- Lateral subsurface stormflow and solute transport in a forested hillslope:
A combined measurement and modeling approach
- Authors: Hanne Laine‐Kaulio; Soile Backnäs, Tuomo Karvonen, Harri Koivusalo, Jeffrey J. McDonnell
Pages: n/a - n/a
Abstract: Preferential flow dominates water movement and solute transport in boreal forest hillslopes. However, only a few model applications to date have accounted for preferential flow at forest sites. Here, we present a parallel and coupled simulation of flow and transport processes in the preferential flow domain and soil matrix of a forested hillslope section in Kangaslampi, Finland, using a new, three‐dimensional, physically‐based dual‐permeability model. Our aim is to simulate lateral subsurface stormflow and solute transport at the slope during a chloride tracer experiment, and to investigate the role of preferential flow in the tracer transport. The model was able to mimic the observed tracer transport during tracer irrigation, but overestimated the dilution velocity of the tracer plume in the highly conductive soil horizons near the soil surface after changing the irrigation to tracer‐free water. According to the model, 140 times more chloride was transported downslope in the preferential flow domain than in the soil matrix during the tracer irrigation. The simulations showed, together with reference simulations with a traditional one pore domain model, that a two pore domain approach was required to simulate the observed flow and transport event. The event was characterized by the transmissivity feedback phenomenon and controlled by preferential flow mechanisms, in particular by lateral by‐pass flow. According to our results, accounting for the slow‐ and fast‐flow domains of soil, as well as the water and solute exchange between the domains, is essential for a successful simulation of flow and solute transport in preferential flow dominated hillslopes.
- Runoff sources and flow paths in a partially burned, upland boreal
catchment underlain by permafrost
- Authors: Koch Joshua C; Kikuchi Colin P, Wickland Kimberly P, Schuster Paul
Pages: n/a - n/a
Abstract: Boreal soils in permafrost regions contain vast quantities of frozen organic material that is released to terrestrial and aquatic environments via subsurface flowpaths as permafrost thaws. Longer flowpaths may allow chemical reduction of solutes, nutrients, and contaminants, with implications for greenhouse gas emissions and aqueous export. Predicting boreal catchment runoff is complicated by soil heterogeneities related to variability in active layer thickness, soil type, fire history, and preferential flow potential. By coupling measurements of permeability, infiltration potential, and water chemistry with a stream chemistry end member mixing model, we tested the hypothesis that organic soils and burned slopes are the primary sources of runoff, and that runoff from burned soils is greater due to increased hydraulic connectivity. Organic soils were more permeable than mineral soils, and 25% of infiltration moved laterally upon reaching the organic‐mineral soil boundary on unburned hillslopes. A large portion of the remaining water infiltrated into deeper, less permeable soils. In contrast, burned hillslopes displayed poorly defined soil horizons, allowing rapid, mineral‐rich runoff through preferential pathways at various depths. On the catchment scale, mineral/organic runoff ratios averaged 1.6 and were as high as 5.2 for an individual storm. Our results suggest that burned soils are the dominant source of water and solutes reaching the stream in summer, whereas unburned soils may provide longer term storage and residence times necessary for production of anaerobic compounds. These results are relevant to predicting how boreal catchment drainage networks and stream export will evolve given continued warming and altered fire regimes.
- Micromodel study of two‐phase flow under transient conditions:
Quantifying effects of specific interfacial area
- Authors: N. K. Karadimitriou; S. M. Hassanizadeh, V. Joekar‐Niasar, P. J. Kleingeld
Pages: n/a - n/a
Abstract: Recent computational studies of two‐phase flow suggest that the role of fluid‐fluid interfaces should be explicitly included in the capillarity equation as well as equations of motion of phases. The aim of this study has been to perform experiments where transient movement of interfaces can be monitored and to determine interfacial variables and quantities under transient conditions. We have performed two‐phase flow experiments in a transparent micro‐model. Specific interfacial area is defined, and calculated from experimental data, as the ratio of the total area of interfaces between two phases per unit volume of the porous medium. Recent studies have shown that all drainage and imbibition data points for capillary pressure, saturation, and specific interfacial area fall on a unique surface. But, up to now, almost all micro‐model studies of two‐phase flow have dealt with quasi‐static or steady‐state flow conditions. Thus, only equilibrium properties have been studied.
We present the first study of two‐phase flow in an elongated PDMS micro‐model under transient conditions with high temporal and spatial resolutions. We have established that different relationships between capillary pressure, saturation, and specific interfacial area are obtained under steady‐state and transient conditions. The difference between the surfaces depends on the capillary number. Furthermore, we use our experimental results to obtain average (macro scale) velocity of fluid‐fluid interfaces and the rate of change of specific interfacial area as a function of time and space. Both terms depend on saturation nonlinearly but show a linear dependence on the rate of change of saturation. We also determine macro‐scale material coefficients that appear in the equation of motion of fluid‐fluid interfaces. This is the first time that these parameters are determined experimentally.
- Exact versus Dupuit interface flow in anisotropic coastal aquifers
- Authors: M. Bakker
Pages: n/a - n/a
Abstract: The Dupuit solution for interface flow towards the coast in a confined aquifer is compared to a new exact solution, which is obtained with the Hodograph method and conformal mapping. The position of the toe of the interface is a function of two dimensionless parameters: the ratio of the hydraulic gradient upstream of the interface where flow is one‐dimensional over the dimensionless density difference, and the ratio of the horizontal hydraulic conductivity over the vertical hydraulic conductivity. The Dupuit interface, which neglects resistance to vertical flow, is a very accurate approximation of the exact interface for isotropic aquifers. The difference in the position of the toe between the exact and Dupuit solutions increases when the vertical anisotropy increases. For highly anistropic aquifers, it is proposed to add an effective resistance layer along the bottom of the sea in Dupuit models. The resistance of the layer is chosen such that the head in the Dupuit model is equal to the head in the exact solution upstream of the interface where flow is one‐dimensional.
- Sensitivity of power functions to aggregation: Bias and uncertainty in
radar rainfall retrieval
- Authors: M. G. Sassi; H. Leijnse, R. Uijlenhoet
Pages: n/a - n/a
Abstract: Rainfall retrieval using weather radar relies on power functions between radar reflectivity Z and rain rate R. The nonlinear nature of these relations complicates the comparison of rainfall estimates employing reflectivities measured at different scales. Transforming Z into R using relations that have been derived for other scales results in a bias and added uncertainty. We investigate the sensitivity of Z‐R relations to spatial and temporal aggregation using high‐resolution reflectivity fields for five rainfall events. Existing Z‐R relations were employed to investigate the behavior of aggregated Z‐R relations with scale, the aggregation bias and the variability of the estimated rain rate. The prefactor and the exponent of aggregated Z‐R relations systematically diverge with scale, showing a break that is event‐dependent in the temporal domain and nearly constant in space. The systematic error associated with the aggregation bias at a given scale can become of the same order as the corresponding random error associated with intermittent sampling. The bias can be constrained by including information about the variability of Z within a certain scale of aggregation, and is largely captured by simple functions of the coefficient of variation of Z. Several descriptors of spatial and temporal variability of the reflectivity field are presented, to establish the links between variability descriptors and resulting aggregation bias. Prefactors in Z‐R relations can be related to multi‐fractal properties of the rainfall field. We find evidence of scaling breaks in the structural analysis of spatial rainfall with aggregation.
- Patterns of local and nonlocal water resource use across the western U.S.
determined via stable isotope intercomparisons
- Authors: Stephen P. Good; Casey D. Kennedy, Jeremy C. Stalker, Lesley A. Chesson, Luciano O. Valenzuela, Melanie M. Beasley, James R. Ehleringer, Gabriel. J. Bowen
Pages: n/a - n/a
Abstract: In the western United States, the mis‐match between public water demands and natural water availability necessitates large inter‐basin transfers of water as well as groundwater mining of fossil aquifers. Here, we identify probable situations of non‐local water use in both space and time based on isotopic comparisons between tap waters and potential water resources within hydrologic basins. Our approach, which considers evaporative enrichment of heavy isotopes during storage and distribution, is used to determine the likelihood of local origin for 612 tap water samples collected from across the western United States. We find that 64% of samples are isotopically distinct from precipitation falling within the local hydrologic basin, a proxy for groundwater with modern recharge, and 31% of samples are isotopically distinct from estimated surface water found within the local basin. Those samples inconsistent with local water sources, which we suggest are likely derived from water imported from other basins or extracted from fossil‐aquifers, are primarily clustered in southern California, the San Francisco Bay area, and central Arizona. Our isotope‐based estimates of non‐local water use are correlated with both hydro‐geomorphic and socio‐economic properties of basins, suggesting that these factors exert a predictable influence on the likelihood that non‐local waters are used to supply tap water. We use these basin properties to develop a regional model of non‐local water resource use that predicts (r2=0.64) isotopically inferred patterns and allows assessment of total inter‐basin transfer and/or fossil aquifer extraction volumes across the western United States.
- A parameter estimation framework for multiscale Kalman smoother algorithm
in precipitation data fusion
- Authors: Shugong Wang; Xu Liang
Pages: n/a - n/a
Abstract: A new effective parameter estimation approach is presented for the Multiscale Kalman Smoother (MKS) algorithm. As demonstrated, it shows promising potentials in deriving better data products involving sources from different spatial scales and precisions. The proposed approach employs a multi‐objective parameter estimation framework, which includes three multi‐objective estimation schemes (MO schemes), rather than using the conventional maximum likelihood scheme (ML scheme), to estimate the MKS parameters. Unlike the ML scheme, the MO schemes are not built on strict statistical assumptions related to prediction errors and observation errors, rather, they directly associate the fused data of multiple scales with multiple objective functions. In the MO schemes, objective functions are defined to facilitate consistency among the fused data at multiple scales and the input data at their original scales as well in terms of spatial patterns and magnitudes. Merits of the new approach are evaluated through a Monte Carlo experiment and a series of comparison analyses using synthetic precipitation data that contain noises which follow either the multiplicative error model or the additive error model. Our results show that the MKS fused precipitation performs better using the MO framework. Improvements are particularly significant for the fused precipitation associated with fine spatial resolutions. This is due mainly to the adoption of more criteria and constraints in the MO framework. The weakness of the original ML scheme, arising from its blindly putting more weights into the data associated with finer resolutions, is circumvented in the proposed new MO framework.
- Improving the surface‐ground water interactions in the Community
Land Model: Case study in the Blue Nile Basin
- Authors: Di D. Wu; Emmanouil N. Anagnostou, Guiling Wang, Semu Moges, Matteo Zampieri
Pages: n/a - n/a
Abstract: Soil moisture is a key water cycle parameter known to interact with atmospheric processes. Arguably, land surface models that simulate land surface processes and surface fluxes to the atmosphere do not capture adequately the spatial variability of soil moisture, particularly over areas with complex topography. In this study, version 3.5 of the Community Land Model (CLM3.5) is applied with a new parameterization in an effort to correct the spatial bias of soil moisture and understand the consequential effects on the simulated water cycle fluxes and states in the Blue Nile basin. This parameterization accounts for a groundwater recharge term from surface water, a process that is not included in CLM, providing an effective two‐way interaction scheme between rivers and groundwater. Using satellite soil moisture data, this parameterized term is shown to have a positive correlation to contributing area, defined at each model grid cell and representing the number of grid cells that drain to that local grid cell. With the new parameterization applied to CLM, soil moisture, soil temperature, evapotranspiration flux, water table depth, and vegetation water content all showed significant differences from the control CLM run (without the parameterization) at or above the 95% confidence level. The differences in the spatial distribution of these variables are expected to affect precipitation simulations from regional climate modeling. As the Blue Nile is a region that has one of the greatest inter‐annual and seasonal precipitation variability globally, the ability to predict this variability is essential for optimal reservoir operations including buffering of water resources during times of drought.
- Spatially variable water table recharge and the hillslope hydrologic
response: Analytical solutions to the linearized hillslope Boussinesq
- Authors: David N. Dralle; Gabrielle F.S. Boisramé, Sally E. Thompson
Pages: n/a - n/a
Abstract: The linearized hillslope Boussinesq equation, introduced by Brutsaert, describes the dynamics of saturated, subsurface flow from hillslopes with shallow, unconfined aquifers. In this paper, we use a new analytical technique to solve the linearized hillslope Boussinesq equation to predict water table dynamics and hillslope discharge to channels. The new solutions extend previous analytical treatments of the linearized hillslope Boussinsq equation to account for the impact of spatiotemporal heterogeneity in water table recharge. The results indicate that the spatial character of recharge may significantly alter both steady‐state subsurface storage characteristics and the transient hillslope hydrologic response, depending strongly on similarity measures of controls on the subsurface flow dynamics. Additionally, we derive new analytical solutions for the linearized hillslope‐storage Boussinesq equation and explore the interaction effects of recharge structure and hillslope morphology on water storage and baseflow recession characteristics. A theoretical recession analysis, for example, demonstrates that decreasing the relative amount of downslope recharge has a similar effect as increasing hillslope convergence. In general, the theory suggests that recharge heterogeneity can serve to diminish or enhance the hydrologic impacts of hillslope morphology.
- Issue Information
- Pages: i - v
- Channel evolution after dam removal in a poorly sorted sediment mixture:
Experiments and numerical model
- Authors: Carles Ferrer‐Boix; Juan Pedro Martín‐Vide, Gary Parker
Pages: n/a - n/a
Abstract: Dam removal is commonly used for river restoration. However, there are still some uncertainties associated with dam removal, mainly related to the sediment transport rates released downstream from the deposit that had previously filled the impoundment. This research studies the physical response to dam removal in the antecedent deposit by answering the following questions: a) how does an initial channel excavated into the deposit evolve, and b) what is the time distribution of the material released during the early stages of the process. These goals are achieved by an experimental campaign using a poorly sorted mixture of sediment in the antecedent deposit. The research shows that for the given conditions of our experiments, the rate at which the sediment is released depends on the height of the removed dam, the water discharge and the maximum potential volume of sediment to be eroded. This investigation provides new insights of the width evolution when the sediment is composed of a poorly‐sorted mixture. This evolution is linked to the bed degradation rates: channel narrows during a rapid incisional phase, and subsequently widens when bed degradation rates decrease. Channel width changes propagate upstream as a convection‐like perturbation associated with a kinematic wave starting at the location of the antecedent dam. These features are modeled through a new numerical model accounting for mixtures. More specifically, a set of equations has been derived for the variation of bed elevation, channel bottom width and bed grain size distribution, that when solved numerically, describe the observed channel processes.
- Falling head ponded infiltration in the nonlinear limit
- Authors: D. Triadis
Pages: n/a - n/a
Abstract: The Green and Ampt infiltration solution represents only an extreme example of behaviour within a larger class of very nonlinear, delta function diffusivity soils. The mathematical analysis of these soils is greatly simplified by the existence of a sharp wetting front below the soil surface. Solutions for more realistic delta function soil models have recently been presented for infiltration under surface saturation without ponding.
After general formulation of the problem, solutions for a full suite of delta function soils are derived for ponded surface water depleted by infiltration. Exact expressions for the cumulative infiltration as a function of time, or the drainage time as a function of the initial ponded depth may take implicit or parametric forms, and are supplemented by simple asymptotic expressions valid for small times, and small and large initial ponded depths.
As with surface saturation without ponding, the Green–Ampt model overestimates the effect of the soil hydraulic conductivity. At the opposing extreme a low‐conductivity model is identified that also takes a very simple mathematical form and appears to be more accurate than the Green–Ampt model for larger ponded depths. Between these two, the nonlinear limit of Gardner's soil is recommended as a physically valid first approximation. Relative discrepancies between different soil models are observed to reach a maximum for intermediate values of the dimensionless initial ponded depth, and in general are smaller than for surface saturation without ponding.
- Nonlinear time series modeling of unconfined groundwater head
- Authors: T. J. Peterson; A. W. Western
Pages: n/a - n/a
Abstract: This paper presents a nonlinear transfer function noise model for time‐series modeling of unconfined groundwater hydrographs. The motivation for its development was that existing groundwater time‐series models were unable to simulate large recharge events and multi‐year droughts. This was because existing methods do not partition rainfall to runoff and do not account for nonlinear soil water drainage. To account for these nonlinear processes, a vertically integrated soil moisture module was added to an existing transfer function noise model. The soil moisture module has a highly flexible structure that allowed 84 different forms to be built. Application of the time‐series model requires numerical calibration of parameters for the transfer functions, noise model and, for the nonlinear models, the soil moisture module. This was undertaken using the Covariance Matrix Adaptation Evolutionary Strategy (CMA‐ES) global calibration scheme. However, reproducible calibration to the global optima was challenging and a number of modifications were required to the transfer function noise model. In trialling the 84 nonlinear models and 2 linear models, each was applied to eleven observation bores within a paired catchment study area in Great Western, Victoria, Australia. In comparison with existing groundwater hydrograph time‐series models, the proposed nonlinear time‐series model performed significantly better at all observation bores during calibration and evaluation periods. Both the linear and nonlinear models were also used to quantify the impact of re‐vegetation within the paired catchment; however, results were inconclusive, which is likely due to time‐series data for the state of the re‐vegetation being unavailable. By analyzing the application of 84 nonlinear models to each bore, an optimal structure for the soil moisture module was identified. It is unlikely, however, that this model structure would be appropriate for all climates and geologies. To encourage further investigations, open‐source code for the highly flexible groundwater time‐series modeling framework is available and we invite others to develop new models.
- Physical context for theoretical approaches to sediment transport
magnitude‐frequency analysis in alluvial channels
- Authors: Joel Sholtes; Kevin Werbylo, Brian Bledsoe
Pages: n/a - n/a
Abstract: Theoretical approaches to magnitude‐frequency analysis (MFA) of sediment transport in channels couple continuous flow probability density functions (PDFs) with power law flow‐sediment transport relations (rating curves) to produce closed‐form equations relating MFA metrics such as the effective discharge, Qeff, and fraction of sediment transported by discharges greater than Qeff, f+, to statistical moments of the flow PDF and rating curve parameters. These approaches have proven useful in understanding the theoretical drivers behind the magnitude and frequency of sediment transport. However, some of their basic assumptions and findings may not apply to natural rivers and streams with more complex flow‐sediment transport relationships or management and design scenarios, which have finite time horizons. We use simple numerical experiments to test the validity of theoretical MFA approaches in predicting the magnitude and frequency of sediment transport. Median values of Qeff and f+ generated from repeated, synthetic, finite flow series diverge from those produced with theoretical approaches using the same underlying flow PDF. The closed‐form relation for f+ is a monotonically‐increasing function of flow variance. However, using finite flow series, we find that f+ increases with flow variance to a threshold that increases with flow record length. By introducing a sediment entrainment threshold, we present a physical mechanism for the observed diverging relationship between Qeff and flow variance in fine and coarse bed channels. Our work shows that through complex and threshold‐driven relationships sediment transport mode, channel morphology, flow variance, and flow record length all interact to influence estimates of what flow frequencies are most responsible for transporting sediment in alluvial channels.
- Use of an entropy‐based metric in multiobjective calibration to
improve model performance
- Authors: I.G. Pechlivanidis; B. Jackson, H. McMillan, H. Gupta
Pages: n/a - n/a
Abstract: Parameter estimation for hydrological models is complicated for many reasons, one of which is the arbitrary emphasis placed, by most traditional measures of fit, on various magnitudes of the model residuals. Recent research has called for the development of robust diagnostic measures that provide insights into which model structural components and/or data may be inadequate. In this regard, the flow duration curve (FDC) represents the historical variability of flow and is considered to be an informative signature of catchment behavior. Here we investigate the potential of using the recently developed conditioned entropy difference metric (CED) in combination with the Kling‐Gupta efficiency (KGE). The CED respects the static information contained in the flow frequency distribution (and hence the FDC), but does not explicitly characterize temporal dynamics. The KGE reweights the importance of various hydrograph components (correlation, bias, variability) in a way that has been demonstrated to provide better model calibrations than the commonly used Nash‐Sutcliffe efficiency, while being explicitly time‐sensitive. We employ both measures within a multi‐objective calibration framework and achieve better performance over the full range of flows than obtained by single‐criteria approaches, or by the common multi‐objective approach that uses log‐transformed and un‐transformed data to balance fitting of low‐ and high‐flow periods. The investigation highlights the potential of CED to complement KGE (and vice versa) during model identification. It is possible that some of the complementarity is due to CED representing more information from moments > 2 than KGE or other common metrics. We therefore suggest that an interesting way forward would be to extend KGE to include higher moments, i.e. use different moments as multiple criteria.
- Evolving many‐objective water management to exploit exascale
- Authors: Patrick M. Reed; David Hadka
Pages: n/a - n/a
Abstract: This study contributes one of the largest parallel scalability experiments ever attempted within the water resources literature to date, encompassing 2000 years of computational time. A severely challenging multiobjective benchmark problem focusing on urban water portfolio planning under uncertainty in the Lower Rio Grande Valley (LRGV) is used to demonstrate that a multi‐master variant of the Borg multiobjective evolutionary algorithm (MOEA) can be used efficiently on more than 524,288 compute cores. The scalability of the multi‐master Borg MOEA enables users to compress up to 20 years of computational work into 20 minutes of actual wall‐clock time. Beyond these temporal efficiency gains, metric‐based statistical assessments of solution quality show that the multi‐master Borg MOEA dramatically enhances the effectiveness and reliability of the algorithm's auto‐adaptive search features. Theoretical algorithmic analysis shows that the multi‐master Borg MOEA could maintain high levels of parallel scalability on future exascale computing platforms (i.e., millions of compute cores). These results mark a fundamental expansion of the scope, computational demands, and difficulties that can be addressed in multiobjective water resources applications.
