- Modeling water demand when households have multiple sources of water
- Authors: Lassina Coulibaly; Paul M. Jakus, John E. Keith
Pages: n/a - n/a
Abstract: A significant portion of the world's population lives in areas where public water delivery systems are unreliable and/or deliver poor quality water. In response, people have developed important alternatives to publicly supplied water. To date, most water demand research has been based on single-equation models for a single source of water, with very few studies that have examined water demand from two sources of water (where all non-public system water sources have been aggregated into a single demand). This modeling approach leads to two outcomes. First, the demand models do not capture the full range of alternatives so the true economic relationship amongst the alternatives is obscured. Second, and more seriously, economic theory predicts that demand for a good becomes more price-elastic as the number of close substitutes increases. If researchers artificially limit the number of alternatives studied to something less than the true number, the price elasticity estimate may be biased downward. This paper examines water demand in a region with near universal access to piped water, but where system reliability and quality is such that many alternative sources of water exist. In extending the demand analysis to four sources of water we are able to (i) demonstrate why households choose the water sources they do, (ii) provide a richer description of the demand relationships among sources, and (iii) calculate own-price elasticity estimates that are more elastic than those generally found in the literature.
- Patterns of similarity of seasonal water balances: A window into
streamflow variability over a range of time scales
- Authors: Wouter R. Berghuijs; Murugesu Sivapalan, Ross A. Woods, Hubert H. G. Savenije
Pages: n/a - n/a
Abstract: Recent hydrologic synthesis efforts have presented evidence that the seasonal water balance is at the core of overall catchment responses, and understanding it will assist in predicting signatures of streamflow variability at other timescales, including inter-annual variability, the flow duration curve, low flows, and floods. In this study we group 321 catchments located across the continental United States into several clusters with similar seasonal water balance behavior. We then delineate the boundaries between these clusters on the basis of a similarity framework based on three hydro-climatic indices that represent aridity, precipitation timing, and snowiness. The clustering of catchments based on the seasonal water balance has a strong relationship not only with regional patterns of the three climate indices but also with regional ecosystem, soil and vegetation classes, which point to the strong dependence of these physiographic characteristics on seasonal climate variations and the hydrologic regimes. Building on these catchment clusters, we demonstrate that the seasonal water balance does have an imprint on signatures of streamflow variability over a wide range of time scales (daily to decadal) and a wide range of states (low-flows to floods). The seasonal water balance is well integrated into variability at seasonal and longer timescales, but is only partly reflected in the signatures at shorter timescales, including flooding responses. Overall, the seasonal water balance has proven to be a similarity measure that serves as a link between both short-term hydrologic responses and long-term adaptation of the landscape with climate.
- A multimodel regression-sampling algorithm for generating rich monthly
- Authors: Chao Li; Vijay P. Singh
Pages: n/a - n/a
Abstract: This paper presents a multi-model regression-sampling algorithm (MRS) for monthly streamflow simulation. MRS is motivated from the acknowledgment that typical nonparametric models tend to simulate sequences exhibiting too close a resemblance to historical records and parametric models have limitations in capturing complex distributional and dependence characteristics, such as multimodality and nonlinear autocorrelation. The aim of MRS is to generate streamflow sequences with rich scenarios, while properly capturing complex distributional and dependence characteristics. The basic assumptions of MRS include: 1) streamflow of a given month depends on a feature vector consisting of streamflow of the previous month and the dynamic aggregated flow of the past 12 months; and 2) streamflow can be multiplicatively decomposed into a deterministic expectation term and a random residual term. Given a current feature vector, MRS first relates the conditional expectation to the feature vector through an ensemble average of multiple regression models (a total number of 7). To infer the conditional distribution of the residual, MRS adopts the k-nearest neighbor concept. More precisely, the conditional distribution is estimated by a gamma kernel smoothed density of historical residuals inside the k-neighborhood of the given feature vector. Rather than obtaining the residuals from the averaged model only, MRS retains all residuals from all the original regression models. In other words, MRS perceives that the original residuals put together would better represent the covariance structure between streamflow and the feature vector. By doing so, the benefit is that a kernel smoothed density of the residual with reliable accuracy can be estimated, which is hardly possible in a single-model framework. It is the smoothed density that ensures the generation of sequences with rich scenarios unseen in historical record. We evaluated MRS at selected stream gauges and compared with several existing models. Results show that: 1) compared with typical nonparametric models, MRS is more apt at generating sequences with richer scenarios; and 2) in contrast to parametric models, MRS can reproduce complex distributional and dependence characteristics. Since MRS is flexible at incorporating different covariates, it can be tailored for other potential applications, such as hydrologic forecasting, downscaling, as well as post-processing deterministic forecasts into probabilistic ones.
