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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: 2)
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: 20)
Asian Journal of Rural Development     Open Access   (Followers: 10)
Australian Journal of Water Resources     Full-text available via subscription   (Followers: 7)
Bubble Science, Engineering & Technology     Hybrid Journal  
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Civil and Environmental Research     Open Access   (Followers: 14)
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: 5)
Hydro Nepal : Journal of Water, Energy and Environment     Open Access   (Followers: 1)
Hydrology Research     Partially Free   (Followers: 10)
Hydrology: Current Research     Open Access   (Followers: 11)
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: 15)
Journal of Hydro-environment Research     Full-text available via subscription   (Followers: 5)
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: 3)
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: 1)
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: 10)
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]   [79 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]
  • 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
    • Authors: Cédric H. David; James S. Famiglietti, Zong‐Liang Yang, Victor Eijkhout
      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
       
  • Hydrology: The interdisciplinary science of water
    • Authors: Richard M. Vogel; Upmanu Lall, Ximing Cai, Balaji Rajagopalan, Peter K. Weiskel, Richard P. Hooper, Nicholas C. Matalas
      Abstract: We live in a world where biophysical and social processes are tightly coupled. Hydrologic systems change in response to a variety of natural and human forces such as climate variability and change, water use and water infrastructure, and land cover change. In turn, changes in hydrologic systems impact socioeconomic, ecological, and climate systems at a number of scales, leading to a coevolution of these interlinked systems. The Harvard Water Program, Hydrosociology, Integrated Water Resources Management, Ecohydrology, Hydromorphology, and Sociohydrology were all introduced to provide distinct, interdisciplinary perspectives on water problems to address the contemporary dynamics of human interaction with the hydrosphere and the evolution of the Earth's hydrologic systems. Each of them addresses scientific, social, and engineering challenges related to how humans influence water systems and vice versa. There are now numerous examples in the literature of how holistic approaches can provide a structure and vision of the future of hydrology. We review selected examples, which taken together, describe the type of theoretical and applied integrated hydrologic analyses and associated curricular content required to address the societal issue of water resources sustainability. We describe a modern interdisciplinary science of hydrology needed to develop an in‐depth understanding of the dynamics of the connectedness between human and natural systems and to determine effective solutions to resolve the complex water problems that the world faces today. Nearly, every theoretical hydrologic model introduced previously is in need of revision to accommodate how climate, land, vegetation, and socioeconomic factors interact, change, and evolve over time.
      PubDate: 2015-06-21T22:53:50.303974-05:
      DOI: 10.1002/2015WR017049
       
  • Water management: Current and future challenges and research directions
    • Authors: William J. Cosgrove; Daniel P. Loucks
      Abstract: Water distinguishes our planet compared to all the others we know about. While the global supply of available freshwater is more than adequate to meet all current and foreseeable water demands, its spatial and temporal distributions are not. There are many regions where our freshwater resources are inadequate to meet domestic, economic development and environmental needs. In such regions, the lack of adequate clean water to meet human drinking water and sanitation needs is indeed a constraint on human health and productivity and hence on economic development as well as on the maintenance of a clean environment and healthy ecosystems. All of us involved in research must find ways to remove these constraints. We face multiple challenges in doing that, especially given a changing and uncertain future climate, and a rapidly growing population that is driving increased social and economic development, globalization, and urbanization. How best to meet these challenges requires research in all aspects of water management. Since 1965, the journal Water Resources Research has played an important role in reporting and disseminating current research related to managing the quantity and quality and cost of this resource. This paper identifies the issues facing water managers today and future research needed to better inform those who strive to create a more sustainable and desirable future. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-20T03:49:57.75354-05:0
      DOI: 10.1002/2014WR016869
       
  • Improving the accuracy of risk prediction from particle‐based
           breakthrough curves reconstructed with kernel density estimators
    • Authors: Erica R. Siirila‐Woodburn; Daniel Fernàndez‐Garcia, Xavier Sanchez‐Vila
      Abstract: While particle tracking techniques are often used in risk frameworks, the number of particles needed to properly derive risk metrics such as average concentration for a given exposure duration is often unknown. If too few particles are used, error may propagate into the risk estimate. In this work we provide a less error‐prone methodology for the direct reconstruction of exposure duration averaged concentration versus time breakthrough curves from particle arrival times at a compliance surface. The approach is based on obtaining a suboptimal kernel density estimator that is applied to the sampled particle arrival times. The corresponding estimates of risk metrics obtained with this method largely outperform those by means of traditional methods (reconstruction of the breakthrough curve followed by the integration of concentration in time over the exposure duration). This is particularly true when the number of particles used in the numerical simulation is small (< 105), and for small exposure times. Percent error in the peak of averaged breakthrough curves is approximately zero for all scenarios and all methods tested when the number of particles is ≥ 105. Our results illustrate that obtaining a representative average exposure concentration is reliant on the information contained in each individual tracked particle, more so when the number of particles is small. They further illustrate the usefulness of defining problem‐specific kernel density estimators to properly reconstruct the observables of interest in a particle tracking framework without relying on the use of an extremely large number of particles. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-20T03:49:45.00438-05:0
      DOI: 10.1002/2014WR016394
       
  • 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
    • Authors: S. Jiménez; R. Brauchler, R. Hu, L. Hu, S. Schmidt, T. Ptak, P. Bayer
      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?
    • Authors: Peter A. Troch; Tim Lahmers, Antonio Meira, Rajarshi Mukherjee, Jonas W. Pedersen, Tirthankar Roy, Rodrigo Valdés‐Pineda
      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
       
  • Updating real‐time flood forecasts via the dynamic system response
           curve method
    • Authors: Wei Si; Weimin Bao, Hoshin V. Gupta
      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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-17T03:06:03.550897-05:
      DOI: 10.1002/2015WR017234
       
  • 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
    • Authors: M. Köhli; M. Schrön, M. Zreda, U. Schmidt, P. Dietrich, S. Zacharias
      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
       
  • Well integrity assessment under temperature and pressure stresses by a 1:1
           scale wellbore experiment
    • Authors: JC. 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 behaviour 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 to 52°C) and pressure (10 to 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:30:05.33578-05:0
      DOI: 10.1002/2014WR016786
       
  • 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
      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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-16T10:29:41.687574-05:
      DOI: 10.1002/2014WR016866
       
  • On the dynamics and kinematics of two‐fluid‐phase flow in
           porous media
    • Authors: W. G. Gray; A. L. Dye, J. E. McClure, L. J. Pyrak‐Nolte, C. T. Miller
      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
    • Authors: Alexandra S. Richey; Brian F. Thomas, Min‐Hui Lo, John T. Reager, James S. Famiglietti, Katalyn Voss, Sean Swenson, Matthew Rodell
      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
    • Authors: Alexandra S. Richey; Brian F. Thomas, Min‐Hui Lo, James S. Famiglietti, Sean Swenson, Matthew Rodell
      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
       
  • Issue Information
    • PubDate: 2015-06-16T06:40:22.834731-05:
      DOI: 10.1002/wrcr.21099
       
  • 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
       
  • Analytical sensitivity analysis of transient groundwater flow in a bounded
           model domain using the adjoint method
    • Authors: Zhiming Lu; Velimir V. Vesselinov
      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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-15T02:08:23.604707-05:
      DOI: 10.1002/2014WR016819
       
  • Uncertainty in training image‐based inversion of hydraulic head data
           constrained to ERT data: Workflow and case study
    • Authors: Hermans Thomas; Nguyen Frédéric, Caers Jef
      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
       
  • Delineation of connectivity structures in 2‐D heterogeneous
           hydraulic conductivity fields
    • Authors: Alina R. Tyukhova; Wolfgang Kinzelbach, Matthias Willmann
      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 2D heterogeneous hydraulic conductivity fields. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-11T16:28:22.654964-05:
      DOI: 10.1002/2014WR015283
       
  • 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
       
  • Reactive transport modeling of geochemical controls on secondary water
           quality impacts at a crude oil spill site near Bemidji, MN
    • Authors: Gene‐Hua Crystal Ng; Barbara A. Bekins, Isabelle M. Cozzarelli, Mary Jo Baedecker, Philip C. Bennett, Richard T. Amos, William N. Herkelrath
      Abstract: Anaerobic biodegradation of organic amendments and contaminants in aquifers can trigger secondary water quality impacts that impair groundwater resources. Reactive transport models help elucidate how diverse geochemical reactions control the spatiotemporal evolution of these impacts. Using extensive monitoring data from a crude oil spill site near Bemidji, Minnesota (USA), we implemented a comprehensive model that simulates secondary plumes of depleted dissolved O2 and elevated concentrations of Mn2+, Fe2+, CH4, and Ca2+ over a two‐dimensional cross section for 30 years following the spill. The model produces observed changes by representing multiple oil constituents and coupled carbonate and hydroxide chemistry. The model includes reactions with carbonates and Fe and Mn mineral phases, outgassing of CH4 and CO2 gas phases, and sorption of Fe, Mn, and H+. Model results demonstrate that most of the carbon loss from the oil (70%) occurs through direct outgassing from the oil source zone, greatly limiting the amount of CH4 cycled down‐gradient. The vast majority of reduced Fe is strongly attenuated on sediments, with most (91%) in the sorbed form in the model. Ferrous carbonates constitute a small fraction of the reduced Fe in simulations, but may be important for furthering the reduction of ferric oxides. The combined effect of concomitant redox reactions, sorption, and dissolved CO2 inputs from source‐zone degradation successfully reproduced observed pH. The model demonstrates that secondary water quality impacts may depend strongly on organic carbon properties, and impacts may decrease due to sorption and direct outgassing from the source zone.
      PubDate: 2015-06-11T03:13:24.559776-05:
      DOI: 10.1002/2015WR016964
       
  • Delta channel networks: 2. Metrics of topologic and dynamic complexity for
           delta comparison, physical inference, and vulnerability assessment
    • Authors: Alejandro Tejedor; Anthony Longjas, Ilya Zaliapin, Efi Foufoula‐Georgiou
      Abstract: Deltas are landforms that deliver water, sediment and nutrient fluxes from upstream rivers to the deltaic surface and eventually to oceans or inland water bodies via multiple pathways. Despite their importance, quantitative frameworks for their analysis lack behind those available for tributary networks. In a companion paper, delta channel networks were conceptualized as directed graphs and spectral graph theory was used to design a quantitative framework for exploring delta connectivity and flux dynamics. Here we use this framework to introduce a suite of graph‐theoretic and entropy‐based metrics, to quantify two components of a delta's complexity: (1) Topologic, imposed by the network connectivity and (2) Dynamic, dictated by the flux partitioning and distribution. The metrics are aimed to facilitate comparing, contrasting, and establishing connections between deltaic structure, process, and form. We illustrate the proposed analysis using seven deltas in diverse morphodynamic environments and of various degrees of channel complexity. By projecting deltas into a topo‐dynamic space whose coordinates are given by topologic and dynamic delta complexity metrics, we show that this space provides a basis for delta comparison and physical insight into their dynamic behavior. The examined metrics are demonstrated to relate to the intuitive notion of vulnerability, measured by the impact of upstream flux changes to the shoreline flux, and reveal that complexity and vulnerability are inversely related. Finally, a spatially explicit metric, akin to a delta width function, is introduced to classify shapes of different delta types.
      PubDate: 2015-06-09T10:17:49.154175-05:
      DOI: 10.1002/2014WR016604
       
  • Delta channel networks: 1. A graph‐theoretic approach for studying
           connectivity and steady state transport on deltaic surfaces
    • Authors: Alejandro Tejedor; Anthony Longjas, Ilya Zaliapin, Efi Foufoula‐Georgiou
      Abstract: River deltas are intricate landscapes with complex channel networks that self‐organize to deliver water, sediment, and nutrients from the apex to the delta top and eventually to the coastal zone. The natural balance of material and energy fluxes, which maintains a stable hydrologic, geomorphologic, and ecological state of a river delta, is often disrupted by external perturbations causing topological and dynamical changes in the delta structure and function. A formal quantitative framework for studying delta channel network connectivity and transport dynamics and their response to change is lacking. Here we present such a framework based on spectral graph theory and demonstrate its value in computing delta's steady state fluxes and identifying upstream (contributing) and downstream (nourishment) areas and fluxes from any point in the network. We use this framework to construct vulnerability maps that quantify the relative change of sediment and water delivery to the shoreline outlets in response to possible perturbations in hundreds of upstream links. The framework is applied to the Wax Lake delta in the Louisiana coast of the U.S. and the Niger delta in West Africa. In a companion paper, we present a comprehensive suite of metrics that quantify topologic and dynamic complexity of delta channel networks and, via application to seven deltas in diverse environments, demonstrate their potential to reveal delta morphodynamics and relate to notions of vulnerability and robustness.
      PubDate: 2015-06-09T10:16:08.315286-05:
      DOI: 10.1002/2014WR016577
       
  • Debates—Perspectives on socio‐hydrology:
           Socio‐hydrologic modeling: Tradeoffs, hypothesis testing, and
           validation
    • Authors: Tara J. Troy; Mitchell Pavao‐Zuckerman, Tom P. Evans
      Abstract: Socio‐hydrology focuses on studying the dynamics and co‐evolution of coupled human and water systems. Recently, several new socio‐hydrologic models have been published that explore these dynamics, and these models offer unique opportunities to better understand these coupled systems and to understand how water problems evolve similarly in different regions. These models also offer challenges, as decisions need to be made by the modeler on trade‐offs between generality, precision, and realism. In addition, traditional hydrologic model validation techniques, such as evaluating simulated streamflow, are insufficient, and new techniques must be developed. As socio‐hydrology progresses, these models offer a robust, invaluable tool to test hypotheses about the relationships between aspects of coupled human‐water systems. They will allow us to explore multiple working hypotheses to greatly expand insights and understanding of coupled socio‐hydrologic systems.
      PubDate: 2015-06-09T10:09:51.95404-05:0
      DOI: 10.1002/2015WR017046
       
  • Debates—Perspectives on socio‐hydrology: Modeling flood risk
           as a public policy problem
    • Authors: Patricia Gober; Howard S. Wheater
      Abstract: Socio‐hydrology views human activities as endogenous to water system dynamics; it is the interaction between human and biophysical processes that threatens the viability of current water systems through positive feedbacks and unintended consequences. Di Baldassarre et al. implement socio‐hydrology as a flood risk problem using the concept of social memory as a vehicle to link human perceptions to flood damage. Their mathematical model has heuristic value in comparing potential flood damages in green versus technological societies. It can also support communities in exploring the potential consequences of policy decisions and evaluating critical policy tradeoffs, for example, between flood protection and economic development. The concept of social memory does not, however, adequately capture the social processes whereby public perceptions are translated into policy action, including the pivotal role played by the media in intensifying or attenuating perceived flood risk, the success of policy entrepreneurs in keeping flood hazard on the public agenda during short windows of opportunity for policy action, and different societal approaches to managing flood risk that derive from cultural values and economic interests. We endorse the value of seeking to capture these dynamics in a simplified conceptual framework, but favor a broader conceptualization of socio‐hydrology that includes a knowledge exchange component, including the way modeling insights and scientific results are communicated to floodplain managers. The social processes used to disseminate the products of socio‐hydrological research are as important as the research results themselves in determining whether modeling is used for real‐world decision making.
      PubDate: 2015-06-09T10:08:06.793939-05:
      DOI: 10.1002/2015WR016945
       
  • Debates—Perspectives on socio‐hydrology: Changing water
           systems and the “tyranny of small
           problems”—Socio‐hydrology
    • Authors: Murugesu Sivapalan
      Abstract: We are well and truly in the Anthropocene. Humans can no longer be considered as mere external drivers or boundary conditions in the hydrologic systems we study. The interactions and feedbacks between human actions and water cycle dynamics on the planet, combined with the evolution of human norms/values in relation to water, are throwing up a range of emergent “big problems.” Understanding and offering sustainable solutions to these “big problems” require a broadening of hydrologic science to embrace the perspectives of both social and natural scientists. The new science of socio‐hydrology was introduced with this in mind, yet faces major challenges due to the wide gulf that separates the knowledge foundations and methodologies of natural and social sciences. Yet, the benefits of working together are enormous, including through adoption of natural science methods for social science problems, and vice versa. Bringing together the perspectives of both social and natural scientists dealing with water is good for hydrologic science, having the salutary effect of revitalizing it as use‐inspired basic science. It is good for management too, in that the broader, holistic perspectives provided by socio‐hydrology can help recognize potential “big” problems that may otherwise be unforeseen and, equally, identify potential “alternative” solutions to otherwise intractable problems.
      PubDate: 2015-06-09T10:06:53.501565-05:
      DOI: 10.1002/2015WR017080
       
  • Debates—Perspectives on socio‐hydrology: Simulating
           hydrologic‐human interactions
    • Authors: Daniel P. Loucks
      PubDate: 2015-06-09T10:05:26.893243-05:
      DOI: 10.1002/2015WR017002
       
  • Debates—Perspectives on socio‐hydrology: Introduction
    • Authors: Alberto Montanari
      PubDate: 2015-06-09T10:04:21.005371-05:
      DOI: 10.1002/2015WR017430
       
  • A simple and efficient unstructured finite volume scheme for solving the
           shallow water equations in overland flow applications
    • Authors: L. Cea; E. Bladé
      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
       
  • Propagation and deposition of stony debris flows at channel confluences
    • Authors: L. M. Stancanelli; S. Lanzoni, E. Foti
      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 contribute 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 experiments 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 influence the stony debris flow mobility while, for adjacent confluences, the degree of obstruction within the receiving channel was strongly influenced by the triggering scenario. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:23:36.468454-05:
      DOI: 10.1002/2015WR017116
       
  • Storage selection functions: A coherent framework for quantifying how
           catchments store and release water and solutes
    • Authors: Andrea Rinaldo; Paolo Benettin, Ciaran Harman, Markus Hrachowitz, Kevin McGuire, Ype Van der Velde, Enrico Bertuzzo, Gianluca Botter
      Abstract: We discuss a recent theoretical approach combining catchment‐scale flow and transport processes into a unified framework. The approach is designed to characterize the hydro‐chemistry of hydrologic systems and to meet the challenges posed by empirical evidence. StorAge Selection functions (SAS) are defined to represent the way catchment storage supplies the outflows with water of different ages, thus regulating the chemical composition of out‐fluxes. Biogeochemical processes are also reflected in the evolving residence time distribution and thus in age‐selection. Here, we make the case for the routine use of SAS functions and look forward to areas where further research is needed. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:23:10.979478-05:
      DOI: 10.1002/2015WR017273
       
  • 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
       
  • 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
      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 semi‐arid Phragmites australis reedbeds. The study combined above‐ground biomass assessments with stable isotope analyses of soils and modelling 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 semi‐arid 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 g.m−2.y−1 and 465 g.m−2.y−1) compared to persistent reedbeds (5.17 g.m−2.y−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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:22:28.85243-05:0
      DOI: 10.1002/2014WR016253
       