- Willingness to pay and willingness to work for improvements of municipal
and community‐managed water services
- Authors: William F. Vásquez
Pages: n/a - n/a
Abstract: This study investigates household preferences, in labor time and monetary terms, for improved water services in Guatemala using sequential contingent valuation questions. The household survey was implemented in areas served by municipal and community‐managed systems, which allows for comparing household preferences under those governance approaches. Results show that respondents with municipal services are willing to pay a substantial increase (more than 200%) in their water bills for reliable supplies of safe drinking water. They are also willing to work approximately 19 hours per month for such improved services when labor hours are proposed as the payment vehicle. In contrast, households with community‐managed services are not willing to pay or work for service improvements, even though they report to be quite dissatisfied with current services. Policy implications are discussed.
- Spatially implemented Bayesian network model to assess environmental
impacts of water managementmain
- Authors: Ryan R. Morrison; Mark C. Stone
Pages: n/a - n/a
Abstract: Bayesian networks (BNs) have become a popular method of assessing environmental impacts of water management. However, spatial attributes that influence ecological processes are rarely included in BN models. We demonstrate the benefits of combining two‐dimensional hydrodynamic and BN modeling frameworks to explicitly incorporate the spatial variability within a system. The impacts of two diversion scenarios on riparian vegetation recruitment at the Gila River, New Mexico, USA, were evaluated using a coupled modeling framework. We focused on five individual sites in the Upper Gila Basin. Our BN model incorporated key ecological drivers based on the “recruitment box” conceptual model, including the timing of seed availability, floodplain inundation, river recession rate, and groundwater depths. Results indicated that recruitment potential decreased by more than 20% at some locations within each study site, relative to existing conditions. The largest impacts occurring along dynamic fluvial landforms, such as side channel and sand bars. Reductions in recruitment potential varied depending on the diversion scenario. Our unique approach allowed us to evaluate recruitment consequences of water management scenarios at a fine spatial scale, which not only helped differentiate impacts at distinct channel locations, but was useful for informing stakeholders of possible ecological impacts. Our findings also demonstrate that minor changes to river flow may have large ecological implications.
- Using a Bayesian hierarchical model to improve Lake Erie cyanobacteria
- Authors: Daniel R. Obenour; Andrew D. Gronewold, Craig A. Stow, Donald Scavia
Pages: n/a - n/a
Abstract: The last decade has seen a dramatic increase in the size of western Lake Erie cyanobacteria blooms, renewing concerns over phosphorus loading, a common driver of freshwater productivity. However, there is considerable uncertainty in the phosphorus load‐bloom relationship, because of other biophysical factors that influence bloom size, and because the observed bloom size is not necessarily the true bloom size, owing to measurement error. In this study, we address these uncertainties by relating late‐summer bloom observations to spring phosphorus load within a Bayesian modeling framework. This flexible framework allows us to evaluate three different forms of the load‐bloom relationship, each with a particular combination of statistical error distribution and response transformation. We find that a novel implementation of a gamma error distribution, along with an untransformed response, results in a model with relatively high predictive skill and realistic uncertainty characterization, when compared to models based on more common statistical formulations. Our results also underscore the benefits of a hierarchical approach that enables assimilation of multiple sets of bloom observations within the calibration processes, allowing for more thorough uncertainty quantification and explicit differentiation between measurement and model error. Finally, in addition to phosphorus loading, the model includes a temporal trend component indicating that Lake Erie has become increasingly susceptible to large cyanobacteria blooms over the study period (2002‐2013). Results suggest that current phosphorus loading targets will be insufficient for reducing the intensity of cyanobacteria blooms to desired levels, so long as the lake remains in a heightened state of bloom susceptibility.
- A drought index accounting for snow
- Authors: Maria Staudinger; Kerstin Stahl, Jan Seibert
Pages: n/a - n/a
Abstract: The Standardized Precipitation Index (SPI) is the most widely used index to characterize droughts that are related to precipitation deficiencies. However, the SPI does not always deliver the relevant information for hydrological drought management particularly in snow influenced catchments. If precipitation is temporarily stored as snow, then there is a significant difference between meteorological and hydrological drought because the delayed release of melt water to the stream. We introduce an extension to the SPI, the Standardized Snow Melt and Rain Index (SMRI), that accounts for rain and snow melt deficits, which effectively influence streamflow. The SMRI can be derived without snow data, using temperature and precipitation to model snow. The value of the new index is illustrated for seven Swiss catchments with different degrees of snow influence. In particular for catchments with a larger component of snowmelt in runoff generation, the SMRI was found to be a worthwhile complementary index to the SPI to characterize streamflow droughts.
- Relating soil specific surface area, water film thickness, and water vapor
- Authors: Tairone Paiva Leão; Markus Tuller
Pages: n/a - n/a
Abstract: Estimation of soil specific surface area (SSA) and dry‐end water vapor adsorption are important for porous media characterization and for prediction of water and vapor fluxes in arid environments. The objective of the presented study was to model water adsorption, film thickness and SSA based on t‐curve theory originally developed for N2 adsorption. Data from 21 source soils with clay contents ranging from 0.6 to 52.2%, was used to estimate specific surface area based on water retention, a t‐curve type method, the linear prediction method and a simplified monolayer method. The water retention and the t‐curve methods were found to be mathematically analogous and were among the most accurate with regard to correlation coefficient (r = 0.97) and root mean square error (RMSE = 11.36 x 103 m2/kg) when compared to measurements obtained with the standard ethylene glycol monoethyl ether (EGME) method. The corrected t‐curve method significantly overestimated SSA when compared to EGME data. Comparison of all considered methods with N2‐BET (BET) measurements disclosed lower correlation coefficients. For soil studies, the vapor adsorption in conjunction with the t‐curve or water retention methods should be preferred for SSA estimation as they show much higher correlation with soil clay content and EGME measurements.
- Embedded resource accounting for coupled natural‐human systems: An
application to water resource impacts of the western U.S. electrical
- Authors: Benjamin L. Ruddell; Elizabeth A. Adams, Richard Rushforth, Vincent C. Tidwell
Pages: n/a - n/a
Abstract: In complex coupled natural‐human systems (CNH), multitype networks link social, environmental, and economic systems with flows of matter, energy, information, and value. Embedded Resource Accounting (ERA) is a systems analysis framework that includes the indirect connections of a multitype CNH network. ERA is conditioned on perceived system boundaries, which may vary according to the accountant's Point of View. Both direct and indirect impacts are implicit whenever two subnetworks interact in such a system; the ratio of two subnetworks' impacts is the Embedded Intensity. For trade in the services of water, this is understood as the indirect component of a Water Footprint, and as ‘virtual water' trade. ERA is a generalization of Input‐Output, Footprint, and Substance Flow methods, and is a type of Life Cycle Analysis.
This paper presents results for the water and electrical energy system in the Western U.S. This system is dominated by California, which outsources the majority of its Water Footprint of electrical energy. Electricity trade increases total water consumption for electricity production in the Western U.S. by 15%, and shifts water use to water‐stressed Colorado River Basin States. A systemic under‐accounting for Water Footprints occurs because State‐level processes discount a portion of the Water Footprint occurring outside of the State boundary.
- Spatial periodicity in bed form‐scale solute and thermal transport
models of the hyporheic zone
- Authors: Tariq Laattoe; Adrian D. Werner, Vincent E.A. Post
Pages: n/a - n/a
Abstract: Spatially periodic solute boundaries force symmetry across a model domain by ensuring that concentrations and concentration gradients are identical at the same location on opposite boundaries. They have been used in multiple publications on a hyporheic zone model of a single ripple or dune style bedform, including variable density flow and reactive transport variants. We evaluate simulations of multi‐bedform models without imposing spatially periodic transport to demonstrate that non‐physical solute distributions arise from the periodic solute transport assumption. That is, the flow field within the single bedform model leads to a transport scenario that violates the forced symmetry of periodic solute boundary conditions, culminating in a physically unrealistic solute distribution. Our results show that lack of symmetry between boundaries is a function of the vertical concentration gradient and two dimensionless parameters characterizing the hyporheic and underflow flow regimes, and the solute exchange between them. We assess the error associated with the spatially periodic assumption based on an analysis of solute fluxes across the lateral bedform model boundaries. While the focus is on steady‐state concentration distributions, the implications for transient solute transport models are also discussed. We conclude that periodic solute transport boundary conditions should be applied only to bedform models that have minimal vertical dispersive and diffusive solute transfer. This includes gaining systems and tracers such as temperature, for which a temporally‐periodic flux reversal occurs across the top boundary.
- A hidden Markov model combined with climate indices for multidecadal
- Authors: C. Bracken; B. Rajagopalan, E. Zagona
Pages: n/a - n/a
Abstract: Hydroclimate time series often exhibit very low year‐to‐year autocorrelation while showing prolonged wet and dry epochs reminiscent of regime shifting behavior. Traditional stochastic time series models cannot capture the regime shifting features thereby misrepresenting the risk of prolonged wet and dry periods, consequently impacting management and planning efforts. Upper Colorado River Basin (UCRB) annual flow series highlights this clearly. To address this, a simulation framework is developed using a Hidden Markov (HM) model in combination with large scale climate indices that drive multidecadal variability. We demonstrate this on the UCRB flows and show that the simulations are able to capture the regime features by reproducing the multidecadal spectral features present in the data where a basic HM model without climate information cannot.
- Pore by pore capillary pressure measurements using X‐ray
microtomography at reservoir conditions: Curvature, snap‐off, and
remobilization of residual CO2
- Authors: Matthew Andrew; Branko Bijeljic, Martin J. Blunt
Pages: n/a - n/a
Abstract: X‐ray microtomography was used to image the shape and size of residual ganglia of supercritical CO2 at resolutions of 3.5 µm and 2 µm and at representative subsurface conditions of temperature and pressure. The capillary pressure for each ganglion was found by measuring the curvature of the CO2‐brine interface, while the pore structure was parameterised using distance maps of the pore‐space. The formation of the residual clusters by snap‐off was examined by comparing the ganglion capillary pressure to local pore topography. The capillary pressure was found to be inversely proportional to the radius of the largest restriction (throat) surrounding the ganglion, which validates the imbibition mechanisms used in pore‐network modelling. The potential mobilization of residual ganglia was assessed using a reformulation of both the capillary (Ncmacro) and Bond numbers (Nbmacro), rigorously based on a balance of pore‐scale forces, with the majority of ganglia remobilized at Ncmacro around 1. Buoyancy forces were found to be small in this system (Nbmacro
- Quantitative generalizations for catchment sediment yield following forest
- Authors: James C. Bathurst; Andrés Iroumé
Pages: n/a - n/a
Abstract: Published data for temperate forests across the world are analyzed to investigate the potential for generalized quantitative expressions of catchment sediment yield impact in the years immediately following logging. Such generalizations would be useful in a variety of forestry and engineering tasks and would aid the spread of knowledge amongst both relevant professionals and new students. Data were assembled for paired catchment studies (51 catchments including 16 controls) that enabled the post‐logging sediment yield impact to be compared with both the pre‐logging period and an undisturbed control catchment, using a specially defined relative response factor. Three categories of impact were derived: low‐moderate, high and very high, defined by specific ranges in the maximum value of the relative response factor. The maximum increase in specific sediment yield (in t km‐2 yr‐1) following logging is one order of magnitude above the control sediment yield at both the annual and storm event scales, at least under normal circumstances of Best Management Practice. There is no apparent relationship between sediment yield and the proportion of catchment logged, at least at the general scale. A cumulative probability distribution for the year in which the maximum post‐logging sediment yield occurs, shows the majority of cases falling in the first two years. These generalizations refer to the broad response to logging as a function of ground disturbance, for example by logging technique, roads and burning. Although limited to order‐of‐magnitude quantification, they provide a basis for first estimates and for a general appreciation of an impact problem.
- Fully integrated modeling of surface‐subsurface solute transport and
the effect of dispersion in tracer hydrograph separation
- Authors: Jessica E. Liggett; Adrian D. Werner, Brian D. Smerdon, Daniel Partington, Craig T. Simmons
Pages: n/a - n/a
Abstract: Tracer hydrograph separation has been widely applied to identify streamflow components, often indicating that pre‐event water comprises a large proportion of stream water. Previous work using numerical modeling suggests that hydrodynamic mixing in the subsurface inflates the pre‐event water contribution to streamflow when derived from tracer‐based hydrograph separation. This study compares the effects of hydrodynamic dispersion, both within the subsurface and at the surface‐subsurface boundary, on the tracer‐based pre‐event water contribution to streamflow. Using a fully integrated surface‐subsurface code, we simulate two hypothetical 2D hillslopes with surface‐subsurface solute exchange represented by different solute transport conceptualizations (i.e. advective and dispersive conditions). Results show that when surface‐subsurface solute transport occurs via advection only, the pre‐event water contribution from the tracer‐based separation agrees well with the hydraulically determined value of pre‐event water from the numerical model, despite dispersion occurring within the subsurface. In this case, subsurface dispersion parameters have little impact on the tracer‐based separation results. However, the pre‐event water contribution from the tracer‐based separation is larger when dispersion at the surface‐subsurface boundary is considered. This work demonstrates that dispersion within the subsurface may not always be a significant factor in apparently large pre‐event water fluxes over a single rainfall event. Instead, dispersion at the surface‐subsurface boundary may increase estimates of pre‐event water contribution. This work also shows that solute transport in numerical models is highly sensitive to the representation of the surface‐subsurface interface. Hence, models of catchment‐scale solute dynamics require careful treatment and sensitivity testing of the surface‐subsurface interface to avoid misinterpretation of real‐world physical processes.
- Parameterization of training images for aquifer 3‐D facies modeling,
integrating geological interpretations and statistical inference
- Authors: Sanjeev Kumar Jha; Alessandro Comunian, Gregoire Mariethoz, Bryce F. J. Kelly
Pages: n/a - n/a
Abstract: We develop a stochastic approach to construct channelized 3D geological models constrained to borehole measurements as well as geological interpretation. The methodology is based on simple 2D geologist‐provided sketches of fluvial depositional elements, which are extruded in the 3rd dimension. Multiple‐point geostatistics (MPS) is used to impair horizontal variability to the structures by introducing geometrical transformation parameters. The sketches provided by the geologist are used as elementary training images, whose statistical information is expanded through randomized transformations. We demonstrate the applicability of the approach by applying it to modeling a fluvial valley filling sequence in the Maules Creek catchment, Australia. The facies models are constrained to borehole logs, spatial information borrowed from an analogue and local orientations derived from the present‐day stream networks. The connectivity in the 3D facies models is evaluated using statistical measures and transport simulations. Comparison with a statistically equivalent variogram‐based model shows that our approach is more suited for building 3D facies models that contain structures specific to the channelized environment and which have a significant influence on the transport processes.
- Coupling ground and airborne geophysical data with upscaling techniques
for regional groundwater modeling of heterogeneous aquifers: Case study of
a sedimentary aquifer intruded by volcanic dykes in Northern Ireland
- Authors: Neil Edwin Matthew Dickson; Jean‐Christophe Comte, Jennifer McKinley, Ulrich Ofterdinger
Pages: n/a - n/a
Abstract: In highly heterogeneous aquifer systems, conceptualization of regional groundwater flow models frequently results in the generalization or negligence of aquifer heterogeneities, both of which may result in erroneous model outputs. The calculation of equivalence related to hydrogeological parameters and applied to upscaling provides a means of accounting for measurement scale information but at regional scale. In this study, the Permo‐Triassic Lagan Valley strategic aquifer in Northern Ireland is observed to be heterogeneous, if not discontinuous, due to sub‐vertical trending low‐permeability Tertiary dolerite dykes. Interpretation of ground and aerial magnetic surveys produces a deterministic solution to dyke locations. By measuring relative permeabilities of both the dykes and the sedimentary host rock, equivalent directional permeabilities, that determine anisotropy calculated as a function of dyke density, are obtained. This provides parameters for larger scale equivalent blocks, which can be directly imported to numerical groundwater flow models. Different conceptual models with different degrees of upscaling are numerically tested and results compared to regional flow observations. Simulation results show that the upscaled permeabilities from geophysical data allow one to properly account for the observed spatial variations of groundwater flow, without requiring artificial distribution of aquifer properties. It is also found that an intermediate degree of upscaling, between accounting for mapped field scale dykes and accounting for one regional anisotropy value (maximum upscaling) provides results the closest to the observations at the regional scale.
- Solute transport in low‐heterogeneity sand boxes: The role of
correlation length and permeability variance
- Authors: Peyman Heidari; Li Li
Pages: n/a - n/a
Abstract: This work examines how heterogeneity structure, in particular correlation length, controls flow and solute transport. We used two‐dimensional (2D) sand boxes (21.9 cm by 20.6 cm) and four modeling approaches, including 2D Advection‐Dispersion Equation (ADE) with explicit heterogeneity structure, 1D ADE with average properties, and non‐local Continuous Time Random Walk (CTRW) and fractional ADE (fADE). The goal is to answer two questions: 1) How and to what extent does correlation length control effective permeability and breakthrough curves (BTC)? 2) Which model can best reproduce data under what conditions? Sand boxes were packed with the same 20% (v/v) fine and 80% (v/v) coarse sands in three patterns that differ in correlation length. The Mixed cases contained uniformly distributed fine and coarse grains. The Four‐zone and One‐zone cases had four and one square fine zones, respectively. A total of 7 experiments were carried out with permeability variance of 0.10 (LC), 0.22 (MC), and 0.43 (HC). Experimental data show that the BTC curves depend strongly on correlation length, especially in the HC cases. The HC One‐zone (HCO) case shows distinct breakthrough steps arising from fast advection in the coarse zone, slow advection in the fine zone, and slow diffusion, while the LCO and MCO BTCs do not exhibit such behavior. With explicit representation of heterogeneity structure, 2D ADE reproduces BTCs well in all cases. CTRW reproduces temporal moments with smaller deviation from data than fADE in all cases except HCO, where fADE has the lowest deviation.
- A new formulation for steady multiaquifer flow; an analytic element for
piecewise constant infiltration
- Authors: O.D.L. Strack; Taha Namazi
Pages: n/a - n/a
Abstract: This paper contains a new formulation for infiltration inside domains bounded by polygons and its application to problems of steady multi‐aquifer flow, using the Dupuit‐Forchheimer approximation and assuming vertical flow in the separating layers. An alternative formulation is presented for leaky aquifer systems where infiltration or extraction is given. Existing formulations of multi‐aquifer flow involve a system of equations that must be solved for the heads in the aquifers. These formulations are abstract, and the relation between the parameters in the solution and physical quantities is hidden. The formulation in the paper aims at linking the system of equations to physical quantities; we have done this in two ways. First, we formulate the problem in terms of leakage potentials, related directly to the leakage through the leaky layers. Second, we introduce the concept of ‘equilibrated leakage’; leakage that is either the result of infiltration, or of some disturbance in the flow pattern, such as that caused by a well. The leakage through the leaky layers tends to some constant value far from a disturbance, e.g., a well, or the boundary of an area of constant infiltration. This concept of equilibrated leakage is useful in practice and helps in understanding the distribution of leakage; we explain this in detail in the paper. The study of problems of steady flow in leaky aquifer systems is inspired by problems of groundwater sustainability, where the overall distribution of flow over long periods of time is important, rather than detailed information.
- Effect of hydrophobicity on colloid transport during two‐phase flow
in a micromodel
- Authors: Qiulan Zhang; S.M. Hassanizadeh, B. Liu, J. F. Schijven, N.K. Karadimitriou
Pages: n/a - n/a
Abstract: The goal of this research was to investigate the difference in behavior of hydrophilic and hydrophobic colloids during transport in two‐phase flow, in general, and their attachment and remobilization characters, in particular. Experiments were performed in a hydrophobic Polydimethylsiloxane (PDMS) micro‐model. Water and fluorinert‐FC43 were used as the two immiscible liquids. Given the fact that PDMS is a hydrophobic material, fluorinert was the wetting phase and water was the non‐wetting phase in this micro‐model. As model colloids, we used hydrophilic polystyrene carboxylate‐modified microspheres (dispersible in water) and hydrophobic fluorous‐modified silica microspheres (dispersible in fluorinert) in separate experiments. Using a confocal laser scanning microscope, we directly observed fluid distribution and colloid movement within pores of the micro‐model. We also obtained concentration breakthrough curves by measuring the fluorescent intensities in the outlet of the micro‐model.
The breakthrough curves during steady‐state flow showed that the colloid attachment rate is inversely related to the background saturation of the fluid in which the colloids were dispersed. Our visualization results showed that the enhanced attachment of hydrophilic colloids at lower water saturations was due to the retention at the fluorinert‐water interface and fluorinert‐water‐solid contact lines. This effect was observed to be much less in the case of hydrophobic colloids (dispersed in fluorinert). In order to explain the colloids behavior, we calculated interaction potential energies of colloids with PDMS surfaces, fluid‐fluid interfaces, and fluid‐fluid‐solid contact lines. Also, balance of forces that control colloid, including DLVO, hydrodynamic, and surface tension forces, were determined. Our calculations showed that there is a stronger repulsive energy barrier between hydrophobic colloids and fluorinert‐water interface and solid‐fluid interface, compared with the hydrophilic colloids. Moreover, hydrophobic colloids were seen to aggregate due to strong attractive forces among them. These aggregates had even less tendency to attach to various interfaces, due to an increase in the corresponding energy barrier. For the colloid retention at fluid‐fluid‐solid contact lines, we found that the role of DLVO interactions was less important than capillary forces.