- Electrical-hydraulic relationships observed for unconsolidated sediments
in the presence of a cobble framework
- Authors: Lee Slater; Warren Barrash, Jeanette Montrey, Andrew Binley
Pages: n/a - n/a
Abstract: Mechanistic models now exist to predict hydraulic conductivity (K) from the spectral induced polarization (SIP) response of granular media. We examined the predictions of such a model on unconsolidated coarse fluvial sediments and compared them to those obtained with a modified Kozeny Carman (KC) model. Samples were retrieved from the Boise Hydrogeophysical Research Site (BHRS), located on a gravel bar adjacent to the Boise River, Idaho. A sample holder (0.102 m diameter and 0.12 m in length) was designed to include the cobble framework in reconstituted samples representing the primary stratigraphic units defined based on porosity variation at this site. SIP (0.001-1000 Hz) and K (from Darcy tests) measurements were recorded for twelve samples, with SIP measurements made as a function of pore fluid conductivity (3-300 mS/m), grain size distribution (GSD) and total porosity. K prediction with the KC model was improved after discounting of the cobble framework and multiplying by the tortuosity resulting from matrix “capillaries” around the cobbles, resulting in estimates within a factor of 5 of the measurements. K prediction with a mechanistic SIP model based on Stern layer polarization (SLP model) that requires an estimate of the GSD also required discounting for the cobble framework to obtain estimates within 0.5 orders of magnitude of the measurements. Similarly, the SLP model over predicts the measured imaginary conductivity (σ˝) unless the cobble framework is discounted, which then results in estimates of σ˝ within a factor of 2 of the measurements. This can be explained by the fact that the cobbles polarize at frequencies well below the minimum measurement frequency (0.001 Hz). The SLP model for K prediction parameterized in terms of the formation factor and imaginary conductivity performed well for the ten samples with a cobble framework without modification as the imaginary conductivity directly senses the matrix grain size characteristics, whereas the formation factor captures the porosity reduction and tortuosity resulting from the presence of the cobble framework (capillary tortuosity). Our findings suggest that the estimation of contrasts in K in coarse sediments may be achievable through measurements of electrical properties after appropriate consideration of the cobble fraction.
- Rescuing degrading aquifers in the Central Coastal Plain of North Carolina
(USA): Just process, effective groundwater management policy, and
- Authors: Alex K. Manda; Wendy A. Klein
Pages: n/a - n/a
Abstract: Strategic management of degrading coastal aquifers in eastern North Carolina (USA) became imperative after a severe imbalance occurred between withdrawal and recharge rates. To ameliorate this growing problem, an aggressive water policy was developed through public input by creating the Central Coastal Plain Capacity Use Area (CCPCUA) to maintain beneficial use of groundwater resources. Insights from social psychology, and socio-legal studies are used to evaluate how procedural justice and public participation played major roles to resolving groundwater resource management problems. A mixed methods approach uses archival data and interviews with various rule-making participants to assess the process of stakeholder involvement that led to creation of the policy. In addition, data analysis techniques are utilized to evaluate the effects of the policy on aquifer health (through water levels) over a ~10-year period. Results suggest that not only did a stakeholder group participate in a process that was deemed fair, understandable, and relatively easy to administer for users and regulators, but public participation resulted in an effective plan that ensures the long-term sustainable use of groundwater. Declining groundwater withdrawals and recovering water levels suggest that the rule is achieving its intended goal of protecting the aquifers from depletion and degradation. This paper touches on global themes that are essential to water demand and consumption, water management techniques, and water resources protection.
- A novel method for estimating the onset of thermal stratification in lakes
from surface water measurements
- Authors: R. Iestyn Woolway; Stephen C. Maberly, Ian D. Jones, Heidrun Feuchtmayr
Pages: n/a - n/a
Abstract: High-frequency surface water temperature measurements were analyzed for 17 annual data series from seven lakes to assess whether the onset of thermal stratification can be determined from time series of surface water temperature measurements alone. Current methods for estimating the start of thermal stratification require depth-resolved temperature measurements, whereas many existing high-frequency measurements are often limited only to the lake surface. In this study, we show that the magnitude of the diel surface water temperature range can be used to estimate the onset of thermal stratification. We assess the accuracy of using the diel range as an estimate of the onset of thermal stratification by applying two methods based on the calculation of (1) the absolute difference in the diel surface temperature range and (2) the magnitude of the diel range from wavelet analysis. Our study shows that the onset of thermal stratification can be accurately estimated by wavelet analysis with a root mean square error of 2.1 days and by the observed diel temperature range method with a root mean square error of 11.8 days. This approach enables existing, and future, high-resolution surface water data sets to be used to estimate the onset of lake stratification. Furthermore, the continuously increasing observational powers of satellites may eventually result in surface water temperature being measured at a sufficiently high temporal resolution at the spatial scales of small lakes to allow the onset of thermal stratification to be estimated remotely.