  • Improved snow interception modeling using canopy parameters derived from
           airborne LIDAR data
    • Authors: David Moeser; M. Stähli, T. Jonas
      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 (∼9,000 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:22:06.813915-05:
      DOI: 10.1002/2014WR016724
       
  • 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
       
  • Evaluating the potential for quantitative monitoring of in situ chemical
           oxidation of aqueous‐phase TCE using in‐phase and quadrature
           electrical conductivity
    • Authors: R. D. Hort; A. Revil, J. Munakata‐Marr, D. Mao
      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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-06T11:03:29.49996-05:0
      DOI: 10.1002/2014WR016868
       
  • River infiltration to a subtropical alluvial aquifer inferred using
           multiple environmental tracers
    • Authors: S. Lamontagne; A.R. Taylor, J. Batlle‐Aguilar, A. Suckow, P. G. Cook, S. D. Smith, U. Morgenstern, M.K. Stewart
      Abstract: Chloride (Cl–), stable isotope ratios of water (δ18O and δ2H), sulfur hexafluoride (SF6), tritium (3H), carbon‐14 (14C), noble gases (4He, Ne and Ar) and hydrometry were used to characterise groundwater‐surface water interactions, in particular infiltration rates, for the Lower Namoi River (New South Wales, Australia). The study period (four sampling campaigns between November 2009 and November 2011) represented the end of a decade‐long drought followed by several high‐flow events. The hydrometry showed that the river was generally losing to the alluvium, except when storm‐derived floodwaves in the river channel generated bank recharge – discharge cycles. Using 3H/14C‐derived estimates of groundwater mean residence times along the transect, infiltration rates ranged from 0.6 – 5 m year−1. However, when using the peak transition age (a more realistic estimate of travel time in highly dispersive environments), the range in infiltration rate was larger (4 – 270 m year−1). Both river water (highest δ2H, δ18O, SF6, 3H and 14C) and an older groundwater source (lowest δ2H, δ18O, SF6, 3H, 14C and highest 4He) were found in the riparian zone. This old groundwater end‐member may represent leakage from an underlying confined aquifer (Great Artesian Basin). Environmental tracers may be used to estimate infiltration rates in this riparian environment but the presence of multiple sources of water and a high dispersion induced by frequent variations in the water table complicates their interpretation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:57:57.278899-05:
      DOI: 10.1002/2014WR015663
       
  • Linear functional minimization for inverse modeling
    • Authors: D. A. Barajas‐Solano; B. Wohlberg, Velimir Vesselinov, D. M. Tartakovsky
      Abstract: We present a novel inverse modeling strategy to estimate spatially distributed parameters of nonlinear models. The maximum a posteriori (MAP) estimators of these parameters are based on a likelihood functional, which contains spatially discrete measurements of the system parameters and spatio‐temporally discrete measurements of the transient system states. The piecewise continuity prior for the parameters is expressed via Total Variation (TV) regularization. The MAP estimator is computed by minimizing a non‐quadratic objective equipped with the TV operator. We apply this inversion algorithm to estimate hydraulic conductivity of a synthetic confined aquifer from measurements of conductivity and hydraulic head. The synthetic conductivity field is composed of a low‐conductivity heterogeneous intrusion into a high‐conductivity heterogeneous medium. Our algorithm accurately reconstructs the location, orientation and extent of the intrusion from the steady‐state data only. Addition of transient measurements of hydraulic head improves the parameter estimation, accurately reconstructing the conductivity field in the vicinity of observation locations. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:56:21.473867-05:
      DOI: 10.1002/2014WR016179
       
  • Ecohydrological modeling in agroecosystems: Examples and challenges
    • Authors: A. Porporato; X. Feng, S. Manzoni, Y. Mau, A.J. Parolari, G. Vico
      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 hydro‐climatic 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:55:58.689909-05:
      DOI: 10.1002/2015WR017289
       
  • Integration of microseismic monitoring data into coupled flow and
           geomechanical models with ensemble Kalman filter
    • Authors: Mohammadali Tarrahi; Behnam Jafarpour, Ahmad Ghassemi
      Abstract: Hydraulic stimulation of low permeability rocks in enhanced geothermal systems, shale resources, and CO2 storage aquifers can trigger microseismic events, also known as micro‐earthquakes (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 multi‐physics processes in these systems, we combine a fully coupled flow and geomechanical model with the Mohr‐Coulomb type rock failure criterion. The resulting multi‐physics 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 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 observations 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 illustrate their applicability for assimilating microseismic data into coupled flow and geomechanical forward models to estimate multi‐physics rock properties. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:55:33.482288-05:
      DOI: 10.1002/2014WR016264
       
  • An analytical framework for flood water conservation considering forecast
           uncertainty and acceptable risk
    • Authors: Wei Ding; Chi Zhang, Yong Peng, Ruijie Zeng, Huicheng Zhou, Ximing Cai
      Abstract: This paper addresses how much flood water can be conserved for use after the flood season through the operation of reservoir by taking into account the residual flood control capacity (the difference between flood conveyance capacity and the expected inflow in a lead time). A two‐stage model for dynamic control of the flood limited water level (the maximum allowed water level during the flood season, DC‐FLWL) is established considering forecast uncertainty and acceptable flood risk. It is found that DC‐FLWL is applicable when the reservoir inflow ranges from small to medium levels of the historical records, while both forecast uncertainty and acceptable risk in the downstream affect the feasible space of DC‐FLWL. As forecast uncertainty increases (under a given risk level) or as acceptable risk level decreases (under a given forecast uncertainty level), the minimum required safety margin for flood control increases, and the chance for DC‐FLWL decreases. The derived hedging rules from the modeling framework illustrate either the dominant role of water conservation or flood control or the tradeoff between the two objectives under different levels of forecast uncertainty and acceptable risk. These rules may provide useful guidelines for conserving water from flood, especially in the area with heavy water stress. The analysis is illustrated via a case study with a real‐world reservoir in northeastern China. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:55:10.903017-05:
      DOI: 10.1002/2015WR017127
       
  • On the control of riverbed incision induced by run‐of‐river
           power plant
    • Authors: Simone Bizzi; Quang Dinh, Dario Bernardi, Simona Denaro, Leonardo Schippa, Rodolfo Soncini‐Sessa
      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 fulfil 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 river bed incision and causing infrastructure instability and ecological degradation. We propose a framework that, by combining physically based modelling, surrogate modelling techniques and Multi‐Objective (MO) optimization, allows to include fluvial geomorphology into MO optimization whose main objectives is the maximization of hydropower revenue and the minimization of river bed degradation. The case study is a run‐of‐the‐river power plant on the River Po (Italy). A 1D mobile‐bed hydro‐morphological model simulated the river bed evolution over a ten 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 modelling 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-06-01T03:54:48.068614-05:
      DOI: 10.1002/2014WR016237
       
  • New scaling model for variables and increments with heavy‐tailed
           distributions
    • Authors: Monica Riva; Shlomo P. Neuman, Alberto Guadagnini
      Abstract: Many hydrological (as well as diverse earth, environmental, ecological, biological, physical, social, financial and other) variables, Y, exhibit frequency distributions that are difficult to reconcile with those of their spatial or temporal increments, ΔY. Whereas distributions of Y (or its logarithm) are at times slightly asymmetric with relatively mild peaks and tails, those of ΔY tend to be symmetric with peaks that grow sharper, and tails that become heavier, as the separation distance (lag) between pairs of Y values decreases. No statistical model known to us captures these behaviors of Y and ΔY in a unified and consistent manner. We propose a new, generalized sub‐Gaussian model that does so. We derive analytical expressions for probability distribution functions (pdfs) of Y and ΔY as well as corresponding lead statistical moments. In our model the peak and tails of the ΔY pdf scale with lag in line with observed behavior. The model allows one to estimate, accurately and efficiently, all relevant parameters by analyzing jointly sample moments of Y and ΔY. We illustrate key features of our new model and method of inference on synthetically generated samples and neutron porosity data from a deep borehole. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:31:11.721308-05:
      DOI: 10.1002/2015WR016998
       
  • Self‐healing of cement fractures under dynamic flow of
           CO2‐rich brine
    • Authors: Peilin Cao; Zuleima T. Karpyn, Li Li
      Abstract: Fractures and defects in wellbore cement can lead to increased possibilities of CO2 leakage from abandoned wells during geological carbon sequestration. To investigate the physicochemical response of defective wellbore cement to CO2‐rich brine, we carried out a reactive flow‐through experiment using an artificially fractured cement sample at a length of 224.8 mm. A brine solution with dissolved CO2 at a pH of approximately 3.9 was injected through the sample at a constant rate of 0.0083 cm3/s. Surface optical profilometry analysis and 3D X‐ray microtomography imaging confirmed fracture closure and self‐healing behavior consistent with the measured permeability decrease. Visual inspection of the reacted fracture surface showed the development of reactive patterns mapping the flow velocity field inside the fracture, as well as restricted flow towards the sample outlet. The post‐experiment permeability of the core sample was measured at half of its initial permeability. A reactive transport model was developed with parameters derived from the experiment to further examine property evolution of fractured cement under dynamic flow of CO2‐rich brine. Sensitivity analysis showed that residence time and the size of initial fracture aperture are the key factors controlling the tendency to self‐healing or fracture opening behavior and therefore determine the long‐term integrity of the wellbore cement. Longer residence time and small apertures promote mineral precipitation, fracture closure, and therefore flow restriction. This work also suggests a narrow threshold separating the fracture opening and self‐sealing behavior. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:24:50.834342-05:
      DOI: 10.1002/2014WR016162
       
  • 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
      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 twelve‐gauge network in the Twin Cities region of Minnesota. Upper‐tail quantiles with non‐exceedance 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 [1997]'s 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:24:29.433918-05:
      DOI: 10.1002/2014WR015399
       
  • A harmonic pulse testing method for leakage detection in deep subsurface
           storage formations
    • Authors: Alexander Y. Sun; Jiemin Lu, Susan Hovorka
      Abstract: Detection of leakage in deep geologic storage formations (e.g., carbon sequestration sites) is a challenging problem. This study investigates an easy‐to‐implement, frequency‐domain leakage detection technology based on harmonic pulse testing (HPT). Unlike conventional constant‐rate pressure interference tests, HPT stimulates a reservoir using periodic injection rates. The fundamental principle underlying HPT‐based leakage detection is that leakage modifies a storage system's frequency response function, thus providing clues of system malfunction. During operations, routine HPTs can be conducted at multiple pulsing frequencies to obtain experimental frequency response functions, using which the possible time‐lapse changes are examined. In this work, a set of analytical frequency response solutions is derived for predicting system responses with and without leaks for single‐phase flow systems. Sensitivity studies show that HPT can effectively reveal the presence of leaks. A search procedure is then prescribed for locating the actual leaks using amplitude and phase information obtained from HPT, and the resulting optimization problem is solved using the genetic algorithm. For multiphase flows, the applicability of HPT‐based leakage detection procedure is exemplified numerically using a carbon sequestration problem. Results show that the detection procedure is applicable if the average reservoir conditions in the testing zone stay relatively constant during the tests, which is a working assumption under many other interpretation methods for pressure interference tests. HPT is a cost‐effective tool that only requires periodic modification of a nominal injection rate. Thus it can be incorporated into existing monitoring plans with little additional investment. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:24:12.658719-05:
      DOI: 10.1002/2014WR016567
       
  • Nonstationarity in seasonality of extreme precipitation: A nonparametric
           circular statistical approach and its application
    • Authors: Nirajan Dhakal; Shaleen Jain, Alexander Gray, Michael Dandy, Esperanza Stancioff
      Abstract: Changes in seasonality of extreme storms have important implications for public safety, stormwater infrastructure and, in general, adaptation strategies in a changing climate. While past research on this topic offers some approaches to characterize seasonality, the methods are somewhat limited in their ability to discern the diversity of distributional types for extreme precipitation dates. Herein, we present a comprehensive approach for assessment of temporal changes in the calendar dates for extreme precipitation within a circular statistics framework which entails: a) three measures to summarize circular random variables (traditional approach), b) four nonparametric statistical tests, and c) a new nonparametric circular density method to provide a robust assessment of the nature of probability distribution and changes. Two 30‐year blocks (1951‐1980 and 1981‐2010) of annual maximum daily precipitation from 10 stations across the state of Maine were used for our analysis. Assessment of seasonality based on nonparametric approach indicated nonstationarity; some stations exhibited shifts in significant mode towards Spring season for the recent time period while some other stations exhibited multimodal seasonal pattern for both the time periods. Nonparametric circular density method, used in this study, allows for an adaptive estimation of seasonal density. Despite the limitation of being sensitive to the smoothing parameter, this method can accurately characterize one or more modes of seasonal peaks, as well as pave the way towards assessment of changes in seasonality over time. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:23:57.285014-05:
      DOI: 10.1002/2014WR016399
       
  • Organic contaminant transport and fate in the subsurface: Evolution of
           knowledge and understanding
    • Authors: Hedeff I. Essaid; Barbara A. Bekins, Isabelle M. Cozzarelli
      Abstract: Toxic organic contaminants may enter the subsurface as slightly soluble and volatile non‐aqueous‐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‐ and macro‐scale 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. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:22:46.061386-05:
      DOI: 10.1002/2015WR017121
       
  • Comparison of two stochastic techniques for reliable urban runoff
           prediction by modeling systematic errors
    • Authors: Dario Del Giudice; Roland Löwe, Henrik Madsen, Peter Steen Mikkelsen, Jörg Rieckermann
      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 grey‐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 one 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 on‐line applications. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:22:27.291045-05:
      DOI: 10.1002/2014WR016678
       
  • A forward analysis on the applicability of tracer breakthrough profiles in
           revealing the pore structure of tight gas sandstone and carbonate rocks
    • Authors: Ayaz Mehmani; Yashar Mehmani, Maša Prodanović, Matthew Balhoff
      Abstract: We explore tracer breakthrough profiles (TBP) as a macroscopic property to infer the pore‐space topology of tight gas sandstone and carbonate rocks at the core scale. The following features were modeled via three‐dimensional multiscale networks: microporosity within dissolved grains and pore‐filling clay, cementation in the absence and presence of microporosity (each classified into uniform, pore‐preferred and throat‐preferred modes), layering, vug and micro‐crack inclusion. A priori knowledge of the extent and location of each process was assumed to be known. With the exception of an equal importance of macropores and pore‐filling micropores, TBPs show little sensitivity to the fraction of micropores present. In general, significant sensitivity of the TBPs was observed for uniform and throat‐preferred cementation. Layering parallel to the fluid flow direction had a considerable impact on TBPs whereas layering perpendicular to flow did not. Micro‐crack orientations seemed of minor importance in affecting TBPs. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-30T03:22:10.994499-05:
      DOI: 10.1002/2015WR016948
       
  • Attribution of streamflow trends in snow‐ and glacier melt dominated
           catchments of the Tarim River, Central Asia
    • Authors: Doris Duethmann; Tobias Bolch, Daniel Farinotti, David Kriegel, Sergiy Vorogushyn, Bruno Merz, Tino Pieczonka, Tong Jiang, Buda Su, Andreas Güntner
      Abstract: Observed streamflow of headwater catchments of the Tarim River (Central Asia) increased by about 30% over the period 1957–2004. This study aims at assessing to which extent these streamflow trends can be attributed to changes in air temperature or precipitation. The analysis includes a data‐based approach using multiple linear regression, and a simulation‐based approach using a hydrological model. The hydrological model considers changes in both glacier area and surface elevation. It was calibrated using a multiobjective optimization algorithm with calibration criteria based on glacier mass balance and daily and interannual variations of discharge. The individual contributions to the overall streamflow trends from changes in glacier geometry, temperature, and precipitation were assessed using simulation experiments with a constant glacier geometry, and with detrended temperature and precipitation time series. The results showed that the observed changes in streamflow were consistent with the changes in temperature and precipitation. In the Sari‐Djaz catchment, increasing temperatures and related increase of glacier melt were identified as the dominant driver, while in the Kakshaal catchment, both increasing temperatures and increasing precipitation played a major role. Comparing the two approaches, an advantage of the simulation‐based approach is the fact that it is based on process‐based relationships implemented in the hydrological model instead of statistical links in the regression model. However, data‐based approaches are less affected by model parameter and structural uncertainties and typically fast to apply. A complementary application of both approaches is recommended. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-25T10:59:54.904649-05:
      DOI: 10.1002/2014WR016716
       
  • Estimating stream filtration from a meandering stream under the Robin
           condition
    • Authors: Ching‐Sheng Huang; Hund‐Der Yeh
      Abstract: This study applies the image well theory in estimating the stream depletion rate (SDR) due to pumping near a meandering stream with a clogged streambed treated as the Robin condition. The stream is considered as an irregular boundary represented by discrete nodes. Image wells are arranged along the stream and near those nodes. On the basis of the Theis [1935] solution and the principle of superposition, the solution for the aquifer drawdown subject to the stream can then be expressed as the sum of the Theis solution and a simple series representing the effect of those image wells. The discharge rates of the image wells are determined by solving a system of equations obtained by substituting the drawdown solution into the Robin condition. Quantitative criteria for assessing the applicability of the image well theory are provided. On the basis of the drawdown solution and Darcy's law, the analytical solution for SDR can then be obtained. A finite element solution is also developed to verify the SDR solution. Temporal SDR distributions predicted by both the analytical solution and finite element solution agree well over the entire period except at late time when the stream filtration rate approaches the pumping rate (i.e., SDR≅1). It is found that a meandering stream has a significant effect on SDR compared with a rectilinear one and the effect should be taken into account in estimating SDR. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-25T10:59:38.802644-05:
      DOI: 10.1002/2015WR016975
       
  • Optimal residential water conservation strategies considering related
           energy in California
    • Authors: Alvar Escriva‐Bou; Jay R. Lund, Manuel Pulido‐Velazquez
      Abstract: Although most freshwater resources are used in agriculture, residential water use is a much more energy intensive user. Based on this, we analyze the increased willingness to adopt water conservation strategies if energy cost is included in the customers' utility function. Using a Water‐Energy‐CO2 emissions model for household water end uses and probability distribution functions for parameters affecting water and water‐related energy use in 10 different locations in California, this research introduces a probabilistic two‐stage optimization model considering technical and behavioral decision variables to obtain the most economical strategies to minimize household water and water‐related energy bills and costs given both water and energy price shocks. Results can likely to be an upper bound of household savings for customers with well‐behaved preferences, and show greater adoption rates to reduce energy intensive appliances when energy is accounted, resulting in an overall 24% reduction in indoor water use that represents a 30 percent reduction in water‐related energy use and a 53 percent reduction in household water‐related CO2 emissions. Previous use patterns and water and energy rate structures can affect greatly the potential benefits for customers and so their behavior. Given that water and energy are somewhat complementary goods for customers, we use results of the optimization to obtain own‐price and cross‐price elasticities of residential water use by simulating increases in water and energy prices. While the results are highly influenced by assumptions due to lack of empirical data, the method presented has no precedent in the literature and hopefully will stimulate the collection of additional relevant data. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-24T22:35:38.454644-05:
      DOI: 10.1002/2014WR016821
       