During transient events, we found that attached colloids become remobilized. The colloids deposited on the solid‐fluid interface were detached by the moving fluid‐fluid‐solid contact lines. But, this happened only when the liquid containing colloids was being displaced by the other liquid. We simulated breakthrough curves using a model based on a coupled system of equations for two‐phase flow, advection‐dispersion of colloids, adsorption to and desorption from fluid‐fluid interfaces and fluid‐solid interfaces. Very good agreements were obtained among measured breakthrough curves, visualization results, and numerical modeling.
- Assimilation of point SWE data into a distributed snow cover model
comparing two contrasting methods
- Authors: Jan Magnusson; David Gustafsson, Fabia Hüsler, Tobias Jonas
Pages: n/a - n/a
Abstract: In alpine and high latitude regions water resource decision making often requires large scale estimates of snow amounts and melt rates. Such estimates are available through distributed snow models which in some situations can be improved by assimilation of remote sensing observations. However, in regions with frequent cloud cover, complex topography, or large snow amounts satellite observations may feature information of limited quality. In this study we examine whether assimilation of snow water equivalent (SWE) data from ground observations can improve model simulations in a region largely lacking reliable remote sensing observations. We combine the model output with the point data using three‐dimensional sequential data assimilation methods, the ensemble Kalman filter and statistical interpolation. The filter performance was assessed by comparing the simulation results against observed SWE and snow covered fraction. We find that a method which assimilates fluxes (snowfall and melt rates computed from SWE) showed higher model performance than a control simulation not utilizing the filter algorithms. However, an alternative approach for updating the model results using the SWE data directly did not show a significantly higher performance than the control simulation. The results show that three‐dimensional data assimilation methods can be useful for transferring information from point snow observations to the distributed snow model.
- Multiobjective optimization of cluster‐scale urban water systems
investigating alternative water sources and level of decentralization
- Authors: J. P. Newman; G. C. Dandy, H. R. Maier
Pages: n/a - n/a
Abstract: In many regions, conventional water supplies are unable to meet projected consumer demand. Consequently, interest has arisen in integrated urban water systems, which involve the reclamation or harvesting of alternative, localised water sources. However, this makes the planning and design of water infrastructure more difficult, as multiple objectives need to be considered, water sources need to be selected from a number of alternatives and end‐uses of these sources need to be specified. In addition, the scale at which each treatment, collection and distribution network should operate needs to be investigated. In order to deal with this complexity, a framework for planning and designing water infrastructure taking into account integrated urban water management principles is presented in this paper and applied to a rural greenfield development. Various options for water supply, and the scale at which they operate were investigated in order to determine the life‐cycle trade‐offs between water savings, cost and GHG emissions as calculated from models calibrated using Australian data. The decision space includes the choice of water sources, storage tanks, treatment facilities and pipes for water conveyance. For each water system analysed, infrastructure components were sized using multiobjective genetic algorithms. The results indicate that local water sources are competitive in terms of cost and GHG emissions, and can reduce demand on the potable system by as much as 54%. Economies of scale in treatment dominated the diseconomies of scale in collection and distribution of water. Therefore, water systems that connect large clusters of households tend to be more cost efficient and have lower GHG emissions. In addition, water systems that recycle wastewater tended to perform better than systems that captured roof‐runoff. Through these results, the framework was shown to be effective at identifying near optimal trade‐offs between competing objectives, thereby enabling informed decisions to be made when planning water systems for greenfield developments.
- Bayesian inference of a lake water quality model by emulating its
- Authors: A. Dietzel; P. Reichert
Pages: n/a - n/a
Abstract: We use a Gaussian stochastic process emulator to interpolate the posterior probability density of a computationally demanding application of the biogeochemical‐ecological lake model BELAMO to accelerate statistical inference of deterministic model and error model parameters. The deterministic model consists of a mechanistic description of key processes influencing the mass balance of nutrients, dissolved oxygen, organic particles, and phyto‐ and zooplankton in the lake. This model is complemented by a Gaussian stochastic process to describe the remaining model bias and by Normal, independent observation errors. A small sub‐sample of the Markov chain representing the posterior of the model parameters is propagated through the full model to get model predictions and uncertainty estimates. We expect this approximation to be more accurate at only slightly higher computational costs compared to using a Normal approximation to the posterior probability density and linear error propagation to the results as we did in an earlier paper. The performance of the two techniques is compared for a didactical example as well as for the lake model. As expected, for the didactical example, the use of the emulator led to posterior marginals of the model parameters that are closer to those calculated by Markov chain simulation using the full model than those based on the Normal approximation. For the lake model, the new technique proved applicable without an excessive increase in computational requirements, but we faced challenges in the choice of the design data set for emulator calibration. As the posterior is a scalar function of the parameters, the suggested technique is an alternative to the emulation of a potentially more complex, structured output of the simulation model that allows for the use of a less case‐specific emulator. This is at the cost that still the full model has to be used for prediction (which can be done with a smaller, approximately independent subsample of the Markov chain).
- A dynamic watershed model for determining the effects of transient storage
on nitrogen export to rivers
- Authors: Dingjiang Chen; Minpeng Hu, Randy A. Dahlgren
Pages: n/a - n/a
Abstract: Legacy anthropogenic nitrogen (N) has been suggested as a major cause for increasing riverine N exports despite significant declines in anthropogenic N inputs in many regions. However, little quantitative knowledge exists concerning the contribution of the legacy N pool to riverine N export. This study developed a dynamic watershed N delivery model to address the role of transient storage of anthropogenic N inputs on riverine N flux. Employing simple mass balance and equivalent substitution rules, the model expresses the transient storage of legacy N mass with a term that combines the previous one year's riverine total N (TN) flux, relevant explanatory variables, and unknown parameters, enabling us to inversely calibrate the model parameters from measurable variables using Bayesian statistics. The model efficacy was demonstrated through application to the Yong'an River watershed in eastern China based on a 31‐year record (1980–2010) of riverine TN fluxes. The model can quantify annual transient storage of legacy N and its resulting contribution to annual riverine N flux. The model also allows partitioning of the complete long‐term mass balance for the fate (e.g., transient storage, riverine export, and loss/retention by denitrification, biomass uptake and wood product export) of annual anthropogenic N inputs. To further improve the model, various N input‐output processes can be specified and long‐term measurements of N fates are required to further verify the model results. This study demonstrates the need to consider transient storage effects as an improvement to current watershed models and for developing and assessing N pollution control measures.
- Hybrid modeling and receding horizon control of sewer networks
- Authors: Bernat Joseph‐Duran; Carlos Ocampo‐Martinez, Gabriela Cembrano
Pages: n/a - n/a
Abstract: In this work, a control‐oriented sewer network model is presented based on a hybrid linear modeling framework. The model equations are described independently for each network element, thus allowing the model to be applied to a broad class of networks. A parameter calibration procedure using data obtained from simulation software that solves the physically‐based model equations is described and validation results are given for a case study. Using the model equations, an optimal control problem to minimize flooding and pollution is formulated to be solved by means of mixed‐integer linear or quadratic programming. A receding horizon control strategy based on this optimal control problem is applied to the case study using the simulation software as a virtual reality. Results of this closed‐loop simulation tests show the effectiveness of the proposed approach in fulfilling the control objectives while complying with physical and operational constraints.
- With or against the tide: The influence of bed form asymmetry on the
formation of macroturbulence and suspended sediment patterns
- Authors: E. Kwoll; M. Becker, C. Winter
Pages: n/a - n/a
Abstract: This study examines tide‐dependent variations in the formation and dynamics of suspended sediment patterns coupled to mean flow and turbulence above asymmetric bedforms. In the Danish Knudedyb inlet, very large primary bedforms remain ebb‐oriented during a tidal cycle while smaller superimposed bedforms reverse direction with each tidal phase. Hydro‐acoustic in‐situ observations reveal pronounced differences in suspended sediment transport patterns between tidal phases caused by the relative orientation of primary bedforms and the mean tidal flow and flow unsteadiness during a single tidal phase. When flow and primary bedform orientation are aligned, water‐depth‐scale macroturbulence develops in the bedform lee‐sides in the presence of flow separation. Macroturbulent flow structures occur at high flow stages and are coupled to increased amounts of sediment in suspension. When flow and bedform orientation are opposed no evidence of flow separation associated with primary bedforms is found. Sediment‐laden macroturbulence at high flow velocities is of a smaller scale and attributed to the superimposed secondary bedforms. The flow structures are advected along the primary bedform stoss‐side (temporary hydraulic lee‐side). The steep primary bedform lee‐side (temporary hydraulic stoss‐side) however, limits transport capabilities beyond the scale of primary bedforms.
- A novel infrastructure modularity index for the segmentation of water
- Authors: O. Giustolisi; L. Ridolfi
Pages: n/a - n/a
Abstract: The search for suitable segmentations is a challenging and urgent issue for the analysis, planning and management of complex water distribution networks (WDNs). In fact, complex and large size hydraulic systems require the division into modules in order to simplify the analysis and the management tasks. In the complex network theory, modularity index has been proposed as a measure of the strength of the network division into modules and its maximization is used in order to identify community of nodes (i.e., modules) which are characterized by strong inter‐connections. Nevertheless, modularity index needs to be revised considering the specificity of the hydraulic systems as infrastructure systems. To this aim, the classic modularity index has been recently modified and tailored for WDNs. Nevertheless, the WDN‐oriented modularity is affected by the resolution limit stemming from classic modularity index. Such a limit hampers the identification/design of small modules and this is a major drawback for technical tasks requiring a detailed resolution of the network segmentation. In order to get over this problem, we propose a novel infrastructure modularity index that is not affected by the resolution limits of the classic one. The rationale and good features of the proposed index are theoretically demonstrated and discussed using two real hydraulic networks.
- Spatiotemporal variation of long‐term drought propensity through
- Authors: Kironmala Chanda; Rajib Maity, Ashish Sharma, Rajeshwar Mehrotra
Pages: n/a - n/a
Abstract: This paper characterizes the long‐term, spatio‐temporal variation of drought propensity through a newly proposed, namely Drought Management Index (DMI) and explores its predictability in order to assess the future drought propensity and adapt drought management policies for a location. The DMI was developed using the Reliability‐Resilience‐Vulnerability (RRV) rationale commonly used in water resources systems analysis, under the assumption that depletion of soil moisture across a vertical soil column is equivalent to the operation of a water supply reservoir, and that drought should be managed not simply using a measure of system reliability, but should also take into account the readiness of the system to bounce back from drought to a normal state. Considering India as a test bed, five year long monthly gridded (0.5° Lat x 0.5° Lon) soil moisture data is used to compute the RRV at each grid location falling within the study domain. The Permanent Wilting Point (PWP) is used as the threshold, indicative of transition into water stress. The association between resilience and vulnerability is then characterized through their joint probability distribution ascertained using Plackett copula models for four broad soil types across India. The joint cumulative distribution functions (CDF) of resilience and vulnerability forms the basis for estimating the DMI as a five‐yearly time series at each grid location assessed. The status of DMI over the past 50 years indicate that drought propensity is consistently low towards northern and north eastern parts of India, but higher in the western part of peninsular India. Based on the observed past behaviour of DMI series on a climatological time scale, a DMI prediction model comprising of deterministic and stochastic components is developed. The predictability of DMI for a lead time of 5 years is found to vary across India, with a Pearson correlation coefficient between observed and predicted DMI above 0.6 over most of the study area, indicating a reasonably good potential for drought management in the medium term water resources planning horizon.
- Orienting the camera and firing lasers to enhance large‐scale
particle image velocimetry for streamflow monitoring
- Authors: Flavia Tauro; Maurizio Porfiri, Salvatore Grimaldi
Pages: n/a - n/a
Abstract: Large scale particle image velocimetry (LSPIV) is a nonintrusive methodology for continuous surface flow monitoring in natural environments. Recent experimental studies demonstrate that LSPIV is a promising technique to estimate flow discharge in riverine systems. Traditionally, LSPIV implementations are based on the use of angled cameras to capture extended fields of view; images are then orthorectified and calibrated through the acquisition of ground reference points. As widely documented in the literature, the identification of ground reference points and image orthorectification are major hurdles in LSPIV. Here, we develop an experimental apparatus to address both of these issues. The proposed platform includes a laser system for remote frame calibration and a low cost camera that is maintained orthogonal with respect to the water surface to minimize image distortions. We study the feasibility of the apparatus on two complex natural riverine environments where the acquisition of ground reference points is prevented and illumination and seeding density conditions are challenging. While our results confirm that velocity estimations can be severely affected by inhomogeneously seeded surface tracers and adverse illumination settings, they demonstrate that LSPIV implementations can benefit from the proposed apparatus. Specifically, the presented system opens novel avenues in the development of stand‐alone platforms for remote surface flow monitoring.
- An adaptive ant colony optimization framework for scheduling environmental
flow management alternatives under varied environmental water availability
- Authors: J. M. Szemis; H.R. Maier, G.C. Dandy
Pages: n/a - n/a
Abstract: Human water use is increasing and, as such, water for the environment is limited and needs to be managed efficiently. One method for achieving this is the scheduling of environmental flow management alternatives (EFMAs) (e.g. releases, wetland regulators), with these schedules generally developed over a number of years. However, the availability of environmental water changes annually as a result of natural variability (e.g. drought, wet years). To incorporate this variation and schedule EFMAs in a operational setting, a previously formulated multi‐objective optimization approach for EFMA schedule development used for long‐term planning has been modified and incorporated into an adaptive framework. As part of this approach, optimal schedules are updated at regular intervals during the planning horizon based on environmental water allocation forecasts, which are obtained using artificial neural networks. In addition, the changes between current and updated schedules can be minimized to reduce any disruptions to long‐term planning. The utility of the approach is assessed by applying it to an 89km section of the River Murray in South Australia. Results indicate that the approach is beneficial under a range of hydrological conditions and an improved ecological response is obtained in a operational setting compared with previous long‐term approaches. Also, it successfully produces trade‐offs between the number of disruptions to schedules and the ecological response, with results suggesting that ecological response increases with minimal alterations required to existing schedules. Overall, the results indicate that the information obtained using the proposed approach potentially aides managers in the efficient management of environmental water.
- Reply to comment by Jeffrey Olsen et al. on “Traveling wave solution
of the Boussinesq equation for groundwater flow in horizontal
- Authors: H. A. Basha
Pages: n/a - n/a
- Effects of rainfall spatial variability and intermittency on shallow
landslide triggering patterns at a catchment scale
- Authors: J. von Ruette; P. Lehmann, D. Or
Pages: n/a - n/a
Abstract: The occurrence of shallow landslides is often associated with intense and prolonged rainfall events, where infiltrating water reduces soil strength and may lead to abrupt mass release. Despite general understanding of the role of rainfall water in slope stability, the prediction of rainfall–induced landslides remains a challenge due to natural heterogeneity that affect hydrologic loading patterns and the largely unobservable internal progressive failures. An often overlooked and potentially important factor is the role of rainfall variability in space and time on landslide triggering that is often obscured by coarse information (e.g. hourly radar–data at spatial resolution of a few kilometers). To quantify potential effects of rainfall variability on failure dynamics, spatial patterns, landslide numbers and volumes, we employed a physically–based ‘Catchment–scale Hydromechanical Landslide Triggering' (CHLT) model [von Ruette et al., 2013] for a study area where a summer storm in 2002 triggered 51 shallow landslides. In numerical experiments based on the CHLT model we applied the measured rainfall amount of 53 mm in different artificial spatio–temporal rainfall patterns, resulting in between 30 and 100 landslides and total released soil volumes between 3,000 and 60,000 m3 for the various scenarios. Results indicate that low intensity rainfall below soil's infiltration capacity resulted in the largest mechanical perturbation. This study illustrates how small scale rainfall variability that is often overlooked by present operational rainfall data may play a key role in shaping landslide patterns.
- USDA‐ARS Riesel Watersheds, Riesel, Texas, USA: Water quality
- Authors: R. Daren Harmel; Richard L. Haney, Douglas R. Smith, Michael White, Kevin W. King
Pages: n/a - n/a
Abstract: The 75 yr legacy database including discharge, sediment loss, land management, and meteorological data for the USDA‐ARS Riesel Watersheds, Riesel, TX, USA, has been available on the web for more than a decade (www.ars.usda.gov/spa/hydro‐data) and used in numerous studies and publications; however, only recently have these data been added to the Sustaining the Earth's Watersheds, Agricultural Research Data System (STEWARDS) database (www.nrrig.mwa.ars.usda.gov/stewards/stewards.html). In addition, water quality data including dissolved inorganic N and P compounds measured from more than 1000 storm runoff events, 1300 baseflow sampling events (lateral subsurface return flow or seepage flow), and 157 precipitation events through 2012 were added. The objectives of this manuscript are to present relevant background information on these data, summarize the data collection and analysis methodology, present the measured data along with cursory analyses, and convey the commitment of the USDA‐ARS Riesel Watersheds to long‐term data accessibility and database enhancement for water quality data and research.
- Perirheic mixing and biogeochemical processing in flow‐through and
backwater floodplain wetlands
- Authors: C. Nathan Jones; Durelle T. Scott, Brandon L. Edwards, Richard F. Keim
Pages: n/a - n/a
Abstract: Inundation hydrology and associated processes control biogeochemical processing in floodplains. To better understand how hydrologic connectivity, residence time, and intrafloodplain mixing vary in floodplain wetlands, we examined how water quality of two contrasting areas in the floodplain of the Atchafalaya River—a flow‐through and a backwater wetland—responded to an annual flood pulse. Large, synoptic sampling campaigns occurred in both wetlands during the rising limb, peak, and falling limb of the hydrograph. Using a combination of conservative and reactive tracers, we inferred three dominant processes that occurred over the course of the flood pulse: flushing (rising limb), advective transport (peak), and organic matter accumulation (falling limb). Biogeochemistry of the two wetlands was similar during the peak while the river overflowed into both. However, during the rising and falling limbs, flow in the backwater wetland experienced much greater residence time. This led to the accumulation of dissolved organic matter and dissolved phosphorus. There were also elevated ratios of dissolved organic carbon to nitrate in the backwater wetland, suggesting nitrogen removal was limited by nitrate transported into the floodplain there. Collectively, our results suggest inclusion of a temporal component into the perirheic concept more fully describes inundation hydrology and biogeochemistry in large river floodplain.
- On the mechanism of field‐scale solute transport: Insights from
numerical simulations and field observations
- Authors: David Russo; Asher Laufer, Zev Gerstl, Daniel Ronen, Noam Weisbrod, Eitan Zentner
Pages: n/a - n/a
Abstract: Field‐scale transport of conservative and reactive solutes through a deep vadose zone was analyzed by means of two different model processes for the local description of the transport. The first is the advection dispersion equation (ADE) model, and the second is the mobile‐immobile (MIM) model. The analyses were performed by means of three‐dimensional (3‐D), numerical simulations of flow and transport considering realistic features of the flow system, pertinent to a turf field irrigated with treated sewage effluents (TSE). Simulated water content and concentration profiles were compared with available measurements of their counterparts. Results of the analyses suggest that the behavior of both solutes in the deep vadose zone of the Glil Yam site is better quantified by the MIM model than by the ADE model. Reconstruction of the shape of the measured solute concentration profiles using the MIM model required relatively small mass transfer coefficient, γ, and relatively large volume fraction of the immobile water, θim. This implies that for an initially non‐zero solute concentration profile, as compared with the MIM model, the ADE model may significantly overestimate the rate at which solutes are loaded in the groundwater. On the contrary, for an initially zero solute concentration profile, as compared with the MIM model, the ADE model may significantly underestimate solute velocities and early arrival times to the water table. These findings stem from the combination of relatively small γ and relatively large θim taken into account in the MIM model. In the first case, this combination forces a considerable portion of the solute mass to reside in the immobile region of the water‐filled pore space, while the opposite is true in the second case.
- Process consistency in models: The importance of system signatures, expert
knowledge, and process complexity
- Authors: M. Hrachowitz; O. Fovet, L. Ruiz, T. Euser, S. Gharari, R. Nijzink, J. Freer, H.H.G. Savenije, C. Gascuel‐Odoux
Pages: n/a - n/a
Abstract: Hydrological models frequently suffer from limited predictive power despite adequate calibration performances. This can indicate insufficient representations of the underlying processes. Thus ways are sought to increase model consistency while satisfying the contrasting priorities of increased model complexity and limited equifinality. In this study the value of a systematic use of hydrological signatures and expert knowledge for increasing model consistency was tested. It was found that a simple conceptual model, constrained by 4 calibration objective functions, was able to adequately reproduce the hydrograph in the calibration period. The model, however, could not reproduce 20 hydrological signatures, indicating a lack of model consistency. Subsequently, testing 11 models, model complexity was increased in a stepwise way and counter‐balanced by “prior constraints”, inferred from expert knowledge to ensure a model which behaves well with respect to the modeller’s perception of the system. We showed that, in spite of unchanged calibration performance, the most complex model set‐up exhibited increased performance in the independent test period and skill to reproduce all 20 signatures, indicating a better system representation. The results suggest that a model may be inadequate despite good performance with respect to multiple calibration objectives and that increasing model complexity, if counter‐balanced by prior constraints, can increase predictive performance of a model and its skill to reproduce hydrological signatures. The results strongly illustrate the need to balance automated model calibration with a more expert‐knowledge driven strategy of constraining models.
