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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: 2)
Acta Limnologica Brasiliensia     Open Access   (Followers: 3)
Advances in Oceanography and Limnology     Open Access   (Followers: 12)
Advances in Water Resource and Protection     Open Access   (Followers: 11)
Advances in Water Resources     Hybrid Journal   (Followers: 44)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Agricultural Water Management     Hybrid Journal   (Followers: 40)
American Journal of Water Resources     Open Access   (Followers: 7)
American Water Works Association     Hybrid Journal   (Followers: 23)
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: 9)
Aquacultural Engineering     Hybrid Journal   (Followers: 7)
Aquaculture     Hybrid Journal   (Followers: 30)
Aquaculture Environment Interactions     Open Access   (Followers: 2)
Aquaculture Research     Hybrid Journal   (Followers: 31)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 36)
Aquatic Geochemistry     Hybrid Journal   (Followers: 4)
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: 13)
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: 19)
CLEAN - Soil, Air, Water     Hybrid Journal   (Followers: 20)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 4)
Cost Effectiveness and Resource Allocation     Open Access   (Followers: 4)
Desalination     Hybrid Journal   (Followers: 7)
Desalination and Water Treatment     Hybrid Journal   (Followers: 12)
Developments in Water Science     Full-text available via subscription   (Followers: 10)
Ecological Chemistry and Engineering S     Open Access   (Followers: 3)
Environmental Science : Water Research & Technology     Full-text available via subscription   (Followers: 6)
Environmental Toxicology     Hybrid Journal   (Followers: 8)
EQA - International Journal of Environmental Quality     Open Access   (Followers: 2)
European journal of water quality - Journal européen d'hydrologie     Full-text available via subscription   (Followers: 6)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 19)
Groundwater for Sustainable Development     Full-text available via subscription   (Followers: 3)
Grundwasser     Hybrid Journal  
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (Followers: 3)
Hydrology Research     Partially Free   (Followers: 15)
Hydrology: Current Research     Open Access   (Followers: 13)
IDA Journal of Desalination and Water Reuse     Hybrid Journal   (Followers: 2)
Ingeniería del agua     Open Access  
International Journal of Climatology     Hybrid Journal   (Followers: 26)
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: 13)
Irrigation Science     Hybrid Journal   (Followers: 4)
Journal of Aquatic Sciences     Full-text available via subscription   (Followers: 3)
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: 5)
Journal of Geophysical Research : Oceans     Partially Free   (Followers: 53)
Journal of Hydro-environment Research     Full-text available via subscription   (Followers: 9)
Journal of Hydroinformatics     Full-text available via subscription   (Followers: 3)
Journal of Hydrology (New Zealand)     Full-text available via subscription   (Followers: 2)
Journal of Hydrology and Hydromechanics     Open Access   (Followers: 3)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 7)
Journal of Limnology     Open Access   (Followers: 7)
Journal of Natural Resources and Development     Open Access   (Followers: 2)
Journal of the American Water Resources Association     Hybrid Journal   (Followers: 31)
Journal of Water and Climate Change     Partially Free   (Followers: 39)
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: 10)
Journal of Water Resource and Protection     Open Access   (Followers: 9)
Journal of Water Resources Planning and Management     Full-text available via subscription   (Followers: 50)
Journal of Water Reuse and Desalination     Partially Free   (Followers: 6)
Journal of Water Security     Open Access   (Followers: 1)
Journal of Water Supply : Research and Technology - AQUA     Partially Free   (Followers: 6)
Journal of Water, Sanitation and Hygiene for Development     Open Access   (Followers: 5)
Jurnal Akuakultur Indonesia     Open Access  
La Houille Blanche     Full-text available via subscription   (Followers: 1)
Lake and Reservoir Management     Hybrid Journal   (Followers: 7)
Lakes & Reservoirs Research & Management     Hybrid Journal   (Followers: 14)
Large Marine Ecosystems     Full-text available via subscription   (Followers: 1)
Liquid Waste Recovery     Open Access   (Followers: 1)
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: 27)
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: 12)
Open Journal of Modern Hydrology     Open Access   (Followers: 5)
Osterreichische Wasser- und Abfallwirtschaft     Hybrid Journal  
Ozone Science & Engineering     Hybrid Journal   (Followers: 1)
Paddy and Water Environment     Hybrid Journal   (Followers: 10)
Research Journal of Environmental Toxicology     Open Access   (Followers: 2)
Reviews in Aquaculture     Hybrid Journal   (Followers: 9)
Revue des sciences de l'eau / Journal of Water Science     Full-text available via subscription   (Followers: 2)
RIBAGUA - Revista Iberoamericana del Agua     Open Access   (Followers: 1)
Riparian Ecology and Conservation     Open Access   (Followers: 7)
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  
Sciences Eaux & Territoires : la Revue du Cemagref     Open Access  
Scientia Marina     Open Access   (Followers: 2)
Smart Water     Open Access  
Society & Natural Resources: An International Journal     Hybrid Journal   (Followers: 18)
Sri Lanka Journal of Aquatic Sciences     Open Access   (Followers: 1)
Sustainability of Water Quality and Ecology     Hybrid Journal   (Followers: 4)
Sustainable Technologies, Systems & Policies     Open Access   (Followers: 7)
Tecnología y Ciencias del Agua     Open Access  
Texas Water Journal     Open Access   (Followers: 2)
Urban Water Journal     Hybrid Journal   (Followers: 14)
Waste Technology     Open Access   (Followers: 3)
Water     Open Access   (Followers: 6)
Water & Sanitation Africa     Full-text available via subscription   (Followers: 4)
Water and Environment Journal     Hybrid Journal   (Followers: 22)
Water Environment Research     Full-text available via subscription   (Followers: 41)
Water International     Hybrid Journal   (Followers: 15)
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: 14)
Water Quality Research Journal of Canada     Full-text available via subscription   (Followers: 3)
Water Research     Hybrid Journal   (Followers: 59)
Water Resources     Hybrid Journal   (Followers: 20)
Water Resources and Economics     Hybrid Journal   (Followers: 5)
Water Resources and Industry     Open Access   (Followers: 3)
Water Resources and Rural Development     Hybrid Journal   (Followers: 2)
Water Resources Management     Hybrid Journal   (Followers: 36)
Water Resources Research     Full-text available via subscription   (Followers: 82)
Water SA     Open Access   (Followers: 1)
Water Science & Technology     Partially Free   (Followers: 25)
Water Science : The National Water Research Center Journal     Open Access   (Followers: 6)
Water Science and Engineering     Open Access   (Followers: 10)
Water Science and Technology : Water Supply     Partially Free   (Followers: 22)
Water Wheel     Open Access   (Followers: 2)
Water, Air, & Soil Pollution     Hybrid Journal   (Followers: 23)
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: 4)

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Journal Cover Water Resources Research
  [SJR: 2.661]   [H-I: 144]   [82 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Print) 0043-1397 - ISSN (Online) 1944-7973
   Published by AGU Homepage  [17 journals]
  • Flow Dependence of Suspended Sediment Gradations
    • Authors: S. A. Gibson; C. Cai
      Abstract: Suspended sediment loads can coarsen or fine as a function of flow. The flow-load gradation relationships can also vary nonmonotonically. This complex relationship between flow and load gradation complicates sediment model boundary condition selection and sediment rating curve analysis. This study analyzed flow-gradation data from 78 gages in the continental United States, exploring trends and tendencies in the flow-gradation relationships. Results were then compared to the flow-gradation trends generated by sediment capacity equations and a meta-analysis of sediment model data. Several systems, with abundant sediment supply fined with flow. However, most gage data and calibrated model inputs coarsened with flow. When nonmonotonic models were considered, one-third to one-half of the gages fit a second-order curve, coarsening over low-to-moderate flows (up to an average annual exceedance probability of ∼30%) and fining over higher flows. The low-flow-coarsening trend was generally stronger than high-flow-fining trends. Many of these second-order trends demonstrated behavior more like “asymptotic coarsening.” They coarsened until they reached a maximum physical grain size limit and gradation fined slightly or remained constant beyond the threshold flow. The dominance of flow-coarsening suggests most of the rivers surveyed (which included a bias toward large, regulated rivers) are supply limited. Supply limited (bed regulated) rivers tend to coarsen with flow, while capacity limited, high supply systems tend to fine with flow. Sediment capacity equations computed a variety of flow-gradation trends. Using transport functions to compute load-gradation model boundary conditions will often diverge from (or even invert) observed trends, especially in supply limited systems.
      PubDate: 2017-11-23T06:00:41.368643-05:
      DOI: 10.1002/2016WR020135
  • A Stochastic Water Balance Framework for Lowland Watersheds
    • Authors: Sally Thompson; Lissa MacVean, Murugesu Sivapalan
      Abstract: The water balance dynamics in lowland watersheds are influenced not only by local hydroclimatic controls on energy and water availability, but also by imports of water from the upstream watershed. These imports result in a stochastic extent of inundation in lowland watersheds that is determined by the local flood regime, watershed topography, and the rate of loss processes such as drainage and evaporation. Thus, lowland watershed water balances depend on two stochastic processes—rainfall and local inundation dynamics. Lowlands are high productivity environments that are disproportionately associated with urbanization, high productivity agriculture, biodiversity, and flood risk. Consequently, they are being rapidly altered by human development—generally with clear economic and social motivation—but also with significant trade-offs in ecosystem services provision, directly related to changes in the components and variability of the lowland water balance. We present a stochastic framework to assess the lowland water balance and its sensitivity to two common human interventions—replacement of native vegetation with alternative land uses, and construction of local flood protection levees. By providing analytical solutions for the mean and PDF of the water balance components, the proposed framework provides a mechanism to connect human interventions to hydrologic outcomes, and, in conjunction with ecosystem service production estimates, to evaluate trade-offs associated with lowland watershed development.
      PubDate: 2017-11-23T05:55:58.001697-05:
      DOI: 10.1002/2017WR021193
  • X-Ray Microtomography of Intermittency in Multiphase Flow at Steady State
           Using a Differential Imaging Method
    • Authors: Ying Gao; Qingyang Lin, Branko Bijeljic, Martin J. Blunt
      Abstract: We imaged the steady-state flow of brine and decane in Bentheimer sandstone. We devised an experimental method based on differential imaging to examine how different flow rates impact the pore-scale distribution of fluids during dynamic flow co-injection. This allows us to elucidate flow regimes (connected, or break-up of the non-wetting phase pathways) for a range of fractional flows at two capillary numbers, Ca, namely 3.0 × 10−7 and 7.5 × 10−6. At the lower Ca, for a fixed fractional flow, the two phases appear to flow in connected unchanging sub-networks of the pore space, consistent with conventional theory. At the higher Ca, we observed that a significant fraction of the pore space contained sometimes oil and sometimes brine during the one-hour scan: this intermittent occupancy, which was interpreted as regions of the pore space that contained both fluid phases for some time, is necessary to explain the flow and dynamic connectivity of the oil phase; pathways of always oil-filled portions of the void space did not span the core. This phase was segmented from the differential image between the 30wt% KI brine image and the scans taken at each fractional flow. Using the grey-scale histogram distribution of the raw images, the oil proportion in the intermittent phase was calculated. The pressure drops at each fractional flow at low and high flow rate were measured by high-precision differential pressure sensors. The relative permeabilities and fractional flow obtained by our experiment at the mm-scale compare well with data from the literature on cm-scale samples.
      PubDate: 2017-11-21T09:25:54.790383-05:
      DOI: 10.1002/2017WR021736
  • On the Texture Angle Detection Used in Space-Time Image Velocimetry (STIV)
           for Robust Stream Flow Monitoring
    • Authors: Ryota Tsubaki
      Abstract: The Space-Time Image Velocimetry (STIV) method evaluates the velocity of a water surface by analyzing a texture angle within a Space-Time Image (STI) obtained from an image sequence of flowing water's surface. The Brightness Gradient Tensor (BGT) has been utilized for calculating the texture angle of the STI within the original STIV. The BGT is sensitive to image quality, especially high-frequency noise, and this fact limits the capability and accuracy of velocity estimations. The objectives of this study were to understand why the BGT is sensitive to high-frequency noise and how to resolve this defect. In the manuscript, derivation of the BGT is first reviewed and then a geometric representation of the BGT is discussed. The reason the BGT is sensitive to high-frequency noise is also discussed, then, based on geometric representations of the BGT, a measure to improve this defect is proposed. To demonstrate differences between the two methods, texture angles from artificial and field image sets were also analyzed using the BGT and the improved BGT.
      PubDate: 2017-11-21T09:25:47.388208-05:
      DOI: 10.1002/2017WR021913
  • Estimating Discharge and Nonpoint Source Nitrate Loading to Streams From
           Three End-Member Pathways Using High-Frequency Water Quality Data
    • Authors: Matthew P. Miller; Anthony J. Tesoriero, Krista Hood, Silvia Terziotti, David M. Wolock
      Abstract: The myriad hydrologic and biogeochemical processes taking place in watersheds occurring across space and time are integrated and reflected in the quantity and quality of water in streams and rivers. Collection of high-frequency water quality data with sensors in surface waters provides new opportunities to disentangle these processes and quantify sources and transport of water and solutes in the coupled groundwater-surface water system. A new approach for separating the streamflow hydrograph into three components was developed and coupled with high-frequency nitrate data to estimate time-variable nitrate loads from chemically dilute quickflow, chemically concentrated quickflow, and slowflow groundwater end-member pathways for periods of up to two years in a groundwater-dominated and a quickflow-dominated stream in central Wisconsin, using only streamflow and in-stream water quality data. The dilute and concentrated quickflow end-members were distinguished using high-frequency specific conductance data. Results indicate that dilute quickflow contributed less than 5% of the nitrate load at both sites, whereas 89±8% of the nitrate load at the groundwater-dominated stream was from slowflow groundwater, and 84±25% of the nitrate load at the quickflow-dominated stream was from concentrated quickflow. Concentrated quickflow nitrate concentrations varied seasonally at both sites, with peak concentrations in the winter that were 2-3 times greater than minimum concentrations during the growing season. Application of this approach provides an opportunity to assess stream vulnerability to non-point source nitrate loading and expected stream responses to current or changing conditions and practices in watersheds.
      PubDate: 2017-11-21T09:25:37.855088-05:
      DOI: 10.1002/2017WR021654
  • A Pseudo Vertical Equilibrium Model for Slow Gravity Drainage Dynamics
    • Authors: Beatrix Becker; Bo Guo, Karl Bandilla, Michael A. Celia, Bernd Flemisch, Rainer Helmig
      Abstract: Vertical equilibrium (VE) models are computationally efficient and have been widely used for modeling fluid migration in the subsurface. However, they rely on the assumption of instant gravity segregation of the two fluid phases which may not be valid especially for systems that have very slow drainage at low wetting phase saturations. In these cases, the time scale for the wetting phase to reach vertical equilibrium can be several orders of magnitude larger than the time scale of interest, rendering conventional VE models unsuitable. Here, we present a pseudo-VE model that relaxes the assumption of instant segregation of the two fluid phases by applying a pseudo-residual saturation inside the plume of the injected fluid that declines over time due to slow vertical drainage. This pseudo-VE model is cast in a multiscale framework for vertically integrated models with the vertical drainage solved as a fine-scale problem. Two types of fine-scale models are developed for the vertical drainage, which lead to two pseudo-VE models. Comparisons with a conventional VE model and a full multidimensional model show that the pseudo-VE models have much wider applicability than the conventional VE model while maintaining the computational benefit of the conventional VE model.
      PubDate: 2017-11-20T12:20:43.859235-05:
      DOI: 10.1002/2017WR021644
  • Global Sensitivity of Simulated Water Balance Indicators Under Future
           Climate Change in the Colorado Basin
    • Authors: Katrina E. Bennett; Jorge R. Urrego Blanco, Alexandra Jonko, Theodore J. Bohn, Adam Atchley, Nathan M. Urban, Richard Middleton
      Abstract: The Colorado River basin is a fundamentally important river for society, ecology and energy in the United States. Streamflow estimates are often provided using modeling tools which rely on uncertain parameters; sensitivity analysis can help determine which parameters impact model results. Despite the fact that simulated flows respond to changing climate and vegetation in the basin, parameter sensitivity of the simulations under climate change has rarely been considered. In this study, we conduct a global sensitivity analysis to relate changes in runoff, evapotranspiration, snow water equivalent and soil moisture to model parameters in the Variable Infiltration Capacity (VIC) hydrologic model. We combine global sensitivity analysis with a space-filling Latin Hypercube sampling of the model parameter space and statistical emulation of the VIC model to examine sensitivities to uncertainties in 46 model parameters following a variance-based approach.We find that snow-dominated regions are much more sensitive to uncertainties in VIC parameters. Although baseflow and runoff changes respond to parameters used in previous sensitivity studies, we discover new key parameter sensitivities. For instance, changes in runoff and evapotranspiration are sensitive to albedo, while changes in snow water equivalent are sensitive to canopy fraction and Leaf Area Index (LAI) in the VIC model. It is critical for improved modeling to narrow uncertainty in these parameters through improved observations and field studies. This is important because LAI and albedo are anticipated to change under future climate and narrowing uncertainty is paramount to advance our application of models such as VIC for water resource management.
      PubDate: 2017-11-20T12:20:40.891781-05:
      DOI: 10.1002/2017WR020471
  • Evaporation in Capillary Porous Media at the Perfect Piston-Like Invasion
           Limit: Evidence of Nonlocal Equilibrium Effects
    • Authors: Alireza Attari Moghaddam; Marc Prat, Evangelos Tsotsas, Abdolreza Kharaghani
      Abstract: The classical continuum modeling of evaporation in capillary porous media is revisited from pore network simulations of the evaporation process. The computed moisture diffusivity is characterized by a minimum corresponding to the transition between liquid and vapor transport mechanisms confirming previous interpretations. Also the study suggests an explanation for the scattering generally observed in the moisture diffusivity obtained from experimental data. The pore network simulations indicate a noticeable non-local equilibrium effect leading to a new interpretation of the vapor pressure-saturation relationship classically introduced to obtain the one-equation continuum model of evaporation. The latter should not be understood as a desorption isotherm as classically considered but rather as a signature of a non-local equilibrium effect. The main outcome of this study is therefore that non-local equilibrium two-equation model must be considered for improving the continuum modeling of evaporation.
      PubDate: 2017-11-20T12:20:34.08072-05:0
      DOI: 10.1002/2017WR021162
  • Using Survey Data to Determine a Numeric Criterion for Nutrient Pollution
    • Authors: Paul M. Jakus; Nanette Nelson, Jeffrey Ostermiller
      Abstract: We present a scientific replication of a benthic algae nuisance threshold study originally conducted in Montana, but we do so using a different sampling methodology in a different state. Respondents are asked to rate eight photographs that depict varying algae conditions. Our initial results show that Utah resident preferences for benthic algae levels are quite similar to those of Montana residents, thus replicating the Montana study. For the full Utah sample, though, Cronbach's α indicated poor internal consistency in rating the photographs, so a ‘monotonicity rule' was used to identify respondents providing monotonic preferences with respect to chlorophyll a densities. Simple graphical analyses are combined with ordered probit analysis to determine the maximum desirable density of chlorophyll a (Chl a). Our analysis indicates that Chl a levels in excess of 150 mg Chl a/m2 are undesirable, but the regression model suggests that those with strictly monotonic preferences were far more likely favor a more stringent standard.
      PubDate: 2017-11-20T12:15:35.354324-05:
      DOI: 10.1002/2017WR021527
  • Interpretation of Ground Temperature Anomalies in Hydrothermal Discharge
    • Authors: Adam N. Price; Cary R. Lindsey, Jerry P. Fairley
      Abstract: Researchers have long noted the potential for shallow hydrothermal fluids to perturb near-surface temperatures. Several investigators have made qualitative or semi-quantitative use of elevated surface temperatures; for example, in snowfall calorimetry, or for tracing subsurface flow paths. However, a quantitative framework connecting surface temperature observations with conditions in the subsurface is currently lacking. Here, we model an area of shallow subsurface flow at Burgdorf Hot Springs, a rustic commercial resort in the Payette National Forest, north of McCall, Idaho USA. We calibrate the model using shallow (0.2 m depth) ground temperature measurements and overburden thickness estimates from seismic refraction studies. The calibrated model predicts negligible loss of heat energy from the laterally-migrating fluids at the Burgdorf site, in spite of the fact that thermal anomalies are observed in the unconsolidated near-surface alluvium. Although elevated near-surface ground temperatures are commonly assumed to result from locally high heat flux, this conflicts with the small apparent heat loss during lateral flow inferred at the Burgdorf site. We hypothesize an alternative explanation for near-surface temperature anomalies that is only weakly dependent on heat flux, and more strongly controlled by the Biot number, a dimensionless parameter that compares the rate at which convection carries heat away from the land surface to the rate at which it is supplied by conduction to the interface.
      PubDate: 2017-11-20T12:15:32.473712-05:
      DOI: 10.1002/2017WR021077
  • Hydraulic Causes for Basin Hydrograph Skewness
    • Authors: Walter Collischonn; Ayan Fleischmann, Rodrigo C. D. Paiva, Alfonso Mejia
      Abstract: It has been suggested that hydrograph skewness depends on the relative dominance between hillslope and channel network transport processes, where the former ones make the hydrograph positively skewed while the latter tends to make it negatively skewed. More recently, however, the role of river hydraulics in shaping the hydrograph has been highlighted. We present a set of numerical modelling experiments using a hydrodynamic model of river networks in which we investigate how channel hydraulics influence the shape of the hydrograph, particularly its skewness. We further investigate the influence of baseflow, rainfall intensity, cross section geometry and basin scale on unit hydrograph response. We show that river hydraulics has a decisive role because positively skewed hydrographs may occur even when water inputs to the river network are negatively skewed, and in catchments whose width function is also negatively skewed. We show additional results related to the effect of the degree of non-linearity in the relationship between celerity and discharge, the effects of baseflow and rainfall intensity. These further confirm that hydraulic factors may be decisive in determining hydrograph shape.
      PubDate: 2017-11-20T12:15:27.705366-05:
      DOI: 10.1002/2017WR021543
  • A Vulnerability-Based, Bottom-Up Assessment of Future Riverine Flood Risk
           Using a Modified Peaks-over-Threshold Approach and a Physically Based
           Hydrologic Model
    • Authors: James Knighton; Scott Steinschneider, M. Todd Walter
      Abstract: There is a chronic disconnection among purely probabilistic flood frequency analysis of flood hazards, flood risks, and hydrological flood mechanisms, which hamper our ability to assess future flood impacts. We present a vulnerability-based approach to estimating riverine flood risk that accommodates a more direct linkage between decision-relevant metrics of risk and the dominant mechanisms that cause riverine flooding. We adapt the conventional peaks-over-threshold (POT) framework to be used with extreme precipitation from different climate processes and rainfall-runoff based model output. We quantify the probability that at least one adverse hydrologic threshold, potentially defined by stakeholders, will be exceeded within the next N years. This approach allows us to consider flood risk as the summation of risk from separate atmospheric mechanisms, and supports a more direct mapping between hazards and societal outcomes. We perform this analysis within a bottom-up framework to consider the relevance and consequences of information, with varying levels of credibility, on changes to atmospheric patterns driving extreme precipitation events. We demonstrate our proposed approach using a case study for Fall Creek in Ithaca, NY, USA, where we estimate the risk of stakeholder-defined flood metrics from three dominant mechanisms: summer convection, tropical cyclones, and spring rain and snowmelt. Using downscaled climate projections, we projected how flood risk associated with a subset of mechanisms may change in the future, and the resultant shift to annual flood risk. The flood risk approach we propose can provide powerful new insights into future flood threats.
      PubDate: 2017-11-20T12:15:24.189814-05:
      DOI: 10.1002/2017WR021036
  • The Rangeland Hydrology and Erosion Model: A Dynamic Approach for
           Predicting Soil Loss on Rangelands
    • Authors: Mariano Hernandez; Mark A. Nearing, Osama Z. Al-Hamdan, Frederick B. Pierson, Gerardo Armendariz, Mark A. Weltz, Kenneth E. Spaeth, C. Jason Williams, Sayjro K. Nouwakpo, David C. Goodrich, Carl L. Unkrich, Mary H. Nichols, Chandra D. Holifield Collins
      Abstract: In this study, we present the improved Rangeland Hydrology and Erosion Model (RHEM V2.3), a process-based erosion prediction tool specific for rangeland application. The article provides the mathematical formulation of the model and parameter estimation equations. Model performance is assessed against data collected from 23 runoff and sediment events in a shrub-dominated semiarid watershed in Arizona, USA. To evaluate the model, two sets of primary model parameters were determined using the RHEM V2.3 and RHEM V1.0 parameter estimation equations. Testing of the parameters indicated that RHEM V2.3 parameter estimation equations provided a 76% improvement over RHEM V1.0 parameter estimation equations. Second, the RHEM V2.3 model was calibrated to measurements from the watershed. The parameters estimated by the new equations were within the lowest and highest values of the calibrated parameter set. These results suggest that the new parameter estimation equations can be applied for this environment to predict sediment yield at the hillslope scale. Furthermore, we also applied the RHEM V2.3 to demonstrate the response of the model as a function of foliar cover and ground cover for 124 data points across Arizona and New Mexico. The dependence of average sediment yield on surface ground cover was moderately stronger than that on foliar cover. These results demonstrate that RHEM V2.3 predicts runoff volume, peak runoff, and sediment yield with sufficient accuracy for broad application to assess and manage rangeland systems.