  • Flow resistance in natural, turbulent channel flows: The need for a
           Fluvial Fluid Mechanics
    • Authors: C. J. Keylock
      Abstract: In fluvial environments, feedbacks between flow, bedforms, sediment, and macrophytes results in a complex fluid dynamics. The assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated. I argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future. Recent work on turbulent dissipation, interscale modulation of the dynamics, intermittency and the role of complex forcings is discussed. An agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex, fluvial environments. This leads to the formulation of modeling tools relevant to fluvial fluid mechanics, rather than a reliance on methods developed elsewhere. One avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology. This would result in a non‐equilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested. Although these ideas are raised in the context of a future fluvial fluid mechanics, they are applicable to any situation where turbulent flows are forced in complicated ways. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-24T21:42:12.386485-05:
      DOI: 10.1002/2015WR016989
       
  • Piece‐wise mixed integer programming for optimal sizing of surge
           control devices in water distribution systems
    • Authors: Olya Skulovich; Russell Bent, David Judi, Lina Perelman Sela, Avi Ostfeld
      Abstract: Despite their potential catastrophic impact, transients are often ignored or presented ad hoc when designing water distribution systems. To address this problem, we introduce a new piece‐wise function fitting model that is integrated with mixed integer programming to optimally place and size surge tanks for transient control. The key features of the algorithm are a model‐driven discretization of the search space, a linear approximation non‐smooth system response surface to transients, and a mixed integer linear programming optimization. Results indicate that high quality solutions can be obtained within a reasonable number of function evaluations and demonstrate the computational effectiveness of the approach through two case studies. The work investigates one type of surge control devices (closed surge tank) for a specified set of transient events. The performance of the algorithm relies on the assumption that there exists a smooth relationship between the objective function and tank size. Results indicate the potential of the approach for the optimal surge control design in water systems. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-24T21:24:25.505337-05:
      DOI: 10.1002/2014WR016256
       
  • Numerical investigation of methane and formation fluid leakage along the
           casing of a decommissioned shale‐gas well
    • Authors: A. Nowamooz; J‐M. Lemieux, J. Molson, R. Therrien
      Abstract: Methane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale‐gas well have been assessed with a multi‐phase flow and multi‐component numerical model. The conceptual model used for the simulations assumes that the target shale formation is 200 m thick, overlain by a 750 m thick caprock, which is in turn overlain by a 50 m thick surficial sand aquifer, the 1000 m geological sequence being intersected by a fully‐penetrating borehole. This succession of geological units is representative of the region targeted for shale gas exploration in the St. Lawrence Lowlands (Québec, Canada). The simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer. The leakage of fluids can subsequently lead to the contamination of groundwater resources and/or, in the case of methane migration to ground surface, to an increase in greenhouse‐gas emissions. The minimum reported surface casing vent flow (measured at ground level) for shale gas wells in Quebec (0.01 m3/day) is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration. The simulations suggest that an adequately cemented borehole (with a casing annulus permeability kc ≤ 1 mD) can prevent methane and brine leakage over a time scale of up to 100 years. However, a poorly cemented borehole (kc ≥ 10 mD) could yield methane leakage rates at the base of an aquifer ranging from 0.04 m³/day to more than 100 m³/day, depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation. These values are compatible with surface casing vent flows reported for shale gas wells in the St. Lawrence Lowlands (Quebec, Canada). The simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years, depending on cementation quality and hydrodynamic properties of the casing annulus. Simulated long‐term brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10−5 m3/day (10 ml/day) to 10−3 m3/day (1 l/day). Based on scoping calculations with a well‐mixed aquifer model, these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration by 1 mg/l, which is significantly below the commonly recommended aesthetic objective of 250 mg/l for chloride. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-21T18:19:00.537751-05:
      DOI: 10.1002/2014WR016146
       
  • On kinematics and flow velocity prediction in step‐pool channels
    • Authors: V. D'Agostino; T. Michelini
      Abstract: This paper verifies methods for the prediction of mean flow velocity at the reach scale in mountain streams, investigating the kinematics of a series of two small‐scale artificial step‐pool sequences and a transitional reach between plane‐bed and step‐pool under well‐controlled hydraulic conditions, and improving the estimation of the energy expenditure between the step crest and the downstream pool. Experimental data were collected using three fish ladder reaches with slopes between 2.6 and 10%. Four types of field measurements were conducted: topographical surveys to extract the thalweg profiles and cross‐sectional geometry of reference cross sections; grain size analyses of the bed surface; steady state runs with a given flow rate (0.005‐0.234 m3/s), and surveying of the water profile in the most significant cross sections. The following main conclusions were reached: i) The dominance of spill resistance at the lowest discharge (pool water depth‐step height ratios of 0.4) causes primary dimensionless head losses of up to 80%, and these losses progressively decrease to approximately 40% when the water discharge and related pool water depth submerge the upstream step height. A specific predictive equation for the head loss was calibrated and verified via data from the Rio Cordon. ii) The verification of literature‐sourced equations to predict the reach‐averaged flow velocity provided suitable results for several of these equations indicating that the use of a specific step‐pool equation does not appear to be crucial to achieving accurate predictions. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-21T18:17:05.574305-05:
      DOI: 10.1002/2014WR016631
       
  • Colloid particle size‐dependent dispersivity
    • Authors: Constantinos V. Chrysikopoulos; Vasileios E. Katzourakis
      Abstract: Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection‐dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 48 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters, and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water saturated porous media. The experimental data set collected in this study demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity. The dispersivity values determined in this laboratory study were compared with 380 dispersivity values from earlier laboratory‐ and field‐scale solute, colloid and biocolloid transport studies published in the literature. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-21T18:02:46.279919-05:
      DOI: 10.1002/2014WR016094
       
  • Microbubble transport in water‐saturated porous media
    • Authors: Y. Ma; X.‐Z Kong, A. Scheuermann, SA. Galindo‐Torres, D. Bringemeier, L. Li
      Abstract: Laboratory experiments were conducted to investigate flow of discrete microbubbles through a water‐saturated porous medium. During the experiments, bubbles, released from a diffuser, moved upward through a quasi‐2D flume filled with transparent water‐based gelbeads and formed a distinct plume that could be well registered by a calibrated camera. Outflowing bubbles were collected on the top of the flume using volumetric burettes for flux measurements. We quantified the scaling behaviors between the gas (bubble) release rates and various characteristic parameters of the bubble plume, including plume tip velocity, plume width and breakthrough time of the plume front. The experiments also revealed circulations of ambient pore water induced by the bubble flow. Based on a simple momentum exchange model, we showed that the relationship between the mean pore water velocity and gas release rate is consistent with the scaling solution for the bubble plume. These findings have important implications for studies of natural gas emission and air sparging, as well as fundamental research on bubble transport in porous media. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-20T05:46:56.287578-05:
      DOI: 10.1002/2014WR016019
       
  • A spatiotemporal precipitation generator based on a censored latent
           Gaussian field
    • Authors: Anastassia Baxevani; Jan Lennatsson
      Abstract: A daily stochastic spatio‐temporal precipitation generator that yields precipitation realisations that are quantitatively consistent, is described. The methodology relies on a latent Gaussian field that drives both the occurrence and intensity of the precipitation process. For the precipitation intensity the marginal distributions, which are space and time dependent, are described by a composite model of a gamma‐distribution for observations below some threshold with a generalized Pareto distribution modeling the excesses above the threshold. Model parameters are estimated from data and extrapolated to locations and times with no direct observations using linear regression of position covariates. One advantage of such a model is that stochastic generator parameters are readily available at any location and time of the year inside the stationarity regions. The methodology is illustrated for a network of 12 locations in Sweden. Performance of the model is judged through its ability to accurately reproduce a series of spatial dependence measures and weather indices. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-20T05:33:05.018448-05:
      DOI: 10.1002/2014WR016455
       
  • On the optimal design of experiments for conceptual and predictive
           discrimination of hydrologic system models
    • Authors: C.P. Kikuchi; T.P.A. Ferre, J.A. Vrugt
      Abstract: Experimental design and data collection constitute two main steps of the iterative research cycle (aka the scientific method). To help evaluate competing hypotheses, it is critical to ensure that the experimental design is appropriate and maximizes information retrieval from the system of interest. Scientific hypothesis testing is implemented by comparing plausible model structures (conceptual discrimination) and sets of predictions (predictive discrimination). This research presents a new Discrimination‐Inference (DI) methodology to identify prospective datasets highly suitable for either conceptual or predictive discrimination. The DI methodology uses preposterior estimation techniques to evaluate the expected change in the conceptual or predictive probabilities, as measured by the Kullback‐Leibler divergence. We present two case studies with increasing complexity to illustrate implementation of the DI for maximizing information withdrawal from a system of interest. The case studies show that highly informative datasets for conceptual discrimination are in general those for which between‐model (conceptual) uncertainty is large relative to the within‐model (parameter) uncertainty, and the redundancy between individual measurements in the set is minimized. The optimal dataset differs if predictive, rather than conceptual, discrimination is the experimental design objective. Our results show that DI analyses highlight measurements that can be used to address critical uncertainties related to the prediction of interest. Finally, we find that the optimal dataset for predictive discrimination is sensitive to the predictive grouping definition in ways that are not immediately apparent from inspection of the model structure and parameter values. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-20T05:18:47.874237-05:
      DOI: 10.1002/2014WR016795
       
  • Landscape reorganization under changing climatic forcing: Results from an
           experimental landscape
    • Authors: Arvind Singh; Liam Reinhardt, Efi Foufoula‐Georgiou
      Abstract: Understanding how landscapes respond to climate dynamics in terms of macro‐scale (average topographic features) and micro‐scale (landform re‐organization) is of interest both for deciphering past climates from today's landscapes and for predicting future landscapes in view of recent climatic trends. Although several studies have addressed macro‐scale response, only a few have focused on quantifying smaller‐scale basin re‐organization. To that goal, a series of controlled laboratory experiments were conducted where a self‐organized complete drainage network emerged under constant precipitation and uplift dynamics. Once steady state was achieved, the landscape was subjected to a five‐fold increase in precipitation (transient state). Throughout the evolution, high resolution spatio‐temporal topographic data in the form of digital elevation models were collected. The steady state landscape was shown to possess three distinct geomorphic regimes (unchannelized hillslopes, debris‐dominated channels, and fluvially‐dominated channels). During transient state, landscape re‐organization was observed to be driven by hillslopes via accelerated erosion, ridge lowering, channel widening, and reduction of basin relief as opposed to channel base‐level reduction. Quantitative metrics on which these conclusions were based included slope‐area curve, correlation analysis of spatial and temporal elevation increments, and wavelet spectral analysis of the evolving landscapes. Our results highlight that landscape re‐organization in response to increased precipitation seems to follow “an arrow of scale”: major elevation change initiates at the hillslope scale driving erosional regime change at intermediate scales and further cascading to geomorphic changes at the channel scale as time evolves. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-20T04:54:27.605226-05:
      DOI: 10.1002/2015WR017161
       
  • Detection and attribution of urbanization effect on flood extremes using
           nonstationary flood frequency models
    • Authors: I. Prosdocimi; T. R. Kjeldsen, J. D. Miller
      Abstract: This study investigates whether long‐term changes in observed series of high flows can be attributed to changes in land‐use via non‐stationary flood frequency analyses. A point process characterization of threshold exceedances is used, which allows for direct inclusion of covariates in the model; as well as a non‐stationary model for block maxima series. In particular, changes in annual, winter and summer block maxima and peaks over threshold extracted from gauged instantaneous flows records in two hydrologically similar catchments located in close proximity to one another in northern England are investigated. The study catchment is characterized by large increases in urbanization levels in recent decades, while the paired control catchment has remained undeveloped during the study period (1970‐2010). To avoid the potential confounding effect of natural variability, a covariate which summarize key climatological properties is included in the flood frequency model. A significant effect of the increasing urbanization levels on high flows is detected, in particular in the summer season. Point process models appear to be superior to block maxima models in their ability to detect the effect of the increase in urbanization levels on high flows. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-20T04:35:55.179548-05:
      DOI: 10.1002/2015WR017065
       
  • Probabilistic inference of multi‐Gaussian fields from indirect
           hydrological data using circulant embedding and dimensionality reduction
    • Authors: Eric Laloy; Niklas Linde, Diederik Jacques, Jasper A. Vrugt
      Abstract: We present a Bayesian inversion method for the joint inference of high‐dimensional multi‐Gaussian hydraulic conductivity fields and associated geostatistical parameters from indirect hydrological data. We combine Gaussian process generation via circulant embedding to decouple the variogram from grid cell specific values, with dimensionality reduction by interpolation to enable Markov chain Monte Carlo (MCMC) simulation. Using the Matérn variogram model, this formulation allows inferring the conductivity values simultaneously with the field smoothness (also called Matérn shape parameter) and other geostatistical parameters such as the mean, sill, integral scales and anisotropy direction(s) and ratio(s). The proposed dimensionality reduction method systematically honors the underlying variogram and is demonstrated to achieve better performance than the Karhunen‐Loéve expansion. We illustrate our inversion approach using synthetic (error corrupted) data from a tracer experiment in a fairly heterogeneous 10,000‐dimensional 2D conductivity field. A 40‐times reduction of the size of the parameter space did not prevent the posterior simulations to appropriately fit the measurement data and the posterior parameter distributions to include the true geostatistical parameter values. Overall, the posterior field realizations covered a wide range of geostatistical models, questioning the common practice of assuming a fixed variogram prior to inference of the hydraulic conductivity values. Our method is shown to be more efficient than sequential Gibbs sampling (SGS) for the considered case study, particularly when implemented on a distributed computing cluster. It is also found to outperform the method of anchored distributions (MAD) for the same computational budget. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-19T06:23:35.672473-05:
      DOI: 10.1002/2014WR016395
       
  • The emergence of topographic steady state in a perpetually dynamic
           self‐organized critical landscape
    • Authors: Liam Reinhardt; Michael A. Ellis
      Abstract: We conducted a series of four physical modelling 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 SOC (self‐organized critical) 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 two‐fold 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 whilst topography remains highly dynamic at smaller length‐scales. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-18T04:02:03.445339-05:
      DOI: 10.1002/2014WR016223
       
  • Water conservation and hydrological transitions in cities in the United
           States
    • Authors: George M. Hornberger; David J. Hess, Jonathan Gilligan
      Abstract: Cities across the world have had to diversify and expand their water‐supply systems in response to demand growth, groundwater depletion and pollution, and instability and inadequacy of regional surface freshwater sources. In the U.S., these problems plague not only the arid Western cities but increasingly cities in the Eastern portions of the country. Although cities continue to seek out new sources of water via Promethean projects of long‐distance supply systems, desalinization plants, and the recharge of aquifers with surface water, they also pursue water conservation because of its low cost and other benefits. We examine water conservation as a complex sociotechnical system comprising interactions of political, sociodemographic, economic, and hydroclimatological factors. We provide quantitative data on the factors that affect more and less advanced transitions in water conservation regimes, and we show that water stress and other hydrological data can only partially predict the transition. We also provide qualitative case studies to identify institutional and political barriers to more advanced water conservation regimes. This interdisciplinary, mixed‐methods approach typifies the need for knowledge that informs hydrologists about how their research may or may not be adopted by decision‐makers. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-18T03:57:44.192176-05:
      DOI: 10.1002/2015WR016943
       
  • An entropy‐based measure of hydrologic complexity and its
           applications
    • Authors: Aldrich Castillo; Fabio Castelli, Dara Entekhabi
      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 10° – 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 inter‐basin 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 baseflow index; while H is inversely related to relief ratio. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-15T21:12:27.098615-05:
      DOI: 10.1002/2014WR016035
       
  • Effects of salinity variations on pore water flow in salt marshes
    • Authors: Chengji Shen; Guangqiu Jin, Pei Xin, Jun Kong, Ling Li
      Abstract: Spatial and temporal salinity variations in surface water and pore water commonly exist in salt marshes under the combined influence of tidal inundation, precipitation, evapotranspiration and inland freshwater input. Laboratory experiments and numerical simulations were conducted to investigate how density gradients associated with salinity variations affect pore‐water flow in the salt marsh system. The results showed that upward salinity (density) gradients could lead to flow instability and the formation of salt fingers. These fingers, varying in size with the distance from the creek, modified significantly the pore‐water flow field, especially in the marsh interior. While the flow instability enhanced local salt transport and mixing considerably, the net effect was small, causing only a slight increase in the overall mass exchange across the marsh surface. In contrast, downward salinity gradients exerted less influence on the pore‐water flow in the marsh soil and slightly weakened the surface water and groundwater exchange across the marsh surface. Numerical simulations revealed similar density effects on pore‐water flow at the field scale under realistic conditions. These findings have important implications for studies of marsh soil conditions concerning plant growth as well as nutrient exchange between the marsh and coastal marine system. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-15T20:53:43.627826-05:
      DOI: 10.1002/2015WR016911
       
  • What time scales are important for monitoring tidally influenced submarine
           groundwater discharge? Insights from a salt marsh
    • Authors: Alicia M. Wilson; Tyler Evans, Willard Moore, Charles A. Schutte, Samantha B. Joye
      Abstract: Submarine groundwater discharge (SGD) varies significantly across time scales ranging from hours to years, but studies that allow quantitative comparisons between different time scales are few. Most of these studies have focused on beach settings, where the combined variations in fresh and saline SGD can be difficult to interpret. We calculated variations in saline SGD based on a 1‐year record of hydraulic head in a salt marsh, where we could isolate variations in saline, tidally‐driven SGD. Observed SGD varied by an order of magnitude over the course of the year. Groundwater discharge was proportional to tidal amplitude and varied by at least a factor of two between spring and neap tides. Monthly average SGD was inversely proportional to average sea level; it increased by nearly a factor of two as sea level declined by ∼50 cm from late summer to late winter. This variation was far larger than that predicted by analytic models, owing to the flat topography and inundation of the marsh platform. The effect of short‐term (days) variations in sea level associated with wind events and storms was small in comparison. SGD is probably proportional to tidal amplitude in nearly all coastal settings, including beaches. Seasonal variations in sea level may not affect the volume of SGD as significantly in coastal settings where the slope of the intertidal zone is relatively constant, but such variations have the potential to strongly affect the composition of SGD. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-15T20:52:52.08277-05:0
      DOI: 10.1002/2014WR015984
       
