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  Subjects -> WATER RESOURCES (Total: 141 journals)
Acta Limnologica Brasiliensia     Open Access   (Followers: 1)
Advances in Oceanography and Limnology     Partially Free   (Followers: 9)
Advances in Water Resource and Protection     Open Access   (Followers: 4)
Advances in Water Resources     Hybrid Journal   (Followers: 21)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 12)
Agricultural Water Management     Hybrid Journal   (Followers: 19)
American Journal of Water Resources     Open Access   (Followers: 1)
American Water Works Association     Hybrid Journal   (Followers: 15)
Anales de Hidrología Médica     Open Access  
Annals of Warsaw University of Life Sciences - SGGW. Land Reclamation     Open Access   (Followers: 1)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 11)
Applied Water Science     Open Access   (Followers: 6)
Aquacultural Engineering     Hybrid Journal   (Followers: 6)
Aquaculture     Hybrid Journal   (Followers: 31)
Aquaculture Research     Hybrid Journal   (Followers: 24)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 20)
Aquatic Geochemistry     Hybrid Journal   (Followers: 1)
Aquatic Living Resources     Hybrid Journal   (Followers: 10)
Aquatic Procedia     Open Access  
Aquatic Science and Technology     Open Access   (Followers: 1)
Aquatic Sciences     Hybrid Journal   (Followers: 10)
Asian Journal of Earth Sciences     Open Access   (Followers: 19)
Asian Journal of Rural Development     Open Access   (Followers: 11)
Australian Journal of Water Resources     Full-text available via subscription   (Followers: 7)
Bubble Science, Engineering & Technology     Hybrid Journal   (Followers: 1)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Civil and Environmental Research     Open Access   (Followers: 15)
CLEAN - Soil, Air, Water     Hybrid Journal   (Followers: 18)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 2)
Cost Effectiveness and Resource Allocation     Open Access   (Followers: 5)
Desalination     Hybrid Journal   (Followers: 10)
Desalination and Water Treatment     Hybrid Journal   (Followers: 11)
Developments in Water Science     Full-text available via subscription   (Followers: 7)
Ecological Chemistry and Engineering S     Open Access   (Followers: 2)
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: 4)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 13)
Grundwasser     Hybrid Journal  
Human Resources for Health     Open Access   (Followers: 6)
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (Followers: 1)
Hydrology Research     Partially Free   (Followers: 10)
Hydrology: Current Research     Open Access   (Followers: 10)
IDA Journal of Desalination and Water Reuse     Hybrid Journal  
Ingeniería del agua     Open Access  
International Journal of Climatology     Hybrid Journal   (Followers: 15)
International Journal of Hydrology Science and Technology     Hybrid Journal   (Followers: 5)
International Journal of Nuclear Desalination     Hybrid Journal   (Followers: 2)
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: 5)
International Journal of Water     Hybrid Journal   (Followers: 11)
International Journal of Water Resources and Environmental Engineering     Open Access   (Followers: 1)
International Journal of Water Resources Development     Hybrid Journal   (Followers: 15)
Irrigation and Drainage     Hybrid Journal   (Followers: 6)
Irrigation Science     Hybrid Journal   (Followers: 4)
Journal of Aquatic Sciences     Full-text available via subscription  
Journal of Contemporary Water Resource & Education     Hybrid Journal   (Followers: 2)
Journal of Environmental Health Science & Engineering     Open Access   (Followers: 1)
Journal of Fisheries and Aquatic Science     Open Access   (Followers: 4)
Journal of Geophysical Research : Oceans     Partially Free   (Followers: 14)
Journal of Hydro-environment Research     Full-text available via subscription   (Followers: 4)
Journal of Hydroinformatics     Full-text available via subscription   (Followers: 2)
Journal of Hydrology (New Zealand)     Full-text available via subscription   (Followers: 2)
Journal of Hydrology and Hydromechanics     Open Access   (Followers: 1)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 4)
Journal of Limnology     Open Access   (Followers: 6)
Journal of the American Water Resources Association     Hybrid Journal   (Followers: 18)
Journal of Water and Climate Change     Partially Free   (Followers: 26)
Journal of Water and Health     Partially Free   (Followers: 1)
Journal of Water Chemistry and Technology     Hybrid Journal   (Followers: 7)
Journal of Water Process Engineering     Full-text available via subscription   (Followers: 2)
Journal of Water Resource and Hydraulic Engineering     Open Access   (Followers: 4)
Journal of Water Resource and Protection     Open Access   (Followers: 5)
Journal of Water Resource Engineering and Management     Full-text available via subscription  
Journal of Water Resources Planning and Management     Full-text available via subscription   (Followers: 27)
Journal of Water Reuse and Desalination     Partially Free   (Followers: 7)
Journal of Water Supply : Research and Technology - Aqua     Partially Free   (Followers: 9)
Journal of Water, Sanitation and Hygiene for Development     Open Access   (Followers: 3)
La Houille Blanche     Full-text available via subscription   (Followers: 1)
Lake and Reservoir Management     Hybrid Journal   (Followers: 4)
Lakes & Reservoirs Research & Management     Hybrid Journal   (Followers: 15)
Large Marine Ecosystems     Full-text available via subscription  
Mangroves and Salt Marshes     Hybrid Journal   (Followers: 3)
Marine and Freshwater Behaviour and Physiology     Hybrid Journal   (Followers: 1)
Marine and Freshwater Living Resources     Open Access  
Marine Ecosystem Stressor Response     Open Access  
Methods in Oceanography : An International Journal     Hybrid Journal   (Followers: 2)
Michigan Journal of Sustainability     Open Access  
New Zealand Journal of Marine and Freshwater Research     Hybrid Journal   (Followers: 4)
Open Journal of Modern Hydrology     Open Access   (Followers: 3)
Osterreichische Wasser- und Abfallwirtschaft     Hybrid Journal  
Ozone Science & Engineering     Hybrid Journal   (Followers: 1)
Paddy and Water Environment     Hybrid Journal   (Followers: 1)
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: 1)
Riparian Ecology and Conservation     Open Access   (Followers: 4)
River Research and Applications     Hybrid Journal   (Followers: 5)
River Systems     Full-text available via subscription   (Followers: 3)

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Journal Cover   Water Resources Research
  [SJR: 2.189]   [H-I: 121]   [78 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 0043-1397 - ISSN (Online) 1944-7973
   Published by American Geophysical Union (AGU) Homepage  [17 journals]
  • 50 years of water resources research legacy and perspectives for the
           science of hydrology introduction
    • Abstract: We present an overview of the contributions collected to celebrate the 50th anniversary of Water Resources Research along with a critical discussion of the legacy and perspectives for the science of hydrology in the 21st century. This collection of papers highlights exciting pathways to the future of water sciences. New monitoring and modeling techniques and increasing opportunities for data and knowledge sharing from hydrological research will provide innovative means to improve water management and to ensure a sustainable development to society. We believe that this set of papers will provide valuable inspiration for future hydrologists, and will support the intensification of international cooperation among scientists. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-24T03:02:29.127788-05:
      DOI: 10.1002/2015WR017998
       
  • An advanced process‐based distributed model for the investigation of
           rainfall‐induced landslides: The effect of process representation
           and boundary conditions
    • Authors: Grigorios G. Anagnostopoulos; Simone Fatichi, Paolo Burlando
      Abstract: Extreme rainfall events are the major driver of shallow landslide occurrences in mountainous and steep terrain regions around the world. Subsurface hydrology has a dominant role on the initiation of rainfall‐induced shallow landslides, since changes in the soil water content affect significantly the soil shear strength. Rainfall infiltration produces an increase of soil water potential, which is followed by a rapid drop in apparent cohesion. Especially on steep slopes of shallow soils, this loss of shear strength can lead to failure even in unsaturated conditions before positive water pressures are developed. We present HYDROlisthisis, a process‐based model, fully distributed in space with fine time resolution, in order to investigate the interactions between surface and subsurface hydrology and shallow landslides initiation. Fundamental elements of the approach are the dependence of shear strength on the three dimensional (3D) field of soil water potential, as well as the temporal evolution of soil water potential during the wetting and drying phases. Specifically, 3D variably saturated flow conditions, including soil hydraulic hysteresis and preferential flow phenomena, are simulated for the subsurface flow, coupled with a surface runoff routine based on the kinematic wave approximation. The geotechnical component of the model is based on a multidimensional limit equilibrium analysis, which takes into account the basic principles of unsaturated soil mechanics. A series of numerical simulations were carried out with various boundary conditions and using different hydrological and geotechnical components. Boundary conditions in terms of distributed soil depth were generated using both empirical and process based models. The effect of including preferential flow and soil hydraulic hysteresis was tested together with the replacement of the infinite slope assumption with the multidimensional limit equilibrium analysis. The results show that boundary conditions play a crucial role in the model performance and that the introduced hydrological (preferential flow and soil hydraulic hysteresis) and geotechnical components (multidimensional limit equilibrium analysis) significantly improve predictive capabilities in the presented case study. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-24T02:58:34.659935-05:
      DOI: 10.1002/2015WR016909
       
  • Internal connectivity of meandering rivers: Statistical generalization of
           channel hydraulic geometry
    • Authors: M.J. Czapiga; V.B. Smith, J.A. Nittrouer, D. Mohrig, G. Parker
      Abstract: The geometry of rivers has been characterized in terms of downstream and at‐a‐station hydraulic geometry, based on individual cross‐sections. Such analyses do not, however, provide insight as to how these cross‐sections are connected. We generalize the concept of hydraulic geometry, using data on bathymetry from four reaches of meandering rivers that include at least five bends. We quantify connectivity in terms of the probability that a connected path exists such that a given attribute remains within specified bounds along it. While the concept is general, here we apply it to vessel navigability. We develop a predictor for navigability in meandering rivers, which requires only the following, relatively easily obtained input: vessel draft, vessel width, bankfull depth, bankfull width, relative difference between current and bankfull water surface elevation, and length of desired navigation path. The predictor is applicable to both bankfull and below‐bankfull stage. A key input parameter is the standard deviation of the probability distribution of depth. This parameter, in and of itself, yields no information on connectivity as it does not capture the spatial orientation of depth variation. We find, however, that a) the probability function for connectivity does depend on this parameter, and b) its use allows for an approximate similarity collapse of the probability function, so providing a quasi‐universal predictive relation applying to all four reaches. The results also suggest potential application to more complex forms for connectivity that involve other or multiple in‐stream physical variables. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-22T01:09:34.11263-05:0
      DOI: 10.1002/2014WR016133
       
  • Is unique scaling of aquifer macrodispersivity supported by field
           data?
    • Authors: A. Zech; S. Attinger, V. Cvetkovic, G. Dagan, P. Dietrich, A. Fiori, Y. Rubin, G. Teutsch
      Abstract: Spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity, which was found to be scale dependent. It increases with travel distance, stabilizing eventually at a constant value. However, the question of its asymptotic behaviour at very large scale is still a matter of debate. It was surmised in the literature that macrodispersivity scales up following a unique scaling law. Attempts to define such a law were made by fitting a regression line in the log‐log representation of an ensemble of macrodispersivities from multiple experiments. The functional relationships differ among the authors, based on the choice of data. Our study revisits the data basis, used for inferring unique scaling, through a detailed analysis of literature marcodispersivities. In addition, values were collected from the most recent tracer tests reported in the literature. We specified a system of criteria for reliability and re‐evaluated the reliability of the reported values. The final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship. On the contrary, our results indicate, that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value. Our investigation concludes that transport, and particularly the macrodispersivity, is formation‐specific, and that modeling of transport cannot be relegated to a unique scaling law. Instead, transport requires characterization of aquifer properties, e.g. spatial distribution of hydraulic conductivity, and the use of adequate models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-22T01:08:59.924487-05:
      DOI: 10.1002/2015WR017220
       
  • Self‐adjustment of stream bed roughness and flow velocity in a steep
           mountain channel
    • Authors: Johannes M. Schneider; Dieter Rickenmann, Jens M. Turowski, James W. Kirchner
      Abstract: Understanding how channel bed morphology affects flow conditions (and vice versa) is important for a wide range of fluvial processes and practical applications. We investigated interactions between bed roughness and flow velocity in a steep, glacier‐fed mountain stream (Riedbach, Ct. Valais, Switzerland) with almost flume‐like boundary conditions. Bed gradient increases along the 1‐km study reach by roughly one order of magnitude (S=3‐41%), with a corresponding increase in streambed roughness, while flow discharge and width remain approximately constant due to the glacial runoff regime. Streambed roughness was characterized by semi‐variograms and standard deviations of point clouds derived from terrestrial laser scanning. Reach‐averaged flow velocity was derived from dye tracer breakthrough curves measured by 10 fluorometers installed along the channel. Commonly used flow resistance approaches (Darcy‐Weisbach equation and dimensionless hydraulic geometry) were used to relate the measured bulk velocity to bed characteristics. As a roughness measure, D84 yielded comparable results to more laborious measures derived from point clouds. Flow resistance behavior across this large range of steep slopes agreed with patterns established in previous studies for both lower‐gradient and steep reaches, regardless of which roughness measures were used. We linked empirical critical shear stress approaches to the variable power equation for flow resistance to investigate the change of bed roughness with channel slope. The predicted increase in D84 with increasing channel slope was in good agreement with field observations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-21T03:15:11.513433-05:
      DOI: 10.1002/2015WR016934
       
  • Does small‐bodied salmon spawning activity enhance streambed
           mobility?
    • Authors: Marwan A. Hassan; Daniele Tonina, Todd H. Buxton
      Abstract: Female salmonids bury and lay their eggs in streambeds by digging a pit, which is then covered with sediment from a second pit. The spawning process alters streambed topography, winnows fine sediment, and mixes sediment in the active layer. The resulting egg nests (redds) contain coarser and looser sediments than those of unspawned streambed areas, and display a dune‐like shape with an amplitude and length that vary with fish size, substrate conditions, and flow conditions. Redds increase local bed surface roughness (
      PubDate: 2015-08-21T03:14:33.02352-05:0
      DOI: 10.1002/2015WR017079
       
  • Climate index weighting of ensemble streamflow forecasts using a simple
           Bayesian approach
    • Authors: A. Allen Bradley; Mohamed Habib, Stuart S. Schwartz
      Abstract: Climate state can be an important predictor of future hydrologic conditions. In ensemble streamflow forecasting, where historical weather inputs or streamflow observations are used to generate the ensemble, climate index weighting is one way to represent the influence of climate state. Using a climate index, each forecast variable member of the ensemble is selectively weighted to reflect the climate state at the time of the forecast. A new approach to climate index weighting of ensemble forecasts is presented. The method is based on a sampling‐resampling approach for Bayesian updating. The original hydrologic ensemble members define a sample drawn from the prior distribution; the relationship between the climate index and the ensemble member forecast variable is used to estimate a likelihood function. Given an observation of the climate index at the time of the forecast, the estimated likelihood function is then used to assign weights to each ensemble member. The weights define the probability of each ensemble member outcome given the observed climate index. The weighted ensemble forecast is then used to estimate the posterior distribution of the forecast variable conditioned on the climate index. The Bayesian climate index weighting approach is easy to apply to hydrologic ensemble forecasts; its parameters do not require calibration with hindcasts, and it adapts to the strength of the relation between climate and the forecast variable, defaulting to equal weighting of ensemble members when no relationship exists. A hydrologic forecasting application illustrates the approach and contrasts it with traditional climate index weighting approaches. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-21T03:13:54.847966-05:
      DOI: 10.1002/2014WR016811
       
  • On the limits of heat as a tracer to estimate reach‐scale
           river‐aquifer exchange flux
    • Authors: Yueqing Xie; Peter G. Cook, Craig T. Simmons, Chunmiao Zheng
      Abstract: For the past few decades, heat has been used to estimate river‐aquifer exchange flux at discrete locations by comparison of river and groundwater temperature. In recent years, heat has also been employed to estimate reach‐scale river‐aquifer exchange flux based only on river temperature. However, there are many more parameters that govern heat exchange and transport in surface water than in groundwater. In this study, we analyzed the sensitivities of surface water temperature to various parameters and assessed the accuracy of temperature‐based estimates of exchange flux in two synthetic rivers and in a field setting. For the large synthetic river with a flow rate of 63 m3 s−1 (i.e., 5.44 × 106 m3 d−1), the upper and lower bounds of the groundwater inflow rate can be determined when the actual groundwater inflow is around 100 m2 d−1. For higher and lower fluxes, only minimum and maximum bounds respectively can be determined. For the small synthetic river with the flow rate of 0.63 m3 s−1 (i.e., 5.44 × 104 m3 d−1), the bounds of the groundwater inflow rate can only be estimated when the actual groundwater inflow rate is near 10 m2 d−1. In the field setting, results show that the inflow rate must be less than 100 m2 d−1, but a lower bound for groundwater inflow cannot be determined. The large ranges of estimated groundwater inflow rates in both theoretical and field settings indicate the need to reduce parameter errors and combine heat measurements with other isotopic and/or chemical methods. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-21T03:13:04.834474-05:
      DOI: 10.1002/2014WR016741
       
  • Simulating riparian disturbance: Reach‐scale impacts on aquatic
           habitat in gravel bed streams
    • Authors: S. L. Davidson; B.C. Eaton
      Abstract: Large wood governs channel morphology, as well as the availability of in‐stream habitat, in many forested streams. In this paper we use a stochastic, physically based model to simulate wood recruitment and in‐stream geomorphic processes, in order to explore the influence of disturbance history on the availability of aquatic habitat. Specifically, we consider the effects of fire on a range of stream sizes by varying the rate of tree toppling over time in a simulated forest characterized by a tree height of 30 m. We also consider the effects of forest harvesting with various riparian buffer sizes, by limiting the lateral extent of the riparian stand. Our results show that pulsed inputs of wood increase the availability and variability of physical habitat in the post‐fire period; reach‐averaged pool area and deposit area double in small streams, while side‐channels increase by over 50% in intermediate‐sized channels. By contrast, forest harvesting reduces the availability of habitat within the reach, though the effects diminish with increasing buffer size or stream width; in laterally stable streams the effects are minimal so long as buffer width is large enough for key pieces to be recruited to the reach. This research emphasizes the importance of natural disturbance in creating and maintaining habitat heterogeneity and shows that scenario‐based numerical modeling provides a useful tool for assessing the historical range of variability associated with natural disturbance, as well as changes in habitat relevant to fish. It can be also used to inform forest harvesting and management. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-21T03:09:46.694136-05:
      DOI: 10.1002/2015WR017124
       
  • Precipitation‐snowmelt timing and snowmelt augmentation of large
           peak flow events, Western Cascades, Oregon
    • Authors: Keith Jennings; Julia A. Jones
      Abstract: This study tested multiple hydrologic mechanisms to explain snowpack dynamics in extreme rain‐on‐snow floods, which occur widely in the temperate and polar regions. We examined 26, 10‐day large storm events over the period 1992 to 2012 in the H.J. Andrews Experimental Forest in western Oregon, using statistical analyses (regression, ANOVA, and wavelet coherence) of hourly snowmelt lysimeter, air and dewpoint temperature, wind speed, precipitation, and discharge data. All events involved snowpack outflow, but only seven events had continuous net snowpack outflow, including three of the five top‐ranked peak discharge events. Peak discharge was not related to precipitation rate, but it was related to the 10‐day sum of precipitation and net snowpack outflow, indicating an increased flood response to continuously melting snowpacks. The two largest peak discharge events in the study had significant wavelet coherence at multiple time scales over several days; a distribution of phase differences between precipitation and net snowpack outflow at the 12 to 32‐hour time scale with a sharp peak at π/2 radians; and strongly correlated snowpack outflow among lysimeters representing 42% of basin area. The recipe for an extreme rain‐on‐snow event includes persistent, slow melt within the snowpack, which appears to produce a near‐saturated zone within the snowpack throughout the landscape, such that the snowpack may transmit pressure waves of precipitation directly to streams, and this process is synchronized across the landscape. Further work is needed to understand the internal dynamics of a melting snowpack throughout a snow‐covered landscape and its contribution to extreme rain‐on‐snow floods. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-19T02:23:25.831962-05:
      DOI: 10.1002/2014WR016877
       
  • The effect of soil surface sealing on vegetation water uptake along a dry
           climatic gradient
    • Authors: Shai Sela; Tal Svoray, Shmuel Assouline
      Abstract: Soil surface sealing is a widespread natural process occurring frequently in bare soil areas between vegetation patches. The low hydraulic conductivity that characterizes the seal layer reduces both infiltration and evaporation fluxes from the soil, and thus has the potential to affect local vegetation water uptake (VWU). This effect is investigated here using experimental data, 2D physically based modelling and a long‐term climatic dataset from three dry sites presenting a climatic gradient in the Negev Desert, Israel. The Feddes VWU parameters for the dominant shrub at the study site (Sarcopoterium spinosum) were acquired using lysimeter experiments. The results indicate that during the season surface sealing could either increase or decrease VWU depending on initial soil water content, rainfall intensity, and the duration of the subsequent drying intervals. These factors have a marked effect on inter‐annual variability of the seal layer effect on VWU, which on average was found to be 26% higher under sealed conditions than in the case of unsealed soil surfaces. The seal layer was found to reduce the period where the vegetation was under water stress by 31% compared with unsealed conditions. This effect was more pronounced for seasons with total rainfall depth higher than 10 cm/y, and was affected by interseasonal climatic variability. These results shed light on the importance of surface sealing in dry environments and its contribution to the resilience of woody vegetation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-19T01:48:50.620541-05:
      DOI: 10.1002/2015WR017109
       
  • A high‐resolution global flood hazard model
    • Authors: Christopher C. Sampson; Andrew M. Smith, Paul B. Bates, Jeffrey C. Neal, Lorenzo Alfieri, Jim E. Freer
      Abstract: Floods are a natural hazard that affect communities worldwide, but to date the vast majority of flood hazard research and mapping has been undertaken by wealthy developed nations. As populations and economies have grown across the developing world, so too has demand from governments, businesses and NGOs for modelled flood hazard data in these data‐scarce regions. We identify six key challenges faced when developing a flood hazard model that can be applied globally, and present a framework methodology that leverages recent cross‐disciplinary advances to tackle each challenge. The model produces return period flood hazard maps at ∼90 m resolution for the whole terrestrial land surface between 56˚S and 60˚N, and results are validated against high resolution government flood hazard datasets from the UK and Canada. The global model is shown to capture between two thirds and three quarters of the area determined to be at risk in the benchmark data without generating excessive false positive predictions. When aggregated to ∼1 km, mean absolute error in flooded fraction falls to ∼5%. The full complexity global model contains an automatically parameterised subgrid channel network, and comparison to both a simplified 2D only variant and an independently developed pan‐European model shows the explicit inclusion of channels to be a critical contributor to improved model performance. Whilst careful processing of existing global terrain datasets enables reasonable model performance in urban areas, adoption of forthcoming next‐generation global terrain datasets will offer the best prospect for a step‐change improvement in model performance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-18T18:37:25.961966-05:
      DOI: 10.1002/2015WR016954
       
  • Inroads of remote sensing into hydrologic science during the WRR era
    • Authors: Dennis P. Lettenmaier; Doug Alsdorf, Jeff Dozier, George J. Huffman, Ming Pan, Eric F. Wood
      Abstract: The first issue of WRR appeared eight years after the launch of Sputnik, but by WRR's 25th anniversary, only seven papers that used remote sensing had appeared. Over the journal's second 25 years, that changed remarkably, and remote sensing is now widely used in hydrology and other geophysical sciences. We attribute this evolution to production of datasets that scientists not well versed in remote sensing can use, and to educational initiatives like NASA's Earth System Science Fellowship program that has supported over a thousand scientists, many in hydrology. We review progress in remote sensing in hydrology from a water balance perspective. We argue that progress is primarily attributable to a creative use of existing and past satellite sensors to estimate such variables as evapotranspiration rates or water storage in lakes and reservoirs and to new and planned missions. Recent transforming technologies include the Gravity Recovery and Climate Experiment (GRACE), the European Soil Moisture and Ocean Salinity (SMOS) and U.S. Soil Moisture Active Passive (SMAP) missions, and the Global Precipitation Measurement (GPM) mission. Future missions include Surface Water and Ocean Topography (SWOT) to measure river discharge and lake, reservoir, and wetland storage. Measurement of some important hydrologic variables remains problematic: retrieval of snow water equivalent (SWE) from space remains elusive especially in mountain areas, even though snow cover extent is well observed, and was the topic of 4 of the first 5 remote sensing papers published in WRR. We argue that this area deserves more strategic thinking from the hydrology community. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-18T18:35:02.831589-05:
      DOI: 10.1002/2015WR017616
       
  • Do we need a Community Hydrological Model?
    • Authors: Markus Weiler; Keith Beven
      Abstract: We believe that there are too many models in hydrology and we should ask ourselves the question, if we are currently wasting time and effort in developing another model again instead of focusing on the development of a community hydrological model. In other fields this kind of models have been quite successful, but due to several reasons, no single community model has been developed in the field of hydrology yet. The concept, strength and weakness of a community model was discussed at the Chapman Conference on Catchment Spatial Behaviour and Complex Organisation held in Luxembourg in September 2014. This discussion as well as out own opinions about the potential of a community models, or at least the necessary discussion to establish one are debated in this commentary. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-18T18:34:17.194351-05:
      DOI: 10.1002/2014WR016731
       
  • Issue Information
    • PubDate: 2015-08-18T13:12:06.474731-05:
      DOI: 10.1002/wrcr.21101
       
  • A new temperature profiling probe for investigating
           groundwater‐surface water interaction
    • Authors: Ramon C Naranjo; Robert Turcotte
      Abstract: Measuring vertically nested temperatures at the streambed interface poses practical challenges that are addressed here with a new discrete subsurface temperature profiling probe. We describe a new temperature probe and its application for heat as a tracer investigations to demonstrate the probe's utility. Accuracy and response time of temperature measurements made at 6 discrete depths in the probe were analyzed in the laboratory using temperature bath experiments. We find the temperature probe to be an accurate and robust instrument that allows for easily installation and long‐term monitoring in highly variable environments. Because the probe is inexpensive and versatile, it is useful for many environmental applications that require temperature data collection for periods of several months in environments that are difficult to access or require minimal disturbance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-14T03:35:39.998884-05:
      DOI: 10.1002/2015WR017574
       