      PubDate: 2017-11-18T06:45:34.903881-05:
      DOI: 10.1002/2017WR020651
  • A Practical, Robust Methodology for Acquiring New Observation Data Using
           Computationally Expensive Groundwater Models
    • Authors: Adam J. Siade; Joel Hall, Robert Karelse
      Abstract: Regional groundwater flow models play an important role in decision-making regarding water resources; however, the uncertainty embedded in model parameters and model assumptions can significantly hinder the reliability of model predictions. One way to reduce this uncertainty is to collect new observation data from the field. However, determining where and when to obtain such data is not straightforward. There exist a number of data-worth and experimental design strategies developed for this purpose. However, these studies often ignore issues related to real-world groundwater models such as, computational expensive, existing observation data, high parameter dimension, etc. In this study, we propose a methodology, based on existing methods and software, to efficiently conduct such analyses for large-scale, complex regional groundwater flow systems for which there is a wealth of available observation data. The method utilizes the well-established d-optimality criterion, and the minimax criterion for robust sampling strategies. The so-called Null-Space Monte Carlo method is used to reduce the computational burden associated with uncertainty quantification. And, a heuristic methodology, based on the concept of the greedy algorithm, is proposed for developing robust designs with subsets of the posterior parameter samples. The proposed methodology is tested on a synthetic regional groundwater model, and subsequently applied to an existing, complex, regional groundwater system in the Perth region of Western Australia. The results indicate that robust designs can be obtained efficiently, within reasonable computational resources, for making regional decisions regarding groundwater level sampling.
      PubDate: 2017-11-15T15:40:34.604035-05:
      DOI: 10.1002/2017WR020814
  • Water Saturation Relations and Their Diffusion-Limited Equilibration in
           Gas Shale: Implications for Gas Flow in Unconventional Reservoirs
    • Authors: Tetsu K. Tokunaga; Weijun Shen, Jiamin Wan, Yongman Kim, Abdullah Cihan, Yingqi Zhang, Stefan Finsterle
      Abstract: Large volumes of water are used for hydraulic fracturing of low permeability shale reservoirs to stimulate gas production, with most of the water remaining unrecovered and distributed in a poorly understood manner within stimulated regions. Because water partitioning into shale pores controls gas release, we measured the water saturation dependence on relative humidity (rh) and capillary pressure (Pc) for imbibition (adsorption) as well as drainage (desorption) on samples of Woodford Shale. Experiments and modeling of water vapor adsorption into shale laminae at rh = 0.31 demonstrated that long times are needed to characterize equilibrium in larger (5 mm thick) pieces of shales, and yielded effective diffusion coefficients from 9 × 10−9 to 3 × 10−8 m2 s−1, similar in magnitude to the literature values for typical low porosity and low permeability rocks. Most of the experiments, conducted at 50 ˚C on crushed shale grains in order to facilitate rapid equilibration, showed significant saturation hysteresis, and that very large Pc (∼1 MPa) are required to drain the shales. These results quantify the severity of the water blocking problem, and suggest that gas production from unconventional reservoirs is largely associated with stimulated regions that have had little or no exposure to injected water. Gravity drainage of water from fractures residing above horizontal wells reconciles gas production in the presence of largely unrecovered injected water, and is discussed in the broader context of unsaturated flow in fractures.
      PubDate: 2017-11-15T15:40:24.247672-05:
      DOI: 10.1002/2017WR021153
  • Intermediate-Scale Experimental Study to Improve Fundamental Understanding
    • Authors: Michael R. Plampin; Mark L. Porter, Rajesh J. Pawar, Tissa H. Illangasekare
      Abstract: To assess the risks of Geologic Carbon Sequestration (GCS), it is crucial to understand the fundamental physicochemical processes that may occur if and when stored CO2 leaks upward from a deep storage reservoir into the shallow subsurface. Intermediate-scale experiments allow for improved understanding of the multiphase evolution processes that control CO2 migration behaviour in the subsurface, because the boundary conditions, initial conditions, and porous media parameters can be better controlled and monitored in the laboratory than in field settings. For this study, a large experimental test bed was designed to mimic a cross-section of a shallow aquifer with layered geologic heterogeneity. As water with aqueous CO2 was injected into the system to mimic a CO2-charged water leakage scenario, the spatiotemporal evolution of the multiphase CO2 plume was monitored. Similar experiments were performed with two different sand combinations to assess the relative effects of different types of geologic facies transitions on the CO2 evolution processes. Significant CO2 attenuation was observed in both scenarios, but by fundamentally different mechanisms. When the porous media layers had very different permeabilities, attenuation was caused by local accumulation (structural trapping) and slow re-dissolution of gas phase CO2. When the permeability difference between the layers was relatively small, on the other hand, gas phase continually evolved over widespread areas near the leading edge of the aqueous plume, which also attenuated CO2 migration. This improved process understanding will aid in the development of models that could be used for effective risk assessment and monitoring programs for GCS projects.
      PubDate: 2017-11-15T09:01:08.9988-05:00
      DOI: 10.1002/2016WR020142
  • Space-Time Patterns of Meteorological Drought Events in the European
           Greater Alpine Region Over the Past 210 Years
    • Authors: K. Haslinger; G. Blöschl
      Abstract: Droughts may have tremendous impacts on humans. However, the space-time characteristics of droughts are not very well understood, as case studies usually focus on individual drought events. Here we investigate the spatiotemporal drought characteristics of a large sample of events over the past 210 years in the Greater Alpine Region of Central Europe. We use monthly precipitation data, and flag, for each grid point, time steps with precipitation below a 20% percentile. We then propose a new method that detects drought events by connecting the flagged elements to space-time drought regions. In contrast to the traditional drought indices that are based on a fixed, prescribed time window, this method is able to identify droughts of different durations in an objective way. The data show multi decadal variations of drought frequency, duration, intensity and severity, but no consistent trends over the 210 year period. The top 5% of events in terms of their severity show a shift in seasonality from winter/spring events in the late 19th century towards autumn events during the last decades of the 20th century. The most severe events center either in the Northwest or the Southeast of the region analyzed. We found no significant correlations of drought frequency, duration, intensity and severity with the temperature increases in the past three decades. Dry springs significantly enhance temperatures during summer droughts, suggesting a soil moisture-temperature feedback.
      PubDate: 2017-11-15T09:00:44.383553-05:
      DOI: 10.1002/2017WR020797
  • Hyporheic Passive Flux Meters Reveal Inverse Vertical Zonation and High
           Seasonality of Nitrogen Processing in an Anthropogenically Modified Stream
           (Holtemme, Germany)
    • Authors: Julia Vanessa Kunz; Michael D. Annable, Suresh Rao, Michael Rode, Dietrich Borchardt
      Abstract: Transformation and retention of nitrogen and other biologically reactive solutes in the hyporheic zones of running water contribute to an essential ecosystem service. However, the synoptic impact of intense agricultural or urban land-uses, elevated nutrient loading, flow alterations, riparian clear-cutting and channelization on the source-sink behavior of solutes in hyporheic zones remains largely uncharacterized and unquantified. Therefore, we studied nutrient dynamics in a hydro-morphologically and chemically modified stream reach using a new monitoring approach allowing the simultaneous measurement of nutrient and water flux through a screened area in the subsurface of rivers (Hyporheic Passive Flux Meter, HPFM). With HPFMs we directly assessed time-integrated lateral hyporheic nitrate fluxes during early spring and mid-summer covering different temperature and discharge regimes.Contrary to our expectations, higher stream discharge coincided with substantially lower hyporheic exchange rates. While in streams featuring a natural morphology, bed-form induced exchange commonly increases with surface flow, the influence of groundwater level was dominant in this reach. Furthermore, in contrast to less impacted environments, where progressive substrate depletion with depths reduces metabolic rates in the subsurface, we identified not the upper, but the intermediate layer of the hyporheic zone as hotspot of nutrient turnover. Overall, the hyporheic zone at the study site functioned partly as nitrate source, partly as a sink. Neither of the commonly used determinants redox state and residence time could explain this source or sink function. Our results give clear evidence to carefully transfer the knowledge of hyporheic zone processes from “natural” systems to anthropologically modified streams.
      PubDate: 2017-11-15T08:56:09.959278-05:
      DOI: 10.1002/2017WR020709
  • Monitoring Streambed Scour/Deposition Under nonideal Temperature Signal
           and Flood Conditions
    • Authors: Timothy DeWeese; Daniele Tonina, Charles Luce
      Abstract: Streambed erosion and deposition are fundamental geomorphic processes in riverbeds, and monitoring their evolution is important for ecological system management and in-stream infrastructure stability. Previous research showed proof of concept that analysis of paired temperature signals of stream and pore waters can simultaneously provide monitoring scour and deposition, stream sediment thermal regime, and seepage velocity information. However, it did not address challenges often associated with natural systems, including non-ideal temperature variations (low amplitude, non-sinusoidal signal and vertical thermal gradients) and natural flooding conditions on monitoring scour and deposition processes over time. Here, we addressed this knowledge gap by testing the proposed thermal scour-deposition chain (TSDC) methodology, with laboratory experiments to test the impact of non-ideal temperature signals under a range of seepage velocities and with a field application during a pulse flood. Both analyses showed excellent match between surveyed and temperature-derived bed elevation changes even under very low temperature signal amplitudes (less than 1°C), non-ideal signal shape (sawtooth shape) and strong and changing vertical thermal gradients (4°C/m). Root mean square errors on predicting the change in streambed elevations were comparable with the median grain size of the streambed sediment. Future research should focus on improved techniques for temperature signal phase and amplitude extractions, as well as TSDC applications over long periods spanning entire hydrographs.
      PubDate: 2017-11-15T08:55:54.528582-05:
      DOI: 10.1002/2017WR020632
  • Optimizing Multireservoir System Operating Policies Using Exogenous
           Hydrologic Variables
    • Authors: Jasson Pina; Amaury Tilmant, Pascal Côté
      Abstract: Stochastic dual dynamic programming (SDDP) is one of the few available algorithms to optimize the operating policies of large-scale hydropower systems. This manuscript presents a variant, called SDDPX, in which exogenous hydrologic variables, such as snow water equivalent and/or sea surface temperature, are included in the state-space vector together with the traditional (endogenous) variables, i.e. past inflows. A re-optimization procedure is also proposed in which SDDPX-derived benefit-to-go functions are employed within a simulation carried out over the historical record of both the endogenous and exogenous hydrologic variables. In SDDPX, release policies are now a function of storages, past inflows and relevant exogenous variables that potentially capture more complex hydrological processes than those found in traditional SDDP formulations. To illustrate the potential gain associated with the use of exogenous variables when operating a multireservoir system, the 3137 MW hydropower system of Rio Tinto (RT) located in the Saguenay-Lac-St-Jean River Basin in Quebec (Canada) is used as a case study. The performance of the system is assessed for various combinations of hydrologic state variables, ranging from the simple lag-one autoregressive model to more complex formulation involving past inflows, snow water equivalent and winter precipitation.
      PubDate: 2017-11-15T08:50:28.699231-05:
      DOI: 10.1002/2017WR021701
  • Recent Extreme Runoff Observations From Coastal Arctic Watersheds in
    • Authors: Svetlana L. Stuefer; Christopher D. Arp, Douglas L. Kane, Anna K. Liljedahl
      Abstract: Arctic coastal watersheds, though rarely monitored, are expected to have increased runoff, as climate models predict more precipitation in the Arctic. This study provides a synthesis of streamflow changes in watersheds of the Alaska Arctic Coastal Plain (AACP) based on available historic discharge data and water balance analysis. A comparison of annual runoff from the Putuligayuk River watershed (471 km2) from the period 1970–1986 (78 ± 24.1 mm/yr) to the period 1999–2015 (122 ± 49.6 mm/yr) shows increasing discharge and interannual variability. From this discontinuous record of 32 years, the three lowest runoff years occurred in 1979, 2007, and 2008, and the three highest runoff years occurred in 2003, 2014, and 2015. Other studied AACP watersheds with shorter discharge records demonstrate similar patterns of dry (2007–2008) and wet (2014–2015) years during common periods of observation. A combination of favorable antecedent surface storage conditions and above-average precipitation is required to generate large volumes of surface runoff. A strong relationship between climate, surface storage, and runoff inherent to AACP watersheds makes these systems highly responsive to sea ice retreat and hydrological intensification. Our new estimates of freshwater flux from the AACP to the Beaufort Sea and Chukchi Sea account for an observed range of runoff variability and provide baseline data for modeling arctic hydrologic systems.
      PubDate: 2017-11-14T06:55:43.040505-05:
      DOI: 10.1002/2017WR020567
  • Revisiting the Analytical Solution Approach to Mixing-Limited Equilibrium
           Multicomponent Reactive Transport Using Mixing Ratios: Identification of
           Basis, Fixing an Error, and Dealing With Multiple Minerals
    • Authors: T. R. Ginn; L. G. Schreyer, X. Sanchez-Vila, M. K. Nassar, A. A. Ali, S. Kräutle
      Abstract: Multicomponent reactive transport involves the solution of a system of nonlinear coupled partial differential equations. A number of methods have been developed to simplify the problem. In the case where all reactions are in instantaneous equilibrium and the mineral assemblage is constant in both space and time, de Simoni et al. (2007) provide an analytical solution that separates transport of aqueous components and minerals using scalar dissipation of “mixing ratios” between a number of boundary/initial solutions. In this approach, aqueous speciation is solved in conventional terms of primary and secondary species, and the mineral dissolution/precipitation rate is given in terms of the scalar dissipation and a chemical transformation term, both involving the secondary species associated with the mineral reaction. However, the identification of the secondary species is nonunique, and so it is not clear how to use the approach in general, a problem that is keenly manifest in the case of multiple minerals which may share aqueous ions. We address this problem by developing an approach to identify the secondary species required in the presence of one or multiple minerals. We also remedy a significant error in the de Simoni et al. (2007) approach. The result is a fixed and extended de Simoni et al. (2007) approach that allows construction of analytical solutions to multicomponent equilibrium reactive transport problems in which the mineral assemblage does not change in space or time and where the transport is described by closed-form solutions of the mixing ratios.
      PubDate: 2017-11-14T06:55:25.613842-05:
      DOI: 10.1002/2017WR020759
  • Pore-Scale Imaging and Analysis of Phase Topologies and Displacement
           Mechanisms for CO2-Brine Two-Phase Flow in Unconsolidated Sand Packs
    • Authors: Pengfei Lv; Yongchen Song, Yu Liu, Bin Wang, Lanlan Jiang, Bohao Wu, Shuyang Liu, Junlin Chen
      Abstract: CO2 storage in saline aquifers is considered a potential solution for CO2 mitigation, owing to its significant capacity and worldwide distribution capability. It is therefore becoming more important to understand the underground CO2/brine flow mechanisms. CO2 migration is primarily controlled by the pore-scale subsurface flows in different saline aquifer sites with variable reservoir formation compositions and reservoir conditions. Variations occur in the state of CO2 phase (gas versus supercritical), brine salinity, and rock wettability, under different reservoir conditions, and may result in different subsurface CO2/brine migration phenomena. In this study, we investigate the drainage and imbibition procedures of CO2 and brine by injecting fluids into unconsolidated sand packs under different conditions of CO2 phase states, brine salinity, and wettability of sand packs. The pore-scale fluid distribution is visualized using micro X-ray computed tomography (micro-CT). It is found that the phase states of CO2, brine salinity, and wettability have low impacts on CO2 distribution during drainage. However, the increase in brine salinity significantly damages the connectedness of the water phase in pore structures and further decreases the CO2-brine interfacial areas. In addition, a pore-scale event called the droplet fragmentation of nonwetting phase is found to occur in the imbibition procedure, which is considered to be beneficial to the dissolution trapping in CO2 geological storages. It is experimentally demonstrated that the pore structure of rock cores is a factor that significantly contributes to droplet fragmentation.
      PubDate: 2017-11-14T06:50:56.430823-05:
      DOI: 10.1002/2016WR020270
  • Understanding the Hydromechanical Behavior of a Fault Zone From Transient
           Surface Tilt and Fluid Pressure Observations at Hourly Time Scales
    • Authors: Jonathan Schuite; Laurent Longuevergne, Olivier Bour, Thomas J. Burbey, Frédérick Boudin, Nicolas Lavenant, Philippe Davy
      Abstract: Flow through reservoirs such as fractured media is powered by head gradients which also generate measurable poroelastic deformation of the rock body. The combined analysis of surface deformation and sub-surface pressure provides valuable insights of a reservoir's structure and hydromechanical properties, which are of interest for deep-seated CO2 or nuclear waste storage for instance. Amongst all surveying tools, surface tiltmeters offer the possibility to grasp hydraulically-induced deformations over a broad range of time scales with a remarkable precision. Here, we investigate the information content of transient surface tilt generated by the pressurization a kilometer scale sub-vertical fault zone. Our approach involves the combination of field data and results of a fully coupled poromechanical model. The signature of pressure changes in the fault zone due to pumping cycles is clearly recognizable in field tilt data and we aim to explain the peculiar features that appear in: 1) tilt time series alone from a set of 4 instruments; 2) the ratio of tilt over pressure. We evidence that the shape of tilt measurements on both sides of a fault zone is sensitive to its diffusivity and its elastic modulus. The ratio of tilt over pressure predominantly encompasses information about the system's dynamic behavior and extent of the fault zone, and allows separating contributions of flow in the different compartments. Hence, tiltmeters are well suited to characterize hydromechanical processes associated to fault zone hydrogeology at short time scales, where space-borne surveying methods fail to recognize any deformation signal.
      PubDate: 2017-11-10T10:45:46.985396-05:
      DOI: 10.1002/2017WR020588
  • Shallow Aquifer Vulnerability From Subsurface Fluid Injection at a
           Proposed Shale Gas Hydraulic Fracturing Site
    • Authors: M. P. Wilson; F. Worrall, R. J. Davies, A. Hart
      Abstract: Groundwater flow resulting from a proposed hydraulic fracturing (fracking) operation was numerically modeled using 91 scenarios. Scenarios were chosen to be a combination of hydrogeological factors that a priori would control the long-term migration of fracking fluids to the shallow subsurface. These factors were induced fracture extent, cross-basin groundwater flow, deep low hydraulic conductivity strata, deep high hydraulic conductivity strata, fault hydraulic conductivity, and overpressure. The study considered the Bowland Basin, northwest England, with fracking of the Bowland Shale at ∼2000 m depth and the shallow aquifer being the Sherwood Sandstone at ∼300-500 m depth. Of the 91 scenarios, 73 scenarios resulted in tracked particles not reaching the shallow aquifer within 10000 years and 18 resulted in travel times less than 10000 years. Four factors proved to have a statistically significant impact on reducing travel time to the aquifer: increased induced fracture extent, absence of deep high hydraulic conductivity strata, relatively low fault hydraulic conductivity, and magnitude of overpressure. Modeling suggests that high hydraulic conductivity formations can be more effective barriers to vertical flow than low hydraulic conductivity formations. Furthermore, low hydraulic conductivity faults can result in subsurface pressure compartmentalization, reducing horizontal groundwater flow and encouraging vertical fluid migration. The modeled worst-case scenario, using unlikely geology and induced fracture lengths, maximum values for strata hydraulic conductivity and with conservative tracer behaviour had a particle travel time of 130 years to the base of the shallow aquifer. This study has identified hydrogeological factors which lead to aquifer vulnerability from shale exploitation.
      PubDate: 2017-11-10T10:45:32.42912-05:0
      DOI: 10.1002/2017WR021234
  • Using Meteorological Analogues for Reordering Postprocessed Precipitation
           Ensembles in Hydrological Forecasting
    • Authors: Joseph Bellier; Guillaume Bontron, Isabella Zin
      Abstract: Meteorological ensemble forecasts are nowadays widely used as input of hydrological models for probabilistic streamflow forecasting. These forcings are frequently biased and have to be statistically post-processed, using most of the time univariate techniques that apply independently to individual locations, lead time and weather variables. Post-processed ensemble forecasts therefore need to be reordered so as to reconstruct suitable multivariate dependence structures. The Schaake shuffle and ensemble copula coupling are the two most popular methods for this purpose. This paper proposes two adaptations of them that make use of meteorological analogues for reconstructing spatio-temporal dependence structures of precipitation forecasts. Performances of the original and adapted techniques are compared through a multi-step verification experiment using real forecasts from the European Centre for Medium-Range Weather Forecasts. This experiment evaluates multivariate precipitation forecasts but also the corresponding streamflow forecasts that derive from hydrological modeling. Results show that the relative performances of the different reordering methods vary depending on the verification step. In particular, the standard Schaake shuffle is found to perform poorly when evaluated on streamflow. This emphasizes the crucial role of the precipitation spatio-temporal dependence structure in hydrological ensemble forecasting.
      PubDate: 2017-11-10T10:45:24.487072-05:
      DOI: 10.1002/2017WR021245
  • Empirical Modeling of Planetary Boundary Layer Dynamics Under Multiple
           Precipitation Scenarios Using a Two-Layer Soil Moisture Approach: An
           Example From a Semiarid Shrubland
    • Authors: Zulia Mayari Sanchez-Mejia; Shirley A. Papuga
      Abstract: In semiarid regions, where water resources are limited and precipitation dynamics are changing, understanding land surface-atmosphere interactions that regulate the coupled soil moisture-precipitation system is key for resource management and planning. We present a modeling approach to study soil moisture and albedo controls on planetary boundary layer height (PBLh). We used Santa Rita Creosote Ameriflux and Tucson Airport atmospheric sounding data to generate empirical relationships between soil moisture, albedo, and PBLh. Empirical relationships showed that ∼50% of the variation in PBLh can be explained by soil moisture and albedo with additional knowledge gained by dividing the soil profile into two layers. Therefore, we coupled these empirical relationships with soil moisture estimated using a two-layer bucket approach to model PBLh under six precipitation scenarios. Overall we observed that decreases in precipitation tend to limit the recovery of the PBL at the end of the wet season. However, increases in winter precipitation despite decreases in summer precipitation may provide opportunities for positive feedbacks that may further generate more winter precipitation. Our results highlight that the response of soil moisture, albedo, and the PBLh will depend not only on changes in annual precipitation, but also on the frequency and intensity of this change. We argue that because albedo and soil moisture data are readily available at multiple temporal and spatial scales, developing empirical relationships that can be used in land surface-atmosphere applications have great potential for exploring the consequences of climate change.
      PubDate: 2017-11-10T04:12:16.057654-05:
      DOI: 10.1002/2016WR020275
  • Concentration-Discharge Relations in the Critical Zone: Implications for
           Resolving Critical Zone Structure, Function, and Evolution
    • Authors: Jon Chorover; Louis A. Derry, William H. McDowell
      Abstract: Critical zone science seeks to develop mechanistic theories that describe critical zone structure, function, and long-term evolution. One postulate is that hydrogeochemical controls on critical zone evolution can be inferred from solute discharges measured down-gradient of reactive flow paths. These flow paths have variable lengths, interfacial compositions, and residence times, and their mixing is reflected in concentration-discharge (C-Q) relations. Motivation for this special section originates from a U.S. Critical Zone Observatories workshop that was held at the University of New Hampshire, 20–22 July 2015. The workshop focused on resolving mechanistic CZ controls over surface water chemical dynamics across the full range of lithogenic (e.g., nonhydrolyzing and hydrolyzing cations and oxyanions) and bioactive solutes (e.g., organic and inorganic forms of C, N, P, and S), including dissolved and colloidal species that may cooccur for a given element. Papers submitted to this special section on “concentration-discharge relations in the critical zone” include those from authors who attended the workshop, as well as others who responded to the open solicitation. Submissions were invited that utilized information pertaining to internal, integrated catchment function (relations between hydrology, biogeochemistry, and landscape structure) to help illuminate controls on observed C-Q relations.
      PubDate: 2017-11-10T04:11:41.964963-05:
      DOI: 10.1002/2017WR021111
  • Are Model Transferability And Complexity Antithetical' Insights From
           Validation of a Variable-Complexity Empirical Snow Model in Space and Time
    • Authors: A. C. Lute; Charles H. Luce
      Abstract: The related challenges of predictions in ungauged basins and predictions in ungauged climates point to the need to develop environmental models that are transferable across both space and time. Hydrologic modeling has historically focused on modelling one or only a few basins using highly parameterized conceptual or physically based models. However, model parameters and structures have been shown to change significantly when calibrated to new basins or time periods, suggesting that model complexity and model transferability may be antithetical. Empirical space-for-time models provide a framework within which to assess model transferability and any tradeoff with model complexity. Using 497 SNOTEL sites in the western U.S., we develop space-for-time models of April 1 SWE and Snow Residence Time based on mean winter temperature and cumulative winter precipitation. The transferability of the models to new conditions (in both space and time) is assessed using non-random cross-validation tests with consideration of the influence of model complexity on transferability. As others have noted, the algorithmic empirical models transfer best when minimal extrapolation in input variables is required. Temporal split-sample validations use pseudoreplicated samples, resulting in the selection of overly complex models, which has implications for the design of hydrologic model validation tests. Finally, we show that low to moderate complexity models transfer most successfully to new conditions in space and time, providing empirical confirmation of the parsimony principal.