  • Mechanisms driving the seasonality of catchment‐scale nitrate
           export: Evidence for riparian ecohydrologic controls
    • Authors: Jonathan M. Duncan; Lawrence E. Band, Peter M. Groffman, Emily S. Bernhardt
      Abstract: Considerable variability in the seasonal patterns of streamwater nitrate (NO3‐) has been observed in forested watersheds throughout the world. While many forested headwater catchments exhibit winter and early spring peaks in NO3‐ concentrations, several watersheds have peak concentrations during the summer months. Pond Branch, a headwater catchment in Maryland monitored for over 10 years, exhibits recurrent and broad summer peaks in both NO3‐ concentrations and watershed export. Higher NO3‐ export from June to September is particularly surprising, given that these summer months typically have the year's lowest discharge. A key challenge is identifying the source(s) of NO3‐ and the mechanism(s) by which it is transported to the watershed outlet during the summer. In this study, we assessed multiple hypotheses (not mutually exclusive) that could account for the seasonal trend including proximal controls of groundwater‐surface water interactions, in‐stream processes, and riparian groundwater‐N cycling interactions, as well as two distal controls: geochemical weathering and senescence of riparian vegetation. A combination of long‐term weekly and limited duration high‐frequency sensor data reveal the importance of riparian ecohydrologic processes during baseflow. In this watershed, patterns of seasonal streamwater NO3‐ concentrations and fluxes depend fundamentally on interactions between groundwater dynamics and nitrogen (N) cycling in the riparian zone. Groundwater tables control nitrification‐denitrification dynamics as well as hydrologic transport. Our results suggest that in many watersheds, a more sophisticated exploration of NO3‐ production and NO3‐ transport mechanisms is required to identify critical points in the landscape and over time that disproportionately drive patterns of watershed NO3‐ export. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-14T17:31:06.903974-05:
      DOI: 10.1002/2015WR016937
       
  • Probabilistic human health risk assessment of degradation‐related
           chemical mixtures in heterogeneous aquifers: Risk statistics, hot spots,
           and preferential channels
    • Authors: Christopher V. Henri; Daniel Fernàndez‐Garcia, Felipe P. J. de Barros
      Abstract: The increasing presence of toxic chemicals released in the subsurface has led to a rapid growth of social concerns and the need to develop and employ models that can predict the impact of groundwater contamination on human health risk under uncertainty. Monitored natural attenuation is a common remediation action in many contamination cases. However, natural attenuation can lead to the production of daughter species of distinct toxicity that may pose challenges in pollution management strategies. The actual threat that these contaminants pose to human health depends on the interplay between the complex structure of the geological media and the toxicity of each pollutant byproduct. This work addresses human health risk for chemical mixtures resulting from the sequential degradation of a contaminant (such as a chlorinated solvent) under uncertainty through high resolution three‐dimensional numerical simulations. We systematically investigate the interaction between aquifer heterogeneity, flow connectivity, contaminant injection model and chemical toxicity in the probabilistic characterization of health risk. We illustrate how chemical‐specific travel times control the regime of the expected risk and its corresponding uncertainties. Results indicate conditions where preferential flow paths can favor the reduction of the overall risk of the chemical mixture. The overall human risk response to aquifer connectivity is shown to be non‐trivial for multi‐species transport. This non‐triviality is a result of the interaction between aquifer heterogeneity and chemical toxicity. To quantify the joint effect of connectivity and toxicity in health risk, we propose a toxicity‐based Damköhler number. Furthermore, we provide a statistical characterization in terms of low‐order moments and the probability density function of the individual and total risks. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:19:20.98095-05:0
      DOI: 10.1002/2014WR016717
       
  • The emergence of hydrogeophysics for improved understanding of subsurface
           processes over multiple scales
    • Authors: Andrew Binley; Susan S. Hubbard, Johan A. Huisman, André Revil, David A. Robinson, Kamini Singha, Lee D. Slater
      Abstract: Geophysics provides a multi‐dimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here, we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of “hydrogeophysics” arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field‐based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time‐lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of “biogeophysics”. Early hydrogeophysical studies often concentrated on relatively small ‘plot‐scale' experiments. More recently, however, the translation to larger‐scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:19:04.38531-05:0
      DOI: 10.1002/2015WR017016
       
  • Exploring scale‐dependent ecohydrological responses in a large
           endorheic river basin through integrated surface water‐groundwater
           modeling
    • Authors: Yong Tian; Yi Zheng, Chunmiao Zheng, Honglang Xiao, Wenjie Fan, Songbing Zou, Bin Wu, Yingying Yao, Aijing Zhang, Jie Liu
      Abstract: Ecohydrological processes in a water‐limited environment are sensitive to both climate conditions and human activities, but the response mechanisms have rarely been explored for large endorheic river basins via an integrated modeling approach. This study established an integrated surface water‐groundwater model for the Heihe River Basin (HRB), China's second largest endorheic river basin, using GSFLOW as the modeling platform. Evapotranspiration (ET) and Leaf Area Index (LAI) data independently derived from remote sensing products were compared and correlated, respectively, with the modeling results. Scale‐dependent interrelationships among ecological, hydrological and human‐impact (i.e., diversion and pumping) variables were revealed through multiple regression analyses. Major study findings include: (1) the independent ET and LAI data enabled the modeler to crosscheck the modeling results from a unique angle not possible with conventional groundwater and streamflow observations; (2) controlling factors for the temporal variability of ET and LAI exhibit notable scale‐dependence, reflecting distinctive climate and human impacts on different land covers; and (3) there exists an intricate linkage between the hydrological regimes in the lower HRB and the middle HRB, essentially equivalent to a tradeoff between the ecosystem health of the lower HRB and the sustainable development of the middle HRB. Overall, the integrated modeling assisted by the independent ET and LAI data has provided a coherent understanding on the regional water cycle, and led to new insights on tackling the existing water conflicts in HRB. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:16:45.601888-05:
      DOI: 10.1002/2015WR016881
       
  • Model‐based analysis of the influence of catchment properties on
           hydrologic partitioning across five mountain headwater subcatchments
    • Authors: Christa Kelleher; Thorsten Wagener, Brian McGlynn
      Abstract: Ungauged headwater basins are an abundant part of the river network, but dominant influences on headwater hydrologic response remain difficult to predict. To address this gap, we investigated the ability of a physically‐based watershed model (the Distributed Hydrology‐Soil‐Vegetation Model) to represent controls on metrics of hydrologic partitioning across five adjacent headwater sub‐catchments. The five study sub‐catchments, located in Tenderfoot Creek Experimental Forest in central Montana, have similar climate but variable topography and vegetation distribution. This facilitated a comparative hydrology approach to interpret how parameters that influence partitioning, detected via global sensitivity analysis, differ across catchments. Model parameters were constrained a priori using existing regional information and expert knowledge. Influential parameters were compared to perceptions of catchment functioning and its variability across sub‐catchments. Despite between‐catchment differences in topography and vegetation, hydrologic partitioning across all metrics and all sub‐catchments was sensitive to a similar subset of snow, vegetation, and soil parameters. Results also highlighted one sub‐catchment with low certainty in parameter sensitivity, indicating that the model poorly represented some complexities in this sub‐catchment likely because an important process is missing or poorly characterized in the mechanistic model. For use in other basins, this method can assess parameter sensitivities as a function of the specific ungauged system to which it is applied. Overall, this approach can be employed to identify dominant modeled controls on catchment response and their agreement with system understanding. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:16:16.052055-05:
      DOI: 10.1002/2014WR016147
       
  • Validation of hydraulic tomography in an unconfined aquifer: A controlled
           sandbox study
    • Authors: Zhanfeng Zhao; Walter A. Illman, Tian.‐ Chyi, J. Yeh, Steven J. Berg, Deqiang Mao
      Abstract: In this study, we demonstrate the effectiveness of hydraulic tomography (HT) that considers variably saturated flow processes in mapping the heterogeneity of both the saturated and unsaturated zones in a laboratory unconfined aquifer. The successive linear estimator (SLE) developed by Mao et al., (2013c) for interpreting HT in unconfined aquifers is utilized to obtain tomograms of hydraulic conductivity (K), specific storage (Ss), and the unsaturated zone parameters [pore size parameter (α) and saturated water content (θs)] for the Gardner‐Russo's model. The estimated tomograms are first evaluated by visually comparing them with stratigraphy visible in the sandbox. Results reveal that the HT analysis is able to accurately capture the location and extent of heterogeneity including high and low K layers within the saturated and unsaturated zones, as well as reasonable distribution patterns of α and θs for the Gardner‐Russo's model. We then validate the estimated tomograms through predictions of drawdown responses of pumping tests not used during the inverse modeling effort. The strong agreement between simulated and observed drawdown curves obtained by pressure transducers and tensiometers demonstrates the robust performance of HT that considers variably saturated flow processes in unconfined aquifers and the unsaturated zone above it. In addition, compared to the case using the homogeneous assumption, HT results, as expected, yield significantly better predictions of drawdowns in both the saturated and unsaturated zones. This comparison further substantiates the unbiased and minimal variance of HT analysis with the SLE algorithm. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:15:44.89663-05:0
      DOI: 10.1002/2015WR016910
       
  • Measurement and simulation of subsurface tracer migration to tile drains
           in low‐permeability, macroporous soil
    • Authors: Joshua M. Bishop; Michael V. Callaghan, Edwin E. Cey, Larry R. Bentley
      Abstract: Multi‐year monitoring and simulation of a conservative tracer was used in this study to investigate preferential flow and macropore‐matrix interactions in low permeability, macroporous soil. 2,6‐Difluorobenzoic acid (DFBA) tracer was applied to a 20 × 20m drip irrigated test plot situated over two tile drains. Tracer movement over the 2009 and 2010 field seasons was monitored using tile drain effluent, suction lysimeters, monitoring wells, and soil cores. Despite similar volumes of water application to the plot in each season, 10 times more water and 14 times more DFBA were captured by the drains in 2010 due to wetter regional hydrologic conditions. The importance of preferential flow along macropores was shown by rapid DFBA breakthrough to the tile (
      PubDate: 2015-05-13T17:15:17.284857-05:
      DOI: 10.1002/2014WR016310
       
  • Temporal dynamics of catchment transit times from stable isotope data
    • Authors: Julian Klaus; Kwok P. Chun, Kevin J. McGuire, Jeffrey J. McDonnell
      Abstract: Time variant catchment transit time distributions are fundamental descriptors of catchment function but yet not fully understood, characterized, and modeled. Here we present a new approach for use with standard runoff and tracer datasets that is based on tracking of tracer and age information and time‐variant catchment mixing. Our new approach is able to deal with non‐stationarity of flow paths and catchment mixing, and an irregular shape of the transit time distribution. The approach extracts information on catchment mixing from the stable isotope time series instead of prior assumptions of mixing or the shape of transit time distribution. We first demonstrate proof of concept of the approach with artificial data; the Nash‐Sutcliffe efficiencies in tracer and instantaneous transit times were >0.9. The model provides very accurate estimates of time variant transit times when the boundary conditions and fluxes are fully known. We then tested the model with real rainfall‐runoff flow and isotope tracer time series from the HJ Andrews Watershed 10 (WS10) in Oregon. Model efficiencies were 0.37 for the 18O modeling for a 2‐year time series; the efficiencies increased to 0.86 for the second year underlying the need of long time tracer time series with a long overlap of tracer input and output. The approach was able to determine time variant transit time of WS10 with field data and showed how it follows the storage dynamics and related changes in flow paths where wet periods with high flows resulted in clearly shorter transit times compared to dry low flow periods. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T17:14:47.118425-05:
      DOI: 10.1002/2014WR016247
       
  • Geomechanics of subsurface water withdrawal and injection
    • Authors: Giuseppe Gambolati; Pietro Teatini
      Abstract: Land subsidence and uplift, ground ruptures, and induced seismicity are the principal geomechanic effects of groundwater withdrawal and injection. The major environmental consequence of groundwater pumping is anthropogenic land subsidence. The first observation concerning land settlement linked to subsurface processes was made in 1926 by the American geologists Pratt and Johnson, who wrote that “the cause of subsidence is to be found in the extensive extraction of fluid from beneath the affected area”. Since then, impressive progress has been made in terms of: a) recognizing the basic hydrologic and geomechanic principles underlying the occurrence; b) measuring aquifer compaction and ground displacements, both vertical and horizontal; c) modelling and predicting the past and future event; d) mitigating environmental impact through aquifer recharge and/or surface water injection. The first milestone in the theory of pumped aquifer consolidation was reached in 1923 by Terzaghi, who introduced the principle of “effective intergranular stress”. In the early 70s the emerging computer technology facilitated development of the first mathematical model of the subsidence of Venice, made by Gambolati and Freeze. Since then the comprehension, measuring, and simulation of the occurrence have improved dramatically. More challenging today are the issues of ground ruptures and induced/triggered seismicity, which call for a shift from the classical continuum approach to discontinuous mechanics. Although well‐known for decades, anthropogenic land subsidence is still threatening large urban centres and deltaic areas worldwide, such as Bangkok, Jakarta, and Mexico City, at rates in the order of 10 cm/yr. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-13T04:22:52.466081-05:
      DOI: 10.1002/2014WR016841
       
  • The spatial and temporal evolution of contributing areas
    • Authors: Fabian Nippgen; Brian L. McGlynn, Ryan E. Emanuel
      Abstract: Predicting runoff source areas and how they change through time is a challenge in hydrology. Topographically induced lateral water redistribution and water removal through evapotranspiration lead to spatially and temporally variable patterns of watershed water storage. These dynamic storage patterns combined with threshold mediation of saturated subsurface throughflow lead to runoff source areas that are dynamic through time. To investigate these processes and their manifestation in watershed runoff, we developed and applied a parsimonious but spatially distributed model (WECOH ‐ Watershed ECOHydrology). Evapotranspiration was measured via an eddy‐covariance tower located within the catchment and disaggregated as a function of vegetation structure. This modeling approach reproduced the stream hydrograph well and was internally consistent with observed watershed runoff patterns and behavior. We further examined the spatial patterns of water storage and their evolution through time by building on past research focused on landscape hydrologic connectivity. The percentage of landscape area connected to the stream network ranged from less than 1% during the fall and winter baseflow period to 71% during snowmelt. Over the course of the two‐year study period 90% of the watershed areas were connected to the stream network for at least one day, leaving 10% of area that never became connected. Runoff source areas during the event shifted from riparian dominated runoff to areas at greater distances from the stream network when hillslopes became connected. Our modeling approach elucidates and enables quantification and prediction of watershed active areas and those active areas connected to the stream network through time. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-12T17:54:50.196832-05:
      DOI: 10.1002/2014WR016719
       
  • Optimizing hydrological consistency by incorporating hydrological
           signatures into model calibration objectives
    • Authors: Mahyar Shafii; Bryan A. Tolson
      Abstract: The simulated outcome of a calibrated hydrologic model should be hydrologically consistent with the measured response data. Hydrologic modelers typically calibrate models to optimize residual‐based goodness‐of‐fit measures, e.g., the Nash‐Sutcliffe Efficiency measure, and then evaluate the obtained results with respect to hydrological signatures, e.g., the flow duration curve indices. The literature indicates that the consideration of a large number of hydrologic signatures has not been addressed in a full multi‐objective optimization context. This research develops a model calibration methodology to achieve hydrological consistency using goodness‐of‐fit measures, many hydrological signatures, as well as a level of acceptability for each signature. The proposed framework relies on a scoring method that transforms any hydrological signature to a calibration objective. These scores are used to develop the hydrological consistency metric, which is maximized to obtain hydrologically consistent parameter sets during calibration. This consistency metric is implemented in different signature‐based calibration formulations that adapt the sampling according to hydrologic signature values. These formulations are compared with the traditional formulations found in the literature for seven case studies. The results reveal that Pareto dominance‐based multi‐objective optimization yields the highest level of consistency among all formulations. Furthermore, it is found that the choice of optimization algorithms does not affect the findings of this research. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-12T17:51:47.119248-05:
      DOI: 10.1002/2014WR016520
       
  • Isotope‐based Fluvial Organic Carbon (ISOFLOC) Model: Model
           Formulation, Sensitivity and Evaluation
    • Authors: William I. Ford; James F. Fox
      Abstract: Watershed‐scale carbon budgets remain poorly understood, in part due to inadequate simulation tools to assess in‐stream carbon fate and transport. A new numerical model termed ISOtope‐based FLuvial Organic Carbon (ISOFLOC) is formulated to simulate the fluvial organic carbon budget in watersheds where hydrologic, sediment transport, and biogeochemical processes are coupled to control benthic and transported carbon composition and flux. One ISOFLOC innovation is the formulation of new stable carbon isotope model subroutines that include isotope fractionation processes in order to estimate carbon isotope source, fate, and transport. A second innovation is the coupling of transfers between carbon pools, including algal particulate organic carbon, fine particulate and dissolved organic carbon, and particulate and dissolved inorganic carbon, to simulate the carbon cycle in a comprehensive manner beyond that of existing watershed water quality models. ISOFLOC was tested and verified in a low‐gradient, agriculturally‐impacted stream. Results of a global sensitivity analysis suggested the isotope response variable had unique sensitivity to the coupled interaction between fluvial shear resistance of algal biomass and the concentration of dissolved inorganic carbon. Model calibration and validation suggested good agreement at event, seasonal, and annual timescales. Multi‐objective uncertainty analysis suggested inclusion of the carbon stable isotope routine reduced uncertainty by 80% for algal particulate organic carbon flux estimates. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-12T17:47:35.39123-05:0
      DOI: 10.1002/2015WR016999
       
  • Identifying multiple timescale rainfall controls on Mojave Desert
           ecohydrology using an integrated data and modeling approach for Larrea
           tridentata
    • Authors: Gene‐Hua Crystal Ng; David R. Bedford, David M. Miller
      Abstract: The perennial shrub Larrea tridentata is widely successful in North American warm deserts but is also susceptible to climatic perturbations. Understanding its response to rainfall variability requires consideration of multiple timescales. We examine intra‐annual to multi‐year relationships using model simulations of soil moisture and vegetation growth over 50 years in the Mojave National Preserve in southeastern California (USA). Ecohydrological model parameters are conditioned on field and remote sensing data using an ensemble Kalman filter. Although no specific periodicities were detected in the rainfall record, simulated leaf‐area‐index exhibits multi‐year dynamics that are driven by multi‐year (∼3‐years) rains, but with up to a 1‐year delay in peak response. Within a multi‐year period, Larrea tridentata is more sensitive to winter rains than summer. In the most active part of the root zone (above ∼80 cm), >1‐year average soil moisture drives vegetation growth, but monthly average soil moisture is controlled by root uptake. Moisture inputs reach the lower part of the root zone (below ∼80 cm) infrequently, but once there they can persist over a year to help sustain plant growth. Parameter estimates highlight efficient plant physiological properties facilitating persistent growth and high soil hydraulic conductivity allowing deep soil moisture stores. We show that soil moisture as an ecological indicator is complicated by bidirectional interactions with vegetation that depend on timescale and depth. Under changing climate, Larrea tridentata will likely be relatively resilient to shorter‐term moisture variability but will exhibit higher sensitivity to shifts in seasonal to multi‐year moisture inputs. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-09T02:50:34.407174-05:
      DOI: 10.1002/2015WR017240
       
