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  Subjects -> WATER RESOURCES (Total: 148 journals)
Showing 1 - 47 of 47 Journals sorted alphabetically
Acque Sotterranee - Italian Journal of Groundwater     Open Access   (Followers: 1)
Acta Limnologica Brasiliensia     Open Access   (Followers: 3)
Advances in Oceanography and Limnology     Open Access   (Followers: 12)
Advances in Water Resource and Protection     Open Access   (Followers: 11)
Advances in Water Resources     Hybrid Journal   (Followers: 43)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Agricultural Water Management     Hybrid Journal   (Followers: 39)
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: 20)
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: 1)
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: 14)
Hydrology: Current Research     Open Access   (Followers: 12)
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: 52)
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: 30)
Journal of Water and Climate Change     Partially Free   (Followers: 37)
Journal of Water and Health     Partially Free   (Followers: 3)
Journal of Water Chemistry and Technology     Hybrid Journal   (Followers: 9)
Journal of Water Process Engineering     Full-text available via subscription   (Followers: 4)
Journal of Water Resource and Hydraulic Engineering     Open Access   (Followers: 9)
Journal of Water Resource and Protection     Open Access   (Followers: 9)
Journal of Water Resource Engineering and Management     Full-text available via subscription   (Followers: 3)
Journal of Water Resources Planning and Management     Full-text available via subscription   (Followers: 49)
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)
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: 26)
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: 11)
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: 58)
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: 80)
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: 3)

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Journal Cover Water Resources Research
  [SJR: 2.661]   [H-I: 144]   [80 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0043-1397 - ISSN (Online) 1944-7973
   Published by AGU Homepage  [17 journals]
  • 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
           Media
    • 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
           Forecasts
    • 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
       
  • Refractive-Light-Transmission Technique Applied to Density-Driven
           Convective Mixing in Porous Media With Implications for Geological CO2
           storage
    • Authors: M. Rasmusson; F. Fagerlund, K. Rasmusson, Y. Tsang, A. Niemi
      Abstract: Density-driven convection has been identified to accelerate the rate of CO2 solubility trapping during geological CO2 storage in deep saline aquifers. In this paper we present an experimental method using the refractive properties of fluids (their impact on light transmission), and an analogous system design, which enables the study of transport mechanisms in saturated porous media. The method is used to investigate solutally induced density-driven convective mixing under conditions relevant to geological CO2 storage. The analogous system design allows us by choice of initial solute concentration and bead size to duplicate a wide range of conditions (Ra values), making it possible to study the convective process in general, and as a laboratory analogue for systems found in the field. We show that the method accurately determines the solute concentration in the system with high spatial and temporal resolution. The onset time of convection (tc), mass flux (F) and flow dynamics are quantified and compared with experimental and numerical findings in the literature. Our data yields a scaling law for tc which gives new insight into its dependence on Ra, indicating tc to be more sensitive to large Ra than previously thought. Furthermore, our data show and explain why F is described equally well by a Ra-dependent or a Ra-independent scaling law. These findings improve the understanding of the physical process of convective mixing in saturated porous media in general, and help to assess the CO2 solubility trapping rate under certain field conditions.
      PubDate: 2017-10-09T12:41:29.736747-05:
      DOI: 10.1002/2017WR020730
       
  • Design of Remediation Actions for Nutrient Mitigation in the Hyporheic
           Zone
    • 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
       
  • 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 towards 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: 2017-10-09T12:40:21.247729-05:
      DOI: 10.1002/2017WR021166
       
  • 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
       
  • Are Model Transferability and Complexity Antithetical' Insights From
           Validation of a Variable-Complexity Empirical Snow Model in Space and Time
           
    • Authors: A. C. Lute; C. 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: 2017-09-28T12:35:37.223468-05:
      DOI: 10.1002/2017WR020752
       
  • 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 tradeoffs associated with lowland watershed development.
      PubDate: 2017-09-28T12:35:30.552742-05:
      DOI: 10.1002/2017WR021193
       
  • 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
       
  • 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
      Abstract: Multicomponent reactive transport involves the solution of a system ofnon-linear 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 non-unique, 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: 2017-09-28T12:35:19.244611-05:
      DOI: 10.1002/2017WR020759
       
  • 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
       
  • Recent Extreme Runoff Observations From Coastal Arctic Watersheds in
           Alaska
    • Authors: Svetlana L. Stuefer; Christopher 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: 2017-09-27T09:10:35.989225-05:
      DOI: 10.1002/2017WR020567
       
  • 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
       
  • 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: 2017-09-25T10:46:17.138739-05:
      DOI: 10.1002/2016WR020270
       
  • 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
       
  • 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: 2017-09-18T08:25:20.632718-05:
      DOI: 10.1002/2016WR020275
       
  • 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
       
  • 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 non-monotonically. 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 non-monotonic 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 towards 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: 2017-09-15T08:10:34.020127-05:
      DOI: 10.1002/2016WR020135
       
  • 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
           Phase
    • 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
       
  • 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. Nouwapko, 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: 2017-09-12T13:50:29.636637-05:
      DOI: 10.1002/2017WR020651
       
  • 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
           Fields
    • 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
       
  • 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
       
  • Equations for hydraulic conductivity estimation from particle size
           distribution: A dimensional analysis
    • Authors: Ji-Peng Wang; Bertrand François, Pierre Lambert
      Abstract: Estimating hydraulic conductivity from particle size distribution (PSD) is an important issue for various engineering problems. Classical models such as Hazen model, Beyer model, and Kozeny-Carman model usually regard the grain diameter at 10% passing (d10) as an effective grain size and the effects of particle size uniformity (in Beyer model) or porosity (in Kozeny-Carman model) are sometimes embedded. This technical note applies the dimensional analysis (Buckingham's ∏ theorem) to analyze the relationship between hydraulic conductivity and particle size distribution (PSD). The porosity is regarded as a dependent variable on the grain size distribution in unconsolidated conditions. It indicates that the coefficient of grain size uniformity and a dimensionless group representing the gravity effect, which is proportional to the mean grain volume, are the main two determinative parameters for estimating hydraulic conductivity. Regression analysis is then carried out on a database comprising 431 samples collected from different depositional environments and new equations are developed for hydraulic conductivity estimation. The new equation, validated in specimens beyond the database, shows an improved prediction comparing to using the classic models.
      PubDate: 2017-09-10T11:10:27.916461-05:
      DOI: 10.1002/2017WR020888
       
  • 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
       
  • Denitrification in the banks of fluctuating rivers: The effects of river
           stage amplitude, sediment hydraulic conductivity and dispersivity, and
           ambient groundwater flow
    • Authors: Pin Shuai; M. Bayani Cardenas, Peter S. K. Knappett, Philip C. Bennett, Bethany T. Neilson
      Abstract: Hyporheic exchange induced by periodic river fluctuations leads to important biogeochemical processes, particularly nitrogen cycling, in riparian zones (RZs) where chemically distinct surface water and groundwater mix. We developed a two-dimensional coupled flow, reactive transport model to study the role of bank storage induced by river fluctuations on removing river-borne nitrate. Sensitivity analyses were conducted to quantify the effects of river amplitude, sediment hydraulic conductivity and dispersivity, and ambient groundwater flow on nitrate removal rate. The simulations showed that nitrification occurred in the shallower zone adjacent to the bank where oxic river water and groundwater interacted while denitrification occurred deeper into the aquifer and in the riverbed sediments where oxygen was depleted. River fluctuations greatly increased the amount of nitrate being removed; the nitrate removal rate increased as river amplitude increased. Similarly, increasing hydraulic conductivity increased overall nitrate removal since it expanded the denitrifying zone but decreased efficiency. In contrast, increasing sediment dispersivity increased the removal efficiency of nitrate because it promoted mixing between electron acceptors and donors. The presence and direction of ambient groundwater flow had a significant impact on nitrate removal rate when compared to neutral conditions. A losing river showed a larger nitrate removal rate, whereas a gaining river showed a smaller nitrate removal rate. Our results demonstrated that daily river fluctuations created denitrification hot spots within the RZ that would not otherwise exist under naturally neutral or gaining conditions.
      PubDate: 2017-09-06T16:11:44.524331-05:
      DOI: 10.1002/2017WR020610
       
  • Effects of spatial configuration of imperviousness and green
           
    • Authors: Theodore C Lim; Claire Welty
      Abstract: Green infrastructure (GI) is an approach to stormwater management that promotes natural processes of infiltration and evapotranspiration, reducing surface runoff to conventional stormwater drainage infrastructure. As more urban areas incorporate GI into their stormwater management plans, greater understanding is needed on the effects of spatial configuration of GI networks on hydrological performance, especially in the context of potential subsurface and lateral interactions between distributed facilities. In this research, we apply a three-dimensional, coupled surface-subsurface, land-atmosphere model, ParFlow.CLM, to a residential urban sewershed in Washington DC that was retrofitted with a network of GI installations between 2009 and 2015. The model was used to test nine additional GI and imperviousness spatial network configurations for the site and was compared with monitored pipe-flow data. Results from the simulations show that GI located in higher flow-accumulation areas of the site intercepted more surface runoff, even during wetter and multi-day events. However, a comparison of the differences between scenarios and levels of variation and noise in monitored data suggests that the differences would only be detectable between the most and least optimal GI/imperviousness configurations.
      PubDate: 2017-09-06T16:10:49.197931-05:
      DOI: 10.1002/2017WR020631
       
  • A game theory analysis of green infrastructure stormwater management
           policies
    • Authors: Reshmina William; Jugal Garg, Ashlynn S. Stillwell
      Abstract: Green stormwater infrastructure has been demonstrated as an innovative water resources management approach that addresses multiple challenges facing urban environments. However, there is little consensus on what policy strategies can be used to best incentivize green infrastructure adoption by private landowners. Game theory, an analysis framework that has historically been under-utilized within the context of stormwater management, is uniquely suited to address this policy question. We used a cooperative game theory framework to investigate the potential impacts of different policy strategies used to incentivize green infrastructure installation. The results indicate that municipal regulation leads to the greatest reduction in pollutant loading. However, the choice of the ‘best' regulatory approach will depend on a variety of different factors including politics and financial considerations. Large, downstream agents have a disproportionate share of bargaining power. Results also reveal that policy impacts are highly dependent on agents' spatial position within the stormwater network, leading to important questions of social equity and environmental justice.
      PubDate: 2017-09-06T16:10:40.519268-05:
      DOI: 10.1002/2017WR021024
       
  • Influence of instantaneous and time-averaged groundwater flows induced by
           waves on the fate of contaminants in a beach aquifer
    • Authors: Spencer Malott; Denis M. O'Carroll, Clare E. Robinson
      Abstract: Wave-induced water exchange and groundwater flows in beach aquifers impact the fate of contaminants including nutrients, fecal bacteria and non-aqueous phase liquids (NAPLs). Waves induce high frequency fluxes in shallow beach sediments. In addition, the phase-averaged effect of waves (wave setup) drives deeper flow recirculations through a beach aquifer. Field data of shallow instantaneous and time-averaged vertical head gradients (fluxes) are first compared with deeper time-averaged fluxes over a period of varying wave conditions. The time-averaged fluxes are equivalent to that which would be simulated assuming a phase-averaged water surface (i.e. wave setup). Based on this comparison, the need to simulate phase-resolved wave motion versus the simplified phase-averaged water surface in predicting contaminant fate is evaluated. While high frequency fluxes cause large surface water volumes to filter through beach sediments, the exchanging water has a short residence time (
      PubDate: 2017-09-06T16:10:35.89996-05:0
      DOI: 10.1002/2017WR020948
       
  • Visualization and quantification of capillary drainage in the pore space
           of laminated sandstone by a porous plate method using differential imaging
           X-ray microtomography
    • Authors: Qingyang Lin; Branko Bijeljic, Holger Rieke, Martin J. Blunt
      Abstract: The experimental determination of capillary pressure drainage curves at the pore scale is of vital importance for the mapping of reservoir fluid distribution. To fully characterize capillary drainage in a complex pore space, we design a differential imaging-based porous plate (DIPP) method using X-ray microtomography. For an exemplar mm-scale laminated sandstone microcore with a porous plate, we quantify the displacement from resolvable macropores and subresolution micropores. Nitrogen (N2) was injected as the nonwetting phase at a constant pressure while the porous plate prevented its escape. The measured porosity and capillary pressure at the imaged saturations agree well with helium measurements and experiments on larger core samples, while providing a pore-scale explanation of the fluid distribution. We observed that the majority of the brine was displaced by N2 in macropores at low capillary pressures, followed by a further brine displacement in micropores when capillary pressure increases. Furthermore, we were able to discern that brine predominantly remained within the subresolution micropores, such as regions of fine lamination. The capillary pressure curve for pressures ranging from 0 to 1151 kPa is provided from the image analysis compares well with the conventional porous plate method for a cm-scale core but was conducted over a period of 10 days rather than up to few months with the conventional porous plate method. Overall, we demonstrate the capability of our method to provide quantitative information on two-phase saturation in heterogeneous core samples for a wide range of capillary pressures even at scales smaller than the micro-CT resolution.
      PubDate: 2017-08-29T07:37:57.055356-05:
      DOI: 10.1002/2017WR021083
       
  • Lattice Boltzmann simulation of CO2 reactive transport in network
           fractured media
    • Authors: Zhiwei Tian; Junye Wang
      Abstract: Carbon dioxide (CO2) geological sequestration plays an important role in mitigating CO2 emissions for climate change. Understanding interactions of the injected CO2 with network fractures and hydrocarbons is key for optimizing and controlling CO2 geological sequestration and evaluating its risks to ground water. However, there is a well-known, difficult process in simulating the dynamic interaction of fracture-matrix, such as dynamic change of matrix porosity, unsaturated processes in rock matrix, and effect of rock mineral properties. In this paper, we develop an explicit model of the fracture-matrix interactions using multilayer bounce-back treatment as a first attempt to simulate CO2 reactive transport in network fractured media through coupling the Dardis's LBM porous model for a new interface treatment. Two kinds of typical fracture networks in porous media are simulated: straight cross network fractures and interleaving network fractures. The reaction rate and porosity distribution are illustrated and well-matched patterns are found. The species concentration distribution and evolution with time steps are also analyzed and compared with different transport properties. The results demonstrate the capability of this model to investigate the complex processes of CO2 geological injection and reactive transport in network fractured media, such as dynamic change of matrix porosity.
      PubDate: 2017-08-28T02:05:36.008485-05:
      DOI: 10.1002/2017WR021063
       
  • Assessment of interstate virtual water flows embedded in agriculture to
           mitigate water scarcity in India (1996–2014)
    • Authors: Suparana Katyaini; Anamika Barua
      Abstract: India is the largest global freshwater user despite being highly water scarce. Agriculture is largest consumer of water and is most affected by water scarcity. Water scarcity is a persistent challenge in India, due to a gap in science and policy spheres. Virtual Water (VW) flows concept to mitigate water scarcity is at the science-policy interface. The paper aims to address the gap in VW research in India by first analyzing the interstate VW-flows embedded in food grains, and then linking these VW-flows with the water scarcity situation in the states, and elements of state and national water policies for the postreforms, and recovery periods of India's agriculture. There were net water savings (WS) of 207.5 PL during 1996–2014, indicating sustainable flows at the national level. WS increased from 11.2 TL/yr (1996–2005) to 25931.7 TL/yr (2005–2014), with the increase in interstate movement of food grains, and yield. However, unsustainable flows are seen at subnational scale, as VW-flows are from highly water-scarce states in North to highly water-scarce states in West and South. These flows are causing a concentration of water scarcity in water-scarce zones/states. Net VW imports were found to be driven by larger population and net VW exports by arable land. Further, the absence of state water policy cripples water management. Therefore, the paper argues that there is a need to rethink policy decisions on agriculture at the national and state level by internalizing water as a factor of production, through VW research.
      PubDate: 2017-08-28T02:00:51.403943-05:
      DOI: 10.1002/2016WR020247
       
  • The complexities of urban flood response: Flood frequency analyses for the
           Charlotte metropolitan region
    • Authors: Zhengzheng Zhou; James A. Smith, Long Yang, Mary Lynn Baeck, Molly Chaney, Marie-Claire Ten Veldhuis, Huiping Deng, Shuguang Liu
      Abstract: We examine urban flood response through data-driven analyses for a diverse sample of “small” watersheds (basin scale ranging from 7.0 to 111.1 km2) in the Charlotte Metropolitan region. These watersheds have experienced extensive urbanization and suburban development since the 1960s. The objective of this study is to develop a broad characterization of land surface and hydrometeorological controls of urban flood hydrology. Our analyses are based on peaks-over-threshold flood data developed from USGS streamflow observations and are motivated by problems of flood hazard characterization for urban regions. We examine flood-producing rainfall using high-resolution (1 km2 spatial resolution and 15 min time resolution), bias-corrected radar rainfall fields that are developed through the Hydro-NEXRAD system. The analyses focus on the 2001–2015 period. The results highlight the complexities of urban flood response. There are striking spatial heterogeneities in flood peak magnitudes, response times, and runoff ratios across the study region. These spatial heterogeneities are mainly linked to watershed scale, the distribution of impervious cover, and storm water management. Contrasting land surface properties also determine the mixture of flood-generating mechanisms for a particular watershed. Warm-season thunderstorm systems and tropical cyclones are main flood agents in Charlotte, with winter/spring storms playing a role in less-urbanized watersheds. The mixture of flood agents exerts a strong impact on the upper tail of flood frequency distributions. Antecedent watershed wetness plays a minor role in urban flood response, compared with less-urbanized watersheds. Implications for flood hazard characterization in urban watersheds and for advances in flood science are discussed.
      PubDate: 2017-08-28T01:55:59.411027-05:
      DOI: 10.1002/2016WR019997
       
  • Non-Fickian dispersion in open-channel flow over a porous bed
    • Authors: Andrea Bottacin-Busolin
      Abstract: Solute transport in rivers has been traditionally represented using one-dimensional models assuming advection and Fickian dispersion along the main flow direction and transient storage in surface and subsurface dead zones. Experimental evidence from several stream tracer studies has shown that the longitudinal scaling of the moments of the breakthrough curves (BTCs) is inconsistent with classic 1-D solute transport models. In this work, simulations of advection and diffusion in a 2-D and 3-D channel flow over a porous bed are presented assuming an exponentially attenuated profile of the transverse mixing coefficient in the porous medium, as suggested by recent experimental and numerical studies. It is shown that the longitudinal transport in the channel is superdiffusive, and the skewness of the concentration distributions can be almost constant over a broad temporal range, with no sign of approaching zero at large times. A sensitivity analysis shows that, at large times, longitudinal dispersion is controlled by the cross-sectional profile of the in-bed transverse mixing coefficient, and by the difference between the average velocity in the channel and in the porous bed. The normalized concentration distributions can be approximated by beta-distributions with time-dependent parameters, and relationships are derived between the scaling of the parameters under power-law approximation and the scaling of the spatial and temporal moments. The results provide new insights into the physical mechanisms that control the anomalous scaling of the moments observed in field tracer studies and opens new possibilities for predictive and inverse modeling of transport processes in rivers and their catchments.
      PubDate: 2017-08-28T01:55:44.823622-05:
      DOI: 10.1002/2016WR020348
       