      PubDate: 2017-11-10T01:25:59.294654-05:
      DOI: 10.1002/2017WR020752
  • Global Anthropogenic Phosphorus Loads to Fresh Water and Associated Grey
           Water Footprints and Water Pollution Levels: A High-Resolution Global
    • Authors: Mesfin M. Mekonnen; Arjen Y. Hoekstra
      Abstract: We estimate the global anthropogenic phosphorus (P) loads to freshwater and the associated grey water footprints (GWFs) for the period 2002-2010, at a spatial resolution of 5 × 5 arc minute, and compare the GWF per river basin to runoff to assess the P-related water pollution level (WPL). The global anthropogenic P load to freshwater systems from both diffuse and point sources is estimated at 1.5 Tg/y. More than half of this total load was in Asia, followed by Europe (19%) and Latin America and the Caribbean (13%). The domestic sector contributed 54% to the total, agriculture 38% and industry 8%. In agriculture, cereals production had the largest contribution to the P load (31%), followed by fruits, vegetables, and oil crops, each contributing 15%. The global total GWF related to anthropogenic P loads is estimated to be 147 × 1012 m3/y, with China contributing 30%, India 8%, USA 7% and Spain and Brazil 6% each. The basins with WPL>1 (where GWF exceeds the basin's assimilation capacity) together cover about 38% of the global land area, 37% of the global river discharge, and provide residence to about 90% of the global population.
      PubDate: 2017-11-08T09:03:45.411409-05:
      DOI: 10.1002/2017WR020448
  • A Data-Driven Approach for Repairing the Hydrological Catchment Signal
           Damage Due to Filtering of GRACE Products
    • Authors: Bramha Dutt Vishwakarma; Martin Horwath, Balaji Devaraju, Andreas Groh, Nico Sneeuw
      Abstract: One of the major sources of uncertainty in mass change estimates from level 02 grace products comes from the signal degradation due to filtering of noisy gravity field products. Filtering suppresses noise but also changes the signal via attenuation and leakage. Therefore, many methods have been devised to tackle the unavoidable signal loss due to filtering. However, most of these methods lack mathematical analysis that is essential for understanding the cause and effect of filtering. Furthermore, they use hydrological models to compute correction terms, such as leakage, bias or scale factor, for repairing the damage due to filtering. Recently a data-driven method was proposed for improving the filtered grace products, which was shown to be superior to three widely used model based methods. However, the method works efficiently only for catchments above a minimum size. This limitation is due to the usage of a uniform layer approximation for deriving a scale factor, which is used to counter the attenuation of the catchment-confined signal. In this contribution, we avoid this approximation, and therefore the usage of scale factor, which lifts the limitation and provides a better mathematical relation. The new data-driven method is able to restore the signal loss due to filtering independent of the catchment size. We validate the method in a realistic grace-type closed-loop simulation environment and compare it with other popular approaches. We show that for 22 out of 32 catchments (small to large size and located in different climatic zones) the improved data-driven method outperforms other methods.
      PubDate: 2017-11-08T09:03:29.079952-05:
      DOI: 10.1002/2017WR021150
  • The Temporal and Spatial Variability of the Confined Aquifer Head and
           Storage Properties in the San Luis Valley, Colorado Inferred from Multiple
           InSAR Missions
    • Authors: Jingyi Chen; Rosemary Knight, Howard A. Zebker
      Abstract: Interferometric Synthetic Aperture Radar (InSAR) data from multiple satellite missions were combined to study the temporal and spatial variability of head and storage properties in a confined aquifer system on a decadal time scale. The area of study was a 4,500 km2 agricultural basin in the San Luis Valley (SLV), Colorado. We had available previous analyses of C-band ERS-1/2 data from June 1992 to November 2000, and L-band ALOS PALSAR data from October 2009 to March 2011. We used C-band Envisat data to fill in the time period from November 2006 to July 2010. In processing the Envisat data, we successfully employed a phase interpolation between persistent scatterer pixels to reduce the impact of vegetation decorrelation, which can significantly reduce the quality of C-band InSAR data over agricultural basins. In comparing the results from the L-band ALOS data and C-band Envisat data in a 10-month overlapping time period, we found that the shorter wavelength of C-band InSAR allowed us to preserve small deformation signals that were not detectable using L-band ALOS data. A significant result was the finding that the elastic storage properties of the SLV confined aquifer system remained stable over the 20 year time period and vary slowly in space, allowing us to combine InSAR data acquired from multiple missions to fill the temporal and spatial gaps in well data. The InSAR estimated head levels were validated with well measurements, which indicate little permanent water-storage loss over the study time period in the SLV.
      PubDate: 2017-11-08T08:51:16.585554-05:
      DOI: 10.1002/2017WR020881
  • Evaporation From Soil Containers With Irregular Shapes
    • Authors: Shmuel Assouline; Kfir Narkis
      Abstract: Evaporation from bare soils under laboratory conditions is generally studied using containers of regular shapes where the vertical edges are parallel to the flow lines in the drying domain. The main objective of this study was to investigate the impact of irregular container shapes, for which the flow lines either converge or diverge toward the surface. Evaporation from initially saturated sand and sandy loam soils packed in cones and inverted cones was compared to evaporation from corresponding cylindrical columns. The initial evaporation rate was higher in the cones, and close to potential evaporation. At the end of the experiment, the cumulative evaporation depth in the sand cone was equal to that in the column but higher than in the inverted cone, while in the sandy loam, the order was cone > column > inverted cone. By comparison to the column, stage 1 evaporation was longer in the cones, and practically similar in the inverted cones. Stage 2 evaporation rate decreased with the increase of the evaporating surface area. These results were more pronounced in the sandy loam. For the sand column, the transition between stage 1 and stage 2 evaporation occurred when the depth of the saturation front was approximately equal to the characteristic length of the soil. However, for the cone and the inverted cone, it occurred for a shallower depth of the saturation front. It seems therefore that the concept of the characteristic length derived from the soil hydraulic properties is related to drying systems of regular shapes.
      PubDate: 2017-11-08T00:36:06.999877-05:
      DOI: 10.1002/2017WR021166
  • A Water Temperature Simulation Model for Rice Paddies With Variable Water
    • Authors: Atsushi Maruyama; Manabu Nemoto, Takahiro Hamasaki, Sachinobu Ishida, Tsuneo Kuwagata
      Abstract: A water temperature simulation model was developed to estimate the effects of water management on the thermal environment in rice paddies. The model was based on two energy balance equations: for the ground and for the vegetation, and considered the water layer and changes in the aerodynamic properties of its surface with water depth. The model was examined with field experiments for water depths of 0 mm (drained conditions) and 100 mm (flooded condition) at two locations. Daily mean water temperatures in the flooded condition were mostly higher than in the drained condition in both locations, and the maximum difference reached 2.6°C. This difference was mainly caused by the difference in surface roughness of the ground. Heat exchange by free convection played an important role in determining water temperature. From the model simulation, the temperature difference between drained and flooded conditions was more apparent under low air temperature and small leaf area index conditions; the maximum difference reached 3°C. Most of this difference occurred when the range of water depth was lower than 50 mm. The season-long variation in modeled water temperature showed good agreement with an observation dataset from rice paddies with various rice-growing seasons, for a diverse range of water depths (root mean square error of 0.8–1.0°C). The proposed model can estimate water temperature for a given water depth, irrigation and drainage conditions, which will improve our understanding of the effect of water management on plant growth and greenhouse gas emissions through the thermal environment of rice paddies.
      PubDate: 2017-11-07T10:42:38.692953-05:
      DOI: 10.1002/2017WR021019
  • Testing the Limits of Temporal Stability: Willingness to Pay Values Among
           Grand Canyon Whitewater Boaters across Decades
    • Authors: Chris Neher; John Duffield, Lucas Bair, David Patterson, Katherine Neher
      Abstract: We directly compare trip willingness to pay (WTP) values between 1985 and 2015 stated preference surveys of private party Grand Canyon boaters using identically designed valuation methods. The temporal gap of 30 years between these two studies is well beyond that of any tests of WTP temporal stability in the literature. Comparisons were made of mean WTP estimates for four hypothetical Colorado River flow level scenarios. WTP values from the 1985 survey were adjusted to 2015 levels using the consumer price index. Mean WTP precision was estimated through simulation. No statistically significant differences were detected between the adjusted Bishop et al. and the current study mean WTP estimates. Examination of pooled models of the data from the studies suggest that while the estimated WTP values are stable over time, the underlying valuation functions may not be, particularly when the data and models are corrected to account for differing bid structures and possible panel effects.
      PubDate: 2017-11-07T10:35:27.659867-05:
      DOI: 10.1002/2017WR020729
  • Advancing Physically-Based Flow Simulations of Alluvial Systems Through
           Atmospheric Noble Gases and the Novel 37Ar Tracer Method
    • Authors: Oliver S. Schilling; Christoph Gerber, Daniel J. Partington, Roland Purtschert, Matthias S. Brennwald, Rolf Kipfer, Daniel Hunkeler, Philip Brunner
      Abstract: To provide a sound understanding of the sources, pathways and residence times of groundwater water in alluvial river-aquifer systems, a combined multi-tracer and modelling experiment was carried out in an important alluvial drinking water wellfield in Switzerland. 222Rn, 3H/3He, atmospheric noble gases and the novel 37Ar-method were used to quantify residence times and mixing ratios of water from different sources. With a half-life of 35.1 days, 37Ar allowed to successfully close a critical observational time gap between 222Rn and 3H/3He for residence times of weeks to months. Covering the entire range of residence times of groundwater in alluvial systems revealed that, to quantify the fractions of water from different sources in such systems, atmospheric noble gases and Helium isotopes are tracers suited for end-member mixing analysis. A comparison between the tracer-based mixing ratios and mixing ratios simulated with a fully-integrated, physically-based flow model showed that models, which are only calibrated against hydraulic heads, cannot reliably reproduce mixing ratios or residence times of alluvial river-aquifer systems. However, the tracer-based mixing ratios allowed the identification of an appropriate flow model parameterization. Consequently, for alluvial systems we recommend the combination of multi-tracer studies that cover all relevant residence times with fully-coupled, physically-based flow modelling to better characterize the complex interactions of river-aquifer systems.
      PubDate: 2017-11-03T15:36:30.911128-05:
      DOI: 10.1002/2017WR020754
  • Probable Maximum Precipitation in the U.S. Pacific Northwest in a Changing
    • Authors: Xiaodong Chen; Faisal Hossain, L. Ruby Leung
      Abstract: The safety of large and aging water infrastructures is gaining attention in water management given the accelerated rate of change in landscape, climate and society. In current engineering practice, such safety is ensured by the design of infrastructure for the Probable Maximum Precipitation (PMP). Recently, several numerical modeling approaches have been proposed to modernize the conventional and ad hoc PMP estimation approach. However, the underlying physics have not been fully investigated and thus differing PMP estimates are sometimes obtained without physics-based interpretations. In this study, we present a hybrid approach that takes advantage of both traditional engineering practice and modern climate science to estimate PMP for current and future climate conditions. The traditional PMP approach is modified and applied to five statistically downscaled CMIP5 model outputs, producing an ensemble of PMP estimates in the Pacific Northwest (PNW) during the historical (1970-2016) and future (2050-2099) time periods. The hybrid approach produced consistent historical PMP estimates as the traditional estimates. PMP in the PNW will increase by 50%±30% of the current design PMP by 2099 under the RCP8.5 scenario. Most of the increase is caused by warming, which mainly affects moisture availability through increased sea surface temperature, with minor contributions from changes in storm efficiency in the future. Moist track change tends to reduce the future PMP. Compared with extreme precipitation, PMP exhibits higher internal variability. Thus long-time records of high-quality data in both precipitation and related meteorological fields (temperature, wind fields) are required to reduce uncertainties in the ensemble PMP estimates.
      PubDate: 2017-11-03T15:31:32.728306-05:
      DOI: 10.1002/2017WR021094
  • A Binomial Modeling Approach for Upscaling Colloid Transport Under
           Unfavorable Attachment Conditions: Emergent Prediction of Nonmonotonic
           Retention Profiles
    • Authors: Markus Hilpert; William P. Johnson
      Abstract: We used a recently developed simple mathematical network model to upscale pore-scale colloid transport information determined under unfavorable attachment conditions. Classical log-linear and non-monotonic retention profiles, both well-reported under favorable and unfavorable attachment conditions, respectively, emerged from our upscaling. The primary attribute of the network is colloid transfer between bulk pore fluid, the near surface fluid domain (NSFD), and attachment (treated as irreversible). The network model accounts for colloid transfer to the NSFD of down-gradient grains and for reentrainment to bulk pore fluid via diffusion or via expulsion at rear flow stagnation zones (RFSZs). The model describes colloid transport by a sequence of random trials in a 1D network of Happel cells, which contain a grain and a pore. Using combinatorial analysis that capitalizes on the binomial coefficient, we derived from the pore-scale information the theoretical residence time distribution of colloids in the network. The transition from log-linear to non-monotonic retention profiles occurs when the conditions underlying classical filtration theory are not fulfilled, i.e., when a NSFD colloid population is maintained. Then, nonmonotonic retention profiles result, potentially both for attached and NSFD colloids. The concentration maxima shift downgradient depending on specific parameter choice. The concentration maxima were also shown to shift downgradient temporally (with continued elution) under conditions where attachment is negligible, explaining experimentally-observed down-gradient transport of retained concentration maxima of adhesion-deficient bacteria. For the case of zero reentrainment, we develop closed form, analytical expressions for the shape and the maximum of the colloid retention profile.
      PubDate: 2017-11-03T15:31:14.693918-05:
      DOI: 10.1002/2017WR021454
  • Nitrogen Subsidies in Glacial Meltwater: Implications for High Elevation
           Aquatic Chains
    • Authors: K. A. Warner; J. E. Saros, K. S. Simon
      Abstract: In certain alpine systems, glacially-fed lakes and streams have nitrate concentrations one to two orders of magnitude higher than lakes and streams fed by snowmelt alone. To better understand how nitrogen subsidies from glacial meltwater propagate down a chain of lakes and streams we assessed the effects of these subsidies in a set of aquatic chains in the central U.S. Rocky Mountains. Algal biomass, algal community assemblage, and nutrient limitation were measured in a chain of lakes and streams fed by glacial meltwater (GSF) and a chain fed by snowmelt alone (SF). Nitrate (NO3-) concentrations in the GSF chain ranged from 228 to 70 μg L−1 declining from the top of the chain to the bottom, while NO3- concentrations in the SF chain were consistently low, 
      PubDate: 2017-11-03T15:31:11.891928-05:
      DOI: 10.1002/2016WR020096
  • BAM: Bayesian AMHG-Manning Inference of Discharge Using Remotely Sensed
           Stream Width, Slope, and Height
    • Authors: M. W. Hagemann; C. J. Gleason, M. T. Durand
      Abstract: The forthcoming Surface Water and Ocean Topography (SWOT) NASA satellite mission will measure water surface width, height, and slope of major rivers worldwide. The resulting data could provide an unprecedented account of river discharge at continental scales, but reliable methods need to be identified prior to launch. Here, we present a novel algorithm for discharge estimation from only remotely sensed stream width, slope, and height at multiple locations along a mass-conserved river segment. The algorithm, termed the Bayesian AMHG-Manning (BAM) algorithm, implements a Bayesian formulation of streamflow uncertainty using a combination of Manning's equation and at-many-stations hydraulic geometry (AMHG). Bayesian methods provide a statistically defensible approach to generating discharge estimates in a physically underconstrained system, but rely on prior distributions that quantify the a priori uncertainty of unknown quantities including discharge and hydraulic equation parameters. These were obtained from literature-reported values and from a USGS dataset of acoustic Doppler current profiler (ADCP) measurements at USGS stream gauges. A dataset of simulated widths, slopes, and heights from 19 rivers was used to evaluate the algorithms using a set of performance metrics. Results across the 19 rivers indicate an improvement in performance of BAM over previously tested methods, and highlight a path forward in solving discharge estimation using solely satellite remote sensing.
      PubDate: 2017-11-03T15:26:15.401202-05:
      DOI: 10.1002/2017WR021626
  • Theoretical and Numerical Investigation of the Cavity Evolution in Gypsum
    • Authors: Wei Li; Herbert H. Einstein
      Abstract: When water flows through a preexisting cylindrical tube in gypsum rock, the non-uniform dissolution alters the tube into an enlarged tapered tube. A 2-D analytical model is developed to study the transport-controlled dissolution in an enlarged tapered tube, with explicit consideration of the tapered geometry and induced radial flow. The analytical model shows that the Graetz solution can be extended to model dissolution in the tapered tube. An alternative form of the governing equations is proposed to take advantage of the invariant quantities in the Graetz solution to facilitate modeling cavity evolution in gypsum rock. A 2-D finite volume model was developed to validate the extended Graetz solution. The time evolution of the transport-controlled and the reaction-controlled dissolution models for a single tube with time-invariant flow rate are compared. This comparison shows that for time-invariant flow rate, the reaction-controlled dissolution model produces a positive feedback between the tube enlargement and dissolution, while the transport-controlled dissolution does not.
      PubDate: 2017-11-01T14:25:22.993022-05:
      DOI: 10.1002/2017WR021776
  • Aquatic Nitrate Retention at River Network Scales Across Flow Conditions
           Determined Using Nested In Situ Sensors
    • Authors: W.M. Wollheim; G.K. Mulukutla, C. Cook, R. O. Carey
      Abstract: Non-point pollution sources are strongly influenced by hydrology and are therefore sensitive to climate variability. Some pollutants entering aquatic ecosystems, e.g. nitrate, can be mitigated by in-stream processes during transport through river networks. Whole river network nitrate retention is difficult to quantify with observations. High frequency, in situ nitrate sensors, deployed in nested locations within a single watershed, can improve estimates of both non-point inputs and aquatic retention at river network scales. We deployed a nested sensor network and associated sampling in the urbanizing Oyster River watershed in coastal New Hampshire, USA, to quantify storm event-scale loading and retention at network scales. An end member analysis used the relative behavior of reactive nitrate and conservative chloride to infer river network fate of nitrate. In the headwater catchments, nitrate and chloride concentrations are both increasingly diluted with increasing storm size. At the mouth of the watershed, chloride is also diluted, but nitrate tended to increase. The end member analysis suggests that this pattern is the result of high retention during small storms (51-78%) that declines to zero during large storms. Although high frequency nitrate sensors did not alter estimates of fluxes over seasonal time periods compared to less frequent grab sampling, they provide the ability to estimate nitrate flux vs. storm size at event scales that is critical for such analyses. Nested sensor networks can improve understanding of the controls of both loading and network scale retention, and therefore also improve management of non-point source pollution.
      PubDate: 2017-11-01T07:55:23.494647-05:
      DOI: 10.1002/2017WR020644
  • Exact Solutions of the Richards Equation with Nonlinear Plant-Root
    • Authors: Philip Broadbridge; Edoardo Daly, Joanna Goard
      Abstract: The Richards equation, commonly used to model water flow in unsaturated soils, is highly nonlinear, thus making it very challenging to solve analytically for situations meaningful in practical applications. The inclusion of realistic forms of root-water uptake rates in this equation adds complications in deriving exact solutions. This study provides for the first time analytical solutions of the Richards equation with a sink term nonlinearly dependent on soil water content. These solutions are applied to irrigation furrows, using Cartesian coordinates, and irrigation from a circular plate, in cylindrical coordinates.
      PubDate: 2017-11-01T07:50:23.04766-05:0
      DOI: 10.1002/2017WR021097
  • Analysis of Thermal Structure of Arctic Lakes at Local and Regional Scales
           Using In Situ and Multi-Date Landsat-8 Data
    • Authors: Yan Huang; Hongxing Liu, Kenneth Hinkel, Bailang Yu, Richard Beck, Jianping Wu
      Abstract: The Arctic coastal plain is covered with numerous thermokarst lakes. These lakes are closely linked to climate and environmental change through their heat and water budgets. We examined the intra-lake thermal structure at the local scale and investigated the water temperature pattern of lakes at the regional scale by utilizing extensive in situ measurements and multi-date Landsat-8 remote sensing data. Our analysis indicates that the lake skin temperatures derived from satellite thermal sensors during most of the ice-free summer period effectively represent the lake bulk temperature because the lakes are typically well-mixed and without significant vertical stratification. With the relatively high- resolution Landsat-8 thermal data, we were able to quantitatively examine intra-lake lateral temperature differences and gradients in relation to geographical location, topography, meteorological factors, and lake morphometry for the first time. Our results suggest that wind speed and direction not only control the vertical stratification but also influences lateral differences and gradients of lake surface temperature. Wind can considerably reduce the intra-lake temperature gradient. Interestingly, we found that geographical location (latitude, longitude, distance to the ocean) and lake morphometry (surface size, depth, volume) not only control lake temperature regionally but also affect the lateral temperature gradient and homogeneity level within each individual lake. For the Arctic coastal plain, at regional scales, inland and southern lakes tend to have larger horizontal temperature differences and gradients compared to coastal and northern lakes. At local scales, large and shallow lakes tend to have large lateral temperature differences relative to small and deep lakes.
      PubDate: 2017-11-01T07:41:41.298296-05:
      DOI: 10.1002/2017WR021335
  • Scaling Dissolved Nutrient Removal in River Networks: A Comparative
           Modeling Investigation
    • Authors: Sheng Ye; Alexander J. Reisinger, Jennifer L. Tank, Michelle A. Baker, Robert O. Hall, Emma J. Rosi, Murugesu Sivapalan
      Abstract: Along the river network, water, sediment, and nutrients are transported, cycled, and altered by coupled hydrological and biogeochemical processes. Our current understanding of the rates and processes controlling the cycling and removal of dissolved inorganic nutrients in river networks is limited due to a lack of empirical measurements in large, (non-wadeable), rivers. The goal of this paper was to develop a coupled hydrological and biogeochemical process model to simulate nutrient uptake at the network scale during summer baseflow conditions. The model was parameterized with literature values from headwater streams, and empirical measurements made in 15 rivers with varying hydrological, biological, and topographic characteristics, to simulate nutrient uptake at the network scale. We applied the coupled model to 15 catchments describing patterns in uptake for three different solutes to determine the role of rivers in network-scale nutrient cycling. Model simulation results, constrained by empirical data, suggested that rivers contributed proportionally more to nutrient removal than headwater streams given the fraction of their length represented in a network. In addition, variability of nutrient removal patterns among catchments was varied among solutes, and as expected, was influenced by nutrient concentration and discharge. Net ammonium uptake was not significantly correlated with any environmental descriptor. In contrast, net daily nitrate removal was linked to suspended chlorophyll a (an indicator of primary producers) and land use characteristics. Finally, suspended sediment characteristics and agricultural land use were correlated with net daily removal of soluble reactive phosphorus, likely reflecting abiotic sorption dynamics. Rivers are understudied relative to streams, and our model suggests that rivers can contribute more to network-scale nutrient removal than would be expected based upon their representative fraction of network channel length.
      PubDate: 2017-10-30T10:05:23.266822-05:
      DOI: 10.1002/2017WR020858
  • Fractional Models Simulating Non-Fickian Behavior in Four-Stage
           Single-Well Push-Pull Tests
    • Authors: Kewei Chen; Hongbin Zhan, Qiang Yang
      Abstract: Four-stage single-well push-pull (SWPP) tracer tests, including injection, chasing, resting and pumping, were conducted in a fractured aquifer at Newark basin. An anomalous transport phenomenon observed in the SWPP tests is the linear decline of breakthrough curves (BTCs) at late time with slope of -1.8 in log-log plots. A time-dependent fractional model is developed to interpret the anomalous transport behavior. This model considers a time-dependent power-law memory function and a time-dependent fractional advection-dispersion operator. The fractional advection-dispersion equations (fADE) are solved in a radial coordinate system using the implicit Euler method. A semi-analytical solution of the first-order rate-limited mobile-immobile model (FORMIM) is derived for comparison. It is found that both the non-local transport in time and space can produce the long-tailed BTC. A smaller time-fractional or space-fractional index leads to a lower peak concentration and a larger late-time slope. The mass distribution of the fractional-in-space (FS) model exhibits power-law decline at the leading plume edge. Early breakthrough during pumping is not observed because the mobile mass at the start of pumping is nonzero and more concentrated near the wellbore. The capacity ratio is an important factor that affects the peak concentration. A larger capacity ratio leads to greater peak concentration. A smaller time-fractional index in the injection, chasing or resting stage will move the BTC downward and the slope of the late time BTC is determined by the space-fractional index over all stages and the time-fractional index in the pumping stage. The capability of the existing models to recover the BTC of the SWPP test is discussed and some guidelines for how to choose the appropriate model to interpret the SWPP test data are proposed.