- Finite element formulation of unilateral boundary conditions for
unsaturated flow in porous continua
- Authors: A. Abati; C. Callari
Pages: n/a - n/a
Abstract: This paper presents the numerical resolution of unilateral boundary conditions able to effectively model several problems of unsaturated flow, as those involving rainfall infiltration and seepage faces. Besides the penalty technique, we also consider the novel regularization of these conditions by means of the more effective augmented Lagrangian method. The performance of the so-obtained finite element method is carefully investigated in terms of accuracy and ill-conditioning effects, including comparisons with analytical solutions and a complete identification of the analogies with the problem of frictionless contact. In this way, we provide a priori estimates of optimal and admissible ranges for the penalty coefficient as functions of permeability and spatial discretization. The proposed method and the estimated coefficient ranges are validated in further numerical examples, involving the propagation of a wetting front due to rainfall and the partial saturation of an aged concrete dam. These applications show that the proposed regularizations do not induce any detrimental effect on solution accuracy and on convergence rate of the employed Newton-Raphson method. Hence, the present approach should be preferred to the commonly used iterative switching between the imposed-flow and the imposed-pressure conditions, which often leads to spurious oscillations and convergence failures.
- A catalog of moisture sources for continental climatic regions
- Authors: Raquel Nieto; Rodrigo Castillo, Anita Drumond, Luis Gimeno
Pages: n/a - n/a
Abstract: This technical note describes a catalog of moisture sources for two sets of continental climatic regions: one based on regions with similar late 20th century mean climate and similar projected late 21st century precipitation changes, and the other widely used in IPCC assessment reports. By illustrating with one region by classification, the European one was selected and we identify and characterize all the major sources of moisture, and analyze their interannual variability and the role of the three dominant modes of global climate variability, including the El Niño-Southern Oscillation (ENSO) and the Northern and Southern Annular Modes (NAM, SAM). We also estimate the influence of those oceanic regions that will see the greatest increases in evaporation rate in future years.
- Comment on “A blueprint for process-based modeling of uncertain
hydrological systems” by Montanari and Koutsoyiannis
- Authors: Grey Nearing
Pages: n/a - n/a
- Interplay of climate seasonality and soil moisture – Rainfall
- Authors: Jun Yin; Amilcare Porporato, John Albertson
Pages: n/a - n/a
Abstract: The soil moisture-rainfall feedback (SMRF) may significantly impact hydro-climatic dynamics, inducing persistent weather conditions that are responsible for prolonged droughts or abnormally wet states. However, externally driven seasonal variability in rainfall and potential evapotranspiration, with the associated patterns of wet and dry conditions, may both interact with such SMRF. In this study, seasonal variations in radiation and precipitation forcing are included in a stochastic SMRF model with the assumption of a soil moisture-dependent average rainfall frequency to explore their effects on the soil moisture probabilistic structure. The theoretical model results, based on a parameterization using data for soil moisture and climate in Illinois, show that average rainfall frequency peaks in late spring when both the soil condition and the SMRF strength favor convective rainfall triggering. Under such conditions, the soil moisture tends to exhibit bimodal behavior until the SMRF strength becomes weak again towards the end of the growing season. Such behavior is reminiscent of the dynamics of a system undergoing a periodic, stochastically forced pitchfork bifurcation. The presence of bimodal soil moisture behavior is also verified using nonparametric statistical tests on soil moisture data. The analysis of wet-to-wet and dry-to-dry soil moisture transitions in the joint probability distribution of soil moisture further corroborates the presence of hydro-climatic persistence in the spring-to-summer transition.
- Reply to comment by G. Nearing on “A blueprint for process-based
modeling of uncertain hydrological systems”
- Authors: Alberto Montanari; Demetris Koutsoyiannis
Pages: n/a - n/a
- Catchments as simple dynamical systems: A case study on methods and data
requirements for parameter identification
- Authors: L.A. Melsen; A.J. Teuling, S.W. van Berkum, P.J.J.F. Torfs, R. Uijlenhoet
Pages: n/a - n/a
Abstract: In many rainfall-runoff models at least some calibration of model parameters has to take place. Especially for ungauged or poorly gauged basins this can be problematic, because there is little or no data available for calibration. A possible solution to overcome the problems caused by data scarcity is to set up a measurement campaign for a limited time period. In this study we determine the minimum amount of data, required to determine robust parameter values for a simple model with two parameters. The model is constructed such that the parameters can be determined not only with automatic calibration, but also by recession analysis and a priori from Boussinesq theory. The model has been applied to a research catchment in Switzerland. For automatic calibration and recession analysis one season (five months) is found to be sufficient to give robust parameters for simulation of high flows over the full observation period. For automatic calibration, this should be the season with the highest precipitation, for recession analysis the season with least evapotranspiration. The Boussinesq equation is able to give good parameter estimates for modelling high flows, but detailed in situ knowledge of the catchment is required. Automatic calibration outperforms recession analysis and Boussinesq theory by far when it comes to parameter estimation with a focus on prediction of low flows. It was shown that a single set of parameters cannot simultaneously describe high and low flows with a reasonable accuracy, suggesting that more than two parameters are needed to characterize subsurface properties.
- Annual bank and point bar morphodynamics of a meandering river determined
by high-accuracy multitemporal laser scanning and flow data
- Authors: Lotsari E; Vaaja M, Flener C, Kaartinen H, Kukko A, Kasvi E, Hyyppä H, Hyyppä J, Alho P.