  • Whither field hydrology? The need for discovery science and outrageous
           hydrological hypotheses
    • Authors: T.P. Burt; J.J. McDonnell
      Abstract: Field hydrology is on the decline. Meanwhile, the need for new field‐derived insight into the age, origin and pathway of water in the headwaters, where most runoff is generated, is more needed than ever. Water Resources Research (WRR) has included some of the most influential papers in field‐based runoff process understanding, particularly in the formative years when the knowledge base was developing rapidly. Here, we take advantage of this 50th anniversary of the journal to highlight a few of these important field‐based papers and show how field scientists have posed strong and sometimes outrageous hypotheses—approaches so needed in an era of largely model‐only research. We chronicle the decline in field work and note that it is not only the quantity of field work that is diminishing but its character is changing too: from discovery science to data collection for model parameterisation. While the latter is a necessary activity, the loss of the former is a major concern if we are to advance the science of watershed hydrology. We outline a vision for field research to seek new fundamental understanding, new mechanistic explanations of how watershed systems work, particularly outside the regions of traditional focus. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-13T08:08:12.087117-05:
      DOI: 10.1002/2014WR016839
       
  • Using RFID and accelerometer‐embedded tracers to measure
           probabilities of transport, step lengths, and rest times in a mountain
           stream
    • Authors: Lindsay Olinde; Joel P. L. Johnson
      Abstract: We present new measurements of bedload tracer transport in a mountain stream over several snowmelt seasons. Cumulative displacements were measured using passive tracers, which consisted of gravel and cobbles embedded with radio frequency identification tags. The timing of bedload motion during eleven transporting events was quantified with active tracers, i.e., accelerometer‐embedded cobbles. Probabilities of cobble transport increased with discharge above a threshold, and exhibited slight to moderate hysteresis during snowmelt hydrographs. Dividing cumulative displacements by the number of movements recorded by each active tracer constrained average step lengths. Average step lengths increased with discharge, and distributions of average step lengths and cumulative displacements were thin‐tailed. Distributions of rest times followed heavy‐tailed power law scaling. Rest time scaling varied somewhat with discharge and with the degree to which tracers were incorporated into the stream bed. The combination of thin‐tailed displacement distributions and heavy‐tailed rest time distributions predict superdiffusive dispersion. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-13T02:29:02.552167-05:
      DOI: 10.1002/2014WR016120
       
  • Dissolved gas dynamics in wetland soils: Root‐mediated gas transfer
           kinetics determined via push‐pull tracer tests
    • Abstract: Gas transfer processes are fundamental to the biogeochemical and water quality functions of wetlands, yet there is limited knowledge of the rates and pathways of soil ‐ atmosphere exchange for gases other than oxygen and methane (CH4). In this study we use a novel push‐pull technique with sulfur hexafluoride (SF6) and helium (He) as dissolved gas tracers to quantify the kinetics of root‐mediated gas transfer, which is a critical efflux pathway for gases from wetland soils. This tracer approach disentangles the effects of physical transport from simultaneous reaction in saturated, vegetated wetland soils. We measured significant seasonal variation in first‐order gas exchange rate constants, with smaller spatial variations between different soil depths and vegetation zones in a New Jersey tidal marsh. Gas transfer rates for most biogeochemical trace gases are expected to be bracketed by the rate constants for SF6 and He, which ranged from ∼10−2 to 2x10−1 h−1 at our site. A modified Damköhler number analysis is used to evaluate the balance between biochemical reaction and root‐driven gas exchange in governing the fate of environmental trace gases in rooted, anaerobic soils. This approach confirmed the importance of plant gas transport for CH4, and showed that root‐driven transport may affect nitrous oxide (N2O) balances in settings where N2O reduction rates are slow This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-13T02:28:19.641147-05:
      DOI: 10.1002/2014WR016803
       
  • On the use of spatially distributed, time‐lapse microgravity surveys
           to inform hydrological modeling
    • Authors: Sebastiano Piccolroaz; Bruno Majone, Francesco Palmieri, Giorgio Cassiani, Alberto Bellin
      Abstract: In the last decades significant technological advances together with improved modeling capabilities fostered a rapid development of geophysical monitoring techniques in support of hydrological modeling. Geophysical monitoring offers the attractive possibility to acquire spatially distributed information on state variables. These provide complementary information about the functioning of the hydrological system to that provided by standard hydrological measurements, which are either intrinsically local or the result of a complex spatial averaging process. Soil water content is an example of state variable, which is relatively simple to measure pointwise (locally) but with a vanishing constraining effect on catchment‐scale modeling, while streamflow data, the typical hydrological measurement, offer limited possibility to disentangle the controlling processes. The objective of this work is to analyze the advantages offered by coupling traditional hydrological data with unconventional geophysical information in inverse modeling of hydrological systems. In particular, we explored how the use of time‐lapse, spatially distributed microgravity measurements may improve the conceptual model identification of a topographically complex Alpine catchment (the Vermigliana catchment, South‐Eastern Alps, Italy). The inclusion of microgravity data resulted in a better constraint of the inversion procedure and an improved capability to identify limitations of concurring conceptual models to a level that would be impossible relying only on streamflow data. This allowed for a better identification of model parameters and a more reliable description of the controlling hydrological processes, with a significant reduction of uncertainty in water storage dynamics with respect to the case when only streamflow data are used. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-11T03:49:46.234693-05:
      DOI: 10.1002/2015WR016994
       
  • Influence of injection mode on transport properties in
           kilometer‐scale three‐dimensional discrete fracture networks
    • Authors: J. D. Hyman; S. L. Painter, H. Viswanathan, N. Makedonska, S. Karra
      Abstract: We investigate how the choice of injection mode impacts transport properties in kilometer‐scale three‐dimensional discrete fracture networks (DFN). The choice of injection mode, resident or flux‐weighted, is designed to mimic different physical phenomena. It has been hypothesized that solute plumes injected under resident conditions evolve to behave similarly to solutes injected under flux‐weighted conditions. Previously, computational limitations have prohibited the large scale simulations required to investigate this hypothesis. We investigate this hypothesis by using a high performance DFN suite, dfnWorks, to simulate flow in kilometer‐scale three‐dimensional DFNs based on fractured granite at the Forsmark site in Sweden, and adopt a Lagrangian approach to simulate transport therein. Results show that after traveling through a pre‐equilibrium region both injection methods exhibit linear scaling of the first moment of travel time and power law scaling of the breakthrough curve with similar exponents, slightly larger than two. The physical mechanisms behind this evolution appear to be the combination of in‐network channeling of mass into larger fractures, which offer reduced resistance to flow, and in‐fracture channeling, which results from the topology of the DFN. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-07T04:39:35.183144-05:
      DOI: 10.1002/2015WR017151
       
  • Multivariate postprocessing techniques for probabilistic hydrological
           forecasting
    • Authors: S. Hemri; D. Lisniak, B. Klein
      Abstract: Hydrologic ensemble forecasts driven by atmospheric ensemble prediction systems need statistical post‐processing in order to account for systematic errors in terms of both location and spread. Runoff is an inherently multivariate process with typical events lasting from hours in case of floods to weeks or even months in case of droughts. This calls for multivariate post‐processing techniques that yield well calibrated forecasts in univariate terms and ensure a realistic temporal dependence structure at the same time. To this end, the univariate ensemble model output statistics (EMOS) post‐processing method is combined with two different copula approaches that ensure multivariate calibration throughout the entire forecast horizon. The domain of this study covers three sub‐catchments of the river Rhine that represent different sizes and hydrological regimes: the Upper Rhine up to the gauge Maxau, the river Moselle up to the gauge Trier, and the river Lahn up to the gauge Kalkofen. In this study the two approaches to model the temporal dependence structure are ensemble copula coupling (ECC), which preserves the dependence structure of the raw ensemble, and a Gaussian copula approach (GCA), which estimates the temporal correlations from training observations. The results indicate that both methods are suitable for modelling the temporal dependencies of probabilistic hydrologic forecasts. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-07T04:38:42.641739-05:
      DOI: 10.1002/2014WR016473
       
  • Semianalytical solutions for transport in aquifer and fractured clay
           matrix system
    • Authors: Junqi Huang; Mark N. Goltz
      Abstract: A three‐dimensional mathematical model that describes transport of contaminant in a horizontal aquifer with simultaneous diffusion into a fractured clay formation is proposed. A group of semi‐analytical solutions is derived based on specific initial and boundary conditions as well as various source functions. The analytical model solutions are evaluated by numerical Laplace inverse transformation and analytical Fourier inverse transformation. The model solutions can be used to study the fate and transport in a three‐dimensional spatial domain in which a non‐aqueous phase liquid exists as a pool atop a fractured low permeability clay layer. The non‐aqueous phase liquid gradually dissolves into the groundwater flowing past the pool, while simultaneously diffusing into the fractured clay formation below the aquifer. Mass transfer of the contaminant into the clay formation is demonstrated to be significantly enhanced by the existence of the fractures, even though the volume of fractures is relatively small compared to the volume of the clay matrix. The model solution is a useful tool in assessing contaminant attenuation processes in a confined aquifer underlain by a fractured clay formation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-07T04:34:18.82607-05:0
      DOI: 10.1002/2014WR016073
       
  • Hydrological partitioning in the critical zone: Recent advances and
           opportunities for developing transferrable understanding of water cycle
           dynamics
    • Authors: Paul D. Brooks; Jon Chorover, Ying Fan, Sarah E. Godsey, Reed M. Maxwell, James P. McNamara, Christina Tague
      Abstract: Hydrology is an integrative discipline linking the broad array of water‐related research with physical, ecological, and social sciences. The increasing breadth of hydrological research, often where subdisciplines of hydrology partner with related sciences, reflects the central importance of water to environmental science, while highlighting the fractured nature of the discipline itself. This lack of coordination among hydrologic subdisciplines has hindered the development of hydrologic theory and integrated models capable of predicting hydrologic partitioning across time and space. The recent development of the concept of the critical zone (CZ), an open system extending from the top of the canopy to the base of groundwater, brings together multiple hydrological subdisciplines with related physical and ecological sciences. Observations obtained by CZ researchers provide a diverse range of complementary process and structural data to evaluate both conceptual and numerical models. Consequently, a cross‐site focus on “critical zone hydrology” has potential to advance the discipline of hydrology and to facilitate the transition of CZ observatories into a research network with immediate societal relevance. Here we review recent work in catchment hydrology and hydrochemistry, hydrogeology, and ecohydrology that highlights a common knowledge gap in how precipitation is partitioned in the critical zone: “how is the amount, routing, and residence time of water in the subsurface related to the biogeophysical structure of the CZ?” Addressing this question will require coordination among hydrologic subdisciplines and interfacing sciences, and catalyze rapid progress in understanding current CZ structure and predicting how climate and land cover changes will affect hydrologic partitioning. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-07T04:33:24.224938-05:
      DOI: 10.1002/2015WR017039
       
  • Well integrity assessment under temperature and pressure stresses by a 1:1
           scale wellbore experiment
    • Authors: J. C. Manceau; J. Tremosa, P. Audigane, C. Lerouge, F. Claret, Y. Lettry, T. Fierz, C. Nussbaum
      Abstract: A new in situ experiment is proposed for observing and understanding well integrity evolution, potentially due to changes that could occur during a well lifetime. The focus is put on temperature and pressure stresses. A small section of a well is reproduced at scale 1:1 in the Opalinus Clay formation, representative of a low permeable caprock formation (in Mont Terri Underground Rock Laboratory, Switzerland). The well‐system behavior is characterized over time both by performing hydro‐tests to quantify the hydraulic properties of the well and their evolution, and sampling the fluids to monitor the chemical composition and its changes. This paper presents the well integrity assessment under different imposed temperature (17–52°C) and pressure (10–28 bar) conditions. The results obtained in this study confirm the ability of the chosen design and observation scale to estimate the evolution of the well integrity over time, the characteristics of the flow along the well‐system and the reasons of the observed evolution. In particular, the estimated effective well permeability is higher than cement or caprock intrinsic permeability, which suggest preferential flow pathways at interfaces especially at the very beginning of the experiment; the significant variations of the effective well permeability observed after setting pressure and temperature stresses indicate that operations could influence well integrity in similar proportions than the cementing process.
      PubDate: 2015-08-06T13:35:23.811524-05:
      DOI: 10.1002/2014WR016786
       
  • The future of water resources systems analysis: Toward a scientific
           framework for sustainable water management
    • Authors: Casey M. Brown; Jay R. Lund, Ximing Cai, Patrick M. Reed, Edith A. Zagona, Avi Ostfeld, Jim Hall, Gregory W. Characklis, Winston Yu, Levi Brekke
      Abstract: This paper presents a short history of water resources systems analysis from its beginnings in the Harvard Water Program, through its continuing evolution toward a general field of water resources systems science. Current systems analysis practice is widespread and addresses the most challenging water issues of our times, including water scarcity and drought, climate change, providing water for food and energy production, decision making amid competing objectives, and bringing economic incentives to bear on water use. The emergence of public recognition and concern for the state of water resources provides an opportune moment for the field to reorient to meet the complex, interdependent, interdisciplinary, and global nature of today's water challenges. At present, water resources systems analysis is limited by low scientific and academic visibility relative to its influence in practice and bridled by localized findings that are difficult to generalize. The evident success of water resource systems analysis in practice (which is set out in this paper) needs in future to be strengthened by substantiating the field as the science of water resources that seeks to predict the water resources variables and outcomes that are important to governments, industries, and the public the world over. Doing so promotes the scientific credibility of the field, provides understanding of the state of water resources and furnishes the basis for predicting the impacts of our water choices.
      PubDate: 2015-08-06T13:33:56.729911-05:
      DOI: 10.1002/2015WR017114
       
  • Simulation of yearly rainfall time series at microscale resolution with
           actual properties: Intermittency, scale invariance, and rainfall
           distribution
    • Abstract: Rainfall is a physical phenomenon resulting from the combination of numerous physical processes involving a wide range of scales, from microphysical processes to the general circulation of the atmosphere. Moreover unlike other geophysical variables such as water vapour concentration, rainfall is characterized by a relaxation behavior that leads to an alternation of wet and dry periods. It follows that rainfall is a complex process which is highly variable both in time and space. Precipitation is thus characterized by the following features: rain/no‐rain intermittency, multiple scaling regimes and extreme events. All these properties are difficult to model simultaneously, especially when a large time and/or space scale domain is required. The aim of this paper is to develop a simulator capable of generating high resolution rain‐rate time series (15 seconds), the main statistical properties of which are close to an observed rain‐rate time series. We also attempt to develop a model having consistent properties even when the fine resolution simulated time series are aggregated to a coarser resolution. In order to break the simulation problem down into sub‐components, the authors have focused their attention on several key properties of rainfall. The simulator is based on a sequential approach in which, firstly, the simulation of rain/no rain durations permits the retrieval of fractal properties of the rain support. Then, the generation of rain‐rates through the use of a multifractal, Fractionally Integrated Flux (FIF), model enables the restitution of the rainfall's multifractal properties. This second step includes a de‐normalization process that was added in order to generate realistic rain‐rate distributions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:59:46.887039-05:
      DOI: 10.1002/2014WR016357
       
  • Mixing effects on nitrogen and oxygen concentrations and the relationship
           to mean residence time in a hyporheic zone of a riffle‐pool sequence
           
    • Authors: Ramon C. Naranjo; Richard G. Niswonger, Clinton Davis
      Abstract: Flow paths and residence times in the hyporheic zone are known to influence biogeochemical processes such as nitrification and denitrification. The exchange across the sediment‐water interface may involve mixing of surface water and groundwater through complex hyporheic flow paths that contribute to highly variable biogeochemically active zones. Despite the recognition of these patterns in the literature, conceptualization and analysis of flow paths and nitrogen transformations beneath riffle‐pool sequences often neglect to consider bed form driven exchange along the entire reach. In this study, the spatial and temporal distribution of dissolved oxygen (DO), nitrate (NO3‐) and ammonium (NH4+) were monitored in the hyporheic zone beneath a riffle‐pool sequence on a losing section of the Truckee River, NV. Spatially‐varying hyporheic exchange and the occurrence of multi‐scale hyporheic mixing cells are shown to influence concentrations of DO and NO3‐ and the mean residence time (MRT) of riffle and pool areas. Distinct patterns observed in piezometers are shown to be influenced by the first large flow event following a steady 8 month period of low flow conditions. Increases in surface water discharge resulted in reversed hydraulic gradients and production of nitrate through nitrification at small vertical spatial scales (0.10 to 0.25 m) beneath the sediment‐water interface. In areas with high downward flow rates and low MRT, denitrification may be limited. The use of a longitudinal two‐dimensional flow model helped identify important mechanisms such as multi‐scale hyporheic mixing cells and spatially varying MRT, an important driver for nitrogen transformation in the riverbed. Our observations of DO and NO3‐ concentrations and model simulations highlight the role of multi‐scale hyporheic mixing cells on MRT and nitrogen transformations in the hyporheic zone of riffle‐pool sequences. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:59:02.66457-05:0
      DOI: 10.1002/2014WR016593
       
  • The effect of lateral confinement on gravel bed river morphology
    • Authors: G.A. Garcia Lugo; W. Bertoldi, A.J. Henshaw, A.M. Gurnell
      Abstract: In this paper we use a physical modelling approach to explore the effect of lateral confinement on gravel bed river planform style, bed morphology, and sediment transport processes. A set of 27 runs was performed in a large flume (25 m long, 2.9 m wide), with constant longitudinal slope (0.01) and uniform grain size (1 mm), changing the water discharge (1.5 to 2.5 l/s) and the channel width (0.15 m to 1.5 m) to model a wide range of channel configurations, from narrow, straight, embanked channels to wide braided networks. The outcomes of each run were characterized by a detailed digital elevation model describing channel morphology, a map of dry areas and areas actively transporting sediment within the channel, and continuous monitoring of the amount of sediment transported through the flume outlet. Analysis reveals strong relationships between unit stream power and parameters describing the channel morphology. In particular, a smooth transition is observed between narrow channels with an almost rectangular cross section profile (with sediment transport occurring across the entire channel width) and complex braided networks where only a limited proportion (30%) of the bed is active. This transition is captured by descriptors of the bed elevation frequency distribution, e.g. standard deviation, skewness and kurtosis. These summary statistics represent potentially useful indicators of bed morphology that are compared with other commonly used summary indicators such as the braiding index and the type and number of bars. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:58:40.807399-05:
      DOI: 10.1002/2015WR017081
       
  • Time scale interactions and the coevolution of humans and water
    • Abstract: We present a co‐evolutionary view of hydrologic systems, revolving around feedbacks between environmental and social processes operating across different time scales. This brings to the fore an emphasis on emergent phenomena in changing water systems, such as the levee effect, adaptation to change, system lock‐in, and system collapse due to resource depletion. Changing human values play a key role in the emergence of these phenomena and should therefore be considered as internal to the system. Guidance is provided for the framing and modeling of these phenomena to test alternative hypotheses about how they arose. A plurality of co‐evolutionary models, from stylized to comprehensive system‐of‐system models, may assist strategic water management for long time scales through facilitating stakeholder participation, exploring the possibility space of alternative futures, and helping to synthesize the observed dynamics in a wide range of case studies. Future research opportunities lie in exploring emergent phenomena arising from time scale interactions through historical, comparative and process studies of human‐water feedbacks. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:57:19.823161-05:
      DOI: 10.1002/2015WR017896
       
  • The impact of transitions between two and three‐fluid phases on
           fluid configuration and fluid‐fluid interfacial area in porous media
           
    • Authors: Kenneth C. Carroll; Kieran McDonald, Justin Marble, Ann E. Russo, Mark L. Brusseau
      Abstract: Multiphase‐fluid distribution and flow is inherent in numerous areas of hydrology. Yet, pore‐scale characterization of transitions between two and three immiscible‐fluids is limited. The objective of this study was to examine the impact of such transitions on the pore‐scale configuration of organic liquid in a multi‐fluid system comprising natural porous media. Three‐dimensional images of an organic liquid (trichloroethene) in two‐phase (organic‐liquid/water) and three‐phase (air/organic‐liquid/water) systems were obtained using X‐ray microtomography before and after drainage and imbibition. Upon transition from a two‐phase to a three‐phase system, a significant portion of the organic liquid (intermediate wetting fluid) was observed to exist as lenses and films in contact with air (nonwetting fluid). In these cases, the air was either encased by or contiguous to the organic liquid. The presence of air resulted in an increase in the surface‐area‐to‐volume ratios for the organic‐liquid blobs. Upon imbibition, the air was displaced downgradient, and concomitantly, the morphology of the organic‐liquid blobs no longer in contact with air reverted to that characteristic of a two‐phase distribution (i.e., more spherical blobs and ganglia). This change in morphology resulted in a reduction in the surface‐area‐to‐volume ratio. These results illustrate the impact of transitions between two‐phase and three‐phase conditions on fluid configuration, and they demonstrate the malleable nature of fluid configuration under dynamic, multiphase‐flow conditions. The results have implications for characterizing and modeling pore‐scale flow and mass‐transfer processes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:53:15.994225-05:
      DOI: 10.1002/2015WR017490
       
  • Self‐affinity and surface‐area‐dependent fluctuations of
           lake‐level time series
    • Authors: Zachary C. Williams; Jon D. Pelletier
      Abstract: We performed power‐spectral analyses on 133 globally distributed lake‐level time series after removing annual variability. Lake‐level power spectra are found to be power‐law functions of frequency over the range of 20 days‐1 to 27 years‐1, suggesting that lake levels are globally a f‐β‐type noise. The spectral exponent (β), i.e. the best‐fit slope of the logarithm of the power spectrum to the logarithm of frequency, is a nonlinear function of lake surface area, indicating that lake size is an important control on the magnitude of water‐level variability over the range of time scales we considered. A simple cellular model for lake‐level fluctuations that reproduces the observed spectral‐scaling properties is presented. The model (an adaptation of a surface‐growth model with random deposition and relaxation) is based on the equations governing flow in an unconfined aquifer with stochastic inputs and outputs of water (e.g. random storms). The agreement between observation and simulation suggests that lake surface area, spatio‐temporal stochastic forcing, and diffusion of the groundwater table are the primary factors controlling lake water‐level variability in natural (unmanaged) lakes. Water‐level variability is generally considered to be a manifestation of climate trends or climate change, yet our work shows that an input with short or no memory (i.e. weather) gives rise to a long‐memory non‐stationary output (lake water‐level). This work forms the basis for a null hypothesis of lake water‐level variability that should be disproven before water‐level trends are to be attributed to climate. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:51:45.788602-05:
      DOI: 10.1002/2015WR017254
       
  • Natural length scales define the range of applicability of the Richards
           equation for capillary flows
    • Authors: Dani Or; Peter Lehmann, Shmuel Assouline
      Abstract: The rapid expansion of remotely‐sensed spatial information and enhanced computational capabilities fuel increasing scientific and public expectations for reliable hydrologic predictions across time and spatial scales. Process‐based hydrologic models often rely on the Richards equation (RE) formalism to represent unsaturated flow processes at different scales which raise the much debated question: does the underlying physics in the RE formulation apply at large scales of practical interest? The study analyses recent findings from various unsaturated flow processes (soil evaporation, internal redistribution, and capillary flow from point sources) revealing inherent characteristic length scales that delineate the range of applicability of the RE. These length scales reflect the role of intrinsic porous medium properties that shape liquid phase continuity and interplay of forces that drive and resist unsaturated flow. The study revisits some of the key assumptions in the RE and their ramifications for numerical discretization. An intrinsic length scale for hydraulic continuity deduced from pore size distribution has been shown to control soil evaporation dynamics (i.e., stage 1 to stage 2 transition), to provide upper bounds for regional evaporative losses, and governs the dynamics of internal redistribution towards field capacity. For large scale hydrologic applications, we show that the extent of lateral flow interactions under most natural capillary gradients rarely exceed a few meters. The study provides a framework for guiding numerical and mathematical models for capillary flows across different scales considering the conditions for coexistence of stationarity, hydraulic continuity and capillary gradients ‐ essential ingredients for physically‐consistent application of the RE. This article is protected by copyright. All rights reserved.
      PubDate: 2015-08-04T03:51:24.129068-05:
      DOI: 10.1002/2015WR017034
       
  • Human‐impacted waters: New perspectives from global high resolution
           monitoring
    • Authors: Serena Ceola; Francesco Laio, Alberto Montanari
      Abstract: The human presence close to streams and rivers is known to have consistently increased worldwide, therefore introducing dramatic anthropogenic and environmental changes. However, a spatio‐temporal detailed analysis is missing to date. In this paper, we propose a novel method to quantify the temporal evolution and the spatial distribution of the anthropogenic presence along streams and rivers and in their immediate proximity at the global scale and at a high spatial resolution (i.e., nearly 1 km at the equator). We use satellite images of nocturnal lights, available as yearly snapshots from 1992 to 2013, and identify five distinct distance classes from the river network position. Our results show a temporal enhancement of human presence across the considered distance classes. In particular, we observed a higher human concentration in the vicinity of the river network, even though the frequency distribution of human beings in space has not significantly changed in the last two decades. Our results prove that fine scale remotely sensed data, as nightlights, may provide new perspectives in water science, improving our understanding of the human impact on water resources and water‐related environments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-31T01:35:31.330298-05:
      DOI: 10.1002/2015WR017482
       
  • Impact of multicomponent ionic transport on pH fronts propagation in
           saturated porous media
    • Authors: Muhammad Muniruzzaman; Massimo Rolle
      Abstract: We investigate the propagation of pH fronts during multicomponent ionic transport in saturated porous media under flow‐through conditions. By performing laboratory bench‐scale experiments combined with numerical modeling we show the important influence of Coulombic effects on proton transport in the presence of ionic admixtures. The experiments were performed in a quasi two‐dimensional flow‐through setup under steady‐state flow and transport conditions. Dilute solutions of hydrochloric acid with MgCl2 (1:2 strong electrolyte) were used as tracer solutions to experimentally test the effect of electrochemical cross‐coupling on the migration of diffusive/dispersive pH fronts. We focus on two experimental scenarios, with different composition of tracer solutions, causing remarkably different effects on the propagation of the acidic fronts with relative differences in the penetration depth of pH fronts of 36% between the two scenarios and of 25% and 15% for each scenario with respect to the transport of ions at liberated state (i.e., without considering the charge effects). Also differences in the dilution of the distinct ions plumes up to 28% and 45% in experiment 1 and 2, respectively, were measured at the outflow of the flow‐through system. The dilution of the pH plumes also changed considerably (26% relative difference) in the two flow‐through experiments only due to the different composition of the pore water solution and to the electrostatic coupling of the ions in the flow‐through setups. Numerical transport simulations were performed to interpret the laboratory experiments. The simulations were based on a multicomponent ionic formulation accurately capturing the Coulombic interactions between the transported ions in the flow‐through system. The results of purely forward simulations show a very good agreement with the high‐resolution measurements performed at the outlet of the flow‐through setup and confirms the importance of charge effects on pH transport in porous media. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-31T01:35:09.54954-05:0
      DOI: 10.1002/2015WR017134
       