- Estimating porosity and solid dielectric permittivity in the Miami
limestone using high‐frequency ground penetrating radar (GPR)
measurements at the laboratory scale
- Authors: Gregory J. Mount; Xavier Comas
Pages: n/a - n/a
Abstract: Subsurface water flow in South Florida is largely controlled by the heterogeneous nature of the karst limestone in the Biscayne aquifer and its upper formation, the Miami Limestone. These heterogeneities are amplified by dissolution structures that induce changes in the aquifer’s material and physical properties (i.e. porosity and dielectric permittivity) and create preferential flow paths. Understanding such patterns are critical for the development of realistic groundwater flow models, particularly in the Everglades, where restoration of hydrological conditions is intended. In this work we used non‐invasive ground penetrating radar (GPR) to estimate the spatial variability in porosity and the dielectric permittivity of the solid phase of the limestone at centimeter scale resolution to evaluate the potential for field‐based GPR studies. A laboratory setup that included high frequency GPR measurements under completely unsaturated and saturated conditions was used to estimate changes in electromagnetic wave velocity through Miami Limestone samples. The Complex Refractive Index Model was used to derive estimates of porosity and dielectric permittivity of the solid phase of the limestone. Porosity estimates of the samples ranged between 45.2 and 66.0 % and showed good correspondence with estimates of porosity using analytical and digital image techniques. Solid dielectric permittivity values ranged between 7.0 and 13.0. This study shows the ability of GPR to image the spatial variability of porosity and dielectric permittivity in the Miami Limestone and shows potential for expanding these results to larger scales and other karst aquifers.
- Analytical solutions for stream‐aquifer flow exchange under varying
head asymmetry and river penetration: Comparison to numerical solutions
and use in regional groundwater models
- Authors: Cinzia Miracapillo; Hubert J. Morel‐Seytoux
Pages: n/a - n/a
Abstract: An analytical approach is presented to characterize the local flow exchange conductance and boundary condition between a stream and a hydraulically connected aquifer. Due to the curvilinear nature of the flow pattern in the vicinity of the stream, with numerical procedures very fine grids would have to be used in order to secure accurate results. This is a waste of numerical efforts when the solution can be obtained analytically. Here we show that the local analytical procedure for the determination of the stream‐aquifer flow exchange (SAFE) coefficient can be integrated within a regional numerical groundwater model through an original boundary condition. This is a very practical result. With this new approach it is quite simple to calculate accurately the discharges on the two sides of the river when the heads are different. This is an important capability for example when wells are present near a river. The results show also that the extent of penetration of the stream is a factor in the estimation of the discharges.
At the very least the results can be used to choose a grid size that will yield correct estimates within an a priori selected acceptable level of accuracy.
- Joint numerical microscale simulations of multiphase flow and NMR
relaxation behavior in porous media using lattice Boltzmann methods
- Authors: O. Mohnke; M. Stiebler, N. Klitzsch
Pages: n/a - n/a
Abstract: Nuclear magnetic resonance (NMR) relaxometry is a useful tool to estimate transport and storage properties of rocks and soils. However, as there is no unique relation between the NMR signal and these properties in rocks, a variety of empirical models on deriving hydraulic properties from NMR relaxometry data have been published. Complementary to laboratory measurements, this paper introduces a numerical framework to jointly simulate NMR relaxometry experiments and two‐phase flow on the micrometer scale. Herein, the NMR diffusion equations were tied to an established Lattice Boltzmann algorithm used in computational fluid dynamics. The numerically simulated NMR data were validated for both surface‐ and diffusion‐limited relaxation regimes using analytical solutions available for fully and partially water saturated simple pore geometries. Subsequently, simulations were compiled using a complex pore space derived from three‐dimensional computer tomography (CT) data of an unconsolidated sand and the results were compared to respective NMR T1 relaxometry data. The NMR transients simulated for different water saturations matched the measured data regarding initial amplitudes (i.e., porosity and saturation) and relaxation behavior (i.e., distribution of water saturated pores). Thus, we provide a simulation tool that enables study of the influences of structural and physicochemical properties, such as pore connectivity and pore coupling, surface relaxivity, or diffusivity, on partially saturated porous media, e.g, rocks or soils, with NMR T1 relaxometry data.
- Water‐saving impacts of Smart Meter technology: An empirical 5 year,
whole‐of‐community study in Sydney, Australia
- Authors: Kirsten Davies; Corinna Doolan, Robin van den Honert, Rose Shi
Pages: n/a - n/a
Abstract: In 2009‐2010 Sydney Water, the primary water utility in Sydney, conducted a comprehensive Smart Metering trial in residential homes in the suburb of Westleigh, in Sydney’s north. The trial involved 1,923 participants residing in 630 households. A whole‐of‐community method of engagement was applied to capture the views of residents from 12 to 70+ years of age. The trial examined the effects of the technology on the water consumption of an intervention group compared with that of a matched control group. After removing properties that had been sold since the beginning of the trial, properties in the study group were matched with a control group property on the basis of the household size, property size and the presence (or otherwise) of a swimming pool. The effects of the technology on consumption were measured and analysed for the period July 2009 to June 2010, coupled with qualitative information that was collected throughout the duration of the study. A key finding was that households with the in‐home display (IHD) installed, reduced their consumption by an average of over 6.8% over the study period when compared to the control group. Since completion of the study the community has not had any further interventions. The trial created an opportunity to examine the longer‐term effects of the technology (June 2008 to September 2013). Consumption data collected over the three year post‐trial period revealed that the participant group consumed 6.4% per month less water when compared to the pre‐trial period, whilst the matched control group consumed 1.3% per month more water when compared to the pre‐trial period. The reduced consumption of the participant group was maintained over time, demonstrating the long term value of this technology.
- Hydrometric transit times along transects on a steep hillslope
- Authors: Sanghyun Kim
Pages: n/a - n/a
Abstract: Field monitoring of isotopes and isotope analyses have been used to approximate water travel time at hillslope scales. This paper introduces an alternate method for estimating a point‐scaled transit time in a soil layer, namely hydrometric transit time (HTT). HTT uses hydrometric measurements to address both matrix flow and bypass flow. Soil matrix flux is approximated through integration of continuous soil moisture profiles and soil water computations. Free surface film modeling of unsaturated flow is used to estimate bypass flow. This flux and storage estimation scheme is applied to a steep hillslope using hydrometric measurements that were estimated over an 8‐month period using a continuous daily approximation of soil moisture profiles. Transit times at several designated points are also evaluated using isotope analyses. Results show that rainfall strongly controls temporal fluctuations. This work highlights the potential role of HTT in revealing the spatial and seasonal variations in the transit time probability density function (PDF) along transects. Mean transit time does not sufficiently characterize transit time variations on a hillslope scale. Accumulated flux distributions identify distinct hydrologic contributions and efficient redistribution of soil water in the downslope area of the hillside.
- Quantifying storage changes in regional Great Lakes watersheds using a
coupled subsurface: Land surface process model and GRACE, MODIS products
- Authors: Jie Niu; Chaopeng Shen, Shu‐Guang Li, Mantha S. Phanikumar
Pages: n/a - n/a
Abstract: As a direct measure of watershed resilience, watershed storage is important for understanding climate change impacts on water resources. In this paper we quantify water budget components and storage changes for two of the largest watersheds in the State of Michigan, USA (the Grand River and the Saginaw Bay watersheds) using remotely sensed data and a process‐based hydrologic model (PAWS) that includes detailed representations of subsurface and land surface processes. Model performance is evaluated using ground‐based observations (streamflows, groundwater heads, soil moisture, soil temperature) as well as satellite‐based estimates of evapotranspiration (Moderate‐resolution Imaging Spectroradiometer, MODIS) and watershed storage changes (Gravity Recovery and Climate Experiment, GRACE). We use the model to compute the annual‐average fluxes due to evapotranspiration, surface runoff, recharge and groundwater contribution to streams and analyze the impacts of land use and land cover (LULC) and soil types on annual hydrologic budgets using correlation analysis. Watershed storage changes based on GRACE data and model results showed similar patterns. Storage was dominated by subsurface components and showed an increasing trend over the past decade. This work provides new estimates of water budgets and storage changes in Great Lakes watersheds and the results are expected to aid in the analysis and interpretation of the current trend of declining lake levels, in understanding projected future impacts of climate change as well as in identifying appropriate climate adaptation strategies.
- Microbial dispersal in unsaturated porous media: Characteristics of motile
bacterial cell motions in unsaturated angular pore networks
- Authors: Ali N. Ebrahimi; Dani Or
Pages: n/a - n/a
Abstract: The dispersal rates of self‐propelled microorganisms affect their spatial interactions and the ecological functioning of microbial communities. Microbial dispersal rates affect risk of contamination of water resources by soil‐borne pathogens, the inoculation of plant roots, or the rates of spoilage of food products. In contrast with the wealth of information on microbial dispersal in water replete systems, very little is known about their dispersal rates in unsaturated porous media. The fragmented aqueous phase occupying complex soil pore spaces suppress motility and limits dispersal ranges in unsaturated soil. The primary objective of this study was to systematically evaluate key factors that shape microbial dispersal in model unsaturated porous media to quantify effects of saturation, pore space geometry and chemotaxis on characteristics of principles that govern motile microbial dispersion in unsaturated soil. We constructed a novel 3D angular pore network model (PNM) to mimic aqueous pathways in soil for different hydration conditions; within the PNM we employed an individual based model that considers physiological and biophysical properties of motile and chemotactic bacteria. The effects of hydration conditions on first passage times in different pore networks were studied showing that fragmentation of aquatic habitats under dry conditions sharply suppresses nutrient transport and microbial dispersal rates in good agreement with limited experimental data. Chemotactically biased mean travel speed of microbial cells across 9 mm saturated PNM was ˜3 mm/hr decreasing exponentially to 0.45 mm/hr for the PNM at matric potential of –15 kPa (for–35 kPa, dispersal practically ceases and the mean travel time to traverse the 9 mm PNM exceeds 1 year). Results indicate that chemotaxis enhances dispersal rates by orders of magnitude relative to random (diffusive) motions. Model predictions considering microbial cell sizes relative to available liquid pathways sizes were in good agreement with experimental results for unsaturated soils. The new modeling platform enables quantitative consideration of key biophysical factors (e.g., pore space heterogeneities and hydration conditions) governing microbial interactions in 3D soil pore spaces.
- Large lakes as sources and sinks of anthropogenic heat—Capacities
- Authors: Gabriel Fink; Martin Schmid, Alfred Wüest
Pages: n/a - n/a
Abstract: The goal of reducing carbon fuel and thereby saving energy will increase the use of lake water for heating and cooling of riparian infrastructures. This raises the question of which heat use designs meet the ecological and technical requirements for lakes, particularly in regard to climate warming. Thus, this study explores heat use effects on the temperature and stratification of a large, deep, temperate lake by applying the one‐dimensional k‐epsilon model SimStrat to various forcing scenarios. Several design parameters, such as extraction and discharge depth, and their effects were assessed. Additionally, 21st‐century climate projections were used to evaluate the effects of climate change relative to those of heat use. Generally, the study showed only minor effects for a realistic heat demand of ±2 W m‐2 quite independent of the heat extraction / discharge modes. Mean water temperature changed less than ±0.2 °C as long as there was no discharge into the deepest layers. Water extraction and discharge at the surface had the least thermal influence. To relate to climate change, heat use was scaled up to +85 W m‐2. Resultant simulations showed that such (unrealistic) anthropogenic, lake‐based “thermal pollution“ would have a comparable influence to that of climate change. Conversely, heat extraction could damp or even compensate climate‐induced warming. The present study concludes that (i) there are minor effects on water temperatures, stratification and seasonal mixing due to heat use of up to ±2 W m‐2 and (ii) those influences are insignificant relative to the expected climate change.
- Spatial and diurnal below canopy evaporation in a desert vineyard:
Measurements and modeling
- Authors: D. Kool; A. Ben‐Gal, N. Agam, J. Šimůnek, J. L. Heitman, T. J. Sauer, N. Lazarovitch
Pages: n/a - n/a
Abstract: Evaporation from the soil surface (E) can be a significant source of water loss in arid areas. In sparsely vegetated systems, E is expected to be a function of soil, climate, irrigation regime, precipitation patterns, and plant canopy development and will therefore change dynamically at both daily and seasonal time scales. The objectives of this research were to quantify E in an isolated, drip‐irrigated vineyard in an arid environment and to simulate below canopy E using the HYDRUS (2‐D/3‐D) model. Specific focus was on variations of E both temporally and spatially across the inter‐row. Continuous above canopy measurements, made in a commercial vineyard, included evapotranspiration, solar radiation, air temperature and humidity, and wind speed and direction. Short‐term intensive measurements below the canopy included actual and potential E and solar radiation along transects between adjacent vine‐rows. Potential and actual E below the canopy were highly variable, both diurnally and with distance from the vine‐row, as a result of shading and distinct wetted areas typical to drip irrigation. While the magnitude of actual E was mostly determined by soil water content, diurnal patterns depended strongly on position relative to the vine‐row due to variable shading patterns. HYDRUS (2‐D/3‐D) successfully simulated the magnitude, diurnal patterns, and spatial distribution of E, including expected deviations as a result of variability in soil saturated hydraulic conductivity.
- Detection of spatially limited high‐porosity layers using crosshole
GPR signal analysis and full‐waveform inversion
- Authors: Anja Klotzsche; Jan van der Kruk, John Bradford, Harry Vereecken
Pages: n/a - n/a
Abstract: High‐permittivity layers, related to high‐porosity layers or impermeable clay lenses, can act as low‐velocity electromagnetic waveguides. Electromagnetic wave phenomena associated with these features are complicated, not well known and not easy to interpret in borehole GPR data. Recently, a novel amplitude analysis approach was developed that is able to detect continuous low‐velocity waveguides and their boundaries between boreholes by using maximum and minimum positions of the trace energy profiles in measured GPR data. By analyzing waveguide models of different thickness, dip, extent, permittivity, and conductivity parameters, we extend the amplitude analysis to detect spatially limited or terminated waveguides. Waveguides that show high‐amplitude elongated wave trains are most probably caused by a change in porosity rather than a change in clay content. In a crosshole GPR data set from the Boise Hydrogeophysical Research Site, two terminated wave‐guiding structures were detected using the extended amplitude analysis. Information gained from the amplitude analysis improved the starting model for full‐waveform inversion which imaged the lateral extent and thickness of terminated waveguides with high resolution. Synthetic data calculated using the inverted permittivity and conductivity models show similar amplitudes and phases, as observed in the measured data, which indicates the reliability of the obtained models. Neutron‐Neutron logging data from three boreholes confirm the changes in porosity and indicate that these layers were high‐porosity sand units within low‐porosity, poorly sorted sand, and gravel units.
- Effects of tidal fluctuations on mixing and spreading in coastal aquifers:
- Authors: María Pool; Vincent E. A. Post, Craig T. Simmons
Pages: n/a - n/a
Abstract: While the hydraulics of tidally dominated groundwater systems have been studied extensively, tidally induced solute spreading in the fresh‐saltwater transition zone of coastal aquifers remains largely unexplored. Here we systematically quantify tidal impacts on solute mixing and spreading in seawater intrusion problems for an idealized homogeneous system. Mixing is characterized by the spatial moments of the solute concentration distribution and quantified by an effective dispersion coefficient. Parametric analysis reveals that the key dimensionless parameter controlling the tidal mixing behavior is the tidal mixing number (
ntm) which depends on the tidal amplitude, the period and the hydraulic diffusivity. We find that for
ntm≤600, tides lead to a significant impact on the shape and location of the interface. The maximum effect on transverse and longitudinal dispersion occurs for large values of storativity, a hydrogeologic parameter that has been previously understated in terms of its significance. Large storativity implies a nonuniform hydraulic response to the tidal forcing, such that the resulting nonuniform time‐dependent velocity field enhances mixing. As a result, the interface spreads mainly at the bottom of the aquifer, where the saline end of the mixing zone migrates seaward, whereas the spatial extent of low salt concentrations migrates landward. These insights critically underpin quantitative guidance on the inclusion and exclusion of tidal effects in the analysis of seawater intrusion.
- Snow depth, density, and SWE estimates derived from GPS reflection data:
Validation in the western U. S.
- Authors: James L. McCreight; Eric E. Small, Kristine M. Larson
Pages: n/a - n/a
Abstract: Geodetic‐quality GPS systems can be used to measure average snow depth in the ∼1000 m2 area around the GPS antenna, a sensing footprint size intermediate between in situ and satellite observations. SWE can be calculated from density estimates modeled on the GPS‐based snow depth time series. We assess the accuracy of GPS‐based snow depth, density, and SWE data at 18 GPS sites via comparison to manual observations. The manual validation survey was completed around the time of peak accumulation at each site. Daily snow depth derived from GPS reflection data is very similar to the mean snow depth measured manually in the ∼1000 m2 scale area around each antenna. This comparison spans site‐averaged depths from 0 to 150 cm. The GPS depth data exhibit a small negative bias (−6 cm) across this range of snow depths. Errors tend to be smaller at sites with more usable GPS ground tracks. Snow bulk density is modeled using the GPS snow depth time series and model parameters are estimated from nearby SNOTEL sites. Modeled density is within 0.02 g cm−3 of the density measured in a single snow pit at the validation sites, for 12 of 18 comparisons. GPS‐based depth and modeled density are multiplied to estimate SWE. SWE estimates are very accurate over the range observed at the validation sites, from 0 to 60 cm (R2 = 0.97 and bias = −2 cm). These results show that the near real‐time GPS snow products have errors small enough for monitoring water resources in snow‐dominated basins.
- Beyond optimality: Multistakeholder robustness trade‐offs for
regional water portfolio planning under deep uncertainty
- Authors: Jonathan D. Herman; Harrison B. Zeff, Patrick M. Reed, Gregory W. Characklis
Pages: n/a - n/a
Abstract: While optimality is a foundational mathematical concept in water resources planning and management, “optimal” solutions may be vulnerable to failure if deeply uncertain future conditions deviate from those assumed during optimization. These vulnerabilities may produce severely asymmetric impacts across a region, making it vital to evaluate the robustness of management strategies as well as their impacts for regional stakeholders. In this study, we contribute a multi‐stakeholder many‐objective robust decision making (MORDM) framework that blends many‐objective search and uncertainty analysis tools to discover key tradeoffs between water supply alternatives and their robustness to deep uncertainties (e.g., population pressures, climate change, financial risks, etc.). The proposed framework is demonstrated for four interconnected water utilities representing major stakeholders in the “Research Triangle” region of North Carolina, USA. The utilities supply well over one million customers and have the ability to collectively manage drought via transfer agreements and shared infrastructure. We show that water portfolios for this region that compose optimal tradeoffs (i.e., Pareto‐approximate solutions) under expected future conditions may suffer significantly degraded performance with only modest changes in deeply uncertain hydrologic and economic factors. We then use the Patient Rule Induction Method (PRIM) to identify which uncertain factors drive the individual and collective vulnerabilities for the four cooperating utilities. Our framework identifies key stakeholder dependencies and robustness tradeoffs associated with cooperative regional planning, which are critical to understanding the tensions between individual versus regional water supply goals. Cooperative demand management was found to be the key factor controlling the robustness of regional water supply planning, dominating other hydroclimatic and economic uncertainties through the 2025 planning horizon. Results suggest that a modest reduction in the projected rate of demand growth (from approximately 3% per year to 2.4%) will substantially improve the utilities’ robustness to future uncertainty and reduce the potential for regional tensions. The proposed multi‐stakeholder MORDM framework offers critical insights into the risks and challenges posed by rising water demands and hydrological uncertainties, providing a planning template for regions now forced to confront rapidly evolving water scarcity risks.
- An intercomparison of statistical downscaling methods used for water
resource assessments in the United States
- Authors: Ethan Gutmann; Tom Pruitt, Martyn P. Clark, Levi Brekke, Jeffrey R. Arnold, David A. Raff, Roy M. Rasmussen
Pages: n/a - n/a
Abstract: Information relevant for most hydrologic applications cannot be obtained directly from the native scale outputs of climate models. As a result the climate model output must be downscaled, often using statistical methods. The plethora of statistical downscaling methods requires end‐users to make a selection. This work is intended to provide end‐users with aid in making an informed selection. We assess four commonly used statistical downscaling methods: daily and monthly‐disaggregated‐to‐daily Bias Corrected Spatial Disaggregation (BCSDd, BCSDm), Asynchronous Regression (AR), and Bias Corrected Constructed Analog (BCCA) as applied to a continental scale domain and a regional domain (BCCAr). These methods are applied to the NCEP/NCAR Reanalysis, as a surrogate for a climate model, to downscale precipitation to a 12km gridded observation dataset. Skill is evaluated by comparing precipitation at daily, monthly, and annual temporal resolutions at individual grid cells and at aggregated scales. BCSDd and the BCCA methods overestimate wet day fraction, and underestimate extreme events. The AR method reproduces extreme events and wet day fraction well at the grid cell scale, but over (under) estimates extreme events (wet day fraction) at aggregated scales. BCSDm reproduces extreme events and wet day fractions well at all space and time scales, but is limited to rescaling current weather patterns. In addition, we analyze the choice of calibration dataset by looking at both a 12km and a 6km observational data set; the 6km observed dataset has more wet days and smaller extreme events than the 12km product, the opposite of expected scaling.
