or density of the suspension at a certain depth within the suspension. In this paper, we propose a new method which is based on the pressure in the suspension at a selected depth, which is an integral measure of all particles in suspension above the measuring depth. We derive a mathematical model which predicts the pressure decrease due to settling of particles as function of the PSD. The PSD of the analyzed sample is identified by fitting the simulated time series of pressure to the observed one by inverse modeling using global optimization. The new method yields the PSD in very high resolution and its experimental realization completely avoids any disturbance by the measuring process. A sensitivity analysis of different soil textures demonstrates that the method yields unbiased estimates of the PSD with very small estimation variance and an absolute error in the clay and silt fraction of less than 0.5%.
      PubDate: 2017-01-06T07:30:35.237401-05:
      DOI: 10.1002/2016WR019830
  • High resolution aquifer characterization using crosshole GPR full-waveform
           tomography: Comparison with direct-push and tracer test data
    • Authors: Nils Gueting; Thomas Vienken, Anja Klotzsche, Jan van der Kruk, Jan Vanderborght, Jef Caers, Harry Vereecken, Andreas Englert
      Pages: 49 - 72
      Abstract: Limited knowledge about the spatial distribution of aquifer properties typically constrains our ability to predict subsurface flow and transport. Here we investigate the value of using high resolution full-waveform inversion of cross-borehole ground penetrating radar (GPR) data for aquifer characterization. By stitching together GPR tomograms from multiple adjacent crosshole planes, we are able to image, with a decimeter scale resolution, the dielectric permittivity and electrical conductivity of an alluvial aquifer along cross sections of 50 m length and 10 m depth. A logistic regression model is employed to predict the spatial distribution of lithological facies on the basis of the GPR results. Vertical profiles of porosity and hydraulic conductivity from direct-push, flowmeter and grain size data suggest that the GPR predicted facies classification is meaningful with regard to porosity and hydraulic conductivity, even though the distributions of individual facies show some overlap and the absolute hydraulic conductivities from the different methods (direct-push, flowmeter, grain size) differ up to approximately one order of magnitude. Comparison of the GPR predicted facies architecture with tracer test data suggests that the plume splitting observed in a tracer experiment was caused by a hydraulically low-conductive sand layer with a thickness of only a few decimeters. Because this sand layer is identified by GPR full-waveform inversion but not by conventional GPR ray-based inversion we conclude that the improvement in spatial resolution due to full-waveform inversion is crucial to detect small-scale aquifer structures that are highly relevant for solute transport.
      PubDate: 2017-01-10T10:15:49.087568-05:
      DOI: 10.1002/2016WR019498
  • Adaptive implicit finite element methods for multicomponent compressible
           flow in heterogeneous and fractured porous media
    • Authors: Joachim Moortgat
      Pages: 73 - 92
      Abstract: This work presents adaptive implicit first-order and second-order discontinuous Galerkin (DG) methods for the transport of multicomponent compressible fluids in heterogeneous and fractured porous media, discretized by triangular, quadrilateral, and hexahedral grids. The adaptive implicit method (AIM) combines the advantages of purely explicit or implicit methods (in time). In grid cells with high fluxes or low pore volumes, the transport update is done implicitly to alleviate the Courant-Friedrichs-Lewy (CFL) time step constraints of the conditionally stable explicit approach. Grid cells with a large CFL condition are updated explicitly. Combined, this allows higher efficiency than explicit methods, but it reduces the “penalty” of implicit methods, which exhibit high numerical dispersion and are more computationally and storage expensive per time step. The advantages of AIM are modest for uniform grids and rock properties. However, in heterogeneous or fractured reservoirs explicit methods may become impractical, while a fully implicit approach introduces unnecessary numerical dispersion and is overkill for low-permeability layers and matrix blocks. In such applications, AIM is shown to be significantly more efficient and accurate. The division between explicit and implicit grid cells is made adaptively in space and time. This allows for a high level of explicitness and can also adapt to high fluxes caused by, e.g., viscous and gravitational flow instabilities. Numerical examples demonstrate the powerful features of AIM to model, e.g., solute transport, carbon sequestration in saline aquifers, and miscible gas injection in fractured oil and gas reservoirs.
      PubDate: 2017-01-10T10:16:13.518423-05:
      DOI: 10.1002/2016WR019644
  • A mechanistic model (BCC-PSSICO) to predict changes in the hydraulic
           properties for bio-amended variably saturated soils
    • Authors: Albert Carles Brangarí; Xavier Sanchez-Vila, Anna Freixa, Anna M. Romaní, Simonetta Rubol, Daniel Fernàndez-Garcia
      Pages: 93 - 109
      Abstract: The accumulation of biofilms in porous media is likely to influence the overall hydraulic properties and, consequently, a sound understanding of the process is required for the proper design and management of many technological applications. In order to bring some light into this phenomenon we present a mechanistic model to study the variably saturated hydraulic properties of bio-amended soils. Special emphasis is laid on the distribution of phases at pore-scale and the mechanisms to retain and let water flow through, providing valuable insights into phenomena behind bioclogging. Our approach consists in modeling the porous media as an ensemble of capillary tubes, obtained from the biofilm-free water retention curve. This methodology is extended by the incorporation of a biofilm composed of bacterial cells and extracellular polymeric substances (EPS). Moreover, such a microbial consortium displays a channeled geometry that shrinks/swells with suction. Analytical equations for the volumetric water content and the relative permeability can then be derived by assuming that biomass reshapes the pore space following specific geometrical patterns. The model is discussed by using data from laboratory studies and other approaches already existing in the literature. It can reproduce (i) displacements of the retention curve toward higher saturations and (ii) permeability reductions of distinct orders of magnitude. Our findings also illustrate how even very small amounts of biofilm may lead to significant changes in the hydraulic properties. We, therefore, state the importance of accounting for the hydraulic characteristics of biofilms and for a complex/more realistic geometry of colonies at the pore-scale.
      PubDate: 2017-01-10T10:15:40.219987-05:
      DOI: 10.1002/2015WR018517
  • Multiple outflows, spatial components, and nonlinearities in age theory
    • Authors: Salvatore Calabrese; Amilcare Porporato
      Pages: 110 - 126
      Abstract: Water age has become an important variable for the characterization of hydrologic systems. The goal of this paper is to analyze the role of multiple outflows, spatial components, and nonlinearities in age theory. We first extend the theory to linear systems with multiple outflows, including the relationship between age distribution at death and survival time distribution at birth. We further show that for each outflow there is a survival time distribution at birth, which normalized corresponds to the impulse-response function for the specific outflow. We also analyze how the impulse-response function affects both the amplitude gain and time delay of the outflow and the long-term average partitioning. With regard to linear spatially extended systems, we link the impulse-response function to the Green's function. This allows us to easily compute the loss function and the age distribution for the system. Finally, we focus on nonlinear systems to analyze the effects of storage-dependent and age distribution-dependent loss functions. By considering the Burgers' equation, we show how the relationships between spatial dynamics and the age distribution are complicated by nonlinearities.
      PubDate: 2017-01-10T10:15:35.048125-05:
      DOI: 10.1002/2016WR019227
  • Intrawellbore kinematic and frictional losses in a horizontal well in a
           bounded confined aquifer
    • Authors: Quanrong Wang; Hongbin Zhan
      Pages: 127 - 141
      Abstract: Horizontal drilling has become an appealing technology for water resource exploration or aquifer remediation in recent decades, due to decreasing operational cost and many technical advantages over vertical wells. However, many previous studies on flow into horizontal wells were based on the Uniform Flux Boundary Condition (UFBC), which does not reflect the physical processes of flow inside the well accurately. In this study, we investigated transient flow into a horizontal well in an anisotropic confined aquifer laterally bounded by two constant-head boundaries. Three types of boundary conditions were employed to treat the horizontal well, including UFBC, Uniform-Head Boundary Condition (UHBC), and Mixed-Type Boundary Condition (MTBC). The MTBC model considered both kinematic and frictional effects inside the horizontal well, in which the kinematic effect referred to the accelerational and fluid-inflow effects. A new solution of UFBC was derived by superimposing the point sink/source solutions along the axis of a horizontal well with a uniform flux distribution. New solutions of UHBC and MTBC were obtained by a hybrid analytical-numerical method, and an iterative method was proposed to determine the well discretization required for achieving sufficiently accurate results. This study showed that the differences among the UFBC, UHBC, and MTBC solutions were obvious near the well screen, decreased with distance from the well, and became negligible near the constant-head boundary. The relationship between the flow rate and the drawdown was nonlinear for the MTBC solution, while it was linear for the UFBC and UHBC solutions.
      PubDate: 2017-01-11T23:40:48.855506-05:
      DOI: 10.1002/2015WR018252
  • Constraining spatial variability in recharge and discharge in an arid
           environment through modeling carbon-14 with improved boundary conditions
    • Authors: Cameron Wood; Peter G. Cook, Glenn A. Harrington, Anthony Knapton
      Pages: 142 - 157
      Abstract: Carbon-14 (14C) has been widely used to estimate groundwater recharge rates in arid regions, and is increasingly being used as a tool to assist numerical model calibration. However, lack of knowledge on 14C inputs to groundwater potentially limits its reliability for constraining spatial variability in recharge. In this study, we use direct measurements of 14C in the unsaturated zone to develop a 14C input map for a regional scale unconfined aquifer in the Ti Tree Basin in central Australia. The map is used as a boundary condition for a 3-D groundwater flow and solute transport model for the basin. The model is calibrated to both groundwater 14C activity and groundwater level, and calibration is achieved by varying recharge rates in 18 hydrogeological zones. We test the sensitivity of the calibration to both the 14C boundary condition, and the number or recharge zones used. The calibrated recharge rates help resolve the conceptual model for the basin, and demonstrate that spatially distributed discharge (through evapotranspiration) is an important part of the water balance. This approach demonstrates the importance of boundary conditions for 14C transport modeling (14C input activity), for improving estimates of spatial variability in recharge and discharge.