  • Supraglacial channel inception: Modeling and processes
    • Authors: E. Mantelli; C. Camporeale, L. Ridolfi
      Abstract: Supraglacial drainage systems play a key role in glacial hydrology. Nevertheless, physical processes leading to spatial organization in supraglacial networks are still an open issue. In the present work we address from a quantitative point of view the question of what is the physics leading to widely observed patterns made up of evenly spaced channels. To this aim, we set up a novel mathematical model describing a condition antecedent channel formation, i.e. the down–glacier flow of a distributed meltwater film, and perform a linear stability analysis to assess whether the ice–water interface undergoes a morphological instability compatible with observed patterns. The instability is detected, its features depending on glacier surface slope, friction factor and water as well as ice thermal conditions. By contrast, in our model channel spacing is solely hydrodynamically driven and relies on the interplay between pressure perturbations, flow‐depth response and Reynolds stresses. Geometrical features of the predicted pattern are quantitatively consistent with available field data. The hydrodynamic origin of supraglacial channel morphogenesis suggests that alluvial patterns might share the same physical controls. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:48:55.301621-05:
      DOI: 10.1002/2015WR017075
       
  • A formulation for vertically integrated groundwater flow in a stratified
           coastal aquifer
    • Authors: O.D.L. Strack; B.K. Ausk
      Abstract: We present the comprehensive discharge potential for steady three‐dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline. The gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer, i.e., the specific discharge vector as a function of three‐dimensional space integrated over the saturated portion of the aquifer. The boundary values of the comprehensive potential along the coast can be computed precisely, given the geometry of the aquifer: the hydraulic conductivities of the strata, the elevations of the horizontal planes that separate the strata, and the elevation of the impermeable base of the aquifer relative to sea level. Boundary conditions of the comprehensive potential may either be given in terms of its gradient, or computed from given heads along the boundaries. The governing equation of the comprehensive potential is the Poisson equation in areas of infiltration and the Laplace equation elsewhere. The computation of interface elevations, piezometric heads, and the vertical distribution of flow, requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads. We adopt the Dupuit‐Forchheimer approximation for this purpose and make use of the Ghyben‐Herzberg equation. We present several applications of the approach, and find that the stratification may have a significant effect on the boundary value of the comprehensive potential, and thus on the flow rates in the aquifer. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:48:27.861155-05:
      DOI: 10.1002/2015WR016887
       
  • Hydrologic issues associated with nuclear waste repositories
    • Abstract: Significant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in underground nuclear waste repositories. The present paper provides an overview of the key hydrologic issues involved, and to highlight advances in their understanding and treatment because of these efforts. The focus is not on the development of radioactive waste repositories and their safety assessment, but instead on the advances in hydrologic science that have emerged from such studies. Work and results associated with three rock types which are being considered to host the repositories, are reviewed, with a different emphasis for each rock type. The first rock type is fractured crystalline rock, for which the discussion will be mainly on flow and transport in saturated fractured rock. The second rock type is unsaturated tuff, for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository. The third rock type is clay‐rich formations, whose permeability is very low in an undisturbed state. In this case, the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances; i.e., on the relevant coupled thermo‐hydro‐mechanical processes. The extensive research results, especially those from multi‐year large‐scale underground research laboratory investigations, represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:48:09.500952-05:
      DOI: 10.1002/2015WR017641
       
  • Status of CO2 storage in deep saline aquifers with emphasis on modeling
           approaches and practical simulations
    • Authors: M. A. Celia; S. Bachu, J. M. Nordbotten, K. W. Bandilla
      Abstract: Carbon capture and storage (CCS) is the only viable technology to mitigate carbon emissions while allowing continued large‐scale use of fossil fuels. The storage part of CCS involves injection of carbon dioxide, captured from large stationary sources, into deep geological formations. Deep saline aquifers have the largest identified storage potential, with estimated storage capacity sufficient to store emissions from large stationary sources for at least a century. This makes CCS a potentially important bridging technology in the transition to carbon‐free energy sources. Injection of CO2 into deep saline aquifers leads to a multi‐component, multi‐phase flow system, in which geomechanics, geochemistry, and non‐isothermal effects may be important. While the general system can be highly complex and involve many coupled, nonlinear partial differential equations, the underlying physics can sometimes lead to important simplifications. For example, the large density difference between injected CO2 and brine may lead to relatively fast buoyant segregation, making an assumption of vertical equilibrium reasonable. Such simplifying assumptions lead to a range of simplified governing equations whose solutions have provided significant practical insights into system behavior, including improved estimates of storage capacity, easy‐to‐compute estimates of CO2 spatial migration and pressure response, and quantitative estimates of leakage risk. When these modeling studies are coupled with observations from well‐characterized injection operations, understanding of the overall system behavior is enhanced significantly. This improved understanding shows that, while economic and policy challenges remain, CO2 storage in deep saline aquifers appears to be a viable technology and can contribute substantially to climate change solutions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:47:28.233481-05:
      DOI: 10.1002/2015WR017609
       
  • Group‐sparsity regularization for ill‐posed subsurface flow
           inverse problems
    • Abstract: Sparse representations provide a flexible and parsimonious description of high‐dimensional model parameters for reconstructing subsurface flow property distributions from limited data. To further constrain ill‐posed inverse problems, group‐sparsity regularization can take advantage of possible relations among the entries of unknown sparse parameters when: (i) groups of sparse elements are either collectively active or inactive; and (ii) only a small subset of the groups is needed to approximate the parameters of interest. Since subsurface properties exhibit strong spatial connectivity patterns, they may lead to sparse descriptions that satisfy the above conditions. When these conditions are established a group‐sparsity regularization can be invoked to facilitate the solution of the resulting inverse problem by promoting sparsity across the groups (and not within each group). The proposed regularization penalizes the number of groups that are active without promoting sparsity within each group. Two implementations are presented in this paper: one based on the multi‐resolution tree structure of Wavelet decomposition, without a need for explicit prior models, and another learned from explicit prior model realizations using sparse principal component analysis (SPCA). In each case, the approach first classifies the parameters of the inverse problem into groups with specific connectivity features, and then takes advantage of the grouped structure to recover the relevant patterns in the solution from the flow data. Several numerical experiments are presented to demonstrate the advantages of additional constraining due to group‐sparsity in solving ill‐posed subsurface model calibration problems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:46:42.272874-05:
      DOI: 10.1002/2014WR016430
       
  • Physically based modeling in catchment hydrology at 50: Survey and outlook
    • Authors: Claudio Paniconi; Mario Putti
      Abstract: Integrated, process‐based numerical models in hydrology are rapidly evolving, spurred by novel theories in mathematical physics, advances in computational methods, insights from laboratory and field experiments, and the need to better understand and predict the potential impacts of population, land use, and climate change on our water resources. At the catchment scale, these simulation models are commonly based on conservation principles for surface and subsurface water flow and solute transport (e.g., the Richards, shallow water, and advection‐dispersion equations), and they require robust numerical techniques for their resolution. Traditional (and still open) challenges in developing reliable and efficient models are associated with heterogeneity and variability in parameters and state variables; nonlinearities and scale effects in process dynamics; and complex or poorly known boundary conditions and initial system states. As catchment modeling enters a highly interdisciplinary era, new challenges arise from the need to maintain physical and numerical consistency in the description of multiple processes that interact over a range of scales and across different compartments of an overall system. This paper first gives an historical overview (past 50 years) of some of the key developments in physically‐based hydrological modeling, emphasizing how the interplay between theory, experiments, and modeling has contributed to advancing the state of the art. The second part of the paper examines some outstanding problems in integrated catchment modeling from the perspective of recent developments in mathematical and computational science. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:26:46.043202-05:
      DOI: 10.1002/2015WR017780
       
  • Bayesian‐information‐gap decision theory with an application
           to CO2 sequestration
    • Authors: D. O'Malley; V.V. Vesselinov
      Abstract: Decisions related to subsurface engineering problems such as groundwater management, fossil fuel production, and geologic carbon sequestration are frequently challenging because of an overabundance of uncertainties (related to conceptualizations, parameters, observations, etc.). Because of the importance of these problems to agriculture, energy, and the climate (respectively), good decisions that are scientifically defensible must be made despite the uncertainties.We describe a general approach to making decisions for challenging problems such as these in the presence of severe uncertainties that combines probabilistic and non‐probabilistic methods. The approach uses Bayesian sampling to assess parametric uncertainty and Information‐Gap Decision Theory (IGDT) to address model inadequacy. The combined approach also resolves an issue that frequently arises when applying Bayesian methods to real‐world engineering problems related to the enumeration of possible outcomes. In the case of zero non‐probabilistic uncertainty, the method reduces to a Bayesian method. To illustrate the approach, we apply it to a site‐selection decision for geologic CO2 sequestration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:26:24.587967-05:
      DOI: 10.1002/2015WR017413
       
  • Stochastic modeling of solute transport in aquifers: From heterogeneity
           characterization to risk analysis
    • Authors: A. Fiori; A. Bellin, V. Cvetkovic, F.P.J. de Barros, G. Dagan
      Abstract: The article presents a few recent developments advanced by the authors in a few key areas of stochastic modeling of solute transport in heterogeneous aquifers. First, a brief review of the Lagrangean approach to modeling plumes longitudinal mass distribution and temporal (the breakthrough curve) mass arrival, is presented. Subsequently, transport in highly heterogeneous aquifers is analyzed by using a recently developed predictive model. It relates the non‐Gaussian BTC to the permeability univariate pdf and integral scale, with application to the MADE field observations. Next, the approach is extended to transport of reactive solute, combinnig the effects of the random velocity field and multirate mass transfer on the BTC, with application to mass attenuation. The following topic is modeling of the local concentration field as affected by mixing and dilution due to pore scale dispersion. The results are applied to the analysis of concentration measurements at the Cape Cod field experiment. The last section incorporates the results of the preceding ones in health risk assesment by analyzing the impact of concentration prediction on risk uncertainty. It is illustrated by assesing the effect of identification of macrodispersivity from field characterization and transport modeling, upon the probability of health risk. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:21:50.431116-05:
      DOI: 10.1002/2015WR017388
       
  • Hydraulic Fracturing Fluid Migration in the Subsurface: A Review and
           Modeling Results
    • Authors: Daniel T. Birdsell; Harihar Rajaram, David Dempsey, Hari Viswanathan
      Abstract: Understanding the transport of hydraulic fracturing (HF) fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated. Topographically driven flow, overpressured shale reservoirs, permeable pathways such as faults or leaky wellbores, the increased formation pressure due to HF fluid injection, and the density contrast of the HF fluid to the surrounding brine can encourage upward HF fluid migration. In contrast, the very low shale permeability and capillary imbibition of water into partially saturated shale may sequester much of the HF fluid, and well production will remove HF fluid from the subsurface. We review the literature on important aspects of HF fluid migration. Single‐phase flow and transport simulations are performed to quantify how much HF fluid is removed via the wellbore with flowback and produced water, how much reaches overlying aquifers, and how much is permanently sequestered by capillary imbibition, which is treated as a sink term based on a semi‐analytical, one‐dimensional solution for two‐phase flow. These simulations include all of the important aspects of HF fluid migration identified in the literature review and are performed in 5 stages to faithfully represent the typical operation of a hydraulically fractured well. No fracturing fluid reaches the aquifer without a permeable pathway. In the presence of a permeable pathway, ten times more fracturing fluid reaches the aquifer if well production and capillary imbibition are not included in the model. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-30T10:21:30.899353-05:
      DOI: 10.1002/2015WR017810
       
  • Potential for real‐time understanding of coupled hydrologic and
           biogeochemical processes in stream ecosystems: Future integration of
           telemetered data with process models for glacial meltwater streams
    • Authors: Diane M McKnight; Karen Cozzetto, James D. S. Cullis, Michael N Gooseff, Christopher Jaros, Joshua C Koch, William B Lyons, Roseanna Neupauer, Adam Wlostowski
      Abstract: While continuous monitoring of stream flow and temperature has been common for some time, there is great potential to expand continuous monitoring to include water quality parameters such as nutrients, turbidity, oxygen and dissolved organic material. In many systems distinguishing between watershed and stream ecosystem controls can be challenging. The usefulness of such monitoring can be enhanced by application of quantitative models to interpret observed patterns in real time. Examples are discussed primarily from the glacial meltwater streams of the McMurdo Dry Valleys, Antarctica. Although the dry valley landscape is barren of plants, many streams harbor thriving cyanobacterial mats. Whereas a daily cycle of stream flow is controlled by the surface energy balance on the glaciers and the temporal pattern of solar exposure, the daily signal for biogeochemical processes controlling water quality is generated along the stream. These features result in an excellent outdoor laboratory for investigating fundamental ecosystem process and the development and validation of process based models. As part of the McMurdo Dry Valleys Long Term Ecological Research project, we have conducted field experiments and developed coupled biogeochemical transport models for the role of hyporheic exchange in controlling weathering reactions, microbial nitrogen cycling, and stream temperature regulation. We have adapted modeling approaches from sediment transport to understand mobilization of stream biomass with increasing flows. These models help to elucidate the role of in‐stream processes in systems where watershed processes also contribute to observed patterns, and may serve as a test case for applying real‐time stream ecosystem models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-29T19:48:22.925274-05:
      DOI: 10.1002/2015WR017618
       
  • Effective parameterizations of three nonwetting phase relative
           permeability models
    • Authors: Zhenlei Yang; Binayak P. Mohanty
      Abstract: Describing convective nonwetting phase flow in unsaturated porous media requires knowledge of the nonwetting phase relative permeability. This study was conducted to formulate and derive a generalized expression for the nonwetting phase relative permeability via combining with the Kosugi water retention function. This generalized formulation is then used to flexibly investigate the Burdine, Mualem and Alexander and Skaggs models' prediction accuracy for relative nonwetting phase permeability. The model and data comparison results show that these three permeability models, if used in their original form, but applied to the nonwetting phase, could not predict the experimental data well. The optimum pore tortuosity and connectivity value is thus obtained for the improved prediction of relative nonwetting phase permeability. As a result, the effective parametrization of (α,β,η) parameters in the modified Burdine, modified Mualem and modified Alexander and Skaggs permeability models were found to be (2.5, 2, 1), (2, 1, 2) and (2.5, 1, 1), respectively. These three suggested models display the highest accuracy among the nine relative permeability models investigated in this study. However, the corresponding discontinuous nonwetting phase and the liquid film flow should be accounted for in future for the improved prediction of nonwetting phase relative permeability at very high and very low water saturation range, respectively. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:15:39.292025-05:
      DOI: 10.1002/2014WR016190
       
  • A review of surrogate models and their application to groundwater modeling
    • Authors: M. J. Asher; B. F. W. Croke, A. J. Jakeman, L. J. M. Peeters
      Abstract: The spatially and temporally variable parameters and inputs to complex groundwater models typically result in long runtimes which hinder comprehensive calibration, sensitivity and uncertainty analysis. Surrogate modeling aims to provide a simpler, and hence faster, model which emulates the specified output of a more complex model in function of its inputs and parameters. In this review paper, we summarize surrogate modeling techniques in three categories: data‐driven, projection, and hierarchical‐based approaches. Data‐driven surrogates approximate a groundwater model through an empirical model that captures the input‐output mapping of the original model. Projection based models reduce the dimensionality of the parameter space by projecting the governing equations onto a basis of orthonormal vectors. In hierarchical or multi‐fidelity methods the surrogate is created by simplifying the representation of the physical system, such as by ignoring certain processes, or reducing the numerical resolution. In discussing the application to groundwater modeling of these methods, we note several imbalances in the existing literature: a large body of work on data‐driven approaches seemingly ignores major drawbacks to the methods; only a fraction of the literature focuses on creating surrogates to reproduce outputs of fully distributed groundwater models, despite these being ubiquitous in practice; and a number of the more advanced surrogate modeling methods are yet to be fully applied in a groundwater modeling context. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:13:31.014591-05:
      DOI: 10.1002/2015WR016967
       
  • Video observations of bed form morphodynamics in a meander bend
    • Authors: Margaret L. Palmsten; Jessica L. Kozarek, Joseph Calantoni
      Abstract: A new optical remote sensing technique for estimating water depth from an oblique camera view is described. The water surface and the bed were imaged simultaneously to create time‐dependent maps of the water surface velocities and the bed elevations that can be used to validate numerical models at high spatial and temporal resolution. The technique was applied in a sandy meander bend at the University of Minnesota Saint Anthony Falls Laboratory Outdoor StreamLab. The root mean square differences between optical estimates of the bed and in situ observations ranged between 0.01 and 0.03 m. Mean bedform wavelength was 0.73 m and mean crest height was 0.07 m, but both varied with distance around the meander bend. Bedform classification varied with distance downstream, and sinuosity of bedforms varied with local radius of curvature. Bedform roughness scaled similarly to other natural riverine environments although wavelength and height magnitude and variability were larger than predicted by empirical formulations for straight reaches. Bedform translation rate varied between 1 and 5 mm s−1. Estimates of velocity from particle image velocimetry (PIV) on the water surface were ∼10% higher than in situ observations collected ∼0.05 m below the water surface. Using the PIV observations to drive simple equations for bedload sediment flux, we explained up to 72% of the observed variance in downstream sediment flux. The new methodology described here provides non‐intrusive, high spatial and temporal resolution measurements of both the bed and the flow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:13:04.943378-05:
      DOI: 10.1002/2014WR016321
       
  • Hierarchical Bayesian clustering for nonstationary flood frequency
           analysis: Application to trends of annual maximum flow in Germany
    • Authors: Xun Sun; Upmanu Lall, Bruno Merz, Nguyen Viet Dung
      Abstract: Especially for extreme precipitation or floods, there is considerable spatial and temporal variability in long term trends or in the response of station time series to large scale climate indices. Consequently, identifying trends or sensitivity of these extremes to climate parameters can be marked by high uncertainty. When one develops a nonstationary frequency analysis model, a key step is the identification of potential trends or effects of climate indices on the station series. An automatic clustering procedure that effectively pools stations where there are similar responses is desirable to reduce the estimation variance, thus improving the identification of trends or responses, and accounting for spatial dependence. This paper presents a new hierarchical Bayesian approach for exploring homogeneity of response in large area data sets, through a multi‐component mixture model. The approach allows the reduction of uncertainties through both full pooling and partial pooling of stations across automatically chosen subsets of the data. We apply the model to study the trends in annual maximum daily stream flow at 68 gauges over Germany. The effects of changing the number of clusters and the parameters used for clustering are demonstrated. The results show that there are large, mainly upward trends in the gauges of the River Rhine Basin in Western Germany and along the main stream of the Danube River in the south, while there are also some small upward trends at gauges in Central and Northern Germany. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:11:48.937392-05:
      DOI: 10.1002/2015WR017117
       
  • Evaluating the relationship between topography and groundwater using
           outputs from a continental‐scale integrated hydrology model
    • Authors: Laura E. Condon; Reed M. Maxwell
      Abstract: We study the influence of topography on groundwater fluxes and water table depths across the Contiguous United States (CONUS). Groundwater tables are often conceptualized as subdued replicas of topography. While it is well known that groundwater configuration is also controlled by geology and climate, nonlinear interactions between these drivers within large real world systems are not well understood and are difficult to characterize given sparse groundwater observations. We address this limitation using the fully integrated physical hydrology model ParFlow to directly simulate groundwater fluxes and water table depths within a complex heterogeneous domain that incorporates all three primary groundwater drivers. Analysis is based on a first of its kind, continental scale, high‐resolution (1km), groundwater‐surface water simulation spanning more than 6.3 million km2. Results show that groundwater fluxes are most strongly driven by topographic gradients (as opposed to gradients in pressure head) in humid regions with small topographic gradients or low conductivity. These regions are generally consistent with the topographically controlled groundwater regions identified in previous studies. However, we also show that areas where topographic slopes drive groundwater flux do not generally have strong correlations between water table depth and elevation. Nonlinear relationships between topography and water table depth are consistent with groundwater flow systems that are dominated by local convergence and could also be influenced by local variability in geology and climate. One of the strengths of the numerical modeling approach is its ability to evaluate continental scale groundwater behavior at a high resolution not possible with other techniques. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:11:38.137896-05:
      DOI: 10.1002/2014WR016774
       
  • A well‐balanced FV scheme for compound channels with complex
           geometry and movable bed
    • Authors: L. Minatti
      Abstract: This work focuses on the implementation of a Shallow Water‐Exner model for compound natural channels with complex geometry and movable bed within the finite volume framework. The model is devised for compound channels modeling: cross‐section overbanks are treated with fixed bed conditions, while the main channel is left free to modify its morphology. A capacitive approach is used for bedload transport modeling, in which the solid flow rates are estimated with bedload transport formulas. The model equations pose some numerical issues in the case of natural channels, where bedload transport may occur for both subcritical and supercritical flows and geometry varies in space. An explicit path‐conservative scheme, designed to overcome all these issues, is presented in the paper. The scheme solves liquid and solid phases dynamics in a coupled manner, in order to correctly model near critical currents/channel interactions and is well‐balanced, that is able to properly reproduce steady states. The Roe and Osher Riemann solvers are implemented, so as to take into account the spatial geometry variations of natural channels. The scheme reaches up to 2nd order accuracy. Validation is performed with fixed and movable bed test cases whose analytical solution is known, and with flume experimental data. An application of the model to a real case study is also shown. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:10:00.885031-05:
      DOI: 10.1002/2014WR016584
       
  • River corridor science: Hydrologic exchange and ecological consequences
           from bed forms to basins
    • Authors: Jud Harvey; Michael Gooseff
      Abstract: Previously regarded as the passive drains of watersheds, over the past 50 years, rivers have progressively been recognized as being actively connected with off channel environments. These connections prolong physical storage and enhance reactive processing to alter water chemistry and downstream transport of materials and energy. Here we propose river corridor science as a concept that integrates downstream transport with lateral and vertical exchange across interfaces. Thus the river corridor, rather than the wetted river channel itself, is an increasingly common unit of study. Main channel exchange with recirculating marginal waters, hyporheic exchange, bank storage, and overbank flow onto floodplains are all included under a broad continuum of interactions known as “hydrologic exchange flows”. Hydrologists, geomorphologists, geochemists, and aquatic and terrestrial ecologists are cooperating in studies that reveal the dynamic interactions among hydrologic exchange flows and consequences for water quality improvement, modulation of river metabolism, habitat provision for vegetation, fish, and wildlife, and other valued ecosystem services. The need for better integration of science and management is keenly felt, from testing effectiveness of stream restoration and riparian buffers all the way to reevaluating the definition of the waters of the United States to clarify the regulatory authority under the Clean Water Act. A major challenge for scientists is linking the small‐scale physical drivers with their larger scale fluvial and geomorphic context and ecological consequences. Although the fine scales of field and laboratory studies are best suited to identifying the fundamental physical and biological processes, that understanding must be successfully linked to cumulative effects at watershed to regional and continental scales. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-27T04:08:42.497175-05:
      DOI: 10.1002/2015WR017617
       
  • In situ determination of surface relaxivities for unconsolidated sediments
    • Authors: Markus Duschl; Petrik Galvosas, Timothy I. Brox, Andreas Pohlmeier, Harry Vereecken
      Abstract: NMR relaxometry has developed into a method for rapid pore size determination of natural porous media. Nevertheless, it is prone to uncertainties because of unknown surface relaxivities which depend mainly on the chemical composition of the pore walls as well as on the interfacial dynamics of the pore fluid. The classical approach for the determination of surface relaxivities is the scaling of NMR relaxation times by surface to volume ratios measured by gas adsorption or mercury intrusion. However, it is preferable that a method for the determination of average pore sizes uses the same substance, water, as probe molecule for both relaxometry and surface to volume measurements. One should also ensure that in both experiments the dynamics of the probe molecule takes place on similar length scales, which are in the order of some microns. Therefore, we employed NMR diffusion measurements with different observation times using bipolar pulsed field gradients and applied them to unconsolidated sediments (two purified sands, two natural sands, and one soil). The evaluation by Mitra's short time model for diffusion in restricted environments yielded information about the surface to volume ratios which is independent of relaxation mechanisms. We point out that methods based on NMR diffusometry yield pore dimensions and surface relaxivities consistent with a pore space as sampled by native pore fluids via the diffusion process. This opens a way to calibrate NMR relaxation measurements with other NMR techniques, providing information about the pore size distribution of natural porous media directly from relaxometry. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-24T10:05:28.876367-05:
      DOI: 10.1002/2014WR016574
       
  • Predicting permeability from the characteristic relaxation time and
           intrinsic formation factor of complex conductivity spectra
    • Authors: A. Revil; A. Binley, L. Mejus, P. Kessouri
      Abstract: Low‐frequency quadrature conductivity spectra of siliclastic materials exhibit typically a characteristic relaxation time, which either corresponds to the peak frequency of the phase or the quadrature conductivity or a typical corner frequency, at which the quadrature conductivity starts to decrease rapidly towards lower frequencies. This characteristic relaxation time can be combined with the (intrinsic) formation factor and a diffusion coefficient to predict the permeability to flow of porous materials at saturation. The intrinsic formation factor can either be determined at several salinities using an electrical conductivity model or at a single salinity using a relationship between the surface and quadrature conductivities. The diffusion coefficient entering into the relationship between the permeability, the characteristic relaxation time and the formation factor, takes only two distinct values for isothermal conditions. For pure silica, the diffusion coefficient of cations, like sodium or potassium, in the Stern layer is equal to the diffusion coefficient of these ions in the bulk pore water, indicating weak sorption of these couterions. For clayey materials and clean sands and sandstones whose surface have been exposed to alumina (possibly iron), the diffusion coefficient of the cations in the Stern layer appears to be 350 times smaller than the diffusion coefficient of the same cations in the pore water. These values are consistent with the values of the ionic mobilities used to determine the amplitude of the low and high‐frequency quadrature conductivities and surface conductivity. The database used to test the model comprises a total of 202 samples. Our analysis reveals that permeability prediction with the proposed model is usually within an order of magnitude from the measured value above 0.1 mD. We also discuss the relationship between the different time constants that have been considered in previous works as characteristic relaxation time, including the mean relaxation time obtained from a Debye decomposition of the spectra and the Cole‐Cole time constant. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-24T09:59:28.634102-05:
      DOI: 10.1002/2015WR017074
       