- Improved regional water management utilizing climate forecasts: An
interbasin transfer model with a risk management framework
- Authors: Weihua Li; A. Sankarasubramanian, R. S. Ranjithan, E. D. Brill
Pages: n/a - n/a
Abstract: Regional water supply systems undergo surplus and deficit conditions due to differences in inflow characteristics as well as due to their seasonal demand patterns. This study proposes a framework for regional water management by proposing an interbasin transfer (IBT) model that uses climate‐information‐based inflow forecast for minimizing the deviations from the end‐of‐season target storage across the participating pools. Using the ensemble streamflow forecast, the IBT water allocation model was applied for two reservoir systems in the North Carolina Triangle Area. Results show that interbasin transfers initiated by the ensemble streamflow forecast could potentially improve the overall water supply reliability as the demand continues to grow in the Triangle Area. To further understand the utility of climate forecasts in facilitating IBT under different spatial correlation structures between inflows and between the initial storages of the two systems, a synthetic experiment was designed to evaluate the framework under inflow forecast having different skills. Findings from the synthetic study can be summarized as follows: (a) inflow forecasts combined with the proposed IBT optimization model provide improved allocation in comparison to the allocations obtained under the no‐transfer scenario as well as under transfers obtained with climatology; (b) spatial correlations between inflows and between initial storages among participating reservoirs could also influence the potential benefits that could be achieved through IBT; (c) IBT is particularly beneficial for systems that experience low correlations between inflows or between initial storages or on both attributes of the regional water supply system. Thus, if both infrastructure and permitting structures exist for promoting interbasin transfers, season‐ahead inflow forecasts could provide added benefits in forecasting surplus/deficit conditions among the participating pools in the regional water supply system.
- Controls on groundwater flow in a semiarid folded and faulted
- Authors: Lyndsay B. Ball; Jonathan Saul Caine, Shemin Ge
Pages: n/a - n/a
Abstract: The major processes controlling groundwater flow in intermountain basins are poorly understood, particularly in basins underlain by folded and faulted bedrock and under regionally realistic hydrogeologic heterogeneity. To explore the role of hydrogeologic heterogeneity and poorly constrained mountain hydrologic conditions on regional groundwater flow in contracted intermountain basins, a series of 3‐D numerical groundwater flow models were developed using the South Park basin, Colorado, USA as a proxy. The models were used to identify the relative importance of different recharge processes to major aquifers, to estimate typical groundwater circulation depths, and to explore hydrogeologic communication between mountain and valley hydrogeologic landscapes. Modeling results show that mountain landscapes develop topographically controlled and predominantly local‐scale to intermediate‐scale flow systems. Permeability heterogeneity of the fold and fault belt and decreased topographic roughness led to permeability controlled flow systems in the valley. The structural position of major aquifers in the valley fold and fault belt was found to control the relative importance of different recharge mechanisms. Alternative mountain recharge model scenarios showed that higher mountain recharge rates led to higher mountain water table elevations and increasingly prominent local flow systems, primarily resulting in increased seepage within the mountain landscape and nonlinear increases in mountain block recharge to the valley. Valley aquifers were found to be relatively insensitive to changing mountain water tables, particularly in structurally isolated aquifers inside the fold and fault belt.
- Approximate Bayesian Computation using Markov Chain Monte Carlo
- Authors: Mojtaba Sadegh; Jasper A. Vrugt
Pages: n/a - n/a
Abstract: The quest for a more powerful method for model evaluation has inspired Vrugt and Sadegh (2013) to introduce “likelihood‐free” inference as vehicle for diagnostic model evaluation. This class of methods is also referred to as Approximate Bayesian Computation (ABC) and relaxes the need for a residual‐based likelihood function in favor of one or multiple different summary statistics that exhibit superior diagnostic power. Here we propose several methodological improvements over commonly used ABC sampling methods to permit inference of complex system models. Our methodology entitled DREAM(ABC) uses the DiffeRential Evolution Adaptive Metropolis algorithm as its main building block and takes advantage of a continuous fitness function to efficiently explore the behavioral model space. Three case studies demonstrate that DREAM(ABC) is at least an order of magnitude more efficient than commonly used ABC sampling methods for more complex models. DREAM(ABC) is also more amenable to distributed, multi‐processor, implementation, a prerequisite to diagnostic inference of CPU‐intensive system models.
- Toward efficiency in heterogeneous multispecies reactive transport
modeling: A particle‐tracking solution for first‐order network
- Authors: Christopher V. Henri; Daniel Fernández‐Garcia
Pages: n/a - n/a
Abstract: Modeling multi‐species reactive transport in natural systems with strong heterogeneities and complex biochemical reactions is a major challenge for assessing groundwater polluted sites with organic and inorganic contaminants. A large variety of these contaminants react according to serial‐parallel reaction networks commonly simplified by a combination of first‐order kinetic reactions. In this context, a random‐walk particle tracking method is presented. This method is capable of efficiently simulating the motion of particles affected by first‐order network reactions in three‐dimensional systems, which are represented by spatially variable physical and biochemical coefficients described at high resolution. The approach is based on the development of transition probabilities that describe the likelihood that particles belonging to a given species and location at a given time will be transformed into and moved to another species and location afterwards. These probabilities are derived from the solution matrix of the spatial moments governing equations. The method is fully coupled with reactions, free of numerical dispersion and overcomes the inherent numerical problems stemming from the incorporation of heterogeneities to reactive transport codes. In doing this, we demonstrate that the motion of particles follows a standard random walk with time‐dependent effective retardation and dispersion parameters that depend on the initial and final chemical state of the particle. The behavior of effective parameters develops as a result of differential retardation effects among species. Moreover, explicit analytic solutions of the transition probability matrix and related particle motions are provided for serial reactions. An example of the effect of heterogeneity on the dechlorination of organic solvents in a three‐dimensional random porous media shows that the power‐law behavior typically observed in conservative tracers breakthrough curves can be largely compromised by the effect of biochemical reactions.
- Quantitative characterization of stream turbidity‐discharge behavior
using event loop shape modeling and power law parameter decorrelation
- Authors: Amanda L. Mather; Richard L. Johnson
Pages: n/a - n/a
Abstract: Turbidity behavior in streams is a complex and dynamic function of both source material supply and event‐driven transport. While the primary controls on turbidity behavior across time and space are still not fully understood, recent increases in the availability of high temporal resolution, co‐located stream turbidity and discharge data provide an opportunity for more‐detailed analysis. Here we examine methods to quantitatively characterize event responses by modeling the shape of turbidity‐discharge hysteresis loops. A total of 1559 events from 20 gages in the Mid‐Atlantic region of the U.S. were modeled using both previously‐reported and new models combining elements of existing models. The results suggest that a more general power law based model, utilizing both a discharge rate of change term and a “supply” term, allows characterization of a wide range of simple and complex events. Additionally, this study explores a decorrelation approach to address the strong correlation frequently observed between the power law model coefficient (a) and exponent (b), with the goal of exposing the underlying behavior of each parameter individually. An examination of seasonal parameter behavior suggests that this approach may facilitate greater physically‐based interpretation of the power law coefficient. The power law parameter decorrelation strategy and the loop models examined here provide a step towards the larger goal of understanding the physical controls on turbidity‐discharge hysteretic behavior.
- Optimizing the scale of markets for water quality trading
- Authors: Martin W. Doyle; Lauren Patterson, Yanyou Chen, Kurt Schnier, Andrew J. Yates
Pages: n/a - n/a
Abstract: Applying market approaches to environmental regulations requires establishing a spatial scale for trading. Spatially large markets usually increase opportunities for abatement cost savings but increase the potential for pollution damages (hotspots); vice‐versa for spatially small markets. We develop a coupled hydrologic‐economic modeling approach for application to point source emissions trading by a large number of sources, and apply this approach to the wastewater treatment plants (WWTPs) within the watershed of the second largest estuary in the U.S. We consider two different administrative structures that govern the trade of emission permits: one‐for‐one trading (the number of permits required for each unit of emission is the same for every WWTP) and trading ratios (the number of permits required for each unit of emissions varies across WWTP). Results show that water quality regulators should allow trading to occur at the river basin scale as an appropriate first‐step policy, as is being done in a limited number of cases via compliance associations. Larger spatial scales may be needed under conditions of increased abatement costs. The optimal scale of the market is generally the same regardless of whether one‐for‐one trading or trading ratios are employed.
- Robust changes and sources of uncertainty in the projected hydrological
regimes of Swiss catchments
- Authors: Nans Addor; Ole Rössler, Nina Köplin, Matthias Huss, Rolf Weingartner, Jan Seibert
Pages: n/a - n/a
Abstract: Projections of discharge are key for future water resources management. These projections are subject to uncertainties, which are difficult to handle in the decision process on adaptation strategies. Uncertainties arise from different sources such as the emission scenarios, the climate models and their post‐processing, the hydrological models and natural variability. Here we present a detailed and quantitative uncertainty assessment, based on recent climate scenarios for Switzerland (CH2011 data set) and covering catchments representative for mid‐latitude alpine areas. This study relies on a particularly wide range of discharge projections resulting from the factorial combination of 3 emission scenarios, 10 to 20 regional climate models, 2 post‐processing methods and 3 hydrological models of different complexity. This enabled us to decompose the uncertainty in the ensemble of projections using analyses of variance (ANOVA). We applied the same modeling setup to 6 catchments to assess the influence of catchment characteristics on the projected streamflow and focused on changes in the annual discharge cycle. The uncertainties captured by our setup originate mainly from the climate models and natural climate variability, but the choice of emission scenario plays a large role by the end of the century. The respective contribution of the different sources of uncertainty varied strongly among the catchments. The discharge changes were compared to the estimated natural decadal variability, which revealed that a climate change signal emerges even under the lowest emission scenario (RCP2.6) by the end of the century. Limiting emissions to RCP2.6 levels would nevertheless reduce the largest regime changes at the end of the 21st century by approximately a factor of two, in comparison to impacts projected for the high emission scenario SRES A2. We finally show that robust regime changes emerge despite the projection uncertainty. These changes are significant and are consistent across a wide range of scenarios and catchments. We propose their identification as a way to aid decision‐making under uncertainty.
- Improving nutrient management practices in agriculture: The role of
risk‐based beliefs in understanding farmers' attitudes toward taking
- Authors: Robyn S. Wilson; Gregory Howard, Elizabeth A. Burnett
Pages: n/a - n/a
Abstract: A recent increase in the amount of dissolved reactive phosphorus (DRP) entering the western Lake Erie basin is likely due to increased spring storm events in combination with issues related to fertilizer application and timing. These factors in combination with warmer lake temperatures have amplified the spread of toxic algal blooms. We assessed the attitudes of farmers in northwest Ohio toward taking at least one additional action to reduce nutrient loss on their farm. Specifically, we (1) identified to what extent farm and farmer characteristics (e.g., age, gross farm sales) as well as risk‐based beliefs (e.g., efficacy, risk perception) influenced attitudes, and (2) assessed how these characteristics and beliefs differ in their predictive ability based on unobservable latent classes of farmers. Risk perception, or a belief that negative impacts to profit and water quality from nutrient loss were likely, was the most consistent predictor of farmer attitudes. Response efficacy, or a belief that taking action on one's farm made a difference, was found to significantly influence attitudes, although this belief was particularly salient for the minority class of farmers who were older and more motivated by profit. Communication efforts should focus on the negative impacts of nutrient loss to both the farm (i.e., profit) and the natural environment (i.e., water quality) to raise individual perceived risk among the majority, while the minority need higher perceived efficacy or more specific information about the economic effectiveness of particular recommended practices.
- Saltwater‐freshwater mixing dynamics in a sandy beach aquifer over
tidal, spring‐neap, and seasonal cycles
- Authors: James W. Heiss; Holly A. Michael
Pages: n/a - n/a
Abstract: The biogeochemical reactivity of sandy beach aquifers is closely linked to physical flow and solute transport processes. Thus, a clearer understanding of the hydrodynamics in the intertidal zone is needed to accurately estimate chemical fluxes to the marine environment. A field and numerical modeling study was conducted over a 1 year timeframe to investigate the combined effects of tidal stage, spring‐neap variability in tidal amplitude, and seasonal inland water table oscillations on intertidal salinity and flow dynamics within a tide‐dominated, microtidal sandy beach aquifer. Measured and simulated salinities revealed an intertidal saline circulation cell with a structure and cross‐sectional mixing zone area that varied over tidal, spring‐neap, and seasonal time scales. The size of the circulation cell and area of the mixing zone were shown for the first time to be most affected by seasonal water table oscillations, followed by tidal amplitude and tidal stage. The intertidal circulation cell expanded horizontally and vertically as the inland water table declined, displacing the fresh discharge zone and lower interface seaward. Over monthly spring‐neap cycles, the center of the circulation cell shifted from beneath the backshore and upper beachface to the base of the beach. Salinity variations in the intertidal zone over semidiurnal tidal cycles were minimal. The dynamics of the circulation cell were similar in simulations with and without a berm. The highly transient nature of intertidal salinity over multiple time scales may have important implications for the types and rates of chemical transformations that occur in groundwater prior to discharge to the ocean.
- A blue/green water‐based accounting framework for assessment of
- Authors: Dulce B. B. Rodrigues; Hoshin V. Gupta, Eduardo M. Mendiondo
Pages: n/a - n/a
Abstract: A comprehensive assessment of water security can incorporate several water‐related concepts, while accounting for Blue and Green Water (BW and GW) types defined in accordance with the hydrological processes involved. Here, we demonstrate how a quantitative analysis of provision probability and use of BW and GW can be conducted, so as to provide indicators of water scarcity and vulnerability at the basin level. To illustrate the approach, we use the Soil and Water Assessment Tool (SWAT) to model the hydrology of an agricultural basin (291 km²) within the Cantareira water supply system in Brazil. To provide a more comprehensive basis for decision‐making, we analyze the BW‐ and GW‐Footprint components against probabilistic levels (50th‐ and 30th‐percentile) of freshwater availability for human activities, during a 23‐year period. Several contrasting situations of BW provision are distinguished, using different hydrological‐based methodologies for specifying monthly Environmental Flow Requirements (EFRs), and the risk of natural EFR violation is evaluated by use of a freshwater provision index. Our results reveal clear spatial and temporal patterns of water scarcity and vulnerability levels within the basin. Taking into account conservation targets for the basin, it appears that the more restrictive EFR methods are more appropriate than the method currently employed at the study basin. The Blue/Green water‐based accounting framework developed here provides a useful integration of hydrologic, ecosystem and human needs information on a monthly basis, thereby improving our understanding of how and where water‐related threats to human and aquatic ecosystem security can arise.
- Examining spatial and temporal variability in snow water equivalent using
a 27 year reanalysis: Kern River watershed, Sierra Nevada
- Authors: Manuela Girotto; Gonzalo Cortés, Steven A. Margulis, Michael Durand
Pages: n/a - n/a
Abstract: This paper used a data assimilation framework to estimate spatially and temporally continuous snow water equivalent (SWE) from a 27 year reanalysis (from water year 1985 to 2011) of the Landsat‐5 record for the Kern River watershed in the Sierra Nevada, California. The data assimilation approach explicitly treats sources of uncertainty from model parameters, meteorological inputs, and observations. The method is comprised of two main components: (1) a coupled land surface model (LSM) and snow depletion curve (SDC) model, which is used to generate an ensemble of predictions of SWE and fractional snow cover area (FSCA) for a given set of prior (uncertain) inputs, and (2) a retrospective reanalysis step, which updates estimation variables to be consistent with the observed fractional snow cover time series. The final posterior SWE estimate is generated from the LSM‐SDC using the posterior estimation variables consistently with all postulated sources of uncertainty in the model, inputs, and observations. A reasonable agreement was found between the SWE reanalysis and in situ SWE observations and streamflow data. The data set was studied to evaluate factors controlling SWE spatial and temporal variability. Elevation was found to be the primary control on spatial patterns of peak‐SWE and day‐of‐peak. The easting coordinate had additional explanatory power, which is hypothesized to be related to rain shadow effects due to the prevailing storm track directions. The spatial patterns were found to be interannually inconsistent. However, drier years and lower elevations were found more variable than wetter years and higher elevations, respectively. Only a very small percentage of the Kern River watershed had a significant trend in peak‐SWE and day‐of‐peak. Trends deemed to be significant were found to be positive (peak‐SWE is increasing and day‐of‐peak occurs later) at higher elevations, but negative (peak‐SWE is decreasing and day‐of‐peak occurs earlier) at lower elevations. The reanalysis approach proved to be useful in terms of identifying subwatershed variability and trends, and could be extended to larger regions and areas where in situ data are sparse or unavailable.
- Identifying sampling locations for field‐scale soil moisture
estimation using K‐means clustering
- Authors: Zach Van Arkel; Amy L. Kaleita
Pages: n/a - n/a
Abstract: Identifying and understanding the impact of field‐scale soil moisture patterns is currently limited by the time and resources required to do sufficient monitoring. This study uses K‐means clustering to find critical sampling points to estimate field‐scale near‐surface soil moisture. Points within the field are clustered based upon topographic and soils data and the points representing the center of those clusters are identified as the critical sampling points. Soil moisture observations at 42 sites across the growing seasons of 4 years were collected several times per week. Using soil moisture observations at the critical sampling points and the number of points within each cluster, a weighted average is found and used as the estimated mean field‐scale soil moisture. Field‐scale soil moisture estimations from this method are compared to the rank stability approach (RSA) to find optimal sampling locations based upon temporal soil moisture data. The clustering approach on soil and topography data resulted in field‐scale average moisture estimates that were as good or better than RSA, but without the need for exhaustive presampling of soil moisture. Using an electromagnetic inductance map as a proxy for soils data significantly improved the estimates over those obtained based on topography alone.
- A significant nexus: Geographically isolated wetlands influence landscape
- Authors: Daniel L. McLaughlin; David A. Kaplan, Matthew J. Cohen
Pages: n/a - n/a
Abstract: Recent U.S. Supreme Court rulings have limited federal protections for geographically isolated wetlands (GIWs) except where a “significant nexus” to a navigable water body is demonstrated. Geographic isolation does not imply GIWs are hydrologically disconnected; indeed, wetland‐groundwater interactions may yield important controls on regional hydrology. Differences in specific yield (Sy) between uplands and inundated GIWs drive differences in water level responses to precipitation and evapotranspiration, leading to frequent reversals in hydraulic gradients that cause GIWs to act as both groundwater sinks and sources. These reversals are predicted to buffer surficial aquifer dynamics and thus baseflow delivery, a process we refer to as landscape hydrologic capacitance. To test this hypothesis, we connected models of soil moisture, upland water table, and wetland stage to simulate hydrology of a low‐relief landscape with GIWs, and explored the influences of total wetland area, individual wetland size, climate, and soil texture on water table and baseflow variation. Increasing total wetland area and decreasing individual wetland size substantially decreased water table and baseflow variation (e.g., reducing baseflow standard deviation by as much as 50%). GIWs also decreased the frequency of extremely high and low water tables and baseflow deliveries. For the same total wetland area, landscapes with fewer (i.e., larger) wetlands exhibited markedly lower hydrologic capacitance than those with more (i.e., smaller) wetlands, highlighting the importance of small GIWs to regional hydrology. Our results suggest that GIWs buffer dynamics of the surficial aquifer and stream baseflow, providing an indirect but significant nexus to the regional hydrologic system.
- The WFDEI meteorological forcing data set: WATCH Forcing Data methodology
applied to ERA‐Interim reanalysis data
- Authors: Graham P. Weedon; Gianpaolo Balsamo, Nicolas Bellouin, Sandra Gomes, Martin J. Best, Pedro Viterbo
Pages: n/a - n/a
Abstract: The WFDEI meteorological forcing dataset has been generated using the same methodology as the widely used WATCH Forcing Data (WFD) by making use of the ERA‐Interim reanalysis data. We discuss the specifics of how changes in the reanalysis and processing have led to improvement over the WFD. We attribute improvements in precipitation and wind speed to the latest reanalysis basis data and improved downwards shortwave fluxes to the changes in the aerosol corrections. Covering 1979‐2012 the WFDEI will allow more thorough comparisons of hydrological and Earth System model outputs with hydrologically‐ and phenologically‐relevant satellite products than using the WFD.
- Trends in water balance components across the Brazilian Cerrado
- Authors: Paulo Tarso S. Oliveira; Mark A. Nearing, M. Susan Moran, David C. Goodrich, Edson Wendland, Hoshin V. Gupta
Pages: n/a - n/a
Abstract: We assess the water balance of the Brazilian Cerrado based on remotely sensed estimates of precipitation (TRMM), evapotranspiration (MOD16), and terrestrial water storage (GRACE) for the period from 2003 to 2010. Uncertainties for each remotely sensed data set were computed, the budget closure was evaluated using measured discharge data for the three largest river basins in the Cerrado, and the Mann‐Kendall test was used to evaluate temporal trends in the water balance components and measured river discharge. The results indicate an overestimation of discharge data, due mainly to the overestimation of rainfall by TRMM version 6. However, better results were obtained when the new release of TRMM 3B42 v7 was used instead. Our results suggest that there have been a) significant increases in average annual evapotranspiration over the entire Cerrado of 51 ± 15 mm yr‐1, b) terrestrial water storage increases of 11 ± 6 mm yr‐1 in the northeast region of the Brazilian Cerrado, and c) runoff decreases of 72 ± 11 mm yr‐1 in isolated spots and in the western part of the State of Mato Grosso. Although complete water budget closure from remote sensing remains a significant challenge due to uncertainties in the data, it provides a useful way to evaluate trends in major water balance components over large regions, identify dry periods, and assess changes in water balance due to land cover and land use change.