  • Changes in dissolved organic carbon and total dissolved nitrogen fluxes
           across subtropical forest ecosystems at different successional stages
    • Authors: Junhua Yan; Kun Li, Wantong Wang, Deqiang Zhang, Guoyi Zhou
      Abstract: Lateral transports of carbon and nitrogen are important processes linking terrestrial ecosystems and aquatic systems. Most previous studies made in temperate forests found that fluxes of carbon and nitrogen by runoff water varied in different forests, but few studies have been made in subtropical forests. This study was to investigate dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) fluxes at the catchment scale along a subtropical forest succession gradient from pine forest (pioneer) to coniferous and broadleaved mixed forest (transitional) to broadleaved forest (mature). Our results showed that DOC concentration significantly decreased (p
      PubDate: 2015-05-09T02:49:46.038846-05:
      DOI: 10.1002/2015WR016912
       
  • Analyzing the effects of excess rainfall properties on the scaling
           structure of peak discharges: Insights from a mesoscale river basin
    • Authors: Tibebu B. Ayalew; Witold F. Krajewski, Ricardo Mantilla
      Abstract: Key theoretical and empirical results from the past two decades have established that peak discharges resulting from a single rainfall‐runoff event in a nested watershed exhibit a power‐law, or scaling, relation to drainage area and that the parameters of the power‐law relation, henceforth referred to as the flood scaling exponent and intercept, change from event to event. To date, only two studies have been conducted using empirical data, both using data from the 21 km2 Goodwin Creek Experimental Watershed that is located in Mississippi, in an effort to uncover the physical processes that control the event‐to‐event variability of the flood scaling parameters. Our study expands the analysis to the mesoscale Iowa River basin (A=32,400 km2), which is located in eastern Iowa, and provides additional insights into the physical processes that control the flood scaling parameters. Using 51 rainfall‐runoff events that we identified over the 12 year period since 2002, we show how the duration and depth of excess rainfall, which is the portion of rainfall that contributes to direct runoff, control the flood scaling exponent and intercept. Moreover, using a diagnostic simulation study that is guided by evidence found in empirical data, we show that the temporal structure of excess rainfall has a significant effect on the scaling structure of peak discharges. These insights will contribute towards ongoing efforts to provide a framework for flood prediction in ungauged basins (PUB). This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-09T02:49:30.471517-05:
      DOI: 10.1002/2014WR016258
       
  • Observations and modeling of hillslope throughflow temperatures in a
           coastal forested catchment
    • Authors: J. A. Leach; R. D. Moore
      Abstract: A growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions, such as hyporheic exchange, groundwater discharge, and hillslope throughflow inputs. Existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures, but none has been evaluated against field measurements of throughflow temperature. In this study, throughflow temperatures were monitored over two winters at fifty locations adjacent to a headwater stream (11 ha catchment area) located in the rain‐on‐snow zone of the Pacific Northwest. Existing approaches to estimating throughflow temperature under‐ or over‐predicted throughflow temperatures by up to 5 ∘C, or were unable to represent the influence of transient snow cover. Therefore, a conceptual‐parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures. The model structure includes an upslope reservoir that drains into a downslope reservoir that, in turn, drains into the stream. Vertical and lateral energy and water fluxes are simulated using simplified process representations. The model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain‐on‐snow events. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-09T02:49:14.620365-05:
      DOI: 10.1002/2014WR016763
       
  • Comment on “Effects of tidal fluctuations on mixing and spreading in
           coastal aquifers: Homogeneous case” by M. Pool, V. E. A. Post, and
           C. T. Simmons
    • Authors: Behzad Ataie‐Ashtiani
      PubDate: 2015-05-09T02:48:22.318186-05:
      DOI: 10.1002/2014WR016303
       
  • Reply to comment by M. Pool, V. E. A. Post, and C. T. Simmons on
           “Effects of tidal fluctuations on mixing and spreading in coastal
           aquifers: Homogeneous case”
    • Authors: María Pool; Vincent E.A. Post, Craig T. Simmons
      PubDate: 2015-05-09T02:48:08.1914-05:00
      DOI: 10.1002/2015WR017111
       
  • Flood response for the watersheds of the Fernow Experimental Forest in the
           central Appalachians
    • Authors: Naomi S. Bates; James A. Smith, Gabriele Villarini
      Abstract: We examine flood response of high‐gradient, forested central Appalachian watersheds through analyses of rainfall, streamflow and piezometer observations from the Fernow Experimental Forest near Parsons, West Virginia. Analyses focus on hydrologic processes that control the “upper tail” of flood distributions. The largest flood peaks in the Fernow are an order of magnitude smaller than record floods in the central Appalachian region (for basins of comparable drainage area). We examine flood distributions in the Fernow using extreme value distributions (Generalized Extreme Value and Generalized Pareto distributions) and compare them to other watersheds in the central Appalachians. To examine the role of antecedent soil moisture on flood response, we installed a network of 415 crest‐stage piezometers on two headwater watersheds (0.30 and 0.14 km2) of the Fernow. Observations show pronounced heterogeneity of subsurface saturation even within the unchannelized swales of headwater watersheds. Shallow perched water tables over large portions of a watershed occur infrequently in forested central Appalachian basins, but may play an important role in extreme flood response. Fernow watersheds include “treated” and control watersheds with stream gaging records extending back to 1951. We examine nonstationarites in flood frequency in the Fernow and show that forest management practices have had relatively minor impacts on flood frequency. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-06T20:23:55.890266-05:
      DOI: 10.1002/2014WR015871
       
  • Seeing the landscape for the trees: Metrics to guide riparian shade
           management in river catchments
    • Authors: Matthew F. Johnson; Robert L. Wilby
      Abstract: Rising water temperature (Tw) due to anthropogenic climate change may have serious consequences for river ecosystems. Conservation and/or expansion of riparian shade could counter warming and buy time for ecosystems to adapt. However, sensitivity of river reaches to direct solar radiation is highly heterogeneous in space and time, so benefits of shading are also expected to be site specific. We use a network of high‐resolution temperature measurements from two upland rivers in the UK, in conjunction with topographic shade modelling, to assess the relative significance of landscape and riparian shade to the thermal behaviour of river reaches. Trees occupy 7% of the study catchments (comparable with the UK national average) yet shade covers 52% of the area and is concentrated along river corridors. Riparian shade is most beneficial for managing Tw at distances 5 to 20 km downstream from the source of the rivers where discharge is modest, flow is dominated by near‐surface hydrological pathways, there is a wide floodplain with little landscape shade, and where cumulative solar exposure times are sufficient to affect Tw. For the rivers studied, we find that approximately 0.5 km of complete shade is necessary to off‐set Tw by 1°C during July (the month with peak Tw) at a headwater site; whereas 1.1 km of shade is required 25 km downstream. Further research is needed to assess the integrated effect of future changes in air temperature, sunshine duration, direct solar radiation and downward diffuse radiation on Tw to help tree planting schemes achieve intended outcomes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-06T20:23:25.368954-05:
      DOI: 10.1002/2014WR016802
       
  • Estimation of the bed shear stress in vegetated and bare channels with
           smooth beds
    • Authors: Judy Q. Yang; Francois Kerger, Heidi M. Nepf
      Abstract: The shear stress at the bed of a channel influences important benthic processes such as sediment transport. Several methods exist to estimate the bed shear stress in bare channels without vegetation, but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production. This study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds. The model, which is supported by measurements, indicates that for both bare and vegetated channels with smooth beds, within a viscous sub‐layer at the bed, the viscous stress decreases linearly with increasing distance from the bed, resulting in a parabolic velocity profile at the bed. For bare channels, the model describes the velocity profile in the overlap region of the Law of the Wall. For emergent canopies of sufficient density (frontal area per unit canopy volume a≥4.3m‐1), the thickness of the linear‐stress layer is set by the stem diameter, leading to a simple estimate for bed shear stress. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-05T22:35:47.028939-05:
      DOI: 10.1002/2014WR016042
       
  • A revised model for microbially induced calcite precipitation ‐
           improvements and new insights based on recent experiments
    • Authors: Johannes Hommel; Ellen Lauchnor, Adrienne Phillips, Robin Gerlach, Alfred B. Cunningham, Rainer Helmig, Anozie Ebigbo, Holger Class
      Abstract: The model for microbially induced calcite precipitation (MICP) published by Ebigbo et al. (2012) has been improved based on new insights obtained from experiments and model calibration. The challenge in constructing a predictive model for permeability reduction in the underground with MICP is the quantification of the complex interaction between flow, transport, biofilm growth, and reaction kinetics. New data from Lauchnor et al. (2015) on whole‐cell ureolysis kinetics from batch experiments was incorporated into the model, which has allowed for a more precise quantification of the relevant parameters as well as a simplification of the reaction kinetics in the equations of the model. Further, the model has been calibrated objectively by inverse modeling using quasi‐1D column experiments and a radial flow experiment. From the post‐processing of the inverse modeling, a comprehensive sensitivity analysis has been performed with focus on the model input parameters that were fitted in the course of the model calibration. It reveals that calcite precipitation and concentrations of and Ca2+ are particularly sensitive to parameters associated with the ureolysis rate and the attachment behavior of biomass. Based on the determined sensitivities and the ranges of values for the estimated parameters in the inversion, it is possible to identify focal areas where further research can have a high impact towards improving the understanding and engineering of MICP. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-05T09:31:01.495044-05:
      DOI: 10.1002/2014WR016503
       
  • Digital catchment observatories: A platform for engagement and knowledge
           exchange between catchment scientists, policy makers, and local
           communities
    • Authors: E. B. Mackay; M. E. Wilkinson, C.J.A. Macleod, K. Beven, B.J. Percy, M.G. Macklin, P.F. Quinn, M. Stutter, P.M. Haygarth
      Abstract: Increasing pressures on the hydrological cycle from our changing planet have led to calls for a refocus of research in the sciences of hydrology and water resources. Opportunities for new and innovative research into these areas are being facilitated by advances in the use of cyberinfrastructure, such as the development of digital catchment observatories. This is enabling research into hydrological issues such as flooding to be approached differently. The ability to combine different sources of data, knowledge and modelling capabilities from different groups such as scientists, policy makers and the general public has the potential to provide novel insights into the way individual catchments respond at different temporal and spatial scales. While the potential benefits of the digital catchment observatory are large, this new way of carrying out research into hydrological sciences is likely to prove challenging on many levels. Along with the obvious technical and infrastructural challenges to this work, an important area for consideration is how to enable a digital observatory to work for a range of potential end‐users, paving the ways for new areas of research through developing a platform effective for engagement and knowledge exchange. Using examples from the recent local‐scale hydrological exemplar in the Environmental Virtual Observatory pilot project (http://www.evo‐uk.org), this commentary considers a number of issues around the communication between and engagement of different users, the use of local knowledge and uncertainty with cloud‐based models and the potential for decision support and directions for future research. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-05T09:20:37.128794-05:
      DOI: 10.1002/2014WR016824
       
  • Stormflow generation: A metaanalysis of field evidence from small,
           forested catchments
    • Authors: Frauke K. Barthold; Ross A. Woods
      Abstract: Combinations of runoff characteristics are commonly used to represent distinct conceptual models of stormflow generation. In this study, three runoff characteristics: hydrograph response, time source of runoff water, and flow path, are used to classify catchments. Published data from the scientific literature are used to provide evidence from small, forested catchments. Each catchment was assigned to one of the eight conceptual models, depending on the combination of quick/slow response, old/new water, and overland/subsurface flow. A standard procedure was developed to objectively diagnose the predominant conceptual model of stormflow generation for each catchment and assess its temporal and spatial support. The literature survey yielded 42 catchments, of which 30 catchments provide a complete set of qualitative runoff characteristics resulting in one of the 8 conceptual models. The majority of these catchments classify as subsurface flow path dominated. No catchments were found for conceptual models representing combinations of quick response – new water – subsurface flow (SSF), slow – new – SSF, slow – old – overland flow (OF) nor new – slow – OF. Of the 30 qualitatively classified catchments, 24 provide a complete set of quantitative measures. In summary, the field support is strong for 19 subsurface‐dominated catchments and is weak for 5 surface flow path dominated catchments (6 catchments had insufficient quantitative data). Two alternative explanations exist that may explain the imbalance of field support between the two flow path classes: (1) the selection of research catchments in past field studies was mainly to explain quick hydrograph response in subsurface dominated catchments; (2) catchments with prevailing subsurface flow paths are more common in nature. We conclude that the selection of research catchments needs to cover a wider variety of environmental conditions which should lead to a broader, and more widely applicable, spectrum of resulting conceptual models and process mechanisms. This is a prerequisite in studies where catchment organization and similarity approaches are used to develop catchment classification systems in order to regionalize stormflow. This article is protected by copyright. All rights reserved.
      PubDate: 2015-05-05T08:59:09.836189-05:
      DOI: 10.1002/2014WR016221
       
  • Declining rainfall and regional variability changes in Jordan
    • Authors: Kazi Rahman; Steven M Gorelick, P James Dennedy‐Frank, Jim Yoon, Bala Rajaratnam
      Abstract: Jordan, with limited rainfall, has per capita water availability of 135 m3/y making it one of the water‐poorest countries in the world. We analyzed the most comprehensive modern rainfall data set to date, consisting of 44 years of daily measurements from 58 stations primarily in the western, populated and agricultural portion of Jordan over the period 1970‐2013 to assess temporal trends, variability, and spatial patterns. From 1995‐2013, 13 of 19 years showed rainfall less than the mean, which has a probability
      PubDate: 2015-05-04T06:06:52.971267-05:
      DOI: 10.1002/2015WR017153
       
  • A new general 1‐D vadose zone flow solution method
    • Authors: Fred L. Ogden; Wencong Lai, Robert C. Steinke, Jianting Zhu, Cary A. Talbot, John L. Wilson
      Abstract: We have developed an alternative to the one‐dimensional partial differential equation (PDE) attributed to Richards [1931] that describes unsaturated porous media flow in homogeneous soil layers. Our solution is a set of three ordinary differential equation (ODEs) derived from unsaturated flux and mass conservation principles. We used a hodograph transformation, the Method of Lines, and a finite water‐content discretization to produce ODEs that accurately simulate infiltration, falling slugs, and groundwater table dynamic effects on vadose zone fluxes. This formulation, which we refer to as "finite water‐content" simulates sharp fronts, and is guaranteed to conserve mass using a finite‐volume solution. Our ODE solution method is explicitly integrable, does not require iterations and therefore has no convergence limits and is computationally efficient. The method accepts boundary fluxes including arbitrary precipitation, bare soil evaporation and evapotranspiration. The method can simulate heterogeneous soils using layers. Results are presented in terms of fluxes and water content profiles. Comparing our method against analytical solutions, laboratory data, and the Hydrus‐1D solver, we find that predictive performance of our finite water‐content ODE method is comparable to or in some cases exceeds that of the solution of Richards' equation, with or without a shallow water table. The presented ODE method is transformative in that it offers accuracy comparable to the Richards [1931] PDE numerical solution, without the numerical complexity, in a form that is robust, continuous, and suitable for use in large watershed and land‐atmosphere simulation models, including regional‐scale models of coupled climate and hydrology. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-28T03:26:33.465914-05:
      DOI: 10.1002/2015WR017126
       
  • On the assessment of reliability in probabilistic hydrometeorological
           event forecasting
    • Authors: Caleb M. DeChant; Hamid Moradkhani
      Abstract: Probabilistic forecasts are commonly used to communicate uncertainty in the occurrence of hydro‐meteorological events. Although probabilistic forecasting is common, conventional methods for assessing the reliability of these forecasts are approximate. Among the most common methods for assessing reliability, the decomposed Brier Score and Reliability Diagram treat an observed string of events as samples from multiple Binomial distributions, but this is an approximation of the forecast reliability, leading to unnecessary loss of information. This article suggests testing the hypothesis of reliability via the Poisson‐Binomial distribution, which is a generalized solution to the Binomial distribution, providing a more accurate model of the probabilistic event forecast verification setting. Further, a two‐stage approach to reliability assessment is suggested to identify errors in the forecast related to both bias and overly/insufficiently sharp forecasts. Such a methodology is shown to more effectively distinguish between reliable and unreliable forecasts, leading to more robust probabilistic forecast verification. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-28T03:01:29.624886-05:
      DOI: 10.1002/2014WR016617
       
  • A general analytical solution for steady flow in heterogeneous porous
           media
    • Authors: J. R. Craig
      Abstract: A novel analytical solution approach for problems of steady flow in two‐dimensional heterogeneous porous media is presented, where the hydraulic conductivity may be be represented as an arbitrary polynomial in space. The solution approach uses Wirtinger calculus and the Bers‐Vekua theory of elliptical functions. The final form of the solution comprises an arbitrary complex polynomial solution to the Laplace equation and additional non‐holomorphic terms which are determined directly from the coefficients of this polynomial. The arbitrary polynomial coefficients may be chosen to satisfy general flow conditions along system boundaries. The approach is also extended to singular flow, such as that induced by pumping wells. The solution is demonstrated to be effectively exact for a number of test cases; the problems are solved to machine precision. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-28T02:54:23.848427-05:
      DOI: 10.1002/2014WR016449
       
  • Debates—Perspectives on sociohydrology: Capturing feedbacks between
           physical and social processes
    • Authors: Giuliano Di Baldassarre; Alberto Viglione, Gemma Carr, Linda Kuil, Kun Yan, Luigia Brandimarte, Günter Blöschl
      Abstract: In flood risk assessment, there remains a lack of analytical frameworks capturing the dynamics emerging from two‐way feedbacks between physical and social processes, such as adaptation and levee effect. The former, “adaptation effect”, relates to the observation that the occurrence of more frequent flooding is often associated with decreasing vulnerability. The latter, “levee effect”, relates to the observation that the non‐occurrence of frequent flooding (possibly caused by flood protection structures, e.g. levees) is often associated to increasing vulnerability. As current analytical frameworks do not capture these dynamics, projections of future flood risk are not realistic. In this paper, we develop a new approach whereby the mutual interactions and continuous feedbacks between floods and societies are explicitly accounted for. Moreover, we show an application of this approach by using a socio‐hydrological model to simulate the behavior of two main prototypes of societies: green societies, which cope with flooding by resettling out of flood‐prone areas; and technological societies, which deal with flooding also by building levees or dikes. This application shows that the proposed approach is able to capture and explain the aforementioned dynamics (i.e. adaptation and levee effect) and therefore contribute to a better understanding of changes in flood risk, within an iterative process of theory development and empirical research. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-28T02:45:40.447951-05:
      DOI: 10.1002/2014WR016416
       
  • Groundwater in the Earth's critical zone—Relevance to
           large‐scale patterns and processes
    • Authors: Ying Fan
      Abstract: Although we have an intuitive understanding of the behavior and functions of groundwater in the Earth's critical zone at the scales of a column (atmosphere‐plant‐soil‐bedrock), along a topo‐sequence (ridge to valley), and across a small catchment (
      PubDate: 2015-04-25T10:22:06.693077-05:
      DOI: 10.1002/2015WR017037
       