Pages: n/a - n/a
Abstract: The knowledge has been insufficient concerning the effects of peak flows, and local bend and flow characteristics on annual morphodynamics of consecutive bends in meandering rivers. Therefore, it was determined how flow peak magnitude and duration affect morphodynamics, how the short-term spatial evolution of a given meander bend associates with the neighboring bends, and how local bend and flow characteristics affect morphodynamics. The annual bank and point bar morphodynamics of eight consecutive bends of a sub-arctic meandering river were analyzed between 2009 and 2012 on the basis of high-accuracy multi-temporal data, measured by mobile and terrestrial laser scanning and an Acoustic Doppler Current Profiler. According to the results, multiple years of highly accurate data are crucial for a broader picture of meandering channel evolution. The results showed for the first time in detail that none of the years were similar in terms of point bar and bank morphodynamics. The duration of point bar submergence and maximum water stage was more important for evolution of the meandering channel than the local effects of each bend. The detailed topographical data of the present study confirmed that the higher the flow and water stage peak the more deposition occurred on point bars. More importantly, the independence of the short-term spatial evolution of meander bends from the association with neighboring bends was confirmed. Erosion patterns did not relate particularly to the sinuosity or radius of curvature. A clear relation between velocity and bend curvature, on which some meander migration models rely, was not found.
- Coping with model error in variational data assimilation using optimal
- Authors: Lipeng Ning; Francesca P. Carli, Ardeshir Mohammad Ebtehaj, Efi Foufoula-Georgiou, Tryphon T. Georgiou
Pages: n/a - n/a
Abstract: Classical variational data assimilation methods address the problem of optimally combining model predictions with observations in the presence of zero-mean Gaussian random errors. However, in many natural systems, uncertainty in model structure and/or model parameters often results in systematic errors or biases. Prior knowledge about such systematic model error for parametric removal is not always feasible in practice, limiting the efficient use of observations for improved prediction. The main contribution of this work is to advocate the relevance of transportation metrics for quantifying non-random model error in variational data assimilation for non-negative natural states and fluxes. Transportation metrics (also known as Wasserstein metrics) originate in the theory of Optimal Mass Transport (OMT) and provide a non-parametric way to compare distributions which is natural in the sense that it penalizes mismatch in the values and relative position of “masses” in the two distributions. We demonstrate the promise of the proposed methodology using 1D and 2D advection-diffusion dynamics with systematic error in the velocity and diffusivity parameters. Moreover, we combine this methodology with additional regularization functionals, such as the ℓ1-norm of the state in a properly chosen domain, to incorporate both model error and potential prior information in the presence of sparsity or sharp fronts in the underlying state of interest.
- A practical formulation of snow surface diffusion by wind for
- Authors: Noriaki Ohara
Pages: n/a - n/a
Abstract: Prediction of snow drift is of importance for structure design and traffic management on snowy and windy prairie landscapes. The snow redistribution by wind is also regarded as one of the largest sources of error in hydrologic snowmelt models. In this study, a snow movement equation was generalized and customized for horizontal two-dimensional watershed-scale applications by incorporating snow transport, wind snow diffusion, and snow gravitational movement. Then, the snow surface diffusion process by wind turbulence was formulated in terms of the autocorrelation functions of the measurable wind velocity field using G.I. Taylor's theorem. However, analysis of the example wind data suggested a delta correlation in wind turbulent component that resulted from subtracting their moving average values from the original wind speed data. The dynamic model based on the proposed formulation was able to effectively reproduce the observed equilibrium snow profiles affected by wind drifting. A two-dimensional model simulation using a 10 m digital elevation model in Muddy Gap, Wyoming was also presented for qualitative validation of the model in the watershed-scale applications. Additionally, the theoretical extension for preferential snow accumulation process was presented in Appendix . These modeling results together with the observations on the prairie suggested the importance of the snow surface diffusion process in addition to the snow transport.
- On the upscaling of chemical transport in fractured rock
- Authors: Vladimir Cvetkovic; Hrvoje Gotovac
Pages: n/a - n/a
Abstract: The impact of flow heterogeneity on chemical transport from single to multiple fractures is investigated. The emphasis is on the dynamic nature of the specific surface area (SSA) due to heterogeneity of the flow, relative to a purely geometrical definition. The flow-dependent SSA is interpreted probabilistically, following inert tracer particles along individual fractures. Upscaling to a fracture network is proposed as a time-domain random walk based on the statistics of SSA for single fractures. Statistics of SSA are investigated for three correlation structures of transmissivity: Multi-Gaussian and two non multi-Gaussian. The mean of SSA stabilises after ca 20 fractures, at different values depending on whether the cubic or quadratic hydraulic law is assumed. The results are tested against comprehensive DFN simulations based on site-specific data but also against direct estimates from a wider range of tracer tests. The proposed time-domain random walk methodology sets bounds for SSA in a 75% confidence interval as ca 1800 1/m and 27000 1/m, with a median of 14000 1/m; these values capture reasonably well both the DFN simulation and tracer test SSA data. Presented results may be particularly relevant when quantifying uncertainty of reactive transport modelling in fractured rock.