- Mathematical analysis of the Saint‐Venant‐Hirano model for
- Authors: G. Stecca; A. Siviglia, A. Blom
Pages: n/a - n/a
Abstract: Sediments of different size are transported in rivers under the action of flow. The first and still most popular sediment continuity model able to deal with mixed sediment is the so called active layer model proposed by Hirano [1971, 1972]. In this paper we consider the one‐dimensional hydro‐morpohodynamic model given by the Saint‐Venant equations for free‐surface flow coupled with the active layer model. We perform a mathematical analysis of this model, extending the previous analysis by Ribberink , including full unsteadiness and grainsize‐selectivity of the transported load by explicitly considering multiple sediment fractions. The presence of multiple fractions gives rise to distinct waves traveling in the downstream direction, for which we provide an analytical approximation of propagation velocity under any Froude regime. We finally investigate the role of different waves in advecting morphodynamic changes through the domain. To this aim, we implement an analytical linearized solver to analyze the propagation of small‐amplitude perturbations of the bed elevation and grainsize distribution of the active layer as described by the system of governing equations. We find that initial gradients in the grainsize distribution of the active layer are able to trigger significant bed variations, which propagate in the downstream direction at faster pace than the “bed” wave arising from the uniform‐sediment Saint‐Venant‐Exner model. We also verify that multiple “sorting” waves carry multiple associated bed perturbations, traveling at different speeds.
- Estimation of the distribution of annual runoff from climatic variables
- Authors: Lihua Xiong; Kun‐xia Yu, Lars Gottschalk
Pages: n/a - n/a
Abstract: An approach of deriving the annual runoff distribution using copulas from an annual rainfall‐runoff model is proposed to provide an alternative annual runoff frequency analysis method in case of changing climatic variables. The annual rainfall‐runoff model is established on the basis of the Budyko formula to estimate annual runoff, with annual precipitation and potential evapotranspiration as input variables. The model contains one single parameter k that guarantees that annual water balance is satisfied. In the derivation of the annual runoff distribution, annual precipitation, annual potential evapotranspiration and parameter k are treated as three random variables, while the annual runoff distribution is obtained by integrating the joint probability density function of the three random variables over the domain constrained by the annual rainfall‐runoff model using the canonical vine copula. This copula‐based derivation approach is tested for 40 watersheds in two large basins in China. The estimated annual runoff distribution performs well in most watersheds. The performance is mainly related to the accuracy of the marginal distribution of precipitation. The copula‐based derivation approach can also be used in ungauged watersheds where the distribution of k at the local site is estimated from the regional information of the k variable, and it also has acceptable performance in most watersheds, while poor performance is observed in a few watersheds with low accuracy in the Budyko formula.
- Using multiple donor sites for enhanced flood estimation in ungauged
- Authors: T. R. Kjeldsen; D. A. Jones, D. G. Morris
Pages: n/a - n/a
Abstract: A new generalized method is presented enabling the use of multiple donor sites when predicting an index flood variable in an ungauged catchment using a hydrological regression model. The method is developed from the premise of having an index flood prediction with minimum variance, which results in a set of optimal weights assigned to each donor site. In the model framework presented here, the weights are determined by the geographical distance between the centroids of the catchments draining to the subject site and the donor sites. The new method was applied to a case study in the United Kingdom using annual maximum series of peak flow from 602 catchments. Results show that the prediction error of the index flood is reduced by using donor sites until a minimum of six donors have been included, after which no or marginal improvements in prediction accuracy are observed. A comparison of these results is made with a variant of the method where donor sites are selected based on connectivity with the subject site through the river network. The results show that only a marginal improvement is obtained by explicitly considering the network structure over spatial proximity. The evaluation is carried out based on a new performance measure that accounts for the sampling variability of the index flood estimates at each site. Other results compare the benefits obtained by adding relevant catchment descriptors to a simple regression model with those obtained by transferring information from local donor sites.
- Hydrogeologic insights for a Devil's Slide‐like system
- Authors: Matthew A. Thomas; Keith Loague
Pages: n/a - n/a
Abstract: Tectonically active coastal margins commonly host landslides that are influenced by hydrologic, geologic, and/or anthropogenic perturbations. The work reported here is motivated by the hydrologically driven, deep‐seated bedrock slides that intersect the (former) Pacific Coast Highway in the active landslide zone at Devil's Slide near Pacifica, California. Numerical simulation of subsurface flow is employed to investigate saturated zone fluid pressure scenarios for 3‐D Devil's Slide‐like systems. The four‐phase concept‐development effort is comprised of 134 hydrogeologic simulation scenarios which investigate fluid pressure response for complex subsurface conditions and historically based climate forcings. Recharge, heterogeneity, and anisotropy are shown to increase fluid pressures in targeted failure‐prone locations by up to 73.8, 10.3, and 1.8 %, respectively. The interaction between fault zone characteristics and topographically driven flow are shown to influence fluid pressures for up to 85% of the approximately 7.0
× 105 m2 study area. Simulated fluid pressures support the known slope instability for the Devil's Slide site. A quantitative hypothesis‐testing discussion explores the likelihood of perched water above the regional water table at the site. Further understanding of hydrologically driven slope movement in the active landslide zone will require additional data focused on rigorous characterization of the unsaturated zone.
- Local‐ and field‐scale stochastic‐advective vertical
solute transport in horizontally heterogeneous unsaturated soils
- Authors: Richa Ojha; A. Prakash, Rao S. Govindaraju
Pages: n/a - n/a
Abstract: Description of field‐scale solute transport in unsaturated soils is essential for assessing the degree of contamination, estimating fluxes past a control plane and for designing remedial measures. The flow field is usually described by numerical solution of the Richards equation followed by numerical solution of the advection‐dispersion equation to describe contaminant movement. These numerical solutions are highly complex, and do not provide the insights that are possible from simpler analytical representations. In this study, analytical solutions at the local scale are developed to describe purely advective vertical transport of a conservative solute along the principle characteristic of the flow field. Local‐scale model development is simplified by using a sharp‐front approximation for water movement. These local solutions are then upscaled to field‐scale solute transport by adopting a lognormally distributed horizontal hydraulic conductivity field to represent the natural heterogeneity observed in field soils. Analytical expressions are developed for the mean behavior of solute transport at the field scale. Comparisons with experimental observations find that trends of field‐scale solute behavior are reasonably reproduced by the model. The accuracy of the proposed solution improves with increasing spatial variability in the hydraulic conductivity as revealed by further comparisons with numerical results of the Richards equation‐based field‐scale solute movement. In some cases, the sharp‐front approximation may lead to anomalous field‐scale behavior depending on the role of pre and postponded conditions in the field, and this limitation is discussed. The proposed method shows promise for describing field‐scale solute movement in loamy sand and sandy loam soils.
- Reimagining cost recovery in Pakistan's irrigation system through
willingness‐to‐pay estimates for irrigation water from a
discrete choice experiment
- Authors: Andrew Reid Bell; M. Azeem Ali Shah, Patrick S. Ward
Pages: n/a - n/a
Abstract: It is widely argued that farmers are unwilling to pay adequate fees for surface water irrigation to recover the costs associated with maintenance and improvement of delivery systems. In this paper, we use a discrete choice experiment to study farmer preferences for irrigation characteristics along two branch canals in Punjab Province in eastern Pakistan. We find that farmers are generally willing to pay well in excess of current surface water irrigation costs for increased surface water reliability and that the amount that farmers are willing to pay is an increasing function of their existing surface water supply as well as location along the main canal branch. This explicit translation of implicit willingness‐to‐pay (WTP) for water (via expenditure on groundwater pumping) to WTP for reliable surface water demonstrates the potential for greatly enhanced cost recovery in the Indus Basin Irrigation System via appropriate setting of water user fees, driven by the higher WTP of those currently receiving reliable supplies.
- Impact of ambient conditions on evaporation from porous media
- Authors: Asaf Ben Neriah; Shmuel Assouline, Uri Shavit, Noam Weisbrod
Pages: n/a - n/a
Abstract: The complexity of soil evaporation, depending on the atmospheric conditions, emphasizes the importance of its quantification under potential changes in ambient air temperature, Ta, and relative humidity, RH. Mass loss, soil matric tension, and meteorological measurements, carried out in a climate‐controlled laboratory, were used to study the effect of ambient conditions on the drying rates of a porous medium. A set of evaporation experiments from initially saturated sand columns were carried out under constant Ta of 6, 15, 25, and 35°C and related RH (0.66, 0.83, 1.08, and 1.41 kPa, respectively). The results show that the expected increase of the stage 1 (S1) evaporation rate with Ta but also revealed an exponential‐like reduction in the duration of S1, which decreased from 29 to 2.3 days (at Ta of 6 and 35°C, respectively). The evaporation rate, e(t), was equal to the potential evaporation, ep(t), under Ta = 6°C, while it was always smaller than ep(t) under higher Ta. The cumulative evaporation during S1 was higher under Ta = 6°C than under the higher temperatures. Evaporation rates during S2 were practically unaffected by ambient conditions. The results were analyzed using a mass transfer formulation linking e(t) with the vapor pressure deficit through a resistance coefficient r. It was shown that rS1 (the resistance during S1) is constant, indicating that the application of such an approach is straightforward during S1. However, for evaporation from a free water surface and S2, the resistances, rBL and rS2, were temperature‐dependent, introducing some complexity for these cases.
- Potential groundwater age tracer found: Halon‐1301 (CF3Br), as
previously identified as CFC‐13 (CF3Cl)
- Authors: Monique Beyer; Rob van der Raaij, Uwe Morgenstern, Bethanna Jackson
Pages: n/a - n/a
Abstract: Groundwater dating using anthropogenic and natural tracer substances is a powerful tool for understanding groundwater dynamics for improved management of groundwater resources. Due to limitations in individual dating methods, often multiple tracers are used to reduce ambiguities. It is commonly accepted there is a need for further complementary age tracers, in addition to current ones (e.g. tritium, SF6 and CFCs). We propose a potential new groundwater age tracer, Halon‐1301 (CF3Br), which can easily be determined using gas chromatography with an attached electron capture detector (GC/ECD) developed by Busenberg and Plummer . Its peak was noted by Busenberg and Plummer , but they believed it to be CFC‐13 (CF3Cl) at that time. We performed rigorous tests on gases containing or excluding Halon‐1301 and CFC‐13, and modern water samples and concluded that the two compounds have extremely similar retention times. Additionally, we found that the ECD response of CFC‐13 is far too low to be detected in groundwater or air using standard volumes and sampling techniques. However the peak areas and concentrations Busenberg and Plummer  reported are in line with what would be expected for Halon‐1301. Thus, we are confident that the peak formerly identified as CFC‐13 is actually Halon‐1301. Busenberg, E. agrees with our findings. We further suggest that Halon‐1301 has potential as a (complementary) age tracer, due to its established atmospheric history, and could hypothetically be used to date groundwater recharged in the 1970s or onwards.
We discuss known relevant properties, such as solubility and stability of Halon‐1301 in the context of how these effect its potential application as a groundwater age tracer. Some open questions remain concerning how conservative Halon‐1301 is – is it subject to degradation, retardation, and/or local contamination in groundwater. We are confident that Halon‐1301 possesses important tracer relevant properties, but further work is required to fully assess its applicability and reliability as a groundwater age tracer in different groundwater environments.
- Antecedent moisture conditions control mercury and dissolved organic
carbon concentration dynamics in a boreal headwater catchment
- Authors: Claire J. Oswald; Brian A. Branfireun
Pages: n/a - n/a
Abstract: The fate and transport of mercury (Hg) deposited on forested upland soils depends on the biogeochemical and hydrological processes occurring in the soil landscape. In this study, total Hg (THg) and dissolved organic carbon (DOC) concentrations were measured in streamwater from a 7.75 ha upland subcatchment of the METAALICUS watershed in northwestern Ontario, Canada. THg and DOC concentration‐discharge relationships were examined at the seasonal‐scale and event‐scale to assess the role of antecedent moisture conditions on the mobilization of these solutes to receiving waters. At the seasonal‐scale, subcatchment discharge poorly explained THg and DOC concentration dynamics; however, the inclusion of antecedent water storage and precipitation metrics in a multiple regression model improved the prediction of THg and DOC concentrations significantly. At the event‐scale, a comparison of THg and DOC concentrations for two small summer storms with similar total discharge showed that the storm following the wet snowmelt period had a significantly lower total flux of THg and DOC than the storm following warm and dry conditions in late summer due to a distinct shift in the concentration‐discharge relationship. Measurements of soil water and groundwater THg and DOC concentrations, as well as a three‐component mixing analysis, suggest that there was an accumulation of potentially‐mobile DOC‐bound THg in the well‐humified organic soil layer in the catchment during the warm and dry summer period and that as the catchment became wetter in the autumn, there was an increase in soil water THg and DOC concentrations and these solutes were subsequently flushed during the autumn storm.
- Economic analysis of the water demand in the hotels and restaurants
sector: Shadow prices and elasticities
- Authors: Ana Angulo; Majed Atwi, Ramón Barberán, Jesús Mur
Pages: n/a - n/a
Abstract: Despite the growing economic importance of tourism, and its impact on relative water shortage, little is known about the role that water plays in the productive process of hotels and restaurants and, therefore, the possible implications of water demand management policy for this sector. This study aims to fill this gap. It is based on the microdata of 676 firms in the sector, operating in the city of Zaragoza (Spain) for a 12 year period. Based on the Translog cost function, we estimate the shadow price of water in the short run and, from a long‐run perspective, its direct price elasticity, its cross elasticities relative to labor, capital, and supplies, and its elasticity with respect to the level of output. The results obtained show that water provides sector firms returns that are on average higher than its price, although in the case of hotels the margin is really narrow. This situation provides policy makers with a margin for applying price increases without affecting the sector's viability, with some caution in the case of hotels. Water demand elasticity equals −0.38 in the case of hotels, but it is not significant in the case of restaurants and bar‐cafes; hence, only in hotels is there potential for influencing water use patterns, encouraging the resource's conservation through pricing policy. Moreover, capital is a substitutive factor of water, and the elasticity of water with respect to output is 0.40, all of which should also be considered by policy makers in water resource management.
- Assessing the value of seasonal climate forecast information through an
end‐to‐end forecasting framework: Application to U.S. 2012
drought in central Illinois
- Authors: Majid Shafiee‐Jood; Ximing Cai, Ligang Chen, Xin‐Zhong Liang, Praveen Kumar
Pages: n/a - n/a
Abstract: This study proposes an end‐to‐end forecasting framework to incorporate operational seasonal climate forecasts to help farmers improve their decisions prior to the crop growth season, which are vulnerable to unanticipated drought conditions. The framework couples a crop growth model with a decision‐making model for rainfed agriculture and translates probabilistic seasonal forecasts into more user‐related information that can be used to support farmers' decisions on crop type and some market choices (e.g., contracts with ethanol refinery). The regional Climate‐Weather Research and Forecasting model (CWRF) driven by two operational general circulation models (GCMs) is used to provide the seasonal forecasts of weather parameters. To better assess the developed framework, CWRF is also driven by observational reanalysis data, which theoretically can be considered as the best seasonal forecast. The proposed framework is applied to the Salt Creek watershed in Illinois that experienced an extreme drought event during 2012 crop growth season. The results show that the forecasts cannot capture the 2012 drought condition in Salt Creek and therefore the suggested decisions can make farmers worse off if the suggestions are adopted. Alternatively, the optimal decisions based on reanalysis‐based CWRF forecasts, which can capture the 2012 drought conditions, make farmers better off by suggesting “no‐contract” with ethanol refineries. This study suggests that the conventional metric used for ex ante value assessment is not capable of providing meaningful information in the case of extreme drought. Also, it is observed that institutional interventions (e.g., crop insurance) highly influences farmers' decisions and, thereby, the assessment of forecast value.
- Bed load fluctuations in a steep channel
- Authors: Tamara Ghilardi; Mário J. Franca, Anton J. Schleiss
Pages: n/a - n/a
Abstract: Bed load transport rate fluctuations have been observed over time in steep rivers and flumes with wide grain size distributions even under constant sediment feeding and water discharge. The observed bed load transport rate pulses are periodic and a consequence of grain sorting. Moreover, the presence of large, relatively immobile boulders, such as erratic stones, which are often present in mountain streams, has an impact on flow conditions. The detailed analysis of a 13 h laboratory experiment is presented in this paper. Boulders were randomly placed in a flume with a steep slope (6.7%), and water and sediment were constantly supplied to the flume. Along with the sediment transport and bulk mean flow velocity, the boulder protrusion, boulder surface, and number of hydraulic jumps, which are indicators of the channel morphology, were measured regularly during the experiment. Periodic bed load transport rate pulses are clearly visible in the data collected during this long‐duration experiment, along with correlated fluctuations in the flow velocity and bed morphology. The links among the bulk velocity, the time evolution of the morphology variables, and the bed load transport rate are analyzed via correlational analysis, showing that the fluctuations are strongly related. A phase analysis of all observed variables is performed, and the average shapes of the time cycles of the fluctuations are shown. Observations indicate that the detected periodic fluctuations correspond to different bed states. Furthermore, the grain size distribution through the channel, which varies in time and space, clearly influences these bed load transport rate pulses. Finally, known bed load transport rate formulae are tested, showing that only the application of a drag shear stress allows a correct estimation of the time fluctuations.
- Robust, low‐cost data loggers for stream temperature, flow
intermittency, and relative conductivity monitoring
- Authors: Thomas P. Chapin; Andrew S. Todd, Matthew P. Zeigler
Pages: n/a - n/a
Abstract: Water temperature and streamflow intermittency are critical parameters influencing aquatic ecosystem health. Low‐cost temperature loggers have made continuous water temperature monitoring relatively simple but determining streamflow timing and intermittency using temperature data alone requires significant and subjective data interpretation. Electrical resistance (ER) sensors have recently been developed to overcome the major limitations of temperature‐based methods for the assessment of streamflow intermittency. This technical note introduces the STIC (Stream Temperature, Intermittency, and Conductivity logger); a robust, low‐cost, simple to build instrument that provides long‐duration, high‐resolution monitoring of both relative conductivity (RC) and temperature. Simultaneously collected temperature and RC data provide unambiguous water temperature and streamflow intermittency information that is crucial for monitoring aquatic ecosystem health and assessing regulatory compliance. With proper calibration, the STIC relative conductivity data can be used to monitor specific conductivity.
- Discontinuous Galerkin flood model formulation: Luxury or necessity?
- Authors: Georges Kesserwani; Yueling Wang
Pages: n/a - n/a
Abstract: The finite volume Godunov‐type flood model formulation is the most comprehensive amongst those currently employed for flood risk modeling. The local Discontinuous Galerkin method constitutes a more complex, rigorous, and extended local Godunov‐type formulation. However, the practical merit associated with such an increase in the level of complexity of the formulation is yet to be decided. This work makes the case for a second‐order Runge‐Kutta Discontinuous Galerkin (RKDG2) formulation and contrasts it with the equivalently accurate finite volume (MUSCL) formulation, both of which solve the Shallow Water Equations (SWE) in two space dimensions. The numerical complexity of both formulations are presented and their capabilities are explored for wide‐ranging diagnostic and real‐scale tests, incorporating all challenging features relevant to flood inundation modeling. Our findings reveal that the extra complexity associated with the RKDG2 model pays off by providing higher‐quality solution behavior on very coarse meshes and improved velocity predictions. The practical implication of this is that improved accuracy for flood modeling simulations will result when terrain data are limited or of a low resolution.
- Modeling spatiotemporal impacts of hydroclimatic extremes on groundwater
recharge at a Mediterranean karst aquifer
- Authors: Andreas Hartmann; Matías Mudarra, Bartolomé Andreo, Ana Marín, Thorsten Wagener, Jens Lange
Pages: n/a - n/a
Abstract: Karst aquifers provide large parts of the water supply for Mediterranean countries, though climate change is expected to have a significant negative impact on water availability. Recharge is therefore a key variable that has to be known for sustainable groundwater use. In this study, we present a new approach that combines two independent methods for karst recharge estimation. The first method derives spatially distributed information of mean annual recharge patterns through GIS analysis. The second is a process‐based karst model that provides spatially lumped but temporally distributed information about recharge. By combining both methods, we add a spatial reference to the lumped simulations of the process‐based model. In this way, we are able to provide spatiotemporal information of recharge and subsurface flow dynamics also during varying hydroclimatic conditions. We find that there is a nonlinear relationship between precipitation and recharge rates resulting in strong decreases of recharge following even moderate decreases of precipitation. This is primarily due to almost constant actual evapotranspiration amounts despite varying hydroclimatic conditions. During the driest year in the record, almost the entire precipitation was consumed as actual evapotranspiration and only little diffuse recharge took place at the high altitudes of our study site. During wettest year, recharge constituted a much larger fraction of precipitation and occurred at the entire study site. Our new method and our findings are significant for decision makers in similar regions that want to prepare for possible changes of hydroclimatic conditions in the future.
- A simple inverse method for the interpretation of pumped flowing fluid
electrical conductivity logs
- Authors: R. S. Moir; A. H. Parker, R. T. Bown
Pages: n/a - n/a
Abstract: Pumped flowing fluid electrical conductivity (FFEC) logs, also known as pumped borehole dilution testing, is an experimentally easy‐to‐perform approach to evaluating vertical variations in the hydraulic conductivity of an aquifer. In contrast to the simplicity of the logging equipment, analysis of the data is complex and laborious. Current methods typically require repeated solution of the advection‐dispersion equation (ADE) for describing the flow in the borehole and comparison with the experimental results. In this paper, we describe a direct solution for determining borehole fluid velocity that bypasses the need for complex numerical computation and repetitive optimization. The method rests on the observation that, while solving the ADE for concentration profile in the borehole (as required for modeling and combined methods) is computationally challenging, the solution for flow distribution along the length of the borehole given concentration data is straightforward. The method can accommodate varying borehole diameters, and uses the fact that multiple profiles are taken in the standard logging approach to reduce the impact of noise. Data from both a simulated borehole and from a field test are successfully analyzed. The method is implemented in a spreadsheet, which is available as supporting information material to this paper.