      PubDate: 2017-10-30T10:00:38.291906-05:
      DOI: 10.1002/2017WR021411
  • What Determines Water Temperature Dynamics in the San Francisco Bay-Delta
    • Authors: J. Vroom; M. van der Wegen, R.C. Martyr-Koller, L.V. Lucas
      Abstract: Water temperature is an important factor determining estuarine species habitat conditions. Water temperature is mainly governed by advection (e.g. from rivers) and atmospheric exchange processes varying strongly over time (day-night, seasonally) and the spatial domain. On a long time scale, climate change will impact water temperature in estuarine systems due to changes in river flow regimes, air temperature and sea level rise.To determine which factors govern estuarine water temperature and its sensitivity to changes in its forcing, we developed a process-based numerical model (Delft3D Flexible Mesh) and applied it to a well-monitored estuarine system (the San Francisco Estuary) for validation. The process-based approach allows for detailed process description and a physics-based analysis of governing processes.The model was calibrated for Water Year 2011 and incorporated 3D hydrodynamics, salinity intrusion, water temperature dynamics and atmospheric coupling. Results show significant skill in reproducing temperature observations on daily, seasonal and yearly timescales. In North San Francisco Bay thermal stratification is present, enhanced by salinity stratification. The temperature of the upstream, fresh water Delta area is captured well in 2D mode, although locally – on a small scale – vertical processes (e.g. stratification) may be important. The impact of upstream river temperature and discharge and atmospheric forcing on water temperatures differs throughout the Delta, possibly depending on dispersion and residence times.Our modeling effort provides a sound basis for future modeling studies including climate change impact on water temperature and associated ecological modeling, e.g. clam and fish habitat and phytoplankton dynamics.
      PubDate: 2017-10-30T09:50:55.453848-05:
      DOI: 10.1002/2016WR020062
  • Large-Scale Controls of the Surface Water Balance Over Land-Insights From
           a Systematic Review and Meta-Analysis
    • Authors: Ryan S. Padrón; Lukas Gudmundsson, Peter Greve, Sonia I. Seneviratne
      Abstract: The long-term surface water balance over land is described by the partitioning of precipitation (P) into runoff and evapotranspiration (ET), and is commonly characterized by the ratio ET/P. The ratio between potential evapotranspiration (PET) and P is explicitly considered to be the primary control of ET/P within the Budyko framework, whereas all other controls are often integrated into a single parameter, ω. Although the joint effect of these additional controlling factors of ET/P can be significant, a detailed understanding of them is yet to be achieved. This study therefore introduces a new global dataset for the long-term mean partitioning of P into ET and runoff in 2733 catchments, which is based on in-situ observations and assembled from a systematic examination of peer-reviewed studies. A total of 26 controls of ET/P that are proposed in the literature are assessed using the new dataset. Results reveal that: (i) factors controlling ET/P vary between regions with different climate types; (ii) controls other than PET/P explain at least 35% of the ET/P variance in all regions, and up to ∼90% in arid climates; (iii) among these, climate factors and catchment slope dominate over other landscape characteristics; and (iv) despite the high attention that vegetation-related indices receive as controls of ET/P, they are found to play a minor and often non-significant role. Overall, this study provides a comprehensive picture on factors controlling the partitioning of P, with valuable insights for model development, watershed management, and the assessment of water resources around the globe.
      PubDate: 2017-10-30T09:45:36.68406-05:0
      DOI: 10.1002/2017WR021215
  • Analytical Solutions to Coupled HM Problems to Highlight the Nonlocal
           Nature of Aquifer Storage
    • Authors: Silvia De Simone; Jesús Carrera
      Abstract: Specific storage reflects the volumetric deformation capacity of permeable media. Classical groundwater hydrology equates elastic storage to medium compressibility (plus fluid compressibility times porosity). However, it is unclear if storage behavior can be represented by a single parameter. Hydraulic gradients act as body forces that push the medium in the direction of flow causing it to deform instantaneously everywhere, i.e., even in regions where pressure would not have changed according to conventional fluid flow. Therefore, actual deformation depends on the mechanical properties of the medium, but also on aquifer geometry and on surrounding strata, which act like constraints to displacements. Here we discuss the question and highlight the non-local nature of storage (i.e., the volume of water released at a point depends on the poroelastic response over the whole aquifer). Proper evaluation of transient pressure and water release from storage requires acknowledging the hydro-mechanical coupling, which generally involves the use of numerical methods. We propose analytical solutions to the HM problem of fluid injection (extraction) into finite aquifers with one-dimensional or cylindrical geometries. We find that pressure response is much faster (virtually instantaneous) and larger than expected from traditional purely hydraulic solutions when aquifer deformation is restrained, whereas the pressure response is reversed (i.e., pressure drop in response to injection) when the permeable medium is free to deform. These findings suggest that accounting for hydro-mechanical coupling may be required when hydraulic testing is performed in low permeability media, which is becoming increasingly demanded for energy-related applications.
      PubDate: 2017-10-26T13:50:22.040369-05:
      DOI: 10.1002/2017WR020824
  • Estimation of Intrinsic Length Scales of Flow in Unsaturated Porous Media
    • Authors: Shmuel Assouline; Valentina Ciriello, Daniel M. Tartakovsky
      Abstract: Characteristic lengths govern processes related to flow in unsaturated porous media, e.g., during drainage or evaporation. One can estimate these lengths, i.e., air-entry pressure head and critical capillary head, from either a water retention curve (WRC) or a hydraulic conductivity function (HCF). We provide new analytical expressions for the characteristic lengths based on a linearized analysis of the WRC and HCF curves. These are then used to investigate the impact of model selection on length-scale estimates, to assess their sensitivity to model parameters, and to provide guidelines for the choice of the alternative expressions under flow scenarios of interest.
      PubDate: 2017-10-26T13:45:21.277098-05:
      DOI: 10.1002/2017WR021629
  • Bed Surface Adjustments to Spatially Variable Flow in Low Relative
           Submergence Regimes
    • Authors: A. Monsalve; E. M. Yager
      Abstract: In mountainous rivers, large relatively immobile grains partly control the local and reach-averaged flow hydraulics and sediment fluxes. When the flow depth is similar to the size of these grains (low relative submergence), heterogeneous flow structures and plunging flow cause spatial distributions of bed surface elevations, textures, and sedimentation rates. To explore how the bed surface responds to these flow variations we conducted a set of experiments in which we varied the relative submergence of staggered hemispheres (simulated large boulders) between runs. All experiments had the same average sediment transport capacity, upstream sediment supply, and initial bed thickness and grain size distribution. We combined our laboratory measurements with a 3D flow model to obtain the detailed flow structure around the hemispheres. The local bed shear stress field displayed substantial variability and controlled the bedload transport rates and direction in which sediment moved. The divergence in bed shear stress caused by the hemispheres promoted size-selective bedload deposition, which formed patches of coarse sediment upstream of the hemisphere. Sediment deposition caused a decrease in local bed shear stress, which combined with the coarser grain size, enhanced the stability of this patch. The region downstream of the hemispheres was largely controlled by a recirculation zone and had little to no change in grain size, bed elevation, and bed shear stress. The formation, development and stability of sediment patches in mountain streams is controlled by the bed shear stress divergence and magnitude and direction of the local bed shear stress field.
      PubDate: 2017-10-26T13:40:28.246596-05:
      DOI: 10.1002/2017WR020845
  • The Gas-Absorption/Chemical-Reaction Method for Measuring Air-Water
           Interfacial Area in Natural Porous Media
    • Authors: Ying Lyu; Mark L. Brusseau, Asma El Ouni, Juliana B. Araujo, Xiaosi Su
      Abstract: The gas-absorption/chemical-reaction (GACR) method used in Chemical Engineering to quantify gas-liquid interfacial area in reactor systems is adapted for the first time to measure the effective air-water interfacial area of natural porous media. Experiments were conducted with the GACR method, and two standard methods (x-ray microtomographic imaging and interfacial partitioning tracer tests) for comparison, using model glass beads and a natural sand. The results of a series of experiments conducted under identical conditions demonstrated that the GACR method exhibited excellent repeatability for maintaining constant water saturation and for measurement of interfacial area (Aia). Coefficients of variation for Aia were 3.5% for the glass beads and 11% for the sand. Estimated maximum interfacial areas (Am) obtained with the GACR method were statistically identical to independent measures of the specific solid surface areas of the media. For example, the Am for the glass beads is 29 (±1) cm−1, compared to 32 (±3), 30 (±2), and 31 (±2) cm−1 determined from geometric calculation, N2/BET measurement, and microtomographic measurement, respectively. This indicates that the method produced accurate measures of interfacial area. Interfacial areas determined with the GACR method were similar to those obtained with the standard methods. For example, Aias of 47 and 44 cm−1 were measured with the GACR and XMT methods, respectively, for the sand at a water saturation of 0.57. The results of the study indicate that the GACR method is a viable alternative for measuring air-water interfacial areas. The method is relatively quick, inexpensive, and requires no specialized instrumentation compared to the standard methods.
      PubDate: 2017-10-26T13:40:22.7464-05:00
      DOI: 10.1002/2017WR021717
  • Copula-Based Modeling of Flood Control Reservoirs
    • Authors: M. Balistrocchi; S. Orlandini, R. Ranzi, B. Bacchi
      Abstract: Copulas are shown in this paper to provide an effective strategy to describe the statistical dependence between peak flow discharge and flood volume featuring hydrographs forcing a flood control reservoir. A 52-year time series of flow discharge observed in the Panaro River (Northern Italian Apennines) is used to fit an event based bivariate distribution and to support time-continuous modeling of a flood control reservoir, located on-line along the river system. With regard to reservoir performances, a method aimed at estimating the bivariate return period is analytically developed, by exploiting the derived distribution theory and a simplified routing scheme. In this approach, the return period is that of the peak flow discharge released downstream from the reservoir. Therefore, in order to verify the reliability of the proposed method, a non-parametric version of its frequency distribution is assessed by means of continuous simulation statistics. Copula derived and non-parametric distributions of the downstream peak flow discharge are found to be in satisfactory agreement. Finally, a comparison of bivariate return period estimates carried out by using alternative approaches is illustrated.
      PubDate: 2017-10-24T14:27:10.907342-05:
      DOI: 10.1002/2017WR021345
  • Cooccurrence of Extreme Daily Rainfall in the French Mediterranean Region
    • Authors: J. Blanchet; Jean-Dominque Creutin
      Abstract: We propose in this paper a statistical framework to study local disparities in the co-occurrence of extreme rainfall in the French Mediterranean region. We employ a region-of-influence approach by studying the likelihood of the 3% largest daily rainfall to occur simultaneously at less than 50km distance, when moving across the region. Our model uses an anisotropic max-stable process allowing us to properly represent the co-occurrence of daily extremes and including the possibility of a preferred direction of co-occurrence. We use this framework on a dense network composed of almost 900 daily stations spread over a 100,000 km2 region of southern France under a Mediterranean influence, with data back to 1948. This density allows us to study the spatial patterns in the co-occurrence of extreme rainfall at fine scale and by so to characterize the main precipitation systems leading to extremes in the region. We show in particular that concomitant extremes are the most likely along the crest line of the Massif Central, which is also the area where the magnitude of extremes is among the largest. This may be of concern for flood risk management.
      PubDate: 2017-10-24T14:26:55.846841-05:
      DOI: 10.1002/2017WR020717
  • Inclusion of Topological Measurements Into Analytic Estimates of Effective
           Permeability in Fractured Media
    • Authors: P. N. Sævik; C. W. Nixon
      Abstract: We demonstrate how topology-based measures of connectivity can be used to improve analytical estimates of effective permeability in 2D fracture networks, which is one of the key parameters necessary for fluid flow simulations at the reservoir scale. Existing methods in this field usually compute fracture connectivity using the average fracture length. This approach is valid for ideally-shaped, randomly distributed fractures, but is not immediately applicable to natural fracture networks. In particular, natural networks tend to be more connected than randomly positioned fractures of comparable lengths, since natural fractures often terminate in each other. The proposed topological connectivity measure is based on the number of intersections and fracture terminations per sampling area, which for statistically stationary networks can be obtained directly from limited outcrop exposures. To evaluate the method, numerical permeability upscaling was performed on a large number of synthetic and natural fracture networks, with varying topology and geometry. The proposed method was seen to provide much more reliable permeability estimates than the length-based approach, across a wide range of fracture patterns. We summarize our results in a single, explicit formula for the effective permeability.
      PubDate: 2017-10-24T14:26:39.094053-05:
      DOI: 10.1002/2017WR020943
  • Revisiting the Fundamental Analytical Solutions of Heat and Mass Transfer:
           The Kernel of Multirate and Multidimensional Diffusion
    • Authors: Quanlin Zhou; Curtis M. Oldenburg, Jonny Rutqvist, Jens T. Birkholzer
      Abstract: There are two types of analytical solutions of temperature/concentration in and heat/mass transfer through boundaries of regularly shaped 1D, 2D, and 3D blocks. These infinite-series solutions with either error functions or exponentials exhibit highly irregular but complementary convergence at different dimensionless times, td. In this paper, approximate solutions were developed by combining the error-function-series solutions for early times and the exponential-series solutions for late times and by using time partitioning at the switchover time, td0. The combined solutions contain either the leading term of both series for normal-accuracy approximations (with less than 0.003 relative error) or the first two terms for high-accuracy approximations (with less than 10−7 relative error) for 1D isotropic (spheres, cylinders, slabs) and 2D/3D rectangular blocks (squares, cubes, rectangles, and rectangular parallelepipeds). This rapid and uniform convergence for rectangular blocks was achieved by employing the same time partitioning with individual dimensionless times for different directions and the product of their combined 1D slab solutions. The switchover dimensionless time was determined to minimize the maximum approximation errors. Furthermore, the analytical solutions of first-order heat/mass flux for 2D/3D rectangular blocks were derived for normal-accuracy approximations. These flux equations contain the early-time solution with a three-term polynomial in td and the late-time solution with the limited-term exponentials for rectangular blocks. The heat/mass flux equations and the combined temperature/concentration solutions form the ultimate kernel for fast simulations of multirate and multidimensional heat/mass transfer in porous/fractured media with millions of low-permeability blocks of varying shapes and sizes.
      PubDate: 2017-10-24T14:26:28.809307-05:
      DOI: 10.1002/2017WR021040
  • Sensitivity of Catchment Transit Times to Rainfall Variability Under
           Present and Future Climates
    • Authors: Daniel C. Wilusz; Ciaran J. Harman, William P. Ball
      Abstract: Hydrologists have a relatively good understanding of how rainfall variability shapes the catchment hydrograph, a reflection of the celerity of hydraulic head propagation. Much less is known about the influence of rainfall variability on catchment transit times, a reflection of water velocities that control solute transport. This work uses catchment-scale lumped parameter models to decompose the relationship between rainfall variability and an important metric of transit times, the time-varying fraction of young water (
      PubDate: 2017-10-24T14:26:25.341249-05:
      DOI: 10.1002/2017WR020894
  • Physical Controls on Biogeochemical Processes in Intertidal Zones of Beach
    • Authors: James W. Heiss; Vincent E.A. Post, Tariq Laattoe, Christopher J. Russoniello, Holly A. Michael
      Abstract: Marine ecosystems are sensitive to inputs of chemicals from submarine groundwater discharge. Tidally-influenced saltwater-freshwater mixing zones in beach aquifers can host biogeochemical transformations that modify chemical loads prior to discharge. A numerical variable-density groundwater flow and reactive transport model was used to evaluate the physical controls on reactivity for mixing-dependent and mixing-independent reactions in beach aquifers, represented as denitrification and sulfate reduction, respectively. A sensitivity analysis was performed across typical values of tidal amplitude, hydraulic conductivity, terrestrial freshwater flux, beach slope, dispersivity, and DOC reactivity. For the model setup and conditions tested, the simulations demonstrate that denitrification can remove up to 100% of terrestrially-derived nitrate, and sulfate reduction can transform up to 8% of seawater-derived sulfate prior to discharge. Tidally-driven mixing between saltwater and freshwater promotes denitrification along the boundary of the intertidal saltwater circulation cell in porewater between 1-10 ppt. The denitrification zone occupies on average 49% of the mixing zone. Denitrification rates are highest on the landward side of the circulation cell and decrease along circulating flow paths. Reactivity for mixing-dependent reactions increases with the size of the mixing zone and solute supply, while mixing-independent reactivity is controlled primarily by solute supply. The results provide insights into the types of beaches most efficient in altering fluxes of chemicals prior to discharge and could be built upon to help engineer beaches to enhance reactivity. The findings have implications for management to protect coastal ecosystems and the estimation of chemical fluxes to the ocean.
      PubDate: 2017-10-24T14:26:16.131782-05:
      DOI: 10.1002/2017WR021110
  • genRE: A Method to Extend Gridded Precipitation Climatology Data Sets in
           Near Real-Time for Hydrological Forecasting Purposes
    • Authors: B. van Osnabrugge; A.H. Weerts, R. Uijlenhoet
      Abstract: To enable operational flood forecasting and drought monitoring, reliable and consistent methods for precipitation interpolation are needed. Such methods need to deal with the deficiencies of sparse operational real-time data compared to quality-controlled offline data sources used in historical analyses. In particular, often a fraction of the measurement network reports in near real-time. For this purpose we present an interpolation method, generalized REGNIE (genRE), which makes use of climatological monthly background grids derived from existing gridded precipitation climatology datasets. We show how genRE can be used to mimic and extend climatological precipitation datasets in near real-time using (sparse) real-time measurement networks in the Rhine basin upstream of the Netherlands (approx. 160.000km2). In the process, we create a 1.2x1.2 km transnational gridded hourly precipitation dataset for the Rhine basin. Precipitation gauge data is collected, spatially interpolated for the period 1996–2015 with genRE and inverse-distance squared weighting (IDW), and then evaluated on the yearly and daily timescale against the HYRAS and EOBS climatological datasets. Hourly fields are compared qualitatively with RADOLAN radar based precipitation estimates. Two sources of uncertainty are evaluated: station density and the impact of different background grids (HYRAS vs EOBS). The results show that the genRE method successfully mimics climatological precipitation datasets (HYRAS/EOBS) over daily, monthly and yearly time frames. We conclude that genRE is a good interpolation method of choice for real-time operational use. genRE has the largest added value over IDW for cases with a low real-time station density and a high resolution background grid.
      PubDate: 2017-10-24T14:26:06.774672-05:
      DOI: 10.1002/2017WR021201
  • Gauging through the Crowd: A Crowd-Sourcing Approach to Urban Rainfall
           Measurement and Stormwater Modeling Implications
    • Authors: Pan Yang; Tze Ling Ng
      Abstract: Accurate rainfall measurement at high spatial and temporal resolutions is critical for the modeling and management of urban stormwater. In this study, we conduct computer simulation experiments to test the potential of a crowd-sourcing approach, where smartphones, surveillance cameras and other devices act as precipitation sensors, as an alternative to the traditional approach of using rain gauges to monitor urban rainfall. The crowd-sourcing approach is promising as it has the potential to provide high-density measurements, albeit with relatively large individual errors. We explore the potential of this approach for urban rainfall monitoring and the subsequent implications for stormwater modeling through a series of simulation experiments involving synthetically generated crowd-sourced rainfall data and a stormwater model. The results show that even under conservative assumptions, crowd-sourced rainfall data lead to more accurate modeling of stormwater flows as compared to rain gauge data. We observe the relative superiority of the crowd-sourcing approach to vary depending on crowd participation rate, measurement accuracy, drainage area, choice of performance statistic, and crowd-sourced observation type. A possible reason for our findings is the differences between the error structures of crowd-sourced and rain gauge rainfall fields resulting from the differences between the errors and densities of the raw measurement data underlying the two field types.
      PubDate: 2017-10-24T14:25:34.986247-05:
      DOI: 10.1002/2017WR020682
  • Disturbance Hydrology: Preparing for an Increasingly Disturbed Future
    • Authors: Benjamin B. Mirus; Brian A. Ebel, Christian H. Mohr, Nicolas Zegre
      Abstract: This special issue is the result of several fruitful conference sessions on disturbance hydrology, which started at the 2013 AGU Fall Meeting in San Francisco and have continued every year since. The stimulating presentations and discussions surrounding those sessions have focused on understanding both the disruption of hydrologic functioning following discrete disturbances, as well as the subsequent recovery or change within the affected watershed system. Whereas some hydrologic disturbances are directly linked to anthropogenic activities, such as resource extraction, the contributions to this special issue focus primarily on those with indirect or less pronounced human involvement, such as bark-beetle infestation, wildfire, and other natural hazards. However, human activities are enhancing the severity and frequency of these seemingly natural disturbances, thereby contributing to acute hydrologic problems and hazards. Major research challenges for our increasingly disturbed planet include the lack of continuous pre- and post-disturbance monitoring, hydrologic impacts that vary spatially and temporally based on environmental and hydroclimatic conditions, and the preponderance of overlapping or compounding disturbance sequences. In addition, a conceptual framework for characterizing commonalities and differences among hydrologic disturbances is still in its infancy. In this introduction to the special issue, we advance the fusion of concepts and terminology from ecology and hydrology to begin filling this gap. We briefly explore some preliminary approaches for comparing different disturbances and their hydrologic impacts, which provides a starting point for further dialogue and research progress.
      PubDate: 2017-10-24T14:25:29.378016-05:
      DOI: 10.1002/2017WR021084
  • Hydropower Optimization Using Artificial Neural Network Surrogate Models
           of a High-Fidelity Hydrodynamics and Water Quality Model
    • Authors: Amelia R. Shaw; Heather Smith Sawyer, Eugene J. LeBoeuf, Mark P. McDonald, Boualem Hadjerioua
      Abstract: Hydropower operations optimization subject to environmental constraints is limited by challenges associated with dimensionality and spatial and temporal resolution. The need for high-fidelity hydrodynamic and water quality models within optimization schemes is driven by improved computational capabilities, increased requirements to meet specific points of compliance with greater resolution, and the need to optimize operations of not just single reservoirs but systems of reservoirs. This study describes an important advancement for computing hourly power generation schemes for a hydropower reservoir using high-fidelity models, surrogate modeling techniques, and optimization methods. The predictive power of the high-fidelity hydrodynamic and water quality model CE-QUAL-W2 is successfully emulated by an artificial neural network, then integrated into a genetic algorithm optimization approach to maximize hydropower generation subject to constraints on dam operations and water quality. This methodology is applied to a multipurpose reservoir near Nashville, Tennessee, USA. The model successfully reproduced high-fidelity reservoir information while enabling 6.8 and 6.6 percent increases in hydropower production value relative to actual operations for dissolved oxygen (DO) limits of 5 and 6 mg/L, respectively, while witnessing an expected decrease in power generation at more restrictive DO constraints. Exploration of simultaneous temperature and DO constraints revealed capability to address multiple water quality constraints at specified locations. The reduced computational requirements of the new modeling approach demonstrated an ability to provide decision support for reservoir operations scheduling while maintaining high-fidelity hydrodynamic and water quality information as part of the optimization decision support routines.
      PubDate: 2017-10-24T14:25:27.281764-05:
      DOI: 10.1002/2017WR021039
  • A Statistical Graphical Model of the California Reservoir System
    • Authors: A. Taeb; J.T. Reager, M. Turmon, V. Chandrasekaran
      Abstract: The recent California drought has highlighted the potential vulnerability of the state's water management infrastructure to multi-year dry intervals. Due to the high complexity of the network, dynamic storage changes in California reservoirs on a state-wide scale have previously been difficult to model using either traditional statistical or physical approaches. Indeed, although there is a significant line of research on exploring models for single (or a small number of) reservoirs, these approaches are not amenable to a system-wide modeling of the California reservoir network due to the spatial and hydrological heterogeneities of the system. In this work, we develop a state-wide statistical graphical model to characterize the dependencies among a collection 55 major California reservoirs across the state; this model is defined with respect to a graph in which the nodes index reservoirs and the edges specify the relationships or dependencies between reservoirs. We obtain and validate this model in a data-driven manner based on reservoir volumes over the period 2003 – 2016. A key feature of our framework is a quantification of the effects of external phenomena that influence the entire reservoir network. We further characterize the degree to which physical factors (e.g. state-wide Palmer Drought Severity Index (PDSI), average temperature, snow pack) and economic factors (e.g. consumer price index, number of agricultural workers) explain these external influences. As a consequence of this analysis, we obtain a system-wide health diagnosis of the reservoir network as a function of PDSI.