  • Full-flow-regime storage-streamflow correlation patterns provide insights
           into hydrologic functioning over the continental US
    • Authors: Kuai Fang; Chaopeng Shen
      Abstract: Inter-annual changes in low, median and high regimes of streamflow have important implications for flood control, irrigation, and ecologic and human health. The Gravity Recovery and Climate Experiment (GRACE) satellites record global terrestrial water storage anomalies (TWSA), providing an opportunity to observe, interpret, and potentially utilize the complex relationships between storage and full-flow-regime streamflow. Here we show that utilizable storage-streamflow correlations exist throughout vastly different climates in the continental US (CONUS) across low to high flow regimes. A panoramic framework, the storage-streamflow correlation spectrum (SSCS), is proposed to examine macroscopic gradients in these relationships. SSCS helps form, corroborate or reject hypotheses about basin hydrologic behaviors. SSCS patterns vary greatly over CONUS with climate, land surface and geologic conditions. Data mining analysis suggests that for catchments with hydrologic settings that favor storage over runoff, e.g., a large fraction of precipitation as snow, thick and highly permeable soil, SSCS values tend to be high. Based on our results, we form the hypotheses that groundwater flow dominates streamflows in Southeastern CONUS and Great Plains, while thin soils in a belt along the Appalachian Mountains impose a limit on water storage. SSCS also suggests shallow water table caused by high-bulk density soil and flat terrain induces rapid runoff in several regions. Our results highlight the importance of subsurface properties and groundwater flow in capturing flood and drought. We propose that SSCS can be used as a fundamental hydrologic signature to constrain models and to provide insights that lead us to better understand hydrologic functioning.
      PubDate: 2017-08-24T11:55:31.516347-05:
      DOI: 10.1002/2016WR020283
       
  • Critical conditions of incipient motion of cohesive sediments
    • Authors: Minxi Zhang; Guoliang Yu
      Abstract: The critical condition of incipient motion of cohesive sediments was investigated in a laboratory study. One hundred experimental runs were performed with sediment samples by varying the yield stress to determine the relationship between the critical condition of incipient motion and the rheological properties of the cohesive sediments. The results indicate that yield stress is a factor that has a major influence on the incipient motion of cohesive sediments. In addition, the critical Shields parameter is found to be exponentially proportional to the yield stress and inversely proportional to the median grain size. The effect of yield stress on the critical Shields parameter is significant for the cohesive sediments and becomes progressively weaker with increasing median grain size. Furthermore, an empirical formula for calculating the critical Shields parameter of cohesive sediments that includes a rheological term and a gravity term is proposed by introducing the yield stress. According to this formula, a modified Shields diagram is obtained in which the values of the critical Shields parameter for cohesive sediments vary within a band that contains countless curves (instead of on a single line) to reflect the influence of the yield stress. This modification of the traditional Shields curve is effective for fine sediments, but the effects tend to vanish for coarse sediments as the behavior of sediments changes from cohesive to non-cohesive. Finally, potential further investigations are discussed.
      PubDate: 2017-08-23T14:05:39.572475-05:
      DOI: 10.1002/2017WR021066
       
  • Capillary trapping quantification in sandstones using NMR relaxometry
    • Authors: Paul R. J. Connolly; Sarah J. Vogt, Stefan Iglauer, Eric F. May, Michael L. Johns
      Abstract: Capillary trapping of a non-wetting phase arising from two-phase immiscible flow in sedimentary rocks is critical to many geoscience scenarios, including oil and gas recovery, aquifer recharge and, with increasing interest, carbon sequestration. Here we demonstrate the successful use of low field 1H Nuclear Magnetic Resonance (NMR) to quantify capillary trapping; specifically we use transverse relaxation time (T2) time measurements to measure both residual water (wetting phase) content and the surface-to-volume ratio distribution (which is proportional to pore size) of the void space occupied by this residual water. Critically we systematically confirm this relationship between T2 and pore size by quantifying inter-pore magnetic field gradients due to magnetic susceptibility contrast, and demonstrate that our measurements at all water saturations are unaffected. Diffusion in such field gradients can potentially severely distort the T2-pore size relationship, rendering it unusable. Measurements are performed for nitrogen injection into a range of water-saturated sandstone plugs at reservoir conditions. Consistent with a water-wet system, water was preferentially displaced from larger pores while relatively little change was observed in the water occupying smaller pore spaces. The impact of cyclic wetting/non-wetting fluid injection was explored and indicated that such a regime increased non-wetting trapping efficiency by the sequential occupation of the most available larger pores by nitrogen. Finally the replacement of nitrogen by CO2 was considered; this revealed that dissolution of paramagnetic minerals from the sandstone caused by its exposure to carbonic acid reduced the in situ bulk fluid T2 relaxation time on a timescale comparable to our core flooding experiments. The implications of this for the T2-pore size relationship are discussed.
      PubDate: 2017-08-23T14:05:28.97878-05:0
      DOI: 10.1002/2017WR020829
       
  • Informing water harvesting technology contract design using choice
           experiments
    • 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
       
  • The influence of interfacial slip on two-phase flow in rough pores
    • Authors: Alec Kucala; Mario J. Martinez, Yifeng Wang, David R. Noble
      Abstract: The migration and trapping of supercritical CO2 (scCO2) in geologic carbon storage is strongly dependent on the geometry and wettability of the pore network in the reservoir rock. During displacement, resident fluids may become trapped in the pits of a rough pore surface forming an immiscible two-phase fluid interface with the invading fluid, allowing apparent slip flow at this interface. We present a two-phase fluid dynamics model, including interfacial tension, to characterize the impact of mineral surface roughness on this slip flow. We show that the slip flow can be cast in more familiar terms as a contact-angle (wettability)-dependent effective permeability to the invading fluid, a nondimensional measurement which relates the interfacial slip to the pore geometry. The analysis shows the surface roughness-induced slip flow can effectively increase or decrease this effective permeability, depending on the wettability and roughness of the mineral surfaces. Configurations of the pore geometry where interfacial slip has a tangible influence on permeability have been identified. The results suggest that for large roughness features, permeability to CO2 may be enhanced by approximately 30% during drainage, while the permeability to brine during reimbibition may be enhanced or diminished by 60%, depending on the contact angle with the mineral surfaces and degrees of roughness. For smaller roughness features, the changes in permeability through interfacial slip are small. A much larger range of effective permeabilities are suggested for general fluid pairs and contact angles, including occlusion of the pore by the trapped phase.
      PubDate: 2017-08-23T07:51:36.295589-05:
      DOI: 10.1002/2016WR020059
       
  • Predicting redox-sensitive contaminant concentrations in groundwater using
           random forest classification
    • Authors: Anthony J. Tesoriero; Jo Ann Gronberg, Paul F. Juckem, Matthew P. Miller, Brian P. Austin
      Abstract: Machine learning techniques were applied to a large (n > 10,000) compliance monitoring database to predict the occurrence of several redox-active constituents in groundwater across a large watershed. Specifically, random forest classification was used to determine the probabilities of detecting elevated concentrations of nitrate, iron, and arsenic in the Fox, Wolf, Peshtigo, and surrounding watersheds in northeastern Wisconsin. Random forest classification is well suited to describe the nonlinear relationships observed among several explanatory variables and the predicted probabilities of elevated concentrations of nitrate, iron, and arsenic. Maps of the probability of elevated nitrate, iron, and arsenic can be used to assess groundwater vulnerability and the vulnerability of streams to contaminants derived from groundwater. Processes responsible for elevated concentrations are elucidated using partial dependence plots. For example, an increase in the probability of elevated iron and arsenic occurred when well depths coincided with the glacial/bedrock interface, suggesting a bedrock source for these constituents. Furthermore, groundwater in contact with Ordovician bedrock has a higher likelihood of elevated iron concentrations, which supports the hypothesis that groundwater liberates iron from a sulfide-bearing secondary cement horizon of Ordovician age. Application of machine learning techniques to existing compliance monitoring data offers an opportunity to broadly assess aquifer and stream vulnerability at regional and national scales and to better understand geochemical processes responsible for observed conditions.
      PubDate: 2017-08-23T01:30:59.256505-05:
      DOI: 10.1002/2016WR020197
       
  • Spectral decomposition of regulatory thresholds for climate-driven
           fluctuations in hydro- and wind power availability
    • Authors: A. Wörman; A. Bottacin-Busolin, N. Zmijewski, J. Riml
      Abstract: Climate-driven fluctuations in the runoff and potential energy of surface water are generally large in comparison to the capacity of hydropower regulation, particularly when hydropower is used to balance the electricity production from covarying renewable energy sources such as wind power. To define the bounds of reservoir storage capacity, we introduce a dedicated reservoir volume that aggregates the storage capacity of several reservoirs to handle runoff from specific watersheds. We show how the storage bounds can be related to a spectrum of the climate-driven modes of variability in water availability and to the covariation between water and wind availability. A regional case study of the entire hydropower system in Sweden indicates that the longest regulation period possible to consider spans from a few days of individual subwatersheds up to several years, with an average limit of a couple of months. Watershed damping of the runoff substantially increases the longest considered regulation period and capacity. The high covariance found between the potential energy of the surface water and wind energy significantly reduces the longest considered regulation period when hydropower is used to balance the fluctuating wind power.
      PubDate: 2017-08-23T01:30:41.186691-05:
      DOI: 10.1002/2017WR020460
       
  • Entropy-based critical reaction time for mixing-controlled reactive
           transport
    • Authors: Gabriele Chiogna; Massimo Rolle
      Abstract: Entropy-based metrics, such as the dilution index, have been proposed to quantify dilution and reactive mixing in solute transport problems. In this work, we derive the transient advection dispersion equation for the entropy density of a reactive plume. We restrict our analysis to the case where the concentration distribution of the transported species is Gaussian and we observe that, even in case of an instantaneous complete bimolecular reaction, dilution caused by dispersive processes dominates the entropy balance at early times and results in the net increase of the entropy density of a reactive species. Successively, the entropy of the reactant decreases until it vanishes. We show the existence of a unique critical value of dilution, which corresponds to the complete consumption of one of the reactants. This critical dilution index is independent of advective and dispersive processes, and depends only on the dimensionality of the problem, on the stoichiometry of the reaction and on the initial concentrations of the reactants. Furthermore, we provide simple analytical expressions to compute the critical reaction time, i.e., the time at which the critical dilution index is reached, for selected flow configurations. Our results show that, differently from the critical dilution index, the critical reaction time depends on solute transport processes such as advection and hydrodynamic dispersion.
      PubDate: 2017-08-23T01:25:57.130114-05:
      DOI: 10.1002/2017WR020522
       
  • Transient effects on confined groundwater age distributions: Considering
           the necessity of time-dependent simulations
    • Authors: Nicholas B. Engdahl
      Abstract: The key concept of transient age distributions is that the age distribution of water at a fixed spatial location may change over time. Most previous studies involving groundwater age have relied on the assumption of a steady state age distribution over time. This assumption simplifies the problem and can also be used for predictive modeling, but few studies have addressed the validity of this assumption directly. We explore the variability of transient age distributions in simplified, confined groundwater flow systems. The main focus is determining when it is necessary to explicitly model the transience. A combination of analytical and numerical methods is used to demonstrate the transient variability of age for several hypothetical velocity fields and trial domains. Transient effects are strongest for samples taken near fluctuating interfaces or boundaries. Lastly, we investigate how heterogeneity and transient boundary signals interact in a 2-D domain. These impacts are difficult to generalize, so the article closes with a set of considerations to assist readers in determining whether or not transience is likely to play a significant role in other applications. The main conclusion is that high-frequency oscillations in flow boundaries have negligible impacts on confined age distributions but long-term trends in flow velocities (increasing or decreasing) can cause significant changes over time.
      PubDate: 2017-08-23T01:20:39.347862-05:
      DOI: 10.1002/2016WR019916
       
  • Prediction and uncertainty analysis of a parsimonious floodplain surface
           water – groundwater interaction model
    • Authors: Nadine Maier; Lutz Breuer, Philipp Kraft
      Abstract: Floodplains provide a variety of hydrological and ecological functions and are therefore of great importance. The flooding frequency, as well as the height and duration of inundations are particularly relevant for ecosystem states and are dependent on the exchange between surface water and groundwater. In this study, we developed a fully distributed model approach to simulate distributed groundwater levels in a floodplain in Hesse, Germany (14.8 km2). To overcome the problem of large computation times we simplified the surface water equation. Thus, the water surface of flooding is at the same level everywhere and the dynamic effect of the flooding is ignored. In this way, it was possible to run the model 5,000 times and investigate its parameter uncertainty using Latin hypercube sampling. Behavioral model runs were selected based on a threshold criterion of a mean root mean square error that was smaller than 0.26 m. All the simulated groundwater wells show an individual RMSE between 0.17 and 0.41 m for the calibration period. Regarding the parameterization, the model shows rather large variance in parameters that are capable of generating good simulations: a range of saturated conductivity of 2,793 m/day, porosity of 0.4 m3/m3, residual wetness of soil of 0.2 m3/m3/soil and range of soil thickness of 2.9 m.
      PubDate: 2017-08-21T13:10:56.450436-05:
      DOI: 10.1002/2017WR020749
       
  • Is the permeability of naturally fractured rocks scale dependent'
    • Authors: Siroos Azizmohammadi; Stephan K. Matthäi
      Abstract: The equivalent permeability, keq of stratified fractured porous rocks and its anisotropy is important for hydrocarbon reservoir engineering, groundwater hydrology, and subsurface contaminant transport. However, it is difficult to constrain this tensor property as it is strongly influenced by infrequent large fractures. Boreholes miss them and their directional sampling bias affects the collected geostatistical data. Samples taken at any scale smaller than that of interest truncate distributions and this bias leads to an incorrect characterization and property upscaling.To better understand this sampling problem, we have investigated a collection of outcrop-data based Discrete Fracture and Matrix (DFM) models with mechanically constrained fracture aperture distributions, trying to establish a useful Representative Elementary Volume (REV). Finite-element analysis and flow-based upscaling have been used to determine keq eigenvalues and anisotropy.While our results indicate a convergence towards a scale-invariant keq REV with increasing sample size, keq magnitude can have multi-modal distributions. REV size relates to the length of dilated fracture segments as opposed to overall fracture length. Tensor orientation and degree of anisotropy also converge with sample size. However, the REV for keq anisotropy is larger than that for keq magnitude. Across scales, tensor orientation varies spatially, reflecting inhomogeneity of the fracture patterns. Inhomogeneity is particularly pronounced where the ambient stress selectively activates late- as opposed to early (through-going) fractures. While we cannot detect any increase of keq with sample size as postulated in some earlier studies, our results highlight a strong keq anisotropy that influences scale dependence.
      PubDate: 2017-08-21T13:10:45.417769-05:
      DOI: 10.1002/2016WR019764
       
  • Making the most out of a hydrological model data set: Sensitivity analyses
           to open the model black-box
    • Authors: E. Borgonovo; X. Lu, E. Plischke, O. Rakovec, M. C. Hill
      Abstract: In this work we investigate methods for gaining greater insight from hydrological model runs conducted for uncertainty quantification and model differentiation. We frame the sensitivity analysis questions in terms of the main purposes of sensitivity analysis: parameter prioritization, trend identification and interaction quantification. For parameter prioritization, we consider variance-based sensitivity measures, sensitivity indices based on the L1-norm, the Kuiper metric and the sensitivity indices of the DELSA methods. For trend identification, we investigate insights derived from graphing the one-way ANOVA sensitivity functions, the recently introduced CUSUNORO plots and derivative scatterplots. For interaction quantification, we consider information delivered by variance-based sensitivity indices. We rely on the so-called given-data principle, in which results from a set of model runs are used to perform a defined set of analyses. One avoids using specific designs for each insight, thus controlling the computational burden. The methodology is applied to a hydrological model of a river in Belgium simulated using the well established Framework for Understanding Structural Errors (FUSE) on five alternative configurations. The findings show that the integration of the chosen methods provide insights unavailable in most other analyses.
      PubDate: 2017-08-21T13:10:32.742372-05:
      DOI: 10.1002/2017WR020767
       
  • Calibration of a modified temperature-light intensity logger for
           quantifying water electrical conductivity
    • Authors: M. A. Gillman; S. F. Lamoureux, M. J. Lafrenière
      Abstract: The STIC (Stream Temperature, Intermittency, and Conductivity) electrical conductivity (EC) logger as presented by Chapin et al. [2014] serves as an inexpensive (∼50 USD) means to assess relative EC in freshwater environments. This communication demonstrates the calibration of the STIC logger for quantifying EC, and provides examples from a month long field deployment in the High Arctic. Calibration models followed multiple non-linear regression and produced calibration curves with high coefficient of determination values (R2 = 0.995 – 0.998; n = 5). Percent error of mean predicted specific conductance at 25°C (SpC) to known SpC ranged in magnitude from -0.6% to 13% (mean = -1.4%), and mean absolute percent error (MAPE) ranged from 2.1% to 13% (mean = 5.3%). Across all tested loggers we found good accuracy and precision, with both error metrics increasing with increasing SpC values. During ten, month-long field deployments, there were no logger failures and full data recovery was achieved. Point SpC measurements at the location of STIC loggers recorded via a more expensive commercial electrical conductivity logger followed similar trends to STIC SpC records, with 1:1.05 and 1:1.08 relationships between the STIC and commercial logger SpC values. These results demonstrate that STIC loggers calibrated to quantify EC are an economical means to increase the spatiotemporal resolution of water quality investigations.
      PubDate: 2017-08-21T13:10:29.046101-05:
      DOI: 10.1002/2017WR020634
       
  • 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
       
  • Smoothing-based compressed state Kalman filter for joint state-parameter
           estimation: Applications in reservoir characterization and CO2 storage
           monitoring
    • Authors: Y. J. Li; Amalia Kokkinaki, Eric F. Darve, Peter K. Kitanidis
      Abstract: The operation of most engineered hydrogeological systems relies on simulating physical processes using numerical models with uncertain parameters and initial conditions. Predictions by such uncertain models can be greatly improved by Kalman-filter techniques that sequentially assimilate monitoring data. Each assimilation constitutes a nonlinear optimization, which is solved by linearizing an objective function about the model prediction and applying a linear correction to this prediction. However, if model parameters and initial conditions are uncertain, the optimization problem becomes strongly nonlinear and a linear correction may yield unphysical results. In this paper, we investigate the utility of one-step ahead smoothing, a variant of the traditional filtering process, to eliminate nonphysical results and reduce estimation artifacts caused by nonlinearities. We present the smoothing-based compressed state Kalman filter (sCSKF), an algorithm that combines one step ahead smoothing, in which current observations are used to correct the state and parameters one step back in time, with a nonensemble covariance compression scheme, that reduces the computational cost by efficiently exploring the high-dimensional state and parameter space. Numerical experiments show that when model parameters are uncertain and the states exhibit hyperbolic behavior with sharp fronts, as in CO2 storage applications, one-step ahead smoothing reduces overshooting errors and, by design, gives physically consistent state and parameter estimates. We compared sCSKF with commonly used data assimilation methods and showed that for the same computational cost, combining one step ahead smoothing and nonensemble compression is advantageous for real-time characterization and monitoring of large-scale hydrogeological systems with sharp moving fronts.
      PubDate: 2017-08-19T03:06:05.296232-05:
      DOI: 10.1002/2016WR020168
       