- Epidemiology of urban water distribution systems
- Authors: Jean‐Pierre Bardet; Richard Little
Pages: n/a - n/a
Abstract: Urban water distribution systems worldwide contain numerous old and fragile pipes that inevitably break, flood streets and damage property, and disrupt economic and social activities. Such breaks often present dramatically in temporal clusters as occurred in Los Angeles during 2009. These clustered pipe breaks share many characteristics with human mortality observed during extreme climatological events such as heat waves or air pollution. Drawing from research and empirical studies in human epidemiology, a framework is introduced to analyze the time variations of disruptive pipe breaks that can help water agencies better understand clustered pipe failures and institute measures to minimize the disruptions caused by them. It is posited that at any time, a cohort of the pipes comprising the water distribution system will be in a weakened state due to fatigue and corrosion. This frail cohort becomes vulnerable during normal operations and ultimately breaks due to rapid increase in crack lengths induced by abnormal stressors. The epidemiological harvesting model developed in this paper simulates an observed time series of monthly pipe breaks and has both explanatory and predictive power. It also demonstrates that models from nonengineering disciplines such as medicine can provide improved insights into the performance of infrastructure systems.
- Comparing vertical profiles of natural tracers in the Williston Basin to
estimate the onset of deep aquifer activation
- Authors: M. Jim Hendry; Glenn A. Harrington
Pages: n/a - n/a
Abstract: Comparing high‐resolution depth profiles of different naturally occurring environmental tracers in aquitards should yield consistent and perhaps complementary information about solute transport mechanisms and the timing of major hydrogeological and climatological events. This study evaluated whether deep, continuous profiles of aquitard pore water chloride concentration could provide further insight into the paleohydrology of the Williston Basin, Canada, than possible using high‐resolution depth profiles of stable H/O isotopes of water (δ18O, δ2H). Pore water samples were obtained from extracts of cores taken over 392 m of the thick Cretaceous shale aquitard. Water samples were also collected from wells installed in the underlying regional sandy aquifer (Mannville Group; 93 m thick) and from seepage inflows into potash mine shafts (to 825 m below ground). Numerical modeling of the 1‐D vertical Cl− profile supported diffusion dominated solute transport in the shales. The modeling also showed a similar time frame for development of the Cl− profile prior to activation of the aquifer as determined from the δ18O profile (20–25 Ma); however, it provided a significantly longer and potentially better‐constrained time frame for evolution of the profile during the activation phase of the aquifer (0.5–1 Ma). The dominant paleoevent reflected in present‐day profiles of both tracers is the introduction of glaciogenic meteoric water to the Mannville aquifer underlying the shale during the Pleistocene. The source area of this water remains to be determined.
- Nonequilibrium water dynamics in the rhizosphere: How mucilage affects
water flow in soils
- Authors: Eva Kroener; Mohsen Zarebanadkouki, Anders Kaestner, Andrea Carminati
Pages: n/a - n/a
Abstract: The flow of water from soil to plant roots is controlled by the properties of the narrow region of soil close to the roots, the rhizosphere. In particular, the hydraulic properties of the rhizosphere are altered by mucilage, a polymeric gel exuded by the roots. In this paper we present experimental results and a conceptual model of water flow in unsaturated soils mixed with mucilage. A central hypothesis of the model is that the different drying/wetting rate of mucilage compared to the bulk soil results in nonequilibrium relations between water content and water potential in the rhizosphere. We coupled this nonequilibrium relation with the Richards equation and obtained a constitutive equation for water flow in soil and mucilage. To test the model assumptions, we measured the water retention curve and the saturated hydraulic conductivity of sandy soil mixed with mucilage from chia seeds. Additionally, we used neutron radiography to image water content in a layer of soil mixed with mucilage during drying and wetting cycles. The radiographs demonstrated the occurrence of nonequilibrium water dynamics in the soil‐mucilage mixture. The experiments were simulated by numerically solving the nonequilibrium model. Our study provides conceptual and experimental evidences that mucilage has a strong impact on soil water dynamics. During drying, mucilage maintains a greater soil water content for an extended time, while during irrigation it delays the soil rewetting. We postulate that mucilage exudation by roots attenuates plant water stress by modulating water content dynamics in the rhizosphere.
- Comment on “Traveling wave solution of the Boussinesq equation for
groundwater flow in horizontal aquifers” by H.A. Basha (pages
- Authors: Jeffrey Olsen; Jeff Mortensen, Aleksey S. Telyakovskiy
Pages: n/a - n/a
Abstract: This article is a comment on Basha  doi:10.1002/wrcr.20168
- A new selection metric for multiobjective hydrologic model calibration
- Authors: Masoud Asadzadeh; Bryan Tolson, Donald H. Burn
Pages: n/a - n/a
Abstract: A novel selection metric called Convex Hull Contribution (CHC) is introduced for solving multi‐objective (MO) optimization problems with Pareto fronts that can be accurately approximated by a convex curve. The hydrologic model calibration literature shows that many bi‐objective calibration problems with a proper setup result in such Pareto fronts. The CHC selection approach identifies a subset of archived non‐dominated solutions whose map in the objective space forms convex approximation of the Pareto front. The optimization algorithm can sample solely from these solutions to more accurately approximate the convex shape of the Pareto front.
It is empirically demonstrated that CHC improves the performance of Pareto Archived Dynamically Dimensioned Search (PA‐DDS) when solving MO problems with convex Pareto fronts. This conclusion is based on the results of several benchmark mathematical problems and several hydrologic model calibration problems with two or three objective functions. The impact of CHC on PA‐DDS performance is most evident when the computational budget is somewhat limited. It is also demonstrated that 1,000 solution evaluations (limited budget in this study) is sufficient for PA‐DDS with CHC‐based selection to achieve very high quality calibration results relative to the results achieved after 10,000 solution evaluations.
- Life in a fishbowl: Prospects for the endangered Devils Hole pupfish
(Cyprinodon diabolis) in a changing climate
- Authors: Mark B. Hausner; Kevin P. Wilson, D. Bailey Gaines, Francisco Suárez, G. Gary Scoppettone, Scott W. Tyler
Pages: n/a - n/a
Abstract: The Devils Hole pupfish (Cyprinodon diabolis) is a federally listed endangered species living solely within the confines of Devils Hole, a geothermal pool ecosystem in the Mojave Desert of the American Southwest. This unique species has suffered a significant, yet unexplained, population decline in the past two decades, with a record low survey of 35 individuals in early 2013. The species survives on a highly variable seasonal input of nutrients and has evolved in a thermal regime lethal to other pupfish species. The short lifespan of the species (approximately 1 year), makes annual recruitment in Devils Hole critical to the persistence of the species, and elevated temperatures on the shallow shelf that comprises the optimal spawning habitat in the ecosystem can significantly reduce egg viability and increase larval mortality. Here we combine computational fluid dynamic modeling and ecological analysis to investigate the timing of thresholds in the seasonal cycles of food supply and temperature. Numerical results indicate a warming climate most impacts the heat loss from the water column, resulting in warming temperatures and reduced buoyancy‐driven circulation. Observed climate change is shown to have already warmed the shallow shelf, and climate change by 2050 is shown to shorten the window of optimum conditions for recruitment by as much as two weeks. While there are many possible reasons for the precipitous decline of this species, the changing climate of the Mojave region is shown to produce thermal and nutrient conditions likely to reduce the success of annual recruitment of young C. diabolis in the future, leading to continued threats to the survival of this unique and enigmatic species.
- Oscillatory pumping wells in phreatic, compressible, and homogeneous
- Authors: G. Dagan; A. Rabinovich
Pages: n/a - n/a
Abstract: Oscillatory well pumping was proposed recently as a tool for hydraulic tomography. Periodic pumping at a few frequencies is carried out through vertical intervals along the pumping well and the periodic head is measured along a few piezometers. The paper presents an analytical solution for the head field in an unconfined aquifer of finite depth under the common assumptions of a linearized water table condition, different horizontal and vertical constant permeabilities, constant specific storativity and water table drainable porosity and small well radius to length ratio. The solution provides the expressions of the amplitude and phase of the head as a function of coordinates, frequency and the problem parameters. The solution simplifies to one pertaining to an upper constant head condition and a rigid aquifer for a wide range of the dimensionless frequency values.
- Blind source separation for groundwater pressure analysis based on
nonnegative matrix factorization
- Authors: Boian S. Alexandrov; Velimir V. Vesselinov
Pages: n/a - n/a
Abstract: The identification of the physical sources causing spatial and temporal fluctuations of aquifer water levels is a challenging, yet a very important hydrogeological task. The fluctuations can be caused by variations in natural and anthropogenic sources such as pumping, recharge, barometric pressures, etc. The source identification can be crucial for conceptualization of the hydrogeological conditions and characterization of aquifer properties. We propose a new computational framework for model‐free inverse analysis of pressure transients based on Non‐negative Matrix Factorization (NMF) method for Blind Source Separation (BSS) coupled with k‐means clustering algorithm, which we call NMFk. NMFk is capable of identifying a set of unique sources from a set of experimentally measured mixed signals, without any information about the sources, their transients, and the physical mechanisms and properties controlling the signal propagation through the subsurface flow medium.Our analysis only requires information about pressure transients at a number of observation points, m, where m ≥ r, and r is the number of unknown unique sources causing the observed fluctuations. We apply this new analysis on a dataset from the Los Alamos National Laboratory site. We demonstrate that the sources identified by NMFk have real physical origins: barometric pressure and water‐supply pumping effects. We also estimate the barometric pressure efficiency of the monitoring wells. The possible applications of the NMFk algorithm are not limited to hydrogeology problems; NMFk can be applied to any problem where temporal system behavior is observed at multiple locations and an unknown number of physical sources are causing these fluctuations.
- Water resources management in a homogenizing world: Averting the growth
and underinvestment trajectory
- Authors: Ali Mirchi; David W Watkins, Casey J Huckins, Kaveh Madani, Peder Hjorth
Pages: n/a - n/a
Abstract: Biotic homogenization, a de facto symptom of a global biodiversity crisis, underscores the urgency of reforming water resources management to focus on the health and viability of ecosystems. Global population and economic growth, coupled with inadequate investment in maintenance of ecological systems, threaten to degrade environmental integrity and ecosystem services that support the global socio‐economic system, indicative of a system governed by the Growth and Underinvestment (G&U) archetype. Water resources management is linked to biotic homogenization and degradation of system integrity through alteration of water systems, ecosystem dynamics, and composition of the biota. Consistent with the G&U archetype, water resources planning primarily treats ecological considerations as exogenous constraints rather than integral, dynamic and responsive parts of the system. It is essential that the ecological considerations be made objectives of water resources development plans to facilitate the analysis of feedbacks and potential trade‐offs between socio‐economic gains and ecological losses. We call for expediting a shift to ecosystem‐based management of water resources, which requires a better understanding of the dynamics and links between water resources management actions, ecological side‐effects, and associated long‐term ramifications for sustainability. To address existing knowledge gaps, models that include dynamics and estimated thresholds for regime shifts or ecosystem degradation need to be developed. Policy levers for implementation of ecosystem‐based water resources management include shifting away from growth‐oriented supply management, better demand management, increased public awareness, and institutional reform that promotes adaptive and transdisciplinary management approaches.
- Continuous estimation of baseflow in snowmelt‐dominated streams and
rivers in the Upper Colorado River Basin: A chemical hydrograph separation
- Authors: Matthew P. Miller; David D. Susong, Christopher L. Shope, Victor M. Heilweil, Bernard J. Stolp
Pages: n/a - n/a
Abstract: Effective science‐based management of water resources in large basins requires a qualitative understanding of hydrologic conditions and quantitative measures of the various components of the water budget, including difficult to measure components such as baseflow discharge to streams. Using widely available discharge and continuously collected specific conductance (SC) data, we adapted and applied a long established chemical hydrograph separation approach to quantify daily and representative annual baseflow discharge at fourteen streams and rivers at large spatial (> 1,000 km2 watersheds) and temporal (up to 37 years) scales in the Upper Colorado River Basin. On average, annual baseflow was 21‐58% of annual stream discharge, 13‐45% of discharge during snowmelt, and 40‐86% of discharge during low‐flow conditions. Results suggest that reservoirs may act to store baseflow discharged to the stream during snowmelt and release that baseflow during low‐flow conditions, and that irrigation return flows may contribute to increases in fall baseflow in heavily irrigated watersheds. The chemical hydrograph separation approach, and associated conceptual model defined here provide a basis for the identification of land use, management, and climate effects on baseflow.
- Reply to comment by S. Iden and W. Durner on “Simple consistent
models for water retention and hydraulic conductivity in the complete
- Authors: A. Peters
Pages: n/a - n/a
- Comment to “Simple consistent models for water retention and
- Authors: Sascha C. Iden; Wolfgang Durner
Pages: n/a - n/a
- One‐dimensional soil temperature simulation with Common Land Model
by assimilating in situ observations and MODIS LST with the ensemble
- Authors: Zhongbo Yu; Xiaolei Fu, Lifeng Luo, Haishen Lü, Qin Ju, Di Liu, Dresden A. Kalin, Dui Huang, Chuanguo Yang, Lili Zhao
Pages: n/a - n/a
Abstract: Soil temperature plays an important role in hydrology, agriculture, and meteorology. In order to improve the accuracy of soil temperature simulation, a soil temperature data assimilation system was developed based on the Ensemble Particle Filter (EnPF) and the Common Land Model (CLM), and then applied in the Walnut Gulch Experimental Watershed (WGEW) in Arizona, United States. Surface soil temperature in situ observations and Moderate Resolution Imaging Spectroradiometer Land Surface Temperature (MODIS LST) data were assimilated into the system. In this study, four different assimilation experiments were conducted: 1) assimilating in situ observations of instantaneous surface soil temperature each hour, 2) assimilating in situ observations of instantaneous surface soil temperature once per day, 3) assimilating verified MODIS LST once per day, and 4) assimilating original MODIS LST once per day. These four experiments reflect a transition from high quality and more frequent in situ observations to lower quality and less frequent remote sensing data in the data assimilation system. The results from these four experiments show that the assimilated results are better than the simulated results without assimilation at all layers except the bottom layer, while the superiority gradually diminishes as the quality and frequency of the observations decrease. This demonstrates that remote sensing data can be assimilated using the ensemble particle filter in poorly gauged catchments to obtain highly accurate soil variables (e.g., soil moisture, soil temperature). Meanwhile, the results also demonstrate that the ensemble particle filter is effective in assimilating soil temperature observations to improve simulations, but the performance of the data assimilation method is affected by the frequency of assimilation and the quality of the input data.
- The benefits of using remotely sensed soil moisture in parameter
identification of large‐scale hydrological models
- Authors: N. Wanders; M.P.F. Bierkens, S.M. de Jong, A. de Roo, D. Karssenberg
Pages: n/a - n/a
Abstract: Large‐scale hydrological models are nowadays mostly calibrated using observed discharge. As a result, a large part of the hydrological system, in particular the unsaturated zone, remains uncalibrated. Soil moisture observations from satellites have the potential to fill this gap. Here we evaluate the added value of remotely sensed soil moisture in calibration of large‐scale hydrological models by addressing two research questions: 1) Which parameters of hydrological models can be identified by calibration with remotely sensed soil moisture? 2) Does calibration with remotely sensed soil moisture lead to an improved calibration of hydrological models compared to calibration based only on discharge observations, such that this leads to improved simulations of soil moisture content and discharge? A dual state and parameter ensemble Kalman filter is used to calibrate the hydrological model LISFLOOD for the Upper Danube. Calibration is done using discharge and remotely sensed soil moisture acquired by AMSR‐E, SMOS and ASCAT.
Calibration with discharge data improves the estimation of groundwater and routing parameters. Calibration with only remotely sensed soil moisture results in an accurate identification of parameters related to land surface processes. For the Upper Danube upstream area up to 40000 km2, calibration on both discharge and soil moisture results in a reduction by 10‐30% in the RMSE for discharge simulations, compared to calibration on discharge alone.
The conclusion is that remotely sensed soil moisture holds potential for calibration of hydrological models, leading to a better simulation of soil moisture content throughout the catchment and a better simulation of discharge in upstream areas.
- Hydrologic routing using nonlinear cascaded reservoirs
- Authors: Dong Ha Kim; Aris P. Georgakakos
Pages: n/a - n/a
Abstract: A key element of hydrologic routing models is the discharge‐storage relationship assumed to follow a certain mathematical form, usually a linear or a power function, with parameters calibrated based on existing inflow‐outflow data. This assumption simplifies the model calibration process, but it also constrains the models to operate by the same function throughout the flow range and is prone to introducing errors. We present a new nonlinear hydrologic river routing approach that only requires that functions are non‐decreasing. River reaches are modeled as conceptual reservoir cascades, with discharge‐storage and loss/gain functions identified by the data. A novel parameter estimation approach is developed to identify these functions and other model parameters within a dynamical optimization framework. It is shown that these functions indeed exhibit different mathematical forms at different regions of their active range and that the new approach is reliable, efficient, and robust under observational uncertainty. The model is demonstrated in lake and river routing applications for the Nile River, but it is also applicable for the estimation of nonlinear, non‐decreasing functional relationships for general dynamic systems in state‐space form.
- Flood forecasting for the Mekong with data‐based models
- Authors: Khurram M. Shahzad; Erich J. Plate
Pages: n/a - n/a
Abstract: In many regions of the world the task of flood forecasting is made difficult because only a limited data base is available for generating a suitable forecast model. This paper demonstrates that in such cases parsimonious data based hydrological models for flood forecasting can be developed if the special conditions of climate and topography are used to advantage. As an example the middle reach of River Mekong in South East Asia is considered, where a data base of discharges from 7 gaging stations on the river and 31 rainfall stations on the sub‐catchments between gaging stations is available for model calibration. Special conditions existing for River Mekong are identified and used in developing first a network connecting all discharge gages, and then models for forecasting discharge increments between gaging stations. Our final forecast model (Model 3) is a linear combination of two structurally different basic models: a model (Model 1) using linear regressions for forecasting discharge increments, and a model (Model 2) using rainfall – runoff models. Although the model based on linear regressions works reasonably well for short times, better results are obtained with rainfall runoff modeling. However, forecast accuracy of model 2 is limited by the quality of rainfall forecasts. For best results both models are combined by taking weighted averages to form Model 3. Model quality is assessed by means of both persistence index PI and standard deviation of forecast error.
- Mapping variability of soil water content and flux across 1–1000 m
scales using the actively heated fiber optic method
- Authors: Chadi Sayde; Javier Benitez Buelga, Leonor Rodriguez‐Sinobas, Laureine El Khoury, Marshall English, Nick van de Giesen, John S. Selker
Pages: n/a - n/a
Abstract: The Actively Heated Fiber Optic (AHFO) method is shown to be capable of measuring soil water content several times per hour at 0.25 m spacing along cables of multiple kilometers in length. AHFO is based on distributed temperature sensing (DTS) observation of the heating and cooling of a buried fiber optic cable resulting from an electrical impulse of energy delivered from the steel cable jacket. The results presented were collected from 750 m of cable buried in three 240 m co‐located transects at 30, 60, and 90 cm depths in an agricultural field under center pivot irrigation. The calibration curve relating soil water content to the thermal response of the soil to a heat pulse of 10 W m‐1 for 1 minute duration was developed in the lab. This calibration was found applicable to the 30 and 60 cm depths cables, while the 90 cm depth cable illustrated the challenges presented by soil heterogeneity for this technique. This method was used to map with high resolution the variability of soil water content and fluxes induced by the non‐uniformity of water application at the surface.
- Assessing the impacts of reservoir operation to floodplain inundation by
combining hydrological, reservoir management, and hydrodynamic models
- Authors: Cherry May Mateo; Naota Hanasaki, Daisuke Komori, Kenji Tanaka, Masashi Kiguchi, Adisorn Champathong, Thada Sukhapunnaphan, Dai Yamazaki, Taikan Oki
Pages: n/a - n/a
Abstract: A catastrophic flood event which caused massive economic losses occurred in Thailand, in 2011. Several studies have already been conducted to analyze the Thai floods but none of them have assessed the impacts of reservoir operation on flood inundation. This study addresses this gap by combining physically‐based hydrological models to explicitly simulate the impacts of reservoir operation on flooding in the Chao Phraya River Basin, Thailand. H08, an integrated water resources model with a reservoir operation module, was combined with CaMa‐Flood, a river routing model for the representation of flood dynamics. The combined H08‐CaMa model was applied to simulate and assess the historical and alternative reservoir operation rules in the two largest reservoirs in the basin. The combined H08‐CaMa model effectively simulated the 2011 flood: regulated flows at a major gauging station have high daily NSE‐coefficient of 92% as compared with observed discharge; spatiotemporal extent of simulated flood inundation match well with those of satellite observations. Simulation results show that through the operation of reservoirs in 2011, flood volume was reduced by 8.6 billion m3 and both flood depth and flood area were reduced by 40% on the average. Nonetheless, simple modifications in reservoir operation proved to further reduce the flood volume by 2.4 million m3 and the flood depth and flood area by 20% on the average. A more realistic simulation of the 2011 Thai flood was made possible by modeling reservoir operation with a hydrodynamic model; the possibility of reducing flood inundation through improved reservoir management was quantified.