      PubDate: 2017-10-20T13:10:34.869149-05:
      DOI: 10.1002/2017WR020412
  • Elimination of the Reaction Rate “scale Effect”: Application of the
           Lagrangian Reactive Particle-Tracking Method to Simulate Mixing-Limited,
           Field-Scale Biodegradation at the Schoolcraft (MI, USA) Site
    • Authors: Dong Ding; David A. Benson, Daniel Fernàndez-Garcia, Christopher V. Henri, David W. Hyndman, Mantha S. Phanikumar, Diogo Bolster
      Abstract: Measured (or empirically fitted) reaction rates at groundwater remediation sites are typically much lower than those found in the same material at the batch- or laboratory-scale. The reduced rates are commonly attributed to poorer mixing at the larger scales. A variety of methods have been proposed to account for this scaling effect in reactive transport. In this study, we use the Lagrangian particle tracking and reaction (PTR) method to simulate a field bioremediation experiment at the Schoolcraft, Michigan site. A denitrifying bacterium, Pseudomonas Stutzeri strain KC (KC), was injected to the aquifer, along with sufficient substrate, to degrade the contaminant, Carbon Tetrachloride (CT), under anaerobic conditions. The PTR method simulates chemical reactions through probabilistic rules of particle collisions, interactions, and transformations to address the scale effect (lower apparent reaction rates for each level of upscaling, from batch- to column- to field-scale). In contrast to a prior Eulerian reaction model, the PTR method is able to match the field-scale experiment using the rate coefficients obtained from batch experiments.
      PubDate: 2017-10-20T13:10:28.065553-05:
      DOI: 10.1002/2017WR021103
  • Constraints on Water Reservoir Lifetimes From Catchment-Wide 10Be Erosion
           Rates: A Case Study From Western Turkey
    • Authors: Caroline Heineke; Ralf Hetzel, Cüneyt Akal, Marcus Christl
      Abstract: The functionality and retention capacity of water reservoirs is generally impaired by upstream erosion and reservoir sedimentation, making a reliable assessment of erosion indispensable to estimate reservoir lifetimes. Widely used river gauging methods may underestimate sediment yield, because they do not record rare, high-magnitude events and may underestimate bedload transport. Hence, reservoir lifetimes calculated from short-term erosion rates should be regarded as maximum values. We propose that erosion rates from cosmogenic 10Be, which commonly integrate over hundreds to thousands of years are useful to complement short-term sediment yield estimates and should be employed to estimate minimum reservoir lifetimes. Here, we present 10Be erosion rates for the drainage basins of six water reservoirs in Western Turkey, which are located in a tectonically active region with easily erodible bedrock. Our 10Be erosion rates for these catchments are high, ranging from ∼170 to ∼1040 t/km2/yr. When linked to reservoir volumes, they yield minimum reservoir lifetimes between 25 ± 5 and 1650 ± 360 years until complete filling, with four reservoirs having minimum lifespans of ≤110 years. In a neighboring region with more resistant bedrock and less tectonic activity, we obtain much lower catchment-wide 10Be erosion rates of ∼33 to ∼95 t/km2/yr, illustrating that differences in lithology and tectonic boundary conditions can cause substantial variations in erosion even at a spatial scale of only ∼50 km. In conclusion, we suggest that both short-term sediment yield estimates and 10Be erosion rates should be employed to predict the lifetimes of reservoirs.
      PubDate: 2017-10-20T13:05:28.680123-05:
      DOI: 10.1002/2017WR020594
  • Comparing Approaches to Deal With Non-Gaussianity of Rainfall Data in
           Kriging-Based Radar-Gauge Rainfall Merging
    • Authors: F. Cecinati; O. Wani, M. A. Rico-Ramirez
      Abstract: Merging radar and rain gauge rainfall data is a technique used to improve the quality of spatial rainfall estimates and in particular the use of Kriging with External Drift (KED) is a very effective radar-rain gauge rainfall merging technique. However, kriging interpolations assume Gaussianity of the process. Rainfall has a strongly skewed, positive, probability distribution, characterized by a discontinuity due to intermittency. In KED rainfall residuals are used, implicitly calculated as the difference between rain gauge data and a linear function of the radar estimates. Rainfall residuals are non-Gaussian as well. The aim of this work is to evaluate the impact of applying KED to non-Gaussian rainfall residuals, and to assess the best techniques to improve Gaussianity. We compare Box-Cox transformations with λ parameters equal to 0.5, 0.25, and 0.1, Box-Cox with time-variant optimization of λ, normal score transformation, and a singularity analysis technique. The results suggest that Box-Cox with λ=0.1 and the singularity analysis are not suitable for KED. Normal score transformation and Box-Cox with optimized λ, or λ=0.25 produce satisfactory results in terms of Gaussianity of the residuals, probability distribution of the merged rainfall products, and rainfall estimate quality, when validated through cross-validation. However, it is observed that Box-Cox transformations are strongly dependent on the temporal and spatial variability of rainfall and on the units used for the rainfall intensity. Overall, applying transformations results in a quantitative improvement of the rainfall estimates only if the correct transformations for the specific dataset are used.
      PubDate: 2017-10-16T10:25:28.199464-05:
      DOI: 10.1002/2016WR020330
  • The NorWeST Summer Stream Temperature Model and Scenarios for the Western
           U.S.: A Crowd-Sourced Database and New Geospatial Tools Foster a
           User-Community and Predict Broad Climate Warming of Rivers and Streams
    • Authors: Daniel J. Isaak; Seth J. Wenger, Erin E. Peterson, Jay M. Ver Hoef, David E. Nagel, Charlie H. Luce, Steven W. Hostetler, Jason B. Dunham, Brett B. Roper, Sherry P. Wollrab, Gwynne L. Chandler, Dona L. Horan, Sharon Parkes-Payne
      Abstract: Thermal regimes are fundamental determinants of aquatic ecosystems, which makes description and prediction of temperatures critical during a period of rapid global change. The advent of inexpensive temperature sensors dramatically increased monitoring in recent decades, and although most monitoring is done by individuals for agency-specific purposes, collectively these efforts constitute a massive distributed sensing array that generates an untapped wealth of data. Using the framework provided by the National Hydrography Dataset, we organized temperature records from dozens of agencies in the western U.S. to create the NorWeST database that hosts>220,000,000 temperature recordings from>22,700 stream and river sites. Spatial-stream-network models were fit to a subset of those data that described mean August water temperatures (AugTw) during 63,641 monitoring site-years to develop accurate temperature models (r2 = 0.91; RMSPE = 1.10 ᵒC; MAPE = 0.72 ᵒC), assess covariate effects, and make predictions at 1-km intervals to create summer climate scenarios. AugTw averaged 14.2 ᵒC (SD = 4.0 ᵒC) during the baseline period of 1993–2011 in 343,000 km of western perennial streams but trend reconstructions also indicated warming had occurred at the rate of 0.17 ᵒC/decade (SD = 0.067 ᵒC/decade) during the 40-year period of 1976–2015. Future scenarios suggest continued warming, although variation will occur within and among river networks due to differences in local climate forcing and stream responsiveness. NorWeST scenarios and data are available online in user-friendly digital formats and are widely used to coordinate monitoring efforts among agencies, for new research, and for conservation planning.
      PubDate: 2017-10-16T10:21:52.49586-05:0
      DOI: 10.1002/2017WR020969
  • Understanding the Role of Climate Characteristics in Drought Propagation
    • Authors: Tushar Apurv; Murugesu Sivapalan, Ximing Cai
      Abstract: In this study, we use numerical experiments with a simple water balance model to understand the roles of key climate characteristics in hydrologic drought propagation and the consequence of human responses to drought events under different climates. The experiments use climate inputs from a range of places with a hypothetical catchment of fixed properties to study drought propagation under different climates. Three drought propagation mechanisms are identified that produce hydrologic droughts with differing characteristics. The first mechanism involves seasonal groundwater recharge cycles, which persist during low rainfall periods, resulting in shorter hydrologic droughts compared to meteorological droughts. The second is characterized by seasonal groundwater recharge cycles that are suppressed during low rainfall periods, resulting in longer hydrologic droughts than meteorological droughts. The third is exemplified by a lack of seasonality in groundwater recharge and a strong control of precipitation over groundwater recharge, resulting in hydrologic droughts of similar duration as meteorological droughts. The roles of seasonality, climate aridity and timing of precipitation in producing these different drought propagation mechanisms are studied. The timing of precipitation is found to have the most significant impact. Furthermore, modeling experiments are performed to understand the role of climate in the interaction between short and long time-scale human activities in response to droughts and the effect of the common practice of groundwater pumping during drought events on long-term groundwater depletion. Interestingly, climates with high inter-annual variability of precipitation are found to be associated with less groundwater depletion than the climates with low inter-annual variability.
      PubDate: 2017-10-16T10:18:22.45467-05:0
      DOI: 10.1002/2017WR021445
  • Nine Hundred Years of Weekly Streamflows: Stochastic Downscaling of
           Ensemble Tree-Ring Reconstructions
    • Authors: David Sauchyn; Nesa Ilich
      Abstract: We combined the methods and advantages of stochastic and paleo-hydrology to estimate 900 years of weekly flows for the North and South Saskatchewan Rivers at Edmonton and Medicine Hat, Alberta, respectively. Regression models of water-year streamflow were constructed using historical naturalized flow data and a pool of 196 tree-ring (earlywood, latewood and annual) ring-width chronologies from 76 sites. The tree-ring models accounted for up to 80% of the inter-annual variability in historical naturalized flows. We developed a new algorithm for generating stochastic time series of weekly flows constrained by the statistical properties of both the historical record and proxy streamflow data, and by the necessary condition that weekly flows correlate between the end of one year and the start of the next. A second innovation, enabled by the density of our tree-ring network, is to derive the paleohydrology from an ensemble of 100 statistically significant reconstructions at each gauge. Using paleoclimatic data to generate long series of weekly flow estimates augments the short historical record with an expanded range of hydrologic variability, including sequences of wet and dry years of greater length and severity. This unique hydrometric time series will enable evaluation of the reliability of current water supply and management systems given the range of hydro-climatic variability and extremes contained in the stochastic paleohydrology. It also could inform evaluation of the uncertainty in climate model projections, given that internal hydro-climatic variability is the dominant source of uncertainty.
      PubDate: 2017-10-16T10:16:35.679922-05:
      DOI: 10.1002/2017WR021585
  • Exploring the Role of Social Media and Individual Behaviors in Flood
           Evacuation Processes: An Agent-Based Modeling Approach
    • Authors: Erhu Du; Ximing Cai, Zhiyong Sun, Barbara Minsker
      Abstract: Flood warnings from various information sources are important for individuals to make evacuation decisions during a flood event. In this study, we develop a general opinion dynamics model to simulate how individuals update their flood hazard awareness when exposed to multiple information sources, including global broadcast, social media, and observations of neighbors' actions. The opinion dynamics model is coupled with a traffic model to simulate the evacuation processes of a residential community with a given transportation network. Through various scenarios, we investigate how social media affect the opinion dynamics and evacuation processes. We find that stronger social media can make evacuation processes more sensitive to the change of global broadcast and neighbor observations, and thus, impose larger uncertainty on evacuation rates (i.e., a large range of evacuation rates corresponding to sources of information). For instance, evacuation rates are lower when social media become more influential and individuals have less trust in global broadcast. Stubborn individuals can significantly affect the opinion dynamics and reduce evacuation rates. In addition, evacuation rates respond to the percentage of stubborn agents in a non-linear manner, i.e., above a threshold, the impact of stubborn agents will be intensified by stronger social media. These results highlight the role of social media in flood evacuation processes and the need to monitor social media so that misinformation can be corrected in a timely manner. The joint impacts of social media, quality of flood warnings and transportation capacity on evacuation rates are also discussed.
      PubDate: 2017-10-16T10:11:07.212132-05:
      DOI: 10.1002/2017WR021192
  • Effect of Unsaturated Flow Modes on Partitioning Dynamics of
           Gravity-Driven Flow at a Simple Fracture Intersection: Laboratory Study
           and Three-Dimensional Smoothed Particle Hydrodynamics Simulations
    • Authors: Jannes Kordilla; Torsten Noffz, Marco Dentz, Tobias Geyer, Alexandre M. Tartakovsky
      Abstract: In this work, we study gravity-driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection. We present laboratory experiments, three-dimensional smoothed particle hydrodynamics (SPH) simulations using a heavily parallelized code, and a theoretical analysis. The flow-rate-dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the SPH model, and the transition ranges agree in SPH simulations and laboratory experiments. We show that flow modes heavily influence the “bypass” behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), the flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer. For the case of rivulet flow, we provide an analytical solution that demonstrates the existence of classical Washburn flow within the horizontal fracture.
      PubDate: 2017-10-16T10:11:04.185823-05:
      DOI: 10.1002/2016WR020236
  • Development of Autonomous Boat-Type Robot for Automated Velocity
           Measurement in Straight Natural River
    • Authors: M. Sanjou; T. Nagasaka
      Abstract: The present study describes an automated system to measure the river flow velocity. A combination of the camera-tracking system and the Proportional/Integral/Derivative (PID) control could enable the boat-type robot to remain in position against the mainstream; this results in reasonable evaluation of the mean velocity by a duty ratio which corresponds to rotation speed of the screw propeller. A laser range finder module was installed to measure the local water depth. Reliable laboratory experiments with the prototype boat robot and electromagnetic velocimetry were conducted to obtain a calibration curve that connects the duty ratio and mean current velocity. The remaining accuracy in the target point was also examined quantitatively. The fluctuation in the spanwise direction is within half of the robot length. It was therefore found that the robot remains well within the target region. We used two-dimensional navigation tests to guarantee that the prototype moved smoothly to the target points and successfully measured the streamwise velocity profiles across the mainstream. Moreover, the present robot was found to move successfully not only in the laboratory flume but also in a small natural river. The robot could move smoothly from the starting point near the operator's site toward the target point where the velocity is measured, and it could evaluate the cross-sectional discharge.
      PubDate: 2017-10-16T10:06:12.795644-05:
      DOI: 10.1002/2017WR020672
  • Multitracer Field Fluorometry: Accounting for Temperature and Turbidity
           Variability During Stream Tracer Tests
    • Authors: Phillip J. Blaen; Nicolai Brekenfeld, Sophie Comer-Warner, Stefan Krause
      Abstract: The use of multi-tracer field fluorometry is increasing in the hydrological sciences. However, obtaining high-quality fluorescence measurements is challenging given the variability in environmental conditions within stream ecosystems. Here, we conducted a series of stream tracer tests to examine the degree to which multi-tracer field fluorometry produces reliable estimates of tracer concentrations under realistic field conditions. Using frequently applied examples of conservative (Uranine) and reactive (Resazurin-Resorufin) fluorescent tracers, we show that in situ measurements of tracer breakthrough curves can deviate markedly from corresponding samples analysed under laboratory conditions. To investigate the effects of key environmental variables on fluorescence measurements, we characterised the response of field fluorometer measurements to changes in temperature, turbidity and tracer concentration. Results showed pronounced negative log-linear effects of temperature on fluorescence measurements for all tracers, with stronger effects observed typically at lower tracer concentrations. We also observed linear effects of turbidity on fluorescence measurements that varied predictably with tracer concentration. Based on our findings, we present methods to correct field fluorometer measurements for variation in these parameters. Our results show how changing environmental conditions can introduce substantial uncertainties in the analysis of fluorescent tracer breakthrough curves, and highlight the importance of accounting for these changes to prevent incorrect inferences being drawn regarding the physical and biogeochemical processes underpinning observed patterns.
      PubDate: 2017-10-16T10:01:01.436242-05:
      DOI: 10.1002/2017WR020815
  • Uncertainty Quantification in Scale-Dependent Models of Flow in Porous
    • Authors: A. M. Tartakovsky; M. Panzeri, G. D. Tartakovsky, A. Guadagnini
      Abstract: Equations governing flow and transport in randomly heterogeneous porous media are stochastic and scale-dependent. In the Moment Equations (ME) method, exact deterministic equations for the leading moments of state variables are obtained at the same support scale as the governing equations. Computable approximations of the MEs can be derived via perturbation expansion in orders of the standard deviation of the random model parameters. As such, their convergence is guaranteed only for standard deviation smaller than one. Here we consider steady-state saturated flow in a porous medium with random second-order stationary conductivity field. We show it is possible to identify a support scale η*, where the typically employed approximate formulations of ME yield accurate (statistical) moments of a target state variable. Therefore, at support scale η* and larger, ME presents an attractive alternative to slowly convergent Monte Carlo (MC) methods whenever lead-order statistical moments of a target state variable are needed. We also demonstrate that a surrogate model for statistical moments could be constructed from MC simulations at larger support scales and be used to accurately estimate moments at smaller scales, where MC simulations are expensive and the ME method is not applicable.
      PubDate: 2017-10-16T10:00:52.88254-05:0
      DOI: 10.1002/2017WR020905
  • Multiple Household Water Sources and Their Use in Remote Communities With
           Evidence From Pacific Island Countries
    • Authors: Mark Elliott; Morgan C. MacDonald, Terence Chan, Annika Kearton, Katherine F. Shields, Jamie K. Bartram, Wade L. Hadwen
      Abstract: Global water research and monitoring typically focus on the household's “main source of drinking-water.” Use of multiple water sources to meet daily household needs has been noted in many developing countries but rarely quantified or reported in detail. We gathered self-reported data using a cross-sectional survey of 405 households in eight communities of the Republic of the Marshall Islands (RMI) and five Solomon Islands (SI) communities. Over 90% of households used multiple sources, with differences in sources and uses between wet and dry seasons. Most RMI households had large rainwater tanks and rationed stored rainwater for drinking throughout the dry season, whereas most SI households collected rainwater in small pots, precluding storage across seasons. Use of a source for cooking was strongly positively correlated with use for drinking, whereas use for cooking was negatively correlated or uncorrelated with non-consumptive uses (e.g., bathing). Dry season water uses implied greater risk of waterborne disease, with fewer (frequently zero) handwashing sources reported and more unimproved sources consumed. Use of multiple sources is fundamental to household water management and feasible to monitor using electronic survey tools. We contend that recognizing multiple water sources can greatly improve understanding of household-level and community-level climate change resilience, that use of multiple sources confounds health impact studies of water interventions, and that incorporating multiple sources into water supply interventions can yield heretofore-unrealized benefits. We propose that failure to consider multiple sources undermines the design and effectiveness of global water monitoring, data interpretation, implementation, policy and research.
      PubDate: 2017-10-16T09:45:28.422975-05:
      DOI: 10.1002/2017WR021047
  • Functional Topology of Evolving Urban Drainage Networks
    • Authors: Soohyun Yang; Kyungrock Paik, Gavan S. McGrath, Christian Urich, Elisabeth Krueger, Praveen Kumar, P. Suresh C. Rao
      Abstract: We investigated the scaling and topology of engineered urban drainage networks (UDNs) in two cities, and further examined UDN evolution over decades. UDN scaling was analyzed using two power-law scaling characteristics widely employed for river networks: (1) Hack's law of length (L)-area (A) [L ∝ Ah], and (2) exceedance probability distribution of upstream contributing area (δ) [P(A ≥ δ) ∼ aδ–ε]. For the smallest UDNs (< 2 km2), length-area scales linearly (h ∼ 1), but power-law scaling (h ∼ 0.6) emerges as the UDNs grow. While P(A ≥ δ) plots for river networks are abruptly truncated, those for UDNs display exponential tempering [P(A ≥ δ)=aδ–ε exp (-cδ)]. The tempering parameter c decreases as the UDNs grow, implying that the distribution evolves in time to resemble those for river networks. However, the power-law exponent ε for large UDNs tends to be greater than the range reported for river networks. Differences in generative processes and engineering design constraints contribute to observed differences in the evolution of UDNs and river networks, including subnet heterogeneity and non-random branching.
      PubDate: 2017-10-16T09:40:51.448265-05:
      DOI: 10.1002/2017WR021555
  • A Lagrangian Transport Eulerian Reaction Spatial (LATERS) Markov Model for
           Prediction of Effective Bimolecular Reactive Transport
    • Authors: Nicole Sund; Giovanni Porta, Diogo Bolster, Rishi Parashar
      Abstract: Prediction of effective transport for mixing driven reactive systems at larger scales, requires accurate representation of mixing at small scales, which poses a significant upscaling challenge. Depending on the problem at hand there can be benefits to using a Lagrangian framework, while in others an Eulerian might have advantages. Here we propose and test a novel hybrid model which attempts to leverage benefits of each. Specifically, our framework provides a Lagrangian closure required for a volume averaging procedure of the advection diffusion reaction equation. This hybrid model is a LAgrangian Transport Eulerian Reaction Spatial Markov model (LATERS Markov model), which extends previous implementations of the Lagrangian Spatial Markov model and maps concentrations to an Eulerian grid to quantify closure terms required to calculate the volume averaged reaction terms. The advantage of this approach is that the Spatial Markov model is known to provide accurate predictions of transport, particularly at preasymptotic early times, when assumptions required by traditional volume averaging closures are least likely to hold; likewise, the Eulerian reaction method is efficient, because it does not require calculation of distances between particles. This manuscript introduces the LATERS Markov model and demonstrates by example its ability to accurately predict bimolecular reactive transport in a simple benchmark 2D porous medium.
      PubDate: 2017-10-13T12:55:22.772977-05:
      DOI: 10.1002/2017WR020821
  • Three-Phase CO2 Flow in A Basalt Fracture Network
    • Authors: Alec O. Gierzynski; Ryan M. Pollyea
      Abstract: Geologic CO2 sequestration in basalt reservoirs is predicated on permanent CO2 isolation via rapid mineralization reactions. This process is supported by a substantial body of evidence, including laboratory experiments documenting rapid mineralization rates, regional storage estimates indicating large, accessible storage reservoirs, and two successful pilot scale studies. Nevertheless, there remains significant uncertainty in the behavior of CO2 flow within basalt fracture networks, particularly in the context estimating physical trapping potential in early time and as CO2 undergoes phase change. In this study, a Monte Carlo numerical model is designed to simulate a supercritical CO2 plume infiltrating a low permeability flood basalt entablature. The fracture network model is based on outcrop-scale LiDAR mapping of Columbia River Basalt, and CO2 flow is simulated within fifty equally probable realizations of the fracture network. The spatial distribution of fracture permeability for each realization is randomly drawn from a basalt aperture distribution, and ensemble results are analyzed with e-type estimates to compute mean and standard deviation of fluid pressure and CO2 saturation. Results of this model after 10 years of simulation suggests that (1) CO2 flow converges on a single dominant flow path, (2) CO2 accumulates at fracture intersections, and (3) variability in permeability can account for a 1.6 m depth interval within which free CO2 may change phase from supercritical fluid to subcritical liquid or gas. In the context of CO2 sequestration in basalt, these results suggest that physical CO2 trapping may be substantially enhanced as carbonate minerals precipitate within the basalt fracture network.
      PubDate: 2017-10-13T12:40:05.702513-05:
      DOI: 10.1002/2017WR021126
  • Symbolic Regression for the Estimation of Transfer Functions of
           Hydrological Models
    • Authors: D. Klotz; M. Herrnegger, K. Schulz
      Abstract: Current concepts for parameter regionalization of spatially distributed rainfall-runoff models rely on the a priori definition of transfer functions that globally map land surface characteristics (such as soil texture, land use, digital elevation, etc.) into the model parameter space. However, these transfer functions are often chosen ad hoc or derived from small-scale experiments. This study proposes and tests an approach for inferring the structure and parametrization of possible transfer functions from runoff data to potentially circumvent these difficulties. The concept uses context free grammars to generate possible proposition for transfer functions. The resulting structure can then be parametrized with classical optimization techniques. Several virtual experiments are performed to examine the potential for an appropriate estimation of transfer function, all of them using a very simple conceptual rainfall-runoff model with data from the Austrian Mur Catchment. The results suggest that a priori defined transfer functions are in general well identifiable by the method. However, the deduction process might be inhibited e.g. by noise in the runoff observation data, often leading to transfer function estimates of lower structural complexity.
      PubDate: 2017-10-13T12:30:38.560338-05:
      DOI: 10.1002/2017WR021253
  • Was That Assumption Necessary' Reconsidering Boundary Conditions for
           Analytical Solutions to Estimate Streambed Fluxes
    • Authors: Charles H. Luce; Daniele Tonina, Ralph Applebee, Timothy DeWeese
      Abstract: Two common refrains about using the one-dimensional advection diffusion equation to estimate fluid fluxes and thermal conductivity from temperature time series in streambeds are that the solution assumes that 1) the surface boundary condition is a sine wave or nearly so, and 2) there is no gradient in mean temperature with depth. Although the mathematical posing of the problem in the original solution to the problem might lead one to believe these constraints exist, the perception that they are a source of error is a fallacy. Here we develop a mathematical proof demonstrating the equivalence of the solution as developed based on an arbitrary (Fourier integral) surface temperature forcing when evaluated at a single given frequency versus that derived considering a single frequency from the beginning. The implication is that any single frequency can be used in the frequency-domain solutions to estimate thermal diffusivity and 1-D fluid flux in streambeds, even if the forcing has multiple frequencies. This means that diurnal variations with asymmetric shapes or gradients in the mean temperature with depth are not actually assumptions, and deviations from them should not cause errors in estimates. Given this clarification, we further explore the potential for using information at multiple frequencies to augment the information derived from time series of temperature.