      PubDate: 2017-01-11T23:35:39.36073-05:0
      DOI: 10.1002/2015WR018424
  • Variational assimilation of streamflow data in distributed flood
    • Authors: Giulia Ercolani; Fabio Castelli
      Pages: 158 - 183
      Abstract: Data assimilation has the potential to improve flood forecasting. However, research efforts are still needed for an effective development of assimilation schemes suitable for operational usage, especially in case of distributed hydrologic models. This work presents a new assimilation system of streamflow data from multiple locations in a distributed hydrologic model. The system adopts a mixed variational-Monte Carlo approach, and is here tested with the hydrologic model MOBIDIC, that is part of the operational flood forecasting chain for Arno river in central Italy. The main objective of the work is to evaluate the actual gain that the system can lead to flood predictions in a real-time operational usage. Accordingly, a specifically designed assessment strategy is employed. It is based on several hindcast experiments that include both high flow and false alarm events in the period 2009–2014 in Arno river basin. Results show that the assimilation system can significantly increase the accuracy of flow predictions in respect to open loop simulations in both cases. Specific performances depend on location and event, but in the majority of cases the error on predicted peak flow is reduced of more than 50% with a lead time of around 10 h. The analysis reveals also that the structure of the hydrologic model, the coherence between observations at various sites, and the initial watershed saturation level, considerably affect the obtainable performances. Conditions that may lead to a worsening of open loop predictions are identified and discussed.
      PubDate: 2017-01-11T23:40:59.318902-05:
      DOI: 10.1002/2016WR019208
  • Decadal variations in groundwater quality: A legacy from nitrate leaching
           and denitrification by pyrite in a sandy aquifer
    • Authors: Søren Jessen; Dieke Postma, Lærke Thorling, Sascha Müller, Jari Leskelä, Peter Engesgaard
      Pages: 184 - 198
      Abstract: Twenty-five years of groundwater quality monitoring in a sandy aquifer beneath agricultural fields showed large temporal and spatial variations in major ion groundwater chemistry, which were linked closely to the nitrate (NO3) content of agricultural recharge. Between 1988 and 2013, the NO3 content of water in the oxidized zone of the aquifer nearly halved, following implementation of action plans to reduce N leaching from agriculture. However, due to denitrification by pyrite oxidation in the aquifer, a plume of sulfate-rich water migrates through the aquifer as a legacy of the historical NO3 loading. Agriculture thus is an important determinant of major ion groundwater chemistry. Temporal and spatial variations in the groundwater quality were simulated using a 2D reactive transport model, which combined effects of the historical NO3 leaching and denitrification, with dispersive mixing into the pristine groundwater residing deeper in the aquifer. Reactant-to-product ratios across reaction fronts are altered by dispersive mixing and transience in reactant input functions. Modelling therefore allowed a direct comparison of observed and simulated ratios of concentrations of NO3 (reactant) in the oxidized zone to those of SO4 (product) in the reduced zone, which aided a stoichiometric assessment of the mechanisms of denitrification. Denitrification by pyrite in the Rabis Creek aquifer results in oxidation of S−1 and Fe2+ in pyrite to S6+ in dissolved SO4 and Fe3+ in Fe-oxide. Neither precipitation of elemental sulfur (S0), nor of jarosite, was supported by observations, and adsorption of sulfate was also dismissed.
      PubDate: 2017-01-11T23:35:43.411433-05:
      DOI: 10.1002/2016WR018995
  • Investigation of representing hysteresis in macroscopic models of
    • Authors: Abdullah Cihan; Jens Birkholzer, Luca Trevisan, Ana Gonzalez-Nicolas, Tissa Illangasekare
      Pages: 199 - 221
      Abstract: Incorporating hysteresis into models is important to accurately capture the two phase flow behavior when porous media systems undergo cycles of drainage and imbibition such as in the cases of injection and post-injection redistribution of CO2 during geological CO2 storage (GCS). In the traditional model of two-phase flow, existing constitutive models that parameterize the hysteresis associated with these processes are generally based on the empirical relationships. This manuscript presents development and testing of mathematical hysteretic capillary pressure—saturation—relative permeability models with the objective of more accurately representing the redistribution of the fluids after injection. The constitutive models are developed by relating macroscopic variables to basic physics of two-phase capillary displacements at pore-scale and void space distribution properties. The modeling approach with the developed constitutive models with and without hysteresis as input is tested against some intermediate-scale flow cell experiments to test the ability of the models to represent movement and capillary trapping of immiscible fluids under macroscopically homogeneous and heterogeneous conditions. The hysteretic two-phase flow model predicted the overall plume migration and distribution during and post injection reasonably well and represented the postinjection behavior of the plume more accurately than the nonhysteretic models. Based on the results in this study, neglecting hysteresis in the constitutive models of the traditional two-phase flow theory can seriously overpredict or underpredict the injected fluid distribution during post-injection under both homogeneous and heterogeneous conditions, depending on the selected value of the residual saturation in the nonhysteretic models.
      PubDate: 2017-01-11T01:30:57.595247-05:
      DOI: 10.1002/2016WR019449
  • Benthic biofilm controls on fine particle dynamics in streams
    • Authors: K. R. Roche; J. D. Drummond, F. Boano, A. I. Packman, T. J. Battin, W. R. Hunter
      Pages: 222 - 236
      Abstract: Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to obtain a range of biofilm characteristics. Fluorescent, 8 µm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30 min period. We measured particle concentrations using a flow cytometer and mesoscale (10 µm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition-resuspension dynamics were determined by fitting results to a stochastic mobile-immobile model, which showed that retention timescales for particles within the biofilm-covered streambeds followed a power-law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers.
      PubDate: 2017-01-11T23:40:39.400191-05:
      DOI: 10.1002/2016WR019041
  • Nutrient processes at the stream-lake interface for a channelized versus
           unmodified stream mouth
    • Authors: Richard Niswonger; Ramon Naranjo, David Smith, Jim Constantz, Kip Allander, Donald Rosenberry, Bethany Neilson, Michael R. Rosen, David Stonestrom
      Pages: 237 - 256
      Abstract: Inorganic forms of nitrogen and phosphorous impact freshwater lakes by stimulating primary production and affecting water quality and ecosystem health. Communities around the world are motivated to sustain and restore freshwater resources and are interested in processes controlling nutrient inputs. We studied the environment where streams flow into lakes, referred to as the stream-lake interface (SLI), for a channelized and unmodified stream outlet. Channelization is done to protect infrastructure or recreational beach areas. We collected hydraulic and nutrient data for surface water and shallow groundwater in two SLIs to develop conceptual models that describe characteristics that are representative of these hydrologic features. Water, heat, and solute transport models were used to evaluate hydrologic conceptualizations and estimate mean residence times of water in the sediment. A nutrient mass balance model is developed to estimate net rates of adsorption and desorption, mineralization, and nitrification along subsurface flow paths. Results indicate that SLIs are dynamic sources of nutrients to lakes and that the common practice of channelizing the stream at the SLI decreases nutrient concentrations in pore water discharging along the lakeshore. This is in contrast to the unmodified SLI that forms a barrier beach that disconnects the stream from the lake and results in higher nutrient concentrations in pore water discharging to the lake. These results are significant because nutrient delivery through pore water seepage at the lakebed from the natural SLI contributes to nearshore algal communities and produces elevated concentrations of inorganic nutrients in the benthic zone where attached algae grow.
      PubDate: 2017-01-11T23:36:00.521917-05:
      DOI: 10.1002/2016WR019538
  • Mixed populations and annual flood frequency estimates in the western
           United States: The role of atmospheric rivers
    • Authors: Nancy A. Barth; Gabriele Villarini, Munir A. Nayak, Kathleen White
      Pages: 257 - 269
      Abstract: The Bulletin 17B framework assumes that the annual peak flow data included in a flood frequency analysis are from a homogeneous population. However, flood frequency analysis over the western United States is complicated by annual peak flow records that frequently contain annual flows generated from distinctly different flood generating mechanisms. These flood series contain multiple zero flows and/or potentially influential low floods (PILFs) that substantially deviate from the overall pattern in the data. Moreover, they often also contain extreme flood events representing different hydrometeorologic agents. Among the different flood generating mechanisms, atmospheric rivers (ARs) are responsible for large, regional-scale floods. The spatial and fractional contribution of ARs in annual peak flow data is examined based on 1375 long-term U.S. Geological Survey (USGS) streamgage sites with at least 30 years of data. Six main areas in which flooding is impacted by ARs at varying degrees were found throughout the western United States. The Pacific Northwest and the northern California coast have the highest fraction of AR-generated peaks (∼80–100%), while eastern Montana, Wyoming, Utah, Colorado, and New Mexico have nearly no impacts from ARs. The individual regions of the central Columbia River Basin in the Pacific Northwest, the Sierra Nevada, the central and southern California coast, and central Arizona all show a mixture of 30–70% AR-generated flood peaks. Analyses related to the largest flood peaks on record and to the estimated annual exceedance probabilities highlight the strong impact of ARs on flood hydrology in this region, together with marked regional differences.
      PubDate: 2017-01-11T23:36:04.668392-05:
      DOI: 10.1002/2016WR019064
  • Nonlinear advection-aridity method for landscape evaporation and its
           application during the growing season in the southern Loess Plateau of the
           Yellow River basin
    • Authors: Wilfried Brutsaert; Wei Li, Atsuhiro Takahashi, Tetsuya Hiyama, Lu Zhang, Wenzhao Liu
      Pages: 270 - 282
      Abstract: The advection-aridity approach to estimate actual evaporation from natural land surfaces is one of the better known implementations of Bouchet's complementary principle. Detailed measurements at 2, 12, and 32 m above the ground surface during the growing seasons of 2004–2007 allowed validation of a generalized nonlinear form of this approach above the highly variable terrain in Changwu County in the southern Loess Plateau of the Yellow River basin in China. The obtained values of the parameters were found to lie well within the ranges to be expected on physical grounds or from previous measurements by different experimental means; calibration on the basis of any one year of data allowed predictions within roughly 5% on average. Relative to the corresponding observed turbulent vapor fluxes, the evaporation rates calculated with measurements at the highest level of 32 m displayed the least scatter but only slightly less than those calculated with measurements at the lower level of 12 m; however, those based on measurements at the lowest level of 2 m displayed considerably more scatter than those derived at the two higher levels. This is consistent with the existence of a blending height at higher elevations above the ground, where the effects of surface variability tend to fade away.