- Capillary pinning and blunting of immiscible gravity currents in porous
- Authors: Benzhong Zhao; Christopher W. MacMinn, Herbert E. Huppert, Ruben Juanes
Pages: n/a - n/a
Abstract: Gravity‐driven flows in the subsurface have attracted recent interest in the context of geological carbon dioxide (CO2) storage, where supercritical CO2 is captured from the flue gas of power plants and injected underground into deep saline aquifers. After injection, the CO2 will spread and migrate as a buoyant gravity current relative to the denser, ambient brine. Although the CO2 and the brine are immiscible, the impact of capillarity on CO2 spreading and migration is poorly understood. We previously studied the early‐time evolution of an immiscible gravity current, showing that capillary pressure hysteresis pins a portion of the macroscopic fluid‐fluid interface and that this can eventually stop the flow. Here, we study the full lifetime of such a gravity current. Using table‐top experiments in packings of glass beads, we show that the horizontal extent of the pinned region grows with time, and that this is ultimately responsible for limiting the migration of the current to a finite distance. We also find that capillarity blunts the leading edge of the current, which contributes to further limiting the migration distance. Using experiments in etched micromodels, we show that the thickness of the blunted nose is controlled by the distribution of pore‐throat sizes and the strength of capillarity relative to buoyancy. We develop a theoretical model that captures the evolution of immiscible gravity currents and predicts the maximum migration distance. By applying this model to representative aquifers, we show that capillary pinning and blunting can exert an important control on gravity currents in the context of geological CO2 storage.
- Calibration of seawater intrusion models: Inverse parameter estimation
using surface electrical resistivity tomography and borehole data
- Authors: J. Beaujean; F. Nguyen, A. Kemna, A. Antonsson, P. Engesgaard
Pages: n/a - n/a
Abstract: Electrical resistivity tomography (ERT) can be used to constrain seawater intrusion models because of its high sensitivity to total dissolved solid contents (TDS) in groundwater and its relatively high lateral coverage. However, the spatial variability of resolution in electrical imaging may prevent the correct recovery of the desired hydrochemical properties such as salt mass fraction. This paper presents a sequential approach to evaluate the feasibility of identifying hydraulic conductivity and dispersivity in density‐dependent flow and transport models from surface ERT‐derived mass fraction. In the course of this study geophysical inversion was performed by using a smoothness constraint Tikhonov approach, whereas the hydrological inversion was performed using a gradient‐based Levenberg‐Marquardt algorithm. Two synthetic benchmarks were tested. They represent a pumping experiment in a homogeneous and heterogeneous coastal aquifer, respectively. These simulations demonstrated that only the lower salt mass fraction of the seawater‐freshwater transition zone can be recovered for different times. This ability has here been quantified in terms of cumulative sensitivity and our study has further demonstrated that the mismatch between the targeted and the recovered salt mass fraction occurs from a certain threshold. We were additionally able to explore the capability of sensitivity‐filtered ERT images using ground surface data only to recover (in both synthetic cases) the hydraulic conductivity while the dispersivity is more difficult to estimate. We attribute the latter mainly to the lack of ERT‐derived data at depth (where resolution is poorer) as well as to the smoothing effect of the ERT inversion.
- Risk‐based water resources planning: Incorporating probabilistic
nonstationary climate uncertainties
- Authors: Edoardo Borgomeo; Jim W. Hall, Fai Fung, Glenn Watts, Keith Colquhoun, Chris Lambert
Pages: n/a - n/a
Abstract: We present a risk‐based approach for incorporating non‐stationary probabilistic climate projections into long‐term water resources planning. The proposed methodology uses non‐stationary synthetic time series of future climates obtained via a stochastic weather generator based on the UK Climate Projections (UKCP09) to construct a probability distribution of the frequency of water shortages in the future. The UKCP09 projections extend well beyond the range of current hydrological variability, providing the basis for testing the robustness of water resources management plans to future climate‐related uncertainties. The non‐stationary nature of the projections combined with the stochastic simulation approach allows for extensive sampling of climatic variability conditioned upon climate model outputs. The probability of exceeding planned frequencies of water shortages of varying severity (defined as Levels of Service for the water supply utility company) is used as a risk metric for water resources planning. Different sources of uncertainty, including demand‐side uncertainties, are considered simultaneously and their impact on the risk metric is evaluated. Supply‐side and demand‐side management strategies can be compared based on how cost‐effective they are at reducing risks to acceptable levels. A case study based on a water supply system in London (UK) is presented to illustrate the methodology. Results indicate an increase in the probability of exceeding the planned Levels of Service across the planning horizon. Under a 1% per annum population growth scenario, the probability of exceeding the planned Levels of Service is as high as 0.5 by 2040. The case study also illustrates how a combination of supply and demand management options may be required to reduce the risk of water shortages.
- Water banking, conjunctive administration, and drought: The interaction of
water markets and prior appropriation in southeastern Idaho
- Authors: Sanchari Ghosh; Kelly M. Cobourn, Levan Elbakidze
Pages: n/a - n/a
Abstract: Despite recognition of the potential economic benefits and increasing interest in developing marketing instruments, water markets have remained thin and slow to evolve due to high transactions costs, third‐party effects, and the persistence of historical institutions for water allocation. Water banks are a marketing instrument that can address these obstacles to trade, allowing irrigators within a region to exchange water in order to mitigate the short‐term effects of drought. Water banks coexist with the institutions governing water allocation, which implies that rule changes, such as adoption of a system of conjunctive surface water‐groundwater administration, carry implications for the economic impacts of banking. This paper assesses and compares the welfare and distributional outcomes for irrigators in the Eastern Snake River Plain of Idaho under a suite of water management and drought scenarios. We find that water banking can offset irrigators’ profit losses during drought, but that its ability to do so depends on whether it facilitates trade across groundwater and surface water users. With conjunctive administration, a bank allowing trade by source realizes 22.23 percent of the maximum potential efficiency gains from trade during a severe drought, while a bank that allows trade across sources realizes 93.47 percent of the maximum potential gains. During drought, conjunctive administration redistributes welfare from groundwater to surface water producers, but banking across sources allows groundwater irrigators to recover 88.4 percent of the profits lost from drought at a cost of 2.2 percent of the profit earned by surface water irrigators.
- A semianalytical solution for the Boussinesq equation with nonhomogeneous
constant boundary conditions
- Authors: Nelson L. Dias; Tomás L. Chor, Ailín Ruiz de Zárate
Pages: n/a - n/a
Abstract: The Boussinesq groundwater equation is widely used in hydrology to predict streamflow from an unconfined aquifer and derive the aquifer’s saturated hydraulic conductivity and drainable porosity, and to predict water table height in drainage engineering. In this work, we solve this equation in an unconfined horizontal aquifer for non‐homogeneous boundary conditions for the water table height. The solution is found in the form of a Taylor series that has a finite radius of convergence which is different for each initial condition. We also present an expression for the flux boundary condition at the origin as a function of the depth of the adjoining stream that automatically satisfies the boundary condition at infinity, and thus eliminates the need for a trial and error approach for the solution, which is accurate to 10‐7. In order to obtain an approximation for the water table height in the region where the series solution diverges, first we computed a diagonal Padé approximation from the series coefficients, which converges in a larger interval than the series, and then we matched it with a new asymptotic approximation for large values of the independent variable. We found that the proposed matched solution is better suited to cases where the water head at the origin is close to the initial water head in the aquifer.
- Climate change, water rights, and water supply: The case of irrigated
agriculture in Idaho
- Authors: Wenchao Xu; Scott E. Lowe, Richard M. Adams
Pages: n/a - n/a
Abstract: We conduct a hedonic analysis to estimate the response of agricultural land use to water supply information under the Prior Appropriation Doctrine by using Idaho as a case study. Our analysis includes long‐term weather trends and water supply conditions as well as seasonal water supply forecasts. A farm‐level panel data set, which accounts for the priority effects of water rights and controls for diversified crop mixes and rotation practices, is used. Our results indicate that farmers respond to long‐term surface and ground water conditions as well as to the seasonal water supply variation. Climate change‐induced variations in weather and water supply conditions could lead to substantial damages to irrigated agriculture. We project substantial losses (up to 32%) of the average crop revenue for major agricultural areas under future climate scenarios in Idaho. Finally, farmers demonstrate significantly varied responses given their water rights priorities, which implies that the distributional impact of climate change is sensitive to institutions such as the Prior Appropriation Doctrine.
- A vertically integrated model with vertical dynamics for CO2 storage
- Authors: Bo Guo; Karl W. Bandilla, Florian Doster, Eirik Keilegavlen, Michael A. Celia
Pages: 6269 - 6284
Abstract: Conventional vertically integrated models for CO2 storage usually adopt a vertical equilibrium (VE) assumption, which states that due to strong buoyancy, CO2 and brine segregate quickly, so that the fluids can be assumed to have essentially hydrostatic pressure distributions in the vertical direction. However, the VE assumption is inappropriate when the time scale of fluid segregation is not small relative to the simulation time. By casting the vertically integrated equations into a multiscale framework, a new vertically integrated model can be developed that relaxes the VE assumption, thereby allowing vertical dynamics to be modeled explicitly. The model maintains much of the computational efficiency of vertical integration while allowing a much wider range of problems to be modeled. Numerical tests of the new model, using injection scenarios with typical parameter sets, show excellent behavior of the new approach for homogeneous geologic formations.
- Including adaptation and mitigation responses to climate change in a
multiobjective evolutionary algorithm framework for urban water supply
systems incorporating GHG emissions
- Authors: F. L. Paton; H. R. Maier, G. C. Dandy
Pages: 6285 - 6304
Abstract: Cities around the world are increasingly involved in climate action and mitigating greenhouse gas (GHG) emissions. However, in the context of responding to climate pressures in the water sector, very few studies have investigated the impacts of changing water use on GHG emissions, even though water resource adaptation often requires greater energy use. Consequently, reducing GHG emissions, and thus focusing on both mitigation and adaptation responses to climate change in planning and managing urban water supply systems, is necessary. Furthermore, the minimization of GHG emissions is likely to conflict with other objectives. Thus, applying a multiobjective evolutionary algorithm (MOEA), which can evolve an approximation of entire trade‐off (Pareto) fronts of multiple objectives in a single run, would be beneficial. Consequently, the main aim of this paper is to incorporate GHG emissions into a MOEA framework to take into consideration both adaptation and mitigation responses to climate change for a city's water supply system. The approach is applied to a case study based on Adelaide's southern water supply system to demonstrate the framework's practical management implications. Results indicate that trade‐offs exist between GHG emissions and risk‐based performance, as well as GHG emissions and economic cost. Solutions containing rainwater tanks are expensive, while GHG emissions greatly increase with increased desalinated water supply. Consequently, while desalination plants may be good adaptation options to climate change due to their climate‐independence, rainwater may be a better mitigation response, albeit more expensive.
- Characterization of flow parameters and evidence of pore clogging during
limestone dissolution experiments
- Authors: L. Luquot; T. S. Roetting, J. Carrera
Pages: 6305 - 6321
Abstract: Rock dissolution induces changes in texture (porosity, pore‐size distribution, or tortuosity) which modify multiphase flow and transport properties (permeability, diffusion coefficient, retention curve). Limestone dissolution will occur during CO2 storage or acid injection for well stimulation. Therefore, characterizing those changes is essential for understanding flow and transport during and after the CO2 injection because they can affect the storage capacity, injectivity, and trapping mechanisms. Yet, few published studies evaluate the changes of hydrodynamic properties due to fluid‐rock interactions. We report seven dissolution experiments performed on four limestone samples by injecting water with pH ranging from 3.5 to 5.0. Sample porosity, diffusion coefficient, and pore‐size distribution were measured before and after each rock attack, which was repeated twice on three of the samples. Permeability was monitored continuously and chemical samples were taken to evaluate calcite dissolution. We find that overall porosity increases over time as expected. But the increase is nonuniform along the sample. At the samples inlets, large pores increase significantly while small pores remain unchanged, which is consistent with wormhole initiation. However, the size of largest pores is reduced at the outlet, which we attribute to clogging by particles dragged from the inlet. As a result, the overall permeability is reduced. Particle dragging is unlikely during supercritical CO2 storage because head gradients are small, but may be expected in the case of dissolved CO2 injection or during well stimulation by acid injection. Our results imply that dissolution is highly localized, which will result in a significant increase in capillary trapping.
- Impact of numerical artifact of the forward model in the inverse solution
of density‐dependent flow problem
- Authors: Mohamed K. Nassar; Timothy R. Ginn
Pages: 6322 - 6338
Abstract: We investigate the effect of computational error on the inversion of a density‐dependent flow and transport model, using SEAWAT and UCODE‐2005 in an inverse identification of hydraulic conductivity and dispersivity using head and concentration data from a 2‐D laboratory experiment. We investigated inversions using three different solution schemes including variation of number of particles and time step length, in terms of the three aspects: the shape and smoothness of the objective function surface, the consequent impacts to the optimization, and the resulting Pareto analyses. This study demonstrates that the inversion is very sensitive to the choice of the forward model solution scheme. In particular, standard finite difference methods provide the smoothest objective function surface; however, this is obtained at the cost of numerical artifacts that can lead to erroneous warping of the objective function surface. Total variation diminishing (TVD) schemes limit these impacts at the cost of more computation time, while the hybrid method of characteristics (HMOC) approach with increased particle numbers and/or reduced time step gives both smoothed and accurate objective function surface. Use of the most accurate methods (TVD and HMOC) did lead to successful inversion of the two parameters; however, with distinct results for Pareto analyses. These results illuminate the sensitivity of the inversion to a number of aspects of the forward solution of the density‐driven flow problem and reveal that parameter values may result that are erroneous but that counteract numerical errors in the solution.
- Extrapolating active layer thickness measurements across Arctic polygonal
terrain using LiDAR and NDVI data sets
- Authors: Chandana Gangodagamage; Joel C. Rowland, Susan S. Hubbard, Steven P. Brumby, Anna K. Liljedahl, Haruko Wainwright, Cathy J. Wilson, Garrett L. Altmann, Baptiste Dafflon, John Peterson, Craig Ulrich, Craig E. Tweedie, Stan D. Wullschleger
Pages: 6339 - 6357
Abstract: Landscape attributes that vary with microtopography, such as active layer thickness (ALT), are labor intensive and difficult to document effectively through in situ methods at kilometer spatial extents, thus rendering remotely sensed methods desirable. Spatially explicit estimates of ALT can provide critically needed data for parameterization, initialization, and evaluation of Arctic terrestrial models. In this work, we demonstrate a new approach using high‐resolution remotely sensed data for estimating centimeter‐scale ALT in a 5 km2 area of ice‐wedge polygon terrain in Barrow, Alaska. We use a simple regression‐based, machine learning data‐fusion algorithm that uses topographic and spectral metrics derived from multisensor data (LiDAR and WorldView‐2) to estimate ALT (2 m spatial resolution) across the study area. Comparison of the ALT estimates with ground‐based measurements, indicates the accuracy (r2 = 0.76, RMSE ±4.4 cm) of the approach. While it is generally accepted that broad climatic variability associated with increasing air temperature will govern the regional averages of ALT, consistent with prior studies, our findings using high‐resolution LiDAR and WorldView‐2 data, show that smaller‐scale variability in ALT is controlled by local eco‐hydro‐geomorphic factors. This work demonstrates a path forward for mapping ALT at high spatial resolution and across sufficiently large regions for improved understanding and predictions of coupled dynamics among permafrost, hydrology, and land‐surface processes from readily available remote sensing data.
- Single‐parameter model of vegetated aquatic flows
- Authors: Ilenia Battiato; Simonetta Rubol
Pages: 6358 - 6369
Abstract: Coupled flows through and over permeable layers occur in a variety of natural phenomena including turbulent flows over submerged vegetation. In this work, we employ a two‐domain approach to model flow through and over submerged canopies. The model, amenable of a closed‐form solution, couples the log‐law and the Darcy‐Brinkman equation, and is characterized by a novel representation of the drag force which does not rely on a parametrization through an unknown drag coefficient. This approach limits to one, i.e., the obstruction permeability, the number of free parameters. Analytical expressions for the average velocity profile through and above the canopies, volumetric flow rate, penetration length, and canopy shear layer parameter are obtained in terms of the canopy layer effective permeability. The model suggests that appropriately rescaled velocities in the canopy and surface layers follow two different scaling laws. The analytical predictions match with the experimental data collected by Ghisalberti and Nepf (2004) and Nepf et al. (2007).
- Modeling irrigation behavior in groundwater systems
- Authors: Timothy Foster; Nicholas Brozović, Adrian P. Butler
Pages: 6370 - 6389
Abstract: Integrated hydro‐economic models have been widely applied to water management problems in regions of intensive groundwater‐fed irrigation. However, policy interpretations may be limited as most existing models do not explicitly consider two important aspects of observed irrigation decision making, namely the limits on instantaneous irrigation rates imposed by well yield and the intraseasonal structure of irrigation planning. We develop a new modeling approach for determining irrigation demand that is based on observed farmer behavior and captures the impacts on production and water use of both well yield and climate. Through a case study of irrigated corn production in the Texas High Plains region of the United States we predict optimal irrigation strategies under variable levels of groundwater supply, and assess the limits of existing models for predicting land and groundwater use decisions by farmers. Our results show that irrigation behavior exhibits complex nonlinear responses to changes in groundwater availability. Declining well yields induce large reductions in the optimal size of irrigated area and irrigation use as constraints on instantaneous application rates limit the ability to maintain sufficient soil moisture to avoid negative impacts on crop yield. We demonstrate that this important behavioral response to limited groundwater availability is not captured by existing modeling approaches, which therefore may be unreliable predictors of irrigation demand, agricultural profitability, and resilience to climate change and aquifer depletion.
- Behavioral response to contamination risk information in a spatially
explicit groundwater environment: Experimental evidence
- Authors: Jingyuan Li; Holly A. Michael, Joshua M. Duke, Kent D. Messer, Jordan F. Suter
Pages: 6390 - 6405
Abstract: This paper assesses the effectiveness of aquifer monitoring information in achieving more sustainable use of a groundwater resource in the absence of management policy. Groundwater user behavior in the face of an irreversible contamination threat is studied by applying methods of experimental economics to scenarios that combine a physics‐based, spatially explicit, numerical groundwater model with different representations of information about an aquifer and its risk of contamination. The results suggest that the threat of catastrophic contamination affects pumping decisions: pumping is significantly reduced in experiments where contamination is possible compared to those where pumping cost is the only factor discouraging groundwater use. The level of information about the state of the aquifer also affects extraction behavior. Pumping rates differ when information that synthesizes data on aquifer conditions (a “risk gauge”) is provided, despite invariant underlying economic incentives, and this result does not depend on whether the risk information is location‐specific or from a whole aquifer perspective. Interestingly, users increase pumping when the risk gauge signals good aquifer status compared to a no‐gauge treatment. When the gauge suggests impending contamination, however, pumping declines significantly, resulting in a lower probability of contamination. The study suggests that providing relatively simple aquifer condition guidance derived from monitoring data can lead to more sustainable use of groundwater resources.
- Inference of reactive transport model parameters using a Bayesian
- Authors: Luca Carniato; Gerrit Schoups, Nick van de Giesen
Pages: 6406 - 6427
Abstract: Parameter estimation of subsurface transport models from multispecies data requires the definition of an objective function that includes different types of measurements. Common approaches are weighted least squares (WLS), where weights are specified a priori for each measurement, and weighted least squares with weight estimation (WLS(we)) where weights are estimated from the data together with the parameters. In this study, we formulate the parameter estimation task as a multivariate Bayesian inference problem. The WLS and WLS(we) methods are special cases in this framework, corresponding to specific prior assumptions about the residual covariance matrix. The Bayesian perspective allows for generalizations to cases where residual correlation is important and for efficient inference by analytically integrating out the variances (weights) and selected covariances from the joint posterior. Specifically, the WLS and WLS(we) methods are compared to a multivariate (MV) approach that accounts for specific residual correlations without the need for explicit estimation of the error parameters. When applied to inference of reactive transport model parameters from column‐scale data on dissolved species concentrations, the following results were obtained: (1) accounting for residual correlation between species provides more accurate parameter estimation for high residual correlation levels whereas its influence for predictive uncertainty is negligible, (2) integrating out the (co)variances leads to an efficient estimation of the full joint posterior with a reduced computational effort compared to the WLS(we) method, and (3) in the presence of model structural errors, none of the methods is able to identify the correct parameter values.
- Assessing the impacts of fiscal reforms on investment in
village‐level irrigation infrastructure
- Authors: Christine E. Boyle; Qiuqiong Huang, Jinxia Wang
Pages: 6428 - 6446
Abstract: This paper investigates investment trends into village‐level irrigation projects and assesses the impact of fiscal reforms including the tax‐for‐fee reform and the elimination of agricultural tax on irrigation investment. The China Water Institutions and Management Panel Survey data show that village leaders, water user associations, farmers, and upper level governments have all contributed to irrigation investment in villages throughout the study period between 1996 and 2007. Both descriptive and multivariate analyses suggest that changes brought by fiscal reforms have significantly reduced village collectives' capacity to fund irrigation infrastructure in villages. There was a significant drop in upper level government investment during the posttax‐for‐fee period (2002–2004 in the sample areas). Since 2005, upper level government has increased its investment to prereform levels and partly filled the public investment void in irrigation infrastructure. Fiscal reforms had the least impact on farmers' investment, which has been the most stable source of funding for village‐level irrigation projects.