  • Dissolved oxygen dynamics under ice: Three winters of high-frequency data
           from Lake Tovel, Italy
    • Authors: Ulrike Obertegger; Biel Obrador, Giovanna Flaim
      Abstract: Under-ice dissolved oxygen (DO) metabolism and DO depletion are poorly understood, limiting our ability to predict how changing winter conditions will affect lake ecosystems. We analyzed under-ice DO dynamics based on high-frequency (HF) data at two depths (5 and 25 m) for three winters (January–March 2014, 2015, and 2016) in oligotrophic Lake Tovel (1178 m above sea level; maximum depth 39 m). Specifically, we assessed diel metabolic rates based on HF data of DO, temperature, and light for winter 2016 and seasonal DO depletion rates based on HF data of DO for all three winters. For 2016, calculations of metabolic rates were possible only for 34% and 3% of days at 5 and 25 m, respectively; these metabolic rates generally indicated net heterotrophy at both depths. Low success in modeling metabolic rates was attributed to low diel DO variability and anomalous diel DO patterns, probably linked to under-ice physical processes. Seasonal DO patterns for the three winters showed increasing, decreasing, or stable DO trends at 5 m while at 25 m patterns always showed decreasing DO trends but with different rates. Our multiyear study permitted us to hypothesize that the observed intraannual and interannual differences in DO depletion can be attributed to variable snow cover determining the penetration of radiation and thus photosynthesis. This study brings new insights to DO dynamics in ice-covered systems, highlights the challenges linked to under-ice lake metabolism, and advocates for a modeling approach that includes physical processes.
      PubDate: 2017-08-19T03:05:24.650564-05:
      DOI: 10.1002/2017WR020599
       
  • Toward seamless large domain parameter estimation for hydrologic models
    • Authors: Naoki Mizukami; Martyn Clark, Andrew J. Newman, Andrew W. Wood, Ethan Gutmann, Bart Nijssen, Oldrich Rakovec, Luis Samaniego
      Abstract: Estimating spatially distributed parameters remains one of the biggest challenges for large domain hydrologic modeling. Many large domain modeling efforts rely on spatially inconsistent parameter fields, e.g., patchwork patterns resulting from individual basin calibrations, parameter fields generated through default transfer functions that relate geophysical attributes to model parameters, or spatially constant, default parameter values. This paper provides an initial assessment of a multi-scale parameter regionalization (MPR) method over large geographical domains to derive seamless parameters in a spatially consistent manner. MPR applies transfer functions at the native scale of the geophysical data, and then scales these model parameters to the desired model resolution. We developed a stand-alone framework called MPR-flex for multi-model use and applied MPR-flex to the Variable Infiltration Capacity model to produce hydrologic simulations over the contiguous USA (CONUS). We first independently calibrate 531 basins across the CONUS to obtain a performance benchmark for each basin. To derive the CONUS parameter fields, we perform a joint MPR calibration using all but the poorest behaved basins to obtain a single set of transfer function parameters that are applied to the entire CONUS. Results show that the CONUS-wide calibration has similar performance compared to previous simulations using a patchwork quilt of partially calibrated parameter sets, but without the spatial discontinuities in parameters that characterize some previous CONUS-domain model simulations. Several avenues to improve CONUS-wide calibration remain, including selection of calibration basins, objective function formulation, as well as MPR-flex improvements including transfer function formations and scaling operator optimization.
      PubDate: 2017-08-18T15:56:51.109574-05:
      DOI: 10.1002/2017WR020401
       
  • Visualizing and quantifying the crossover from capillary fingering to
           viscous fingering in a rough fracture
    • Authors: Yi-Feng Chen; Shu Fang, Dong-Sheng Wu, Ran Hu
      Abstract: Immiscible fluid-fluid displacement in permeable media is important in many subsurface processes, including enhanced oil recovery and geological CO2 sequestration. Controlled by capillary and viscous forces, displacement patterns of one fluid displacing another more viscous one exhibit capillary and viscous fingering, and crossover between the two. Although extensive studies investigated viscous and capillary fingering in porous media, a few studies focused on the crossover in rough fractures, and how viscous and capillary forces affect the crossover remains unclear. Using a transparent fracture-visualization system, we studied how the two forces impact the crossover in a horizontal rough fracture. Drainage experiments of water displacing oil were conducted at seven flow rates (capillary number log10Ca ranging from −7.07 to −3.07) and four viscosity ratios (M=1/1000,1/500,1/100 and 1/50). We consistently observed lower invading fluid saturations in the crossover zone. We also proposed a phase diagram for the displacement patterns in a rough fracture that is consistent with similar studies in porous media. Based on real-time imaging and statistical analysis of the invasion morphology, we showed that the competition between capillary and viscous forces is responsible for the saturation reduction in the crossover zone. In this zone, finger propagation toward the outlet (characteristic of viscous fingering) as well as void-filling in the transverse/backward directions (characteristic of capillary fingering), are both suppressed. Therefore, the invading fluid tends to occupy larger apertures with higher characteristic front velocity, promoting void-filling toward the outlet with thinner finger growth and resulting in a larger volume of defending fluid left behind.
      PubDate: 2017-08-18T15:52:38.660707-05:
      DOI: 10.1002/2017WR021051
       
  • Improving ecosystem-scale modeling of evapotranspiration using ecological
           mechanisms that account for compensatory responses following disturbance
    • Authors: David J. Millar; Brent E. Ewers, D. Scott Mackay, Scott Peckham, David E. Reed, Adewale Sekoni
      Abstract: Mountain pine beetle outbreaks in western North America have led to extensive forest mortality, justifiably generating interest in improving our understanding of how this type of ecological disturbance affects hydrological cycles. While observational studies and simulations have been used to elucidate the effects of mountain beetle mortality on hydrological fluxes, an ecologically-mechanistic model of forest evapotranspiration (ET) evaluated against field data has yet to be developed. In this work, we use the Terrestrial Regional Ecosystem Exchange Simulator (TREES) to incorporate the ecohydrological impacts of mountain pine beetle disturbance on ET for a lodgepole pine-dominated forest equipped with an eddy covariance tower. An existing degree-day model was incorporated that predicted the life cycle of mountain pine beetles, along with an empirically-derived submodel that allowed sap flux to decline as a function of temperature-dependent blue stain fungal growth. The eddy covariance footprint was divided into multiple cohorts for multiple growing seasons, including representations of recently attacked trees and the compensatory effects of regenerating understory, using two different spatial scaling methods. Our results showed that using a multiple cohort approach matched eddy covariance-measured ecosystem-scale ET fluxes well, and showed improved performance compared to model simulations assuming a binary framework of only areas of live and dead overstory. Cumulative growing season ecosystem-scale ET fluxes were 8 – 29% greater using the multi-cohort approach during years in which beetle attacks occurred, highlighting the importance of including compensatory ecological mechanism in ET models.
      PubDate: 2017-08-18T15:51:31.58737-05:0
      DOI: 10.1002/2017WR020823
       
  • Limits of heat as a tracer to quantify transient lateral river-aquifer
           exchanges
    • Authors: Yueqing Xie; Jordi Batlle-Aguilar
      Abstract: The application of heat as a tracer for assessing river-aquifer exchanges has been mainly limited to vertical flow through the riverbed. Lateral river-aquifer exchanges become more important than vertical riverbed exchanges if the river is deeply incised into an aquifer. Few studies have examined lateral river-aquifer exchanges and the ability of heat to constrain such exchanges. This study aims to perform a robust assessment of the limits of heat as a tracer to quantify lateral river-aquifer exchanges. The study is based on a section of the Meuse River in Belgium, a river predominantly gaining in the studied area and becoming intermittently losing in the winter time. A calibrated transect model shows that river temperature can affect groundwater temperature up to 9 m into the aquifer. An accompanying synthetic modelling investigation using Monte Carlo simulation shows that heat data for distances between 4 and 9 m from the river can reduce the uncertainty of river-aquifer exchanges for conditions similar to those of the transect model. The ability of heat to reduce the river-aquifer exchange uncertainty improves with distance from the river because of the reduction in the number of acceptable model realizations. The optimal distance is 8 m from the river where the groundwater temperature is no longer affected by the river temperature. The synthetic modelling also indicates that heat alone cannot constrain river-aquifer exchanges better than the commonly used hydraulic head. However, when combined with hydraulic head, heat can significantly reduce the uncertainty of river-aquifer lateral exchanges under gaining conditions.
      PubDate: 2017-08-18T15:51:25.570551-05:
      DOI: 10.1002/2017WR021120
       
  • A stable computation of log-derivatives from noisy drawdown data
    • Authors: Gustavo Ramos; Jesus Carrera, Susana Gómez, Carlos Minutti, Rodolfo Camacho
      Abstract: Pumping tests interpretation is an art that involves dealing with noise coming from multiple sources and conceptual model uncertainty. Interpretation is greatly helped by diagnostic plots, which include drawdown data and their derivative with respect to log-time, called log-derivative. Log-derivatives are especially useful to complement geological understanding in helping to identify the underlying model of fluid flow because they are sensitive to subtle variations in the response to pumping of aquifers and oil reservoirs. The main problem with their use lies in the calculation of the log-derivatives themselves, which may display fluctuations when data are noisy. To overcome this difficulty, we propose a variational regularization approach based on the minimization of a functional consisting of two terms: one ensuring that the computed log-derivatives honor measurements and one that penalizes fluctuations. The minimization leads to a diffusion-like differential equation in the log-derivatives, and boundary conditions that are appropriate for well hydraulics (i.e., radial flow, wellbore storage, fractal behavior, etc.). We have solved this equation by finite differences. We tested the methodology on two synthetic examples showing that a robust solution is obtained. We also report the resulting log-derivative for a real case.
      PubDate: 2017-08-18T15:51:21.045408-05:
      DOI: 10.1002/2017WR020811
       
  • Ephemeral and intermittent runoff generation processes in a low relief,
           highly weathered catchment
    • Authors: Margaret A. Zimmer; Brian L. McGlynn
      Abstract: Most field-based approaches that address runoff generation questions have been conducted in steep landscapes with shallow soils. Runoff generation processes in low relief landscapes with deep soils remain less understood. We addressed this by characterizing dominant runoff generating flow paths by monitoring the timing and magnitude of precipitation, runoff, shallow soil moisture, and shallow and deep groundwater dynamics in a 3.3 ha ephemeral-to-intermittent drainage network in the Piedmont region of North Carolina, USA. This Piedmont region is gently sloped with highly weathered soils characterized by shallow impeding layers due to decreases in saturated hydraulic conductivity with depth. Our results indicated two dominant catchment storage states driven by seasonal evapotranspiration. Within these states, distinct flow paths were activated, resulting in divergent hydrograph recessions. Groundwater dynamics during precipitation events with different input characteristics and contrasting storage states showed distinct shallow and deep groundwater flow path behavior could produce similar runoff magnitudes. During an event with low antecedent storage, activation of a shallow, perched, transient water table dominated runoff production. During an event with high antecedent storage, the deeper water table activated shallow flow paths by rising into the shallow transmissive soil horizons. Despite these differing processes, the relationship between active surface drainage length (ASDL) and runoff was consistent. Hysteretic behavior between ASDL and runoff suggested that while seasonal ASDLs can be predicted based on runoff, the mechanisms and source areas producing flow can be highly variable and not easily estimated from runoff alone. These processes and flow paths have significant implications for stream chemistry across seasons and storage states.
      PubDate: 2017-08-18T09:40:33.994237-05:
      DOI: 10.1002/2016WR019742
       
  • Direct measurements of lift and drag on shallowly submerged cobbles in
           steep streams: Implications for flow resistance and sediment transport
    • Authors: Michael P. Lamb; Fanny Brun, Brian M. Fuller
      Abstract: Steep mountain streams have higher resistance to flow and lower sediment-transport rates than expected by comparison with low gradient rivers, and often these differences are attributed to reduced near-bed flow velocities and stresses associated with form drag on channel forms and immobile boulders. However, few studies have directly measured drag and lift forces acting on bed sediment for shallow flows over coarse sediment, which ultimately control sediment transport rates and grain-scale flow resistance. Here we report on particle lift and drag force measurements in flume experiments using a planar, fixed cobble bed over a wide range of channel slopes (0.004 
      PubDate: 2017-08-18T08:10:57.168925-05:
      DOI: 10.1002/2017WR020883
       
  • Using system dynamics simulation for assessment of hydropower system
           safety
    • Authors: L. M. King; S. P. Simonovic, D. N. D. Hartford
      Abstract: Hydropower infrastructure systems are complex, high consequence structures which must be operated safely to avoid catastrophic impacts to human life, the environment, and the economy. Dam safety practitioners must have an in-depth understanding of how these systems function under various operating conditions in order to ensure the appropriate measures are taken to reduce system vulnerability. Simulation of system operating conditions allows modelers to investigate system performance from the beginning of an undesirable event to full system recovery. System dynamics simulation facilitates the modeling of dynamic interactions among complex arrangements of system components, providing outputs of system performance that can be used to quantify safety. This paper presents the framework for a modeling approach that can be used to simulate a range of potential operating conditions for a hydropower infrastructure system. Details of the generic hydropower infrastructure system simulation model are provided. A case study is used to evaluate system outcomes in response to a particular earthquake scenario, with two system safety performance measures shown. Results indicate that the simulation model is able to estimate potential measures of system safety which relate to flow conveyance and flow retention. A comparison of operational and upgrade strategies is shown to demonstrate the utility of the model for comparing various operational response strategies, capital upgrade alternatives, and maintenance regimes. Results show that seismic upgrades to the spillway gates provide the largest improvement in system performance for the system and scenario of interest.
      PubDate: 2017-08-18T07:06:01.400781-05:
      DOI: 10.1002/2017WR020834
       
  • Role of organic phosphorus in sediment in a shallow eutrophic lake
    • Authors: Ryuichiro Shinohara; Mikiya Hiroki, Ayato Kohzu, Akio Imai, Tetsunori Inoue, Eiichi Furusato, Kazuhiro Komatsu, Takayuki Satou, Noriko Tomioka, Koichi Shimotori, Shingo Miura
      Abstract: We tested the hypothesis that mineralization of molybdenum unreactive phosphorus (MUP) in pore water is the major pathway for the changes in the concentration of molybdenum-reactive P (MRP) in pore water and inorganic P in sediment particles. The concentration of inorganic P in the sediment particles increased from December to April in Lake Kasumigaura, whereas concentrations of organic P in the sediment particles and MUP in pore water decreased. These results suggest that MUP mineralization plays a key role as the source of MRP, whereas desorption of inorganic P from the sediment particles into the pore water is a minor process. One-dimensional numerical simulation of sediment particles and the pore water supported the hypothesis. Diffusive flux of MUP was small in pore water, even in near-surface layers, so mineralization was the dominant process for changing the MUP concentration in the pore water. For MRP, diffusion was the dominant process in the surface layer, whereas adsorption onto the sediment was the dominant process in deeper layers. Researchers usually ignore organic P in the sediment, but organic P in sediment particles and the pore water is a key source of inorganic P in the sediment particles and pore water; our results suggest that in Lake Kasumigaura, organic P in the sediment is an important source, even at depths more than 1 cm below the sediment surface. In contrast, the large molecular size of MUP in pore water hampers diffusion of MUP from the sediment into the overlying water.
      PubDate: 2017-08-18T07:00:53.442697-05:
      DOI: 10.1002/2017WR020486
       
  • Complex conductivity of soils
    • Authors: A. Revil; A. Coperey, Z. Shao, N. Florsch, I. L. Fabricius, Y. Deng, J. R. Delsman, P. S. Pauw, M. Karaoulis, P. G. B. de Louw, E. S. van Baaren, W. Dabekaussen, A. Menkovic, J. L. Gunnink
      Abstract: The complex conductivity of soils remains poorly known despite the growing importance of this method in hydrogeophysics. In order to fill this gap of knowledge, we investigate the complex conductivity of 71 soils samples (including four peat samples) and one clean sand in the frequency range 0.1 Hz to 45 kHz. The soil samples are saturated with six different NaCl brines with conductivities (0.031, 0.53, 1.15, 5.7, 14.7, and 22 S m−1, NaCl, 25°C) in order to determine their intrinsic formation factor and surface conductivity. This data set is used to test the predictions of the dynamic Stern polarization model of porous media in terms of relationship between the quadrature conductivity and the surface conductivity. We also investigate the relationship between the normalized chargeability (the difference of in-phase conductivity between two frequencies) and the quadrature conductivity at the geometric mean frequency. This data set confirms the relationships between the surface conductivity, the quadrature conductivity, and the normalized chargeability. The normalized chargeability depends linearly on the cation exchange capacity and specific surface area while the chargeability shows no dependence on these parameters. These new data and the dynamic Stern layer polarization model are observed to be mutually consistent. Traditionally, in hydrogeophysics, surface conductivity is neglected in the analysis of resistivity data. The relationships we have developed can be used in field conditions to avoid neglecting surface conductivity in the interpretation of DC resistivity tomograms. We also investigate the effects of temperature and saturation and, here again, the dynamic Stern layer predictions and the experimental observations are mutually consistent.
      PubDate: 2017-08-18T05:10:56.230103-05:
      DOI: 10.1002/2017WR020655
       
  • Ecohydrological interfaces as hot spots of ecosystem processes
    • Authors: Stefan Krause; Jörg Lewandowski, Nancy B. Grimm, David M. Hannah, Gilles Pinay, Karlie McDonald, Eugènia Martí, Alba Argerich, Laurent Pfister, Julian Klaus, Tom Battin, Scott T. Larned, Jacob Schelker, Jan Fleckenstein, Christian Schmidt, Michael O. Rivett, Glenn Watts, Francesc Sabater, Albert Sorolla, Valentina Turk
      Abstract: The movement of water, matter, organisms, and energy can be altered substantially at ecohydrological interfaces, the dynamic transition zones that often develop within ecotones or boundaries between adjacent ecosystems. Interdisciplinary research over the last two decades has indicated that ecohydrological interfaces are often “hot spots” of ecological, biogeochemical, and hydrological processes and may provide refuge for biota during extreme events. Ecohydrological interfaces can have significant impact on global hydrological and biogeochemical cycles, biodiversity, pollutant removal, and ecosystem resilience to disturbance. The organizational principles (i.e., the drivers and controls) of spatially and temporally variable processes at ecohydrological interfaces are poorly understood and require the integrated analysis of hydrological, biogeochemical, and ecological processes. Our rudimentary understanding of the interactions between different drivers and controls critically limits our ability to predict complex system responses to change. In this paper, we explore similarities and contrasts in the functioning of diverse freshwater ecohydrological interfaces across spatial and temporal scales. We use this comparison to develop an integrated, interdisciplinary framework, including a roadmap for analyzing ecohydrological processes and their interactions in ecosystems. We argue that, in order to fully account for their nonlinear process dynamics, ecohydrological interfaces need to be conceptualized as unique, spatially and temporally dynamic entities, which represents a step change from their current representation as boundary conditions at investigated ecosystems.
      PubDate: 2017-08-17T08:30:51.581518-05:
      DOI: 10.1002/2016WR019516
       