      PubDate: 2017-01-11T23:35:51.810848-05:
      DOI: 10.1002/2016WR019472
  • Strengths and weaknesses of temporal stability analysis for monitoring and
           estimating grid-mean soil moisture in a high-intensity irrigated
           agricultural landscape
    • Authors: Youhua Ran; Xin Li, Rui Jin, Jian Kang, Michael H. Cosh
      Pages: 283 - 301
      Abstract: Monitoring and estimating grid-mean soil moisture is very important for assessing many hydrological, biological, and biogeochemical processes and for validating remotely sensed surface soil moisture products. Temporal stability analysis (TSA) is a valuable tool for identifying a small number of representative sampling points to estimate the grid-mean soil moisture content. This analysis was evaluated and improved using high-quality surface soil moisture data that were acquired by a wireless sensor network in a high-intensity irrigated agricultural landscape in an arid region of northwestern China. The performance of the TSA was limited in areas where the representative error was dominated by random events, such as irrigation events. This shortcoming can be effectively mitigated by using a stratified TSA (STSA) method, proposed in this paper. In addition, the following methods were proposed for rapidly and efficiently identifying representative sampling points when using TSA. (1) Instantaneous measurements can be used to identify representative sampling points to some extent; however, the error resulting from this method is significant when validating remotely sensed soil moisture products. Thus, additional representative sampling points should be considered to reduce this error. (2) The calibration period can be determined from the time span of the full range of the grid-mean soil moisture content during the monitoring period. (3) The representative error is sensitive to the number of calibration sampling points, especially when only a few representative sampling points are used. Multiple sampling points are recommended to reduce data loss and improve the likelihood of representativeness at two scales.
      PubDate: 2017-01-13T02:50:47.04193-05:0
      DOI: 10.1002/2015WR018182
  • Measuring household consumption and waste in unmetered, intermittent piped
           water systems
    • Authors: Emily Kumpel; Cleo Woelfle-Erskine, Isha Ray, Kara L. Nelson
      Pages: 302 - 315
      Abstract: Measurements of household water consumption are extremely difficult in intermittent water supply (IWS) regimes in low- and middle-income countries, where water is delivered for short durations, taps are shared, metering is limited, and household storage infrastructure varies widely. Nonetheless, consumption estimates are necessary for utilities to improve water delivery. We estimated household water use in Hubli-Dharwad, India, with a mixed-methods approach combining (limited) metered data, storage container inventories, and structured observations. We developed a typology of household water access according to infrastructure conditions based on the presence of an overhead storage tank and a shared tap. For households with overhead tanks, container measurements and metered data produced statistically similar consumption volumes; for households without overhead tanks, stored volumes underestimated consumption because of significant water use directly from the tap during delivery periods. Households that shared taps consumed much less water than those that did not. We used our water use calculations to estimate waste at the household level and in the distribution system. Very few households used 135 L/person/d, the Government of India design standard for urban systems. Most wasted little water even when unmetered, however, unaccounted-for water in the neighborhood distribution systems was around 50%. Thus, conservation efforts should target loss reduction in the network rather than at households.
      PubDate: 2017-01-13T02:56:01.072523-05:
      DOI: 10.1002/2016WR019702
  • Direct and indirect urban water footprints of the United States
    • Authors: Christopher M. Chini; Megan Konar, Ashlynn S. Stillwell
      Pages: 316 - 327
      Abstract: The water footprint of the urban environment is not limited to direct water consumption (i.e., municipal supplies); embedded water in imported resources, or virtual water transfers, provides an additional component of the urban water footprint. Using empirical data, our analysis extends traditional urban water footprinting analysis to quantify both direct and indirect urban resources for the United States. We determine direct water volumes and their embedded energy through open records requests of water utilities. The indirect component of the urban water footprint includes water indirectly consumed through energy and food, relating to the food-energy-water nexus. We comprehensively quantify the indirect water footprint for 74 metropolitan statistical areas through the combination of various databases, including the Commodity Flow Survey of the U.S. Census Bureau, the U.S. Department of Agriculture, the Water Footprint Network, and the Energy Information Administration. We then analyze spatial heterogeneity in both direct and indirect water footprints, determining the average urban water footprint in the United States to be 1.64 million gallons of water per person per year [6200 m3/person/yr or 17,000 L/person/d], dominated by indirect water. Additionally, our study of the urban water cycle extends beyond considering only water resources to include embedded energy and equivalent carbon dioxide emissions. The inclusion of multiple sectors of the urban water cycle and their underlying processes provides important insights to the overall urban environment, the interdependencies of the food-energy-water nexus, and water resource sustainability. Our results provide opportunities for benchmarking the urban energy-water nexus, water footprints, and climate change potential.
      PubDate: 2017-01-13T02:45:28.984484-05:
      DOI: 10.1002/2016WR019473
  • High frequency measurements of reach scale nitrogen uptake in a fourth
           order river with contrasting hydromorphology and variable water chemistry
           (Weiße Elster, Germany)
    • Authors: Julia Vanessa Kunz; Robert Hensley, Lisa Brase, Dietrich Borchardt, Michael Rode
      Pages: 328 - 343
      Abstract: River networks exhibit a globally important capacity to retain and process nitrogen. However direct measurement of in-stream removal in higher order streams and rivers has been extremely limited. The recent advent of automated sensors has allowed high frequency measurements, and the development of new passive methods of quantifying nitrogen uptake which are scalable across river size. Here we extend these methods to higher order streams with anthropogenically elevated nitrogen levels, substantial tributaries, complex input signals, and multiple N species. We use a combination of two station time-series and longitudinal profiling of nitrate to assess differences in nitrogen processing dynamics in a natural versus a channelized impounded reach with WWTP effluent impacted water chemistry. Our results suggest that net mass removal rates of nitrate were markedly higher in the unmodified reach. Additionally, seasonal variations in temperature and insolation affected the relative contribution of assimilatory versus dissimilatory uptake processes, with the latter exhibiting a stronger positive dependence on temperature. From a methodological perspective, we demonstrate that a mass balance approach based on high frequency data can be useful in deriving quantitative uptake estimates, even under dynamic inputs and lateral tributary inflow. However, uncertainty in diffuse groundwater inputs and more importantly the effects of alternative nitrogen species, in this case ammonium, pose considerable challenges to this method.
      PubDate: 2017-01-13T02:51:32.942715-05:
      DOI: 10.1002/2016WR019355
  • The moving-boundary approach for modeling gravity-driven stable and
           unstable flow in soils
    • Authors: Naaran Brindt; Rony Wallach
      Pages: 344 - 360
      Abstract: The Richards equation is unsuccessful at describing gravity-driven unstable flow with nonmonotonic water content distribution. This shortcoming is resolved in the current study by introducing the moving-boundary approach. Following this approach, the flow domain is divided into two subdomains with a sharp change in fluid saturation between them (moving boundary). The upper subdomain consists of water and air, whose relationship varies with space and time following the imposed boundary condition at the soil surface calculated by the Richards equation. The lower subdomain consists of an initially dry soil that remains constant. The location of the boundary between the two subdomains is part of the solution, rendering the problem nonlinear. The moving boundary solution was used after verification to demonstrate the effect of contact angle, soil characteristic curves and incoming flux on the dynamic water-entry pressure of the soil, which depends on the soil's wettability, incoming flux at the soil surface and the wetting front's propagation rate. Lower soil wettability hinders spontaneous invasion of the dry pores and, together with a higher input flux, induces water accumulation behind the wetting front (saturation overshoot). The wetting front starts to propagate once the pressure building up behind it exceeds the dynamic water-entry pressure. To conclude, the physically based novel moving-boundary approach for solving stable and gravity-driven unstable flow in soils was developed and verified. It supports the conjecture that saturation overshoot is a prerequisite for gravity-driven fingering.
      PubDate: 2017-01-13T02:51:14.153863-05:
      DOI: 10.1002/2016WR019252
  • Effect of low-concentration rhamnolipid biosurfactant on Pseudomonas
           aeruginosa transport in natural porous media
    • Authors: Guansheng Liu; Hua Zhong, Yongbing Jiang, Mark L Brusseau, Jiesheng Huang, Liangsheng Shi, Zhifeng Liu, Yang Liu, Guangming Zeng
      Pages: 361 - 375
      Abstract: Enhanced transport of microbes in subsurface is a focus in bioaugmentation applications for remediation of groundwater. In this study, the effect of low-concentration monorhamnolipid biosurfactant on transport of Pseudomonas aeruginosa ATCC 9027 in natural porous media (silica sand and a sandy soil) with or without hexadecane as the nonaqueous phase liquids (NAPLs) was studied with miscible-displacement experiments using artificial groundwater as the background solution. Transport of two types of cells was investigated, glucose-grown and hexadecane-grown cells with lower and higher cell surface hydrophobicity (CSH), respectively. A clean-bed colloid deposition model was used to calculate deposition rate coefficients (k) for quantitative assessment on the effect of the rhamnolipid on the transport. In the absence of NAPLs, significant cell retention was observed in the sand (81% and 82% for glucose-grown and hexadecane-grown cells, respectively). Addition of low-concentration rhamnolipid enhanced cell transport, with 40 mg/L of rhamnolipid reducing retention to 50% and 60% for glucose-grown and hexadecane-grown cells, respectively. The k values for both glucose-grown and hexadecane-grown cells correlated linearly with rhamnolipid-dependent CSH quantitatively measured using a bacterial-adhesion-to-hydrocarbon method. Retention of cells by the soil was nearly complete (>99%). Forty milligrams per liter of rhamnolipid reduced the retention to 95%. The presence of NAPLs in the sand enhanced the retention of hexadecane-grown cells with higher CSH. Transport of cells in the presence of NAPLs was enhanced by rhamnolipid at all concentrations tested, and the relative enhancement was greater than in the absence of NAPLs. This study shows the importance of hydrophobic interaction on bacterial transport in natural porous media and the potential of using low-concentration rhamnolipid for facilitating cell transport in subsurface for bioaugmentation efforts.