- The delivery of dissolved organic carbon from a forested hillslope to a
headwater stream in southeastern Pennsylvania, USA
- Authors: Yi Mei; George M. Hornberger, Louis A. Kaplan, J. Denis Newbold, Anthony K. Aufdenkampe
Pages: n/a - n/a
Abstract: Riparian soils, rich in organic carbon, act as a source of dissolved organic carbon (DOC) to the adjacent stream, but the hydrologic factors that control the delivery of DOC are not well characterized. A mechanistic two-dimensional, variably saturated flow and reactive transport finite element model (FEM) was developed to explore both biodegradable DOC (BDOC) and refractory DOC (RDOC) delivery processes during storms for a hillslope transect in a southeastern Pennsylvania piedmont watershed. The model indicated that DOC concentrations in outflow from a hillslope peaked on the falling limb of the discharge hydrograph, a temporal sequence consistent with a flushing hypothesis. Factors that control the lag time between the stream water peak discharge and peak DOC concentration were analyzed using a Monte Carlo simulation coupled with a multiple linear regression. The results are consistent with previous studies showing that the majority of DOC delivered to a stream during storms originates from the riparian zone. Further, the model suggests that the duration of the flood wave and hydraulic properties of the riparian soil play important roles in controlling the lag time between peak discharge and peak DOC concentration in outflow from a hillslope.
- Scale-dependent energy conservation and its connection to flow field
instability in porous media
- Authors: M.R. Deinert
Pages: n/a - n/a
Abstract: It has been known for decades that isothermal flow fields in porous media can become unstable, resulting in the growth of preferential flow paths and non-monotonic moisture profiles. The standard approach to modeling isothermal fluid transport in a porous systems is to use Richards equation with equilibrium relationships for the driving potential and monotonic transport coefficients. However, it is well known that under these conditions, solutions to Richards' equation are unconditionally stable. This has left open the question of whether Richards' equation could predict the onset of flow field instability, and what is required to model it. Importantly, past work has shown that pore scale processes can actually cause non-equilibrium driving potentials to arise in unsaturated media. How these can lead to flow field instability can be understood using a form of spectral perturbation theory. Here the driving potential is represented using a Fourier expansion, which is then substituted into Richards equation. The results show that the evolution of perturbations to the flow field are affected by the interaction between different wavelength components in the Fourier expansion. In particular, there are situations where non-equilibrium driving potentials can set up conditions that would allow the onset of instability in solutions to Richards' equation.
- Systematic assessment of the uncertainty in integrated surface
water-groundwater modeling based on the probabilistic collocation method
- Authors: Bin Wu; Yi Zheng, Yong Tian, Xin Wu, Yingying Yao, Feng Han, Jie Liu, Chunmiao Zheng
Pages: n/a - n/a
Abstract: Systematic uncertainty analysis (UA) has rarely been conducted for integrated modeling of surface water-groundwater (SW-GW) systems, which is subject to significant uncertainty, especially at a large basin scale. The main objective of this study was to explore an innovative framework in which a systematic UA can be effectively and efficiently performed for integrated SW-GW models of large river basins, and to illuminate how process understanding, model calibration, data collection and management can benefit from such a systematic UA. The framework is based on the computationally efficient Probabilistic Collocation Method (PCM) linked with a complex simulation model. The applicability and advantages of the framework were evaluated and validated through an integrated SW-GW model for the Zhangye Basin in the middle Heihe River Basin, northwest China. The framework for systematic UA allows for a holistic assessment of the modeling uncertainty, yielding valuable insights into the hydrological processes, model structure, data deficit, and potential effectiveness of management. The study shows that, under the complex SW-GW interactions, the modeling uncertainty has great spatial and temporal variabilities, and is highly output dependent. Overall, this study confirms that a systematic UA should play a critical role in integrated SW-GW modeling of large river basins, and the PCM-based approach is a promising option to fulfill this role.
- Absolute versus temporal anomaly and percent of saturation soil moisture
spatial variability for six networks worldwide
- Authors: L. Brocca; G. Zucco, H. Mittelbach, T. Moramarco, S.I. Seneviratne
Pages: n/a - n/a
Abstract: The analysis of the spatial-temporal variability of soil moisture can be carried out considering the absolute (original) soil moisture values or relative values, such as the percent of saturation or temporal anomalies. Over large areas, soil moisture data measured at different sites can be characterized by large differences in their minimum, mean, and maximum absolute values, even though in relative terms their temporal patterns are very similar. In these cases, the analysis considering absolute compared with percent of saturation or temporal anomaly soil moisture values can provide very different results with significant consequences for their use in hydrological applications and climate science.