      PubDate: 2017-10-13T12:30:32.840795-05:
      DOI: 10.1002/2017WR020618
  • Experimental Investigation of Hysteretic Dynamic Capillarity Effect in
           Unsaturated Flow
    • Authors: L. Zhuang; S.M. Hassanizadeh, C. Qin, A. de Waal
      Abstract: The difference between average pressures of two immiscible fluids is commonly assumed to be the same as macroscopic capillary pressure, which is considered to be a function of saturation only. However, under transient conditions, a dependence of this pressure difference on the time rate of saturation change has been observed by many researchers. This is commonly referred to as dynamic capillarity effect. As a first-order approximation, the dynamic term is assumed to be linearly dependent on the time rate of change of saturation, through a material coefficient denoted by τ. In this study, a series of laboratory experiments were carried out to quantify the dynamic capillarity effect in an unsaturated sandy soil. Primary, main and scanning drainage experiments, under both static and dynamic conditions, were performed on a sandy soil in a small cell. The value of the dynamic capillarity coefficient τ was calculated from the air-water pressure differences and average saturation values during static and dynamic drainage experiments. We found a dependence of τ on saturation, which showed a similar trend for all drainage conditions. However, at any given saturation, the value of τ for primary drainage was larger than the value for main drainage and that was in turn larger than the value for scanning drainage. Each data set was fit a simple log-linear equation, with different values of fitting parameters. This non-uniqueness of the relationship between τ and saturation and possible causes are discussed.
      PubDate: 2017-10-13T12:30:26.818404-05:
      DOI: 10.1002/2017WR020895
  • Analog Based Post-Processing of Navigation-Related Hydrological Ensemble
    • Authors: S. Hemri; B. Klein
      Abstract: Inland waterway transport benefits from probabilistic forecasts of water levels as they allow to optimize the ship load and, hence, to minimize the transport costs. Probabilistic state-of-the-art hydrologic ensemble forecasts inherit biases and dispersion errors from the atmospheric ensemble forecasts they are driven with. The use of statistical post-processing techniques like ensemble model output statistics (EMOS) allows for a reduction of these systematic errors by fitting a statistical model based on training data. In this study, training periods for EMOS are selected based on forecast analogs, i.e.∼historical forecasts that are similar to the forecast to be verified. Due to the strong autocorrelation of water levels, forecast analogs have to be selected based on entire forecast hydrographs in order to guarantee similar hydrograph shapes. Custom-tailored measures of similarity for forecast hydrographs comprise hydrological series distance (SD), the hydrological matching algorithm (HMA), and dynamic time warping (DTW). Verification against observations reveals that EMOS forecasts for water level at three gauges along the river Rhine with training periods selected based on SD, HMA, and DTW compare favorably with reference EMOS forecasts, which are based on either seasonal training periods or on training periods obtained by dividing the hydrological forecast trajectories into runoff regimes.
      PubDate: 2017-10-13T12:30:20.768296-05:
      DOI: 10.1002/2017WR020684
  • Estimating the Spatial Extent of Unsaturated Zones in Heterogeneous
           River-Aquifer Systems
    • Authors: Oliver S. Schilling; Dylan J. Irvine, Harrie-Jan Hendricks Franssen, Philip Brunner
      Abstract: The presence of unsaturated zones at the river-aquifer interface has large implications on numerous hydraulic and chemical processes. However, the hydrological and geological controls that influence the development of unsaturated zones have so far only been analyzed with simplified conceptualizations of flow processes, or homogeneous conceptualizations of the hydraulic conductivity in either the aquifer or the riverbed. We systematically investigated the influence of heterogeneous structures in both the riverbed and the aquifer on the development of unsaturated zones. A stochastic 1-D criterion that takes both riverbed and aquifer heterogeneity into account was developed using a Monte Carlo sampling technique. The approach allows the reliable estimation of the upper bound of the spatial extent of unsaturated areas underneath a riverbed. Through systematic numerical modelling experiments, we furthermore show that horizontal capillary forces can reduce the spatial extent of unsaturated zones under clogged areas. This analysis shows how the spatial structure of clogging layers and aquifers influence the propensity for unsaturated zones to develop: In riverbeds where clogged areas are made up of many small, spatially disconnected patches with a diameter in the order of 1 m, unsaturated areas are less likely to develop compared to riverbeds where large clogged areas exist adjacent to unclogged areas. A combination of the stochastic 1-D criterion with an analysis of the spatial structure of the clogging layers and the potential for resaturation can help develop an appropriate conceptual model and inform the choice of a suitable numerical simulator for river-aquifer systems.
      PubDate: 2017-10-10T17:05:46.451445-05:
      DOI: 10.1002/2017WR020409
  • Similarity Assessment of Land Surface Model Outputs in the North American
           Land Data Assimilation System (NLDAS)
    • Authors: Sujay V. Kumar; Shugong Wang, David M. Mocko, Christa D. Peters-Lidard, Youlong Xia
      Abstract: Multi-model ensembles are often used to produce ensemble mean estimates that tend to have increased simulation skill over any individual model output. If multi-model outputs are too similar, an individual LSM would add little additional information to the multi-model ensemble, whereas if the models are too dissimilar, it may be indicative of systematic errors in their formulations or configurations. The article presents a formal similarity assessment of the North American Land Data Assimilation System (NLDAS) multi-model ensemble outputs to assess their utility to the ensemble, using a confirmatory factor analysis. Outputs from four NLDAS Phase 2 models currently running in operations at NOAA/NCEP and four new/upgraded models that are under consideration for the next Phase of NLDAS are employed in this study. The results show that the runoff estimates from the LSMs were most dissimilar whereas the models showed greater similarity for root zone soil moisture, snow water equivalent and terrestrial water storage. Generally, the NLDAS operational models showed weaker association with the common factor of the ensemble and the newer versions of the LSMs showed stronger association with the common factor, with the model similarity increasing at longer timescales. Tradeoffs between the similarity metrics and accuracy measures indicated that the NLDAS operational models demonstrate a larger span in the similarity-accuracy space compared to the new LSMs. The results of the article indicate that simultaneous consideration of model similarity and accuracy at the relevant timescales is necessary in the development of multi-model ensemble.
      PubDate: 2017-10-10T16:46:24.256568-05:
      DOI: 10.1002/2017WR020635
  • Deconstructing the Effects of Flow on DOC, Nitrate, and Major Ion
           Interactions Using a High-Frequency Aquatic Sensor Network
    • Authors: L.E. Koenig; M.D. Shattuck, L.E. Snyder, J.D. Potter, W.H. McDowell
      Abstract: Streams provide a physical linkage between land and downstream river networks, delivering solutes derived from multiple catchment sources. We analyzed high-frequency time series of stream solutes to characterize the timing and magnitude of major ion, nutrient and organic matter transport over event, seasonal, and annual timescales as well as to assess whether nitrate (NO3-) and dissolved organic carbon (DOC) transport are coupled in catchments, which would be expected if they are subject to similar biogeochemical controls throughout the watershed. Our dataset includes in situ observations of NO3-, fluorescent dissolved organic matter (DOC proxy), and specific conductance spanning 2 – 4 years in 10 streams and rivers across New Hampshire, including observations of nearly 700 individual hydrologic events. We found a positive response of NO3- and DOC to flow in forested streams, but watershed development led to a negative relationship between NO3- and discharge, and thus a de-coupling of the overall NO3- and DOC responses to flow. On event and seasonal timescales, NO3- and DOC consistently displayed different behavior. For example, in several streams FDOM yield was greatest during summer storms while NO3- yield was greatest during winter storms. Most streams had generalizable storm NO3- and DOC responses, but differences in the timing of NO3- and DOC transport suggest different catchment sources. Further, certain events, including rain-on-snow and summer storms following dry antecedent conditions, yielded disproportionate NO3- responses. High-frequency data allow for increased understanding of the processes controlling solute variability and will help elucidate their responses to changing climatic regimes.
      PubDate: 2017-10-09T13:01:11.545024-05:
      DOI: 10.1002/2017WR020739
  • Situating Green Infrastructure in Context: A Framework for Adaptive
           Socio-Hydrology in Cities
    • Authors: L.A. Schifman; D.L. Herrmann, W.D. Shuster, A. Ossola, A. Garmestani, M.E. Hopton
      Abstract: Management of urban hydrologic processes using green infrastructure (GI) has largely focused on stormwater management. Thus, design and implementation of GI usually rely on physical site characteristics and local rainfall patterns, and do not typically account for human or social dimensions. This traditional approach leads to highly centralized stormwater management in a disconnected urban landscape, and can deemphasize additional benefits that GI offers, such as increased property value, greenspace aesthetics, heat island amelioration, carbon sequestration, and habitat for biodiversity. We propose a Framework for Adaptive Socio-Hydrology (FrASH) in which GI planning and implementation moves from a purely hydrology-driven perspective to an integrated socio-hydrological approach. This allows for an iterative, multifaceted decision-making process that would enable a network of stakeholders to collaboratively set a dynamic, context-guided project plan for the installation of GI, rather than a ‘one-size-fits-all' installation. We explain how different sectors (e.g., governance, non-governmental organizations, academia, and industry) can create a connected network of organizations that work towards a common goal. Through a graphical Chambered Nautilus model, FrASH is experimentally applied to contrasting GI case studies and shows that this multi-stakeholder, connected, de-centralized network with a co-evolving decision-making project plan results in enhanced multi-functionality, potentially allowing for the management of resilience in urban systems at multiple scales.
      PubDate: 2017-10-09T12:55:24.380714-05:
      DOI: 10.1002/2017WR020926
  • Modeling Transport of Cesium in Grimsel Granodiorite With Micrometer Scale
           Heterogeneities and Dynamic Update of Kd
    • Authors: Mikko Voutilainen; Pekka Kekäläinen, Marja Siitari-Kauppi, Paul Sardini, Eveliina Muuri, Jussi Timonen, Andrew Martin
      Abstract: Transport and retardation of cesium in Grimsel granodiorite taking into account heterogeneity of mineral and pore structure was studied using rock samples overcored from an in situ diffusion test at the Grimsel Test Site. The field test was part of the Long-term Diffusion project (LTD) designed to characterize retardation properties (diffusion and distribution coefficients) under in situ conditions. Results of the LTD experiment for cesium showed that in-diffusion profiles and spatial concentration distributions were strongly influenced by the heterogeneous pore structure and mineral distribution. In order to study the effect of heterogeneity on the in-diffusion profile and spatial concentration distribution, a Time Domain Random Walk (TDRW) method was applied along with a feature for modeling chemical sorption in geological materials. A heterogeneous mineral structure of Grimsel granodiorite was constructed using X-ray micro computed tomography (X-μCT) and the map was linked to previous results for mineral specific porosities and distribution coefficients (Kd) that were determined using C-14-PMMA autoradiography and batch sorption experiments, respectively. After this the heterogeneous structure contains information on local porosity and Kd in 3D. It was found that the heterogeneity of the mineral structure on the micrometer scale affects significantly the diffusion and sorption of cesium in Grimsel granodiorite at the centimeter scale. Furthermore, the modeled in-diffusion profiles and spatial concentration distributions show similar shape and pattern to those from the LTD experiment. It was concluded that the use of detailed structure characterization and quantitative data on heterogeneity can significantly improve the interpretation and evaluation of transport experiments.
      PubDate: 2017-10-09T12:55:20.260347-05:
      DOI: 10.1002/2017WR020695
  • A KDE-Based Random Walk Method for Modeling Reactive Transport With
           Complex Kinetics in Porous Media
    • Authors: Guillem Sole-Mari; Daniel Fernàndez-Garcia, Paula Rodríguez-Escales, Xavier Sanchez-Vila
      Abstract: In recent years a large body of literature has been devoted to study reactive transport of solutes in porous media based on pure Lagrangian formulations. Such approaches have also been extended to accommodate second-order bimolecular reactions, in which the reaction rate is proportional to the concentrations of the reactants. Rather, in some cases, chemical reactions involving two reactants follow more complicated rate laws. Some examples are (1) reaction rate laws written in terms of powers of concentrations, (2) redox reactions incorporating a limiting term (e.g. Michaelis-Menten), or (3) any reaction where the activity coefficients vary with the concentration of the reactants, just to name a few. We provide a methodology to account for complex kinetic bimolecular reactions in a fully Lagrangian framework where each particle represents a fraction of the total mass of a specific solute. The method, built as an extension to the second-order case, is based on the concept of optimal Kernel Density Estimator, which allows the concentrations to be written in terms of particle locations, hence transferring the concept of reaction rate to that of particle location distribution. By doing so, we can update the probability of particles reacting without the need to fully reconstruct the concentration maps. The performance and convergence of the method is tested for several illustrative examples that simulate the Advection-Dispersion-Reaction Equation in a 1D homogeneous column. Finally, a 2D application example is presented evaluating the need of fully describing non-bilinear chemical kinetics in a randomly heterogeneous porous medium.
      PubDate: 2017-10-09T12:50:32.869207-05:
      DOI: 10.1002/2017WR021064
  • Prediction of Hydrologic Characteristics for Ungauged Catchments to
           Support Hydro-Ecological Modeling
    • Authors: Nick R. Bond; Mark J. Kennard
      Abstract: Hydrologic variability is a fundamental driver of ecological processes and species distribution patterns within river systems, yet the paucity of gauges in many catchments means that streamflow data is often unavailable for ecological survey sites. Filling this data-gap is an important challenge in hydro-ecological research. To address this gap, we first test the ability to spatially extrapolate hydrologic metrics calculated from gauged streamflow data to ungauged sites as a function of stream distance and catchment area. Secondly, we examine the ability of statistical models to predict flow regime metrics based on climate and catchment physiographic variables. Our assessment focused on Australia's largest catchment, the Murray-Darling Basin (MDB). We found hydrologic metrics were predictable only between sites within ∼25 km of one another. Beyond this correlations between sites declined quickly. We found less than 40% of fish survey sites from a recent basin-wide monitoring program (n=777 sites) to fall within this 25 km range, thereby greatly limiting the ability to utilize gauge data for direct spatial transposition of hydrologic metrics to biological survey sites. In contrast, statistical model based transposition proved effective in predicting ecologically relevant aspects of the flow regime (including metrics describing central tendency, high and low-flows intermittency, seasonality and variability) across the entire gauge network (median R2 ∼0.54, range 0.39-0.94). Modelled hydrologic metrics thus offer a useful alternative to empirical data when examining biological survey data from ungauged sites. More widespread use of these statistical tools and modelled metrics could expand our understanding of flow-ecology relationships.
      PubDate: 2017-10-09T12:45:55.459559-05:
      DOI: 10.1002/2017WR021119
  • Evaluating the Effects of Tracer Choice and End-Member Definitions on
           Hydrograph Separation Results Across Nested Seasonally Cold Watersheds
    • Authors: Samuel Bansah; Genevieve Ali
      Abstract: Isotope-based hydrograph separation (IHS) is a widely used method in studies of runoff generation and streamflow partitioning. Challenges in choosing and characterizing appropriate tracers and end-members have, however, led to presumably highly uncertain IHS results. Here we tested the effects of end-member definitions and tracer choices on IHS results in nested Prairie watersheds of varying size and landscape characteristics. Specifically, the consideration of eight potential “new” water end-members, eight potential “old” water end-members, and two stable water isotope tracers led to 80 potential IHS results for each stream water sample. IHS-related uncertainty was evaluated using a Gaussian error propagation method. Results show that choosing an appropriate “new” water end-member is most challenging during the freshet: highly variable “old” water fractions associated with high uncertainties were attributed to changing conditions from melting snow only to rain-on-snow. In summer and fall, it was rather the choice of an appropriate “old” water end-member that was most problematic. IHS results obtained using δ18O versus δ2H as a tracer were significantly different except in the flattest and most wind-sheltered watersheds examined. Overall, δ2H-based IHS results were more uncertain than their δ18O-based counterparts. Recommendations are therefore made toward careful selection of a tracer and a sampling strategy aimed at characterizing the most appropriate end-members for IHS, especially when dealing with seasonally cold watersheds.
      PubDate: 2017-10-09T12:45:26.889605-05:
      DOI: 10.1002/2016WR020252
  • On the Control of Solute Mass Fluxes and Concentrations Below Fields
           Irrigated With Low-Quality Water: A Numerical Study
    • Authors: David Russo
      Abstract: The main goal of this study was to test the performance of irrigation water-based and soil-based approaches to control nitrate and chloride mass fluxes and concentrations below the root zone of agricultural fields irrigated with treated waste water (TWW). Using numerical simulations of flow and transport in relatively a fine-textured, unsaturated, spatially heterogeneous, flow domain, scenarios examined include: (i) irrigating with TWW only (REF); (ii) irrigation water is substituted between TWW and desalinized water (ADW); (iii) soil includes a capillary barrier (CB) and irrigating with TWW only (CB+TWW); and (iv) combination of (ii) and a CB (CB+ADW). Considering groundwater quality protection, plausible goals are: (i) to minimize solute discharges leaving the root zone, and, (ii) to maximize the probability that solute concentrations leaving the root zone will not exceed a prescribed, critical value. Results of the analyses suggest that in the case of a seasonal crop (a corn field) subject to irrigations only, with respect to the first goal, the CB+TWW and CB+ADW scenarios provide similar, excellent results, better than the ADW scenario; with respect to the second goal, however, the CB+ADW scenario gave substantially better results than the CB+TWW scenario. In the case a multi-year, perennial crop (a citrus orchard), subject to a sequence of irrigation and rainfall periods, for both solutes, and, particularly, nitrate, with respect to the two goals, both the ADW and CB+ADW scenarios perform better than the CB+TWW scenario. As compared with the REF and CB+TWW scenarios, the ADW and CB+ADW scenarios substantially reduce nitrogen mass fluxes to the groundwater and to the atmosphere, and, essentially, did not reduce nitrogen mass fluxes to the trees. Similar results, even better, were demonstrated for a relatively coarse-textured, spatially heterogeneous soil.
      PubDate: 2017-10-09T12:45:22.987936-05:
      DOI: 10.1002/2017WR021067
  • Statistical Formulation of Generalized Tracer Retention in Fractured Rock
    • Authors: Vladimir Cvetkovic
      Abstract: We study tracer retention in fractured rock by combing Lagrangian and time-domain random walk frameworks, as well as a statistical representation of the retention process. Mass transfer is quantified by the retention time distribution that follows from a Lagrangian coupling between advective transport and mass exchange processes, applicable for advection-dominated transport. A unifying parametrisation is presented for generalised diffusion using two rates denoted by k1 and k2 where k1 is a forward rate and k2 a reverse rate, plus an exponent as an additional parameter. For the Fickian diffusion model, k1 and k2 are related to measurable retention properties of the fracture-matrix by the method of moments, whereas for the non-Fickian case dimensional analysis is used. The derived retention time distributions are exemplified for interpreting tracer tests as well as for predictive modelling of expected tracer breakthrough. We show that non-Fickian effects can be notable when transport is upscaled based on a non-Fickian interpretation of a tracer test for which deviations from Fickianity are relatively small. The statistical representation of retention clearly shows the significance of the forward rate k1 which depends on the active specific surface area and is the most difficult parameter to characterise in the field.
      PubDate: 2017-10-09T12:45:20.219882-05:
      DOI: 10.1002/2017WR021187
  • Design of Remediation Actions for Nutrient Mitigation in the Hyporheic
    • Authors: I. Morén; A. Wörman, J. Riml
      Abstract: Although hyporheic exchange has been shown to be of great importance for the overall water quality of streams, it is rarely considered quantitatively in stream remediation projects. A main driver of hyporheic exchange is the hydraulic head fluctuation along the streambed, which can be enhanced by modifications of the streambed topography. Here we present an analytical 2D spectral subsurface flow model to estimate the hyporheic exchange associated with streambed topographies over a wide range of spatial scales; a model that was validated using tracer-test-results and measurements of hydraulic conductivity. Specifically, engineered steps in the stream were shown to induce a larger hyporheic exchange velocity and shorter hyporheic residence times compared to the observed topography in Tullstorps Brook, Sweden. Hyporheic properties were used to parameterize a longitudinal transport model that accounted for reactions in terms of first-order decay and instantaneous adsorption. Theoretical analyses of the mitigation effect for nitrate due to denitrification in the hyporheic zone shows that there is a Damköhler number of the hyporheic zone, associated with several different stream geomorphologies, that optimizes nitrate mass removal on stream reach scale. This optimum can be limited by the available hydraulic head gradient given by the slope of the stream and the geological constraints of the streambed. The model illustrates the complex interactions between design strategies for nutrient mitigation, hyporheic flow patterns and stream biogeochemistry, and highlights the importance to diagnose a stream prior remediation, specifically to evaluate if remediation targets are transport or reaction controlled.
      PubDate: 2017-10-09T12:41:14.913927-05:
      DOI: 10.1002/2016WR020127
  • Coupled Long-Term Simulation of Reach-Scale Water and Heat Fluxes Across
           the River-Groundwater Interface for Retrieving Hyporheic Residence Times
           and Temperature Dynamics
    • Authors: Matthias Munz; Sascha E. Oswald, Christian Schmidt
      Abstract: Flow patterns in conjunction with seasonal and diurnal temperature variations control ecological and biogeochemical conditions in hyporheic sediments. In particular, hyporheic temperatures have a great impact on many temperature-sensitive microbial processes. In this study, we used 3-D coupled water flow and heat transport simulations applying the HydroGeoSphere code in combination with high resolution observations of hydraulic heads and temperatures to quantify reach-scale water and heat flux across the river-groundwater interface and hyporheic temperature dynamics of a lowland gravel-bed river. The model was calibrated in order to constrain estimates of the most sensitive model parameters. The magnitude and variations of the simulated temperatures matched the observed ones, with an average mean absolute error of 0.7°C and an average Nash Sutcliffe Efficiency of 0.87. Our results indicate that non-submerged streambed structures such as gravel bars cause substantial thermal heterogeneity within the saturated sediment at the reach-scale. Individual hyporheic flow path temperatures strongly depend on the flow path residence time, flow path depth, river and groundwater temperature. Variations in individual hyporheic flow path temperatures were up to 7.9°C, significantly higher than the daily average (2.8°C), but still lower than the average seasonal hyporheic temperature difference (19.2°C). The distribution between flow path temperatures and residence times follow a power law relationship with exponent of about 0.37. Based on this empirical relation, we further estimated the influence of hyporheic flow path residence time and temperature on oxygen consumption which was found to partly increase by up to 29% in simulations.
      PubDate: 2017-10-09T12:41:10.704102-05:
      DOI: 10.1002/2017WR020667
  • Observed Hydrologic Impacts of Landfalling Atmospheric Rivers in the Salt
           and Verde River basins of Arizona, United States
    • Authors: Eleonora M.C. Demaria; Francina Dominguez, Huancui Hu, Gerd von Glinski, Marcos Robles, Jonathan Skindlov, James Walter
      Abstract: Atmospheric Rivers (ARs), narrow atmospheric water vapor corridors, can contribute substantially to winter precipitation in the semiarid Southwest U.S., where natural ecosystems and humans compete for over-allocated water resources. We investigate the hydrologic impacts of 122 ARs that occurred in the Salt and Verde River basins in northeastern Arizona during the cold seasons from 1979-2009. We focus on the relationship between precipitation, snow water equivalent (SWE), soil moisture, and extreme flooding. During the cold season (October through March) ARs contribute an average of 25/29% of total seasonal precipitation for the Salt/Verde River basins, respectively. However, they contribute disproportionately to total heavy precipitation and account for 64%/72% of extreme total daily precipitation (exceeding the 98th percentile). Excess precipitation during AR occurrences contributes to snow accumulation; on the other hand, warmer than normal temperatures during AR landfallings are linked to rain-on-snow processes, an increase in the basins' area contributing to runoff generation, and higher melting lines. Although not all AR events are linked to extreme flooding in the basins, they do account for larger runoff coefficients. On average, ARs generate 43% of the annual maximum flows for the period studied, with 25% of the events exceeding the 10-year return period. Our analysis shows that the devastating 1993 flooding event in the region was caused by AR events. These results illustrate the importance of AR activity on the hydrology of inland semi-arid regions: ARs are critical for water resources, but they can also lead to extreme flooding that affects infrastructure and human activities.