      PubDate: 2017-01-13T02:51:35.466633-05:
      DOI: 10.1002/2016WR019832
  • A platform for probabilistic Multimodel and Multiproduct Streamflow
    • Authors: Tirthankar Roy; Aleix Serrat-Capdevila, Hoshin Gupta, Juan Valdes
      Pages: 376 - 399
      Abstract: We develop and test a probabilistic real-time streamflow-forecasting platform, Multimodel and Multiproduct Streamflow Forecasting (MMSF), that uses information provided by a suite of hydrologic models and satellite precipitation products (SPPs). The SPPs are bias-corrected before being used as inputs to the hydrologic models, and model calibration is carried out independently for each of the model-product combinations (MPCs). Forecasts generated from the calibrated models are further bias-corrected to compensate for the deficiencies within the models, and then probabilistically merged using a variety of model averaging techniques. Use of bias-corrected SPPs in streamflow forecasting applications can overcome several issues associated with sparsely gauged basins and enable robust forecasting capabilities. Bias correction of streamflow significantly improves the forecasts in terms of accuracy and precision for all different cases considered. Results show that the merging of individual forecasts from different MPCs provides additional improvements. All the merging techniques applied in this study produce similar results, however, the Inverse Weighted Averaging (IVA) proves to be slightly superior in most cases. We demonstrate the implementation of the MMSF platform for real-time streamflow monitoring and forecasting in the Mara River basin of Africa (Kenya & Tanzania) in order to provide improved monitoring and forecasting tools to inform water management decisions.
      PubDate: 2017-01-17T11:45:57.443325-05:
      DOI: 10.1002/2016WR019752
  • A 277 year cool season dam inflow reconstruction for Tasmania,
           southeastern Australia
    • Authors: K. J. Allen; S. C. Nichols, R. Evans, S. Allie, G. Carson, F. Ling, E.R. Cook, G. Lee, P. J. Baker
      Pages: 400 - 414
      Abstract: Seasonal variability is a significant source of uncertainty in projected changes to precipitation across southeastern Australia (SEA). While existing instrumental records provide seasonal data for recent decades, most proxy records (e.g., tree rings, corals, speleothems) offer only annual reconstructions of hydroclimate. We present the first cool-season (July–August) reconstruction of dam inflow (Lake Burbury) for western Tasmania in SEA based on tree-ring width (Athrotaxis selaginoides) and mean latewood cell wall thickness (Phyllocladus aspleniifolius) chronologies. The reconstruction, produced using principal component regression, verifies back to 1731 and is moderately skillful, explaining around 23% of the variance. According to the reconstruction, relatively low inflow periods occurred around 1860, the early 1900s and 1970, while relatively high inflows occurred in the 1770s and 1810s. Highest reconstructed inflows occurred in 1816, and lowest in 1909. Comparison with available documentary and instrumental records indicates that the reconstruction better captures high rather than low flow events. There is virtually no correlation between our reconstruction and another for December–January inflow for the same catchment, a result consistent with the relationship between seasonal instrumental data. This suggests that conditions in one season have not generally reflected conditions in the other season over the instrumental record, or for the past 277 years. This illustrates the value of obtaining reconstructions of regional hydroclimatic variability for multiple individual seasons in regions where dry and wet seasons are not strongly defined. The results also indicate that the hydroclimate of the southeastern Australian region cannot be adequately represented by a single regional reconstruction.
      PubDate: 2017-01-17T11:46:30.548145-05:
      DOI: 10.1002/2016WR018906
  • Unsaturated hydraulic properties of Sphagnum moss and peat reveal trimodal
           pore-size distributions
    • Authors: Tobias K. D. Weber; Sascha C. Iden, Wolfgang Durner
      Pages: 415 - 434
      Abstract: In ombrotrophic peatlands, the moisture content of the vadose zone (acrotelm) controls oxygen diffusion rates, redox state, and the turnover of organic matter. Whether peatlands act as sinks or sources of atmospheric carbon thus relies on variably saturated flow processes. The Richards equation is the standard model for water flow in soils, but it is not clear whether it can be applied to simulate water flow in live Sphagnum moss. Transient laboratory evaporation experiments were conducted to observe evaporative water fluxes in the acrotelm, containing living Sphagnum moss, and a deeper layer containing decomposed moss peat. The experimental data were evaluated by inverse modeling using the Richards equation as process model for variably-saturated flow. It was tested whether water fluxes and time series of measured pressure heads during evaporation could be simulated. The results showed that the measurements could be matched very well providing the hydraulic properties are represented by a suitable model. For this, a trimodal parametrization of the underlying pore-size distribution was necessary which reflects three distinct pore systems of the Sphagnum constituted by inter-, intra-, and inner-plant water. While the traditional van Genuchten-Mualem model led to great discrepancies, the physically more comprehensive Peters-Durner-Iden model which accounts for capillary and noncapillary flow, led to a more consistent description of the observations. We conclude that the Richards equation is a valid process description for variably saturated moisture fluxes over a wide pressure range in peatlands supporting the conceptualization of the live moss as part of the vadose zone.
      PubDate: 2017-01-17T11:46:35.611334-05:
      DOI: 10.1002/2016WR019707
  • A narrative method for analyzing transitions in urban water management:
           The case of the Miami-Dade Water and Sewer Department
    • Authors: Galen Treuer; Elizabeth Koebele, Aaron Deslatte, Kathleen Ernst, Margaret Garcia, Kim Manago
      Abstract: Although the water management sector is often characterized as resistant to risk and change, urban areas across the United States are increasingly interested in creating opportunities to transition toward more sustainable water management practices. These transitions are complex and difficult to predict – the product of water managers acting in response to numerous biophysical, regulatory, and political factors within institutional constraints. Gaining a better understanding of how these transitions occur is crucial for continuing to improve water management. This paper presents a replicable methodology for analyzing how urban water utilities transition toward sustainability. The method combines standardized quantitative measures of variables that influence transitions with contextual qualitative information about a utility's unique decision making context to produce structured, data-driven narratives. Data-narratives document the broader context, the utility's pre-transition history, key events during an accelerated period of change, and the consequences of transition. Eventually, these narratives should be compared across cases to develop empirically-testable hypotheses about the drivers of and barriers to utility-level urban water management transition. The methodology is illustrated through the case of the Miami-Dade Water and Sewer Department (WASD) in Miami-Dade County, Florida and its transition towards more sustainable water management in the 2000s, during which per capita water use declined, conservation measures were enacted, water rates increased, and climate adaptive planning became the new norm. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T18:25:37.939699-05:
      DOI: 10.1002/2016WR019658
  • A long-term perspective of the hydroclimatological impacts of atmospheric
           rivers over the central United States
    • Authors: Munir Ahmad Nayak; Gabriele Villarini
      Abstract: The focus of this study is on the climatology of atmospheric rivers (ARs) over the central United States using six atmospheric reanalysis products. This climatology is used to understand the long-term impacts of ARs on annual precipitation, precipitation extremes, and flooding over the central United States. The relationship between the frequency of ARs and three prominent large-scale atmospheric modes [Pacific-North American (PNA) teleconnection, Artic Oscillation (AO), and North Atlantic Oscillation (NAO)] is investigated, and the results are used to statistically model the frequency of ARs at the seasonal scale.AR characteristics (e.g., frequency, duration) are generally robust across the different reanalysis products. ARs exhibit a marked seasonality, with the largest activity in winter (more than ten ARs per season on average), and the lowest in summer (less than two ARs per season on average). Overall, the duration of most ARs is less than three days, but exceptionally persistent ARs (more than six days) are also observed.The year-to-year variations in the total annual precipitation over the central United States are largely explained by the variations in AR-related precipitation. Moreover, 40% of the top 1% daily precipitation extremes are associated with ARs, and more than 70% of the annual instantaneous peak discharges and peaks-over-threshold floods are associated with these storms, in particular during winter and spring.The seasonal frequency of ARs can be described in terms of large-scale atmospheric modes, with PNA playing a major role in particular in winter and spring. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T18:25:33.190963-05:
      DOI: 10.1002/2016WR019033
  • Experiment on temporal variation of bedload transport in response to
           changes in sediment supply in streams
    • Authors: Maria A. Elgueta-Astaburuaga; Marwan A. Hassan
      Abstract: A flume experiment was conducted to study channel adjustment to episodic sediment supply in mountain streams. The bulk sediment used for the bed and feed included grain sizes 0.5-64 mm with geometric mean Dg (bulk) of 5.7 mm. Water discharge was held constant for 40 h, and 300 kg of sediment was supplied through a range of scenarios. Bed slope, sediment storage, sediment transport and bed surface texture responded to sediment supply. During the first of seven runs, bed slope decreased from 0.022 m/m (flume slope) to 0.018 m/m due to sediment starvation. Bed slope increased beginning in the second run as the bed aggraded due to preferential storage of grains >8 mm. Transport rate and bed-surface particle size were significantly affected by magnitude–frequency of sediment feed. Under constant feed, transport rate increased gradually and Dg (surface) ranged between 12-15 mm. Instead, sediment pulses caused a pronounced increase in sediment transport rate and surface fining, trends that were inverted as sediment evacuated. At the run-scale, sediment transport and storage behaved as with constant feed if pulse relaxation time exceeded time between pulses. The increase in transport rate and surface fining were proportional to pulse size. After the 300 kg pulse, transport rate reached 100 g m−1 s−1 and Dg (surface) was 12 mm. Textural differences on the initial bed surface influenced the patterns of sediment transport. Channel adjustment was controlled by magnitude-frequency of sediment feed and not by total feed. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:41:34.463736-05:
      DOI: 10.1002/2016WR019460
  • Estimating snow water equivalent in a Sierra Nevada watershed via
           spaceborne radiance data assimilation
    • Authors: Dongyue Li; Michael Durand, Steven A. Margulis
      Abstract: This paper demonstrates improved retrieval of snow water equivalent (SWE) from spaceborne passive microwave measurements for the sparsely-forested Upper Kern watershed (511 km2) in the southern Sierra Nevada (USA). This is accomplished by assimilating AMSR-E 36.5 GHz measurements into model predictions of SWE at 90-m spatial resolution using the Ensemble Batch Smoother (EnBS) data assimilation framework. For each water year (WY) from 2003 to 2008, SWE was estimated for the accumulation season (October 1st to April 1st) with the assimilation of the measurements in the dry snow season (December 1st to February 28th). The EnBS SWE estimation was validated against snow courses and snow pillows. On average, the EnBS accumulation season SWE RMSE was 77.4 mm (13.1%, relative to peak accumulation), despite deep snow (average peak SWE of 545 mm). The prior model estimate without assimilation had an accumulation season average RMSE of 119.7 mm. After assimilation, the overall bias of the accumulation season SWE estimates was reduced by 84.2%, and the RMSE reduced by 35.4%. The assimilation also reduced the bias and the RMSE of the April 1st SWE estimates by 80.9% and 45.4%, respectively. The EnBS is expected to work well above treeline and for dry snow. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:36:49.256351-05:
      DOI: 10.1002/2016WR018878
  • Improving physically based snow simulations by assimilating snow depths
           using the particle filter
    • Authors: Jan Magnusson; Adam Winstral, Andreas S. Stordal, Richard Essery, Tobias Jonas
      Abstract: Data assimilation can help to ensure that model results remain close to observations despite potential errors in the model, parameters and inputs. In this study, we test whether assimilation of snow depth observations using the particle filter, a generic data assimilation method, improves the results of a multi-layer energy-balance snow model, and compare the results against a direct insertion method. At the field site Col de Porte in France, the particle filter reduces errors in SWE, snowpack runoff and soil temperature when forcing the model with coarse resolution reanalysis data, which is a typical input scenario for operational simulations. For those variables, the model performance after assimilation of snow depths is similar to model performance when forcing with high quality, locally observed input data. Using the particle filter, we could also estimate a snowfall correction factor accurately at Col de Porte. The assimilation of snow depths also improves forecasts with lead-times of, at least, seven days. At further forty sites in Switzerland, the assimilation of snow depths in a model forced with numerical weather prediction data reduces the root-mean-squared-error for SWE by 64% compared to the a model without assimilation. The direct-insertion method shows similar performance as the particle filter, but is likely to produce inconsistencies between modelled variables. The particle filter, on the other hand, avoids such limitations without loss of performance. The methods proposed in this study efficiently reduces errors in snow simulations, seems applicable for different climatic and geographic regions and are easy to deploy. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:36:47.119095-05:
      DOI: 10.1002/2016WR019092
  • The complementary relationship between actual and potential evaporation
           for spatially heterogeneous surfaces
    • Authors: Milad Aminzadeh; Dani Or
      Abstract: The Complementary Relationship (CR) between actual and potential evaporation offers an attractive framework for estimating actual evaporation of drying land surfaces from simple meteorological measurements. Land surfaces are often heterogeneous with variable soil types, land cover, and local hydrologic conditions that give rise to spatially variable evaporation dynamics. The main aim is to incorporate effects of spatial heterogeneities on estimates of actual evaporation in the CR framework. The study extends the physically based approach of Aminzadeh et al. [2016] and proposes upscaling schemes for land-atmosphere interactions affecting reference evaporation from heterogeneous surfaces comprised of vegetation and bare soil patches. For small-scale surface heterogeneity relative to the extent of convective boundary layer (CBL), area averaged atmospheric boundary conditions were imposed over the domain of interest to integrate contributions from patches with different dynamics. For large-scale heterogeneity (large patches relative to the scale of the mean CBL), fluxes from each patch were weighted by their respective areas. Preliminary results are in reasonable agreement with available field measurements and illustrate various effects of heterogeneous surface evaporative fluxes on the CR response. The results also highlight hidden dynamics not captured by standard CR, such as ability of vegetated patches to support steady evaporative fluxes until the onset of water stress while bare soil has already dried out. The study provides new insights into the roles of different vegetation types, land cover fraction, and atmospheric conditions on regional CR behavior hence advancing predictive capabilities of actual evapotranspiration from spatially heterogeneous land surfaces. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:30:31.910056-05:
      DOI: 10.1002/2016WR019759
  • Tidal controls on riverbed denitrification along a tidal freshwater zone
    • Authors: Deon Knights; Audrey H. Sawyer, Rebecca Barnes, Cole Musial, Samuel Bray
      Abstract: In coastal rivers, tidal pumping enhances the exchange of oxygen-rich river water across the sediment-water interface, controlling nitrogen cycling in riverbed sediment. We developed a one-dimensional, fluid flow and solute transport model that quantifies the influence of tidal pumping on nitrate removal and applied it to the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA). In field observations and models, both oxygenated river water and anoxic groundwater deliver nitrate to carbon-rich riverbed sediment. A zone of nitrate removal forms beneath the aerobic interval, which expands and contracts over daily timescales due to tidal pumping. At high tide when oxygen-rich river water infiltrates into the bed, denitrification rates decrease by 25% relative to low tide. In the absence of tidal pumping, our model predicts that the aerobic zone would be thinner, and denitrification rates would increase by 10%. As tidal amplitude increases towards the coast, nitrate removal rates should decrease due to enhanced oxygen exchange across the sediment-water interface, based on sensitivity analysis. Denitrification hot spots in TFZs are more likely to occur in less permeable sediment under lower tidal ranges and higher rates of ambient groundwater discharge. Our models suggest that tidal pumping is not efficient at removing surface water nitrate but can remove up to 81% of nitrate from discharging groundwater in the TFZ of White Clay Creek. Given the high population densities of coastal watersheds, the reactive riverbeds of TFZs play a critical role in mitigating new nitrogen loads to coasts. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:30:28.088092-05:
      DOI: 10.1002/2016WR019405
  • Single discharge events increase reactive efficiency of the hyporheic zone
    • Authors: Nico Trauth; Jan H. Fleckenstein
      Abstract: In this study, we investigate the impact of single stream discharge events on water exchange, solute transport and reactions in the hyporheic zone below a natural in-stream gravel bar. We set up a reactive transport groundwater model with stream flow scenarios that vary by event duration and peak discharge. A steady ambient groundwater flow field is assumed that results in losing, neutral, or gaining stream conditions depending on the stream stage. Across the streambed dissolved oxygen, organic carbon and nitrate are transported into the subsurface. Additional nitrate is received from upwelling groundwater. Aerobic respiration and denitrification are simulated for scenarios with different stream solute concentrations.Results show that hyporheic exchange flux, solute transport and consumption increase during events. However, their intensities depend highly on the interplay between event characteristics and ambient groundwater conditions. During events where reversals in the hydraulic gradient occur stream water and solutes infiltrate deeper into the aquifer where they have more time to react. For those events, the reactive efficiency of the hyporheic zone (solute consumption as fraction of influx) for aerobic respiration and denitrification is up to 2.7 and 10 times higher compared to base flow conditions. The fraction of stream nitrate load consumed in the hyporheic zone increases with stream discharge (up to 150 mg/m2/hour), but remains below the value under base flow conditions for weak events. Events also increase denitrification of groundwater borne nitrate, but groundwater nitrate flux to the stream decreases by up to 33% due to temporary gradient reversals. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-29T05:30:24.972738-05:
      DOI: 10.1002/2016WR019488
  • Primary weathering rates, water transit times, and concentration-discharge
           relations: A theoretical analysis for the critical zone
    • Authors: Ali Ameli; Keith Beven, Martin Erlandsson, Irena Creed, Jeffrey J. McDonnell, Kevin Bishop
      Abstract: The permeability architecture of the critical zone exerts a major influence on the hydrogeochemistry of the critical zone. Water flowpath dynamics drive the spatio-temporal pattern of geochemical evolution and resulting streamflow concentration-discharge (C-Q) relation, but these flowpaths are complex and difficult to map quantitatively. Here, we couple a new integrated flow and particle tracking transport model with a general reversible Transition-State-Theory style dissolution rate-law to explore theoretically how C-Q relations and concentration in the critical zone respond to decline in saturated hydraulic conductivity (Ks) with soil depth. We do this for a range of flow rates and mineral reaction kinetics.Our results show that for minerals with a high ratio of equilibrium concentration (Ceq) to intrinsic weathering rate (Rmax), vertical heterogeneity in Ks enhances the gradient of weathering-derived solute concentration in the critical zone and strengthens the inverse stream C-Q relation. As CeqRmax decreases, the spatial distribution of concentration in the critical zone becomes more uniform for a wide range of flow rates, and stream C-Q relation approaches chemostatic behaviour, regardless of the degree of vertical heterogeneity in Ks. These findings suggest that the transport-controlled mechanisms in the hillslope can lead to chemostatic C-Q relations in the stream while the hillslope surface reaction-controlled mechanisms are associated with an inverse stream C-Q relation. In addition, as CeqRmax decreases, the concentration in the critical zone and stream become less dependent on groundwater age (or transit time). This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T19:10:35.146545-05:
      DOI: 10.1002/2016WR019448
  • The dynamic response of the water retention curve in unsaturated soils
           during drainage to acoustic excitations
    • Authors: Wei-Cheng Lo; Chi-Chin Yang, Shao-Yiu Hsu, Chu-Hui Chen, Chao- Lung Yeh, Markus Hilpert
      Abstract: We examined the effects of acoustic excitations on the water retention curve, i.e., the relationship between capillary pressure (PC) and water saturation (SW) in unsaturated porous media, during drainage. The water retention curves were measured under static and dynamic conditions, where water was withdrawn from a sandbox with three different pumping rates, 12.6, 19.7, and 25.2 mL/s. Excitations with frequencies of 75, 100, 125, and 150 Hz were applied. The acoustic excitations had no effect on the static water retention curve but altered the dynamic water retention curve. The acoustic excitations lowered the dynamic PC, especially under the dynamic condition where the pumping rate was 25.2 mL/s and when SW varied between 0.6 and 0.95. The differences between the capillary pressures measured under static and dynamic conditions decreased when acoustic excitations were applied. We link this finding to the change in contact angle induced by the acoustic excitation. The dynamic coefficients, τ, for the dynamic water retention curves that we fitted to the experimental data were smaller with than without acoustic excitations. We attribute the decrease of the dynamic coefficient to the combination of the increase in the permeability and the decline in the air-entry pressure caused by adding acoustic excitations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T05:14:40.017021-05:
      DOI: 10.1002/2016WR018833
  • Imaging and quantification of spreading and trapping of carbon dioxide in
           saline aquifers using meter-scale laboratory experiments
    • Authors: Luca Trevisan; Ronny Pini, Abdullah Cihan, Jens T. Birkholzer, Quanlin Zhou, Ana González-Nicolás, Tissa H. Illangasekare