  • The science and practice of river restoration
    • Authors: Ellen Wohl; Stuart N. Lane, Andrew C. Wilcox
      Abstract: River restoration is one of the most prominent areas of applied water‐resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human‐altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration as a social process. We also examine challenges for scientific understanding in river restoration. These include: how physical complexity supports biogeochemical function, stream metabolism, and stream ecosystem productivity; characterizing response curves of different river components; understanding sediment dynamics; and increasing appreciation of the importance of incorporating climate change considerations and resiliency into restoration planning. Finally, we examine changes in river restoration within the past decade, such as increasing use of stream mitigation banking; development of new tools and technologies; different types of process‐based restoration; growing recognition of the importance of biological‐physical feedbacks in rivers; increasing expectations of water quality improvements from restoration; and more effective communication between practitioners and river scientists. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-24T09:58:46.047619-05:
      DOI: 10.1002/2014WR016874
       
  • Controls on the breach geometry and flood hydrograph during overtopping of
           noncohesive earthen dams
    • Authors: Joseph S. Walder; Richard M. Iverson, Jonathan W. Godt, Matthew Logan, Stephen A. Solovitz
      Abstract: Overtopping failure of non‐cohesive earthen dams was investigated in 13 large‐scale experiments with dams built of compacted, damp, fine‐grained sand. Breaching was initiated by cutting a notch across the dam crest and allowing water escaping from a finite upstream reservoir to form its own channel. The channel developed a stepped profile, and upstream migration of the steps, which coalesced into a headcut, led to the establishment of hydraulic control (critical flow) at the channel head, or breach crest, an arcuate erosional feature that functions hydraulically as a weir. Novel photogrammetric methods, along with underwater videography, revealed that the retreating headcut maintained a slope near the angle of friction of the sand, while the cross section at the breach crest maintained a geometrically similar shape through time. That cross‐sectional shape was nearly unaffected by slope failures, contrary to the assumption in many models of dam breaching. Flood hydrographs were quite reproducible–for sets of dams ranging in height from 0.55 m to 0.98 m–when the time datum was chosen as the time that the migrating headcut intersected the breach crest. Peak discharge increased almost linearly as a function of initial dam height. Early‐time variability between flood hydrographs for nominally identical dams is probably a reflection of subtle experiment‐to‐experiment differences in groundwater hydrology and the interaction between surface water and groundwater. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-22T03:59:36.092041-05:
      DOI: 10.1002/2014WR016620
       
  • Quantifying the impacts of climate change and ecological restoration on
           streamflow changes based on a Budyko hydrological model in China's Loess
           Plateau
    • Authors: Wei Liang; Dan Bai, Feiyu Wang, Bojie Fu, Junping Yan, Shuai Wang, Yuting Yang, Di Long, Minquan Feng
      Abstract: Understanding hydrological effects of ecological restoration (ER) is fundamental to develop effective measures guiding future ER and to adapt climate change in China's Loess Plateau (LP). Streamflow (Q) is an important indicator of hydrological processes that represents the combined effects of climatic and land surface conditions. Here, fourteen catchments located in the LP were chosen to explore the Q response to different driving factors during the period 1961‐2009 by using elasticity and decomposition methods based on the Budyko framework. Our results show that: (1) annual Q exhibited a decreasing trend in all catchments (‐0.30 ∼ ‐1.71 mm y−2), with an average reduction of ‐0.87 mm y−2. The runoff coefficient in flood season and non‐flood season were both decreasing between two periods divided by the changing point in annual Q series; (2) the precipitation (P) and potential evapotranspiration (E0) elasticity of Q are 2.75 and ‐1.75, respectively, indicating that Q is more sensitive to changes in P than that in E0; (3) the two methods consistently demonstrated that, on average, ER (62%) contributing to Q reduction was much larger than that of climate change (38%). In addition, parameter n that entails catchment characteristics in the Budyko framework showed positive correlation with the relative area of ER measures in all catchments (eight of them are statistically significant with p
      PubDate: 2015-07-22T03:58:16.971353-05:
      DOI: 10.1002/2014WR016589
       
  • Imbibition of hydraulic fracturing fluids into partially saturated shale
    • Authors: Daniel T. Birdsell; Harihar Rajaram, Greg Lackey
      Abstract: Recent studies suggest that imbibition of hydraulic fracturing fluids into partially saturated shale is an important mechanism that restricts their migration, thus reducing the risk of groundwater contamination. We present computations of imbibition based on an exact semi‐analytical solution [McWhorter and Sunada, 1990] for spontaneous imbibition. These computations lead to quantitative estimates of an imbibition rate parameter (A) with units of LT−1/2 for shale, which is related to porous medium and fluid properties, and the initial water saturation. Our calculations suggest that significant fractions of injected fluid volumes (15‐95%) can be imbibed in shale gas systems, whereas imbibition volumes in shale oil systems is much lower (3‐27%). We present a non‐dimensionalization of A, which provides insights into the critical factors controlling imbibition, and facilitates the estimation of A based on readily measured porous medium and fluid properties. For a given set of medium and fluid properties, A varies by less than factors of ∼1.8 (gas non‐wetting phase) and ∼3.4 (oil non‐wetting phase) over the range of initial water saturations reported for the Marcellus shale (0.05‐0.6). However, for higher initial water saturations, A decreases significantly. The intrinsic permeability of the shale and the viscosity of the fluids are the most important properties controlling the imbibition rate. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-22T03:57:45.015575-05:
      DOI: 10.1002/2015WR017621
       
  • Water balance‐based actual evapotranspiration reconstruction from
           ground and satellite observations over the conterminous United States
    • Authors: Zhanming Wan; Ke Zhang, Xianwu Xue, Zhen Hong, Yang Hong, Jonathan J. Gourley
      Abstract: The objective of this study is to produce an observationally based monthly evapotranspiration (ET) product using the simple water balance equation across the conterminous United States (CONUS). We adopted the best quality ground‐ and satellite‐based observations of the water budget components, i.e., precipitation, runoff, and water storage change, while ET is computed as the residual. Precipitation data is provided by the bias‐corrected PRISM observation‐based precipitation dataset, while runoff comes from observed monthly streamflow values at 592 USGS stream gauging stations that have been screened by strict quality controls. We developed a land surface model‐based downscaling approach to disaggregate the monthly GRACE equivalent water thickness data to daily, 0.125º values. The derived ET computed as the residual from the water balance equation is evaluated against three sets of existing ET products. The similar spatial patterns and small differences between the reconstructed ET in this study and the other three products show the reliability of the observationally based approach. The new ET product and the disaggregated GRACE data provide a unique, important hydro‐meteorological data set that can be used to evaluate the other ET products as a benchmark dataset, assess recent hydrological and climatological changes, and terrestrial water and energy cycle dynamics across the CONUS. These products will also be valuable for studies and applications in drought assessment, water resources management, and climate change evaluation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-22T03:56:20.495779-05:
      DOI: 10.1002/2015WR017311
       
  • Improving the representation of hydrologic processes in Earth System
           Models
    • Authors: Martyn P. Clark; Ying Fan, David M. Lawrence, Jennifer C. Adam, Diogo Bolster, David J. Gochis, Richard P. Hooper, Mukesh Kumar, L. Ruby Leung, D. Scott Mackay, Reed M. Maxwell, Chaopeng Shen, Sean C. Swenson, Xubin Zeng
      Abstract: Many of the scientific and societal challenges in understanding and preparing for global environmental change rest upon our ability to understand and predict the water cycle change at large river basin, continent, and global scales. However, current large‐scale land models (as a component of Earth System Models, or ESMs) do not yet reflect the best hydrologic process understanding or utilize the large amount of hydrologic observations for model testing. This paper discusses the opportunities and key challenges to improve hydrologic process representations and benchmarking in ESM land models, suggesting that (1) land model development can benefit from recent advances in hydrology, both through incorporating key processes (e.g., groundwater‐surface interactions) and new approaches to describe multi‐scale spatial variability and hydrologic connectivity; (2) accelerating model advances requires comprehensive hydrologic benchmarking in order to systematically evaluate competing alternatives, understand model weaknesses, and prioritize model development needs, and (3) stronger collaboration is needed between the hydrology and ESM modeling communities, both through greater engagement of hydrologists in ESM land model development, and through rigorous evaluation of ESM hydrology performance in research watersheds or Critical Zone Observatories. Such coordinated efforts in advancing hydrology in ESMs have the potential to substantially impact energy, carbon and nutrient cycle prediction capabilities through the fundamental role hydrologic processes play in regulating these cycles. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-22T03:55:20.742189-05:
      DOI: 10.1002/2015WR017096
       
  • Computationally inexpensive identification of noninformative model
           parameters by sequential screening
    • Abstract: Environmental models tend to require increasing computational time and resources as physical process descriptions are improved or new descriptions are incorporated. Many‐query applications such as sensitivity analysis or model calibration usually require a large number of model evaluations leading to high computational demand. This often limits the feasibility of rigorous analyses. Here we present a fully automated sequential screening method that selects only informative parameters for a given model output. The method requires a number of model evaluations that is approximately ten times the number of model parameters. It was tested using the mesoscale hydrologic model mHM in three hydrologically unique European river catchments. It identified around 20 informative parameters out of 52, with different informative parameters in each catchment. The screening method was evaluated with subsequent analyses using all 52 as well as only the informative parameters. Subsequent Sobol's global sensitivity analysis led to almost identical results yet required 40\% fewer model evaluations after screening. mHM was calibrated with all and with only informative parameters in the three catchments. Model performances for daily discharge were equally high in both cases with Nash‐Sutcliffe efficiencies above 0.82. Calibration using only the informative parameters needed just one third of the number of model evaluations. The universality of the sequential screening method was demonstrated using several general test functions from the literature. We therefore recommend the use of the computationally inexpensive sequential screening method prior to rigorous analyses on complex environmental models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T07:52:33.560854-05:
      DOI: 10.1002/2015WR016907
       
  • Charting unknown waters—On the role of surprise in flood risk
           assessment and management
    • Abstract: Unexpected incidents, failures and disasters are abundant in the history of flooding events. In this paper we introduce the metaphors of terra incognita and terra maligna to illustrate unknown and wicked flood situations, respectively. We argue that surprise is a neglected element in flood risk assessment and management. Two sources of surprise are identified: (1) the complexity of flood risk systems, represented by non‐linearities, interdependencies and non‐stationarities, and (2) cognitive biases in human perception and decision making. Flood risk assessment and management are particularly prone to cognitive biases due to the rarity and uniqueness of extremes, and the nature of human risk perception. We reflect on possible approaches to better understanding and reducing the potential for surprise and its adverse consequences which may be supported by conceptually charting maps that separate terra incognita from terra cognita, and terra maligna from terra benigna. We conclude that flood risk assessment and management should account for the potential for surprise and devastating consequences which will require a shift in thinking. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T07:51:45.100885-05:
      DOI: 10.1002/2015WR017464
       
  • Integrating social and physical sciences in water management
    • Authors: Jay R. Lund
      Abstract: Water management has always required more than physical science. This paper reviews the accomplishments of integrating social with physical sciences for water management in the last 50 years. Particular successes are highlighted to illustrate how fundamentals from both physical science and social science have been brought together to improve the performance of water management systems. Some forward‐looking lessons for managing practical and academic interdisciplinary research for water management also are provided. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T07:51:07.836281-05:
      DOI: 10.1002/2015WR017125
       
  • Impact of prescribed burning on blanket peat hydrology
    • Authors: Joseph Holden; Sheila M. Palmer, Kerrylyn Johnston, Catherine Wearing, Brian Irvine, Lee E. Brown
      Abstract: Fire is known to impact soil properties and hydrological flowpaths. However, the impact of prescribed vegetation burning on blanket peatland hydrology is poorly understood. We studied ten blanket peat headwater catchments. Five were subject to prescribed burning, while five were unburnt controls. Within the burnt catchments we studied plots where the last burn occurred ∼2 (B2), 4 (B4), 7 (B7) or greater than 10 years (B10+) prior to the start of measurements. These were compared with plots at similar topographic wetness index locations in the control catchments. Plots subject to prescribed vegetation burning had significantly deeper water tables (difference in means = 5.3 cm) and greater water‐table variability than unburnt plots. Water‐table depths were significantly different between burn age classes (B2>B4>B7>B10+) while B10+ water tables were not significantly different to the unburnt controls. Overland flow was less common on burnt peat than on unburnt peat, recorded in 9% and 17% of all runoff trap visits, respectively. Storm lag times and hydrograph recession limb periods were significantly greater (by ∼ 1 hr and 13 hr on average, respectively) in the burnt catchments overall, but for the largest 20% of storms sampled, there was no significant difference in storm lag times between burnt and unburnt catchments. For the largest 20% of storms the hydrograph intensity of burnt catchments was significantly greater than those of unburnt catchments (means of 4.2 x10−5 s−1 and 3.4 × 10−5 s−1, respectively), thereby indicating a non‐linear streamflow response to prescribed burning. Together, these results from plots to whole river catchments indicate that prescribed vegetation burning has important effects on blanket peatland hydrology at a range of spatial scales. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T07:50:41.549393-05:
      DOI: 10.1002/2014WR016782
       
  • Continental U.S. streamflow trends from 1940 to 2009 and their
           relationships with watershed spatial characteristics
    • Authors: Joshua S. Rice; Ryan E. Emanuel, James M. Vose, Stacy A. C. Nelson
      Abstract: Changes in streamflow are an important area of ongoing research in the hydrologic sciences. To better understand spatial patterns in past changes in streamflow, we examined relationships between watershed scale spatial characteristics and trends in streamflow. Trends in streamflow were identified by analyzing mean daily flow observations between 1940 and 2009 from 967 U. S. Geological Survey stream gages. Results indicated that streamflow across the continental U.S., as a whole, increased while becoming less extreme between 1940 and 2009. However, substantial departures from the continental U.S. (CONUS) scale pattern occurred at the regional scale, including increased annual maxima, decreased annual minima, overall drying trends, and changes in streamflow variability. A subset of watersheds belonging to a reference dataset exhibited significantly smaller trend magnitudes than those observed in non‐reference watersheds. Boosted regression tree models were applied to examine the influence of watershed characteristics on streamflow trend magnitudes at both the CONUS and regional scale. Geographic location was found to be of particular importance at the CONUS scale while local variability in hydroclimate and topography tended to have a strong influence on regional scale patterns in streamflow trends. This methodology facilitates detailed, data‐driven analyses of how the characteristics of individual watersheds interact with large scale hydroclimate forces to influence how changes in streamflow manifest. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:58:16.738769-05:
      DOI: 10.1002/2014WR016367
       
  • Modeling mixed retention and early arrivals in multidimensional
           heterogeneous media using an explicit Lagrangian scheme
    • Authors: Yong Zhang; Mark M. Meerschaert, Boris Baeumer, Eric M. LaBolle
      Abstract: This study develops an explicit two‐step Lagrangian scheme based on the renewal‐reward process to capture transient anomalous diffusion with mixed retention and early arrivals in multi‐dimensional media. The resulting 3$d$anomalous transport simulator provides a flexible platform for modeling transport. The first step explicitly models retention due to mass exchange between one mobile zone and any number of parallel immobile zones. The mobile component of the renewal process can be calculated as either an exponential random variable or a pre‐assigned time step, and the subsequent random immobile time follows a Hyper‐exponential distribution for finite immobile zones or a tempered stable distribution for infinite immobile zones with an exponentially tempered power‐law memory function. The second step describes well‐documented early arrivals which can follow streamlines due to mechanical dispersion using the method of subordination to regional flow. Applicability and implementation of the Lagrangian solver are further checked against transport observed in various media. Results show that, although the time‐nonlocal model parameters are predictable for transport with retention in alluvial settings, the standard time‐nonlocal model cannot capture early arrivals. Retention and early arrivals observed in porous and fractured media can be efficiently modeled by our Lagrangian solver, allowing anomalous transport to be incorporated into 2d/3d models with irregular flow fields. Extensions of the particle‐tracking approach are also discussed for transport with parameters conditioned on local aquifer properties, as required by transient flow and non‐stationary media. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:56:31.897402-05:
      DOI: 10.1002/2015WR016902
       
  • A space and time scale‐dependent nonlinear geostatistical approach
           for downscaling daily precipitation and temperature
    • Authors: Sanjeev Kumar Jha; Gregoire Mariethoz, Jason Evans, Matthew F. McCabe, Ashish Sharma
      Abstract: A geostatistical framework is proposed to downscale daily precipitation and temperature. The methodology is based on multiple‐point geostatistics (MPS), where a multivariate training image is used to represent the spatial relationship between daily precipitation and daily temperature over several years. Here, the training image consists of daily rainfall and temperature outputs from the Weather Research and Forecasting (WRF) model at 50 km and 10 km resolution for a twenty year period ranging from 1985 to 2004. The data are used to predict downscaled climate variables for the year 2005. The result, for each downscaled pixel, is daily time series of precipitation and temperature that are spatially dependent. Comparison of predicted precipitation and temperature against a reference dataset indicates that both the seasonal average climate response together with the temporal variability are well reproduced. The explicit inclusion of time dependence is explored by considering the climate properties of the previous day as an additional variable. Comparison of simulations with and without inclusion of time dependence shows that the temporal dependence only slightly improves the daily prediction because the temporal variability is already well represented in the conditioning data. Overall, the study shows that the multiple‐point geostatistics approach is an efficient tool to be used for statistical downscaling to obtain local scale estimates of precipitation and temperature from General Circulation Models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:55:50.956511-05:
      DOI: 10.1002/2014WR016729
       
  • Complexity and organization in hydrology: A personal view
    • Authors: Rafael L. Bras
      Abstract: The hydrologic cycle is an exquisitely coordinated and, balanced interaction between the atmosphere, the ocean and the land that controls, among other things, the planet's temperature by moving large quantities of matter and energy. The system is incredibly complex with a myriad of positive and negative feedbacks acting at a variety of scales. Much of what we experience in our natural and altered environments results from these complex interactions. Surprisingly (or maybe not) this complexity many times results in beautifully organized expressions of the hydrologic state that are commonly amenable to fairly simple explanations. This paper illustrates hydrologic complexity and organization in the context of the author's and collaborator's work during the past decades, a lot published in Water Resources Research. Topics include the impact of soil moisture on the atmosphere and vice‐versa, the impact of deforestation on the Amazon cloud climate and precipitation, the estimation of surface energy and mass fluxes, the self‐organization of landscapes and river basins over very long time periods and the roles of vegetation on landscape evolution. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:55:26.235581-05:
      DOI: 10.1002/2015WR016958
       
  • Reliability, return periods, and risk under nonstationarity
    • Authors: Laura Read; Richard M. Vogel
      Abstract: Water resources design has widely used the average return period as a concept to inform management and communication of the risk of experiencing an exceedance event within a planning horizon. Even though nonstationarity is often apparent, in practice hydrologic design often mistakenly assumes that the probability of exceedance, p, is constant from year to year which leads to an average return period To equal to 1/p; this expression is far more complex under nonstationarity. Even for stationary processes the common application of an average return period is problematic: it does not account for planning horizon, is an average value that may not be representative of the time to the next flood, and is generally not applied in other areas of water planning. We combine existing theoretical and empirical results from the literature to provide the first general, comprehensive description of the probabilistic behavior of the return period and reliability under nonstationarity. We show that under nonstationarity, the underlying distribution of the return period exhibits a more complex shape than the exponential distribution under stationary conditions. Using a nonstationary lognormal model, we document the increased complexity and challenges associated with planning for future flood events over a planning horizon. We compare application of the average return period with the more common concept of reliability and recommend replacing the average return period with reliability as a more practical way to communicate event likelihood in both stationary and nonstationary contexts. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:54:41.365582-05:
      DOI: 10.1002/2015WR017089
       
  • Scenario tree reduction in stochastic programming with recourse for
           hydropower operations
    • Abstract: A stochastic programming with recourse model requires the consequences of recourse actions be modeled for all possible realizations of the stochastic variables. Continuous stochastic variables are approximated by scenario trees. This paper evaluates the impact of scenario tree reduction on model performance for hydropower operations and suggests procedures to determine the optimal level of scenario tree reduction. We first establish a stochastic programming model for the optimal operation of a cascaded system of reservoirs for hydropower production. We then use the neural gas method to generate scenario trees and employ a Monte Carlo method to systematically reduce the scenario trees. We conduct in‐sample and out‐of‐sample tests to evaluate the impact of scenario tree reduction on the objective function of the hydropower optimization model. We then apply a statistical hypothesis test to determine the significance of the impact due to scenario tree reduction. We develop a stochastic programming with recourse model and apply it to real‐time operation for hydropower production to determine the loss in solution accuracy due to scenario tree reduction. We apply the proposed methodology to the Qingjiang cascade system of reservoirs in China. The results show: (1) The neural gas method preserves the mean value of the original streamflow series but introduces bias to variance, cross variance and lag‐one co‐variance due to information loss when the original tree is systematically reduced; (2) Reducing the scenario number by as much as 40% results in insignificant change in the objective function and solution quality, but significantly reduces computational demand. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:54:16.967006-05:
      DOI: 10.1002/2014WR016828
       
  • Untangling the effects of shallow groundwater and soil texture as drivers
           of subfield‐scale yield variability
    • Authors: Samuel C. Zipper; Mehmet Evren Soylu, Eric G. Booth, Steven P. Loheide
      Abstract: Water table depth (WTD), soil texture, and growing season weather conditions all play critical roles in determining agricultural yield; however, the interactions among these three variables have never been explored in a systematic way. Using a combination of field observations and biophysical modeling, we answer two questions: (1) under what conditions can a shallow water table provide a groundwater yield subsidy and/or penalty to corn production?; and, (2) how do soil texture and growing season weather conditions influence the relationship between WTD and corn yield? Subfield‐scale yield patterns during a dry (2012) and wet (2013) growing season are used to identify sensitivity to weather. Areas of the field that are negatively impacted by wet growing seasons have the shallowest observed WTD (< 1 m), while areas with consistently strong yield have intermediate WTD (1‐3 m). Parts of the field that perform consistently poorly are characterized by deep WTD (> 3 m) and coarse soil textures. Modeling results find that beneficial impacts of shallow groundwater are more common than negative impacts under the conditions studied, and that the optimum WTD is shallower in coarser soils. While groundwater yield subsidies have a higher frequency and magnitude in coarse‐grained soils, the optimum WTD responds to growing season weather at a relatively constant rate across soil types. We conclude that soil texture defines a baseline upon which WTD and weather interact to determine overall yield. Our work has implications for water resource management, climate/land use change impacts on agricultural production, and precision agriculture. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-21T03:53:47.528324-05:
      DOI: 10.1002/2015WR017522
       
  • Appreciation of peer reviewers for 2014
    • PubDate: 2015-07-16T11:51:13.264781-05:
      DOI: 10.1002/2015WR017828
       
  • FINIFLUX an implicit finite element model for quantification of
           groundwater fluxes and hyporheic exchange in streams and rivers using
           radon
    • Authors: S. Frei; B.S. Gilfedder
      Abstract: A quantitative understanding of groundwater‐surface water interactions is vital for sustainable management of water quantity and quality. The noble gas radon‐222 (Rn) is becoming increasingly used as a sensitive tracer to quantify groundwater discharge to wetlands, lakes and rivers; a development driven by technical and methodological advances in Rn measurement. However, quantitative interpretation of these data is not trivial, and the methods used to date are based on the simplest solutions to the mass‐balance equation (e.g. first order finite difference, inversion). Here we present a new implicit numerical model (FINIFLUX) based on finite elements for quantifying groundwater discharge to streams and rivers using Rn surveys at the reach scale (1‐50 km). The model is coupled to a state‐of‐the‐art parameter optimization code Parallel‐PEST to iteratively solve the mass‐balance equation for groundwater discharge and hyporheic exchange. The major benefit of this model is that it is programed to be very simple to use, reduces nonuniqueness and provides numerically stable estimates of groundwater fluxes and hyporheic residence times from field data. FINIFLUX was tested against an analytical solution and then implemented on two German rivers of differing magnitude, the Salzach (∼112 m3 s−1) and the Rote Main (∼4 m3 s−1) . We show that using previous inversion techniques numerical instability can lead to physically impossible negative values, whereas the new model provides stable positive values for all scenarios. We hope that by making FINIFLUX freely available to the community that Rn might find wider application in quantifying groundwater discharge to streams and rivers and thus assist in a combined management of surface and ground water systems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-15T08:53:41.030985-05:
      DOI: 10.1002/2015WR017212
       
  • Predicting the resilience and recovery of aquatic systems: A framework for
           model evolution within environmental observatories
    • Authors: Matthew R. Hipsey; David P. Hamilton, Paul C. Hanson, Cayelan C. Carey, Janaine Z. Coletti, Jordan S. Read, Bas W. Ibelings, Fiona Valesini, Justin D. Brookes
      Abstract: Maintaining the health of aquatic systems is an essential component of sustainable catchment management, however, degradation of water quality and aquatic habitat continues to challenge scientists and policy‐makers. To support management and restoration efforts aquatic system models are required that are able to capture the often complex trajectories that these systems display in response to multiple stressors. This paper explores the abilities and limitations of current model approaches in meeting this challenge, and outlines a strategy based on integration of flexible model libraries and data from observation networks, within a learning framework, as a means to improve the accuracy and scope of model predictions. The framework is comprised of a data assimilation component that utilizes diverse data streams from sensor networks, and a second component whereby model structural evolution can occur once the model is assessed against theoretically relevant metrics of system function. Given the scale and trans‐disciplinary nature of the prediction challenge, network science initiatives are identified as a means to develop and integrate diverse model libraries and workflows, and to obtain consensus on diagnostic approaches to model assessment that can guide model adaptation. We outline how such a framework can help us explore the theory of how aquatic systems respond to change by bridging bottom‐up and top‐down lines of enquiry, and, in doing so, also advance the role of prediction in aquatic ecosystem management. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-15T08:52:45.073527-05:
      DOI: 10.1002/2015WR017175
       