  • Reassessing the role of temperature in precipitation oxygen isotopes
           across the eastern and central United States through weekly
           precipitation-day data
    • Authors: Pete D. Akers; Jeffrey M. Welker, George A. Brook
      Abstract: Air temperature is correlated with precipitation oxygen isotope (δ18Oprcp) variability for much of the eastern and central United States, but the nature of this δ18Oprcp-temperature relationship is largely based on data coarsely aggregated at a monthly resolution. We constructed a database of 6177 weeks of isotope and precipitation-day air temperature data from 25 sites to determine how more precise data change our understanding of this classic relationship. Because the δ18Oprcp-temperature relationship is not perfectly linear, trends in the regression residuals suggest the influence of additional environmental factors such as moisture recycling and extratropical cyclone interactions. Additionally, the temporal relationships between δ18Oprcp and temperature observed in the weekly data at individual sites can explain broader spatial patterns observed across the study region. For 20 of 25 sites, the δ18Oprcp-temperature relationship slope is higher for colder precipitation than for warmer precipitation. Accordingly, northern and western sites with relatively more cold precipitation events have steeper overall relationships with higher slope values than southeastern sites that have more warm precipitation events. Although the magnitude of δ18Oprcp variability increases to the north and west, the fraction of δ18Oprcp variability explained by temperature increases due to wider annual temperature ranges, producing stronger relationships in these regions. When our δ18Oprcp-temperature data is grouped by month, we observe significant variations in the relationship from month to month. This argues against a principal causative role for temperature and suggests the existence of an alternative environmental control on δ18Oprcp values that simply co-varies seasonally with temperature.
      PubDate: 2017-08-14T08:56:18.639237-05:
      DOI: 10.1002/2017WR020569
       
  • Climatic and physiographic controls of spatial variability in surface
           water balance over the contiguous United States using the Budyko
           relationship
    • Authors: John T. Abatzoglou; Darren L. Ficklin
      Abstract: The geographic variability in the partitioning of precipitation into surface runoff (Q) and evapotranspiration (ET) is fundamental to understanding regional water availability. The Budyko equation suggests this partitioning is strictly a function of aridity, yet observed deviations from this relationship for individual watersheds impede using the framework to model surface water balance in ungauged catchments and under future climate and land use scenarios. A set of climatic, physiographic, and vegetation metrics were used to model the spatial variability in the partitioning of precipitation for 211 watersheds across the contiguous United States (CONUS) within Budyko's framework through the free parameter ω (Fu, 1981). A generalized additive model found that four widely available variables, precipitation seasonality, the ratio of soil water holding capacity to precipitation, topographic slope, and the fraction of precipitation falling as snow, explained 81.2% of the variability in ω. The ω model applied to the Budyko equation explained 97% of the spatial variability in long-term Q for an independent set of watersheds. The ω model was also applied to estimate the long-term water balance across the CONUS for both contemporary and mid-21st century conditions. The modeled partitioning of observed precipitation to Q and ET compared favorably across the CONUS with estimates from more sophisticated land-surface modeling efforts. For mid-21st century conditions, the model simulated an increase in the fraction of precipitation used by ET across the CONUS with declines in Q for much of the eastern CONUS and mountainous watersheds across the western US.
      PubDate: 2017-08-14T08:55:47.443457-05:
      DOI: 10.1002/2017WR020843
       
  • Baseflow recession from unsaturated-saturated porous media considering
           lateral unsaturated discharge and aquifer compressibility
    • Authors: Xiuyu Liang; Hongbin Zhan, You-Kuan Zhang, Keith Schilling
      Abstract: Unsaturated flow is an important process in baseflow recessions and its effect is rarely investigated. A mathematical model for a coupled unsaturated-saturated flow in a horizontally unconfined aquifer with time-dependent infiltrations is presented. The effects of the lateral discharge of the unsaturated zone and aquifer compressibility are specifically taken into consideration. Semi-analytical solutions for hydraulic heads and discharges are derived using Laplace transform and Cosine transform. The solutions are compared with solutions of the linearized Boussinesq equation (LB solution) and the linearized Laplace equation (LL solution), respectively. A larger dimensionless constitutive exponent κD (a smaller retention capacity) of the unsaturated zone leads to a smaller discharge during the infiltration period and a larger discharge after the infiltration. The lateral discharge of the unsaturated zone is significant when κD ≤1, and becomes negligible when κD κD≥100. The compressibility of the aquifer has a non-negligible impact on the discharge at early times. For late times, the power index b of the recession curve -dQ/dt∼ aQb, is 1 and independent of κD, where Q is the baseflow and a is a constant lumped aquifer parameter. For early times, b is approximately equal to 3 but it approaches infinity when t0. The present solution is applied to synthetic and field cases. The present solution matched the synthetic data better than both the LL and LB solutions, with a minimum relative error of 16% for estimate of hydraulic conductivity. The present solution was applied to the observed streamflow discharge in Iowa, and the estimated values of the aquifer parameters were reasonable.
      PubDate: 2017-08-14T08:55:42.563294-05:
      DOI: 10.1002/2017WR020938
       
  • Coordinating water conservation efforts through tradable credits: A proof
           of concept for drought response in the San Francisco Bay Area
    • Authors: Patricia Gonzales; Yujie Sun, Newsha Ajami
      Abstract: Water utilities are increasingly relying on water efficiency and conservation to extend the availability of supplies. Despite spatial and institutional inter-dependency of many utilities, these demand-side management initiatives have traditionally been tackled by individual utilities operating in isolation. In this study, we introduce a policy framework for water conservation credits that enables collaboration at the regional scale. Under the proposed approach, utilities have the flexibility to invest in water conservation measures that are appropriate for their specific service area. When utilities have insufficient capacity for local cost-effective measures, they may opt to purchase credits, contributing to fund subsidies for utilities that do have that capacity and can provide the credits, while the region as a whole benefits from more reliable water supplies. This work aims to provide insights on the potential impacts of a water conservation credit policy framework when utilities are given the option to collaborate in their efforts. We model utility decisions as rational cost-minimizing actors subject to different decision-making dynamics and water demand scenarios, and demonstrate the institutional characteristics needed for the proposed policy to be effective. We apply this model to a counterfactual case study of water utility members of the Bay Area Water Supply and Conservation Agency in California during the drought period of June 2015 to May 2016. Our scenario analysis indicates that, when the institutional structure and incentives are appropriately defined, water agencies can achieve economic benefits from collaborating in their conservation efforts, especially if they coordinate more closely in their decision-making.
      PubDate: 2017-08-14T08:55:24.004833-05:
      DOI: 10.1002/2017WR020636
       
  • Irrigation, Risk Aversion, and Water Right Priority under Water Supply
           Uncertainty
    • Authors: Man Li; Wenchao Xu, Mark W. Rosegrant
      Abstract: This paper explores the impacts of a water right's allocative priority―as an indicator of farmers' risk-bearing ability―on land irrigation under water supply uncertainty. We develop and use an economic model to simulate farmers' land irrigation decision and associated economic returns in eastern Idaho. Results indicate that the optimal acreage of land irrigated increases with water right priority when hydroclimate risk exhibits a negatively-skewed or right-truncated distribution. Simulation results suggest that prior appropriation enables senior water rights holders to allocate a higher proportion of their land to irrigation, six times as much as junior rights holders do, creating a gap in the annual expected net revenue reaching up to $141.4 acre−1 or $55,800 per farm between the two groups. The optimal irrigated acreage, expected net revenue, and shadow value of a water right's priority are subject to substantial changes under a changing climate in the future, where temporal variation in water supply risks significantly affects the profitability of agricultural land use under the priority-based water sharing mechanism.
      PubDate: 2017-08-14T08:50:28.950791-05:
      DOI: 10.1002/2016WR019779
       
  • Nonlinear empirical modeling to estimate phosphorus exports using
           continuous records of turbidity and discharge
    • Authors: Camille Minaudo; Remi Dupas, Chantal Gascuel-Odoux, Ophelie Fovet, Per-Erik Mellander, Philip Jordan, Mairead Shore, Florentina Moatar
      Abstract: We tested an empirical modelling approach using relatively low-cost continuous records of turbidity and discharge as proxies to estimate phosphorus (P) concentrations at a sub-hourly time step for estimating loads. The method takes into account non-linearity and hysteresis effects during storm events, and hydrological conditions variability. High-frequency records of total P and reactive P originating from four contrasting European agricultural catchments in terms of P loads were used to test the method. The models were calibrated on weekly grab sampling data combined with 10 storms surveyed sub-hourly per year (weekly+ survey) and then used to reconstruct P concentrations during all storm events for computing annual loads. For total P, results showed that this modelling approach allowed the estimation of annual loads with limited uncertainties (≈ -10% ± 15%), more reliable than estimations based on simple linear regressions using turbidity, based on interpolated weekly+ data without storm event reconstruction, or on discharge weighted calculations from weekly series or monthly series. For reactive P, load uncertainties based on the non-linear model were similar to uncertainties based on storm event reconstruction using simple linear regression (≈ 20% ± 30%), and remained lower than uncertainties obtained without storm reconstruction on weekly or monthly series, but larger than uncertainties based on interpolated weekly+ data (≈ -15% ± 20%). These empirical models showed we could estimate reliable P exports from non-continuous P time series when using continuous proxies, and this could potentially be very useful for completing time-series datasets in high-frequency surveys, even over extended periods.
      PubDate: 2017-08-14T08:50:26.147142-05:
      DOI: 10.1002/2017WR020590
       
  • Revisiting the horizontal redistribution of water in soils: Experiments
           and numerical modeling
    • Authors: L. Zhuang; S.M. Hassanizadeh, P. J. Kleingeld, M.Th. van Genuchten
      Abstract: A series of experiments and related numerical simulations were carried out to study one-dimensional water redistribution processes in an unsaturated soil. A long horizontal Plexiglas box was packed as homogenously as possible with sand. The sandbox was divided into two sections using a very thin metal plate, with one section initially fully saturated and the other section only partially saturated. Initial saturation in the dry section was set to 0.2, 0.4 or 0.6 in three different experiments. Redistribution between the wet and dry sections started as soon as the metal plate was removed. Changes in water saturation at various locations along the sandbox were measured as a function of time using a dual-energy gamma system. Also, air and water pressures were measured using two different kinds of tensiometers at various locations as a function of time. The saturation discontinuity was found to persist during the entire experiments, while observed water pressures were found to become continuous immediately after the experiments started. Two models, the standard Richards equation and an interfacial area model, were used to simulate the experiments. Both models showed some deviations between the simulated water pressures and the measured data at early times during redistribution. The standard model could only simulate the observed saturation distributions reasonably well for the experiment with the lowest initial water saturation in the dry section. The interfacial area model could reproduce observed saturation distributions of all three experiments, albeit by fitting one of the parameters in the surface area production term.
      PubDate: 2017-08-03T08:55:24.859937-05:
      DOI: 10.1002/2017WR020410
       
  • Modeling sediment transport with an integrated view of the biofilm effects
    • Authors: H. W. Fang; H. J. Lai, W. Cheng, L. Huang, G. J. He
      Abstract: Most natural sediment is invariably covered by biofilms in reservoirs and lakes, which have significant influence on bedform dynamics and sediment transport, and also play a crucial role in natural river evolution, pollutant transport, and habitat changes. However, most models for sediment transport are based on experiments using clean sediments without biological materials. In this study, a three-dimensional mathematical model of hydrodynamics and sediment transport is presented with a comprehensive consideration of the biofilm effects. The changes of the bed resistance mainly due to the different bedform dynamics of the biofilm-coated sediment (bio-sediment), which affect the hydrodynamic characteristics, are considered. Moreover, the variations of parameters related to sediment transport after the biofilm growth are integrated, including the significant changes of the incipient velocity, settling velocity, reference concentration and equilibrium bed-load transport rate, etc. The proposed model is applied to evaluate the effects of biofilms on the hydrodynamic characteristics and sediment transport in laboratory experiments. Results indicate that the mean velocity increases after the biofilm growth, and the turbulence intensity near the river bed decreases under the same flow condition. Meanwhile, biofilm inhibits sediment from moving independently. Thus, the moderate erosion is observed for bio-sediment resulting in smaller suspended sediment concentrations. The proposed model can reasonably reflect these sediment transport characteristics with biofilms, and the approach to integration of the biological impact could also be used in other modeling of sediment transport, which can be further applied to provide references for the integrated management of natural aqueous systems.
      PubDate: 2017-08-03T08:51:08.569232-05:
      DOI: 10.1002/2017WR020628
       
  • Spectral model for long-term computation of thermodynamics and potential
           evaporation in shallow wetlands
    • Authors: Alberto de la Fuente; Carolina Meruane
      Abstract: Altiplanic wetlands are unique ecosystems located in the elevated plateaus of Chile, Argentina, Peru and Bolivia. These ecosystems are under threat due to changes in land use, groundwater extractions and climate change that will modify the water balance through changes in precipitation and evaporation rates. Long-term prediction of the fate of aquatic ecosystems imposes computational constraints that make finding a solution impossible in some cases. In this article, we present a spectral model for long-term simulations of the thermodynamics of shallow wetlands in the limit case when the water depth tends to zero. This spectral model solves for water and sediment temperatures, as well as heat, momentum and mass exchanged with the atmosphere. The parameters of the model (water depth, thermal properties of the sediments and surface albedo) and the atmospheric downscaling were calibrated using the MODIS product of the land surface temperature. Moreover, the performance of the daily evaporation rates predicted by the model was evaluated against daily pan evaporation data measured between 1964 and 2012. The spectral model was able to correctly represent both seasonal fluctuation and climatic trends observed in daily evaporation rates. It is concluded that the spectral model presented in this article is a suitable tool for assessing the global climate change effects on shallow wetlands whose thermodynamics is forced by heat exchanges with the atmosphere and modulated by the heat reservoir role of the sediments.
      PubDate: 2017-08-03T08:50:48.980233-05:
      DOI: 10.1002/2017WR020515
       
  • Entropy production in a box: Analysis of instabilities in confined
           hydrothermal systems
    • Authors: N. Börsing; J. F. Wellmann, J. Niederau, K. Regenauer-Lieb
      Abstract: We evaulate if the concept of thermal entropy production can be used as a measure to characterize hydrothermal convection in a confined porous medium as a valuable, thermodynamically-motivated addition to the standard Rayleigh number analysis. Entropy production has been used widely in the field of mechanical and chemical engineering as a way to characterise the thermodynamic state and irreversibility of an investigated system. Pinoneering studies have since adapted these concepts to natural systems, and we apply this measure here to investigate the specific case of hydrothermal convection in a “box-shaped” confined porous medium, as a simplified analogue for, e.g., hydrothermal convection in deep geothermal aquifers. We perform various detailed numerical experiments to assess the response of the convective system to changing boundary conditions or domain aspect ratios, and then determine the resulting entropy production for each experiment. In systems close to the critical Rayleigh number, we derive results that are in accordance to the analytically derived predictions. At higher Rayleigh numbers however, we observe multiple possible convection modes, and the analysis of the integrated entropy production reveals distinct curves of entropy production that provide an insight into the hydrothermal behaviour in the system, both for cases of homogeneous materials, as well as for heterogeneous spatial material distributions. We conclude that the average thermal entropy production characterizes the internal behaviour of hydrothermal systems with a meaningful thermodynamic measure, and we expect that it can be useful for the investigation of convection systems in many similar hydrogeological and geophysical settings.
      PubDate: 2017-08-03T08:50:43.766491-05:
      DOI: 10.1002/2017WR020427
       
  • The impact of conventional space-time aggregation on the dynamics of
           continuous-time rainfall
    • Authors: John Sansom; Jan Bulla, Trevor Carey-Smith, Peter Thomson
      Abstract: Rainfall is a continuous-time phenomenon typically characterised by precipitation states such as rain, showers and dry whose dependence varies over a variety of space-time scales. Here attention is focussed on the effective identification of rain and shower precipitation states over a region where these states have been determined by a hidden semi-Markov model of continuous-time precipitation. The states identified provide an accurate description of precipitation dynamics and can be regarded as close proxies to synoptic weather types of the same name. The stochastic properties and structure of these states (rather than precipitation amounts) are explored and delineated. A primary objective of the paper is to better understand the impact of conventional space-time aggregation on the dynamics of rainfall. What aggregation time scales result in more faithful descriptions of the space-time dynamics of continuous-time rainfall' While rain might be expected to be more spatially coherent than showers and involve longer time scales, dry periods involve much longer time and space scales again than either rain or showers. These issues are discussed and conclusions drawn which provide guidance and insights useful for the development of space-time precipitation models and, more generally, the design of rainfall observation networks and data archives.
      PubDate: 2017-08-03T08:50:35.473174-05:
      DOI: 10.1002/2017WR021074
       
  • Validation of a 30 m resolution flood hazard model of the conterminous
           United States
    • Authors: Oliver E. J. Wing; Paul D. Bates, Christopher C. Sampson, Andrew M. Smith, Kris A. Johnson, Tyler A. Erickson
      Abstract: This paper reports the development of a ∼30m resolution two-dimensional hydrodynamic model of the conterminous US using only publicly available data. The model employs a highly efficient numerical solution of the local inertial form of the shallow water equations which simulates fluvial flooding in catchments down to 50 km2 and pluvial flooding in all catchments. Importantly, we use the US Geological Survey (USGS) National Elevation Dataset to determine topography; the US Army Corps of Engineers National Levee Dataset to explicitly represent known flood defenses; and global regionalized flood frequency analysis to characterize return period flows and rainfalls. We validate these simulations against the complete catalogue of Federal Emergency Management Agency (FEMA) Special Flood Hazard Area (SFHA) maps and detailed local hydraulic models developed by the USGS. Where the FEMA SFHAs are based on high quality local models, the continental-scale model attains a Hit Rate of 86%. This correspondence improves in temperate areas and for basins above 400 km2. Against the higher quality USGS data the average Hit Rate reaches 92% for the 1 in 100-year flood, and 90% for all flood return periods. Given typical hydraulic modeling uncertainties in the FEMA maps and USGS model outputs (e.g. errors in estimating return period flows), it is probable that the continental-scale model can replicate both to within error. The results show that continental-scale models may now offer sufficient rigor to inform some decision-making needs with dramatically lower cost and greater coverage than approaches based on a patchwork of local studies.
      PubDate: 2017-08-01T08:00:34.749834-05:
      DOI: 10.1002/2017WR020917
       
  • Subsurface flow in lowland river gravel bars
    • Authors: E. N. Bray; T. Dunne
      Abstract: Geomorphic and hydraulic processes, which form gravel bars in large lowland rivers, have distinctive characteristics that control the magnitude and spatial patterns of infiltration and exfiltration between rivers and their immediate subsurface environments. We present a bedform-infiltration relation together with a set of field measurements along two reaches of the San Joaquin River, CA to illustrate the conditions required for infiltration and exfiltration of flow between a stream and its undulating bed, and a numerical model to investigate the factors that affect paths and residence times of flow through barforms at different discharges. It is shown that asymmetry of bar morphology is a first-order control on the extent and location of infiltration, which would otherwise produce equal areas of infiltration and exfiltration under the assumption of sinusoidal bedforms. Hydraulic conductivity varies by orders of magnitude due to fine sediment accumulation and downstream coarsening related to the process of bar evolution. This systematic variability not only controls the magnitude of infiltration, but also the residence time of flow through the bed. The lowest hydraulic conductivity along the reach occurred where the difference between the topographic gradient and the water-surface gradient is at a maximum and thus where infiltration would be greatest into a homogeneous bar, indicating the importance of managing sand supply to maintain the ventilation and flow through salmon spawning riffles. Numerical simulations corroborate our interpretation that infiltration patterns and rates are controlled by distinctive features of bar morphology.
      PubDate: 2017-08-01T07:55:39.641257-05:
      DOI: 10.1002/2016WR019514
       