      PubDate: 2017-10-09T12:40:37.137015-05:
      DOI: 10.1002/2017WR020778
  • Synoptic Sampling to Determine Distributed Groundwater-Surface Water
           Nitrate Loading and Removal Potential Along a Lowland River
    • Authors: Henry Pai; Sandra R. Villamizar, Thomas C. Harmon
      Abstract: Delineating pollutant reactive transport pathways that connect local land use patterns to surface water is an important goal. This work illustrates high resolution river mapping of salinity or specific conductance (SC) and nitrate (NO3-) as a potential part of achieving this goal. We observed longitudinal river SC and nitrate distributions using high-resolution synoptic in situ sensing along the lower Merced River (38 river km) in Central California (USA) from 2010 to 2012. We calibrated a distributed groundwater-surface water (GW-SW) discharge model for a conservative solute using 13 synoptic SC sampling events at flows ranging from 1.3 to 31.6 m3 s−1. Nitrogen loads ranged from 0.3 to 1.6 kg N d−1 and were greater following an extended high flow period during a wet winter. Applying the distributed GW-SW discharge estimates to a simplistic reactive nitrate transport model, the model reproduced observed river nitrate distribution well (RRMSE = 5-21%), with dimensionless watershed-averaged nitrate removal (kt) ranging from 0 to 0.43. Estimates were uncertain due to GW nitrate data variability, but the resulting range was consistent with prior removal estimates. At the segment scale, estimated GW-SW nitrate loading ranged from 0 to 17 g NO3- s−1 km−1. Local loading peaked near the middle of the study reach, a location that coincides with a shallow clay lens and with confined animal feed operations in close proximity to the river. Overall, the results demonstrate the potential for high resolution synoptic monitoring to support GW-SW modeling efforts aimed at understanding and managing nonpoint source pollution.
      PubDate: 2017-10-09T12:40:26.324195-05:
      DOI: 10.1002/2017WR020677
  • Flow Signature Analysis of Water Consumption in Nonresidential Building
           Water Networks Using High- and Medium-Resolution Smart Meter Data: Two
           Case Studies
    • Authors: Eoghan Clifford; Sean Mulligan, Joanne Comer, Louise Hannon
      Abstract: Real-time monitoring of water consumption activities can be an effective mechanism to achieve efficient water network management. This approach, largely enabled by the advent of smart metering technologies, is gradually being practiced in domestic and industrial contexts. In particular, identifying water consumption habits from flow-signatures, i.e. the specific end-usage patterns, is being investigated as a means for conservation in both the residential and non-residential context. However, the quality of meter data is bivariate (dependent on number of meters and data temporal resolution) and as a result, planning a smart metering scheme is relatively difficult with no generic design approach available. In this study, a comprehensive medium- to high-resolution smart metering program was implemented at two non-residential trial sites to evaluate the effect of spatial and temporal data aggregation. It was found that medium-resolution water meter data was capable of exposing regular, continuous, peak use and diurnal patterns which reflect group wide end-usage characteristics. The high-resolution meter data permitted flow-signature at a personal end-use level. Through this unique opportunity to observe water usage characteristics via flow signature patterns newly defined hydraulic based design coefficients determined from Poisson rectangular pulse were developed to intuitively aid in the process of pattern discovery with implications for automated activity recognition applications. A smart meter classification and siting index was introduced which categorizes meter resolution in terms of their suitable application.
      PubDate: 2017-09-29T14:20:34.490947-05:
      DOI: 10.1002/2017WR020639
  • A Lagging Model for Describing Drawdown Induced by A Constant-Rate Pumping
           in A Leaky Confined Aquifer
    • Authors: Ye-Chen Lin; Hund-Der Yeh
      Abstract: This study proposes a generalized Darcy's law with considering phase lags in both the water flux and drawdown gradient to develop a lagging flow model for describing drawdown induced by constant-rate pumping (CRP) in a leaky confined aquifer. The present model has a mathematical formulation similar to the dual-porosity model. The Laplace-domain solution of the model with the effect of wellbore storage is derived by the Laplace transform method. The time-domain solution for the case of neglecting the wellbore storage and well radius is developed by the use of Laplace transform and Weber transform. The results of sensitivity analysis based on the solution indicate that the drawdown is very sensitive to the change in each of the transmissivity and storativity. Also, a study for the lagging effect on the drawdown indicates that its influence is significant associated with the lag times. The present solution is also employed to analyze a data set taken from a CRP test conducted in a fractured aquifer in South Dakota, USA. The results show the prediction of this new solution with considering the phase lags has very good fit to the field data, especially at early pumping time. In addition, the phase lags seem to have a scale effect as indicated in the results. In other words, the lagging behavior is positively correlated with the observed distance in the Madison aquifer.
      PubDate: 2017-09-28T12:35:25.94523-05:0
      DOI: 10.1002/2017WR021115
  • Simulating Small-Scale Rainfall Fields Conditioned by Weather State and
           Elevation: A Data-Driven Approach Based On Rainfall Radar Images
    • Authors: Fabio Oriani; Noa Ohana-Levi, Francesco Marra, Julien Straubhaar, Gregoire Mariethoz, Philippe Renard, Arnon Karnieli, Efrat Morin
      Abstract: The quantification of spatial rainfall is critical for distributed hydrological modeling. Rainfall spatial patterns generated by similar weather conditions can be extremely diverse. This variability can have a significant impact on hydrological processes. Stochastic simulation allows generating multiple realizations of spatial rainfall or filling missing data. The simulated data can then be used as input for numerical models to study the uncertainty on hydrological forecasts. In this paper, we use the direct sampling technique to generate stochastic simulations of high-resolution (1-km) daily rainfall fields, conditioned by elevation and weather state. The technique associates historical radar estimates to variables describing the daily weather conditions, such as the rainfall type and mean intensity, and selects radar images accordingly to form a conditional training image set of each day. Rainfall fields are then generated by resampling pixels from these images. The simulation at each location is conditioned by neighbor patterns of rainfall amount and elevation. The technique is tested on the simulation of daily rainfall amount for the eastern Mediterranean. The results show that it can generate realistic rainfall fields for different weather types, preserving the temporal weather pattern, the spatial features, and the complex relation with elevation. The concept of conditional training image provides added value to multiple-point simulation techniques dealing with extremely non-stationary heterogeneities and extensive datasets.
      PubDate: 2017-09-28T12:35:23.090982-05:
      DOI: 10.1002/2017WR020876
  • Geochemical Evolution of Groundwater Flowing Through Arsenic Source
           Sediments in an Aquifer System of West Bengal, India
    • Authors: A. J. Desbarats; T. Pal, P. K. Mukherjee, R. D. Beckie
      Abstract: The source of geogenic arsenic (As) contaminating a shallow aquifer in West Bengal was traced to fine-grained sediments deposited in an abandoned river channel. Along with As-bearing phases, these sediments contain 0.46% co-deposited organic carbon. The release of As and the geochemistry of groundwater within the channel-fill deposits is investigated using a detailed mass balance model supported by aqueous, solid-phase, and mineralogical data. The model describes the evolution of groundwater chemistry along a flow path extending from its recharge in an abandoned channel pond, through the channel fill, to the underlying aquifer. Variations in groundwater composition are explained in terms of mineral weathering of host sediments driven by organic carbon decay. Arsenic is released through the reductive dissolution of goethite and the weathering of chlorite. Concomitantly, some As is sequestered in precipitating vivianite. These competing processes reach equilibrium deeper in the channel-fill sequence as groundwater As concentrations stabilize. The model yields estimates of mineral reaction (or precipitation) rates including rates of organic carbon oxidation (1.15 mmol C L−1 a−1) and net As release (4.57 × 10−4 mmol L−1 a−1). Fine-grained, slightly permeable, deposits such as channel fill containing reactive organic carbon and As-bearing goethite and phyllosilicates are centers of intense chemical weathering conducive to As mobilization.
      PubDate: 2017-09-28T12:30:23.730453-05:
      DOI: 10.1002/2017WR020863
  • Interpreting Repeated Temperature-Depth Profiles For Groundwater Flow
    • Authors: Victor F. Bense; Barret L. Kurylyk, Jonathan van Daal, Martine J. van der Ploeg, Sean K. Carey
      Abstract: Temperature can be used to trace groundwater flows due to thermal disturbances of subsurface advection. Prior hydrogeological studies that have used temperature-depth profiles to estimate vertical groundwater fluxes have either ignored the influence of climate change by employing steady-state analytical solutions or applied transient techniques to study temperature-depth profiles recorded at only a single point in time. Transient analyses of a single profile are predicated on the accurate determination of an unknown profile at some time in the past to form the initial condition. In this study, we use both analytical solutions and a numerical model to demonstrate that boreholes with temperature-depth profiles recorded at multiple times can be analyzed to either overcome the uncertainty associated with estimating unknown initial conditions or to form an additional check for the profile fitting. We further illustrate that the common approach of assuming a linear initial temperature-depth profile can result in significant errors for groundwater flux estimates. Profiles obtained from a borehole in the Veluwe area, Netherlands in both 1978 and 2016 are analysed for an illustrative example. Since many temperature-depth profiles were collected in the late 1970s and 1980s, these previously profiled boreholes represent a significant and underexploited opportunity to obtain repeat measurements that can be used for similar analyses at other sites around the world.
      PubDate: 2017-09-27T09:10:38.237547-05:
      DOI: 10.1002/2017WR021496
  • Impact of Hydrogeological Uncertainty on Estimation of Environmental Risks
           Posed by Hydrocarbon Transportation Networks
    • Authors: V. Ciriello; I. Lauriola, S. Bonvicini, V. Cozzani, V. Di Federico, Daniel M. Tartakovsky
      Abstract: Ubiquitous hydrogeological uncertainty undermines the veracity of quantitative predictions of soil and groundwater contamination due to accidental hydrocarbon spills from onshore pipelines. Such predictions, therefore, must be accompanied by quantification of predictive uncertainty, especially when they are used for environmental risk assessment. We quantify the impact of parametric uncertainty on temporal evolution of two key risk indices, volumes of unsaturated and saturated soil contaminated by a surface spill of light non-aqueous-phase liquids. This is accomplished by treating the relevant uncertain parameters as random variables and deploying two alternative probabilistic models to estimate their effect on predictive uncertainty. A physics-based model is solved with a stochastic collocation method and is supplemented by a global sensitivity analysis. A second model represents the quantities of interest as polynomials of random inputs and has a virtually negligible computational cost, which enables one to explore any number of risk-related contamination scenarios. For a typical oil-spill scenario, our method can be used to identify key flow and transport parameters affecting the risk indices, to elucidate texture-dependent behavior of different soils, and to evaluate, with a degree of confidence specified by the decision-maker, the extent of contamination and the correspondent remediation costs.
      PubDate: 2017-09-27T09:10:20.386624-05:
      DOI: 10.1002/2017WR021368
  • Multiscale Investigation on Biofilm Distribution and its Impact on
           Macroscopic Biogeochemical Reaction Rates
    • Authors: Zhifeng Yan; Chongxuan Liu, Yuanyuan Liu, Vanessa L Bailey
      Abstract: Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models, and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.
      PubDate: 2017-09-25T13:50:25.574125-05:
      DOI: 10.1002/2017WR020570
  • A Framework for Validation of Remotely Sensed Precipitation and
           Evapotranspiration Based on the Budyko Hypothesis
    • Authors: Akash Koppa; Mekonnen Gebremichael
      Abstract: Despite offering spatially and temporally continuous measurements, the use of remotely-sensed P and E in data-scarce catchments is hindered by the lack of ground-based measurements that enable comprehensive validation. This study proposes a novel validation framework that characterizes the combined error in the long-term average estimates of remotely sensed P and E by making use of the Budyko hypothesis, specifically Fu's equation. A Root Mean Square Error (RMSE) based error metric that is capable of translating individual biases in P and E estimates onto the Budyko space is developed. A controlled sensitivity experiment using data from Model Parameter Estimation Experiment (MOPEX) catchments in United States showed that the developed error metric is more sensitive to biases in P compared to biases in estimates of E. Validating the framework using combinations of different satellite-based estimates of P and E revealed that the framework succeeds in arriving at the same conclusions as a traditional validation method with regards to the quality of P and E datasets. The framework offers a physically consistent, parametrically efficient basis for the selection of remotely sensed P and E datasets for hydrologic studies. Due to lack of consideration for catchment storage in the formulation of Fu's equation, the developed error metric is limited to long temporal time scales. As a result, the error metric is capable of characterizing the bias in P and E datasets and not the variance.
      PubDate: 2017-09-25T10:42:00.598928-05:
      DOI: 10.1002/2017WR020593
  • Weather Typing-Based Flood Frequency Analysis Verified for Exceptional
           Historical Events of Past 500 Years Along the Meuse River
    • Authors: J. De Niel; G. Demarée, P. Willems
      Abstract: Governments, policy makers and water managers are pushed by recent socio-economic developments such as population growth and increased urbanization inclusive of occupation of floodplains to impose very stringent regulations on the design of hydrological structures. These structures need to withstand storms with return periods typically ranging between 1,250 and 10,000 years. Such quantification involves extrapolations of systematically measured instrumental data, possibly complemented by quantitative and/or qualitative historical data and paleoflood data. The accuracy of the extrapolations is, however, highly unclear in practice.In order to evaluate extreme river peak flow extrapolation and accuracy, we studied historical and instrumental data of the past 500 years along the Meuse river. We moreover propose an alternative method for the estimation of the extreme value distribution of river peak flows, based on weather types derived by sea level pressure reconstructions. This approach results in a more accurate estimation of the tail of the distribution, where current methods are underestimating the design levels related to extreme high return periods. The design flood for a 1,250 year return period is estimated at 4,800 m3s−1 for the proposed method, compared with 3,450 m3s−1 and 3,900 m3s−1 for a traditional method and a previous study.
      PubDate: 2017-09-25T10:38:38.190227-05:
      DOI: 10.1002/2017WR020803
  • Minimum Hydraulic Resistance and Least Resistance Path in Heterogeneous
           Porous Media
    • Authors: Calogero B. Rizzo; Felipe P. J. de Barros
      Abstract: The transport dynamics of a solute plume within a porous media are strictly related to the hydrogeological properties. Despite progress in simulation techniques, quantifying transport in strongly heterogeneous geological formations is still a challenge. It is well established that the heterogeneity of the hydraulic conductivity (K) field is one of the main factors controlling the solute transport phenomena. Increasing the heterogeneity level of the K-field will enhance the probability of having preferential paths, that are fundamental in predicting the first time arrivals. In this work, we focus on the relationship between the connectivity structure of the K-field to transport quantities. We compute connectivity based on the concept of hydraulic resistance and the corresponding least resistance paths. We present a new efficient algorithm based on graph theory that enables to extract useful information from the K-field without resorting to the solution of the governing equations for flow and transport. For this reason, an exhaustive and fast analysis can be carried out using a Monte Carlo framework for randomly generated K-fields which enables the computation of the least resistance path and its uncertainty. We examine the minimum hydraulic resistance for both multi-Gaussian (MG) and non-MG log K-fields. The analysis carried out indicates that the expected value of the minimum hydraulic resistance between two points scales exponentially with the standard deviation of the log K-field. Given the strong correlation with plume's first time arrival, our results illustrate how hydraulic resistance and least resistance path can be used as a computationally efficient risk metric.
      PubDate: 2017-09-25T10:37:37.359633-05:
      DOI: 10.1002/2017WR020418
  • A Global Assessment of Runoff Sensitivity to Changes in Precipitation,
           Potential Evaporation, and Other Factors
    • Authors: Wouter R. Berghuijs; Joshua R. Larsen, Tim H.M. van Emmerik, Ross A. Woods
      Abstract: Precipitation (P) and potential evaporation (Ep) are commonly studied drivers of changing freshwater availability, as aridity (Ep/P) explains ∼90% of the spatial differences in mean runoff across the globe. However, it is unclear if changes in aridity over time are also the most important cause for temporal changes in mean runoff and how this degree of importance varies regionally. We show that previous global assessments that address these questions do not properly account for changes due to precipitation, and thereby strongly underestimate the effects of precipitation on runoff. To resolve this shortcoming, we provide an improved Budyko-based global assessment of the relative and absolute sensitivity of precipitation, potential evaporation, and other factors to changes in mean annual runoff. The absolute elasticity of runoff to potential evaporation changes is always lower than the elasticity to precipitation changes. The global pattern indicates that for 83% of the land grid cells runoff is most sensitive to precipitation changes, while other factors dominate for the remaining 17%. This dominant role of precipitation contradicts previous global assessments, which considered the impacts of aridity changes as a ratio. We highlight that dryland regions generally display high absolute sensitivities of runoff to changes in precipitation, however within dryland regions the relative sensitivity of runoff to changes in other factors (e.g. changing climatic variability, CO2 – vegetation feedbacks and anthropogenic modifications to the landscape) is often far higher. Nonetheless, at the global scale, surface water resources are most sensitive to temporal changes in precipitation.
      PubDate: 2017-09-25T10:37:30.673841-05:
      DOI: 10.1002/2017WR021593
  • The Impact of Urbanization on Temporal Changes in Sediment Transport in a
           Gravel-Bed Channel in Southern Ontario, Canada
    • Authors: B. D. Plumb; W. K. Annable, P. J. Thompson, M. A. Hassan
      Abstract: A field investigation has been undertaken to characterize the event-based bedload transport dynamics of a highly urbanized gravel-bed stream. A combination of direct bedload and tracer particle measurements were taken over a three-year period during which time approximately 30 sediment mobilizing events occurred. Sediment transport measurements were used to calibrate a fractional bedload transport model and combined with hydrometric data which represent four different land-use conditions (ranging from rural to highly urbanized) to analyze the differences in discharge magnitude and frequency and its impact on sediment transport. Fractional transport analysis of the bedload measurements indicates that frequent intermediate discharge events can mobilize sand and fine gravel to an approximate equally mobile condition, however, the transport rates at these discharges exhibit greater variability than at discharges above the bankfull discharge. Path lengths of the coarse fraction, measured using tracer clasts, are insensitive to peak discharge, and instead transport at distances less than those reported in other gravel-bed channels, which is attributed to the shorter duration discharge events common to urban streams. The magnitude-frequency analysis reveals that the frequency, time and volume of competent sediment mobilizing events is increasing with urbanization. Variability in effective discharges suggests that a range of discharges, spanning between frequent, low magnitude events to less frequent, high magnitude events are geomorphically significant. However, trends in the different land-use scenarios suggest that urbanization is shifting the geomorphic significance towards more frequent, lower magnitude events.
      PubDate: 2017-09-25T10:37:20.223833-05:
      DOI: 10.1002/2016WR020288
  • Role of Micro-Topographic Variability on the Distribution of Inorganic
           Soil-Nitrogen Age in Intensively Managed Landscape
    • Authors: Dong K. Woo; Praveen Kumar
      Abstract: How does the variability of topography structure the spatial heterogeneity of nutrient dynamics' In particular, what role does micro-topographic depression play in the spatial and temporal dynamics of nitrate, ammonia, and ammonium' We explore these questions using the 3D simulation of their joint dynamics of concentration and age. To explicitly resolve micro-topographic variability and its control on moisture, vegetation, and carbon-nitrogen dynamics, we use a high-resolution LiDAR data over an agricultural site under a corn-soybean rotation in the Intensively Managed landscapes Critical Zone Observatory in the U.S. Midwest. We utilize a hybrid CPU-GPU parallel computing architecture to reduce the computational cost associated with such high-resolution simulations. Our results show that in areas that present closed topographic depressions, relatively lower nitrate concentration and age are observed compared to elsewhere. The periodic ponding in depressions increases the downward flux of water that carries more dissolved nitrate to the deeper soil layer. However, the variability in the depressions is relatively higher as a result of the episodic ponding pattern. When aggregate efflux from the soil domain at the bottom of the soil is considered, we find a gradual decrease in the age on the rising limb of nitrate efflux and a gradual increase on the falling limb. In addition, the age of the nitrate efflux ranges from 4 to 7 years. These are significantly higher as compared to the ages associated with a non-reactive tracer indicating that they provide an inaccurate estimate of residence time of a reactive constituent through the soil column.
      PubDate: 2017-09-18T08:26:33.676376-05:
      DOI: 10.1002/2017WR021053
  • The Pathway-Flow Relative Permeability of CO2: Measurement by Lowered
           Pressure Drops
    • Authors: Yi Zhang; Osamu Nishizawa, Hyuck Park, Tamotsu Kiyama, Xinglin Lei, Ziqiu Xue
      Abstract: We introduce a simple method to measure the relative permeability of supercritical CO2 in low-permeability rocks. The method is built on the assumption of the stability of formed CO2 percolation pathway under lowered pressure drops. Initially, a continuous CO2 flow pathway is created under a relatively high-pressure drop. Then, several subsequent steps of lowered pressure drops are performed while monitoring the associated flow rates. When the pressure drop is lower than a threshold value, the created flow pathway is assumed to be adequately stable and does not vary significantly during successive flows, with the average saturation and flow rate achieving a quasi-steady state. The relative permeability of CO2 is then calculated from the relationship between the pressure drop and flow rate at several lowered pressure drops according to the extended form of Darcy's law. We demonstrate this method using both numerical modeling and an experimental test using X-ray CT imaging. The results indicate the validity of the assumption for the stability of flow pathway under lowered pressure drops. A linear relationship between the lowered pressure drops and the corresponding CO2 flow rate is found. Furthermore, the measurement results suggest that the relative permeability of CO2 can still be high in low-permeability rocks if the CO2 saturation is higher than the threshold value required to build a flow pathway. The proposed method is important for measuring the pathway-flow relative permeability of non-wetting fluids in low-permeability rocks.
      PubDate: 2017-09-18T08:25:28.429972-05:
      DOI: 10.1002/2017WR020580
  • The Growth of Hydrological Understanding: Technologies, Ideas and Societal
           Needs Shape the Field
    • Authors: Murugesu Sivapalan; Günter Blöschl
      Abstract: Inspired by the work of Newton, Darwin and Wegener, this paper tracks the drivers and dynamics that have shaped the growth of hydrological understanding over the last century. On the basis of an interpretation of this history the paper then speculates about what kind of future is in store for hydrology and how we can better prepare for it. The historical narrative underpinning this analysis indicates that progress in hydrological understanding is brought about by changing societal needs and technological opportunities: new ideas are generated by hydrologists through addressing societal needs with the technologies of their time. We suggest that progress in hydrological understanding over the last century has expressed itself through repeated cycles of euphoria and disenchantment, which have served as stimuli for the progress. The progress, for it to happen, also needed inspirational leaders as well as a supportive scientific community that provided the backdrop to major advances in the field. The paper concludes that, in a similar way to how Newton, Darwin and Wegener conducted their research, hydrology too can benefit from synthesis activities aimed at “connecting the dots”.
      PubDate: 2017-09-18T08:20:20.555602-05:
      DOI: 10.1002/2017WR021396
  • Flow and Residence Times of Dynamic River Bank Storage and
           Sinuosity-Driven Hyporheic Exchange
    • Authors: J. D. Gomez-Velez; J. L. Wilson, M. B. Cardenas, J. W. Harvey
      Abstract: Hydrologic exchange fluxes (HEFs) vary significantly along river corridors due to spatio-temporal changes in discharge and geomorphology. This variability results in the emergence of biogeochemical hot-spots and hot-moments that ultimately control solute and energy transport and ecosystem services from the local to the watershed scales. In this work, we use a reduced-order model to gain mechanistic understanding of river bank storage and sinuosity-driven hyporheic exchange induced by transient river discharge. This is the first time that a systematic analysis of both processes is presented and serves as an initial step to propose parsimonious, physics-based models for better predictions of water quality at the large watershed scale. The effects of channel sinuosity, alluvial valley slope, hydraulic conductivity, and river stage forcing intensity and duration are encapsulated in dimensionless variables that can be easily estimated or constrained. We find that the importance of perturbations in the hyporheic zone's flux, residence times, and geometry is mainly explained by two dimensionless variables representing the ratio of the hydraulic time constant of the aquifer and the duration of the event (Γd) and the importance of the ambient groundwater flow (Δh*). Our model additionally shows that even systems with small sensitivity, resulting in small changes in the hyporheic zone extent, are characterized by highly variable exchange fluxes and residence times. These findings highlight the importance of including dynamic changes in hyporheic zones for typical HEF models such as the transient storage model.
      PubDate: 2017-09-15T08:11:13.684942-05:
      DOI: 10.1002/2017WR021362
  • Automated River Reach Definition Strategies: Applications for the Surface
           Water and Ocean Topography Mission
    • Authors: Renato Prata de Moraes Frasson; Rui Wei, Michael Durand, J. Toby Minear, Alessio Domeneghetti, Guy Schumann, Brent A. Williams, Ernesto Rodriguez, Christophe Picamilh, Christine Lion, Tamlin Pavelsky, Pierre-André Garambois
      Abstract: The upcoming Surface Water and Ocean Topography (SWOT) mission will measure water surface heights and widths for rivers wider than 100 m. At its native resolution, SWOT height errors are expected to be on the order of meters, which prevents the calculation of water surface slopes and the use of slope-dependent discharge equations. To mitigate height and width errors, the high-resolution measurements will be grouped into reaches (∼5 to 15 km), where slope and discharge are estimated. We describe three automated river segmentation strategies for defining optimum reaches for discharge estimation: 1) arbitrary lengths, 2) identification of hydraulic controls, 3) sinuosity. We test our methodologies on 9 and 14 simulated SWOT overpasses over the Sacramento and the Po Rivers respectively, which we compare against hydraulic models of each river. Our results show that generally, height, width, and slope errors decrease with increasing reach length. However, the hydraulic controls and the sinuosity methods led to better slopes and often height errors that were either smaller or comparable to those of arbitrary reaches of compatible sizes. Estimated discharge errors caused by the propagation of height, width, and slope errors through the discharge equation were often smaller for sinuosity (on average 8.5% for the Sacramento and 6.9% for the Po) and hydraulic controls (Sacramento: 7.3% and Po: 5.9%) reaches than for arbitrary reaches of comparable lengths (Sacramento: 8.6% and Po: 7.8%). This analysis suggests that reach definition methods that preserve the hydraulic properties of the river network may lead to better discharge estimates.