  • The change of nature and the nature of change in agricultural landscapes:
           Hydrologic regime shifts modulate ecological transitions
    • Abstract: Hydrology in many agricultural landscapes around the world is changing in unprecedented ways due to the development of extensive surface and subsurface drainage systems that optimize productivity. This plumbing of the landscape alters water pathways, timings, and storage, creating new regimes of hydrologic response and driving a chain of environmental changes in sediment dynamics, nutrient cycling, and river ecology. In this work we non‐parametrically quantify the nature of hydrologic change in the Minnesota River Basin, an intensively managed agricultural landscape, and study how this change might modulate ecological transitions. During the growing season when climate effects are shown to be minimal, daily streamflow hydrographs exhibit sharper rising limbs and stronger dependence on the previous‐day precipitation. We also find a changed storage‐discharge relationship and show that the artificial landscape connectivity has most drastically affected the rainfall‐runoff relationship at intermediate quantiles. Considering the whole year, we show that the combined climate and land‐use change effects reduce the inherent nonlinearity in the dynamics of daily streamflow, perhaps reflecting a more linearized engineered hydrologic system. Using a simplified dynamic interaction model that couples hydrology to river ecology, we demonstrate how the observed hydrologic change and/or the discharge‐driven sediment generation dynamics may have modulated a regime shift in river ecology, namely extirpation of native mussel populations. We posit that such non‐parametric analyses and reduced complexity modeling can provide more insight than highly parameterized models and can guide development of vulnerability assessments and integrated watershed management frameworks. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:12:19.638963-05:
      DOI: 10.1002/2015WR017637
       
  • A novel equation for determining the suction stress of unsaturated soils
           from the water retention curve based on wetted surface area in pores
    • Authors: Roberto Greco; Rudy Gargano
      Abstract: A novel equation is proposed for the evaluation of the suction stress of an unsaturated soil. The equation, based on the assumption that suction is transmitted to soil solid particles only through their wet external surface, allows to easily derive the soil suction characteristic curve from the water retention curve. The proposed equation has been verified against published experimental data of suction stress smaller than 1MPa for soils of various characteristics. In all cases, an excellent agreement between predicted and observed values of suction stress is achieved, showing that the proposed equation performs better than other currently adopted expressions for the evaluation of soil suction stress. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:11:27.487319-05:
      DOI: 10.1002/2014WR016541
       
  • Surface water types and sediment distribution patterns at the confluence
           of mega rivers: The Solimões‐Amazon and Negro rivers junction
    • Authors: Edward Park; Edgardo M. Latrubesse
      Abstract: Large river channel confluences are recognized as critical fluvial features because both intensive and extensive hydrophysical and geoecological processes take place at this interface. However, identifications of suspended sediment routing patterns through channel junctions and the roles of tributaries on downstream sediment transport in large rivers are still poorly explored. In this paper, we propose a remote sensing‐based approach to characterize the spatiotemporal patterns of the post‐confluence suspended sediment transport by mapping the surface water distribution in the ultimate example of large river confluence on Earth where distinct water types meet: The Solimões‐Amazon (white water) and Negro (black water) rivers. The surface water types distribution was modeled for three different years: average hydrological condition (2007) and two years when extreme events occurred (drought‐2005 and flood‐2009). Amazonian surface water domination along the main channel is highest during the water discharge rising season. Surface water mixing along the main channel depends on the hydrological seasons with the highest mixed‐homogenized area observed during water discharge peak season and the lowest during discharge rising season. Water mixture also depends on the yearly hydrological regime with the highest rates of water mixing in 2009, followed by 2005 and 2007. We conclude that the dominant mixing patterns observed in this study have been persistent over a decadal scale and the anabranching patterns contribute to avoid a faster mixing in a shorter distance. Our proposed approach can be applied to a variety of morphodynamic and environmental analyses in confluences of large rivers around the world. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:00:40.510543-05:
      DOI: 10.1002/2014WR016757
       
  • On the use of rhodamine WT for the characterization of stream
           hydrodynamics and transient storage
    • Authors: Robert L. Runkel
      Abstract: Recent advances in fluorometry have led to increased use of rhodamine WT as a tracer in streams and rivers. In light of this increased use, a review of the dye's behavior in freshwater systems is presented. Studies in the groundwater literature indicate that rhodamine WT is trans ported non‐conservatively, with sorption removing substantial amounts of tracer mass. Column studies document a two‐step breakthrough curve in which two structural isomers are chromato graphically separated. Although the potential for nonconservative transport is acknowledged in the surface water literature, many studies assume that sorptive losses will not affect the character ization of physical transport processes. A literature review and modeling analysis indicates that this assumption is valid for quantification of physical properties that are based on the bulk of the tracer mass (traveltime), and invalid for the characterization of processes represented by the tracer tail (transient storage attributable to hyporheic exchange). Rhodamine WT should be considered nonconservative in the hyporheic zone due to nonconservative behavior demonstrated for similar conditions in groundwater. As such, rhodamine WT should not be used as a quantitative tracer in hyporheic zone investigations, including the study of long flow paths and the development of models describing hyporheic zone processes. Rhodamine WT may be used to qualitatively char acterize storage in large systems, where there are few practical alternatives. Qualitative investiga tions should rely on early portions of the tracer profile, making use of the temporal resolution afforded by in situ fluorometry, while discarding later parts of the tracer profile that are adversely affected by sorption. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:00:36.949838-05:
      DOI: 10.1002/2015WR017201
       
  • Reintroducing radiometric surface temperature into the
           Penman‐Monteith formulation
    • Authors: Kaniska Mallick; Eva Boegh, Ivonne Trebs, Joseph G. Alfieri, William P. Kustas, John H. Prueger, Dev Niyogi, Narendra Das, Darren T. Drewry, Lucien Hoffmann, Andrew J. Jarvis
      Abstract: Here we demonstrate a novel method to physically integrate the radiometric surface temperature (TR) into the Penman‐Monteith (PM) formulation for estimating the terrestrial sensible and latent heat fluxes (H and λE) in the framework of a modified Surface Temperature Initiated Closure (STIC). It combines TR data with standard energy balance closure models for deriving a hybrid closure that does not require parameterization of the surface (or stomatal) and aerodynamic conductances (gS and gB). STIC is formed by the simultaneous solution of four state equations and it uses TR as an additional data source for retrieving the ‘near surface' moisture availability (M) and the Priestley‐Taylor coefficient (α). The performance of STIC is tested using high temporal resolution TR observations collected from different international surface energy flux experiments in conjunction with corresponding net radiation (RN), ground heat flux (G), air temperature (TA) and relative humidity (RH) measurements. A comparison of the STIC outputs with the eddy covariance measurements of λE and H revealed a RMSD of 7% to 16% and 40% to 74% in half‐hourly λE and H estimates. These statistics were 5% to 13% and 10% to 44% in daily λE and H. The errors and uncertainties in both surface fluxes are comparable to the models that typically use land surface parameterizations for determining the unobserved components (gS and gB) of the surface energy balance models. However, the scheme is simpler, has the capabilities for generating spatially explicit surface energy fluxes and independent of sub‐models for boundary layer developments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:00:35.067112-05:
      DOI: 10.1002/2014WR016106
       
  • A model of the sociohydrologic dynamics in a semiarid catchment: Isolating
           feedbacks in the coupled human‐hydrology system
    • Authors: Y. Elshafei; M. Sivapalan, J.Z. Coletti, M. R. Hipsey
      Abstract: The challenge of sustainable freshwater management requires identification and characterization of the underlying components and dynamic interactions within the coupled human‐hydrology system. This paper builds a model that captures the dynamic water balance evolution and coupled human response within the Lake Toolibin catchment in West Australia's wheatbelt region. Two sub‐catchments in different parts of the landscape were selected to examine the key emergent properties of the coupled socio‐hydrology system over a 100 year period, by analyzing the two‐way feedbacks of land‐use management (human system feedback) and land degradation (natural system feedback). Using a relatively simple parameterization of community sensitivity to land degradation within the model, we identified positive and negative feedbacks, the presence of threshold behavior, timescale differences between fast and slow moving variables, differences in time lags resulting from disparate resistance levels of the natural system, and the degree of adaptive learning inherent in the human system. Specifically, the valley floor sub‐catchment transitioned through four phases ‐ Expansion, Contraction, Recession and Recovery ‐ demonstrating a threshold shift in the human feedback after 60 years, whilst the upslope sub‐catchment appears to still be in the Contraction phase, with no sign of reaching a threshold shift in 100 years. These results demonstrate that the model is capable of isolating the two‐way feedbacks of the coupled system, and has implications for resilience theory, suggesting that greater resistance in the underlying natural system counteracts the onset of a negative feedback loop and instigation of adaptive behaviors in the human system. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:00:31.809442-05:
      DOI: 10.1002/2015WR017048
       
  • Interdependence of chronic hydraulic dysfunction and canopy processes can
           improve integrated models of tree response to drought
    • Authors: D. Scott Mackay; David E. Roberts, Brent E. Ewers, John S. Sperry, Nathan G. McDowell, William T. Pockman
      Abstract: Hydraulic systems of plants have evolved in the context of carbon allocation and fitness tradeoffs of maximizing carbon gain and water transport in the face of short‐ and long‐term fluctuations in environmental conditions. The resulting diversity of traits include a continuum of isohydry‐anisohydry or high to low relative stomatal closure during drought, shedding of canopy foliage or disconnecting roots from soil to survive drought, and adjusting root areas to efficiently manage canopy water costs associated with photosynthesis. These traits are examined within TREES, an integrated model that explicitly couples photosynthesis and carbon allocation to soil‐plant hydraulics and canopy processes. Key advances of the model are its ability to account for differences in soil and xylem cavitation, transience of hydraulic impairment associated with delayed or no refilling of xylem, and carbon allocation to plant structures based on photosynthetic uptake of carbon and hydraulic limitations to water transport. The model was used to examine hydraulic traits of co‐occurring isohydric (piñon pine) and anisohydric (one‐seed juniper) trees from a field‐based experimental drought. Model predictions of both transpiration and leaf water potential were improved when there was no refilling of xylem over simulations where xylem was able refill in response to soil water recharge. Model experiments with alternative root‐to‐leaf area ratios (RR/L) showed the RR/L that supports maximum cumulative water use is not beneficial for supporting maximum carbon gain during extended drought, illustrating how a process model reveals tradeoffs in plant traits. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T10:00:26.379507-05:
      DOI: 10.1002/2015WR017244
       
  • Persistent questions of heterogeneity, uncertainty, and scale in
           subsurface flow and transport
    • Authors: Peter K. Kitanidis
      Abstract: When Water Resources Research was launched in 1965, heterogeneity, uncertainty, and scale issues in subsurface hydrology were in the backburner. Only about ten years later, under the stimulus of dealing with solute transport problems, these problems received attention. The stochastic approach brought tools to deal both with problems of upscaling, also known as homogenization and coarse‐graining, and uncertainty quantification. Effective conductivity and effective dispersion, also known as macrodispersion, coefficients in statistically homogeneous formations were extensively studied. Mixing, in its role of affecting reaction rates, started receiving attention. While in the dispersion problem emphasis was on Fickian representations, more sophisticated models have also been studied. Uncertainty quantification in the inverse problem has also made progress and geostatistical ideas, as well as ideas originating in signal processing, influenced how we approach problems of inference like interpolation and inverse modeling. My view is that we should emphasize information aspects, i.e., the collection of more and better data, their correct assimilation, the quantification of uncertainty associated with predictions, and the selection of designs or policies that accurately reflect what we actually know and thus manage risk. Progress in this department has been hampered by ingrained ideas, inadequate training, and inadequate resources. Research in problems of upscaling will continue to shed new light and provide better tools to deal with onerous problems. At the same time, no cure is more universally potent than using a more refined grid. Finally, although research is active, the diffusion of research results to education and practice has been slow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T08:50:50.022649-05:
      DOI: 10.1002/2015WR017639
       
  • The relative stability of salmon redds and unspawned streambeds
    • Authors: Todd H. Buxton; John M. Buffington, Elowyn M. Yager, Marwan A. Hassan, Alexander K. Fremier
      Abstract: Where female salmon build nests (“redds”), streambed material is mixed, fine sediment is winnowed, and bed material is moved into a tailspill mound resembling the shape of a dune. Completed redd surfaces are coarser and better sorted than unspawned beds, which is thought to increase redd stability because larger grains are heavier and harder to move, and sorting increases friction angles for mobility. However, spawning also loosens sediment and creates topography that accelerates flow, which can increase particle mobility. We address these factors controlling the relative stability of redds and unspawned beds in flume experiments where redds were constructed with a technique that mimics the nesting behavior of female salmon. Although redds exhibited relatively coarse surfaces, measured entrainment forces indicate particle loosening by spawning lowered grain resistance to motion by 12‐37% on average compared to unspawned beds. In addition, for the same discharges, boundary shear stress was 13‐41% higher on a redd due to flow convergence on the tailspill. Visual measurements of particle entrainment further indicated redd instability, as bed average shear stress was 22% lower at incipient motion and 29% lower at the discharge that mobilized all grain sizes on a redd. Overall, results demonstrate redds are unstable compared to unspawned beds, which increases the risk of scour for buried eggs, but may facilitate fine‐sediment flushing and improve the quality of spawning gravels for future generations of spawners. Therefore, managing salmon returns to increase streambed disturbance may be an effective tool for reducing sedimentation impacts on salmon reproduction. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T08:04:03.190656-05:
      DOI: 10.1002/2015WR016908
       
  • Johnson SB as general functional form for raindrop size distribution
    • Authors: Katia Cugerone; Carlo De Michele
      Abstract: Drop size distribution represents the statistical synthesis of rainfall dynamics at particle size scale. Gamma and Lognormal distributions have been widely used in literature to approximate the drop diameter variability, contrarily to the natural upper boundary of the variable, with almost always site‐specific studies and without the support of statistical goodness‐of‐fit tests. In this work, we present an extensive statistical investigation of raindrop size distribution based on eight datasets, well distributed on the Earth's surface, which have been analysed by using skewness‐kurtosis plane, AIC and BIC indices and Kolmogorov‐Smirnov test. Here, for the first time, the Johnson SB is proposed as general functional form to describe the drop diameter variability specifically at 1‐minute time scale. Additional analyses demonstrate that the model is well suitable even for larger time intervals (≥ 1 min). This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T08:03:59.010511-05:
      DOI: 10.1002/2014WR016484
       
  • Predicting colloid transport through saturated porous media: A critical
           review
    • Authors: Ian L. Molnar; William P. Johnson, Jason I. Gerhard, Clinton S. Willson, Denis M. O'Carroll
      Abstract: Understanding and predicting colloid transport and retention in water saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport research before the 1990's included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid‐surface repulsion, respectively). Second, we review the continuum‐scale modeling strategies used to describe observed transport behavior. Third, we review two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore‐scale colloid trajectories, and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities include: improving mechanistic descriptions, and subsequent correlation equations, for nanoparticle (i.e., Brownian particle) transport through soil, developing mechanistic descriptions of colloid retention in so‐called ‘unfavorable' conditions via methods such as the ‘discrete heterogeneity' approach, and employing imaging techniques such as x‐ray tomography to develop realistic expressions for grain topology and mineral distribution that can aid the development of these mechanistic approaches. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-14T08:03:56.270827-05:
      DOI: 10.1002/2015WR017318
       
  • Four‐dimensional electrical conductivity monitoring of
           stage‐driven river water intrusion: Accounting for water table
           effects using a transient mesh boundary and conditional inversion
           constraints
    • Authors: Tim Johnson; Roelof Versteeg, Jon Thomle, Glenn Hammond, Xingyuan Chen, John Zachara
      Abstract: This paper describes and demonstrates two methods of providing a‐priori information to the surface‐based time‐lapse three‐dimensional electrical resistivity tomography (ERT) problem for monitoring stage‐driven or tide‐driven surface water intrusion into aquifers. First, a mesh boundary is implemented that conforms to the known location of the water table through time, thereby enabling the inversion to place a sharp bulk conductivity contrast at that boundary without penalty. Second, a non‐linear inequality constraint is used to allow only positive or negative transient changes in EC to occur within the saturated zone, dependent on the relative contrast in fluid electrical conductivity between surface water and groundwater. A 3D field experiment demonstrates that time‐lapse imaging results using traditional smoothness constraints are unable to delineate river water intrusion. The water table and inequality constraints provide the inversion with the additional information necessary to resolve the spatial extent of river water intrusion through time. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-08T03:54:04.020935-05:
      DOI: 10.1002/2014WR016129
       
  • Multimodel analysis of anisotropic diffusive tracer‐gas transport in
           a deep arid unsaturated zone
    • Authors: Christopher T. Green; Michelle A. Walvoord, Brian J. Andraski, Robert G. Striegl, David A. Stonestrom
      Abstract: Gas transport in the unsaturated zone affects contaminant flux and remediation, interpretation of groundwater travel times from atmospheric tracers, and mass‐budgets of environmentally important gases. Although unsaturated zone transport of gases is commonly treated as dominated by diffusion, the characteristics of transport in deep layered sediments remain uncertain. In this study, we use a multi‐model approach to analyze results of a gas‐tracer (SF6) test to clarify characteristics of gas transport in deep unsaturated alluvium. Thirty‐five separate models with distinct diffusivity structures were calibrated to the tracer‐test data and were compared on the basis of Akaike Information Criteria estimates of posterior model probability. Models included analytical and numerical solutions. Analytical models provided estimates of bulk‐scale apparent diffusivities at the scale of 10's of meters. Numerical models provided information on local‐scale diffusivities and feasible lithological features producing the observed tracer breakthrough curves. The combined approaches indicate significant anisotropy of bulk‐scale diffusivity, likely associated with high‐diffusivity layers. Both approaches indicated that diffusivities in some intervals were greater than expected from standard models relating porosity to diffusivity. High apparent diffusivities and anisotropic diffusivity structures were consistent with previous observations at the study site of rapid lateral transport and limited vertical spreading of gas‐phase contaminants. Additional processes such as advective oscillations may be involved. These results indicate that gases in deep, layered unsaturated zone sediments can spread laterally more quickly, and produce higher peak concentrations, than predicted by homogeneous, isotropic diffusion models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-08T03:53:34.834806-05:
      DOI: 10.1002/2014WR016055
       
  • Abiotic control of underwater light in a drinking water reservoir: Photon
           budget analysis and implications for water quality monitoring
    • Authors: Shohei Watanabe; Isabelle Laurion, Stiig Markager, Warwick F. Vincent
      Abstract: In optically complex inland waters, the underwater attenuation of photosynthetically active radiation (PAR) is controlled by a variable combination of absorption and scattering components of the lake or river water. Here we applied a photon budget approach to identify the main optical components affecting PAR attenuation in Lake St. Charles, a drinking water reservoir for Quebec City, Canada. This analysis showed the dominant role of colored dissolved organic matter (CDOM) absorption (average of 44% of total absorption during the sampling period), but with large changes over depth in the absolute and relative contribution of the individual absorption components (water, non‐algal particulates, phytoplankton and CDOM) to PAR attenuation. This pronounced vertical variation occurred because of the large spectral changes in the light field with depth, and it strongly affected the average in situ diffuse absorption coefficients in the water column. For example the diffuse absorption coefficient for pure‐water in the ambient light field was ten‐fold higher than the value previously measured in the blue open ocean and erroneously applied to lakes and coastal waters. Photon absorption budget calculations for a range of limnological conditions confirmed that phytoplankton had little direct influence on underwater light, even at chlorophyll a values above those observed during harmful algal blooms in the lake. These results imply that traditional measures of water quality such as Secchi depth and radiometric transparency do not provide a meaningful estimate of the biological state of the water column in CDOM‐colored lakes and reservoirs. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-04T02:23:07.094953-05:
      DOI: 10.1002/2014WR015617
       
  • Morphodynamic response of a variable‐width channel to changes in
           sediment supply
    • Authors: Peter A. Nelson; Andrew K. Brew, Jacob A. Morgan
      Abstract: River channels commonly exhibit downstream variations in channel width, which can lead to the development of alternating shallow and deep areas known as riffle‐pool sequences. The response of these channels to variations in sediment supply remains largely unexplored. Here we investigate the morphodynamic response of a variable‐width channel to changes in sediment supply through laboratory experiments conducted in a straight flume in which we imposed sinusoidal variations in width. We first developed equilibrium conditions under a constant sediment supply, then eliminated the sediment feed to create a degraded, armored bed. This sediment‐starved bed was subjected to two types of sediment supply increases: a return to the initial constant supply, and the introduction of a well‐sorted sediment pulse (analogous to gravel augmentation). Riffles and pools formed in wide and narrow areas, respectively, and the location of and relief between riffles and pools remained the same throughout all experimental runs, regardless of the sediment supply. The primary channel response to changes in supply was adjustment of the overall slope. The sediment pulse evolved primarily through dispersion rather than translation, which contrasts with prior gravel augmentation experiments conducted in constant‐width channels and suggests that width variation and resulting riffle‐pool topography enhances pulse dispersion. Our results indicate that width variation is a primary control on the location and relief of riffles and pools in straight channels, and sediment supply changes are unlikely to affect riffle‐pool morphology when bank geometry is fixed and water discharge is steady. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T10:06:41.402408-05:
      DOI: 10.1002/2014WR016806
       
  • Catchment‐scale Richards equation‐based modeling of
           evapotranspiration via boundary condition switching and root water uptake
           schemes
    • Authors: Matteo Camporese; Edoardo Daly, Claudio Paniconi
      Abstract: In arid and semi‐arid climate catchments, where annual evapotranspiration (ET) and rainfall are typically comparable, modeling ET is important for proper assessment of water availability and sustainable land use management. The aim of the present study is to assess different parsimonious schemes for representing ET in a process‐based model of coupled surface and subsurface flow. A simplified method for computing ET based on a switching procedure for the boundary conditions of the Richards equation at the soil surface is compared to a sink term approach that includes root water uptake, root distribution, root water compensation, and water and oxygen stress. The study site for the analysis is a small pasture catchment in southeastern Australia. A comprehensive sensitivity analysis carried out on the parameters of the sink term shows that the maximum root depth is the dominant control on catchment‐scale ET and streamflow. Comparison with the boundary condition switching method demonstrates that this simpler scheme (only one parameter) can successfully reproduce ET when the vegetation root depth is shallow (not exceeding approximately 50 cm). For deeper rooting systems, the switching scheme fails to match the ET fluxes and is affected by numerical artifacts, generating physically unrealistic soil moisture dynamics. It is further shown that when transpiration is the dominant contribution to ET, the inclusion of oxygen stress and root water compensation in the model can have a considerable effect on the estimation of both ET and streamflow; this is mostly due to the water fluxes associated with the riparian zone. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T10:03:47.990421-05:
      DOI: 10.1002/2015WR017139
       
  • Under‐canopy turbulence and root water uptake of a Tibetan meadow
           ecosystem modeled by Noah‐MP
    • Authors: Donghai Zheng; Rogier Van Der Velde, Zhongbo Su, Jun Wen, Martijn J. Booij, Arjen Y. Hoekstra, Xin Wang
      Abstract: The Noah‐MP land surface model adopts a multi‐parameterization framework to accommodate various alternative parameterizations for more than 10 physical processes. In this paper, the parameterizations implemented in Noah‐MP associated with under‐canopy turbulence and root water uptake are enhanced with: i) an under‐canopy turbulence scheme currently adopted by the Community Land Model (CLM), ii) two vertical root distribution functions, i.e. an exponential and an asymptotic formulation, and iii) three soil water stress functions (βt) controlling root water uptake, e.g. a soil water potential (ψ)‐based function, a non‐linear soil moisture (θ)‐based power function and an empirical threshold approach considering preferential uptake from the moist part of the soil column. A comprehensive dataset of in‐situ micro‐meteorological observations and profile soil moisture/temperature measurements collected from an alpine meadow site in the northeastern Tibetan Plateau is utilized to assess the impact of the augmentations on the Noah‐MP performance. The results indicate that i) implementation of the CLM under‐canopy turbulence scheme greatly resolves the overestimation of sensible heat flux and underestimation of soil temperature across the profile, ii) both exponential and asymptotic vertical root distribution functions better represent the Tibetan conditions enabling a better representation of the measured soil moisture dynamics, and iii) the ψ‐based βt functions overestimate surface soil moisture, the default linear θ‐based βt function underestimates latent heat flux during the dry‐down, while both the nonlinear power function and empirical threshold approach simultaneously simulate well soil moisture, and latent and sensible heat fluxes. Additionally, the parameter uncertainty associated with soil water stress function and hydraulic parameterization is addressed. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T10:02:59.34875-05:0
      DOI: 10.1002/2015WR017115
       
  • Enhancement of plume dilution in two and three‐dimensional porous
           media by flow focusing in high‐permeability inclusions
    • Authors: Yu Ye; Gabriele Chiogna, Olaf A. Cirpka, Peter Grathwohl, Massimo Rolle
      Abstract: In porous media, lateral mass exchange exerts a significant influence on the dilution of solute plumes in quasi‐steady state. This process is one of the main mechanisms controlling transport of continuously emitted conservative tracers in groundwater and is fundamental for the understanding of many degradation processes. We investigate the effects of high‐permeability inclusions on transverse mixing in three‐dimensional versus two‐dimensional systems by experimental, theoretical and numerical analyses. Our results show that mixing enhancement strongly depends on the system dimensionality and on the parameterization used to model transverse dispersion. In particular, no enhancement of transverse mixing would occur in three‐dimensional media if the local transverse dispersion coefficient was uniform and flow focusing in both transverse directions was identical, which is fundamentally different from the two‐dimensional case. However, the velocity and grain size dependence of the transverse dispersion coefficient and the correlation between hydraulic conductivity and grain size lead to prevailing mixing enhancement within the inclusions, regardless of dimensionality. We perform steady‐state bench‐scale experiments with multiple tracers in three‐dimensional and quasi two‐dimensional flow‐through systems at two different velocities (1 m/day and 5 m/day). We quantify transverse mixing by the flux‐related dilution index and compare the experimental results with model simulations. The experiments confirm that, although dilution is larger in three‐dimensional systems, the enhancement of transverse mixing due to flow focusing is less effective than in two‐dimensional systems. The spatial arrangement of the high‐permeability inclusions significantly affects the degree of mixing enhancement. We also observe more pronounced compound‐specific effects in the dilution of solute plumes in three‐dimensional porous media than in two‐dimensional ones. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T10:02:05.050969-05:
      DOI: 10.1002/2015WR016962
       