  • Long-term morphodynamics of muddy backbarrier basins: Fill in or empty
           out'
    • Authors: G. Mariotti; A. Canestrelli
      Abstract: The long-term (3000 years) morphodynamics of an idealized muddy backbarrier tidal basins is studied using a shallow-water hydrodynamics and wind-wave model (Deltf3D-FLOW-WAVE), modified to include fully-coupled marsh organogenic accretion, biostabilization, drag increase, and wave-induced marsh edge erosion. The latter process is implemented with a novel probabilistic algorithm. Starting from an initially empty basin with a uniform bed slope, a network of channels incise the mudflat, sediment is released, and marshes establish at the basin landward margin. If enough mud is supplied to the basin from the shelf, marsh progradation counteracts marsh edge erosion and marshes expand. Marsh expansion does not completely fill the basin, but leaves open a few km-wide channels, large enough for waves to resuspend sediment. Starting from a basin (almost) filled with marshes, a drop in the external mud supply or an increase in the rate of relative sea level rise cause the basin to empty out by marsh edge erosion, while the marsh platform, aided by reworking of the sediment released by marsh retreat and mudflat deepening, keeps pace even with fast rates (10 mm/yr) of relative sea level rise. Even if the marsh does not drown, the marsh retreats faster if the rate of sea level rise increases, because more sediment is sequestered to fill the newly created accommodation space and is thus not available for marsh progradation. This study suggests that prediction of marsh erosion requires a basin-scale sediment budget, and that edge erosion, not platform drowning, is likely to dominate marsh loss.
      PubDate: 2017-07-26T12:06:21.735195-05:
      DOI: 10.1002/2017WR020461
       
  • Homogeneity testing for spatially correlated data in multivariate regional
           frequency analysis
    • Authors: Tereza Šimková
      Abstract: Identification of homogeneous regions is a key task in regional frequency analysis (RFA) to obtain adequate quantile estimates for an event of interest. Recently, the frequently used univariate Hosking-Wallis L-moment homogeneity test was extended to the multivariate case. Multivariate L-moments are used as a tool to define the test statistic and copula models to describe the statistical behavior of the analyzed dependent variables. To avoid drawbacks in fitting a parametric joint distribution to the data and a rejection threshold which is based on simulations, its nonparametric alternatives were also proposed. Although the simulation studies performed demonstrated the usefulness of both the parametric and nonparametric tests, the powers obtained were valid only for regions without intersite dependence. Examples from practice nevertheless demonstrate that intersite correlation may be expected for some kinds of data. To overcome the problem of cross-correlation between stations, the parametric testing procedure is generalized using D-vine copulas to model intersite dependence when generating synthetic homogeneous regions during the testing procedure. Monte Carlo simulations were performed and illustrate how intersite dependence negatively impacts the multivariate L-moment homogeneity tests by significantly reducing their powers. The results of simulations also demonstrate the superiority of the proposed modification over both the original parametric and nonparametric procedures inasmuch as it improves the heterogeneity detection and avoids miscategorization of a region. The modified test is also applied in a case study for meteorological data in the Czech Republic.
      PubDate: 2017-07-26T08:50:45.233458-05:
      DOI: 10.1002/2016WR020295
       
  • Isolating roughness scales of gravel-bed patches
    • Authors: Stephane Bertin; Jane Groom, Heide Friedrich
      Abstract: There is a growing consensus that gravel-bed roughness should be parameterized based on bed-surface topography, not only sediment size. One benefit is the possible identification of various spatial scales of surface roughness and evaluation of their respective contributions to flow resistance (and also to bedload transport). The absence of relationships between roughness at the different scales is apparent in previous work, which currently limits roughness parameterization from topography and application in flow modeling. This study examines the use of moving-window detrending on gravel-bed digital elevation models (DEMs) for isolating roughness scales and their respective signatures. A large dataset of 35 water-worked gravel-bed patches from both the laboratory and the field was used for the analysis. The measured bed topography was separated into two distinct DEMs: one representing grains, the other representing small bedforms. For all DEMs, bed-elevation parameters measuring vertical roughness, imbrication, and spatial correlations were determined. Our results show distinct topographic signatures between grain and bedform DEMs. We show strong positive linear relationships between grain vertical roughness and the size of the bed-surface material. Surface sediment arrangement also determined bedform shape, with groupings of coarse sediment forming humps on the surface, and finer sediment sheltered in hollows. Patch-scale vertical roughness could not be estimated simply as the sum of grain and bedform vertical roughness. Instead, our results suggest weighted summation and the existence of universal weighting coefficients. Practical applications for studies on gravel-bed roughness and flow modeling using DEMs are discussed.
      PubDate: 2017-07-26T08:50:42.950186-05:
      DOI: 10.1002/2016WR020205
       
  • Abundance and morphometry changes across the high mountain lake-size
           gradient in the tropical Andes of Southern Ecuador
    • Authors: Pablo V. Mosquera; Henrietta Hampel, Raúl F. Vázquez, Miguel Alonso, Jordi Catalan
      Abstract: The number, size, and shape of lakes are key determinants of the ecological functionality of a lake district. The lake area scaling relationships with lake number and volume enable upscaling biogeochemical processes and spatially considering organisms' metapopulation dynamics. These relationships vary regionally depending on the geomorphological context, particularly in the range of lake area 104 m2, and 50% of the water resources are held in a few ones (ca. 10) deeper than 18 m. Therefore, mid and large lakes are by far more biogeochemically relevant than ponds and shallow lakes in this tropical mountain lake district.
      PubDate: 2017-07-26T08:50:31.863771-05:
      DOI: 10.1002/2017WR020902
       
  • Input variable sensitivity assessment for sediment transport relations
    • Authors: Roberto Fernández; Marcelo H. Garcia
      Abstract: A methodology to assess input-variable sensitivity for sediment transport relations is presented. The Mean Value First Order Second Moment Method (MVFOSM) is applied to two bedload transport equations showing that it may be used to rank all input variables in terms of how their specific variance affects the overall variance of the sediment transport estimation. In sites where data are scarce or nonexistent, the results obtained may be used to i) determine what variables would have the largest impact when estimating sediment loads in the absence of field observations and ii) design field campaigns to specifically measure those variables for which a given transport equation is most sensitive; In sites where data are readily available, the results would allow quantifying the effect that the variance associated with each input variable has on the varaince of the sediment transport estimates. An application of the method to two transport relations using data from a tropical mountain river in Costa Rica is implemented to exemplify the potential of the method in places where input data are limited. Results are compared against Monte Carlo simulations to assess the reliability of the method and validate its results. For both of the sediment transport relations used in the sensitivity analysis, accurate knowledge of sediment size was found to have more impact on sediment transport predictions than precise knowledge of other input variables such as channel slope and flow discharge.
      PubDate: 2017-07-26T08:50:28.481738-05:
      DOI: 10.1002/2016WR020249
       
  • Deriving adaptive operating rules of hydropower reservoirs using
           time-varying parameters generated by the EnKF
    • Authors: Maoyuan Feng; Pan Liu, Shenglian Guo, Liangsheng Shi, Chao Deng, Bo Ming
      Abstract: Operating rules have been used widely to decide reservoir operations because of their capacity for coping with uncertain inflow. However, stationary operating rules lack adaptability; thus, under changing environmental conditions, they cause inefficient reservoir operation. This paper derives adaptive operating rules based on time-varying parameters generated using the ensemble Kalman filter (EnKF). A deterministic optimization model is established to obtain optimal water releases, which are further taken as observations of the reservoir simulation model. The EnKF is formulated to update the operating rules sequentially, providing a series of time-varying parameters. To identify the index that dominates the variations of the operating rules, three hydrologic factors are selected: the reservoir inflow, ratio of future inflow to current available water, and available water. Finally, adaptive operating rules are derived by fitting the time-varying parameters with the identified dominant hydrologic factor. China's Three Gorges Reservoir was selected as a case study. Results show that (1) the EnKF has the capability of capturing the variations of the operating rules, (2) reservoir inflow is the factor that dominates the variations of the operating rules, and (3) the derived adaptive operating rules are effective in improving hydropower benefits compared with stationary operating rules. The insightful findings of this study could be used to help adapt reservoir operations to mitigate the effects of changing environmental conditions.
      PubDate: 2017-07-26T08:50:24.3625-05:00
      DOI: 10.1002/2016WR020180
       
  • Temporal variability in the importance of hydrologic, biotic, and climatic
           descriptors of dissolved oxygen dynamics in a shallow tidal-marsh creek
    • Authors: Natalie G. Nelson; Rafael Muñoz-Carpena, Patrick J. Neale, Maria Tzortziou, J. Patrick Megonigal
      Abstract: Due to strong abiotic forcing, dissolved oxygen (DO) in shallow tidal creeks often disobeys the conventional explanation of general aquatic DO cycling as biologically-regulated. In the present work, we seek to quantify the relative importance of abiotic (hydrologic and climatic), and biotic (primary productivity as represented by chlorophyll-a) descriptors of tidal creek DO. By fitting multiple linear regression models of DO to hourly chlorophyll-a, water quality, hydrology, and weather data collected in a tidal creek of a Chesapeake Bay marsh (Maryland, USA), temporal shifts (summer – early winter) in the relative importance of tidal creek DO descriptors were uncovered. Moreover, this analysis identified an alternative approach to evaluating tidal stage as a driver of DO by dividing stage into two DO-relevant variables: stage above and below bankfull depth. Within the hydrologic variable class, stage below bankfull depth dominated as an important descriptor, thus highlighting the role of pore water drainage and mixing as influential processes forcing tidal creek DO. Study findings suggest that tidal creek DO dynamics are explained by a balance of hydrologic, climatic, and biotic descriptors during warmer seasons due to many of these variables (i.e., chlorophyll-a, water temperature) acting as tracers of estuarine-marsh water mixing; conversely, in early winter months when estuarine and marsh waters differ less distinctly, hydrologic variables increase in relative importance as descriptors of tidal creek DO. These findings underline important distinctions in the underlying mechanisms dictating DO variability in shallow tidal marsh-creek environments relative to open water estuarine systems.
      PubDate: 2017-07-24T07:56:20.539069-05:
      DOI: 10.1002/2016WR020196
       
  • Generation of complex karstic conduit networks with a hydro-chemical model
    • Authors: Rob de Rooij; Wendy Graham
      Abstract: In this paper we present a hydro-chemical model that can be used to generate plausible karstic conduit networks that honor what is known about geology, hydrology and topography of a karst system. To make the model applicable to a range of natural karst systems, we introduce a flexible and physically realistic flow boundary condition along the land surface. Moreover, whereas comparable existing speleogenesis models use an explicit reactive-transport scheme, we propose an implicit reactive-transport scheme to permit a coarser spatial discretization of the conduit cells. An application to a real karst system illustrates that the model can generate a realistic karstic network that reproduces observed hydrologic behavior in terms of current spring flow rates, regional hydraulic head field as well as average groundwater residence times. Our model provides a useful tool to generate ensembles of possible karstic conduit networks that may be used within a stochastic framework to analyze flow and transport prediction uncertainty associated with a lack of knowledge about network geometry.
      PubDate: 2017-07-24T07:55:24.605446-05:
      DOI: 10.1002/2017WR020768
       
  • Rival framings: A framework for discovering how problem formulation
           uncertainties shape risk management tradeoffs in water resources systems
    • Authors: J. D. Quinn; P. M. Reed, M. Giuliani, A. Castelletti
      Abstract: Managing water resources systems requires coordinated operation of system infrastructure to mitigate the impacts of hydrologic extremes while balancing conflicting multi-sectoral demands. Traditionally, recommended management strategies are derived by optimizing system operations under a single problem framing that is assumed to accurately represent the system objectives, tacitly ignoring the myriad of effects that could arise from simplifications and mathematical assumptions made when formulating the problem. This study illustrates the benefits of a rival framings framework in which analysts instead interrogate multiple competing hypotheses of how complex water management problems should be formulated. Analyzing rival framings helps discover unintended consequences resulting from inherent biases of alternative problem formulations. We illustrate this on the monsoonal Red River basin in Vietnam by optimizing operations of the system's four largest reservoirs under several different multi-objective problem framings. In each rival framing, we specify different quantitative representations of the system's objectives related to hydropower production, agricultural water supply and flood protection of the capital city of Hanoi. We find that some formulations result in counterintuitive behavior. In particular, policies designed to minimize expected flood damages inadvertently increase the risk of catastrophic flood events in favor of hydropower production, while min-max objectives commonly used in robust optimization provide poor representations of system tradeoffs due to their instability. This study highlights the importance of carefully formulating and evaluating alternative mathematical abstractions of stakeholder objectives describing the multi-sectoral water demands and risks associated with hydrologic extremes.
      PubDate: 2017-07-21T08:55:53.138588-05:
      DOI: 10.1002/2017WR020524
       
  • Modeling invasive alien plant species in river systems: Interaction with
           native ecosystem engineers and effects on hydro-morphodynamic processes
    • Authors: M. van Oorschot; M.G. Kleinhans, G.W. Geerling, G. Egger, R.S.E.W. Leuven, H. Middelkoop
      Abstract: Invasive alien plant species negatively impact native plant communities by out-competing species or changing abiotic and biotic conditions in their introduced range. River systems are especially vulnerable to biological invasions, because waterways can function as invasion corridors. Understanding interactions of invasive and native species and their combined effects on river dynamics is essential for developing cost-effective management strategies. However, numerical models for simulating long-term effects of these processes are lacking. This paper investigates how an invasive alien plant species affects native riparian vegetation and hydro-morphodynamics. A morphodynamic model has been coupled to a dynamic vegetation model that predicts establishment, growth and mortality of riparian trees. We introduced an invasive alien species with life-history traits based on Japanese Knotweed (Fallopia japonica), and investigated effects of low- and high propagule pressure on invasion speed, native vegetation and hydro-morphodynamic processes. Results show that high propagule pressure leads to a decline in native species cover due to competition and the creation of unfavorable native colonization sites. With low propagule pressure the invader facilitates native seedling survival by creating favorable hydro-morphodynamic conditions at colonization sites. With high invader abundance, water levels are raised and sediment transport is reduced during the growing season. In winter, when the above-ground invader biomass is gone, results are reversed and the floodplain is more prone to erosion. Invasion effects thus depend on seasonal above- and below ground dynamic vegetation properties and persistence of the invader, on the characteristics of native species it replaces, and the combined interactions with hydro-morphodynamics.
      PubDate: 2017-07-20T08:38:42.971683-05:
      DOI: 10.1002/2017WR020854
       
  • Process-based interpretation of conceptual hydrological model performance
           using a multinational catchment set
    • Authors: C. Poncelet; R. Merz, B. Merz, J. Parajka, L. Oudin, V. Andréassian, C. Perrin
      Abstract: Most of previous assessments of hydrologic model performance are fragmented, based on small number of catchments, different methods or time periods and do not link the results to landscape or climate characteristics. This study uses a large-sample hydrology to identify major catchment controls on daily runoff simulations. It is based on a conceptual lumped hydrological model (GR6J), a collection of 29 catchment characteristics, a multinational set of 1103 catchments located in Austria, France and Germany and four runoff model efficiency criteria. Two analyses are conducted to assess how features and criteria are linked: (i) a one-dimensional analysis based on the Kruskal-Wallis test and (ii) a multidimensional analysis based on regression trees and investigating the interplay between features. The catchment features most affecting model performance are the flashiness of precipitation and streamflow (computed as the ratio of absolute day-to-day fluctuations by the total amount in a year), the seasonality of evaporation, the catchment area and the catchment aridity. Nonflashy, nonseasonal, large and nonarid catchments show the best performance for all the tested criteria. We argue that this higher performance is due to fewer nonlinear responses (higher correlation between precipitation and streamflow) and lower input and output variability for such catchments. Finally we show that, compared to national sets, multinational sets increase results transferability because they explore a wider range of hydro-climatic conditions.
      PubDate: 2017-07-20T08:36:16.548456-05:
      DOI: 10.1002/2016WR019991
       
  • Managed aquifer recharge through off-season irrigation in agricultural
           regions
    • Authors: Richard G. Niswonger; Eric D. Morway, Enrique Triana, Justin L. Huntington
      Abstract: Options for increasing reservoir storage in developed regions are limited and prohibitively expensive. Projected increases in demand call for new long-term water storage to help sustain agriculture, municipalities, industry, and ecological services. Managed aquifer recharge (MAR) is becoming an integral component of water resources around the world. However, MAR faces challenges, including infrastructure costs, difficulty in enhancing recharge, water quality issues, and lack of available water supplies. Here we examine, through simulation modeling of a hypothetical agricultural subbasin in the western US, the potential of agricultural managed aquifer recharge (Ag-MAR) via canal seepage and off-season field irrigation. Weather phenomenon in many regions around the world exhibit decadal and other multi-year cycles of extreme precipitation. An on-going challenge is to develop approaches to store greater amounts of water during these events. Simulations presented herein incorporate Ag-MAR programs and demonstrate that there is potential to enhance regional recharge by 7-13%, increase crop consumptive use by 9-12%, and increase natural vegetation consumption by 20-30%, where larger relative increases occur for lower aquifer hydraulic conductivity and higher specific yield values. Annual Increases in groundwater levels were 7 m, and sustained levels following several years of drought were greater than 2 m. Results demonstrate that Ag-MAR has great potential to enhance long-term sustainability of water resources in agricultural basins.
      PubDate: 2017-07-20T08:35:52.415366-05:
      DOI: 10.1002/2017WR020458
       
  • Hydrologic Impacts of changes in climate and glacier extent in the Gulf of
           Alaska watershed
    • Authors: J.P. Beamer; D.F. Hill, D. McGrath, A. Arendt, C. Kienholz
      Abstract: High-resolution regional-scale hydrologic models were used to quantify the response of late 21st century runoff from the Gulf of Alaska (GOA) watershed to changes in regional climate and glacier extent. NCEP Climate Forecast System Reanalysis data were combined with five Coupled Model Intercomparison Project Phase 5 General Circulation Models (GCM) for two representative concentration pathway (RCP) scenarios (4.5 and 8.5) to develop meteorological forcing for the period 2070–2099. A hypsographic model was used to estimate future glacier extent given assumed equilibrium line altitude (ELA) increases of 200 and 400 m. GCM predictions show an increase in annual precipitation of 12% for RCP 4.5 and 21% for RCP 8.5, and an increase in annual temperature of 2.5°C for RCP 4.5 and 4.3°C for RCP 8.5, averaged across the GOA. Scenarios with perturbed climate and glaciers predict annual GOA-wide runoff to increase by 9% for RCP4.5/ELA200 case and 14% for the RCP8.5/ELA400 case. The glacier runoff decreased by 14% for RCP4.5/ELA200 and by 34% for the RCP8.5/ELA400 case. Inter-model variability in annual runoff was found to be approximately twice the variability in precipitation input. Additionally, there are significant changes in runoff partitioning and increases in snowpack runoff are dominated by increases in rain-on-snow events. We present results aggregated across the entire GOA and also for individual watersheds to illustrate the range in hydrologic regime changes, and explore the sensitivities of these results by independently perturbing only climate forcings and only glacier cover.
      PubDate: 2017-07-20T08:35:33.013802-05:
      DOI: 10.1002/2016WR020033
       