In this study, in situ observations from six soil moisture networks in Italy, Spain, France, Switzerland, Australia and United States are collected and analyzed to investigate the spatial soil moisture variability over large areas (250-150’000 km²). Specifically, the statistical and temporal stability analyses of soil moisture have been carried out for absolute, temporal anomaly, and percent of saturation values (using two different formulations for temporal anomalies). The results highlight that the spatial variability of the soil moisture dynamic (i.e., temporal anomalies) is significantly lower than that of the absolute soil moisture values. The spatial variance of the time-invariant component (temporal mean of each site) is the predominant contribution to the total spatial variance of absolute soil moisture data. Moreover, half of the networks show a minimum in the spatial variability for intermediate conditions when the temporal anomalies are considered, in contrast with the widely recognized behaviour of absolute soil moisture data. The analyses with percent saturation data show qualitatively similar results as those for the temporal anomalies because of the applied normalization which reduces spatial variability induced by differences in mean absolute soil moisture only. Overall, we find that the analysis of the spatial-temporal variability of absolute soil moisture does not apply to temporal anomalies or percent of saturation values.
- Calibration and correction procedures for cosmic-ray neutron soil moisture
probes located across Australia
- Authors: Aaron Hawdon; David McJannet, Jim Wallace
Pages: n/a - n/a
Abstract: The cosmic-ray probe (CRP) provides continuous estimates of soil moisture over an area of ∼30 ha by counting fast neutrons produced from cosmic rays which are predominantly moderated by water molecules in the soil. This paper describes the setup, measurement correction procedures, and field calibration of CRPs at nine locations across Australia with contrasting soil type, climate, and land cover. These probes form the inaugural Australian CRP network, which is known as CosmOz. CRP measurements require neutron count rates to be corrected for effects of atmospheric pressure, water vapor pressure changes, and variations in incoming neutron intensity. We assess the magnitude and importance of these corrections and present standardized approaches for network-wide analysis. In particular, we present a new approach to correct for incoming neutron intensity variations and test its performance against existing procedures used in other studies. Our field calibration results indicate that a generalized calibration function for relating neutron counts to soil moisture is suitable for all soil types, with the possible exception of very sandy soils with low water content. Using multiple calibration data sets, we demonstrate that the generalized calibration function only applies after accounting for persistent sources of hydrogen in the soil profile. Finally, we demonstrate that by following standardized correction procedures and scaling neutron counting rates of all CRPs to a single reference location, differences in calibrations between sites are related to site biomass. This observation provides a means for estimating biomass at a given location or for deriving coefficients for the calibration function in the absence of field calibration data.
- Estimating information entropy for hydrological data: One-dimensional case
- Authors: Wei Gong; Dawen Yang, Hoshin V. Gupta, Grey Nearing
Pages: n/a - n/a
Abstract: There has been a recent resurgence of interest in the application of Information Theory to problems of system identification in the Earth and Environmental Sciences. While the concept of entropy has found increased application, little attention has yet been given to the practical problems of estimating entropy when dealing with the unique characteristics of two commonly used kinds of hydrologic data: rainfall and runoff. In this paper, we discuss four important issues of practical relevance that can bias the computation of entropy if not properly handled. The first (zero effect) arises when precipitation and ephemeral streamflow data must be viewed as arising from a discrete-continuous hybrid distribution due to the occurrence of many zero values (e.g., days with no rain/no runoff). Second, in the widely used bin-counting method for estimation of PDF's, significant error can be introduced if the bin width is not carefully selected. The third (measurement effect) arises due to the fact that continuously varying hydrologic variables can typically only be observed discretely to some degree of precision. The Fourth (skewness effect) arises when the distribution of a variable is significantly skewed. Here we present an approach that can deal with all four of these issues, and test them with artificially generated and real hydrological data. The results indicate that the method is accurate and robust.
- Increasing life expectancy of water resources literature
- Authors: M. Heistermann; T. Francke, C. Georgi, A. Bronstert
Pages: n/a - n/a
Abstract: In a study from 2008, Larivière and colleagues showed, for the field of natural sciences and engineering, that the median age of cited references is increasing over time. This result was considered counterintuitive: with the advent of electronic search engines, online journal issues and open access publications, one could have expected that cited literature is becoming younger. That study has motivated us to take a closer look at the changes in the age distribution of references that have been cited in water resources journals since 1965. Not only could we confirm the findings of Larivière and colleagues. We were also able to show that the aging is mainly happening in the oldest 10–25% of an average reference list. This is consistent with our analysis of top-cited papers in the field of water resources. Rankings based on total citations since 1965 consistently show the dominance of old literature, including text books and research papers in equal shares. For most top-cited old-timers, citations are still growing exponentially. There is strong evidence that most citations are attracted by publications that introduced methods which meanwhile belong to the standard toolset of researchers and practitioners in the field of water resources. Although we think that this trend should not be overinterpreted as a sign of stagnancy, there might be cause for concern regarding how authors select their references. We question the increasing citation of textbook knowledge as it holds the risk that reference lists become overcrowded, and that the readability of papers deteriorates.