  • Uncertainty in modeled and observed climate change impacts on American
           Midwest hydrology
    • Authors: Jonathan M. Winter; Pat J.‐F. Yeh, Xiaojing Fu, Elfatih A.B. Eltahir
      Abstract: An important potential consequence of climate change is the modification of the water cycle in agricultural areas, such as the American Midwest. Soil moisture is the integrand of the water cycle, reflecting dynamics of precipitation, evapotranspiration, and runoff in space and time, and a key determinant of yield. Here we present projected changes in the hydrologic cycle over a representative area of the American Midwest from regional climate model experiments that sample a range of model configurations. While significant summer soil moisture drying is predicted in some ensemble members others predict soil moisture wetting, with the sign of soil moisture response strongly influenced by our choice of boundary conditions. To resolve the contradictory predictions of soil moisture across ensemble members, we assess an extensive and unique observational dataset of the water budget in Illinois. No statistically significant monotonic trends are found in observed soil moisture, precipitation, streamflow, groundwater level, or 2‐m air temperature over a recent 26‐year period (soil moisture 25 years). Based on this analysis of model simulations and observations, we conclude that the sign of climate change impacts on the regional hydrology of the American Midwest remains uncertain. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-25T10:16:43.000234-05:
      DOI: 10.1002/2014WR016056
       
  • Partitioning of evapotranspiration using high frequency water vapor
           isotopic measurement over a rice paddy field
    • Authors: Zhongwang Wei; Kei Yoshimura, Atsushi Okazaki, Wonsik Kim, Zhongfang Liu, Masaharu Yokoi
      Abstract: Partitioning ecosystem evapotranspiration (ET) into soil evaporation (E) and transpiration (T) is crucial for understanding hydrological processes. In this study, by using high‐frequency isotope measurements and continuous surface water measurements, we investigated the isotope ratios in soil‐vegetation‐atmosphere transfer and the physical mechanisms involved over a paddy field for a full growing season. The isotopic signals of δET, δT, and δE were determined by the Keeling plot method, surface water isotopic measurements, and the Craig‐Gordon model, respectively. The fraction of transpiration in evapotranspiration (FT) ranged from 0.2 to 1, with an almost continuous increase in the early growing season and a relatively constant value close to 1 later in the year. The result was supported by FT derived from simulated T and eddy correlation measured ET. The seasonal change in the transpiration fraction could be described quite well as a function of the LAI (FT=0.67LAI0.25, R2 = 0.80), implying that transpiration plays a dominant role in the soil‐vegetation‐atmosphere continuum during the growing season. The two end‐member uncertainty analysis suggested that further improvement in the estimation of δT and δET is necessary for partitioning evapotranspiration using the isotopic method. In the estimation of δET, the assumptions underlying Keeling plot method were rarely met and the uncertainty was quite large. A high frequency of precise isotopic measurements in surface water was also necessary for δT estimation. Furthermore, special care must be taken concerning the kinetic fractionation parameter in the Craig and Gordon Equation for δE estimation under low‐LAI conditions. The results demonstrated the robustness of using isotope measurements for partitioning evapotranspiration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-24T04:37:42.383442-05:
      DOI: 10.1002/2014WR016737
       
  • On the effect of connectivity on solute transport in spatially
           heterogeneous combined unsaturated‐saturated flow systems
    • Authors: David Russo
      Abstract: Detailed numerical analyses of flow and transport were used to investigate the effect of spatially connected features on transport in three‐dimensional (3‐D), spatially heterogeneous, combined vadose zone‐groundwater flow systems. Formations with spatially connected fine‐ and coarse‐textured features (F‐ and C‐formations, respectively), representing the10th and the 90th percentiles of the distributions of the formation's hydraulic parameters, respectively, were considered here. Results of the analyses suggest that in steady‐state flow, when the unsaturated zone of the combined flow domains is relatively wet, as compared with a Multivariate‐Gaussian (MG) formation, spatially connected features may reduce the solute first arrival time, particularly in the C‐formation, and may enhance the spreading of the solute breakthrough, particularly in the F‐formation. The effect of the spatially connected features on the hydrological response, however, decreases as the unsaturated zone becomes drier. The latter result stems from the decrease in the fraction of the water‐filled, pore‐space occupied by the connected structures, with decreasing water content. The latter finding also explains the result that the response of more realistic, combined flow systems, whose unsaturated zone is associated with relatively low, intermittent water contents, is essentially independent of the spatially connected features of the formations, regardless of their soil texture. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-23T23:50:59.381516-05:
      DOI: 10.1002/2014WR016434
       
  • On the probabilistic structure of water age
    • Authors: Amilcare Porporato; Salvatore Calabrese
      Abstract: The age distribution of water in hydrologic systems has received renewed interest recently, especially in relation to watershed response to rainfall inputs. The purpose of this contribution is first to draw attention to existing theories of age distributions in population dynamics, fluid mechanics and stochastic groundwater, and in particular to the McKendrick‐von Foerster equation and its generalizations and solutions. A second and more important goal is to clarify that, when hydrologic fluxes are modeled by means of time‐varying stochastic processes, the age distributions must themselves be treated as random functions. Once their probabilistic structure is obtained, it can be used to characterize the variability of age distributions in real systems and thus help quantify the inherent uncertainty in the field determination of water age. We illustrate these concepts with reference to a stochastic storage model, which has been used as a minimalist model of soil moisture and streamflow dynamics. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-23T23:50:39.606397-05:
      DOI: 10.1002/2015WR017027
       
  • Assessment of reservoir system variable forecasts
    • Authors: Martin Kistenmacher; Aris P. Georgakakos
      Abstract: Forecast ensembles are a convenient means to model water resources uncertainties and to inform planning and management processes. For multi‐purpose reservoir systems, forecast types include (i) forecasts of upcoming inflows, and (ii) forecasts of system variables and outputs such as reservoir levels, releases, flood damage risks, hydropower production, water supply withdrawals, water quality conditions, navigation opportunities, and environmental flows, among others. Forecasts of system variables and outputs are conditional on forecasted inflows as well as on specific management policies, and can provide useful information for decision making processes. Unlike inflow forecasts (in ensemble or other forms), which have been the subject of many previous studies, reservoir system variable and output forecasts are not formally assessed in water resources management theory or practice. This article addresses this gap and develops methods to rectify potential reservoir system forecast inconsistencies and improve the quality of management‐relevant information provided to stakeholders and managers. The overarching conclusion is that system variable and output forecast consistency is critical for robust reservoir management and needs to be routinely assessed for any management model used to inform planning and management processes. The above are demonstrated through an application from the Sacramento‐American‐San Joaquin reservoir system in northern California. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-20T08:55:39.90964-05:0
      DOI: 10.1002/2014WR016564
       
  • Rainfall hotspots over the southern tropical Andes: Spatial distribution,
           rainfall intensity and relations with large‐scale atmospheric
           circulation
    • Authors: Jhan Carlo Espinoza; Steven Paul Chavez, Josyane Ronchail, Clémentine Junquas, Ken Takahashi, Waldo Lavado
      Abstract: The Andes/Amazon transition is among the rainiest regions of the world and the interactions between large‐scale circulation and the topography that determine its complex rainfall distribution remain poorly known. This work provides an in‐depth analysis of the spatial distribution, variability and intensity of rainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis is based on comprehensive daily rainfall datasets from meteorological stations in Peru and Bolivia. We compare our results with high‐resolution rainfall TRMM‐PR 2A25 estimations. Hotspot regions are identified at low elevations in the Andean foothills (400‐700 masl) and in windward conditions at Quincemil and Chipiriri, where more than 4,000 mm rainfall per year are recorded. Orographic effects and exposure to easterly winds produce a strong annual rainfall gradient between the lowlands and the Andes that can reach 190 mm/km. Although TRMM‐PR reproduces the spatial distribution satisfactorily, it underestimates rainfall by 35% in the hotspot regions. In the Peruvian hotspot, exceptional rainfall occurs during the austral dry season (around 1,000 mm in June‐July‐August; JJA), but not in the Bolivian hotspot. The direction of the low‐level winds over the Andean foothills partly explains this difference in the seasonal rainfall cycle. At intraseasonal scales in JJA, we found that, during northerly wind regimes, positive rainfall anomalies predominate over the lowland and the eastern flank of the Andes, whereas less rain falls at higher altitudes. On the other hand, during southerly regimes, rainfall anomalies are negative in the hotspot regions. The influence of cross‐equatorial winds is particularly clear below 2000 masl. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-17T07:14:33.899686-05:
      DOI: 10.1002/2014WR016273
       
  • Controls on the diurnal streamflow cycles in two subbasins of an alpine
           headwater catchment
    • Authors: Raphael Mutzner; Steven V. Weijs, Paolo Tarolli, Marc Calaf, Holly J. Oldroyd, Marc B. Parlange
      Abstract: In high altitude alpine catchments, diurnal streamflow cycles are typically dominated by snowmelt or ice melt. Evapotranspiration‐induced diurnal streamflow cycles are less observed in these catchments but might happen simultaneously. During a field campaign in the summer 2012 in an alpine catchment in the Swiss Alps (Val Ferret catchment, 20.4 km2, glaciarized area: 2%), we observed a transition in the early season from a snowmelt to an evapotranspiration‐induced diurnal streamflow cycle in one of two monitored sub‐basins. The two different cycles were of comparable amplitudes and the transition happened within a time span of several days. In the second monitored sub‐basin, we observed an ice melt‐dominated diurnal cycle during the entire season due to the presence of a small glacier. Comparisons between ice melt and evapotranspiration cycles showed that the two processes were happening at the same times of day but with a different sign and a different shape. The amplitude of the ice melt cycle decreased exponentially during the season and was larger than the amplitude of the evapotranspiration cycle which was relatively constant during the season. Our study suggests that an evapotranspiration‐dominated diurnal streamflow cycle could damp the ice melt‐dominated diurnal streamflow cycle. The two types of diurnal streamflow cycles were separated using a method based on the identification of the active riparian area and measurement of evapotranspiration. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-16T23:45:47.329035-05:
      DOI: 10.1002/2014WR016581
       
  • Assessment of flow regime alterations over a spectrum of temporal scales
           using wavelet‐based approaches
    • Authors: Fu‐Chun Wu; Ching‐Fu Chang, Jenq‐Tzong Shiau
      Abstract: The full range of natural flow regime is essential for sustaining the riverine ecosystems and biodiversity, yet there are still limited tools available for assessment of flow regime alterations over a spectrum of temporal scales. Wavelet analysis has proven useful for detecting hydrologic alterations at multiple scales via the wavelet power spectrum (WPS) series. The existing approach based on the global WPS (GWPS) ratio tends to be dominated by the rare high‐power flows so that alterations of the more frequent low‐power flows are often underrepresented. We devise a new approach based on individual deviations between WPS (DWPS) that are root‐mean‐squared to yield the global DWPS (GDWPS). We test these two approaches on the three reaches of the Feitsui Reservoir system (Taiwan) that are subjected to different classes of anthropogenic interventions. The GDWPS reveal unique features that are not detected with the GWPS ratios. We also segregate the effects of individual sub‐flow components on the overall flow regime alterations using the sub‐flow GDWPS. The results show that the daily hydropeaking waves below the reservoir not only intensified the flow oscillations at daily scale but most significantly eliminated subweekly flow variability. Alterations of flow regime were most severe below the diversion weir, where the residual hydropeaking resulted in a maximum impact at daily scale while the post‐diversion null flows led to large hydrologic alterations over submonthly scales. The smallest impacts below the confluence reveal that the hydrologic alterations at scales longer than 2 days were substantially mitigated with the joining of the unregulated tributary flows, whereas the daily‐scale hydrologic alteration was retained because of the hydropeaking inherited from the reservoir releases. The proposed DWPS approach unravels for the first time the details of flow regime alterations at these intermediate scales that are overridden by the low‐frequency high‐power flows when the long‐term averaged GWPS are used. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T14:14:21.504563-05:
      DOI: 10.1002/2014WR016595
       
  • Chute cutoff as a morphological response to stream reconstruction: The
           possible role of backwater
    • Authors: J.P.C. Eekhout; A.J.F. Hoitink
      Abstract: Stream restoration efforts often aim at creating new unconstrained meandering channels without weirs and bank revetments. In reconstructed streams, the initial morphological response of the new streams is often rapid, until a dynamic equilibrium is reached. Here we report on a chute cutoff that occurred within 3 months after realization of a stream restoration project, caused by a plug bar that formed in response to a backwater effect. The temporal evolution of the morphology of both the new and the old channel was monitored over a period of nearly 8 months, including pre‐cutoff conditions. The observations can be separated into three stages. Stage 1 is the initial period leading to cutoff vulnerability, stage 2 is the actual cutoff, and stage 3 is the morphological adjustment in response to the cutoff. In stage 1, a plug bar was deposited in one of the channel bends. Hydrodynamic model results show the location of the plug bar coincides with a region where bed shear stress decreased in downstream direction due to backwater. Longitudinal channel bed profiles show that the channel slope decreased soon after channel reconstruction. Hence, sediment from upstream was available to form the plug bar. After the plug bar was deposited, an embayment formed in the floodplain at a location where the former channel was located (stage 2). The former channel was filled with sediment prior to channel construction. It is likely that the sediment at this location was less consolidated, and therefore, prone to erosion. The chute channel continued to incise and widen into the floodplain and, after 6 months, acted as the main channel, conveying the discharge during the majority of time (stage 3). The cutoff channel gradually continued to fill with sediment, from the moment the plug bar formed until the chute channel incised into the floodplain. Sedimentary successions of the deposited material show upward fining, which is in agreement with observations of chute cutoffs in rivers. Although the artificial setting limits the degree in which the observed processes can be projected on natural rivers, the observations prompt to investigate the role of backwater effects in natural chute initiation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T14:14:00.300438-05:
      DOI: 10.1002/2014WR016539
       
  • Abiotic and biotic controls of soil moisture spatio‐temporal
           variability and the occurrence of hysteresis
    • Authors: Simone Fatichi; Gabriel G. Katul, Valeriy Y. Ivanov, Christoforos Pappas, Athanasios Paschalis, Ada Consolo, Jongho Kim, Paolo Burlando
      Abstract: An expression that separates biotic and abiotic controls on the temporal dynamics of the soil moisture spatial coefficient of variation Cv(θ) was explored via numerical simulations using a mechanistic ecohydrological model, Tethys‐Chloris. Continuous soil moisture spatio‐temporal dynamics at an exemplary hillslope domain were computed for six case studies characterized by different climate and vegetation cover and for three configurations of soil properties. It was shown that abiotic controls largely exceed their biotic counterparts in wet climates. Biotic controls on Cv(θ) were found to be more pronounced in Mediterranean climates. The relation between Cv(θ) and spatial mean soil moisture θ¯ was found to be unique in wet locations, regardless of the soil properties. For the case of homogeneous soil texture, hysteretic cycles between Cv(θ) and θ¯ were observed in all Mediterranean climate locations considered here and to a lesser extent in a deciduous temperate forest. Heterogeneity in soil properties increased Cv(θ) to values commensurate with field observations and weakened signatures of hysteresis at all of the studied locations. This finding highlights the role of site‐specific heterogeneities in hiding or even eliminating the signature of climatic and biotic controls on Cv(θ), thereby offering a new perspective on causes of confounding results reported across field experiments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T14:13:33.001229-05:
      DOI: 10.1002/2014WR016102
       
  • A framework to identify Pareto‐efficient subdaily environmental flow
           constraints on hydropower reservoirs using a grid‐wide power
           dispatch model
    • Authors: Marcelo A. Olivares; Jannik Haas, Rodrigo Palma‐Behnke, Carlos Benavides
      Abstract: Hydrologic alteration due to hydropeaking reservoir operations is a main concern worldwide. Subdaily environmental flow constraints (ECs) on operations can be promising alternatives for mitigating negative impacts. However, those constraints reduce the flexibility of hydropower plants, potentially with higher costs for the power system. To study the economic and environmental efficiency of ECs, this work proposes a novel framework comprising four steps: i) assessment of the current subdaily hydrologic alteration; ii) formulation and implementation of a short‐term, grid‐wide hydrothermal coordination model; iii) design of ECs in the form of maximum ramping rates (MRRs) and minimum flows (MIFs) for selected hydropower reservoirs; and iv) identification of Pareto‐efficient solutions in terms of grid‐wide costs and the Richard‐Baker flashiness index for subdaily hydrologic alteration (SDHA). The framework was applied to Chile's main power grid, assessing 25 EC cases, involving five MIFs and five MRRs. Each case was run for a dry, normal and wet water year type. Three Pareto‐efficient ECs are found, with remarkably small cost increase below 2% and a SDHA improvement between 28% and 90%. While the case involving the highest MIF worsens the flashiness of another basin, the other two have no negative effect on other basins and can be recommended for implementation. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T03:11:36.864962-05:
      DOI: 10.1002/2014WR016215
       
  • Modeling the Release of E. coli D21g with Transients in Water Content
    • Authors: Scott A. Bradford; Yusong Wang, Saeed Torkzaban, Jiri Šimůnek
      Abstract: Transients in water content are well known to mobilize colloids that are retained in the vadose zone. However, there is no consensus on the proper model formulation to simulate colloid release during drainage and imbibition. We present a model that relates colloid release to changes in the air‐water interfacial area (Aaw) with transients in water content. Colloid release from the solid‐water interface (SWI) is modeled in two steps. First, a fraction of the colloids on the SWI partitions to the mobile aqueous phase and air‐water interface (AWI) when the Aaw increases during drainage. Second, colloids that are retained on the AWI or at the air‐water‐solid triple line are released during imbibition as the AWI is destroyed. The developed model was used to describe the release of Escherichia coli D21g during cycles of drainage and imbibition under various saturation conditions. Simulations provided a reasonable description of experimental D21g release results. Only two model parameters were optimized to the D21g release data: (i) the cell fraction that was released from the SWI (fr); and (ii) the cell fraction that partitioned from the SWI to the AWI (fawi). Numerical simulations indicated that cell release was proportional to fr and the initial amount of retention on the SWI and AWI. Drainage to a lower water content enhanced cell release, especially during subsequent imbibition, because more bacteria on the SWI were partitioned to the AWI and/or aqueous phase. Imbibition to a larger water content produced greater colloid release because of higher flow rates, and more destruction of the AWI (smaller Aaw). Variation in the value of fawi was found to have a pronounced influence on the amount of cell release in both drainage and imbibition due to changes in the partitioning of cells from the SWI to the aqueous phase and the AWI. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T02:43:13.545621-05:
      DOI: 10.1002/2014WR016566
       