  • Remote determination of the velocity index and mean streamwise velocity
           profiles
    • Authors: E. D. Johnson; E. A. Cowen
      Abstract: When determining volumetric discharge from surface measurements of currents in a river or open channel, the velocity index is typically used to convert surface velocities to depth-averaged velocities. The velocity index is given by, k = Ub/Usurf, where Ub is the depth-averaged velocity and Usurf is the local surface velocity. The USGS (United States Geological Survey) standard value for this coefficient, k = 0.85, was determined from a series of laboratory experiments and has been widely used in the field and in laboratory measurements of volumetric discharge despite evidence that the velocity index is site-specific. Numerous studies have documented that the velocity index varies with Reynolds number, flow depth, relative bed roughness and with the presence of secondary flows. A remote method of determining depth-averaged velocity and hence the velocity index is developed here. The technique leverages the findings of Johnson and Cowen [2017] and permits remote determination of the velocity power law exponent thereby, enabling remote prediction of the vertical structure of the mean streamwise velocity, the depth-averaged velocity and the velocity index.
      PubDate: 2017-07-20T08:35:29.211547-05:
      DOI: 10.1002/2017WR020504
       
  • Dynamics of nitrate concentration-discharge patterns in an urban watershed
    • Authors: Jonathan M. Duncan; Claire Welty, John T. Kemper, Peter M. Groffman, Lawrence E. Band
      Abstract: Concentration-discharge (c-Q) relations have been used to infer watershed-scale processes governing solute fluxes. Prior studies have documented inconsistent concentration-discharge patterns at the storm event scale driven by changes in end-member concentrations. Other studies have evaluated c-Q data from all periods in a composite fashion to quantify chemostasis (relatively invariant changes in concentration over several orders of magnitude variation in streamflow). Here we examine three-years of high-frequency nitrate and discharge data (49,861 data points) to complement 14 years of weekly data (699 data points) for an urban stream in Baltimore, MD USA to quantify c-Q relationships. We show that these relationships are variable through time and depend on the temporal scale at which they are investigated. On a storm-event scale, the sensor data exhibit a watershed-specific dQ/Q threshold when storms switch from counter-clockwise to clockwise c-Q behavior. On a seasonal scale, we show the influence of hydrologic variability and in-stream metabolism as controls on stream nitrate concentrations and fluxes. On a composite scale, we evaluate the c-Q data for chemostasis using analysis of both c-Q slopes and CVc/CVQ, as a function of time. The slopes of c-Q data for both long-term weekly and high frequency data sets are in close agreement on an annual basis and vary between dry and wet years; the CVc/CVQ analysis is less sensitive to hydroclimate variability. This work highlights the value of both long-term and high-frequency c-Q data collection for calculating and analyzing solute fluxes.
      PubDate: 2017-07-18T13:50:42.663974-05:
      DOI: 10.1002/2017WR020500
       
  • Covariation in patterns of turbulence-driven hyporheic flow and
           denitrification enhances reach-scale nitrogen removal
    • Authors: Angang Li; Antoine F. Aubeneau, Diogo Bolster, Jennifer L. Tank, Aaron I. Packman
      Abstract: Co-injections of conservative tracers and nutrients are commonly used to assess travel time distributions and nutrient removal in streams. However, in-stream tracer data often lack information on long-term hyporheic storage, and removal rate coefficients are often assumed to be uniform despite plentiful evidence that microbially-mediated transformations, such as denitrification, exhibit strong spatial variability in the hyporheic zone. We used process-based particle tracking simulations to explore the coupled effects of spatial patterns in hyporheic flow and denitrification on reach-scale nitrogen removal. We simulated whole-stream nitrogen dynamics with exponential, layered, and uniform profiles of hyporheic denitrification. We also simulated nitrogen dynamics in Little Rabbit Creek, an agricultural headwater stream in the Kalamazoo River Basin (Michigan, U.S.) where vertical profiles of hyporheic denitrification were measured in situ. Covariation between porewater velocity and mixing causes rapid exchange in the near-surface bioactive region and substantially prolonged exchange in the deeper hyporheic. Patterns of hyporheic denitrification covary with patterns of hyporheic flow. This covariation directly controls tailing of in-stream breakthrough curves and hence reach-scale nutrient removal. Enhanced denitrification near the sediment-water interface strongly tempers breakthrough curve tails at timescales associated with flushing of the near-surface region, while more spatially uniform denitrification causes weaker tempering over a wider range of hyporheic exchange timescales. At the reach scale, overall nitrogen removal increases with heterogeneity of hyporheic denitrification, indicating that covariation between flow and denitrification – particularly the rapid flushing of highly bioactive regions near the sediment-water interface – controls whole-stream transformation rates.
      PubDate: 2017-07-15T03:30:53.654769-05:
      DOI: 10.1002/2016WR019949
       
  • Regional sensitivities of seasonal snowpack to elevation, aspect, and
           vegetation cover in western North America
    • Authors: Christopher J. Tennant; Adrian A. Harpold, Kathleen Ann Lohse, Sarah E. Godsey, Benjamin T. Crosby, Laurel G. Larsen, Paul D. Brooks, Robert W. Van Kirk, Nancy F. Glenn
      Abstract: In mountains with seasonal snow-cover, the effects of climate change on snowpack will be constrained by landscape-vegetation interactions with the atmosphere. Airborne lidar surveys used to estimate snow depth, topography, and vegetation were coupled with reanalysis climate products to quantify these interactions and to highlight potential snowpack sensitivities to climate and vegetation change across the western U.S. at Rocky Mountain (RM), Northern Basin and Range (NBR), and Sierra Nevada (SNV) sites. In forest and shrub areas, elevation captured the greatest amount of variability in snow depth (16-79%) but aspect explained more variability (11-40%) in alpine areas. Aspect was most important at RM sites where incoming shortwave to incoming net radiation (SW:NetR) was highest (∼0.5), capturing 17-37% of snow depth variability in forests and 32-37% in shrub areas. Forest vegetation height exhibited negative relationships with snow depth and explained 3-6% of its variability at sites with greater longwave inputs (NBR and SNV). Variability in the importance of physiography suggest differential sensitivities of snowpack to climate and vegetation change. The high SW:NetR and importance of aspect suggests RM sites may be more responsive to decreases in SW:NetR driven by warming or increases in humidity or cloud-cover. Reduced canopy-cover could increase snow depths at SNV sites, and NBR and SNV sites are currently more sensitive to shifts from snow to rain. The consistent importance of aspect and elevation suggest that changes in SW:NetR and the elevation of the rain/snow transition zone could have widespread and varied effects on western U.S. snowpacks.
      PubDate: 2017-07-15T03:10:27.056293-05:
      DOI: 10.1002/2016WR019374
       
  • The costs of delay in infrastructure investments: A comparison of 2001 and
           2014 household water supply coping costs in the Kathmandu Valley, Nepal
    • Authors: Yogendra Gurung; Jane Zhao, Bal Kumar KC, Xun Wu, Bhim Suwal, Dale Whittington
      Abstract: In 2001 we conducted a survey of 1500 randomly sampled households in Kathmandu to determine the costs people were incurring to cope with Kathmandu's poor quality, unreliable piped water supply system. From 2001 until 2014 there was little additional public investment in the municipal water supply system. In the summer of 2014 we attempted to re-interview all 1500 households in our 2001 sample to determine how they had managed to deal with the growing water shortage and the deteriorating condition of the piped water infrastructure in Kathmandu, and to compare their coping costs in 2014 with those we first estimated in 2001.Average household coping costs more than doubled in real terms over the period from 2001 to 2014, from US$5 to US$12 per month (measured in 2014 prices). The composition of household coping costs changed from 2001 to 2014, as households responded to the deteriorating condition of the piped water infrastructure by drilling more private wells, purchasing water from both tanker truck and bottled water vendors, and installing more storage tanks. These investments and expenditures resulted in a decline in the time households spend collecting water from outside the home. Our analysis suggests that the significant increase in coping costs between 2001 to 2014 may provide an opportunity for the municipal water utility to substantially increase water tariffs if the quantity and quality of piped services can be improved. However, the capital investments made by some households in private wells, pumping and treatment systems, and storage tanks in response to the delay in infrastructure investment may lock them into current patterns of water use, at least in the short run, and thus make it difficult to predict how they would respond to tariff increases for improved piped water services.
      PubDate: 2017-07-05T08:55:40.838607-05:
      DOI: 10.1002/2016WR019529
       
  • Bayesian spectral likelihood for hydrological parameter inference
    • Authors: Bettina Schaefli; Dmitri Kavetski
      Abstract: This paper proposes a spectral-domain likelihood function for the Bayesian estimation of hydrological model parameters from a time series of model residuals. The spectral-domain error model is based on the Power-Density-Spectrum (PDS) of the stochastic process assumed to describe residual errors. The Bayesian Spectral Likelihood (BSL) is mathematically equivalent to the corresponding Bayesian Time-domain Likelihood (BTL) and yields the same inference when all residual error assumptions are satisfied (and all residual error parameters are inferred). However, the BSL likelihood function does not depend on the residual error distribution in the original time-domain, which offers a theoretical advantage in terms of robustness for hydrological parameter inference. The theoretical properties of BSL are demonstrated and compared to BTL and a previously proposed spectral likelihood by Montanari and Toth (2007), using a set of synthetic case studies and a real case study based on the Leaf River catchment in the US. The empirical analyses confirm the theoretical properties of BSL when applied to heteroscedastic and autocorrelated error models (where heteroscedasticity is represented using the log-transformation and autocorrelation is represented using an AR(1) process). Unlike MTL, the use of BSL did not introduce additional parametric uncertainty compared to BTL. Future work will explore the application of BSL to challenging modeling scenarios in arid catchments and “indirect” calibration with non-concomitant input/output time series.
      PubDate: 2017-07-05T08:55:23.155604-05:
      DOI: 10.1002/2016WR019465
       
  • Suspended sediment and turbidity after road construction/improvement and
           forest harvest in streams of the Trask River Watershed Study, Oregon
    • Authors: Ivan Arismendi; Jeremiah D. Groom, Maryanne Reiter, Sherri L. Johnson, Liz Dent, Mark Meleason, Alba Argerich, Arne E. Skaugset
      Abstract: Transport of fine-grained sediment from unpaved forest roads into streams is a concern due to the potential negative effects of additional suspended sediment on aquatic ecosystems. Here, we compared turbidity and suspended sediment concentration (SSC) dynamics in five non-fish bearing coastal Oregon streams above and below road crossings, during three consecutive time periods (‘before', ‘after road construction/improvement', and ‘after forest harvest and hauling'). We hypothesized that the combined effects of road construction/improvement and the hauling following forest harvest would increase turbidity and SSC in these streams. We tested whether the differences between paired samples from above and below road crossing exceeded various biological thresholds, using literature values of biological responses to increases in SSC and turbidity. Overall, we found minimal increases of both turbidity and SSC after road improvement, forest harvest, and hauling. Because flow is often used as a surrogate for turbidity or SSC we examined these relationships using data from locations above road crossings that were unaffected by roads or forest harvest and hauling. In addition, we examined the association between turbidity and SSC for these background locations. We found a positive, but in some cases weak association between flow and turbidity, and between flow and SSC; the relationship between turbidity and SSC was more robust, but also inconsistent among sites over time. In these low order streams, the concentrations and transport of suspended sediment seems to be highly influenced by the variability of local conditions. Our study provides an expanded understanding of current forest road management practice effects on fine-grained sediment in streams and introduces alternative metrics using multiple thresholds to evaluate potential indicators of biological relevance.
      PubDate: 2017-06-26T08:14:44.220173-05:
      DOI: 10.1002/2016WR020198
       
  • Environmental hedging: Theory and method for reconciling reservoir
           operations for downstream ecology and water supply
    • Authors: L. E. Adams; J. R. Lund, P. B. Moyle, R. M. Quiñones, J. D. Herman, T. A. O'Rear
      Abstract: Building reservoir release schedules to manage engineered river systems can involve costly tradeoffs between storing and releasing water. As a result, the design of release schedules requires metrics that quantify the benefit and damages created by releases to the downstream ecosystem. Such metrics should support making operational decisions under uncertain hydrologic conditions, including drought and flood seasons. This study addresses this need and develops a reservoir operation rule structure and method to maximize downstream environmental benefit while meeting human water demands. The result is a general approach for hedging downstream environmental objectives. A multi-stage stochastic mixed-integer non-linear program with Markov Chains, identifies optimal "environmental hedging," releases to maximize environmental benefits subject to probabilistic seasonal hydrologic conditions, current, past, and future environmental demand, human water supply needs, infrastructure limitations, population dynamics, drought storage protection, and the river's carrying capacity. Environmental hedging ‘hedges bets' for drought by reducing releases for fish, sometimes intentionally killing some fish early to reduce the likelihood of large fish kills and storage crises later. This approach is applied to Folsom reservoir in California to support survival of fall-run Chinook salmon in the Lower American River for a range of carryover and initial storage cases. Benefit is measured in terms of fish survival; maintaining self-sustaining native fish populations is a significant indicator of ecosystem function. Environmental hedging meets human demand and outperforms other operating rules, including the current Folsom operating strategy, based on metrics of fish extirpation and water supply reliability.
      PubDate: 2017-06-23T07:40:30.059204-05:
      DOI: 10.1002/2016WR020128
       
  • Concentration-discharge relationships in headwater streams of the Sierra
           Nevada, California
    • Authors: Carolyn T. Hunsaker; Dale W. Johnson
      Abstract: We examined streamwater concentration-discharge relationships for eight small, forest watersheds ranging in elevation from 1,485 to 2,465 m in the southern Sierra Nevada. These headwater streams revealed nearly chemostatic behavior by current definitions for K+, Ca2+, Mg2+, Na+, Cl- and SO42- in most cases but not for NH4+. NO3-, or ortho-P. The latter ions were somewhat enriched during high flows. All ions studied showed a dilution process at lower flows (< 50 l sec−1) with the concentration-discharge relationship being more chemostatic at higher flows. While previous studies in the Sierra Nevada have reported peak concentrations of NH4+, NO3-, and SO42- during snowmelt, the headwater systems of the Kings River Experimental Watersheds experience peak concentrations of these ions during the fall rains after the dry summer. These forested watersheds span the rain-snow transition zone, are 49 to 228 ha in size, and have soils derived from granite. A statistically significant relationship between soils and streamwater concentrations for ortho-P, Ca2+, and Na+ strongly suggests that soil chemistry has a major influence on streamwater chemistry. Factors controlling streamwater NH4+, NO3-, and SO42- concentrations are less clear, but one possible source of spikes in these ions during storm events is input from O-horizon runoff where high concentrations were measured. Overall, streamwater concentation-discharge relationships for these Sierran watersheds are similar to those found in other watershed systems (nearly chemostatic); however, the dominant processes controlling these relationships are probably localized because of different watershed characteristics like soil chemistry, vegetation cover, hydrologic flow paths, and weather patterns.
      PubDate: 2017-04-25T10:50:47.401121-05:
      DOI: 10.1002/2016WR019693
       
  • Issue Information
    • Pages: 6355 - 6358
      PubDate: 2017-09-20T02:43:59.102557-05:
      DOI: 10.1002/wrcr.22255
       
  • Wettability impact on supercritical CO2 capillary trapping: Pore-scale
           visualization and quantification
    • Authors: Ran Hu; Jiamin Wan, Yongman Kim, Tetsu K. Tokunaga
      Pages: 6377 - 6394
      Abstract: How the wettability of pore surfaces affects supercritical (sc) CO2 capillary trapping in geologic carbon sequestration (GCS) is not well understood, and available evidence appears inconsistent. Using a high-pressure micromodel-microscopy system with image analysis, we studied the impact of wettability on scCO2 capillary trapping during short-term brine flooding (80 s, 8–667 pore volumes). Experiments on brine displacing scCO2 were conducted at 8.5 MPa and 45°C in water-wet (static contact angle θ = 20° ± 8°) and intermediate-wet (θ = 94° ± 13°) homogeneous micromodels under four different flow rates (capillary number Ca ranging from 9 × 10−6 to 8 × 10−4) with a total of eight conditions (four replicates for each). Brine invasion processes were recorded and statistical analysis was performed for over 2000 images of scCO2 saturations, and scCO2 cluster characteristics. The trapped scCO2 saturation under intermediate-wet conditions is 15% higher than under water-wet conditions under the slowest flow rate (Ca ∼ 9 × 10−6). Based on the visualization and scCO2 cluster analysis, we show that the scCO2 trapping process in our micromodels is governed by bypass trapping that is enhanced by the larger contact angle. Smaller contact angles enhance cooperative pore filling and widen brine fingers (or channels), leading to smaller volumes of scCO2 being bypassed. Increased flow rates suppress this wettability effect.
      PubDate: 2017-08-01T04:35:56.81079-05:0
      DOI: 10.1002/2017WR020721
       
  • Water quality and ecosystem management: Data-driven reality check of
           effects in streams and lakes
    • Authors: Georgia Destouni; Ida Fischer, Carmen Prieto
      Pages: 6395 - 6406
      Abstract: This study investigates nutrient-related water quality conditions and change trends in the first management periods of the EU Water Framework Directive (WFD; since 2009) and Baltic Sea Action Plan (BASP; since 2007). With mitigation of nutrients in inland waters and their discharges to the Baltic Sea being a common WFD and BSAP target, we use Sweden as a case study of observable effects, by compiling and analyzing all openly available water and nutrient monitoring data across Sweden since 2003. The data compilation reveals that nutrient monitoring covers only around 1% (down to 0.2% for nutrient loads) of the total number of WFD-classified stream and lake water bodies in Sweden. The data analysis further shows that the hydro-climatically driven water discharge dominates the determination of waterborne loads of both total phosphorus and total nitrogen across Sweden. Both water discharge and the related nutrient loads are in turn well correlated with the ecosystem status classification of Swedish water bodies. Nutrient concentrations do not exhibit such correlation and their changes over the study period are on average small, but concentration increases are found for moderate-to-bad status waters, for which both the WFD and the BSAP have instead targeted concentration decreases. In general, these results indicate insufficient distinction and mitigation of human-driven nutrient components in inland waters and their discharges to the sea by the internationally harmonized applications of the WFD and the BSAP. The results call for further comparative investigations of observable large-scale effects of such regulatory/management frameworks in different parts of the world.
      PubDate: 2017-08-01T04:25:46.954433-05:
      DOI: 10.1002/2016WR019954
       