  • Run‐of‐river power plants in Alpine regions: Whither optimal
           capacity?
    • Authors: G. Lazzaro; G. Botter
      Abstract: Although run‐of‐river hydropower represents a key source of renewable energy, it can not prevent stresses on river ecosystems and human well‐being. This is especially true in Alpine regions, where the outflow of a plant is placed several kilometers downstream of the intake, inducing the depletion of river reaches of considerable length. Here, multi‐objective optimization is used in the design of the capacity of run‐of‐river plants to identify optimal trade‐offs between two contrasting objectives: the maximization of the profitability and the minimization of the hydrologic disturbance between the intake and the outflow. The latter is evaluated considering different flow metrics: mean discharge, temporal autocorrelation and streamflow variability. Efficient and Pareto‐optimal plant sizes are devised for two representative case studies belonging to the Piave river (Italy). Our results show that the optimal design capacity is strongly affected by the flow regime at the plant intake. In persistent regimes with a reduced flow variability, the optimal trade‐off between economic exploitation and hydrologic disturbance is obtained for a narrow range of capacities sensibly smaller than the economic optimum. In erratic regimes featured by an enhanced flow variability, instead, the Pareto front is discontinuous and multiple trade‐offs can be identified, which imply either smaller or larger plants compared to the economic optimum. In particular, large capacities reduce the impact of the plant on the streamflow variability at seasonal and interannual timescale. Multi‐objective analysis could provide a clue for the development of policy actions based on the evaluation of the environmental footprint of run‐of‐river plants. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T10:00:08.744839-05:
      DOI: 10.1002/2014WR016642
       
  • Discharge and water‐depth estimates for ungauged rivers: Combining
           hydrologic, hydraulic, and inverse modeling with stage and
           water‐area measurements from satellites
    • Abstract: Anticipating future global freshwater scarcity and providing mitigation require timely knowledge of spatiotemporal dynamics of discharge for gauged and, more challengingly, ungauged rivers. This study describes a coupled hydrologic (SWAT) and hydraulic (XSECT) modeling approach set in a Genetic Algorithm framework for estimating discharge and water depth for ungauged rivers from space. The method was tested in the Red River of the North basin by comparing simulated discharges and depths from 2006 to 2010 to in‐situ observations from across the basin. Results showed that calibration using only remotely‐sensed data (i.e., water levels from ENVISAT altimetry and water extents from LANDSAT) along the main stem of the Red River yielded daily and monthly estimates of river discharge, which correlated to measured discharges at three gaging stations on the main stem with R2 values averaging 0.822 and 0.924, respectively. The comparisons of modeled and measured discharges were also extended to smaller tributaries, yielding a mean R2 of 0.809 over seven gaging stations. The modeling approach also provided estimates of water depth that correlate to observations at four stations with an average R2 of 0.831. We conclude that the integrated modeling approach is able to estimate discharge and water depth from space for larger ungauged rivers. This study also implies that in‐situ discharge data may not be necessary for successful hydrologic model calibration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T09:58:23.798684-05:
      DOI: 10.1002/2015WR016971
       
  • Improved reservoir sizing utilizing observed and reconstructed streamflows
           within a Bayesian combination framework
    • Authors: Jason Patskoski; A. Sankarasubramanian
      Abstract: Reservoir sizing is a critical task as the storage in a reservoir must be sufficient to supply water during extended droughts. Typically, sequent peak algorithm (SQP) is used with observed streamflow to obtain reservoir storage estimates. To overcome the limited sample length of observed streamflow, synthetic streamflow traces estimated from observed streamflow characteristics are provided with SQP to estimate the distribution of storage. However, the parameters in the stochastic streamflow generation model are derived from the observed record and are still unrepresentative of the long term drought records. Paleo‐streamflow time series, usually reconstructed using tree ring chronologies, span for a longer period than the observed streamflow and provide additional insight into the pre‐instrumental drought record. This study investigates the capability of reconstructed streamflow records in reducing the uncertainty in reservoir storage estimation. For this purpose, we propose a Bayesian framework that combines observed and reconstructed streamflow for estimating the parameters of the stochastic streamflow generation model. By utilizing reconstructed streamflow records from two potential stations over the Southeastern US, the distribution of storage estimated using the combined streamflows is compared with the distribution of storage estimated using observed streamflow alone based on split‐sample validation. Results show that combining observed and reconstructed streamflow yield stochastic streamflow generation parameters more representative of the longer streamflow record resulting in improved reservoir storage estimates. We also generalize the findings through a synthetic experiment by generating reconstructed streamflow records of different sample length and skill. The analysis shows that uncertainty in storage estimates reduces by incorporating reconstruction records with higher skill and longer sample lengths. Potential applications of the proposed methodology are also discussed. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T09:57:34.245682-05:
      DOI: 10.1002/2014WR016189
       
  • Impacts of evaporation on subsurface flow and salt accumulation in a
           tidally influenced beach
    • Authors: Xiaolong Geng; Michel C. Boufadel
      Abstract: We coupled a mass‐transfer formulation of evaporation to the density‐dependent variably‐saturated finite element model MARUN to predict the salinity under realistic conditions in a beach in the Gulf of Mexico. The results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation. The results also showed that for the relatively wet atmospheric conditions, the maximum evaporation did not occur from the supra‐tidal zone, rather from the intertidal zone, and it was due to the difference in moisture between pore water and atmosphere. The highest salinity occurred during the spring tide period, and extended into the neap tide period. When the atmospheric condition was assumed to be constant and conducive to large evaporation (high temperature and low air humidity), the maximum salinity region shifted to the supra‐tidal zone and persisted there due to low mixing. The maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case. However, the maximum was more landward than the (more realistic) variable atmospheric condition case, which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties. The constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supra‐tidal zone but they are dampened in the intertidal zone. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T09:56:40.350425-05:
      DOI: 10.1002/2015WR016886
       
  • Gas pressure gradients in unsaturated porous media and the assumption of
           infinite gas mobility
    • Authors: Lili Hou; Brent E. Sleep, Tohren C. G. Kibbey
      Abstract: The assumption that gas is infinitely mobile, moving without viscous pressure drops, is common in studies of unsaturated flow in porous media. The objectives of this work were to use experimental measurements to examine that assumption in systems experiencing rapid drainage, and to explore the extent to which observed pressure drops could be described by conventional multiphase flow simulation tracking viscous flow in both phases. Because many published studies have used vented columns in an effort to equilibrate pore gas pressures with inlet gas, an additional objective of the work was to use experimental measurements to explore the ability of column vents to equilibrate pore gas with inlet gas during dynamic drainage. Results of the work suggest that gas pressure gradients can be significant, and that the assumption of infinite gas mobility is likely to be unsatisfactory in many systems where moderately rapid saturation change occurs. While vents have the potential to influence flow by providing additional gas inlets, experimental results of this work show almost no impact on pore gas pressures from a vent similar in size to those in other published studies. An equation developed as a part of the work suggests that the spatial slope of gas pressure with distance away from the front during dynamic drainage is proportional to the ratio of outflow Darcy velocity to saturated hydraulic conductivity for vertical columns. As such, systems with more rapid saturation change also have a greater potential to exhibit experimental artifacts related to gas pressure gradients. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-03T09:50:00.716464-05:
      DOI: 10.1002/2015WR017189
       
  • The morphology of streams restored for market and nonmarket purposes:
           Insights from a mixed natural‐social science approach
    • Authors: Martin W. Doyle; Jai Singh, Rebecca Lave, Morgan M. Robertson
      Abstract: We use geomorphic surveys to quantify the differences between restored and non‐restored streams, and the difference between streams restored for market purposes (compensatory mitigation) from those restored for non‐market programs. We also analyze the social and political‐economic drivers of the stream restoration and mitigation industry using analysis of policy documents and interviews with key personnel including regulators, mitigation bankers, stream designers, and scientists. Restored streams are typically wider and geomorphically more homogenous than non‐restored streams. Streams restored for the mitigation market are typically headwater streams and part of a large, complex of long restored main channels and many restored tributaries; streams restored for non‐market purposes are typically shorter and consist of the main channel only. Interviews reveal that designers integrate many influences including economic and regulatory constraints, but traditions of practice have a large influence as well. Thus, social forces shape the morphology of restored streams. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-02T04:36:01.783348-05:
      DOI: 10.1002/2015WR017030
       
  • Climatic and landscape controls on water transit times and silicate
           mineral weathering in the critical zone
    • Abstract: The critical zone (CZ) can be conceptualized as an open system reactor that is continually transforming energy and water fluxes into an internal structural organization and dissipative products. In this study, we test a controlling factor on water transit times (WTT) and mineral weathering called Effective Energy and Mass Transfer (EEMT). We hypothesize that EEMT, quantified based on local climatic variables, can effectively predict WTT within – and mineral weathering products from – the CZ. This study tests whether EEMT or static landscape characteristics are good predictors of WTT, aqueous phase solutes, and silicate weathering products. Our study site is located around Redondo Peak, a rhyolitic volcanic resurgent dome, in northern New Mexico. At Redondo Peak springs drain slopes along an energy gradient created by differences in terrain aspect. This investigation uses major solute concentrations, the calculated mineral mass undergoing dissolution, and the age tracer tritium and relates them quantitatively to EEMT and landscape characteristics. We found significant correlations between EEMT, WTT and mineral weathering products. Significant correlations were observed between dissolved weathering products (Na+ and DIC), 3H concentrations and maximum EEMT. In contrast, landscape characteristics such as contributing area of spring, slope gradient, elevation, and flow path length were not as effective predictive variables of WTT, solute concentrations, and mineral weathering products. These results highlight the interrelationship between landscape, hydrological, and biogeochemical processes and suggest that basic climatic data embodied in EEMT can be used to scale hydrological and hydrochemical responses in other sites. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-02T04:31:24.868147-05:
      DOI: 10.1002/2015WR017018
       
  • Control of coupling mass balance error in a process‐based numerical
           model of surface‐subsurface flow interaction
    • Authors: Marcello Fiorentini; Stefano Orlandini, Claudio Paniconi
      Abstract: A process‐based numerical model of integrated surface–subsurface flow is analyzed in order to identify, track, and reduce the mass balance errors affiliated with the model's coupling scheme. The sources of coupling error include a surface–subsurface grid interface that requires node‐to‐cell and cell‐to‐node interpolation of exchange fluxes and ponding heads, and a sequential iterative time matching procedure that includes a time lag in these same exchange terms. Based on numerical experiments carried out for two synthetic test cases and for a complex drainage basin in northern Italy, it is shown that the coupling mass balance error increases during the flood recession limb when the rate of change in the fluxes exchanged between the surface and subsurface is highest. A dimensionless index that quantifies the degree of coupling and a saturated area index are introduced to monitor the sensitivity of the model to coupling error. Error reduction is achieved through improvements to the heuristic procedure used to control and adapt the time step interval and to the interpolation algorithm used to pass exchange variables from nodes to cells. The analysis presented illustrates the tradeoffs between a flexible description of surface and subsurface flow processes and the numerical errors inherent in sequential iterative coupling with staggered nodal points at the land surface interface, and it reveals mitigation strategies that are applicable to all integrated models sharing this coupling and discretization approach. This article is protected by copyright. All rights reserved.
      PubDate: 2015-07-02T03:32:06.182273-05:
      DOI: 10.1002/2014WR016816
       
  • Source, transport, and evolution of saline groundwater in a shallow
           holocene aquifer on the tidal deltaplain of southwest Bangladesh
    • Authors: Scott C. Worland; George M. Hornberger, Steven L. Goodbred
      Abstract: Deltaic groundwater resources are often vulnerable to degradation from seawater intrusion or through interaction with saline paleowaters. The Ganges‐Brahmaputra‐Meghna River delta, in Bangladesh and West Bengal, India, is a particularly vulnerable area with an estimated twenty million coastal inhabitants directly affected by saline drinking water. The shallow groundwater of the coastal regions is primarily brackish with pockets of fresher water. A small scale hydrologic investigation of groundwater salinity beneath an embanked tidal channel island was undertaken to explore possible hydrogeological explanations of the distribution of water salinities in the shallow aquifer. This study employs a combination of 3H and 14C dating, electromagnetic subsurface mapping, and a 2D solute transport model. The authors conclude that the shallow ground‐water salinity can best be explained by the slow infiltration of meteoric water into paleo‐brackish estuarine water that was deposited during the early‐mid Holocene. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-30T08:20:55.62569-05:0
      DOI: 10.1002/2014WR016262
       
  • Hydrocomplexity: Addressing water security and emergent environmental
           risks
    • Authors: Praveen Kumar
      Abstract: Water security and emergent environmental risks are among the most significant societal concerns. They are highly inter‐linked to other global risks such as those related to climate, human health, food, human migration, biodiversity loss, urban sustainability, etc. Emergent risks result from the confluence of unanticipated interactions from evolving inter‐dependencies between complex systems, such as those embedded in the water cycle. They are associated with the novelty of dynamical possibilities that have significant potential consequences to human and ecological systems, and not with probabilities based on historical precedence. To ensure water security we need to be able to anticipate the likelihood of risk possibilities as they present the prospect of the most impact through cascade of vulnerabilities. They arise due to a confluence of non‐stationary drivers that include growing population, climate change, demographic shifts, urban growth, and economic expansion, among others, which create novel inter‐dependencies leading to a potential of cascading network effects. Hydrocomplexity aims to address water security and emergent risks through the development of science, methods, and practices with the potential to foster a “Blue Revolution” akin to the Green revolution for food security. It blends both hard infrastructure based solution with soft knowledge driven solutions to increase the range of planning and design, management, mitigation and adaptation strategies. It provides a conceptual and synthetic framework to enable us to integrate discovery science and engineering, observational and information science, computational and communication systems, and social and institutional approaches to address consequential water and environmental challenges. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-30T07:52:12.650222-05:
      DOI: 10.1002/2015WR017342
       
  • Analysis of convergent flow tracer tests in a heterogeneous sandy box with
           connected gravel channels
    • Authors: Antonio Molinari; D. Pedretti, C. Fallico
      Abstract: We analyzed the behavior of convergent flow tracer tests performed in a 3D heterogeneous sandbox in presence of connected gravel channels under laboratory‐controlled conditions. We focused on the evaluation of connectivity metrics based on characteristic times calculated from experimental breakthrough curves (BTCs), and the selection of upscaling model parameters related to connectivity. A conservative compound was injected from several piezometers in the box and depth‐integrated BTCs were measured at the central pumping well. Results show that transport was largely affected by the presence of gravel channels, which generate anomalous transport behavior such as BTC tailing and double peaks. Connectivity indicators based on BTC peak times provided better information about the presence of connected gravel channels in the box. One of these indicators, β, was defined as the relative temporal separation of the BTCs peaks from the BTCs centers of mass. The mathematical equivalence between β and the capacity coefficient adopted in mass‐transfer‐based formulations suggests how connectivity metrics could be directly embedded in mass‐transfer formulations. This finding is in line with previous theoretical studies and was corroborated by reproducing a few representative experimental BTCs using a 1D semi‐analytical bimodal solution embedding a mass‐transfer term. Model results show a good agreement with experimental BTCs when the capacity coefficient was constrained by measured β. Models that do not embed adequate connectivity metrics or do not adequately reproduce connectivity showed poor matching with observed BTCs. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-30T07:51:35.571723-05:
      DOI: 10.1002/2014WR016216
       
  • Enhanced fixed‐size parallel speedup with the Muskingum method using
           a trans‐boundary approach and a large subbasins approximation
    • Abstract: This study presents a new algorithm for parallel computation of river flow that builds on recent work demonstrating the relative independence of distant river reaches in the update step of the Muskingum method. The algorithm is designed to achieve enhanced fixed‐size parallel speedup and uses a mathematical approximation applied at the boundaries of large sub‐basins. In order to use such an algorithm, a balanced domain decomposition method that differs from the traditional classifications of river reaches and sub‐basins and based on network topology is developed. An application of the algorithm and domain decomposition method to the Mississippi River Basin results in an 8‐fold decrease in computing time with 16 computing cores which is unprecedented for Muskingum‐type algorithms applied in classic parallel‐computing paradigms having a one‐to‐one relationship between cores and sub‐basins. An estimated 300 km between upstream and downstream reaches of sub‐basins guarantees the applicability of the algorithm in our study and motivates further investigation of domain decomposition methods. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-24T10:42:54.609095-05:
      DOI: 10.1002/2014WR016650
       
  • White water: 50 years of snow research in WRR and the outlook for the
           future
    • Authors: Matthew Sturm
      Abstract: Over the past 50 years, 239 papers related to snow have been published in Water Resources Research (WRR). Seminal papers on virtually every facet of snow physics and snow water resources have appeared in the journal. These include papers on drifting snow, the snow surface energy balance, the effect of grain size on albedo, chemical elution, water movement through snow, and canopy interception. In particular, papers in WRR have explored the distribution of snow across different landscapes, providing data, process knowledge, and the basis for virtually all of the distributed snow models in use today. In this paper I review these key contributions and provide some personal thoughts on what is likely to be the focus and nature of papers published in the next few decades, a period that is likely to see an increasing ability to map snow cover in detail, which should serve as a basis for the further development and improvement of snow models. It will also be an uncertain future, with profound changes in snow climatology predicted. I expect WRR will continue to play a key role in documenting and understanding these important cryospheric changes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-24T10:28:38.312554-05:
      DOI: 10.1002/2015WR017242
       
  • A novel framework for discharge uncertainty quantification applied to 500
           UK gauging stations
    • Authors: G. Coxon; J. Freer, I. K. Westerberg, T. Wagener, R. Woods, P. J. Smith
      Abstract: Benchmarking the quality of river discharge data and understanding its information content for hydrological analyses is an important task for hydrologic science. There is a wide variety of techniques to assess discharge uncertainty. However, few studies have developed generalised approaches to quantify discharge uncertainty. This study presents a generalised framework for estimating discharge uncertainty at many gauging stations with different errors in the stage‐discharge relationship. The methodology utilises a non‐parametric LOWESS regression within a novel framework that accounts for uncertainty in the stage‐discharge measurements, scatter in the stage‐discharge data and multi‐section rating curves. The framework was applied to 500 gauging stations in England and Wales and we evaluated the magnitude of discharge uncertainty at low, mean and high flow points on the rating curve. The framework was shown to be robust, versatile and able to capture place‐specific uncertainties for a number of different examples. Our study revealed a wide range of discharge uncertainties (10–397% discharge uncertainty interval widths), but the majority of the gauging stations (over 80%) had mean and high flow uncertainty intervals of less than 40%. We identified some regional differences in the stage‐discharge relationships, however the results show that local conditions dominated in determining the magnitude of discharge uncertainty at a gauging station. This highlights the importance of estimating discharge uncertainty for each gauging station prior to using those data in hydrological analyses. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-23T18:17:56.74263-05:0
      DOI: 10.1002/2014WR016532
       
  • Numerical stability analysis of two‐dimensional solute transport
           along a discrete fracture in a porous rock matrix
    • Authors: N. Watanabe; O. Kolditz
      Abstract: This work reports numerical stability conditions in two‐dimensional solute transport simulations including discrete fractures surrounded by an impermeable rock matrix. We use an advective‐dispersive problem described in\cite{Tang1981} and examine the stability of the Crank‐Nicolson Galerkin Finite Element Method (CN‐GFEM). The stability conditions are analyzed in terms of the spatial discretization length perpendicular to the fracture, the flow velocity, the diffusion coefficient, the matrix porosity, the fracture aperture, and the fracture longitudinal dispersivity. In addition, we verify applicability of the recently developed Finite Element Method ‐ Flux Corrected Transport (FEM‐FCT) method by\cite{Kuzmin2009} to suppress oscillations in the hybrid system, with a comparison to the commonly utilized Streamline Upwinding/Petrov‐Galerkin (SUPG) method.Major findings of this study are (1) the mesh von Neumann number (Fo) ≥ 0.373$must be satisfied to avoid undershooting in the matrix, (2) in addition to an upper bound, the Courant number also has a lower bound in the fracture in cases of low dispersivity, and (3) the FEM‐FCT method can effectively suppress the oscillations in both the fracture and the matrix. The results imply that, in cases of low dispersivity, pre‐refinement of a numerical mesh is not sufficient to avoid the instability in the hybrid system if a problem involves evolutionary flow fields and dynamic material parameters. Applying the FEM‐FCT method to such problems is recommended if negative concentrations cannot be tolerated and computing time is not a strong issue. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-23T10:51:20.56903-05:0
      DOI: 10.1002/2015WR017164
       
  • Suppressed convective rainfall by agricultural expansion in southeastern
           Burkina Faso
    • Authors: Theophile Mande; Natalie C Ceperley, Gabriel G Katul, Scott W Tyler, Hamma Yacouba, Marc B. Parlange
      Abstract: With the ‘green economy' being promoted as a path to sustainable development and food security within the African continent, the influx of agricultural land is proliferating at a rapid pace often replacing natural savannah forests. Where agriculture is primarily rain‐fed, the possible adverse impacts of agricultural land influx on rainfall occurrences in water limited areas such as West Africa warrant attention. Using field observations complemented by model calculations in southeastern Burkina Faso, the main causes of a 10‐30% suppressed daytime rainfall recorded over agricultural fields when referenced to natural savannah forests are examined. Measurements and model runs reveal that the crossing of the mixed layer height and lifting condensation levels, a necessary condition for cloud formation and subsequent rainfall occurrence, was 30% more frequent above the natural savannah forest. This increase in crossing statistics was primarily explained by increases in measured sensible heat flux above the savannah forest rather than differences in lifting condensation heights. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-19T17:52:50.548453-05:
      DOI: 10.1002/2015WR017144
       
  • Economic cost of water deliveries for peace and the environment in Israel:
           An integrated water resources management approach
    • Authors: Frank A. Ward; Nir Becker
      Abstract: This paper presents a framework for discovering an economically viable water sharing plan among neighboring communities for promoting peace and environmental protection. Its application is to the Middle East in which Israel may be facing water supply obligations to address environmental requirements and for a possible a peace agreement with its Palestinian neighbors. The framework consists of integrating external factors, constraints, policy instruments, and targets. Our findings from a constrained optimization analysis of Israel's national water system show that the costs of increased deliveries are dependent on two major issues: (1) achieving integrated water resources management (IWRM) in which efficient combinations of expansion from several supply sources and reductions in demands occur over time, and (2) the cost of desalination technologies. We identify a $US 1.46 billion price tag, in present value terms, from using integrated management of demand reduction and supply expansion under current desalination costs. Adjustment costs will decline both with anticipated reductions in desalination costs and with an efficient implementation of IWRM. These adjustments can contribute to moderating regional tensions and protecting key ecological assets while addressing water scarcity in a volatile corner of the world. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-19T17:52:26.788292-05:
      DOI: 10.1002/2014WR016783
       
  • Prediction of solute transport in a heterogeneous aquifer utilizing
           hydraulic conductivity and specific storage tomograms
    • Abstract: A sequential procedure of hydraulic tomographical inversion is applied to characterize at high resolution the spatial heterogeneity of hydraulic conductivity and specific storage at the field test site Stegemühle, Germany. The shallow aquifer at this site is examined by five short‐ term multi‐level pumping tests with 30 pumping‐observation pairs between two wells. Utilizing travel time diagnostics of the recorded pressure response curves, fast eikonal based inversion is shown to deliver insight into the sedimentary structures. Thus, the structural information from the generated travel time tomogram is exploited to constrain full calibration of the pressure response curves. Based on lateral extrapolation from the measured inter‐well profile, a three‐dimensional reconstruction of the aquifer is obtained. It is demonstrated that calibration of spatially variable specific storage in addition to hydraulic conductivity can improve the fitting of the model while the structural features are only slightly changed. At the field site, two tracer tests with uranine and sodium‐naphthionate were also performed and their concentrations were monitored for two months. The measured tracer breakthrough curves are employed for independent validation of the hydraulic tomographical reconstruction. It is demonstrated that major features of the observed solute transport can be reproduced, and structures relevant for macro‐dispersive tracer spreading could be resolved. However, for the mildly heterogeneous aquifer, the tracer breakthrough curves can also be approximated by a simplified homogeneous model with higher dispersivity. Therefore improved validation results that capture specific characteristics of the breakthrough curves would require additional hydraulic measurements. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T10:32:13.319259-05:
      DOI: 10.1002/2014WR016402
       
  • Long‐term observation of permeability in sedimentary rocks under
           high‐temperature and stress conditions and its interpretation
           mediated by microstructural investigations
    • Authors: Hideaki Yasuhara; Naoki Kinoshita, Hiroaki Ohfuji, Manabu Takahashi, Kazumasa Ito, Kiyoshi Kishida
      Abstract: In this study, a series of long‐term, intermittent permeability experiments utilizing Berea sandstone and Horonobe mudstone samples, with and without a single artificial fracture, is conducted for more than 1000 days to examine the evolution of rock permeability under relatively high temperature and confining pressure conditions. Effluent element concentrations are also measured throughout the experiments. Before and after flow‐through experiments, rock samples are prepared for X‐ray diffraction, X‐ray fluorescence, and scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy to examine the mineralogical changes between pre‐ and post‐experimental samples, and also for micro‐focus X‐ray CT to evaluate the alteration of the microstructure. Although there are exceptions, the observed, qualitative evolution of permeability is found to be generally consistent in both the intact and the fractured rock samples – the permeability in the intact rock samples increases with time after experiencing no significant changes in permeability for the first several hundred days, while that in the fractured rock samples decreases with time. An evaluation of the Damkohler number and of the net dissolution, using the measured element concentrations, reveals that the increase in permeability can most likely be attributed to the relative dominance of the mineral dissolution in the pore spaces, while the decrease can most likely be attributed to the mineral dissolution/crushing at the propping asperities within the fracture. Taking supplemental observations by micro‐focus X‐ray CT and using the intact sandstone samples, a slight increase in relatively large pore spaces is seen. This supports the increase in permeability observed in the flow‐through experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T09:15:32.781214-05:
      DOI: 10.1002/2014WR016427
       