  • Hyporheic zone hydrologic science: a historical account of its emergence
           and a prospectus
    • Authors: M. Bayani Cardenas
      Abstract: The hyporheic zone, defined by shallow subsurface pathways through river beds and banks beginning and ending at the river, is an integral and unique component of fluvial systems. It hosts myriad hydrologically‐controlled processes that are potentially coupled in complex ways. Understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale. Thus, the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of Water Resources Research. This manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in Water Resources Research, from the birth of the concept of the hyporheic zone as a hydrologic black box (sometimes referred to as transient storage zone), to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view, to its mature emergence as an interdisciplinary research field that employs the wide array of state‐of‐the‐art tools available to the modern hydrologist. The field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth. There are exciting opportunities for scientists that are able to tightly link the allied fields of geology, geomorphology, hydrology, geochemistry and ecology to tackle the many open problems in hyporheic zone science. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-14T02:35:17.377517-05:
      DOI: 10.1002/2015WR017028
       
  • Long‐range seasonal streamflow forecasting over the Iberian
           Peninsula using large‐scale atmospheric and oceanic information
    • Authors: J.M. Hidalgo‐Muñoz; S.R. Gámiz‐Fortis, Y. Castro‐Díez, D. Argüeso, M.J. Esteban‐Parra
      Abstract: Identifying the relationship between large‐scale climate signals and seasonal streamflow may provide a valuable tool for long‐range seasonal forecasting in regions under water stress, such as the Iberian Peninsula (IP). The skill of the main teleconnection indices as predictors of seasonal streamflow in the IP was evaluated. The streamflow database used was composed of 382 stations, covering the period 1975‐2008. Predictions were made using a leave‐one‐out cross‐validation approach based on multiple linear regression, combining Variance Inflation Factor and Stepwise Backward selection to avoid multicollinearity and select the best subset of predictors. Predictions were made for four forecasting scenarios, from one to four seasons in advance. The correlation coefficient (RHO), Root Mean Square Error Skill Score (RMSESS) and the Gerrity Skill Score (GSS) were used to evaluate the forecasting skill. For autumn streamflow, good forecasting skill (RHO>0.5, RMSESS>20%, GSS>0.4) was found for a third of the stations located in the Mediterranean Andalusian Basin, the North Atlantic Oscillation of the previous winter being the main predictor. Also, fair forecasting skill (RHO>0.44, RMSESS>10%, GSS>0.2) was found in stations in the northwestern IP (16 of these located in the Douro and Tagus Basins) with two seasons in advance. For winter streamflow, fair forecasting skill was found for one season in advance in 168 stations, with the Snow Advance Index as the main predictor. Finally, forecasting was poorer for spring streamflow than for autumn and winter, since only 16 stations showed fair forecasting skill in with one season in advance, particularly in north‐western of IP. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-08T08:29:41.951008-05:
      DOI: 10.1002/2014WR016826
       
  • Coupled and uncoupled hydrogeophysical inversions using ensemble Kalman
           filter assimilation of ERT‐monitored tracer test data
    • Authors: Matteo Camporese; Giorgio Cassiani, Rita Deiana, Paolo Salandin, Andrew Binley
      Abstract: Recent advances in geophysical methods have been increasingly exploited as inverse modeling tools in groundwater hydrology. In particular, several attempts to constrain the hydrogeophysical inverse problem to reduce inversion errors have been made using time‐lapse geophysical measurements through both coupled and uncoupled (also known as sequential) inversion approaches. Despite the appeal and popularity of coupled inversion approaches, their superiority over uncoupled methods has not been proven conclusively; the goal of this work is to provide an objective comparison between the two approaches within a specific inversion modeling framework based on the ensemble Kalman filter (EnKF). Using EnKF and a model of Lagrangian transport, we compare the performance of a fully coupled and uncoupled inversion method for the reconstruction of heterogeneous saturated hydraulic conductivity fields through the assimilation of ERT‐monitored tracer test data. The two inversion approaches are tested in a number of different scenarios, including isotropic and anisotropic synthetic aquifers, where we change the geostatistical parameters used to generate the prior ensemble of hydraulic conductivity fields. Our results show that the coupled approach outperforms the uncoupled when the prior statistics are close to the ones used to generate the true field. Otherwise, the coupled approach is heavily affected by “filter inbreeding” (an undesired effect of variance underestimation typical of EnKF), while the uncoupled approach is more robust, being able to correct biased prior information thanks to its capability of capturing the solute travel times even in presence of inversion artifacts such as the violation of mass balance. Furthermore, the coupled approach is more computationally intensive than the uncoupled, due to the much larger number of forward runs required by the electrical model. Overall, we conclude that the relative merit of the coupled versus the uncoupled approach cannot be assumed a priori and should be assessed case by case. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-08T08:12:23.141702-05:
      DOI: 10.1002/2014WR016017
       
  • Drag force parameters of rigid and flexible vegetal elements
    • Authors: John A. Chapman; Bruce N. Wilson, John S. Gulliver
      Abstract: This paper compares parameters that characterize vegetation flexibility effects on flow resistance and drag. Drag forces have been measured in a flume for simple cylindrical obstructions of the same shape and size but with different flexibility under several flow conditions. This data set is used to fit drag parameters and to relate their value to flexibility through the Cauchy Number. A formulation is presented where the drag coefficient is evaluated as a function of a new calibration velocity parameter which is related to the elastic modulus of the obstruction. While the use of a Vogel exponent and reference velocity provides a similar response, the reference velocity when used is somewhat nebulous and appears to have a critical impact on the parameter and the drag force calculated. The proposed formulation for drag reduction is more consistently estimated for the range of flexibilities in this study. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-08T08:02:35.737137-05:
      DOI: 10.1002/2014WR015436
       
  • Hydroeconomic optimization of integrated water management and transfers
           under stochastic surface water supply
    • Authors: Tingju Zhu; Guilherme Fernandes Marques, Jay R. Lund
      Abstract: Efficient re‐allocation and conjunctive operation of existing water supplies is gaining importance as demands grow, competitions among users intensify, and new supplies become more costly. This paper analyzes the roles and benefits of conjunctive use of surface water and groundwater and market‐based water transfers in an integrated regional water system where agricultural and urban water users coordinate supply and demand management based on supply reliability and economic values of water. Agricultural users optimize land and water use for annual and perennial crops to maximize farm income, while urban users choose short‐term and long‐term water conservation actions to maintain reliability and minimize costs. The temporal order of these decisions is represented in a two‐stage optimization that maximizes the net expected benefits of crop production, urban conservation and water management including conjunctive use and water transfers. Long‐term decisions are in the first stage and short‐term decisions are in a second stage based on probabilities of water availability events. Analytical and numerical analyses are made. Results show that conjunctive use and water transfers can substantially stabilize farmer's income and reduce system costs by reducing expensive urban water conservation or construction. Water transfers can equalize marginal values of water across users, while conjunctive use minimizes water marginal value differences in time. Model results are useful for exploring the integration of different water demands and supplies through water transfers, conjunctive use, and conservation, providing valuable insights for improving system management. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-08T07:26:20.445264-05:
      DOI: 10.1002/2014WR016519
       
  • Using the level set method to study the effects of heterogeneity and
           anisotropy on hyporheic exchange
    • Authors: Cheng Chen; Lingzao Zeng
      Abstract: The level set method was used to simulate the interface movement when a conservative solute migrated from stream water to subsurface water, and study the effects of streambed heterogeneity and anisotropy on solute penetration. The level set method is a numerical technique for tracking moving interfaces based on the idea that the interface is a level set curve of a higher‐dimensional function. Numerical simulations were compared to experiments conducted in a recirculating flume. Streambed heterogeneity led to water exchange between multiple bedforms, while in homogeneous streambeds the water exchange was restricted within a single bedform. A thin layer of homogeneous sediments at the top of the heterogeneous streambeds significantly increased the interfacial water influx, resulting in faster solute penetration and stream concentration decrease. Streambed heterogeneity generated horizontal preferential flow paths in the upper part of the bed while decreasing pore water velocities deeper in the bed, which hindered vertical penetration and consequently led to slower stream concentration decrease. Decreasing vertical permeability or increasing horizontal permeability led to slower vertical penetration and stream concentration decrease. Decreasing vertical permeability had a much more significant impact on solute penetration than increasing horizontal permeability, because mass transfer in hyporheic exchange is greatly dominated by vertical advection which depends primarily on the vertical permeability. This study was the first to apply the level set method in the study of hyporheic exchange. The theoretical and numerical methods have important applications in subsurface flow and transport processes. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-06T09:04:19.486983-05:
      DOI: 10.1002/2014WR016444
       
  • Canopy influence on snow depth distribution in a pine stand determined
           from terrestrial laser data
    • Authors: J. Revuelto; J.I. López‐Moreno, C. Azorin‐Molina, S.M. Vicente‐Serrano
      Abstract: In this study we analyzed the effects of the forest canopy and trunks of a pine stand in the central Spanish Pyrenees on the snow depth (SD) distribution. Using LiDAR technology with a terrestrial laser scanner (TLS), high‐resolution data on the SD distribution were acquired during the 2011–12 and 2012–13 snow seasons, which were two years having very contrasting climatic and snow accumulation conditions. Average SD evolution in open and canopy areas was characterized. Principal component analysis was applied to identify days having similar spatial patterns of SD distribution. There was a clear contrast in the temporal variability of the snowpack in different areas of the forest stand, corresponding generally to beneath the canopy, and in open sites. The canopy and openings showed markedly different accumulation and melting, with higher snow accumulation found in openings. Differences ranged from 14 to 80% reduction (average 49%) in the SD beneath the canopy relative to open sites. The difference in SD between open and canopy areas increased throughout the snow season. The surveyed days were classified in terms of SD distribution, and included days associated with: high SD, low SD, intense melting conditions and periods when the SD distribution was driven by wind conditions. The SD increased with distance from the trunks to a distance of 3.5–4.5 m, coinciding with the average size of the crown of individual trees. This article is protected by copyright. All rights reserved.
      PubDate: 2015-04-06T08:33:20.705984-05:
      DOI: 10.1002/2014WR016496
       
  • Diagnosis of insidious data disasters
    • Authors: Jessica D. Lundquist; Nicholas E. Wayand, Adam Massmann, Martyn P. Clark, Fred Lott, Nicoleta C. Cristea
      Abstract: Everyone taking field observations has a story of data collection gone wrong, and in most cases, the errors in the data are immediately obvious. A more challenging problem occurs when the errors are insidious, i.e., not readily detectable, and the error‐laden data appear useful for model testing and development. We present two case studies, one related to the water balance in the snow‐fed Tuolumne River, Sierra Nevada, California, combined with modeling using the Distributed Hydrology Soil Vegetation Model (DHSVM); and one related to the energy balance at Snoqualmie Pass, Washington, combined with modeling using the Structure for Unifying Multiple Modeling Alternatives (SUMMA). In the Tuolumne, modeled streamflow in one year was more than twice as large as observed; at Snoqualmie, modeled nighttime surface temperatures were biased by about +10 °C. Both appeared to be modeling failures, until detective work uncovered observational errors. We conclude with a discussion of what these cases teach us about science in an age of specialized research, when one person collects data, a separate person conducts model simulations, and a computer is charged with data quality‐assurance. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-24T14:53:51.432389-05:
      DOI: 10.1002/2014WR016585
       
  • Potential accumulation of contaminated sediments in a reservoir of a
           high‐Andean watershed: Morphodynamic connections with geochemical
           processes
    • Authors: María Teresa Contreras; Daniel Müllendorff, Pablo Pastén, Gonzalo E. Pizarro, Chris Paola, Cristián Escauriaza
      Abstract: Rapid changes due to anthropic interventions in high‐altitude environments, such as the Altiplano region in South America, require new approaches to understand the connections between physical and geochemical processes. Alterations of the water quality linked to the river morphology can affect the ecosystems and human development in the long‐term. The future construction of a reservoir in the Lluta river, located in northern Chile, will change the spatial distribution of arsenic‐rich sediments, which can have significant effects on the lower parts of the watershed. In this investigation we develop a coupled numerical model to predict and evaluate the interactions between morphodynamic changes in the Lluta reservoir [based on the work of Kostic and Parker, 2003a,b], and conditions that can potentially desorb arsenic from the sediments. Assuming that contaminants are mobilized under anaerobic conditions, we calculate the oxygen concentration within the sediments to study the interactions of the delta progradation with the potential arsenic release. This work provides a framework for future studies aimed to analyze the complex connections between morphodynamics and water quality, when contaminant‐rich sediments accumulate in a reservoir. The tool can also help to design effective risk management and remediation strategies in these extreme environments. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-23T03:23:22.081512-05:
      DOI: 10.1002/2014WR016130
       
  • What do we mean by sensitivity analysis? The need for comprehensive
           characterization of ‘Global’ sensitivity in Earth and
           Environmental Systems Models
    • Authors: Saman Razavi; Hoshin V. Gupta
      Abstract: Sensitivity analysis is an essential paradigm in Earth and Environmental Systems modelling. However, the term ‘sensitivity' has a clear definition, based in partial derivatives, only when specified locally around a particular point (e.g., optimal solution) in the problem space. Accordingly, no unique definition exists for ‘global sensitivity' across the problem space, when considering one or more model responses to different factors such as model parameters or forcings. A variety of approaches have been proposed for global sensitivity analysis, based on different philosophies and theories, and each of these formally characterizes a different ‘intuitive' understanding of sensitivity. These approaches focus on different properties of the model response at a fundamental level and may therefore lead to different (even conflicting) conclusions about the underlying sensitivities. Here, we revisit the theoretical basis for sensitivity analysis, summarize and critically evaluate existing approaches in the literature, and demonstrate their flaws and shortcomings through conceptual examples. We also demonstrate the difficulty involved in interpreting ‘global' interaction effects, which may undermine the value of exiting interpretive approaches. With this background, we identify several important properties of response surfaces that are associated with the understanding and interpretation of sensitivities in the context of Earth and Environmental System models. Finally, we highlight the need for a new, comprehensive framework for sensitivity analysis that effectively characterizes all of the important sensitivity‐related properties of model response surfaces. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-23T03:03:33.617051-05:
      DOI: 10.1002/2014WR016527
       
  • Estimation of soil salinity in a drip irrigation system by using joint
           inversion of multicoil electromagnetic induction measurements
    • Authors: Khan Zaib Jadoon; Davood Moghadas, Aurangzeb Jadoon, Thomas M. Missimer, Samir K. Al‐Mashharawi, Matthew F. McCabe
      Abstract: Low frequency electromagnetic induction (EMI) is becoming a useful tool for soil characterization due to its fast measurement capability and sensitivity to soil moisture and salinity. In this research, a new EMI system (the CMD mini‐Explorer) is used for sub‐surface characterization of soil salinity in a drip irrigation system via a joint inversion approach of multi‐configuration EMI measurements. EMI measurements were conducted across a farm where Acacia trees are irrigated with brackish water. In‐situ measurements of vertical bulk electrical conductivity (σb) were recorded in different pits along one of the transects to calibrate the EMI measurements and to compare with the modeled electrical conductivity (σ) obtained by the joint inversion of multi‐configuration EMI measurements. Estimates of σ were then converted into the universal standard of soil salinity measurement (i.e. electrical conductivity of a saturated soil paste extract – ECe). Soil apparent electrical conductivity (ECa) was repeatedly measured with the CMD mini‐Explorer to investigate the temperature stability of the new system at a fixed location, where the ambient air temperature increased from 26 °C to 46 °C. Results indicate that the new EMI system is very stable in high temperature environments, especially above 40 °C, where most other approaches give unstable measurements. In addition, the distribution pattern of soil salinity is well estimated quantitatively by the joint inversion of multi‐component EMI measurements. The approach of joint inversion of EMI measurements allows for the quantitative mapping of the soil salinity distribution pattern and can be utilized for the management of soil salinity. This article is protected by copyright. All rights reserved.
      PubDate: 2015-03-13T06:34:49.016563-05:
      DOI: 10.1002/2014WR016245
       
  • Global change and the groundwater management challenge
    • Authors: Steven M. Gorelick; Chunmiao Zheng
      Pages: 3031 - 3051
      Abstract: With rivers in critical regions already exploited to capacity throughout the world and groundwater overdraft as well as large‐scale contamination occurring in many areas, we have entered an era in which multiple simultaneous stresses will drive water management. Increasingly, groundwater resources are taking a more prominent role in providing freshwater supplies. We discuss the competing fresh groundwater needs for human consumption, food production, energy, and the environment, as well as physical hazards, and conflicts due to transboundary overexploitation. During the past 50 years, groundwater management modeling has focused on combining simulation with optimization methods to inspect important problems ranging from contaminant remediation to agricultural irrigation management. The compound challenges now faced by water planners require a new generation of aquifer management models that address the broad impacts of global change on aquifer storage and depletion trajectory management, land subsidence, groundwater‐dependent ecosystems, seawater intrusion, anthropogenic and geogenic contamination, supply vulnerability, and long‐term sustainability. The scope of research efforts is only beginning to address complex interactions using multiagent system models that are not readily formulated as optimization problems and that consider a suite of human behavioral responses.
      PubDate: 2015-05-03T07:26:21.477024-05:
      DOI: 10.1002/2014WR016825
       
  • An exact analytical solution for steady seepage from a perched Aquifer to
           a low‐permeable sublayer: Kirkham‐Brock's legacy revisited
    • Authors: A. R. Kacimov; Yu. V. Obnosov
      Pages: 3093 - 3107
      Abstract: An analytical solution is obtained for steady 2‐D potential seepage flow from a nonclogged and nonlined soil channel into a highly permeable porous layer, with phreatic surfaces tapering toward a horizontal interface with a subjacent low‐permeable formation. Along this boundary, a vertical component of the Darcian velocity vector equals the formation saturated hydraulic conductivity. The image of the physical flow domain in the hodograph plane is a circular polygon, a triangle or digon in a limiting case of a “phreatic jet” impinging on the low‐permeable substratum. The polygon is mapped onto an auxiliary half plane, where the complex physical coordinate and complex potential are reconstructed by the Polubarinova‐Kochina method, i.e., by solution of a Riemann BVP. The seepage flow rate from the channel, free surfaces, and a saturated (water‐logged) area are found for different thicknesses of the top layer, channel widths, and conductivity ratios of the two strata. In particular, the earlier results of Brock, Kirkham, and Youngs, which are based on a numerical solution, Dupuit‐Forchheimer (DF) approximation, and approximate potential model, are confirmed in the full 2‐D models. Sufficiently far from the channel, the phreatic surface and interface make a wedge. For a sufficiently deep substratum, three zones are analytically distinguished: an almost vertical 1‐D descending flow, an almost wedge‐configured 1‐D flow, and an essentially 2‐D zone in between, where neither a standard infiltration theory nor DF analysis are valid.
      PubDate: 2015-05-02T03:07:45.428514-05:
      DOI: 10.1002/2014WR016304
       