  • Estimating rainfall time series and model parameter distributions using
           model data reduction and inversion techniques
    • Authors: Ashley J. Wright; Jeffrey P. Walker, Valentijn R. N. Pauwels
      Pages: 6407 - 6424
      Abstract: Floods are devastating natural hazards. To provide accurate, precise, and timely flood forecasts, there is a need to understand the uncertainties associated within an entire rainfall time series, even when rainfall was not observed. The estimation of an entire rainfall time series and model parameter distributions from streamflow observations in complex dynamic catchments adds skill to current areal rainfall estimation methods, allows for the uncertainty of entire rainfall input time series to be considered when estimating model parameters, and provides the ability to improve rainfall estimates from poorly gauged catchments. Current methods to estimate entire rainfall time series from streamflow records are unable to adequately invert complex nonlinear hydrologic systems. This study aims to explore the use of wavelets in the estimation of rainfall time series from streamflow records. Using the Discrete Wavelet Transform (DWT) to reduce rainfall dimensionality for the catchment of Warwick, Queensland, Australia, it is shown that model parameter distributions and an entire rainfall time series can be estimated. Including rainfall in the estimation process improves streamflow simulations by a factor of up to 1.78. This is achieved while estimating an entire rainfall time series, inclusive of days when none was observed. It is shown that the choice of wavelet can have a considerable impact on the robustness of the inversion. Combining the use of a likelihood function that considers rainfall and streamflow errors with the use of the DWT as a model data reduction technique allows the joint inference of hydrologic model parameters along with rainfall.
      PubDate: 2017-08-01T04:32:13.546819-05:
      DOI: 10.1002/2017WR020442
       
  • Water security, risk, and economic growth: Insights from a dynamical
           systems model
    • Authors: Simon Dadson; Jim W. Hall, Dustin Garrick, Claudia Sadoff, David Grey, Dale Whittington
      Pages: 6425 - 6438
      Abstract: Investments in the physical infrastructure, human capital, and institutions needed for water resources management have been noteworthy in the development of most civilizations. These investments affect the economy in two distinct ways: (i) by improving the factor productivity of water in multiple economic sectors, especially those that are water intensive such as agriculture and energy and (ii) by reducing acute and chronic harmful effects of water-related hazards like floods, droughts, and water-related diseases. The need for capital investment to mitigate risks and promote economic growth is widely acknowledged, but prior conceptual work on the relationship between water-related investments and economic growth has focused on the productive and harmful roles of water in the economy independently. Here the two influences are combined using a simple, dynamical systems model of water-related investment, risk, and growth. In cases where initial water security is low, initial investment in water-related assets enables growth. Without such investment, losses due to water-related hazards exert a drag on economic growth and may create a poverty trap. The presence and location of the poverty trap is context-specific and depends on the exposure of productive water-related assets to water-related risk. Exogenous changes in water-related risk can potentially push an economy away from a growth path toward a poverty trap. Our investigation shows that an inverted-U-shaped investment relation between the level of investment in water security and the current level of water security leads to faster rates of growth than the alternatives that we consider here, and that this relation is responsible for the “S”-curve that is posited in the literature. These results illustrate the importance of accounting for environmental and health risks in economic models and offer insights for the design of robust policies for investment in water-related productive assets to manage risk, in the face of environmental change.
      PubDate: 2017-08-03T00:25:31.737864-05:
      DOI: 10.1002/2017WR020640
       
  • Methane emission through ebullition from an estuarine mudflat: 2. Field
           observations and modeling of occurrence probability
    • Authors: Xi Chen; Karina V. R. Schäfer, Lee Slater
      Pages: 6439 - 6453
      Abstract: Ebullition can transport methane (CH4) at a much faster rate than other pathways, albeit over limited time and area, in wetland soils and sediments. However, field observations present large uncertainties in ebullition occurrences and statistic models are needed to describe the function relationship between probability of ebullition occurrence and water level changes. A flow-through chamber was designed and installed in a mudflat of an estuarine temperate marsh. Episodic increases in CH4 concentration signaling ebullition events were observed during ebbing tides (15 events over 456 ebbing tides) and occasionally during flooding tides (4 events over 455 flooding tides). Ebullition occurrence functions were defined using logistic regression as the relative initial and end water levels, as well as tidal amplitudes were found to be the key functional variables related to ebullition events. Ebullition of methane was restricted by a surface frozen layer during winter; melting of this layer during spring thaw caused increases in CH4 concentration, with ebullition fluxes similar to those associated with large fluctuations in water level around spring tides. Our findings suggest that initial and end relative water levels, in addition to tidal amplitude, partly regulate ebullition events in tidal wetlands, modulated by the lunar cycle, storage of gas bubbles at different depths and seasonal changes in the surface frozen layer. Maximum tidal strength over a few days, rather than hourly water level, may be more closely associated with the possibility of ebullition occurrence as it represents a trade-off time scale in between hourly and lunar periods.
      PubDate: 2017-08-04T07:40:45.00787-05:0
      DOI: 10.1002/2016WR019720
       
  • The impact of water quality in Narragansett Bay on housing prices
    • Authors: Tingting Liu; James J. Opaluch, Emi Uchida
      Pages: 6454 - 6471
      Abstract: We examine the impact of water quality in Narragansett Bay on housing prices in coastal towns and cities using a hedonic housing-price model. Unlike other hedonic studies of water quality, we test whether housing market responds to average water quality or more to extreme events. We also test the spatial and temporal extent of effects of water quality on housing prices. We find that poor coastal water quality, measured in terms of the concentration of chlorophyll, has a negative impact on housing prices that diminishes with distance from the shoreline. Furthermore, our finding suggests that housing prices are most influenced by the extreme environmental conditions, which may be accompanied by unpleasant odors, discoloration, and even fish kills. We further predict potential increases in home values associated under water quality improvement scenarios and find an increase in the values of homes in coastal communities along Narragansett Bay of about $18 million up to $136 million.
      PubDate: 2017-08-04T07:35:42.555732-05:
      DOI: 10.1002/2016WR019606
       
  • Tundra water budget and implications of precipitation underestimation
    • Authors: Anna K. Liljedahl; Larry D. Hinzman, Douglas L. Kane, Walter C. Oechel, Craig E. Tweedie, Donatella Zona
      Pages: 6472 - 6486
      Abstract: Difficulties in obtaining accurate precipitation measurements have limited meaningful hydrologic assessment for over a century due to performance challenges of conventional snowfall and rainfall gauges in windy environments. Here, we compare snowfall observations and bias adjusted snowfall to end-of-winter snow accumulation measurements on the ground for 16 years (1999–2014) and assess the implication of precipitation underestimation on the water balance for a low-gradient tundra wetland near Utqiagvik (formerly Barrow), Alaska (2007–2009). In agreement with other studies, and not accounting for sublimation, conventional snowfall gauges captured 23–56% of end-of-winter snow accumulation. Once snowfall and rainfall are bias adjusted, long-term annual precipitation estimates more than double (from 123 to 274 mm), highlighting the risk of studies using conventional or unadjusted precipitation that dramatically under-represent water balance components. Applying conventional precipitation information to the water balance analysis produced consistent storage deficits (79 to 152 mm) that were all larger than the largest actual deficit (75 mm), which was observed in the unusually low rainfall summer of 2007. Year-to-year variability in adjusted rainfall (±33 mm) was larger than evapotranspiration (±13 mm). Measured interannual variability in partitioning of snow into runoff (29% in 2008 to 68% in 2009) in years with similar end-of-winter snow accumulation (180 and 164 mm, respectively) highlights the importance of the previous summer's rainfall (25 and 60 mm, respectively) on spring runoff production. Incorrect representation of precipitation can therefore have major implications for Arctic water budget descriptions that in turn can alter estimates of carbon and energy fluxes.
      PubDate: 2017-08-04T05:32:17.786911-05:
      DOI: 10.1002/2016WR020001
       
  • Monitoring and simulation of salinity changes in response to tide and
           storm surges in a sandy coastal aquifer system
    • Authors: S. Huizer; M. C. Karaoulis, G. H. P. Oude Essink, M. F. P. Bierkens
      Pages: 6487 - 6509
      Abstract: Tidal dynamics and especially storm surges can have an extensive impact on coastal fresh groundwater resources. Combined with the prospect of sea-level rise and the reliance of many people on these resources, this demonstrates the need to assess the vulnerability of coastal areas to these threats. In this study, we investigated the impact of tides and storm surges on coastal groundwater at a pilot location on the Dutch coast (viz., the Sand Engine). To monitor changes in groundwater salinity under a variety of conditions, we performed automated measurements with electrical resistivity tomography for a period of 2 months between November 2014 and January 2015. The obtained resistivity images were converted to salinity images, and these images served effectively as observations of the impact of tidal fluctuations, saltwater overwash during storm surges, and the recovery of the freshwater lens after land-surface inundations. Most of the observed changes in groundwater head and salinity could be reproduced with a two-dimensional variable-density groundwater flow and salt transport model. This shows that groundwater models can be used to make accurate predictions of the impact of tides and storm surges on fresh groundwater resources, given a thorough understanding of the (local) system. Comparisons of measurements and model simulations also showed that morphological changes and wave run-up can have a strong impact on the extent of land-surface inundations in (low-elevation) dynamic coastal environments, and can therefore substantially affect coastal fresh groundwater resources.
      PubDate: 2017-08-04T08:01:39.563826-05:
      DOI: 10.1002/2016WR020339
       
  • Simulating the long-term impacts of drainage and restoration on the
           ecohydrology of peatlands
    • Authors: Dylan M. Young; Andy J. Baird, Paul J. Morris, Joseph Holden
      Pages: 6510 - 6522
      Abstract: Drainage alters the carbon storage and accumulation functions of peatlands, but the long-term effects of drainage ditches, and their restoration, on peatland development are poorly understood. Timescales of monitoring studies in ditch-drained and restored peatlands are typically limited to a few years, and occasionally decades. In addition, experimental studies seldom monitor spatial changes in peat structure caused by ditches, despite such changes affecting water flow and water retention in peat. Ecosystem models offer an alternative to experimental studies and can help explain how complex systems such as peatlands may respond to external disturbances. Here we report on a 2-D application of a peatland development model (DigiBog) to explore how contour-parallel ditches, and their damming, affect the ecohydrology of peatlands over decades to centuries, using blanket peatlands as a case study. Drainage resulted in the rapid loss of peat due to increased oxic decay. The majority of these losses occurred in the first 100 years after the ditch was created, but water table dynamics were altered even centuries later. Restoration halted the loss of peat and encouraged net peat accumulation, although the amount lost in 100 years of drainage had not been replaced 200 years after the ditch was dammed. Restoration of ditches in sloping peatlands brought about more peat regrowth downslope of the restored ditch than further upslope. Our study demonstrates the potential for spatially distributed ecosystem-scale models as tools to explore complex spatiotemporal responses to disturbance, and to support land managers in making decisions about peatland drainage and restoration.
      PubDate: 2017-08-04T07:51:18.335132-05:
      DOI: 10.1002/2016WR019898
       
  • Environmental drivers of denitrification rates and denitrifying gene
           abundances in channels and riparian areas
    • Authors: Abigail Tomasek; Jessica L. Kozarek, Miki Hondzo, Nicole Lurndahl, Michael J. Sadowsky, Ping Wang, Christopher Staley
      Pages: 6523 - 6538
      Abstract: Intensive agriculture in the Midwestern United States contributes to excess nitrogen in surface water and groundwater, negatively affecting human health and aquatic ecosystems. Complete denitrification removes reactive nitrogen from aquatic environments and releases inert dinitrogen gas. We examined denitrification rates and the abundances of denitrifying genes and total bacteria at three sites in an agricultural watershed and in an experimental stream in Minnesota. Sampling was conducted along transects with a gradient from always inundated (in-channel), to periodically inundated, to noninundated conditions to determine how denitrification rates and gene abundances varied from channels to riparian areas with different inundation histories. Results indicate a coupling between environmental parameters, gene abundances, and denitrification rates at the in-channel locations, and limited to no coupling at the periodically inundated and noninundated locations, respectively. Nutrient-amended potential denitrification rates for the in-channel locations were significantly correlated (α = 0.05) with five of six measured denitrifying gene abundances, whereas the periodically inundated and noninundated locations were each only significantly correlated with the abundance of one denitrifying gene. These results suggest that DNA-based analysis of denitrifying gene abundances alone cannot predict functional responses (denitrification potential), especially in studies with varying hydrologic regimes. A scaling analysis was performed to develop a predictive functional relationship relating environmental parameters to denitrification rates for in-channel locations. This method could be applied to other geographic and climatic regions to predict the occurrence of denitrification hot spots.
      PubDate: 2017-08-04T07:41:03.86814-05:0
      DOI: 10.1002/2016WR019566
       
  • Reducing equifinality using isotopes in a process-based stream nitrogen
           model highlights the flux of algal nitrogen from agricultural streams
    • Authors: William I. Ford; James F. Fox, Erik Pollock
      Pages: 6539 - 6561
      Abstract: The fate of bioavailable nitrogen species transported through agricultural landscapes remains highly uncertain given complexities of measuring fluxes impacting the fluvial N cycle. We present and test a new numerical model named Technology for Removable Annual Nitrogen in Streams For Ecosystem Restoration (TRANSFER), which aims to reduce model uncertainty due to erroneous parameterization, i.e., equifinality, in stream nitrogen cycle assessment and quantify the significance of transient and permanent removal pathways. TRANSFER couples nitrogen elemental and stable isotope mass-balance equations with existing hydrologic, hydraulic, sediment transport, algal biomass, and sediment organic matter mass-balance subroutines and a robust GLUE-like uncertainty analysis. We test the model in an agriculturally impacted, third-order stream reach located in the Bluegrass Region of Central Kentucky. Results of the multiobjective model evaluation for the model application highlight the ability of sediment nitrogen fingerprints including elemental concentrations and stable N isotope signatures to reduce equifinality of the stream N model. Advancements in the numerical simulations allow for illumination of the significance of algal sloughing fluxes for the first time in relation to denitrification. Broadly, model estimates suggest that denitrification is slightly greater than algal N sloughing (10.7% and 6.3% of dissolved N load on average), highlighting the potential for overestimation of denitrification by 37%. We highlight the significance of the transient N pool given the potential for the N store to be regenerated to the water column in downstream reaches, leading to harmful and nuisance algal bloom development.
      PubDate: 2017-08-04T08:04:48.685843-05:
      DOI: 10.1002/2017WR020607
       
  • The potential of GRACE gravimetry to detect the heavy rainfall-induced
           impoundment of a small reservoir in the upper Yellow River
    • Authors: Shuang Yi; Chunqiao Song, Qiuyu Wang, Linsong Wang, Kosuke Heki, Wenke Sun
      Pages: 6562 - 6578
      Abstract: Artificial reservoirs are important indicators of anthropogenic impacts on environments, and their cumulative influences on the local water storage will change the gravity signal. However, because of their small signal size, such gravity changes are seldom studied using satellite gravimetry from the Gravity Recovery and Climate Experiment (GRACE). Here we investigate the ability of GRACE to detect water storage changes in the Longyangxia Reservoir (LR), which is situated in the upper main stem of the Yellow River. Three different GRACE solutions from the CSR, GFZ, and JPL with three different processing filters are compared here. We find that heavy precipitation in the summer of 2005 caused the LR water storage to increase by 37.9 m in height, which is equivalent to 13.0 Gt in mass, and that the CSR solutions with a DDK4 filter show the best performance in revealing the synthetic gravity signals. We also obtain 109 pairs of reservoir inundation area measurements from satellite imagery and water level changes from laser altimetry and in situ observations to derive the area-height ratios for the LR. The root mean square of GRACE series in the LR is reduced by 39% after removing synthetic signals caused by mass changes in the LR or by 62% if the GRACE series is further smoothed. We conclude that GRACE data show promising potential in detecting water storage changes in this ∼400 km2 reservoir and that a small signal size is not a restricting factor for detection using GRACE data.
      PubDate: 2017-08-04T07:45:48.874276-05:
      DOI: 10.1002/2017WR020793
       
  • Nonstationarity in threshold response of stormflow in southern Appalachian
           headwater catchments
    • Authors: Charles I. Scaife; Lawrence E. Band
      Pages: 6579 - 6596
      Abstract: Threshold behavior of stormflow response is an emergent pattern observed in several studies demonstrating subsurface storage controls on catchment rainfall-runoff dynamics. These studies demonstrate a distinct transition from negligible stormflow discharge response to rapid, linearly increasing stormflow identified by a single, uniquely defined threshold as a basic catchment attribute that relates to geophysical properties. Utilizing precipitation, streamflow, and soil moisture data spanning 15 years from three catchments at the Coweeta Hydrologic Laboratory (CHL), we analyze how threshold behavior forms and varies at several timescales. We pose three hypotheses: (1) stormflow thresholds form at CHL as a function of antecedent soil moisture and gross precipitation, (2) thresholds vary seasonally and interannually, and (3) threshold variation through time implies greater long-term complexity of runoff controls beyond catchment geophysical properties, including forest canopy ecohydrologic feedbacks. We isolate threshold behavior of stormflow using piecewise regression analysis in short to long-term data sets with respect to antecedent soil moisture index and gross precipitation. We use this to investigate threshold variation over seasonal, interannual, and decadal timescales that encompass hydroclimatic extremes. Seasonal analysis reveals that thresholds are more variable between growing seasons than between dormant seasons. In growing seasons with greater water stress, stormflow thresholds are lower after controlling for soil moisture storage suggesting more complex, long-term rainfall-runoff relationships as a result of forest canopy response to water stress. We present a conceptual model of how vegetation-climate interactions influence long-term rainfall-runoff relationships creating interannual variability of stormflow thresholds and linear stormflow response.
      PubDate: 2017-08-04T05:35:58.648708-05:
      DOI: 10.1002/2017WR020376
       
  • Revealing the economic value of managed aquifer recharge: Evidence from a
           contingent valuation study in Italy
    • Authors: D. Damigos; G. Tentes, M. Balzarini, F. Furlanis, A. Vianello
      Pages: 6597 - 6611
      Abstract: Managed aquifer recharge [MAR) is a promising water management tool toward restoring groundwater balance and securing groundwater ecosystem services (i.e., water for drinking, industrial or irrigation use, control of land subsidence, maintenance of environmental flows to groundwater dependent ecosystems, etc.). Obviously, MAR projects can improve the quality of lives of the people by several ways. Thus, from a social perspective, the benefits of MAR cannot and should not be based only on market revenues or costs. Although the value of groundwater, from a social perspective, has been a subject of socio-economic research, literature on the value of MAR per se is very limited. This paper, focusing on Italy which is a country with extensive utilization of MAR, aims to estimate the economic value of MAR and makes a first step toward filling this gap in the literature. For this purpose, the Contingent Valuation method was implemented to provide a monetary estimate and to explore the factors influencing people's attitude and willingness to pay for MAR. The results show that society holds not only use but also significant nonuse values, which are a part of the total economic value (TEV) of groundwater according to related research efforts. To this end, MAR valuation highlights its social importance for groundwater conservation and provides a solid basis for incorporating its nonmarket benefits into groundwater management policies and assessments.
      PubDate: 2017-08-04T07:35:35.461864-05:
      DOI: 10.1002/2016WR020281
       