  • Catchment coevolution: A useful framework for improving predictions of
           hydrological change?
    • Abstract: The notion that landscape features have co‐evolved over time is well known in the Earth sciences. Hydrologists have recently called for a more rigorous connection between emerging spatial patterns of landscape features and the hydrological response of catchments, and have termed this concept catchment co‐evolution. In this paper we review recent literature on this subject and attempt to synthesize what we've learned into a general framework that would improve predictions of hydrologic change. We first present empirical evidence of the interaction and feedback of landscape evolution and changes in hydrological response. From this review it is clear that the independent drivers of catchment co‐evolution are climate, geology and tectonics. We identify common currency that allows comparing the levels of activity of these independent drivers, such that, at least conceptually, we can quantify the rate of evolution or aging. Knowing the hydrologic age of a catchment by itself is not very meaningful without linking age to hydrologic response. Two avenues of investigation have been used to understand the relationship between (differences in) age and hydrological response: (i) one that is based on relating present landscape features to runoff processes that are hypothesized to be responsible for the current fingerprints in the landscape; and (ii) one that takes advantage of an experimental design known as space‐for‐time substitution. Both methods have yielded significant insights in the hydrologic response of landscapes with different histories. If we want to make accurate predictions of hydrologic change we will also need to be able to predict how the catchment will further co‐evolve in association with changes in the activity levels of the drivers (e.g. climate). There is ample evidence in the literature that suggests that whole‐system prediction of catchment co‐evolution is, at least in principle, plausible. With this imperative we outline a research agenda that implements the concepts of catchment co‐evolution for building a holistic framework towards improving predictions of hydrologic change. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T08:58:38.187774-05:
      DOI: 10.1002/2015WR017032
       
  • Global hydrology 2015: State, trends, and directions
    • Authors: Marc F.P. Bierkens
      Abstract: Global hydrology has come a long way since the first introduction of the primitive land surface model of Manabe (1969) and the declaration of the “Emergence of Global Hydrology” by Eagleson (1986). Hydrological sub‐models of varying complexity are now part of global climate models, of models calculating global terrestrial carbon sequestration, of earth system models and even of integrated assessment models. This paper reviews the current state of global hydrological modeling, discusses past and recent developments and extrapolates these to future challenges and directions. First, established domains of global hydrological model applications are discussed, in terms of societal and science questions posed, the type of models developed and recent advances therein. Next, a genealogy of global hydrological models is given. After reviewing recent efforts to connect model components from different domains, new domains are identified where global hydrology is now starting to become an integral part of the analyses. Finally, inspired by these new domains of application, persistent and emerging challenges are identified as well as the directions global hydrology is likely to take in the coming decade and beyond. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T07:17:43.752591-05:
      DOI: 10.1002/2015WR017173
       
  • Using in situ vertical displacements to characterize changes in moisture
           load
    • Authors: Lawrence C. Murdoch; Clay E. Freeman, Leonid N. Germanovich, Colby Thrash, Scott DeWolf
      Abstract: Changes in soil moisture content alter the load on underlying material, and we have developed a technique for characterizing this effect by using an extensometer to measure the displacement caused by the load change. The extensometer is pushed into soil at depths of 5 m or more, and displacement between two anchors separated by ∼1.5 m is measured with a resolution of better than 0.01 μm (10−8 m). The instrument is sensitive to load changes at the ground surface within a radial distance that is roughly twice its depth, potentially providing a method for averaging changes in water content over 100s of m2 or more. During a field trial at a site in South Carolina, compressive displacements in unsaturated saprolite were strongly correlated to rainfall with a calibration factor of 0.16 µm displacement per mm of rainfall ± 0.002 µm/mm (R2 = 0.95). Estimates of the net change in water volume per unit area made using the calibration factor from rainfall were similar to independent estimates of evapotranspiration. The technique was affected by barometric pressure variations, but the sensitivity was less than expected and does not hinder meaningful application. A companion instrument demonstrated the displacement signal was repeatable. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T06:48:25.822693-05:
      DOI: 10.1002/2015WR017335
       
  • Spatial considerations of stream hydraulics in reach‐scale
           temperature modeling
    • Authors: Noah M. Schmadel; Bethany T. Neilson, Justin E. Heavilin
      Abstract: While a myriad of processes control water temperature, the most significant in streams without notable shading or groundwater inputs are surface heat fluxes at the air‐water interface. These fluxes are particularly sensitive to parameters representing the water surface area to volume ratio. Channel geometry dictates this ratio; however, it is currently unclear how spatial variability in stream hydraulics influences temperature predictions or how the contribution of the boundary condition influences interpretation of processes most sensitive to this variability. To investigate these influences over long reach scales, we used high‐resolution spatial observations collected over a 25‐km reach within a Laplace‐domain solution to a two‐zone temperature transient storage model. We found that for the study reach and flow condition, changes in the surface area to volume ratio did not generally coincide with changes in stream temperature. Though, notable changes in cumulative mean residence time corresponded with changes in the temperature extremes throughout the study reach. The surface heat fluxes were clearly the most sensitive to spatially variable hydraulics that translated into high residence times once the contribution of the boundary condition decayed. Consistent with solute transport, reach segment lengths that reflect the spatial correlation in observations were necessary to capture the spatial influences of hydraulics on temperature predictions. This approach provides a fundamental step for determining whether spatial detail related to stream hydraulics is important to support accurate temperature predictions and how best to represent that detail. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T04:16:07.079979-05:
      DOI: 10.1002/2015WR016931
       
  • Water security and the science agenda
    • Authors: Howard S. Wheater; Patricia Gober
      Abstract: The freshwater environment is facing unprecedented global pressures. Unsustainable use of surface and groundwater is ubiquitous. Gross pollution is seen in developing economies, nutrient pollution is a global threat to aquatic ecosystems, and flood damage is increasing. Droughts have severe local consequences, but effects on food can be global. These current pressures are set in the context of rapid environmental change and socio‐economic development, population growth and weak and fragmented governance. We ask what should be the role of the water science community in addressing water security challenges. Deeper understanding of aquatic and terrestrial environments and their interactions with the climate system is needed, along with trans‐disciplinary analysis of vulnerabilities to environmental and societal change. The human dimension must be fully integrated into water science research and viewed as an endogenous component of water system dynamics. Land and water management are inextricably linked, and thus more cross‐sector coordination of research and policy is imperative. To solve real‐world problems, the products of science must emerge from an iterative, collaborative, two‐way exchange with management and policy communities. Science must produce knowledge that is deemed to be credible, legitimate, and salient by relevant stakeholders, and the social process of linking science to policy is thus vital to efforts to solve water problems. The paper shows how a large‐scale catchment‐based observatory can be used to practice trans‐disciplinary science integration and address the Anthropocene's water problems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:31:41.171935-05:
      DOI: 10.1002/2015WR016892
       
  • Hydraulic fracturing water use variability in the United States and
           potential environmental implications
    • Authors: Tanya J. Gallegos; Brian A. Varela, Seth S. Haines, Mark A. Engle
      Abstract: Until now, up‐to‐date, comprehensive, spatial, national‐scale data on hydraulic fracturing water volumes have been lacking. Water volumes used to hydraulically fracture over 263,859 oil and gas wells drilled between 2000 and 2014 were compiled and used to create the first U.S. map of hydraulic fracturing water use. Further analysis of these data shows that although 15,275 m3 and 19,425 m3 of water was used to hydraulically fracture individual horizontal oil and gas wells, respectively, in 2014, about 42 percent of wells were actually either vertical or directional, which required less than 2,600 m3 water per well. The highest average hydraulic fracturing water usage (10,000 − 36,620 m3 per well) in watersheds across the United States was correlated with shale gas areas (versus coalbed methane, tight oil, or tight gas) where the greatest proportion of hydraulically fractured wells were horizontally drilled, reflecting that the natural reservoir properties influence water use. This analysis also demonstrates that many oil and gas resources within a given basin are developed using a mix of horizontal, vertical and some directional wells, explaining why large volume hydraulic fracturing water usage is not widespread. This spatial variability in hydraulic fracturing water use relates to the potential for environmental impacts such as water availability, water quality, wastewater disposal, and possible wastewater injection‐induced earthquakes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:31:19.96567-05:0
      DOI: 10.1002/2015WR017278
       
  • Numerical rivers: A synthetic streamflow generator for water resources
           vulnerability assessments
    • Authors: Edoardo Borgomeo; Christopher L. Farmer, Jim W. Hall
      Abstract: The vulnerability of water supplies to shortage depends on the complex interplay between streamflow variability and the management and demands of the water system. Assessments of water supply vulnerability to potential changes in streamflow require methods capable of generating a wide range of possible streamflow sequences. This paper presents a method to generate synthetic monthly streamflow sequences that reproduce the statistics of the historical record and that can express climate‐induced changes in user‐specified streamflow characteristics. The streamflow sequences are numerically simulated through random sampling from a parametric or a non‐parametric distribution fitted to the historical data whilst shuffling the values in the time series until a sequence matching a set of desired temporal properties is generated. The desired properties are specified in an objective function which is optimised using simulated annealing. The properties in the objective function can be manipulated to generate streamflow sequences that exhibit climate‐induced changes in streamflow characteristics such as inter‐annual variability or persistence. The method is applied to monthly streamflow data from the Thames River at Kingston (UK) to generate sequences that reproduce historical streamflow statistics at the monthly and annual time scales and to generate perturbed synthetic sequences expressing changes in short term persistence and inter‐annual variability. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:30:47.014781-05:
      DOI: 10.1002/2014WR016827
       
  • Footprint characteristics revised for field‐scale soil moisture
           monitoring with cosmic‐ray neutrons
    • Abstract: Cosmic‐ray neutron probes are widely used to monitor environmental water content near the surface. The method averages over tens of hectares and is unrivaled in serving representative data for agriculture and hydrological models at the hectometer scale. Recent experiments, however, indicate that the sensor response to environmental heterogeneity is not fully understood. Knowledge of the support volume is a prerequisite for the proper interpretation and validation of hydrogeophysical data. In a previous study, several physical simplifications have been introduced into a neutron transport model in order to derive the characteristics of the cosmic‐ray probe's footprint. We utilize a refined source and energy spectrum for cosmic‐ray neutrons and simulate their response to a variety of environmental conditions. Results indicate that the method is particularly sensitive to soil moisture in the first tens of meters around the probe, whereas the radial weights are changing dynamically with ambient water. The footprint radius ranges from 130 to 240m depending on air humidity, soil moisture and vegetation. The moisturedependent penetration depth of 15 to 83cm decreases exponentially with distance to the sensor. However, the footprint circle remains almost isotropic in complex terrain with nearby rivers, roads or hill slopes. Our findings suggest that a dynamically weighted average of point measurements is essential for accurate calibration and validation. The new insights will have important impact on signal interpretation, sensor installation, data interpolation from mobile surveys, and the choice of appropriate resolutions for data assimilation into hydrological models. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:30:26.044871-05:
      DOI: 10.1002/2015WR017169
       
  • On the dynamics and kinematics of two‐fluid‐phase flow in
           porous media
    • Abstract: A model formulated in terms of both conservation and kinematic equations for phases and interfaces in two‐fluid‐phase flow in a porous medium system is summarized. Macroscale kinematic equations are derived as extensions of averaging theorems and do not rely on conservation principles. Models based on both conservation and kinematic equations can describe multiphase flow with varying fidelity. When only phase‐based equations are considered, a model similar in form to the traditional model for two‐fluid‐phase flow results. When interface conservation and kinematic equations are also included, a novel formulation results that naturally includes evolution equations that express dynamic changes in fluid saturations, pressures, the capillary pressure, and the fluid‐fluid interfacial area density in a two‐fluid‐system. This dynamic equation set is unique to this work, and the importance of the modeled physics is shown through both microfluidic experiments and high‐resolution lattice Boltzmann simulations. The validation work shows that the relaxation of interface distribution and shape toward an equilibrium state is a slow process relative to the time scale typically allowed for a system to approach an apparent equilibrium state based upon observations of fluid saturations and external pressure measurements. Consequently, most pressure‐saturation data intended to denote an equilibrium state is likely a sampling from a dynamic system undergoing changes of interfacial curvatures that are not typically monitored. The results confirm the importance of kinematic analysis in combination with conservation equations for faithful modeling of system physics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:29:21.227429-05:
      DOI: 10.1002/2015WR016921
       
  • Bridging the gap between models and measurements of peat hydraulic
           conductivity
    • Authors: Paul J. Morris; Andy J. Baird, Lisa R. Belyea
      Abstract: Peat saturated hydraulic conductivity, Ksat, declines strongly with increasing degree of decomposition, providing a potentially important negative ecohydrological feedback that may buffer peatlands from climate‐induced drying. However, the quantitative nature of this relationship is poorly understood. We measured downcore changes in Ksat and carbon‐to‐nitrogen concentration quotients (C/N) in fourteen shallow (∼0.5 m deep, 0.1 m diameter) peat cores from a Swedish raised bog. We used the C/N measurements to approximate the fraction of original peat mass remaining. A linear mixed effects (LME) model predicts log10(Ksat) from i) our C/N‐derived estimate of fractional remaining mass; ii) depth; iii) microhabitat (hummock, hollow); and iv) location (treeless bog center, treed bog margin). The LME model indicated no significant random effects or interactions between predictors, so we derived a non‐linear multiple regression (NLMR) model to predict Ksat on its original scale. Both LME and NLMR models predict that Ksat decreases exponentially with depth and that Ksat is lower beneath hollows than beneath hummocks for equivalent depths below the surface. Fractional remaining mass was an important predictor in the LME model, but not in the NLMR model. The distinction between central and marginal areas of the bog was not an important predictor. We demonstrate for the first time that the relationship between fractional remaining mass and Ksat is log‐linear, and suggest revisions that should be made to peatland development models. In particular, depth – usually ignored in modeling studies – exerted a strong control over Ksat independently of decomposition and should be included explicitly in model algorithms. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:27:23.236252-05:
      DOI: 10.1002/2015WR017264
       
  • Quantifying renewable groundwater stress with GRACE
    • Abstract: Groundwater is an increasingly important water supply source globally. Understanding the amount of groundwater used versus the volume available is crucial to evaluate future water availability. We present a groundwater stress assessment to quantify the relationship between groundwater use and availability in the world's 37 largest aquifer systems. We quantify stress according to a ratio of groundwater use to availability, which we call the Renewable Groundwater Stress ratio. The impact of quantifying groundwater use based on nationally reported groundwater withdrawal statistics is compared to a novel approach to quantify use based on remote sensing observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Four characteristic stress regimes are defined: Overstressed, Variable Stress, Human‐dominated Stress, and Unstressed. The regimes are a function of the sign of use (positive or negative) and the sign of groundwater availability, defined as mean annual recharge. The ability to mitigate and adapt to stressed conditions, where use exceeds sustainable water availability, is a function of economic capacity and land use patterns. Therefore, we qualitatively explore the relationship between stress and anthropogenic biomes. We find that estimates of groundwater stress based on withdrawal statistics are unable to capture the range of characteristic stress regimes, especially in regions dominated by sparsely populated biome types with limited cropland. GRACE‐based estimates of use and stress can holistically quantify the impact of groundwater use on stress, resulting in both greater magnitudes of stress and more variability of stress between regions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T07:00:02.195135-05:
      DOI: 10.1002/2015WR017349
       
  • Uncertainty in global groundwater storage estimates in a total groundwater
           stress framework
    • Abstract: Groundwater is a finite resource under continuous external pressures. Current unsustainable groundwater use threatens the resilience of aquifer systems and their ability to provide a long‐term water source. Groundwater storage is considered to be a factor of groundwater resilience, although the extent to which resilience can be maintained has yet to be explored in depth. In this study, we assess the limit of groundwater resilience in the world's largest groundwater systems with remote sensing observations. The Total Groundwater Stress (TGS) ratio, defined as the ratio of total storage to the groundwater depletion rate, is used to explore the timescales to depletion in the world's largest aquifer systems and associated groundwater buffer capacity. We find that the current state of knowledge of large‐scale groundwater storage has uncertainty ranges across orders of magnitude that severely limit the characterization of resilience in the study aquifers. Additionally, we show that groundwater availability, traditionally defined as recharge and re‐defined in this study as total storage, can alter the systems that are considered to be stressed versus unstressed. We find that remote sensing observations from NASA's Gravity Recovery and Climate Experiment can assist in providing such information at the scale of a whole aquifer. For example, we demonstrate that a groundwater depletion rate in the Northwest Sahara Aquifer System of 2.69 ± 0.8 km3 per year would result in the aquifer being depleted to 90% of its total storage in as few as 50 years given an initial storage estimate of 70 km3 [Swezey, 1999]. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T07:00:01.068748-05:
      DOI: 10.1002/2015WR017351
       
  • Preliminary December‐January inflow and streamflow reconstructions
           from tree‐rings for western Tasmania, southeastern Australia
    • Authors: K.J. Allen; S.C. Nichols, R. Evans, E.R. Cook, S. Allie, G. Carson, F. Ling, P.J. Baker
      Abstract: Projected decreases and changes in the seasonal distribution of precipitation will have profound impacts on southeastern Australia, including its ability to generate renewable hydroelectricity. Recent decreases in precipitation over the region may be significant in the context of instrumental records, but the question of whether these decreases are within long‐term natural variability remains. To help address this issue, we present December‐January streamflow and dam inflow reconstructions for southeastern Australia. These reconstructions for the Tasmanian west coast are based solely on local tree‐ring chronologies and span up to 1600 years. Non‐parametric estimates, however, indicate good model skill for the last 458 years (streamflow) and 478 years (dam inflow). The reconstructions indicate that 20th century conditions were well within the range of historical variability, and were in fact relatively wet. The period from ca. 1600 – 1750 CE was one of enhanced variability and a high proportion of low and high flow events occurred in the 17th century. There are significant relationships between streamflow and inflow reconstructions and large‐scale ocean‐atmosphere processes such as ENSO and the Southern Annular Mode. Critically, our two reconstructions rely heavily on new tree‐ring chronologies based on properties such as tracheid radial diameter, cell wall thickness and density, underscoring the importance of these different types of chronologies in reconstructions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-15T02:15:20.551822-05:
      DOI: 10.1002/2015WR017062
       
  • Uncertainty in training image‐based inversion of hydraulic head data
           constrained to ERT data: Workflow and case study
    • Abstract: In inverse problems, investigating uncertainty in the posterior distribution of model parameters is as important as matching data. In recent years, most efforts have focused on techniques to sample the posterior distribution with reasonable computational costs. Within a Bayesian context, this posterior depends on the prior distribution. However, most of the studies ignore modeling the prior with realistic geological uncertainty. In this paper, we propose a workflow inspired by a Popper‐Bayes philosophy, that data should first be used to falsify models, then only be considered for matching. We propose a workflow consisting of three steps: (1) in defining the prior, we interpret multiple alternative geological scenarios from literature (architecture of facies) and site specific data (proportions of facies). Prior spatial uncertainty is modeled using multiple‐point geostatistics, where each scenario is defined using a training image. (2) We validate these prior geological scenarios by simulating electrical resistivity tomography (ERT) data on realizations of each scenario and comparing them to field ERT in a lower dimensional space. In this second step, the idea is to probabilistically falsify scenarios with ERT, meaning that scenarios which are incompatible receive an updated probability of zero while compatible scenarios receive a non‐zero updated belief. (3) We constrain the hydrogeological model with hydraulic head and ERT using a stochastic search method. The workflow is applied to a synthetic and a field case studies in an alluvial aquifer. This study highlights the importance of considering and estimate prior uncertainty (without data) through a process of probabilistic falsification. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-15T02:04:12.855245-05:
      DOI: 10.1002/2014WR016460
       
  • Use of a forest sapwood area index to explain long‐term variability
           in mean annual evapotranspiration and streamflow in moist eucalypt forests
           
    • Authors: Richard G. Benyon; Patrick N.J. Lane, Dominik Jaskierniak, George Kuczera, Shane R. Haydon
      Abstract: Mean sapwood thickness, measured in fifteen 73 year old Eucalyptus regnans and E. delegatensis stands, correlated strongly with forest overstorey stocking density (R2 0.72). This curvilinear relationship was used with routine forest stocking density and basal area measurements to estimate sapwood area of the forest overstorey at various times in 15 research catchments in undisturbed and disturbed forests located in the Great Dividing Range, Victoria, Australia. Up to 45 years of annual precipitation and streamflow data available from the 15 catchments was used to examine relationships between mean annual loss (evapotranspiration estimated as mean annual precipitation minus mean annual streamflow), and sapwood area. Catchment mean sapwood area correlated strongly (R2 0.88) with catchment mean annual loss. Variation in sapwood area accounted for 68% more variation in mean annual streamflow than precipitation alone (R2 0.90 compared with R2 0.22). Changes in sapwood area accounted for 96% of the changes in mean annual loss observed after forest thinning or clear‐cutting and regeneration. We conclude that forest inventory data can be used reliably to predict spatial and temporal variation in catchment annual losses and streamflow in response to natural and imposed disturbances in even‐aged forests. Consequently, recent advances in mapping of sapwood area using airborne light detection and ranging will enable high resolution spatial and temporal mapping of mean annual loss and mean annual streamflow over large areas of forested catchment. This will be particularly beneficial in management of water resources from forested catchments subject to disturbance but lacking reliable long‐term (years to decades) streamflow records. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-15T01:34:48.204835-05:
      DOI: 10.1002/2015WR017321
       
  • On the assessment of aridity with changes in atmospheric CO2
    • Authors: Michael L. Roderick; Peter Greve, Graham D. Farquhar
      Abstract: A recent interpretation of climate model projections concluded that “warmer is more arid”. In contrast, dust records and other evidence have led the geoscience community to conclude that “warmer is less arid” leading to an aridity paradox. The “warmer is more arid” interpretation is based on a projected increase in the vapour pressure deficit (∼ 7‐9% K−1) that results in a projected increase in potential evaporation that greatly exceeds the projected increase in precipitation. However, the increase in potential evaporation does not result in an increase in (actual) evaporation which remains more or less constant in the model output. We use that to explain why projected changes in the long‐term aridity can be assessed by directly interrogating the climate model output. To that end, we equate precipitation with meteorological aridity and runoff with hydrologic aridity. A third perspective, agro‐ecological aridity, is not directly related to the water lost but rather to the carbon gain and is equated with the photosynthetic uptake of CO2. We re‐examine the same climate model output and conclude that “warmer is less arid” from all perspectives and in agreement with the geological records. Future research will need to add the critical regional and seasonal perspectives to the aridity assessments described here. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-11T16:29:08.159897-05:
      DOI: 10.1002/2015WR017031
       
  • Climate and agricultural land use change impacts on streamflow in the
           upper midwestern United States
    • Authors: Satish C. Gupta; Andrew C. Kessler, Melinda K. Brown, Francis Zvomuya
      Abstract: Increased streamflow and its associated impacts on water quality have frequently been linked to changes in land use and land cover (LULC) such as tile drainage, cultivation of prairies, and increased adoption of soybeans (Glycine max) in modern day cropping systems. This study evaluated the relative importance of changes in precipitation and LULC on streamflow in 29 Hydrologic Unit Code 008 watersheds in the Upper Midwestern United States. The evaluation was done by statistically testing the changes in slope and intercept of the relationships between ln(annual streamflow) vs. annual precipitation for the periods prior to 1975 (pre‐change period) and after 1976 (post‐change period). A significant shift either in slope or intercept of these relationships was assumed to be an indication of LULC changes whereas a lack of significant shift suggested a single relationship driven by precipitation. All 29 watersheds showed no statistical difference in slope or intercept of the relationships between the two periods. However, a simpler model that kept the slope constant for the two periods showed a slight upward shift in the intercept value for 10 watersheds in the post‐change period. A comparison of five‐year moving averages also revealed that the increased streamflows in the post change period are mainly due to an increase in precipitation. Minimal or the lack of LULC change impact on streamflow results from comparable evapotranspiration in the two time periods. We also show how incorrect assumptions in previously published studies minimized precipitation change impacts and heightened the LULC change impacts on streamflows. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-11T16:27:44.286444-05:
      DOI: 10.1002/2015WR017323
       
  • A simple and efficient unstructured finite volume scheme for solving the
           shallow water equations in overland flow applications
    • Abstract: This paper presents the Decoupled Hydrological Discretisation (DHD) scheme for solving the shallow water equations in hydrological applications involving surface runoff in rural and urban basins. The name of the scheme is motivated by the fact that the three equations which form the two‐dimensional shallow water system are discretised independently from each other and thus, the numerical scheme is decoupled in a mathematical sense. Its main advantages compared to other classic finite volume schemes for the shallow water equations are its simplicity to code and the lower computational cost per time step. The validation of the scheme is presented in five test cases involving overland flow and rainfall‐runoff transformation over topographies of different complexity. The scheme is compared to the finite volume scheme ofRoe [1986], to the simple inertia formulation [Bates et al., 2010], and to the diffusive wave model. The test cases show that the DHD scheme is able to compute subcritical and supercritical flows in rural and urban environments, and that in overland flow applications it gives similar results to the second order scheme of Roe with a lower computational cost. The results obtained with the simple inertia and diffusive wave models are very similar to those obtained with the DHD scheme in rural basins in which the bed friction and topography dominate the flow hydrodynamics but they deteriorate in typical urban configurations in which the presence of supercritical flow conditions and small scale patterns boost the relevance of the inertial terms in the momentum equations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:24:02.049984-05:
      DOI: 10.1002/2014WR016547
       