- Analytical optimization of demand management strategies across all urban
water use sectors
- Authors: Kenneth Friedman; James P. Heaney, Miguel Morales, John Palenchar
Pages: n/a - n/a
Abstract: An effective urban water demand management program can greatly influence both peak and average demand and therefore long-term water supply and infrastructure planning. Although a theoretical framework for evaluating residential indoor demand management has been well established, little has been done to evaluate other water use sectors such as residential irrigation in a compatible manner for integrating these results into an overall solution. This paper presents a systematic procedure to evaluate the optimal blend of single family residential irrigation demand management strategies to achieve a specified goal based on performance functions derived from parcel level tax assessor's data linked to customer level monthly water billing data. This framework is then generalized to apply to any urban water sector, as exponential functions can be fit to all resulting cumulative water savings functions. Two alternative formulations are presented: maximize net benefits, or minimize total costs subject to satisfying a target water savings. Explicit analytical solutions are presented for both formulations based on appropriate exponential best fits of performance functions. A direct result of this solution is the dual variable which represents the marginal cost of water saved at a specified target water savings goal. A case study of 16,303 single family irrigators in Gainesville Regional Utilities utilizing high quality tax assessor and monthly billing data along with parcel level GIS data provides an illustrative example of these techniques. Spatial clustering of targeted homes can be easily performed in GIS to identify priority demand management areas.
- Analytical solutions for flow in porous media with multicomponent cation
- Authors: Ashwin Venkatraman; Marc Hesse, Larry W. Lake, Russell T. Johns
Pages: n/a - n/a
Abstract: Multicomponent cation exchange reactions have important applications in groundwater remediation, disposal of nuclear wastes as well as enhanced oil recovery. The hyperbolic theory of conservation laws can be used to explain the nature of displacements observed during flow with cation exchange reactions between flowing aqueous phase and stationary solid phase. Analytical solutions have been developed to predict the effluent profiles for a particular case of heterovalent cations (Na+, Ca2+ and Mg2+) and an anion (Cl-) for any combination of constant injection and constant initial composition using this theory. We assume local equilibrium, neglect dispersion and model the displacement as a Riemann problem using mass action laws, the charge conservation equation and the cation exchange capacity equation. The theoretical predictions have been compared with experimental data available at two scales - the laboratory scale and the field scale. The theory agrees well with the experimental data at both scales. Analytical theory predictions show good agreement with numerical model, developed using finite differences.
- Linking groundwater use and stress to specific crops using the groundwater
footprint in the Central Valley and High Plains aquifer systems, U.S.
- Authors: Laurent Esnault; Tom Gleeson, Yoshihide Wada, Jens Heinke, Dieter Gerten, Elizabeth Flanary, Marc F. P. Bierkens, Ludovicus P. H. van Beek
Pages: n/a - n/a
Abstract: A number of aquifers worldwide are being depleted, mainly by agricultural activities, yet groundwater stress has not been explicitly linked to specific agricultural crops. Using the newly developed concept of the groundwater footprint (the area required to sustain groundwater use and groundwater-dependent ecosystem services), we develop a methodology to derive crop-specific groundwater footprints. We illustrate this method by calculating high-resolution groundwater footprint estimates of crops in two heavily used aquifer systems: the Central Valley and High Plains, U.S. In both aquifer systems, hay and haylage, corn, and cotton have the largest groundwater footprints, which highlights that most of the groundwater stress is induced by crops meant for cattle feed. Our results are coherent with other studies in the High Plains but suggest lower groundwater stress in the Central Valley, likely due to artificial recharge from surface water diversions which were not taken into account in previous estimates. Uncertainties of recharge and irrigation application efficiency contribute the most to the total relative uncertainty of the groundwater footprint to aquifer area ratios. Our results and methodology will be useful for hydrologists, water resource managers, and policy makers concerned with which crops are causing the well-documented groundwater stress in semiarid to arid agricultural regions around the world.
- Reply to comment by J. S. Selker et al. on “Capabilities and
limitations of tracing spatial temperature patterns by fiber-optic
distributed temperature sensing”
- Authors: S. Krause; L. Rose, N. J. Cassidy
Pages: n/a - n/a
- Groundwater flow dynamics and arsenic source characterization in an
aquifer system of West Bengal, India
- Authors: A. J. Desbarats; C. E. M. Koenig, T. Pal, P. K. Mukherjee, R. D. Beckie
Pages: n/a - n/a
Abstract: Numerical groundwater flow modeling, reverse particle tracking, and environmental tracers are used to locate the source of geogenic As affecting an aquifer in West Bengal. The aquifer is hosted by point-bar sands deposited in a meandering fluvial environment. Wells tapping the aquifer exhibit As concentrations up to 531 μg/L. High-As groundwaters are recharged in ponds marking an abandoned river channel. The source of As is traced to the underlying fine-grained channel-fill sediments. Arsenic release within these sediments is accompanied by a concomitant release of Br and DOC indicating that these species may be decay products of natural organobromines codeposited along with As. Mass transfer of As to the dissolved phase and its flushing from source sediments are described using a simplified reactive solute transport model. Based on this model, a characteristic reaction time for mass transfer is estimated at 6.7 years. Average groundwater residence times in the source are estimated to have declined from 16.6 to 6.6 years with the advent of intensive irrigation pumping. The ratio of residence and reaction times, a Damköhler number, has declined correspondingly from 2.49 to 0.99, indicating a shift from transport to reaction rate limited As mobilization. Greater insight into the As problem in SE Asia may be achieved by shifting the focus of field investigations from aquifers to potential contamination sources in aquitards.