      Abstract: The role of capillary forces during buoyant migration of CO2 is critical towards plume immobilization within the post-injection phase of a geological carbon sequestration operation. However, the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in-situ plume evolution. To overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic CO2 plumes in the presence of a background hydraulic gradient, we conducted two unique long-term experiments in a 2.44 m × 0.5 m tank. X-ray attenuation allowed measuring the evolution of a CO2-surrogate fluid saturation, thus providing direct insight into capillarity- and buoyancy-dominated flow processes occurring under successive drainage and imbibition conditions. The comparison of saturation distributions between two experimental campaigns suggests that layered-type heterogeneity plays an important role on non-wetting phase (NWP) migration and trapping, because it leads to (i) longer displacement times (3.6 months vs. 24 days) to reach stable trapping conditions, (ii) limited vertical migration of the plume (with center of mass at 39% vs. 55% of aquifer thickness), and (iii) immobilization of a larger fraction of injected NWP mass (67.2% vs. 51.5% of injected volume) as compared to the homogenous scenario. While these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the subsurface, they also highlight the importance of characterizing it at scales that are below seismic resolution (1-10 m). This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T05:14:38.298008-05:
      DOI: 10.1002/2016WR019749
  • Effects of initial aquifer conditions on economic benefits from
           groundwater conservation
    • Authors: T. Foster; N. Brozović, A. P. Butler
      Abstract: Worldwide, there is growing recognition of the need to reduce agricultural groundwater use in response to rapid rates of aquifer depletion. To date, however, few studies have evaluated how benefits of conservation vary along an aquifer's depletion pathway. To address this question, we develop an integrated modeling framework that couples an agro-economic model of farmers' field-level irrigation decision-making with a borehole-scale groundwater flow model. Unique to this framework is the explicit consideration of the dynamic reductions in well yields that occur as an aquifer is depleted, and how these changes in intraseasonal groundwater supply affect farmers' ability to manage production risks caused by climate variability and, in particular, drought. For an illustrative case study in the High Plains region of the United States, we apply our model to analyze the value of groundwater conservation activities for different initial aquifer conditions. Our results demonstrate that there is a range of initial conditions for which reducing pumping will have long-term economic benefits for farmers by slowing reductions in well yields and prolonging the usable lifetime of an aquifer for high-value irrigated agriculture. In contrast, restrictions on pumping that are applied too early or too late will provide limited welfare benefits. We suggest, therefore, that there are ‘windows of opportunity’ to implement groundwater conservation, which will depend on complex feedbacks between local hydrology, climate, crop growth, and economics. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T05:05:14.149166-05:
      DOI: 10.1002/2016WR019365
  • Optimal adaptation to extreme rainfalls in current and future climate
    • Authors: Dan Rosbjerg
      Abstract: More intense and frequent rainfalls have increased the number of urban flooding events in recent years, prompting adaptation efforts. Economic optimization is considered an efficient tool to decide on the design level for adaptation. The costs associated with a flooding to the T-year level and the annual capital and operational costs of adapting to this level are described with log-linear relations. The total flooding costs are developed as the expected annual damage of flooding above the T-year level plus the annual capital and operational costs for ensuring no flooding below the T-year level. The value of the return period T that corresponds to the minimum of the sum of these costs will then be the optimal adaptation level.The change in climate, however, is expected to continue in the next century, which calls for expansion of the above model. The change can be expressed in terms of a climate factor (the ratio between the future and the current design level) which is assumed to increase in time. This implies increasing costs of flooding in the future for many places in the world. The optimal adaptation level is found for immediate as well as for delayed adaptation. In these cases the optimum is determined by considering the net present value of the incurred costs during a sufficiently long time span. Immediate as well as delayed adaptation is considered. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T04:55:33.208137-05:
      DOI: 10.1002/2016WR019718
  • Numerical study on CO2 leakage detection using electrical streaming
           potential (SP) data
    • Authors: Henrik Büsing; Christian Vogt, Anozie Ebigbo, Norbert Klitzsch
      Abstract: We study the feasibility of detecting carbon dioxide (CO2) movement in the overburden of a storage reservoir due to CO2 leakage through an abandoned well by self-potential measurements at the surface. This is achieved with three-dimensional numerical (SP) modeling of two-phase fluid flow and electrokinetic coupling between flow and streaming potential. We find that, in typical leakage scenarios, for leaky and/or injection wells with conductive metal casing, self-potential signals originating from injection can be identified at the surface. As the injection signal is also observed at the leaky well with metal casing, SP monitoring can be applied for detecting abandoned wells. However, leakage signals are much smaller than the injection signal and thus masked by the latter.We present three alternatives to overcome this problem: (i) simulate the streaming potential of the non-leaky scenario and subtract the result from the measured streaming potential data; (ii) exploit the symmetry of the injection signal by analysing the potential difference of dipoles with the dipole center at the injection well; or (iii) measure SP during periods where the injection is interrupted. In our judgement, the most promising approach for detecting a real-world CO2 leakage is by combining methods (i) and (ii), because this would give the highest signal from the leakage and omit signals originating from the injection well. Consequently, we recommend SP as monitoring method for subsurface CO2 storage, especially because a leakage can be detected shortly after the injection started even before CO2 arrives at the leaky well. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T04:55:29.26324-05:0
      DOI: 10.1002/2016WR019803
  • Assessing convection permitting resolutions of WRF for the purpose of
           water resource impact assessment and vulnerability work: A southeast
           Australian case study
    • Authors: Marie Ekström; Eric Gilleland
      Abstract: Convective permitting simulations are increasingly pursued for providing physically more credible climate projections of rainfall. Their value is likely to be greater for regions where increased resolution not only resolves physical processes better, but also the topographic features of the target domain. Here we assess the skill of convective permitting simulations to simulate rainfall for water resource assessment work in a climate change context for southeast Australia. Output on 2- and 10-km grid-length resolution from a 5-year regional climate model simulation is assessed for skill in simulating mean seasonal climatologies for days with low or high observed rainfall intensities. Comparison is conducted on spatial grids and for 25 catchments across the study region. No significant difference in skill was found in the loss differential when using absolute error for spatial fields of mean climatologies. Measures focusing on spatial similarity and accuracy in position of high rainfall areas indicate somewhat better skill in the 2-km simulation with regard to positioning (in autumn and winter), and with regard to spatial variability (in autumn and spring). Significant difference in skill was shown when comparing the simulated datasets on a catchment basis; seasonally 5-7 catchments in favour of the 10-km output and somewhat less for the 2-km output (3-6 catchments). When using correlation skill as the test measure, results are overwhelmingly in favour of the 2-km output. We cautiously suggest that results may be overly pessimistic for the 2-km simulation because of inadequate representation of rainfall in high altitude areas in observations. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T04:55:26.391814-05:
      DOI: 10.1002/2016WR019545
  • Improving operating policies of large-scale surface-groundwater systems
           through stochastic programming
    • Authors: H. Macian-Sorribes; A. Tilmant, M. Pulido-Velazquez
      Abstract: The management of large-scale water resource systems with surface and groundwater resources requires considering stream-aquifer interactions. Optimization models applied of large-scale systems have either employed deterministic optimization (with perfect foreknowledge of future inflows, which hinders their applicability to real-life operations) or stochastic programming (in which stream-aquifer interaction is often neglected due to the computational burden associated with these methods). In this paper, stream-aquifer interaction is integrated in a stochastic programming framework by combining the Stochastic Dual Dynamic Programming (SDDP) optimization algorithm with the Embedded Multireservoir Model (EMM). The resulting extension of the SDDP algorithm, named Combined Surface-Groundwater SDDP (CSG-SDDP), is able to properly represent the stream-aquifer interaction within stochastic optimization models of large-scale surface-groundwater resources systems. The algorithm is applied to build a hydroeconomic model for the Jucar River Basin (Spain), in which stream-aquifer interactions are essential to the characterization of water resources in the system. Besides the uncertainties regarding the economic characterization of the demand functions, the results show that the economic efficiency of the operating policies under the current system can be improved by better management of groundwater and surface resources. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-27T04:55:24.177521-05:
      DOI: 10.1002/2016WR019573
  • A coupled three-dimensional hydrodynamic model for predicting hypolimnetic
           oxygenation and epilimnetic mixing in a shallow eutrophic reservoir
    • Authors: Shengyang Chen; Chengwang Lei, Cayelan C. Carey, Paul A. Gantzer, John C. Little
      Abstract: Artificial mixing and hypolimnetic oxygenation are two common methods for improving water quality in reservoirs. To examine the effects of their operation on the thermal structure of the water column, we used a three-dimensional hydrodynamic model coupled with a newly developed water-jet model and an existing linear bubble-plume model in conjunction with whole-reservoir in-situ mixing experiments in a drinking-water reservoir. This reservoir has a side-stream supersaturation (SSS) hypolimnetic oxygenation system and a bubble-plume epilimnetic mixing (EM) system installed to reduce hypolimnetic hypoxia and algal blooms. The results show that the SSS successfully adds dissolved oxygen to the hypolimnion without destratifying the reservoir, whereas the EM, located at the lower metalimnetic boundary, deepens this boundary and partially mixes the metalimnion and epilimnion. The newly developed water-jet model coupled with the hydrodynamic model can successfully predict the variation of the thermal structure in the reservoir. The extent to which the SSS and EM systems affect the thermal structure of the reservoir is also quantified by further application of the coupled hydrodynamic model. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-26T19:50:57.875276-05:
      DOI: 10.1002/2016WR019279
  • Quantifying nitrate and oxygen reduction rates in the hyporheic zone using
           222Rn to upscale biogeochemical turnover in rivers
    • Authors: M. Pittroff; S. Frei, B.S. Gilfedder