  • Predictive performance of rainfall thresholds for shallow landslides in
           Switzerland from gridded daily data
    • Authors: Elena Leonarduzzi; Peter Molnar, Brian W. McArdell
      Pages: 6612 - 6625
      Abstract: A high-resolution gridded daily precipitation data set was combined with a landslide inventory containing over 2000 events in the period 1972–2012 to analyze rainfall thresholds which lead to landsliding in Switzerland. We colocated triggering rainfall to landslides, developed distributions of triggering and nontriggering rainfall event properties, and determined rainfall thresholds and intensity-duration ID curves and validated their performance. The best predictive performance was obtained by the intensity-duration ID threshold curve, followed by peak daily intensity Imax and mean event intensity Imean. Event duration by itself had very low predictive power. A single country-wide threshold of Imax = 28 mm/d was extended into space by regionalization based on surface erodibility and local climate (mean daily precipitation). It was found that wetter local climate and lower erodibility led to significantly higher rainfall thresholds required to trigger landslides. However, we showed that the improvement in model performance due to regionalization was marginal and much lower than what can be achieved by having a high-quality landslide database. Reference cases in which the landslide locations and timing were randomized and the landslide sample size was reduced showed the sensitivity of the Imax rainfall threshold model. Jack-knife and cross-validation experiments demonstrated that the model was robust. The results reported here highlight the potential of using rainfall ID threshold curves and rainfall threshold values for predicting the occurrence of landslides on a country or regional scale with possible applications in landslide warning systems, even with daily data.
      PubDate: 2017-08-04T07:57:02.585395-05:
      DOI: 10.1002/2017WR021044
       
  • Insights into mountain precipitation and snowpack from a basin-scale
           wireless-sensor network
    • Authors: Z. Zhang; S. Glaser, R. Bales, M. Conklin, R. Rice, D. Marks
      Pages: 6626 - 6641
      Abstract: A spatially distributed wireless-sensor network, installed across the 2154 km2 portion of the 5311 km2 American River basin above 1500 m elevation, provided spatial measurements of temperature, relative humidity, and snow depth in the Sierra Nevada, California. The network consisted of 10 sensor clusters, each with 10 measurement nodes, distributed to capture the variability in topography and vegetation cover. The sensor network captured significant spatial heterogeneity in rain versus snow precipitation for water-year 2014, variability that was not apparent in the more limited operational data. Using daily dew-point temperature to track temporal elevational changes in the rain-snow transition, the amount of snow accumulation at each node was used to estimate the fraction of rain versus snow. This resulted in an underestimate of total precipitation below the 0°C dew-point elevation, which averaged 1730 m across 10 precipitation events, indicating that measuring snow does not capture total precipitation. We suggest blending lower elevation rain gauge data with higher-elevation sensor-node data for each event to estimate total precipitation. Blended estimates were on average 15–30% higher than using either set of measurements alone. Using data from the current operational snow-pillow sites gives even lower estimates of basin-wide precipitation. Given the increasing importance of liquid precipitation in a warming climate, a strategy that blends distributed measurements of both liquid and solid precipitation will provide more accurate basin-wide precipitation estimates, plus spatial and temporal patters of snow accumulation and melt in a basin.
      PubDate: 2017-08-04T05:31:35.697441-05:
      DOI: 10.1002/2016WR018825
       
  • Hyporheic hot moments: Dissolved oxygen dynamics in the hyporheic zone in
           response to surface flow perturbations
    • Authors: Matthew H. Kaufman; M. Bayani Cardenas, Jim Buttles, Adam J. Kessler, Perran L. M. Cook
      Pages: 6642 - 6662
      Abstract: Dissolved oxygen (DO) is a key environmental variable that drives and feeds back with numerous processes. In the aquatic sediment that makes up the hyporheic zone, DO may exhibit pronounced spatial gradients and complex patterns which control the distribution of a series of redox processes. Yet, little is known regarding the dynamics of hyporheic zone DO, especially under transitional flow regimes. Considering the natural tendency of rivers to be highly responsive to external forcing, these temporal dynamics are potentially just as important and pronounced as the spatial gradients. Here we use laboratory flume experiments and multiphysics flow and reactive transport modeling to investigate surface flow controls on the depth of oxygen penetration in the bed as well as the area of oxygenated sediment. We show that the hyporheic zone DO conditions respond over time scales of hours-to-days when subjected to practically instantaneous surface flow perturbations. Additionally, the flume experiments demonstrate that hyporheic zone DO conditions respond faster to surface flow acceleration than to deceleration. Finally, we found that the morphology of the dissolved oxygen plume front depends on surface flow acceleration or deceleration. This study thus shows that the highly dynamic nature of typical streams and rivers drives equally dynamic redox conditions in the hyporheic zone. Because the redox conditions and their distribution within the hyporheic zone are important from biological, ecological, and contaminant perspectives, this hyporheic redox dynamism has the potential to impact system scale aquatic chemical cycles.
      PubDate: 2017-08-07T06:37:52.922796-05:
      DOI: 10.1002/2016WR020296
       
  • A framework for the analysis of noncohesive bank erosion algorithms in
           morphodynamic modeling
    • Authors: G. Stecca; R. Measures, D. M. Hicks
      Pages: 6663 - 6686
      Abstract: In this paper, we analyze the performance of several noncohesive bank erosion algorithms to be embedded into two-dimensional models for river hydromorphodynamics on nonmoving meshes. To avoid the complexity of analyzing two-dimensional model results arising from the nonlinear interaction between flow, fluvial transport, and bank erosion, we develop a simplified framework. In detail, we reduce the two-dimensional morphodynamic model to a cross-sectional model under the assumption of longitudinal morphodynamic equilibrium, and apply bank erosion algorithms therein. To build candidate bank erosion models, we break down bank erosion algorithms into three modeling steps: identification of the bank, computation of sediment fluxes due to bank erosion, and bank updating. Different potential models are created by choosing different options for each step. We assess model performance against surveyed bank erosion over a flood event in the transitional Selwyn River, New Zealand. This study is preliminary to implementation of bank erosion in a fully two-dimensional setting, to model braided planform dynamics.
      PubDate: 2017-08-08T04:56:58.016817-05:
      DOI: 10.1002/2017WR020756
       
  • Stochastic analysis of unsaturated steady flows above the water table
    • Authors: Gerardo Severino; Maddalena Scarfato, Alessandro Comegna
      Pages: 6687 - 6708
      Abstract: Steady flow takes place into a three-dimensional partially saturated porous medium where, due to their spatial variability, the saturated conductivity Ks, and the relative conductivity Kr are modeled as random space functions (RSF)s. As a consequence, the flow variables (FVs), i.e., pressure-head and specific flux, are also RSFs. The focus of the present paper consists into quantifying the uncertainty of the FVs above the water table. The simple expressions (most of which in closed form) of the second-order moments pertaining to the FVs allow one to follow the transitional behavior from the zone close to the water table (where the FVs are nonstationary), till to their far-field limit (where the FVs become stationary RSFs). In particular, it is shown how the stationary limits (and the distance from the water table at which stationarity is attained) depend upon the statistical structure of the RSFs Ks, Kr, and the infiltrating rate. The mean pressure head 〈Ψ〉 has been also computed, and it is expressed as 〈Ψ〉=Ψ0(1+ψ), being ψ a characteristic heterogeneity function which modifies the zero-order approximation Ψ0 of the pressure head (valid for a vadose zone of uniform soil properties) to account for the spatial variability of Ks and Kr. Two asymptotic limits, i.e., close (near field) and away (far field) from the water table, are derived into a very general manner, whereas the transitional behavior of ψ between the near/far field can be determined after specifying the shape of the various input soil properties. Besides the theoretical interest, results of the present paper are useful for practical purposes, as well. Indeed, the model is tested against to real data, and in particular it is shown how it is possible for the specific case study to grasp the behavior of the FVs within an environment (i.e., the vadose zone close to the water table) which is generally very difficult to access by direct inspection.
      PubDate: 2017-08-08T05:11:03.234254-05:
      DOI: 10.1002/2017WR020554
       
  • Mapping the temporary and perennial character of whole river networks
    • Authors: A. M. González-Ferreras; J. Barquín
      Pages: 6709 - 6724
      Abstract: Knowledge of the spatial distribution of temporary and perennial river channels in a whole catchment is important for effective integrated basin management and river biodiversity conservation. However, this information is usually not available or is incomplete. In this study, we present a statistically based methodology to classify river segments from a whole river network (Deva-Cares catchment, Northern Spain) as temporary or perennial. This method is based on an a priori classification of a subset of river segments as temporary or perennial, using field surveys and aerial images, and then running Random Forest models to predict classification membership for the rest of the river network. The independent variables and the river network were derived following a computer-based geospatial simulation of riverine landscapes. The model results show high values of overall accuracy, sensitivity, and specificity for the evaluation of the fitted model to the training and testing data set (≥0.9). The most important independent variables were catchment area, area occupied by broadleaf forest, minimum monthly precipitation in August, and average catchment elevation. The final map shows 7525 temporary river segments (1012.5 km) and 3731 perennial river segments (662.5 km). A subsequent validation of the mapping results using River Habitat Survey data and expert knowledge supported the validity of the proposed maps. We conclude that the proposed methodology is a valid method for mapping the limits of flow permanence that could substantially increase our understanding of the spatial links between terrestrial and aquatic interfaces, improving the research, management, and conservation of river biodiversity and functioning.
      PubDate: 2017-08-08T05:05:29.083682-05:
      DOI: 10.1002/2017WR020390
       
  • Bringing the “social” into sociohydrology: Conservation policy support
           in the Central Great Plains of Kansas, USA
    • Authors: Matthew R. Sanderson; Jason S. Bergtold, Jessica L. Heier Stamm, Marcellus M. Caldas, Steven M. Ramsey
      Pages: 6725 - 6743
      Abstract: Identifying means of empirically modeling the human component of a coupled, human-water system becomes critically important to further advances in sociohydrology. We develop a social-psychological model of environmental decision making that addresses four key challenges of incorporating social science into integrated models. We use the model to explain preferences for three conservation policies designed to conserve and protect water resources and aquatic ecosystems in the Smoky Hill River Basin, a semiarid agricultural region in the Central U.S. Great Plains. Further, we compare the model's capacity to explain policy preferences among members of two groups in the River Basin: agricultural producers and members of nonfarming communities. We find that financial obligation is the strongest and most consistent explanation of support for conservation policies among members of both groups. We also find that policy support is grounded in cultural values—deeply held ideas about right and wrong. Environmental values are particularly important explanations of policy support. The constellations of values invoked to make decisions about policies, and the social-psychological pathways linking values to policy support, can vary across policies and types of agents (farmers and nonfarmers). We discuss the implications of the results for future research in sociohydrology.
      PubDate: 2017-08-08T05:11:10.761978-05:
      DOI: 10.1002/2017WR020659
       
  • Toward best practice framing of uncertainty in scientific publications: A
           review of Water Resources Research abstracts
    • Authors: Joseph H. A. Guillaume; Casey Helgeson, Sondoss Elsawah, Anthony J. Jakeman, Matti Kummu
      Pages: 6744 - 6762
      Abstract: Uncertainty is recognized as a key issue in water resources research, among other sciences. Discussions of uncertainty typically focus on tools and techniques applied within an analysis, e.g., uncertainty quantification and model validation. But uncertainty is also addressed outside the analysis, in writing scientific publications. The language that authors use conveys their perspective of the role of uncertainty when interpreting a claim—what we call here “framing” the uncertainty. This article promotes awareness of uncertainty framing in four ways. (1) It proposes a typology of eighteen uncertainty frames, addressing five questions about uncertainty. (2) It describes the context in which uncertainty framing occurs. This is an interdisciplinary topic, involving philosophy of science, science studies, linguistics, rhetoric, and argumentation. (3) We analyze the use of uncertainty frames in a sample of 177 abstracts from the Water Resources Research journal in 2015. This helped develop and tentatively verify the typology, and provides a snapshot of current practice. (4) We make provocative recommendations to achieve a more influential, dynamic science. Current practice in uncertainty framing might be described as carefully considered incremental science. In addition to uncertainty quantification and degree of belief (present in ∼5% of abstracts), uncertainty is addressed by a combination of limiting scope, deferring to further work (∼25%) and indicating evidence is sufficient (∼40%)—or uncertainty is completely ignored (∼8%). There is a need for public debate within our discipline to decide in what context different uncertainty frames are appropriate. Uncertainty framing cannot remain a hidden practice evaluated only by lone reviewers.
      PubDate: 2017-08-09T07:10:29.921907-05:
      DOI: 10.1002/2017WR020609
       
  • Large-scale inverse model analyses employing fast randomized data
           reduction
    • Authors: Youzuo Lin; Ellen B. Le, Daniel O'Malley, Velimir V. Vesselinov, Tan Bui-Thanh
      Pages: 6784 - 6801
      Abstract: When the number of observations is large, it is computationally challenging to apply classical inverse modeling techniques. We have developed a new computationally efficient technique for solving inverse problems with a large number of observations (e.g., on the order of 107 or greater). Our method, which we call the randomized geostatistical approach (RGA), is built upon the principal component geostatistical approach (PCGA). We employ a data reduction technique combined with the PCGA to improve the computational efficiency and reduce the memory usage. Specifically, we employ a randomized numerical linear algebra technique based on a so-called “sketching” matrix to effectively reduce the dimension of the observations without losing the information content needed for the inverse analysis. In this way, the computational and memory costs for RGA scale with the information content rather than the size of the calibration data. Our algorithm is coded in Julia and implemented in the MADS open-source high-performance computational framework (http://mads.lanl.gov). We apply our new inverse modeling method to invert for a synthetic transmissivity field. Compared to a standard geostatistical approach (GA), our method is more efficient when the number of observations is large. Most importantly, our method is capable of solving larger inverse problems than the standard GA and PCGA approaches. Therefore, our new model inversion method is a powerful tool for solving large-scale inverse problems. The method can be applied in any field and is not limited to hydrogeological applications such as the characterization of aquifer heterogeneity.
      PubDate: 2017-08-12T06:15:29.482685-05:
      DOI: 10.1002/2016WR020299
       
  • An evaluation of terrain-based downscaling of fractional snow covered area
           data sets based on LiDAR-derived snow data and orthoimagery
    • Authors: Nicoleta C. Cristea; Ian Breckheimer, Mark S. Raleigh, Janneke HilleRisLambers, Jessica D. Lundquist
      Pages: 6802 - 6820
      Abstract: Reliable maps of snow-covered areas at scales of meters to tens of meters, with daily temporal resolution, are essential to understanding snow heterogeneity, melt runoff, energy exchange, and ecological processes. Here we develop a parsimonious downscaling routine that can be applied to fractional snow covered area (fSCA) products from satellite platforms such as the Moderate Resolution Imaging Spectroradiometer (MODIS) that provide daily ∼500 m data, to derive higher-resolution snow presence/absence grids. The method uses a composite index combining both the topographic position index (TPI) to represent accumulation effects and the diurnal anisotropic heat (DAH, sun exposure) index to represent ablation effects. The procedure is evaluated and calibrated using airborne-derived high-resolution data sets across the Tuolumne watershed, CA using 11 scenes in 2014 to downscale to 30 m resolution. The average matching F score was 0.83. We then tested our method's transferability in time and space by comparing against the Tuolumne watershed in water years 2013 and 2015, and over an entirely different site, Mt. Rainier, WA in 2009 and 2011, to assess applicability to other topographic and climatic conditions. For application to sites without validation data, we recommend equal weights for the TPI and DAH indices and close TPI neighborhoods (60 and 27 m for downscaling to 30 and 3 m, respectively), which worked well in both our study areas. The method is less effective in forested areas, which still requires site-specific treatment. We demonstrate that the procedure can even be applied to downscale to 3 m resolution, a very fine scale relevant to alpine ecohydrology research.
      PubDate: 2017-08-12T07:40:55.406629-05:
      DOI: 10.1002/2017WR020799
       
  • Design of optimal groundwater monitoring well network using stochastic
           modeling and reduced-rank spatial prediction
    • Authors: J. Sreekanth; Henry Lau, D. E. Pagendam
      Pages: 6821 - 6840
      Abstract: A method for the stochastic design of groundwater quality observation well network is presented. The method uses calibration-constrained Null-space Monte Carlo analysis for the stochastic simulation of the reduction ratio of peak concentration and the time corresponding to this in an injection well field. The numerical groundwater model simulations are constrained with a limited amount of field measurements. The objective of the monitoring network design is to identify optimal monitoring locations that allow for prediction of spatial fields from the data collected at limited number of points in the spatial domain. These locations need to be robust to different possible outcomes simulated using the stochastic model runs, and result in good spatial predictions, regardless of which one of the many possibilities turned out to be the true representation of nature. Multiple simulated fields of concentration and time are used to identify a small set of empirical orthogonal functions (spatial basis functions) for reduced-rank prediction of the spatial patterns in these two fields. The Differential Evolution algorithm was used to find the monitoring locations that allowed for optimal reconstruction of all the simulated fields (potential future states of reality) from the set of empirical orthogonal functions. The applicability is demonstrated for designing a monitoring network for an injection well field. Optimal locations of 10 monitoring wells were identified. The method has the capability to simultaneously identify the optimal locations and inform optimal times for monitoring reduction ratio of peak concentration. The method is flexible to iteratively combine stochastic modeling and monitoring for optimal groundwater management.
      PubDate: 2017-08-12T07:40:35.291549-05:
      DOI: 10.1002/2017WR020385
       
  • Quantitative mapping of solute accumulation in a soil-root system by
           magnetic resonance imaging
    • Authors: S. Haber-Pohlmeier; J. Vanderborght, A. Pohlmeier
      Pages: 7469 - 7480
      Abstract: Differential uptake of water and solutes by plant roots generates heterogeneous concentration distributions in soils. Noninvasive observations of root system architecture and concentration patterns therefore provide information about root water and solute uptake. We present the application of magnetic resonance imaging (MRI) to image and monitor root architecture and the distribution of a tracer, GdDTPA2− (Gadolinium-diethylenetriaminepentacetate) noninvasively during an infiltration experiment in a soil column planted with white lupin. We show that inversion recovery preparation within the MRI imaging sequence can quantitatively map concentrations of a tracer in a complex root-soil system. Instead of a simple T1 weighting, the procedure is extended by a wide range of inversion times to precisely map T1 and subsequently to cover a much broader concentration range of the solute. The derived concentrations patterns were consistent with mass balances and showed that the GdDTPA2− tracer represents a solute that is excluded by roots. Monitoring and imaging the accumulation of the tracer in the root zone therefore offers the potential to determine where and by which roots water is taken up.
      PubDate: 2017-08-04T07:56:43.692439-05:
      DOI: 10.1002/2017WR020832
       
  • An explicit, parsimonious, and accurate estimate for ponded infiltration
           into soils using the Green and Ampt approach
    • Authors: John S. Selker; Shmuel Assouline
      Pages: 7481 - 7487
      Abstract: The Green and Ampt solution for vertical ponded infiltration is implicit in time, which makes the result often cumbersome to apply. Here we present a simple explicit solution for the position of the wetting front in time based on approximating the term describing early time behavior by means of the sum of gravitational flow and the exact solution for capillary imbibition. The result is within 1% of the exact implicit solution of vertical Green and Ampt infiltration. We also check the overall accuracy of the Green and Ampt approach, and find it to be within 15% of numerical simulation results for the same soils obtained with the Richards equation. Hence, the proposed approximation adds essentially no error to the Green and Ampt approach, but greatly simplifies computation of infiltration. The approximation also makes explicit the role of the representation of capillarity, which can be adjusted in ways not possible with the implicit result. We find that predictions can be markedly improved by adjusting capillary versus gravitational drivers per soil texture, revealing both a limitation of the Green and Ampt approach, but also providing a potential refinement of Green and Ampt predictions per soil type (demonstrated for sandy and clayey soils). Further, the new approximation allows for simple computation of useful quantities such as flux and cumulative infiltration.
      PubDate: 2017-08-12T07:45:23.31379-05:0
      DOI: 10.1002/2017WR021020
       
 
 
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