      PubDate: 2017-09-15T08:10:30.033433-05:
      DOI: 10.1002/2017WR020887
  • Changes in Pore Water Quality After Peatland Restoration: Assessment of a
           Large-Scale, Replicated Before-After-Control-Impact Study in Finland
    • Authors: Meseret Walle Menberu; Hannu Marttila, Teemu Tahvanainen, Janne S. Kotiaho, Reijo Hokkanen, Bjørn Kløve, Anna-Kaisa Ronkanen
      Abstract: Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures, but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically over-restored (inundated) showed higher Ptot, Ntot and DOC than well or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2-6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0-4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year post-restoration, but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, watertable level, and soil and air temperature.
      PubDate: 2017-09-13T09:35:49.327822-05:
      DOI: 10.1002/2017WR020630
  • Using paired in Situ High Frequency Nitrate Measurements to Better
           Understand Controls on Nitrate Concentrations and Estimate Nitrification
           Rates in a Wastewater Impacted River
    • Authors: T. E. C. Kraus; K. O'Donnell, B. D. Downing, J. R. Burau, B.A. Bergamaschi
      Abstract: We used paired continuous nitrate (NO3-) measurements along a tidally-affected river receiving wastewater discharge rich in ammonium (NH4+) to quantify rates of change in NO3- concentration (RΔNO3) and estimate nitrification rates. NO3- sensors were deployed 30 km apart in the Sacramento River, California (USA), with the upstream station located immediately above the regional wastewater treatment plant (WWTP). We used a travel-time model to track water transit between the stations and estimated RΔNO3 every 15-minutes (October 2013-September 2014). Water temperature was strongly related to changes in NO3- concentration. In the presence of wastewater, RΔNO3 was generally positive, ranging from about 7 µM d−1 in the summer to near zero in the winter. Numerous periods when the WTTP halted discharge allowed the RΔNO3 to be estimated under no-effluent conditions, and revealed that in the absence of effluent net gains in NO3- were substantially lower but still positive in the summer and negative (net sink) in the winter. Nitrification rates of effluent derived NH4 (RNitrific_E) were estimated from the difference between RΔNO3 measured in the presence versus absence of effluent, and ranged from 1.5-3.4 µM d−1, which is within literature values but ten-fold greater than recently reported for this region. RNitrific_E was generally lower in winter (∼2 µM d−1) than summer (∼3 µM d−1). This in situ, high frequency approach provides advantages over traditional discrete sampling, incubation, and tracer methods, and allows measurements to be made over broad areas for extended periods of time. Incorporating this approach into environmental monitoring programs will facilitate our ability to protect and manage aquatic systems.
      PubDate: 2017-09-13T09:35:28.249057-05:
      DOI: 10.1002/2017WR020670
  • 20th-Century Hydro-Meteorological Reconstructions to Study the
           Multidecadal Variations of the Water Cycle Over France
    • Authors: R. Bonnet; J. Boé, G. Dayon, E. Martin
      Abstract: Characterizing and understanding the multi-decadal variations of the continental hydrological cycle is a challenging issue given the limitation of observed data-sets. In this paper, a new approach to derive 20th century hydrological reconstructions over France with an hydrological model is presented. The method combines the results of long-term atmospheric reanalyses downscaled with a stochastic statistical method and homogenized station observations to derive the meteorological forcing needed for hydrological modeling. Different methodological choices are tested and evaluated. We show that using homogenized observations to constrain the results of statistical downscaling help to improve the reproduction of precipitation, temperature and river flows variability. In particular, it corrects some unrealistic long-term trends associated with the atmospheric reanalyses. Observationally-constrained reconstructions therefore constitute a valuable dataset to study the multi-decadal hydrological variations over France. Thanks to these reconstructions, we confirm that the multi-decadal variations previously noted in French river flows have mainly a climatic origin. Moreover, we show that multi-decadal variations exist in other hydrological variables (evapotranspiration, snow cover and soil moisture). Depending on the region, the persistence from spring to summer of soil moisture or snow anomalies generated during spring by temperature and precipitation variations may explain river flows variations in summer, when no concomitant climate variations exist.
      PubDate: 2017-09-13T08:14:02.855379-05:
      DOI: 10.1002/2017WR020596
  • Early-Time Solution of the Horizontal Unconfined Aquifer in the Build-Up
    • Authors: Elias Gravanis; Evangelos Akylas
      Abstract: We derive the early-time solution of the Boussinesq equation for the horizontal unconfined aquifer in the build-up phase under constant recharge and zero inflow. The solution is expressed as a power series of a suitable similarity variable, which is constructed so that to satisfy the boundary conditions at both ends of the aquifer, that is, it is a polynomial approximation of the exact solution. The series turns out to be asymptotic and it is regularized by re-summation techniques that are used to define divergent series. The outflow rate in this regime is linear in time, and the (dimensionless) coefficient is calculated to eight significant figures. The local error of the series is quantified by its deviation from satisfying the self-similar Boussinesq equation at every point. The local error turns out to be everywhere positive, hence, so is the integrated error, which in turn quantifies the degree of convergence of the series to the exact solution.
      PubDate: 2017-09-12T14:00:20.702366-05:
      DOI: 10.1002/2016WR019567
  • Effects of the Structure of Water Rights on Agricultural Production During
           Drought: A Spatiotemporal Analysis of California's Central Valley
    • Authors: K. S. Nelson; E. K. Burchfield
      Abstract: California's Central Valley region has been called the “bread-basket” of the United States. The region is home to one of the most productive agricultural systems on the planet. Such high levels of agricultural productivity require large amounts of fresh water for irrigation. However, the long-term availability of water required to sustain high levels of agricultural production is being called into question following the latest drought in California. In this paper, we use Bayesian multilevel spatiotemporal modeling techniques to examine the influence of the structure of surface water rights in the Central Valley on agricultural production during the recent drought. California is an important place to study these dynamics as it is the only state to recognize the two dominant approaches to surface water management in the United States: riparian and appropriative rights. In this study, Bayesian spatiotemporal modeling is employed to account for spatial processes that have the potential to influence the effects of water right structures on agricultural production. Results suggest that, after accounting for spatiotemporal dependencies in the data, seniority in surface water access significantly improves crop health and productivity on cultivated lands, but does not independently affect the ability to maintain cultivated extent. In addition, agricultural productivity in watersheds with more junior surface water rights show less sensitivity to cumulative drought exposure than other watersheds, however the extent of cultivation in these same watersheds is relatively more sensitive to cumulative drought exposure.
      PubDate: 2017-09-12T13:55:58.373109-05:
      DOI: 10.1002/2017WR020666
  • Role of Sectoral Transformation in the Evolution of Water Management Norms
           in Agricultural Catchments: A Socio-hydrologic Modeling Analysis
    • Authors: M. Roobavannan; J. Kandasamy, S. Pande, S. Vigneswaran, M. Sivapalan
      Abstract: This study is focused on the water-agriculture-environment nexus as it played out in the Murrumbidgee River Basin, eastern Australia, and how co-evolution of society and water management actually transpired. Over 100 years of agricultural development the Murrumbidgee Basin experienced a “pendulum swing” in terms of water allocation, initially exclusively for agriculture production changing over to reallocation back to the environment. In this paper, we hypothesize that in the competition for water between economic livelihood and environmental wellbeing, economic diversification was the key to swinging community sentiment in favor of environmental protection, and triggering policy action that resulted in more water allocation to the environment. To test this hypothesis, we developed a socio-hydrology model to link the dynamics of the whole economy (both agriculture and industry composed of manufacturing and services) to the community's sensitivity towards the environment. Changing community sensitivity influenced how water was allocated and governed and how the agricultural sector grew relative to the industrial sector (composed of manufacturing and services sectors). In this way we show that economic diversification played a key role in influencing the community's values and preferences with respect to the environment and economic growth. Without diversification, model simulations show that the community would not have been sufficiently sensitive and willing enough to act to restore the environment, highlighting the key role of sectoral transformation in achieving the goal of sustainable agricultural development.
      PubDate: 2017-09-12T13:55:24.075972-05:
      DOI: 10.1002/2017WR020671
  • Interaction Between Ecohydrologic Dynamics and Microtopographic
           Variability Under Climate Change
    • Authors: Phong V. V. Le; Praveen Kumar
      Abstract: Vegetation acclimation resulting from elevated atmospheric CO2 concentration, along with response to increased temperature and altered rainfall pattern, is expected to result in emergent behavior in ecologic and hydrologic functions. We hypothesize that microtopographic variability, which are landscape features typically of the length scale of the order of meters, such as topographic depressions, will play an important role in determining this dynamics by altering the persistence and variability of moisture. To investigates these emergent ecohydrologic dynamics, we develop a modeling framework, Dhara, which explicitly incorporates the control of microtopographic variability on vegetation, moisture, and energy dynamics. The intensive computational demand from such a modeling framework that allows coupling of multi-layer modeling of the soil-vegetation continuum with 3-D surface-subsurface flow processes is addressed using hybrid CPU-GPU parallel computing framework. The study is performed for different climate change scenarios for an intensively managed agricultural landscape in central Illinois, U.S.A., which is dominated by row crop agriculture, primarily soybean (Glycine max) and maize (Zea mays). We show that rising CO2 concentration will decrease evapotranspiration, thus increasing soil moisture and surface water ponding in topographic depressions. However, increased atmospheric demand from higher air temperature overcomes this conservative behavior resulting in a net increase of evapotranspiration, leading to reduction in both soil moisture storage and persistence of ponding. These results shed light on the linkage between vegetation acclimation under climate change and microtopography variability controls on ecohydrologic processes.
      PubDate: 2017-09-12T13:50:40.355564-05:
      DOI: 10.1002/2017WR020377
  • On the Longitudinal Dispersion in Conservative Transport Through
           Heterogeneous Porous Formations at Finite Peclet Numbers
    • Authors: Gerardo Severino; Salvatore Cuomo, Angelo Sommella, Guido D'urso
      Abstract: We consider transport of a conservative solute through an aquifer as determined: i) by the advective velocity, which depends upon the hydraulic conductivity K, and ii) by the local spreading due to the pore-scale dispersion (PSD). The flow is steady, and it takes place in a porous formation where, owing to its erratic spatial variations, the hydraulic log-conductivity Y ≡ ln K is modeled as a stationary Gaussian random field. The relative effect of the above mechanisms i)-ii) is quantified by the Peclet number (Pe) which, in most of the previous studies, was considered infinite (i.e. no PSD) due to the overtake of advective heterogeneities upon the PSD. Here, we aim at generalizing such studies by accounting for the impact of finite Pe on conservative transport. Previous studies on the topic required extensive numerical computations [see, e.g. Fiori, 1996]. In the present note we remove the computational burden by adopting the rational approximate expression of Dagan and Cvetkovic [1993] for the covariance of the velocity field. This allows one to obtain closed form expressions for the quantities characterizing the longitudinal plume's dispersion. Transport can be straightforwardly investigated by dealing with a modified Peclet number (Pe¯) incorporating both the PSD and the aquifer's anisotropy. The satisfactory match to Cape Cod field data suggests that the present theoretical results lend themselves as a useful tool to assess the impact of the PSD upon conservative transport through heterogeneous porous formations.
      PubDate: 2017-09-12T13:50:22.041095-05:
      DOI: 10.1002/2017WR020904
  • Fusion of Time-Lapse Gravity Survey and Hydraulic Tomography for
           Estimating Spatial Varying Hydraulic Conductivity and Specific Yield
    • Authors: Jui-Pin Tsai; Tian-Chyi Jim Yeh, Ching-Chung Cheng, Yuanyuan Zha, Liang-Cheng Chang, Cheinway Hwang, Yu-Li Wang, Yonghong Hao
      Abstract: Hydraulic conductivity (K) and specific yield (Sy) are important aquifer parameters, pertinent to groundwater resources management and protection. These parameters are commonly estimated through a traditional cross-well pumping test. Employing the traditional approach to obtain detailed spatial distributions of the parameters over a large area is generally formidable. For this reason, this study proposes a stochastic method that integrates hydraulic head and time-lapse gravity based on hydraulic tomography (HT) to efficiently derive the spatial distribution of K and Sy over a large area. This method is demonstrated using several synthetic experiments. Results of these experiments show that the K and Sy fields estimated by joint inversion of the gravity and head data set from sequential injection tests in unconfined aquifers are superior to those from the HT based on head data alone. We attribute this advantage to the mass constraint imposed on HT by gravity measurements. Besides, we find that gravity measurement can detect the change of aquifer's groundwater storage at kilometer scale, as such they can extend HT's effectiveness over greater volumes of the aquifer. Furthermore, we find that the accuracy of the estimated fields is improved as the number of the gravity stations is increased. The gravity station's location, however, has minor effects on the estimates if its effective gravity integration radius covers the well field.
      PubDate: 2017-09-12T13:45:47.002971-05:
      DOI: 10.1002/2017WR020459
  • Pre-Darcy Flow in Porous Media
    • Authors: Morteza Dejam; Hassan Hassanzadeh, Zhangxin Chen
      Abstract: Fluid flow in porous media is very important in a wide range of science and engineering applications. The entire establishment of fluid flow application in porous media is based on the use of an experimental law proposed by Darcy in 1856. There are evidences in the literature that the flow of a fluid in consolidated and unconsolidated porous media does not follow Darcy law at very low fluxes, which is called pre-Darcy flow. In this paper, the unsteady flow regimes of a slightly compressible fluid under the linear and radial pre-Darcy flow conditions are modeled and the corresponding highly nonlinear diffusivity equations are solved analytically by aid of a generalized Boltzmann transformation technique. The influence of pre-Darcy flow on the pressure diffusion for homogenous porous media is studied in terms of the nonlinear exponent and the threshold pressure gradient. In addition, the pressure gradient, flux, and cumulative production per unit area are compared with the classical solution of the diffusivity equation based on Darcy flow. The presented results advance our understanding of fluid flow in low permeability media such as shale and tight formations where pre-Darcy is the dominant flow regime.
      PubDate: 2017-09-12T13:40:28.335826-05:
      DOI: 10.1002/2017WR021257
  • Evidence for the Activation of Shallow Preferential Flow Paths in a
           Tropical Panama Watershed Using Germanium and Silicon
    • Authors: Christopher B. Gardner; Guy F. Litt, W. Berry Lyons, Fred L. Ogden
      Abstract: In humid tropical watersheds, the hydrologic flow paths taken by rain event waters and how they interact with groundwater and soil matrix water to form streamflow are poorly understood. Preferential flow paths (PFPs) confound storm infiltration processes, especially in the humid tropics where PFPs are common. This work applies germanium (Ge) and silicon (Si) as natural flow path tracers in conjunction with water stable isotopes and electrical conductivity to examine the rapid delivery of shallow soil water, the activation of PFPs, and event water partitioning in an experimental catchment in central Panama. We employed a three component mixing model for hydrograph separation using the following end-member waters: (i) baseflow (high [Si], low ≥, low Ge/Si ratio), (ii) dilute canopy throughfall (low [Si], low ≥), and (iii) shallow ( ∼35 mm), we detected the third shallow soil water component with an elevated ≥ and Ge/Si ratio. This component reached its maximum during the hydrograph's receding limb coincident with the maximum event fraction, and increased proportionally to the total storm rainfall exceeding ∼35 mm. Only shallow (
      PubDate: 2017-09-12T13:35:42.161641-05:
      DOI: 10.1002/2017WR020429
  • Hydrologic Impacts of Landslide Disturbances: Implications for
           Remobilization and Hazard Persistence
    • Authors: Ben B. Mirus; Joel B. Smith, Rex L. Baum
      Abstract: Landslides typically alter hillslope topography, but may also change the hydrologic connectivity and subsurface water-storage dynamics. In settings where mobile materials are not completely evacuated from steep slopes, influences of landslide disturbances on hillslope hydrology and susceptibility to subsequent failures remain poorly characterized. Since landslides often recur at the site of previous failures, we examine differences between a stable vegetated hillslope (VH) and a recent landslide (LS). These neighboring hillslopes exhibit similar topography and are situated on steep landslide-prone coastal bluffs of glacial deposits along the northeastern shore of Puget Sound, Washington. Our control hillslope, VH, is mantled by a heterogeneous colluvium, supporting a dense forest. In early 2013, our test hillslope, LS, also supported a forest before a landslide substantially altered the topography and disturbed the hillslope. In 2015, we observed a clay-rich landslide deposit at LS with sparse vegetation and limited root reinforcement, soil structures, and macropores. Our characterization of the sites also found matrix porosity and hydraulic conductivity are both lower at LS. Continuous monitoring during 2015-2016 revealed reduced effective precipitation at VH (due to canopy interception), an earlier seasonal transition to near-saturated conditions at LS, and longer persistence of positive pore pressures and slower drainage at LS (both seasonally and between major storm events). These differences, along with episodic, complex slope failures at LS support the hypothesis that, despite a reduced average slope, other disturbances introduced by landsliding may promote the hydrologic conditions leading to slope instability, thus contributing to the persistence of landslide hazards.
      PubDate: 2017-09-12T13:25:33.543767-05:
      DOI: 10.1002/2017WR020842
  • Nonlinear filtering effects of reservoirs on flood frequency curves at the
           regional scale
    • Authors: Wei Wang; Hong-Yi Li, L. Ruby Leung, Wondmagegn Yigzaw, Jianshi Zhao, Hui Lu, Zhiqun Deng, Yonas Demisie, Günter Blöschl
      Abstract: Reservoir operations may alter the characteristics of Flood Frequency Curve (FFC) and challenge the basic assumption of stationarity used in flood frequency analysis. This paper presents a combined data-modeling analysis of reservoir as a nonlinear filter of runoff routing that alters the FFCs. A dimensionless Reservoir Impact Index (RII), defined as the total upstream reservoir storage capacity normalized by the annual streamflow volume, is used to quantify reservoir regulation effects. Analyses are performed for 388 river stations in the contiguous U.S. using the first two moments of the FFC, mean annual maximum flood (MAF) and coefficient of variations (CV), calculated for the pre- and post-dam periods. It is found that MAF generally decreases with increasing RII but stabilizes when RII exceeds a threshold value, and CV increases with RII until a threshold value beyond which CV decreases with RII. Hence depending on the magnitude of RII, reservoir regulation acts as a filter to increase or reduce the nonlinearity of the natural runoff routing process and alters flood characteristics. The non-linear relationships of MAF and CV with RII can be captured by three reservoir models with different levels of complexity, suggesting that they emerge from the basic flood control function of reservoirs. However, the threshold RII values in the nonlinear relationships depend on the more detailed reservoir operations and objectives that can only be captured by the more complex reservoir models. Our conceptual model may help improve flood-risk assessment and mitigation in regulated river systems at the regional scale.
      PubDate: 2017-09-08T08:50:30.717794-05:
      DOI: 10.1002/2017WR020871
  • Seasonal and spatial dynamics of gas ebullition in a temperate
           water-storage reservoir
    • Authors: Michal Tušer; Tomáš Picek, Zuzana Sajdlová, Tomáš Jůza, Milan Muška, Jaroslava Frouzová
      Abstract: Gas ebullition of river impoundments plays an increasingly significant role, particularly in transporting methane CH4 from their sediments to the atmosphere, and contributing to the global carbon budget and global warming. Quantifying stochastic and episodic nature of gas ebullition is complicated especially when conventionally conducted by using coverage-limited gas traps. Current knowledge of seasonality in a reservoir's gas ebullition is lacking in the literature. For this reason, advanced acoustic surveying was intensively applied to determine spatiotemporal distributions of gas ebullition in a European water-storage reservoir for two years. Additionally, the sampling was accompanied with gas collecting for analyzing gas composition. The gas released from the reservoir was primarily composed of CH4 (on average 52%, up to 94%). The longitudinal distribution of gas ebullition was mainly determined by a proximity to the river inflow as a source of organic matter. A magnitude of ebullitive fluxes within the reservoir varied up to 1,300 mL m−2 d−1 (30 mmol CH4 m−2 d−1). The most significant period of ebullition has turned out to be in fall, on average reaching a sevenfold ebullitive flux (70 mL m−2 d−1, 1.6 mmol CH4 m−2 d−1) higher than in the rest of the season. A substantial contribution to the fall peak was induced by an expansion of gas ebullition into greater depths, covering two thirds of the reservoir in late fall. The study demonstrates that the ebullitive fluxes of the temperate water storage reservoir were correlated to season, depth, and inflow proximity.
      PubDate: 2017-09-07T08:21:13.518316-05:
      DOI: 10.1002/2017WR020694
  • Informing water harvesting technology contract design using choice
    • Authors: Solomon Tarfasa; Roy Brouwer, Oleg Sheremet, Jetske Bouma
      Abstract: Introducing water harvesting technology is expected to be more effective and last longer if farm households are involved in their design. The main objective of this study is to inform policymakers in Ethiopia about the most important terms and conditions to incentivize farmers to enter into a contractual agreement to invest in water harvesting on their land. In order to test the influence of the way the specific contractual terms and conditions are communicated to farm households, many of whom are illiterate, a split sample approach is applied with and without visual aids for technical, institutional and economic contract characteristics. Both samples generate significantly different results, highlighting the importance of how information is conveyed to farm households. This pattern is confirmed when examining the self-reported importance attached to the various contract characteristics. Equality constrained latent class models show that contract characteristics for which visual aids were developed are considered more attentively, emphasizing the importance of adequate communication tools in a developing country context where literacy rates are limited to increase water technology innovation uptake and reduce farm household vulnerability to droughts.
      PubDate: 2017-08-23T14:05:25.779867-05:
      DOI: 10.1002/2016WR020154
  • A distance transform for continuous parameterization of discrete geologic
           facies for subsurface flow model calibration
    • Authors: Siavash Hakim Elahi; Behnam Jafarpour
      Abstract: Construction of predictive subsurface flow models involves subjective interpretation and interpolation of spatially limited data, often using imperfect modeling assumptions. Hence, the process can introduce significant uncertainty and bias in predicting the flow and transport behavior of these systems. In particular, the uncertainty in the facies distribution in complex geologic environments, such as alluvial/fluvial channels, can be consequential for forecasting the dynamic response of these systems to perturbations due to pumping and development activities. Conventional model calibration techniques that are designed to update continuous model parameters cannot be used to estimate discrete parameters from flow and pressure data. We present a distance transform approach for converting discrete facies models to continuous parameters that can be updated using continuous model calibration methods. Distance transforms are widely used in discrete image processing, where the discrete values in each pixel are replaced with their distance (i.e., a continuous variable) to the nearest boundary cell. After updating the continuous distance maps during model calibration, a back-transformation is applied to retrieve the updated facies maps. To preserve large-scale facies connectivity, truncated singular value decomposition (SVD) parametrization may be used to represent the distance maps with low-rank parameters. A variant of the ensemble smoother, ES-MDA is used to update the continuous parameters of the inversion (either distance maps or their SVD coefficients if used). The distance transform method addresses an important problem in facies model calibration where model updating can result in losing facies connectivity and discreteness.
      PubDate: 2017-08-23T14:05:22.773841-05:
      DOI: 10.1002/2016WR019853
  • Sea level adaptation decisions under uncertainty
    • Authors: T. L. Thorarinsdottir; P. Guttorp, M. Drews, P. Skougaard Kaspersen, K. de Bruin
      Abstract: Sea level rise has serious consequences for harbor infrastructure, storm drains and sewer systems, and many other issues. Adapting to sea level rise requires comparing different possible adaptation strategies, comparing the cost of different actions (including no action), and assessing where and at what point in time the chosen strategy should be implemented. All these decisions must be made under considerable uncertainty–in the amount of sea level rise, in the cost and prioritization of adaptation actions, and in the implications of no action. Here we develop two illustrative examples: for Bergen on Norway's west coast and for Esbjerg on the west coast of Denmark, to highlight how technical efforts to understand and quantify uncertainties in hydrologic projections can be coupled with concrete decision-problems framed by the needs of the end-users using statistical formulations. Different components of uncertainty are visualized. We demonstrate the value of uncertainties and show for example that failing to take uncertainty into account can result in the median projected damage costs being an order of magnitude smaller.
      PubDate: 2017-08-21T13:05:33.502229-05:
      DOI: 10.1002/2016WR020354
  • Issue Information
    • Pages: 8135 - 8136
      PubDate: 2017-11-17T09:12:49.682055-05:
      DOI: 10.1002/wrcr.22257
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