      Abstract: Quantifying and upscaling chemical turnover in the hyporheic zone (HZ) is difficult due to limited reaction rate data, unknown carbon quality, and few methods for upscaling local measurements to river networks. Here we develop a method for quantifying reaction kinetics in-situ in the HZ and upscaling biogeochemical turnover to catchment scales. Radon-222 was used to quantify water residence times in the HZ of the Roter Main River (RM), Germany. Residence times were then combined with O2, NO3-, CO2, DOC and carbon quality (EEMs, SUVA) data to estimate Monod and first-order reaction rates. Monod parameters µmax and ksat for NO3- reduction were 11 µmol l−1 h−1 and 52 µmol l−1 respectively while the first-order rate was 0.04 h−1. Carbon quality was highly bioavailable in the HZ and is unlikely to be limiting. Reaction kinetics were incorporated into the FINIFLUX model to upscale NO3- mass loss over a 32 km reach of the RM. The aims were to (1) to estimate hyporheic efficiency using Damköhler numbers (Da), and (2) calculate NO3- mass loss in the HZ over the reach. The Da analysis suggests that the hyporheic zone is inefficient for NO3- processing, however this is somewhat misleading as the largest NO3- mass loss occurs at the shortest residence times where Da≪1. This is due to the largest water flux occurring in the uppermost part of the sediment profile. Nitrate processing in the HZ accounted for 24 kg NO3- h−1 over the reach, which was 20% of the NO3- flux from the catchment. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-26T19:50:45.980957-05:
      DOI: 10.1002/2016WR018917
  • Constraining the annual groundwater contribution to the water balance of
           an agricultural floodplain using radon: The importance of floods
    • Authors: Jackie R. Webb; Isaac R. Santos, Barbara Robson, Ben Macdonald, Luke Jeffrey, Damien T. Maher
      Abstract: The water balance of drained floodplains is highly dynamic with complex groundwater-surface water interactions operating over varying spatial and temporal scales. Here, we hypothesise that the majority of groundwater discharge will follow flood events in a modified wetland. To test this hypothesis, we developed a detailed water balance that quantifies the contribution of groundwater discharge to the annual water budget of an extensively drained agricultural floodplain. A clear relationship between surface water radon measurements and groundwater level indicated alternating connection-disconnection dynamics between the drains and shallow groundwater. This relationship was used to develop a radon mass balance to quantitatively model groundwater discharge continuously throughout the year. Groundwater discharge varied by four orders of magnitude over the study period, with daily average rates ranging from 0 to 27,200 m3 d−1, peaking just a few hours after floods receded. Flood events occurred only 12% of the time yet contributed 72 to 76% of the total groundwater discharge. During flood recession periods, aerial groundwater discharge rates reached up to 325 cm d−1 which were some of the highest rates ever estimated. We proposed that the high drainage density of this site (12.4 km constructed drains km−2 catchment area) enhanced groundwater discharge during wet periods due to increased connectivity with the soil. Overall, groundwater discharge contributed 30-80% to the total surface water discharge. This study offers insight into the dynamic behaviour of groundwater within an extensively drained floodplain, and the importance of capturing flood events to quantify total groundwater contribution to floodplain water balances. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-26T19:50:29.731006-05:
      DOI: 10.1002/2016WR019735
  • Impact of social preparedness on flood early warning systems
    • Authors: M. Girons Lopez; G. Di Baldassarre, J. Seibert
      Abstract: Flood early warning systems play a major role in the disaster risk reduction paradigm as cost-effective methods to mitigate flood disaster damage. The connections and feedbacks between the hydrological and social spheres of early warning systems are increasingly being considered as key aspects for successful flood mitigation. The behavior of the public and first responders during flood situations, determined by their preparedness, is heavily influenced by many behavioral traits such as perceived benefits, risk awareness, or even denial.In this study we use the recency of flood experiences as a proxy for social preparedness to assess its impact on the efficiency of flood early warning systems through a simple stylized model and implemented this model using a simple mathematical description. The main findings, which are based on synthetic data, point to the importance of social preparedness for flood loss mitigation, especially in circumstances where the technical forecasting and warning capabilities are limited. Furthermore, we found that efforts to promote and preserve social preparedness may help to reduce disaster-induced losses by almost one half. The findings provide important insights into the role of social preparedness that may help guide decision-making in the field of flood early warning systems. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-23T07:03:36.080183-05:
      DOI: 10.1002/2016WR019387
  • The influence of mixing on stable isotope ratios in porous media: A
           revised Rayleigh model
    • Authors: Jennifer L. Druhan; Kate Maher
      Abstract: For an irreversible reaction, the Rayleigh or distillation-type relationship between stable isotope enrichment and reactant concentration is compromised if fluid samples are characterized by a range of water ages or different extents of reaction progress. Such mixed samples are rarely avoided in the standard methods of sampling fluid from natural porous media. As a result, application of a Rayleigh model to stable isotope ratios measured in aquifers commonly requires a diminished or effective fractionation factor relative to the intrinsic value obtained in the absence of transport effects. Thus, quantitative application of intrinsic parameter values to a fractionating reaction occurring in porous media flow requires revision to the functional form of the relationship between reactant concentration and isotope fractionation. Here, we derive a series of analytical solutions for the relationship between fractionation and flow subject to non-uniform fluid travel time distributions. These solutions are unique from previous approaches in that they avoid the use of a dispersion coefficient. The results are demonstrated against multi-component reactive transport simulations of stable isotope fractionation in homogeneous and spatially correlated heterogeneous flow fields, and applied to a dataset of stable Cr isotope enrichment obtained from a contaminated aquifer. We show that the flux-weighted isotope ratio of a solute is more sensitive to the effects of physical heterogeneity than solute concentrations. Our results support an updated functional form of the traditional Rayleigh model that describes the relationship between reactant concentration and isotope fractionation and is valid for a mixed-fluid sample. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:41:26.267521-05:
      DOI: 10.1002/2016WR019666
  • Flood type-specific construction of synthetic design hydrographs
    • Authors: Manuela I. Brunner; Daniel Viviroli, Anna E. Sikorska, Olivier Vannier, Anne-Catherine Favre, Jan Seibert
      Abstract: Accurate estimates of flood peaks, corresponding volumes and hydrographs are required to design safe and cost-effective hydraulic structures. In this paper, we propose a statistical approach for the estimation of the design variables peak and volume by constructing synthetic design hydrographs for different flood types such as flash-floods, short-rain floods, long-rain floods, and rain-on-snow floods. Our approach relies on the fitting of probability density functions to observed flood hydrographs of a certain flood type and accounts for the dependence between peak discharge and flood volume. It makes use of the statistical information contained in the data and retains the process information of the flood type. The method was tested based on data from 39 meso-scale catchments in Switzerland and provides catchment specific and flood type specific synthetic design hydrographs for all of these catchments. We demonstrate that flood type specific synthetic design hydrographs are meaningful in flood risk management when combined with knowledge on the seasonality and the frequency of different flood types. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:41:12.774727-05:
      DOI: 10.1002/2016WR019535
  • Development of a discrete-continuum VDFST-CFP numerical model for
           simulating seawater intrusion to a coastal karst aquifer with a conduit
    • Authors: Zexuan Xu; Bill X. Hu
      Abstract: A hybrid discrete-continuum numerical model, Variable-Density Flow and Solute Transport - Conduit Flow Process (VDFST-CFP), is developed to simulate seawater intrusion to a coastal karst aquifer with a conduit network. The Darcy-Weisbach equation is applied to simulate the non-laminar groundwater flow in the conduit system that is conceptualized as pipes, while the Darcy equation is used for laminar groundwater flow in the continuum porous medium. Density-dependent groundwater flow with appropriate additional density terms in the conduit is analytically derived. The flow and transport equations are coupled, and numerically solved by the finite difference method with an implicit iteration procedure. Two synthetic benchmarks are developed to compare the VDFST-CFP model results with other numerical models, such as the variable-density SEAWAT, constant-density continuum MODFLOW/MT3DMS and constant-density discrete-continuum CFPv2/UMT3D models. The VDFST-CFP model compares reasonably well with the other model results in both conduit and porous medium domains, and well describes water and salt exchange between the two systems. Under turbulent flow conditions within the conduit, the Darcy-Weisbach equation calculates the flow rate more accurately without the overestimation by the Darcy equation. Sensitivity analysis indicates that conduit diameter, friction factor, matrix hydraulic conductivity, and effective medium porosity are important parameters in the VDFST-CFP model. The pros and cons of the VDFST-CFP model are discussed, including the model assumptions and simplifications, limitations of the discrete-continuum modeling method, and the convergence criteria. In general, the newly developed VDFST-CFP model provides a new numerical modeling method for simulating seawater intrusion in a coastal karst aquifer with conduits. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:40:55.025203-05:
      DOI: 10.1002/2016WR018758
  • A hierarchical Bayesian model for regionalized seasonal forecasts:
           Application to low flows in the northeastern United States
    • Authors: Kuk-Hyun Ahn; Richard Palmer, Scott Steinschneider
      Abstract: This study presents a regional, probabilistic framework for seasonal forecasts of extreme low summer flows in the northeastern United States conditioned on antecedent climate and hydrologic conditions. The model is developed to explore three innovations in hierarchical modeling for seasonal forecasting at ungaged sites: 1) predictive climate teleconnections are inferred directly from ocean fields instead of pre-defined climate indices, 2) a parsimonious modeling structure is introduced to allow climate teleconnections to vary spatially across streamflow gages, and 3) climate teleconnections and antecedent hydrologic conditions are considered jointly for regional forecast development. The proposed model is developed and calibrated in a hierarchical Bayesian framework to pool regional information across sites and enhance regionalization skill. The model is validated in a cross-validation framework along with five simpler nested formulations to test specific hypotheses embedded in the full model structure. Results indicate that each of the three innovations improve out-of-sample summer low-flow forecasts, with the greatest benefits derived from the spatially heterogeneous effect of climate teleconnections. We conclude with a discussion of possible model improvements from a better representation of antecedent hydrologic conditions at ungaged sites. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:35:29.39997-05:0
      DOI: 10.1002/2016WR019605
  • Water storage in a changing environment: The impact of allocation
           institutions on value
    • Authors: Alexander Maas; Andre Dozier, Dale T. Manning, Christopher Goemans