  • Applicability of bed load transport models for mixed size sediments in
           steep streams considering macroroughness
    • Authors: Johannes M. Schneider; Dieter Rickenmann, Jens M. Turowski, Kristin Bunte, James W. Kirchner
      Abstract: In steep mountain streams, macro‐roughness elements typically increase both flow energy dissipation and the threshold of motion compared to lower‐gradient channels, reducing the part of the flow energy available for bedload transport. Bedload transport models typically take account of these effects either by reducing the acting bed shear stress or by increasing the critical parameters for particle entrainment. Here, we evaluate bedload transport models for mixed‐size sediments and models based on a median grain size using a large field dataset of fractional bedload transport rates. We derive reference shear stresses and bedload transport relations based on both the total boundary shear stress and a reduced (or “effective”) shear stress that accounts for flow resistance due to macro‐roughness. When reference shear stresses are derived from the total boundary shear stress they are closely related to channel slope, but when they are derived from the effective shear stress, they are almost invariant with channel slope. The performance of bedload transport models is generally comparable when using the total shear stress and a channel slope‐related reference shear stress, or when using the effective shear stress and a constant reference shear stress. However, dimensionless bedload transport relations are significantly steeper for the total stress approach, whereas they are similar to the commonly used fractional Wilcock and Crowe (WC) transport model for the effective stress approach. This similarity in the relations allows the WC model, developed for lower‐gradient streams, to be used in combination with an effective shear stress approach, in steep mountain streams. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:22:49.32292-05:0
      DOI: 10.1002/2014WR016417
       
  • Food security and sustainable resource management
    • Authors: Dennis McLaughlin; Wolfgang Kinzelbach
      Abstract: The projected growth in global food demand until mid‐century will challenge our ability to continue recent increases in crop yield and will have a significant impact on natural resources. The water and land requirements of current agriculture are significantly less than global reserves but local shortages are common and have serious impacts on food security. Recent increases in global trade have mitigated some of the effects of spatial and temporal variability. However, trade has a limited impact on low‐income populations who remain dependent on subsistence agriculture and local resources. Potential adverse environmental impacts of increased agricultural production include unsustainable depletion of water and soil resources, major changes in the global nitrogen and phosphorous cycles, human health problems related to excessive nutrient and pesticide use, and loss of habitats that contribute to agricultural productivity. Some typical case studies from China illustrate the connections between the need for increased food production and environmental stress. Sustainable options for decreasing food demand and for increasing production include reduction of food losses on both the producer and consumer ends, elimination of unsustainable practices such as prolonged groundwater overdraft, closing of yield gaps with controlled expansions of nutrient application and irrigation, increases in crop yield and pest resistance through advances in biotechnology, and moderate expansion of rain fed cropland. Calculations based on reasonable assumptions suggest that such measures could meet the food needs of an increasing global population while protecting the environment. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:21:48.551185-05:
      DOI: 10.1002/2015WR017053
       
  • Organic contaminant transport and fate in the subsurface: Evolution of
           knowledge and understanding
    • Authors: Hedeff I. Essaid; Barbara A. Bekins, Isabelle M. Cozzarelli
      Pages: 4861 - 4902
      Abstract: Toxic organic contaminants may enter the subsurface as slightly soluble and volatile nonaqueous phase liquids (NAPLs) or as dissolved solutes resulting in contaminant plumes emanating from the source zone. A large body of research published in Water Resources Research has been devoted to characterizing and understanding processes controlling the transport and fate of these organic contaminants and the effectiveness of natural attenuation, bioremediation, and other remedial technologies. These contributions include studies of NAPL flow, entrapment, and interphase mass transfer that have advanced from the analysis of simple systems with uniform properties and equilibrium contaminant phase partitioning to complex systems with pore‐scale and macroscale heterogeneity and rate‐limited interphase mass transfer. Understanding of the fate of dissolved organic plumes has advanced from when biodegradation was thought to require oxygen to recognition of the importance of anaerobic biodegradation, multiple redox zones, microbial enzyme kinetics, and mixing of organic contaminants and electron acceptors at plume fringes. Challenges remain in understanding the impacts of physical, chemical, biological, and hydrogeological heterogeneity, pore‐scale interactions, and mixing on the fate of organic contaminants. Further effort is needed to successfully incorporate these processes into field‐scale predictions of transport and fate. Regulations have greatly reduced the frequency of new point‐source contamination problems; however, remediation at many legacy plumes remains challenging. A number of fields of current relevance are benefiting from research advances from point‐source contaminant research. These include geologic carbon sequestration, nonpoint‐source contamination, aquifer storage and recovery, the fate of contaminants from oil and gas development, and enhanced bioremediation.
      PubDate: 2015-07-02T10:53:24.697014-05:
      DOI: 10.1002/2015WR017121
       
  • The emergence of topographic steady state in a perpetually dynamic
           self‐organized critical landscape
    • Authors: Liam Reinhardt; Michael A. Ellis
      Pages: 4986 - 5003
      Abstract: We conducted a series of four physical modeling experiments of mountain growth at differing rates of uplift and three distinct climates ranging from relatively wet to relatively dry. The spatial and temporal pattern of landscape behavior is characterized by ∼f−1 scaling in sediment discharge and power law scaling in the magnitude and frequency of ridge movement in all four experiments. We find that internally generated self‐organized critical (SOC) processes generate dynamically stable catchment geometries after ∼1 relief depths of erosion: these regularly spaced catchments have an average outlet‐spacing ratio of 2.16, well within the range of values reported in field studies. Once formed, large catchment bounding ridges oscillate about a critically balanced mean location, with occasional large‐scale changes in catchment size. Ridge movement appears to be driven by the competition for discharge as landslides push ridges back and forth. These dynamics lead to the emergence of a complex twofold scaling in catchment dynamics that is fully established by 1.8 relief depths of erosion; at this stage, a clear threshold has emerged separating two distinct scaling regimes, where large ridge mobility is insensitive to relief and small ridge mobility is relief dependent. Overall, we demonstrate that the development of dynamically stable large‐scale landforms is related to the emergence of a complex‐system hierarchy in topographic dynamics. Once formed, these landscapes do not evolve; statistical properties such as average topography and discharge become stationary while topography remains highly dynamic at smaller length scales.
      PubDate: 2015-07-01T10:39:00.102681-05:
      DOI: 10.1002/2014WR016223
       
  • Comparison of two stochastic techniques for reliable urban runoff
           prediction by modeling systematic errors
    • Pages: 5004 - 5022
      Abstract: In urban rainfall‐runoff, commonly applied statistical techniques for uncertainty quantification mostly ignore systematic output errors originating from simplified models and erroneous inputs. Consequently, the resulting predictive uncertainty is often unreliable. Our objective is to present two approaches which use stochastic processes to describe systematic deviations and to discuss their advantages and drawbacks for urban drainage modeling. The two methodologies are an external bias description (EBD) and an internal noise description (IND, also known as stochastic gray‐box modeling). They emerge from different fields and have not yet been compared in environmental modeling. To compare the two approaches, we develop a unifying terminology, evaluate them theoretically, and apply them to conceptual rainfall‐runoff modeling in the same drainage system. Our results show that both approaches can provide probabilistic predictions of wastewater discharge in a similarly reliable way, both for periods ranging from a few hours up to more than 1 week ahead of time. The EBD produces more accurate predictions on long horizons but relies on computationally heavy MCMC routines for parameter inferences. These properties make it more suitable for off‐line applications. The IND can help in diagnosing the causes of output errors and is computationally inexpensive. It produces best results on short forecast horizons that are typical for online applications.
      PubDate: 2015-07-02T10:54:26.272662-05:
      DOI: 10.1002/2014WR016678
       
  • On the control of riverbed incision induced by run‐of‐river
           power plant
    • Pages: 5023 - 5040
      Abstract: Water resource management (WRM) through dams or reservoirs is worldwide necessary to support key human‐related activities, ranging from hydropower production to water allocation and flood risk mitigation. Designing of reservoir operations aims primarily to fulfill the main purpose (or purposes) for which the structure has been built. However, it is well known that reservoirs strongly influence river geomorphic processes, causing sediment deficits downstream, altering water, and sediment fluxes, leading to riverbed incision and causing infrastructure instability and ecological degradation. We propose a framework that, by combining physically based modeling, surrogate modeling techniques, and multiobjective (MO) optimization, allows to include fluvial geomorphology into MO optimization whose main objectives are the maximization of hydropower revenue and the minimization of riverbed degradation. The case study is a run‐of‐the‐river power plant on the River Po (Italy). A 1‐D mobile‐bed hydro‐morphological model simulated the riverbed evolution over a 10 year horizon for alternatives operation rules of the power plant. The knowledge provided by such a physically based model is integrated into a MO optimization routine via surrogate modeling using the response surface methodology. Hence, this framework overcomes the high computational costs that so far hindered the integration of river geomorphology into WRM. We provided numerical proof that river morphologic processes and hydropower production are indeed in conflict but that the conflict may be mitigated with appropriate control strategies.
      PubDate: 2015-07-02T10:53:51.695784-05:
      DOI: 10.1002/2014WR016237
       
  • Improved snow interception modeling using canopy parameters derived from
           airborne LiDAR data
    • Pages: 5041 - 5059
      Abstract: Forest snow interception can account for large snow storage differences between open and forested areas. The effect of interception can also lead to significant variations in sublimation, with estimates varying from 5 to 60% of total snowfall. Most current interception models utilize canopy closure and LAI to partition interception from snowfall and calculate interception efficiency as an exponential decrease of interception efficiency with increasing precipitation. However, as demonstrated, these models can show specific deficiencies within heterogeneous canopy. Seven field areas were equipped with 1932 surveyed points within various canopy density regimes in three elevation bands surrounding Davos, Switzerland. Snow interception measurements were taken from 2012 to 2014 (∼9000 samples) and compared with measurements at two open sites. The measured data indicated the presence of snow bridging from a demonstrated increase in interception efficiency as precipitation increased until a maximum was reached. As precipitation increased beyond this maximum, the data then exhibited a decrease in interception efficiency. Standard and novel canopy parameters were developed using aerial LiDAR data. These included estimates of LAI, canopy closure, distance to canopy, gap fraction, and various tree size parameters. These canopy metrics and the underlying efficiency distribution were then integrated to formulate a conceptual model based upon the snow interception measurements. This model gave a ∼27% increase in the r2 (from 0.39 to 0.66) and a ∼40% reduction in RMSE (from 5.19 to 3.39) for both calibration and validation data sets when compared to previous models at the point scale. When upscaled to larger grid sizes, the model demonstrated further increases in performance.
      PubDate: 2015-07-03T23:06:04.722524-05:
      DOI: 10.1002/2014WR016724
       
  • Analytical sensitivity analysis of transient groundwater flow in a bounded
           model domain using the adjoint method
    • Authors: Zhiming Lu; Velimir V. Vesselinov
      Pages: 5060 - 5080
      Abstract: Sensitivity analyses are an important component of any modeling exercise. We have developed an analytical methodology based on the adjoint method to compute sensitivities of a state variable (hydraulic head) to model parameters (hydraulic conductivity and storage coefficient) for transient groundwater flow in a confined and randomly heterogeneous aquifer under ambient and pumping conditions. For a special case of two‐dimensional rectangular domains, these sensitivities are represented in terms of the problem configuration (the domain size, boundary configuration, medium properties, pumping schedules and rates, and observation locations and times), and there is no need to actually solve the adjoint equations. As an example, we present analyses of the obtained solution for typical groundwater flow conditions. Analytical solutions allow us to calculate sensitivities efficiently, which can be useful for model‐based analyses such as parameter estimation, data‐worth evaluation, and optimal experimental design related to sampling frequency and locations of observation wells. The analytical approach is not limited to groundwater applications but can be extended to any other mathematical problem with similar governing equations and under similar conceptual conditions.
      PubDate: 2015-07-03T23:04:17.930093-05:
      DOI: 10.1002/2014WR016819
       
  • Ecohydrological modeling in agroecosystems: Examples and challenges
    • Authors: A. Porporato; X. Feng, S. Manzoni, Y. Mau, A. J. Parolari, G. Vico
      Pages: 5081 - 5099
      Abstract: Human societies are increasingly altering the water and biogeochemical cycles to both improve ecosystem productivity and reduce risks associated with the unpredictable variability of climatic drivers. These alterations, however, often cause large negative environmental consequences, raising the question as to how societies can ensure a sustainable use of natural resources for the future. Here we discuss how ecohydrological modeling may address these broad questions with special attention to agroecosystems. The challenges related to modeling the two‐way interaction between society and environment are illustrated by means of a dynamical model in which soil and water quality supports the growth of human society but is also degraded by excessive pressure, leading to critical transitions and sustained societal growth‐collapse cycles. We then focus on the coupled dynamics of soil water and solutes (nutrients or contaminants), emphasizing the modeling challenges, presented by the strong nonlinearities in the soil and plant system and the unpredictable hydroclimatic forcing, that need to be overcome to quantitatively analyze problems of soil water sustainability in both natural and agricultural ecosystems. We discuss applications of this framework to problems of irrigation, soil salinization, and fertilization and emphasize how optimal solutions for large‐scale, long‐term planning of soil and water resources in agroecosystems under uncertainty could be provided by methods from stochastic control, informed by physically and mathematically sound descriptions of ecohydrological and biogeochemical interactions.
      PubDate: 2015-07-04T06:20:22.311602-05:
      DOI: 10.1002/2015WR017289
       
  • Propagation and deposition of stony debris flows at channel confluences
    • Authors: L. M. Stancanelli; S. Lanzoni, E. Foti
      Pages: 5100 - 5116
      Abstract: The fluid dynamics of stony debris flows generated in two small tributaries adjacent to each other and flowing into a main receiving channel was analyzed experimentally at a laboratory scale. The analysis on the propagation along the tributaries and deposition in the main channel provide information about sediment‐water mobility, dangerous damming, and potential hazard. Debris flows were generated by releasing a preset water discharge over an erodible layer of saturated gravels material. As a consequence, the debris flow sediment concentration varied accordingly to the entrainment rate which, in turn, was strongly controlled by the tributary slope. The data collected by acoustic level sensors, pore fluid pressure transducers, and a load cell were used to characterize the evolution of bulk density and solid concentration of the sediment‐water mixture. These two parameters were relevant to assess the stony debris flow mobility which contributes to determine the shape of sediment deposits in the main channel. The detailed bed topography surveys carried out in the main channel at the end of each experiment provided information on the morphology of these deposits and on the interplay of adjacent confluences. The influences of confluence angle, tributary slopes, and triggering conditions have been investigated, for a total of 18 different configurations. Within the investigated range of parameters, the slope angle was the parameter that mainly influences the stony debris flow mobility while, for adjacent confluences, the degree of obstruction within the receiving channel was strongly influenced by the triggering scenario.
      PubDate: 2015-07-04T06:19:46.411599-05:
      DOI: 10.1002/2015WR017116
       
  • Tamarix transpiration along a semiarid river has negligible impact on
           water resources
    • Authors: Alyson K. McDonald; Bradford P. Wilcox, Georgianne W. Moore, Charles R. Hart, Zhuping Sheng, M. Keith Owens
      Pages: 5117 - 5127
      Abstract: The proliferation of saltcedar (Tamarix spp.) along regulated rivers in the western United States has transformed riparian plant communities. It is commonly assumed that transpiration by these alien plants has led to large losses of water that would otherwise contribute to streamflow. Control of saltcedar, therefore, has been considered a viable strategy for conserving water and increasing streamflow in these regions. In an effort to better understand the linkage between transpiration by saltcedar and streamflow, we monitored transpiration, stream stage, and groundwater elevations within a saltcedar stand along the Pecos River during June 2004. Transpiration, as determined by sap flow measurements, exhibited a strong diel pattern; stream stage did not. Diel fluctuations in groundwater levels were observed, but only in one well, which was located in the center of the saltcedar stand. In that well, the correlation between maximal transpiration and minimal groundwater elevation was weak (R2 = 0.16). No effects of transpiration were detected in other wells within the saltcedar stand, nor in the stream stage. The primary reason, we believe, is that the saltcedar stand along this reach of the Pecos River has relatively low sapwood area and a limited spatial extent resulting in very low transpiration compared with the stream discharge. Our results are important because they provide a mechanistic explanation for the lack of increase in streamflow following large‐scale control of invasive trees along semiarid rivers.
      PubDate: 2015-07-04T06:19:11.861769-05:
      DOI: 10.1002/2014WR016866
       
  • Updating real‐time flood forecasts via the dynamic system response
           curve method
    • Authors: Wei Si; Weimin Bao, Hoshin V. Gupta
      Pages: 5128 - 5144
      Abstract: The accuracy of flood forecasts generated using spatially lumped hydrological models can be severely affected by errors in the estimates of areal mean rainfall. The quality of the latter depends both on the size and type of errors in point‐based rainfall measurements, and on the density and spatial arrangement of rain gauges in the basin. Here we use error feedback correction, based on the dynamic system response curve (DSRC) method, to compute updated estimates of the rainfall inputs. The method is evaluated via synthetic and real‐data cases, showing that the method works as theoretically expected. The ability of the method to improve the accuracy of real‐time flood forecasts is then demonstrated using 20 basins of different sizes and having different rain gauge densities. We find that the degree of forecast improvement is more significant for larger basins and for basins with lower rain gauge density. The method is relatively simple to apply and can improve the accuracy and stability of real‐time model predictions without increasing either model complexity and/or the number of model parameters.
      PubDate: 2015-07-06T07:02:06.339713-05:
      DOI: 10.1002/2015WR017234
       
  • An entropy‐based measure of hydrologic complexity and its
           applications
    • Authors: Aldrich Castillo; Fabio Castelli, Dara Entekhabi
      Pages: 5145 - 5160
      Abstract: Basin response and hydrologic fluxes are functions of hydrologic states, most notably of soil moisture. However, characterization of hillslope‐scale soil moisture is challenging since it is both spatially heterogeneous and dynamic. This paper introduces an entropy‐based and discretization‐invariant dimensionless index of hydrologic complexity H that measures the distance of a given distribution of soil moisture from a Dirac delta (most organization) and a uniform distribution (widest distribution). Applying the distributed hydrologic model MOBIDIC to seven test basins with areas ranging 100−103 km2 and representing semiarid and temperate climates, H is shown to capture distributional characteristics of soil moisture fields. It can also track the temporal evolution of the distributional features. Furthermore, this paper explores how basin attributes affect the characteristic H, and how H can be used to explain interbasin variability in hydrologic response. Relationships are found only by grouping basins with the same climate or size. For the semiarid basins, H scales with catchment area, topographic wetness, infiltration ratio, and base flow index; while H is inversely related to relief ratio.
      PubDate: 2015-07-14T08:24:22.807659-05:
      DOI: 10.1002/2014WR016035
       
  • The relationship between Monte Carlo estimators of heterogeneity and error
           for daily to monthly time steps in a small Minnesota precipitation gauge
           network
    • Authors: Michael Wright; Celso Ferreira, Mark Houck, Jason Giovannettone
      Pages: 5161 - 5176
      Abstract: Precipitation quantile estimates are used in engineering, agriculture, and a variety of other disciplines. Index flood regional frequency methods pool normalized gauge data in the case of homogeneity among the constituent gauges of the region. Unitless regional quantile estimates are outputted and rescaled at each gauge. Because violation of the homogeneity hypothesis is a major component of quantile estimation error in regional frequency analysis, heterogeneity estimators should be “reasonable proxies” of the error of quantile estimation. In this study, three Monte Carlo heterogeneity statistics tested in Hosking and Wallis (1997) are plotted against Monte Carlo estimates of quantile error for all five‐or‐more‐gauge regionalizations in a 12 gauge network in the Twin Cities region of Minnesota. Upper‐tail quantiles with nonexceedance probabilities of 0.75 and above are examined at time steps ranging from daily to monthly. A linear relationship between heterogeneity and error estimates is found and quantified using Pearson's r score. Two of Hosking and Wallis's (1997) heterogeneity measures, incorporating the coefficient of variation in one case and additionally the skewness in the other, are found to be reasonable proxies for quantile error at the L‐moment ratio values characterizing these data. This result, in addition to confirming the utility of a commonly used coefficient of variation‐based heterogeneity statistic, provides evidence for the utility of a heterogeneity measure that incorporates skewness information.
      PubDate: 2015-07-14T08:24:06.970675-05:
      DOI: 10.1002/2014WR015399
       
  • Integration of microseismic monitoring data into coupled flow and
           geomechanical models with ensemble Kalman filter
    • Authors: Mohammadali Tarrahi; Behnam Jafarpour, Ahmad Ghassemi
      Pages: 5177 - 5197
      Abstract: Hydraulic stimulation of low‐permeability rocks in enhanced geothermal systems, shale resources, and CO2 storage aquifers can trigger microseismic events, also known as microearthquakes (MEQs). The distribution of microseismic source locations in the reservoir may reveal important information about the distribution of hydraulic and geomechanical rock properties. In this paper, we present a framework for conditioning heterogeneous rock permeability and geomechanical property distributions on microseismic data. To simulate the multiphysics processes in these systems, we combine a fully coupled flow and geomechanical model with the Mohr‐Coulomb type rock failure criterion. The resulting multiphysics simulation constitutes the forecast model that relates microseismic source locations to reservoir rock properties. We adopt this forward model in an ensemble Kalman filter (EnKF) data assimilation framework to jointly estimate reservoir permeability and geomechanical property distributions from injection‐induced microseismic response measurements. We show that integration of a large number of spatially correlated microseismic data with practical ensemble sizes can lead to severe underestimation of ensemble spread, and eventually ensemble collapse. To mitigate the variance underestimation issue, two low‐rank data representation schemes are presented and discussed. In the first approach, microseismic data are projected onto a low‐dimensional subspace defined by the left singular vectors of the perturbed observation matrix. The second method uses a coarser grid for representing the microseismic data. A series of numerical experiments is presented to evaluate the performance of the proposed methods and to illustrate their applicability for assimilating microseismic data into coupled flow and geomechanical forward models to estimate multiphysics rock properties.
      PubDate: 2015-07-14T08:25:07.243824-05:
      DOI: 10.1002/2014WR016264
       
  • Evaluating the potential for quantitative monitoring of in situ chemical
           oxidation of aqueous‐phase TCE using in‐phase and quadrature
           electrical conductivity
    • Pages: 5239 - 5259
      Abstract: Electrical resistivity measurements can potentially be used to remotely monitor fate and transport of ionic oxidants such as permanganate ( MnO4−) during in situ chemical oxidation (ISCO) of contaminants like trichloroethene (TCE). Time‐lapse two‐dimensional bulk conductivity and induced polarization surveys conducted during a sand tank ISCO simulation demonstrated that MnO4− plume movement could be monitored in a qualitative manner using bulk conductivity tomograms, although chargeability was below sensitivity limits. We also examined changes to in‐phase and quadrature electrical conductivity resulting from ion injection, MnO2 and Cl− production, and pH change during TCE and humate oxidation by MnO4− in homogeneous aqueous solutions and saturated porous media samples. Data from the homogeneous samples demonstrated that inversion of the sand tank resistivity data using a common Tikhonov regularization approach was insufficient to recover an accurate conductivity distribution within the tank. While changes to in‐phase conductivity could be successfully modeled, quadrature conductivity values could not be directly related to TCE oxidation product or MnO4− concentrations at frequencies consistent with field induced polarization surveys, limiting the utility of quadrature conductivity for monitoring ISCO.
      PubDate: 2015-07-14T08:24:17.119078-05:
      DOI: 10.1002/2014WR016868
       
  • Vegetation persistence and carbon storage: Implications for environmental
           water management for Phragmites australis
    • Authors: Kai Whitaker; Kerrylee Rogers, Neil Saintilan, Debashish Mazumder, Li Wen, R. J. Morrison
      Pages: 5284 - 5300
      Abstract: Environmental water allocations are used to improve the ecological health of wetlands. There is now increasing demand for allocations to improve ecosystem productivity and respiration, and enhance carbon sequestration. Despite global recognition of wetlands as carbon sinks, information regarding carbon dynamics is lacking. This is the first study estimating carbon sequestration for semiarid Phragmites australis reedbeds. The study combined aboveground biomass assessments with stable isotope analyses of soils and modeling of biomass using Normalized Digital Vegetation Index (NDVI) to investigate the capacity of environmental water allocations to improve carbon storage. The study considered relationships between soil organic carbon (SOC), carbon sources, and reedbed persistence in the Macquarie Marshes, a regulated semiarid floodplain of the Murray‐Darling Basin, Australia. SOC storage levels to 1 m soil depth were higher in persistent reedbeds (167 Mg ha−1) than ephemeral reedbeds (116–138 Mg ha−1). In situ P. australis was the predominant source of surface SOC at persistent reedbeds; mixed sources of surface SOC were proposed for ephemeral reedbeds. 13C enrichment with increasing soil depth occurred in persistent and ephemeral reedbeds and may not relate to flow characteristics. Despite high SOC at persistent reedbeds, differences in the rate of accretion contributed to significantly higher rates of carbon sequestration at ephemeral reedbeds (approximately 554 and 465 g m−2 yr−1) compared to persistent reedbeds (5.17 g m−2 yr−1). However, under current water regimes, rapid accretion at ephemeral reedbeds cannot be maintained. Effective management of persistent P. australis reedbeds may enhance carbon sequestration in the Macquarie Marshes and floodplain wetlands more generally.
      PubDate: 2015-07-14T08:24:03.303062-05:
      DOI: 10.1002/2014WR016253
       
  • Delineation of connectivity structures in 2‐D heterogeneous
           hydraulic conductivity fields
    • Authors: Alina R. Tyukhova; Wolfgang Kinzelbach, Matthias Willmann
      Pages: 5846 - 5854
      Abstract: Connectivity is a critical aquifer property controlling anomalous transport behavior at large scales. But connectivity cannot be easily defined in a continuous field based on information of the hydraulic conductivity alone. We conceptualize it as a connecting structure—a connected subset of a continuous hydraulic conductivity field that consists of paths of least hydraulic resistance. We develop a simple and robust numerical method to delineate the connectivity structure using information of the hydraulic conductivity field only. First, the topology of the connectivity structure is determined by finding the path(s) of least resistance between two opposite boundaries. And second, a series of connectivity structures are created by inflating and shrinking the individual channels. Finally, we apply this methodology to different heterogeneous fields. We show that our method captures the main flow channels as well as the pathways of early time solute arrivals. We find our method informative to study connectivity in 2‐D heterogeneous hydraulic conductivity fields.
      PubDate: 2015-07-03T23:04:44.937131-05:
      DOI: 10.1002/2014WR015283
       
 
 
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