  • Validation of finite water‐content vadose zone dynamics method using
           column experiments with a moving water table and applied surface flux
    • Authors: Fred L. Ogden; Wencong Lai, Robert C. Steinke, Jianting Zhu
      Pages: 3108 - 3125
      Abstract: Data from laboratory experiments on a 143 cm tall and 14.5 cm diameter column, packed with Wedron sand with varied constant upper boundary fluxes and water table velocities for both falling and rising water tables are used to validate a finite water‐content vadose zone simulation methodology. The one‐dimensional finite water‐content Talbot and Ogden (2008) (T‐O) infiltration and redistribution method was improved to simulate groundwater table dynamic effects and compared against the numerical solution of the Richards equation using Hydrus‐1D. Both numerical solutions agreed satisfactorily with time series measurements of water content. Results showed similar performance for both methods, with the T‐O method on average having higher Nash‐Sutcliffe efficiencies and smaller absolute biases. Hydrus‐1D was more accurate in predicting deponding times in the case of a falling water table, while Hydrus‐1D and the T‐O method had similar errors in predicted ponding times in the case of a rising water table in six of nine tests. The improved T‐O method was able to predict general features of vadose zone moisture dynamics with moving water table and surface infiltration using an explicit, mass‐conservative formulation. The advantage of an explicit formulation is that it is numerically simple, using forward Euler solution methodology, and is guaranteed to converge and to conserve mass. These properties make the improved T‐O method presented in this paper a robust and computationally efficient alternative to the numerical solution of the Richards equation in hydrological modeling applications involving groundwater table dynamic effects on vadose zone soil moistures.
      PubDate: 2015-05-02T03:08:01.949457-05:
      DOI: 10.1002/2014WR016454
       
  • Water‐quality trading: Can we get the prices of pollution right?
    • Authors: Yoshifumi Konishi; Jay S. Coggins, Bin Wang
      Pages: 3126 - 3144
      Abstract: Water‐quality trading requires inducing permit prices that account properly for spatially explicit damage relationships. We compare recent work by Hung and Shaw (2005) and Farrow et al. (2005) for river systems exhibiting branching and nonlinear damages. The Hung‐Shaw scheme is robust to nonlinear damages, but not to hot spots occurring at the confluence of two branches. The Farrow et al. (2005) scheme is robust to branching, but not to nonlinear damages. We also compare the two schemes to each other. Neither dominates from a welfare perspective, but the comparison appears to tilt in favor of the Farrow et al. scheme.
      PubDate: 2015-05-02T03:07:40.046189-05:
      DOI: 10.1002/2014WR015560
       
  • Comparison of three dual‐source remote sensing evapotranspiration
           models during the MUSOEXE‐12 campaign: Revisit of model physics
    • Authors: Yuting Yang; Di Long, Huade Guan, Wei Liang, Craig Simmons, Okke Batelaan
      Pages: 3145 - 3165
      Abstract: Various remote sensing‐based terrestrial evapotranspiration (ET) models have been developed during the past four decades. These models vary in conceptual and mathematical representations of the physics, consequently leading to different performances. Examination of uncertainties associated with limitations in model physics will be useful for model selection and improvement. Here, three dual‐source remote sensing ET models (i.e., the Hybrid dual‐source scheme and Trapezoid framework‐based ET Model (HTEM), the Two‐Source Energy Balance (TSEB) model, and the MOD16 ET algorithm) using ASTER images were compared during the MUSOEXE‐12 campaign in the Heihe River Basin in Northwest China, aiming to better understand the differences in model physics that potentially lead to differences in model performance. Model results were first compared against observations from a dense network of eddy covariance towers and isotope‐based evaporation (E) and transpiration (T) partitioning. Results show that HTEM outperformed the other two models in simulating ET and its partitioning, whereas MOD16 performed worst (i.e., ET root‐mean‐square errors are 42.3 W/m2 (HTEM), 49.8 W/m2 (TSEB), and 95.3 W/m2 (MOD16)). On to model limitations, HTEM tends to underestimate ET under high advection due mostly to the underestimation of temperatures for the wet edge in its trapezoidal space. For TSEB, large uncertainties occur in determining the initial Priestley‐Taylor coefficient and the iteration procedure for ET partitioning, leading to overestimation/underestimation of T/E in most cases, particularly over sparse vegetation. Primary use of meteorological data for MOD16 does not effectively capture the soil moisture restriction on ET, and therefore results in unreasonable spatial ET patterns.
      PubDate: 2015-05-03T07:27:52.082519-05:
      DOI: 10.1002/2014WR015619
       
  • Mathematical equivalence between time‐dependent single‐rate
           and multirate mass transfer models
    • Authors: D. Fernàndez‐Garcia; X. Sanchez‐Vila
      Pages: 3166 - 3180
      Abstract: The often observed tailing of tracer breakthrough curves is caused by a multitude of mass transfer processes taking place over multiple scales. Yet, in some cases, it is convenient to fit a transport model with a single‐rate mass transfer coefficient that lumps all the non‐Fickian observed behavior. Since mass transfer processes take place at all characteristic times, the single‐rate mass transfer coefficient derived from measurements in the laboratory or in the field vary with time ω(t). The literature review and tracer experiments compiled by Haggerty et al. (2004) from a number of sites worldwide suggest that the characteristic mass transfer time, which is proportional to ω(t)−1, scales as a power law of the advective and experiment duration. This paper studies the mathematical equivalence between the multirate mass transfer model (MRMT) and a time‐dependent single‐rate mass transfer model (t‐SRMT). In doing this, we provide new insights into the previously observed scale‐dependence of mass transfer coefficients. The memory function, g(t), which is the most salient feature of the MRMT model, determines the influence of the past values of concentrations on its present state. We found that the t‐SRMT model can also be expressed by means of a memory function φ(t,τ). In this case, though the memory function is nonstationary, meaning that in general it cannot be written as φ(t−τ). Nevertheless, the full behavior of the concentrations using a single time‐dependent rate ω(t) is approximately analogous to that of the MRMT model provided that the equality ω(t)=−dln⁡g(t)/dt holds and the field capacity is properly chosen. This relationship suggests that when the memory function is a power law, g(t)∼t1−k, the equivalent mass transfer coefficient scales as ω(t)∼t−1, nicely fitting without calibration the estimated mass transfer coefficients compiled by Haggerty et al. (2004).
      PubDate: 2015-05-03T07:25:44.740629-05:
      DOI: 10.1002/2014WR016348
       
  • Biodegradation of subsurface oil in a tidally influenced sand beach:
           Impact of hydraulics and interaction with pore water chemistry
    • Authors: Xiaolong Geng; Michel C. Boufadel, Kenneth Lee, Stewart Abrams, Makram Suidan
      Pages: 3193 - 3218
      Abstract: The aerobic biodegradation of oil in tidally influenced beaches was investigated numerically in this work using realistic beach and tide conditions. A numerical model BIOMARUN, coupling a multiple‐Monod kinetic model BIOB to a density‐dependent variably saturated groundwater flow model 2‐D MARUN, was used to simulate the biodegradation of low‐solubility hydrocarbon and transport processes of associated solute species (i.e., oxygen and nitrogen) in a tidally influenced beach environment. It was found that different limiting factors affect different portions of the beach. In the upper intertidal zone, where the inland incoming nutrient concentration was large (1.2 mg N/L), oil biodegradation occurred deeper in the beach (i.e., 0.3 m below the surface). In the midintertidal zone, a reversal was noted where the biodegradation was fast at shallow locations (i.e., 0.1 m below the surface), and it was due to the decrease of oxygen with depth due to consumption, which made oxygen the limiting factor for biodegradation. Oxygen concentration in the midintertidal zone exhibited two peaks as a function of time. One peak was associated with the high tide, when dissolved oxygen laden seawater filled the beach and a second oxygen peak was observed during low tides, and it was due to pore oxygen replenishment from the atmosphere. The effect of the capillary fringe (CF) height was investigated, and it was found that there is an optimal CF for the maximum biodegradation of oil in the beach. Too large a CF (i.e., very fine material) would attenuate oxygen replenishment (either from seawater or the atmosphere), while too small a CF (i.e., very coarse material) would reduce the interaction between microorganisms and oil in the upper intertidal zone due to rapid reduction in the soil moisture at low tide.
      PubDate: 2015-05-08T02:59:10.28158-05:0
      DOI: 10.1002/2014WR016870
       
  • Should hydraulic tomography data be interpreted using geostatistical
           inverse modeling? A laboratory sandbox investigation
    • Authors: Walter A. Illman; Steven J. Berg, Zhanfeng Zhao
      Pages: 3219 - 3237
      Abstract: The robust performance of hydraulic tomography (HT) based on geostatistics has been demonstrated through numerous synthetic, laboratory, and field studies. While geostatistical inverse methods offer many advantages, one key disadvantage is its highly parameterized nature, which renders it computationally intensive for large‐scale problems. Another issue is that geostatistics‐based HT may produce overly smooth images of subsurface heterogeneity when there are few monitoring interval data. Therefore, some may question the utility of the geostatistical inversion approach in certain situations and seek alternative approaches. To investigate these issues, we simultaneously calibrated different groundwater models with varying subsurface conceptualizations and parameter resolutions using a laboratory sandbox aquifer. The compared models included: (1) isotropic and anisotropic effective parameter models; (2) a heterogeneous model that faithfully represents the geological features; and (3) a heterogeneous model based on geostatistical inverse modeling. The performance of these models was assessed by quantitatively examining the results from model calibration and validation. Calibration data consisted of steady state drawdown data from eight pumping tests and validation data consisted of data from 16 separate pumping tests not used in the calibration effort. Results revealed that the geostatistical inversion approach performed the best among the approaches compared, although the geological model that faithfully represented stratigraphy came a close second. In addition, when the number of pumping tests available for inverse modeling was small, the geological modeling approach yielded more robust validation results. This suggests that better knowledge of stratigraphy obtained via geophysics or other means may contribute to improved results for HT.
      PubDate: 2015-05-08T02:59:34.564365-05:
      DOI: 10.1002/2014WR016552
       
  • Assimilation of stream discharge for flood forecasting: Updating a
           semidistributed model with an integrated data assimilation scheme
    • Authors: Yuan Li; Dongryeol Ryu, Andrew W. Western, Q. J. Wang
      Pages: 3238 - 3258
      Abstract: Real‐time discharge observations can be assimilated into flood models to improve forecast accuracy; however, the presence of time lags in the routing process and a lack of methods to quantitatively represent different sources of uncertainties challenge the implementation of data assimilation techniques for operational flood forecasting. To address these issues, an integrated error parameter estimation and lag‐aware data assimilation (IEELA) scheme was recently developed for a lumped model. The scheme combines an ensemble‐based maximum a posteriori (MAP) error estimation approach with a lag‐aware ensemble Kalman smoother (EnKS). In this study, the IEELA scheme is extended to a semidistributed model to provide for more general application in flood forecasting by including spatial and temporal correlations in model uncertainties between subcatchments. The result reveals that using a semidistributed model leads to more accurate forecasts than a lumped model in an open‐loop scenario. The IEELA scheme improves the forecast accuracy significantly in both lumped and semidistributed models, and the superiority of the semidistributed model remains in the data assimilation scenario. However, the improvements resulting from IEELA are confined to the outlet of the catchment where the discharge observations are assimilated. Forecasts at “ungauged” internal locations are not improved, and in some instances, even become less accurate.
      PubDate: 2015-05-08T02:58:40.367867-05:
      DOI: 10.1002/2014WR016667
       
  • Modeling chloride transport using travel time distributions at Plynlimon,
           Wales
    • Authors: Paolo Benettin; James W. Kirchner, Andrea Rinaldo, Gianluca Botter
      Pages: 3259 - 3276
      Abstract: Here we present a theoretical interpretation of high‐frequency, high‐quality tracer time series from the Hafren catchment at Plynlimon in mid‐Wales. We make use of the formulation of transport by travel time distributions to model chloride transport originating from atmospheric deposition and compute catchment‐scale travel time distributions. The relevance of the approach lies in the explanatory power of the chosen tools, particularly to highlight hydrologic processes otherwise clouded by the integrated nature of the measured outflux signal. The analysis reveals the key role of residual storages that are poorly visible in the hydrological response, but are shown to strongly affect water quality dynamics. A significant accuracy in reproducing data is shown by our calibrated model. A detailed representation of catchment‐scale travel time distributions has been derived, including the time evolution of the overall dispersion processes (which can be expressed in terms of time‐varying storage sampling functions). Mean computed travel times span a broad range of values (from 80 to 800 days) depending on the catchment state. Results also suggest that, in the average, discharge waters are younger than storage water. The model proves able to capture high‐frequency fluctuations in the measured chloride concentrations, which are broadly explained by the sharp transition between groundwaters and faster flows originating from topsoil layers.
      PubDate: 2015-05-08T02:57:58.597247-05:
      DOI: 10.1002/2014WR016600
       
  • A multiobjective short‐term optimal operation model for a cascade
           system of reservoirs considering the impact on long‐term energy
           production
    • Authors: Bin Xu; Ping‐An Zhong, Zachary Stanko, Yunfa Zhao, William W.‐G. Yeh
      Pages: 3353 - 3369
      Abstract: This paper examines the impact of short‐term operation on long‐term energy production. We propose a multiobjective optimization model for the short‐term, daily operation of a system of cascade reservoirs. The two objectives considered in the daily model are: (1) minimizing the total amount of water released and (2) maximizing the stored energy in the system. Optimizing short‐term operation without considering its impact on long‐term energy production does not guarantee maximum energy production in the system. Therefore, a major goal of this paper is to identify desirable short‐term operation strategies that, at the same time, optimize long‐term energy production. First, we solve the daily model for 1 month (30 days) using a nondominated genetic algorithm (NSGAII). We then use the nondominated solutions obtained by NSGAII to assess the impact on long‐term energy production using a monthly model. We use historical monthly inflows to characterize the inflow variability. We apply the proposed methodology to the Qingjiang cascade system of reservoirs in China. The results show: (1) in average hydrology scenarios, the solution maximizing stored energy produces the most overall long‐term energy production; (2) in moderately wet hydrology scenarios, the solution minimizing water released outperforms the maximizing stored energy solution; and (3) when extremely wet hydrology scenarios are expected, a compromise solution is the best strategy.
      PubDate: 2015-05-08T03:04:10.098371-05:
      DOI: 10.1002/2014WR015964
       
  • Does improved SSTA prediction ensure better seasonal rainfall
           forecasts?
    • Authors: Mohammad Zaved Kaiser Khan; Ashish Sharma, Rajeshwar Mehrotra, Andrew Schepen, Q. J. Wang
      Pages: 3370 - 3383
      Abstract: Seasonal rainfall forecasts in Australia are issued based on concurrent sea surface temperature anomalies (SSTAs) using a Bayesian model averaging (BMA) approach. The SSTA fields are derived from the Predictive Ocean‐Atmosphere Model for Australia (POAMA) initialized in the preceding season. This study investigates the merits of the rainfall forecasted using POAMA SSTAs in contrast to that forecasted using a multimodel combination of SSTAs derived using five existing models. In addition, seasonal rainfall forecasts derived from multimodel and POAMA SSTA fields are subsequently combined to obtain a single weighted forecast over Australia. These three forecasts are compared against “idealized” forecasts where observed SSTAs are used instead of those predicted. The results indicate that while seasonal rainfall forecasts derived using multimodel‐based SSTA indices offer improvements in selected seasons over a majority of grid cells in comparison to the case where a single SSTA model is used in two seasons, these improvements are not as significant as the improvements in the SSTA field that drive the rainfall forecasting model. The forecasts derived from the combination of multimodel and POAMA SSTA indices forecasts are found to offer greater improvements over the multimodel or the POAMA forecasts for a majority of grid cells in all seasons. It is also observed that these combined forecasts are touching the upper limits of forecastability, which are reached when observed SSTAs are used to forecast the rainfall. This suggests that further improvements in rainfall forecasting are only possible through the use of an improved forecasting algorithm, and not the driver (SSTA) information used in the current study.
      PubDate: 2015-05-08T03:05:14.401171-05:
      DOI: 10.1002/2014WR015997
       
  • Multimodel framework for characterization of transport in porous media
    • Authors: Valentina Ciriello; Yaniv Edery, Alberto Guadagnini, Brian Berkowitz
      Pages: 3384 - 3402
      Abstract: We consider modeling approaches to characterize solute transport in porous media, integrating them into a unique theoretical and experimental framework for model evaluation and data interpretation. To date, development of (conservative and reactive chemical) transport models and formulation of model calibration methods grounded on sensitivity‐based collection of measurements have been pursued in parallel. Key questions that remain include: For a given set of measurements, which conceptual picture of the transport processes, as embodied in a mathematical model or models, is most appropriate? What are the most valuable space‐time locations for solute concentration measurements, depending on the model selected? How is model parameter uncertainty propagated to model output, and how does this propagation affect model calibration? We address these questions by merging parallel streams of research—model formulation, reduction, calibration, sensitivity analysis, and discrimination—offering our view on an emerging framework that guides (i) selection of an appropriate number and location of time‐dependent concentration measurements given a transport model and (ii) assessment (through discrimination criteria) of the relative benefit of applying any particular model from a set of several models. Our strategy is to employ metrics to quantify the relative contribution of each uncertain model parameter to the variability of the model output. We evaluate these metrics through construction of a surrogate (or “meta”) transport model that has the additional benefit of enabling sensitivity analysis and model calibration at a highly reduced computational cost. We demonstrate the applicability of this framework, focusing on transport of reactive chemicals in laboratory‐scale porous media.
      PubDate: 2015-05-08T03:04:33.668216-05:
      DOI: 10.1002/2015WR017047
       
  • Balancing water scarcity and quality for sustainable irrigated agriculture
    • Authors: Shmuel Assouline; David Russo, Avner Silber, Dani Or
      Pages: 3419 - 3436
      Abstract: The challenge of meeting the projected doubling of global demand for food by 2050 is monumental. It is further exacerbated by the limited prospects for land expansion and rapidly dwindling water resources. A promising strategy for increasing crop yields per unit land requires the expansion of irrigated agriculture and the harnessing of water sources previously considered “marginal” (saline, treated effluent, and desalinated water). Such an expansion, however, must carefully consider potential long‐term risks on soil hydroecological functioning. The study provides critical analyses of use of marginal water and management approaches to map out potential risks. Long‐term application of treated effluent (TE) for irrigation has shown adverse impacts on soil transport properties, and introduces certain health risks due to the persistent exposure of soil biota to anthropogenic compounds (e.g., promoting antibiotic resistance). The availability of desalinated water (DS) for irrigation expands management options and improves yields while reducing irrigation amounts and salt loading into the soil. Quantitative models are used to delineate trends associated with long‐term use of TE and DS considering agricultural, hydrological, and environmental aspects. The primary challenges to the sustainability of agroecosystems lies with the hazards of saline and sodic conditions, and the unintended consequences on soil hydroecological functioning. Multidisciplinary approaches that combine new scientific knowhow with legislative, economic, and societal tools are required to ensure safe and sustainable use of water resources of different qualities. The new scientific knowhow should provide quantitative models for integrating key biophysical processes with ecological interactions at appropriate spatial and temporal scales.
      PubDate: 2015-05-08T03:03:43.253086-05:
      DOI: 10.1002/2015WR017071
       
 
 
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