      Abstract: As populations increase in arid regions of the world, investment in water infrastructure improves resource management by increasing control over the location and timing of water allocation. Many studies have explored freer trade as a substitute for additional infrastructure investment. We instead quantify how water allocation institutions, reservoir management objectives, and storage capacity influence the value derived from a reservoir system. We develop a stochastic dynamic programming model of a reservoir system that faces within-year variation in weather-dependent water demand as well as stochastic semi-annual inflows. We parameterize the model using the Colorado-Big Thompson system, which transports stored water from the West Slope of the Rocky Mountains to the East Slope. We then evaluate the performance of the system under five institutional settings. Our results suggest that rigid allocation mechanisms and inefficient management objectives result in a decrease of up to 13% in the value generated from stored water when compared to a free trade scenario, an impact on par with predicted losses associated with climate-change-induced inflow reductions. We also find that under biased management objectives, increasing storage capacity can decrease the social value obtained from stored water. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:35:25.879298-05:
      DOI: 10.1002/2016WR019239
  • Impact of evapotranspiration process representation on runoff projections
           from conceptual rainfall-runoff models
    • Authors: Danlu Guo; Seth Westra, Holger R. Maier
      Abstract: Conceptual rainfall-runoff models are commonly used to estimate potential changes in runoff due to climate change. The development of these models has generally focused on reproducing runoff characteristics, with less scrutiny on other important processes such as the conversion from potential evapotranspiration (PET) to actual evapotranspiration (AET). This study uses three conceptual rainfall-runoff models (GR4J, AWBM and IHACRES_CMD) and five catchments in climatologically different regions of Australia to explore the role of ET process representation on the sensitivity of runoff to plausible future changes in PET. The changes in PET were simulated using the Penman-Monteith model and by perturbing each of the driving variables (temperature, solar radiation, humidity and wind) separately. Surprisingly, the results showed the potential of a more than seven-fold difference in runoff sensitivity per unit change in annual average PET, depending on both the rainfall-runoff model and the climate variable used to perturb PET. These differences were largely due to different ways used to convert PET to AET in the conceptual rainfall-runoff models, with particular dependencies on the daily wet/dry status, as well as the seasonal variations in store levels. By comparing the temporal patterns in simulated AET with eddy-covariance-based observations at two of the study locations, we highlighted some unrealistic behaviour in the simulated AET from AWBM. Such process-based evaluations are useful for scrutinizing the representation of physical processes in alternative conceptual rainfall-runoff models, which can be particularly useful for selecting models for projecting runoff under a changing climate. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-22T04:35:23.13321-05:0
      DOI: 10.1002/2016WR019627
  • An analytical test case for snow models
    • Authors: Martyn P. Clark; Bart Nijssen, Charles H. Luce
      Abstract: This paper develops general analytical solutions for examples of water movement through snow and compares the derived analytical solutions to numerical simulations from a coupled energy and mass balance model. The intended use of the test cases is to evaluate the impact of different numerical approximations, especially different vertical discretization strategies and different time stepping schemes. The analytical solutions provide both outflow from the snowpack, as well as vertical profiles of temperature and volumetric liquid water content at different times throughout the analysis period. The derived analytical solutions have close correspondence with model simulations in most cases. The most pronounced differences between the numerical simulations and the analytical solutions are for the fresh snow test case, where the numerical simulations predict earlier arrival of snowpack outflow. The analytical solutions provide a useful test case for physically motivated snow models because the solutions can be used to evaluate the coupling of hydrology and thermodynamics as well as the unsaturated flow of water through porous media. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-17T10:23:33.218477-05:
      DOI: 10.1002/2016WR019672
  • Phase exposure-dependent exchange
    • Authors: T. R. Ginn; L. G. Schreyer, K. Zamani
      Abstract: Solutes and suspended material often experience delays during exchange between phases one of which may be moving. Consequently transport often exhibits combined effects of advection/dispersion, and delays associated with exchange between phases. Such processes are ubiquitous and include transport in porous/fractured media, watersheds, rivers, forest canopies, urban infrastructure systems and networks. Upscaling approaches often treat the transport and delay mechanisms together, yielding macroscopic “anomalous transport” models. When interaction with the immobile phase is responsible for the delays, it is not the transport that is anomalous, but the lack of it, due to delays. We model such exchanges with a simple generalization of first-order kinetics completely independent of transport. Specifically, we introduce a remobilization rate coefficient that depends on the time in immobile-phase. Memory-function formulations of exchange (with or without transport) can be cast in this framework, and can represent practically all time-nonlocal mass balance models including multirate mass transfer and its equivalent counterparts in the continuous time random walk and time-fractional advection dispersion formalisms, as well as equilibrium exchange. Our model can address delayed single-/multi-event remobilizations as in delay-differential equations and periodic remobilizations that may be useful in sediment transport modeling. It is also possible to link delay mechanisms with transport if so desired, or to superpose an additional source of nonlocality through the transport operator. This approach allows for mechanistic characterization of the mass transfer process with measurable parameters, and the full set of processes representable by these generalized kinetics is a new open question. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-17T10:23:32.103845-05:
      DOI: 10.1002/2016WR019755
  • The integrated hydrologic model intercomparison project, IH-MIP2: A second
           set of benchmark results to diagnose integrated hydrology and feedbacks
    • Authors: Stefan Kollet; Mauro Sulis, Reed Maxwell, Claudio Paniconi, Mario Putti, Giacomo Bertoldi, Ethan T. Coon, Emanuele Cordano, Stefano Endrizzi, Evgeny Kikinzon, Emmanuel Mouche, Claude Mügler, Young-Jin Park, Jens Christian Refsgaard, Simon Stisen, Edward Sudicky
      Abstract: Emphasizing the physical intricacies of integrated hydrology and feedbacks in simulating connected, variably-saturated groundwater-surface water systems, the Integrated Hydrologic Model Intercomparison Project initiated a second phase (IH-MIP2), increasing the complexity of the benchmarks of the first phase. The models that took part in the intercomparison were ATS, Cast3M, CATHY, GEOtop, HydroGeoSphere, MIKE-SHE, and ParFlow. IH-MIP2 benchmarks included a tilted v-catchment with 3D subsurface; a superslab case expanding the slab case of the first phase with an additional horizontal subsurface heterogeneity; and the Borden field rainfall-runoff experiment. The analyses encompassed time series of saturated, unsaturated, and ponded storages, as well as discharge. Vertical cross sections and profiles were also inspected in the superslab and Borden benchmarks. An analysis of agreement was performed including systematic and unsystematic deviations between the different models. Results show generally good agreement between the different models, which lends confidence in the fundamental physical and numerical implementation of the governing equations in the different models. Differences can be attributed to the varying level of detail in the mathematical and numerical representation or in the parameterization of physical processes, in particular with regard to ponded storage and friction slope in the calculation of overland flow. These differences may become important for specific applications such as detailed inundation modeling or when strong inhomogeneities are present in the simulation domain. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-17T10:23:23.228012-05:
      DOI: 10.1002/2016WR019191
  • Experimental study of the effect of grain sizes in a bimodal mixture on
           bed slope, bed texture, and the transition to washload
    • Authors: K. M. Hill; John Gaffney, Sarah Baumgardner, Peter Wilcock, Chris Paola
      Abstract: When fine sediment is added to a coarse-grained system, the mobility and composition of the bed can change dramatically. We conducted a series of flume experiments to determine how the size of fine particles introduced to an active gravel bed influences the mobility and composition of the bed. We initiated our experiments using a constant water discharge and feed rate of gravel. After the system reached steady state, we doubled the feed rate by supplying a second sediment of equal or lesser size, creating size ratios from 1:1 to 1:150. As we decreased the relative size of the fine particles, the system transitioned among three regimes: (1) For particle size ratios close to one, the bed slope increased to transport the additional load of similar-sized particles. The bed surface remained planar and unchanged. (2) For intermediate particle size ratios, the bed slope decreased with the additional fines. The bed surface became patchy with regions of fine and coarse grains. (3) For the largest particle size ratios (the smallest fines), the bed slope remained relatively unchanged. The subsurface became clogged with fine sediment, but fine particles were not present in the surface layer. This third regime constitutes washload, defined by those fractions that do not affect bed-material transport conditions. Our results indicate washload should be defined in terms of three conditions: small grain size relative to that of the bed material, full suspension based on the Rouse number, and a small rate of fine sediment supply relative to transport capacity. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-17T10:23:12.960013-05:
      DOI: 10.1002/2016WR019172
  • Evaporation fractionation in a peatland drainage network affects stream
           water isotope composition
    • Authors: Matthias Sprenger; Doerthe Tetzlaff, Claire Tunaley, Jonathan Dick, Chris Soulsby
      Abstract: There is increasing interest in improving understanding of evaporation within a catchment for an enhanced representation of dominant processes in hydrological models. We used a dual-isotope approach within a nested experimental design in a boreal catchment in the Scottish Highlands (Bruntland Burn) to quantify the spatio-temporal dynamics of evaporation fractionation in a peatland drainage network and its effect on stream water isotopes. We conducted spatially distributed water sampling within the saturated peatland under different wetness conditions. We used the lc-excess – which describes the offset of a water sample from the local meteoric water line in the dual-isotope space - to understand the development of kinetic fractionation during runoff in a peatland network. The evaporation fractionation signal correlated positively with the potential evapotranspiration and negatively with the discharge. The variability of the isotopic enrichment within the peatland drainage network was higher with higher potential evapotranspiration and lower with higher discharge. We found an increased evaporation fractionation towards the center of the peatland, while groundwater seepage from minerogenic soils influenced the isotopic signal at the edge of the peatland. The evaporation signal was imprinted on the stream water, as the discharge from a peatland dominated sub-catchment showed a more intense deviation from the local meteoric water line than the discharge from the Bruntland Burn. The findings underline that evaporation fractionation within peatland drainage networks affects the isotopic signal of headwater catchments, which questions the common assumption in hydrological modelling that the isotopic composition of stream waters did not undergo fractionation processes. This article is protected by copyright. All rights reserved.
      PubDate: 2016-12-15T20:15:25.437939-05:
      DOI: 10.1002/2016WR019258
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