- Navigating financial and supply reliability tradeoffs in regional drought
- Authors: Harrison B. Zeff; Joseph R. Kasprzyk, Jonathan D. Herman, Patrick M. Reed, Gregory W. Characklis
Pages: n/a - n/a
Abstract: Rising development costs and growing concerns over environmental impacts have led many communities to explore more diversified water management strategies. These “portfolio”-style approaches integrate existing supply infrastructure with other options such as conservation measures or water transfers. Diversified water supply portfolios have been shown to reduce the capacity and costs required to meet demand, while also providing greater adaptability to changing hydrologic conditions. However, this additional flexibility can also cause unexpected reductions in revenue (from conservation) or increased costs (from transfers). The resulting financial instability can act as a substantial disincentive to utilities seeking to implement more innovative water management techniques. This study seeks to design portfolios that employ financial tools (e.g., contingency funds and index insurance) to reduce fluctuations in revenues and costs, allowing these strategies to achieve improved performance without sacrificing financial stability. This analysis is applied to the development of coordinated regional supply portfolios in the “Research Triangle” region of North Carolina, an area comprising four rapidly growing municipalities. The actions of each independent utility become interconnected when shared infrastructure is utilized to enable interutility transfers, requiring the evaluation of regional tradeoffs in up to five performance and financial objectives. Diversified strategies introduce significant tradeoffs between achieving reliability goals and introducing burdensome variability in annual revenues and/or costs. Financial mitigation tools can mitigate the impacts of this variability, allowing for an alternative suite of improved solutions. This analysis provides a general template for utilities seeking to navigate the tradeoffs associated with more flexible, portfolio-style management approaches.
- Analytical model for flow duration curves in seasonally dry climates
- Authors: Marc F. Müller; David N. Dralle, Sally E. Thompson
Pages: n/a - n/a
Abstract: Flow duration curves (FDC) display streamflow values against their relative excedence time. They provide critical information for watershed management by representing the variation in the availability and reliability of surface water to supply ecosystem services and satisfy anthropogenic needs. FDCs are particularly revealing in seasonally dry climates, where surface water supplies are highly variable. While useful, the empirical computation of FDCs is data intensive and challenging in sparsely gauged regions, meaning that there is a need for robust, predictive models to evaluate FDCs with simple parameterization.
Here, we derive a process-based analytical expression for FDCs in seasonally dry climates. During the wet season, streamflow is modeled as a stochastic variable driven by rainfall, following the stochastic analytical model of Botte et al. [2007a]. During the dry season, streamflow is modeled as a deterministic recession with a stochastic initial condition that accounts for the carryover of catchment storage across seasons. The resulting FDC model is applied to 38 catchments in Nepal, coastal California and Western Australia, where FDCs are successfully modeled using five physically meaningful parameters with minimal calibration. A Monte Carlo analysis revealed that the model is robust to deviations from its assumptions of Poissonian rainfall, exponentially distributed response times and constant seasonal timing.
The approach successfully models period-of-record FDCs and allows inter-annual and intra-annual sources of variations in dry season streamflow to be separated. The resulting median annual FDCs and confidence intervals allow the simulation of the consequences of inter-annual flow variations for infrastructure projects. We present an example using run-of-river hydropower in Nepal as a case study.
- Cholera in the Lake Kivu region (DRC): Integrating remote sensing and
spatially explicit epidemiological modeling
- Authors: Flavio Finger; Allyn Knox, Enrico Bertuzzo, Lorenzo Mari, Didier Bompangue, Marino Gatto, Ignacio Rodriguez-Iturbe, Andrea Rinaldo
Pages: n/a - n/a
Abstract: Mathematical models of cholera dynamics can not only help in identifying environmental drivers and processes that influence disease transmission, but may also represent valuable tools for the prediction of the epidemiological patterns in time and space as well as for the allocation of health care resources. Cholera outbreaks have been reported in the Democratic Republic of the Congo since the 1970s. They have been ravaging the shore of Lake Kivu in the east of the country repeatedly during the last decades. Here we employ a spatially explicit, inhomogeneous Markov chain model to describe cholera incidence in eight health zones on the shore of the lake. Remotely sensed datasets of chlorophyll concentration in the lake, precipitation and indices of global climate anomalies are used as environmental drivers in addition to baseline seasonality. The effect of human mobility is also modelled mechanistically. We test several models on a multi-year dataset of reported cholera cases. The best fourteen models, accounting for different environmental drivers, and selected using the Akaike information criterion, are formally compared via proper cross-validation. Among these, the one accounting for seasonality, El Niñno Southern Oscillation, precipitation and human mobility outperforms the others in cross-validation. Some drivers (such as human mobility and rainfall) are retained only by a few models, possibly indicating that the mechanisms through which they influence cholera dynamics in the area will have to be investigated further.
- Correlation between groundwater flow and deformation in the fractured
carbonate Gran Sasso aquifer (INFN underground laboratories, central
- Authors: A. Amoruso; L. Crescentini, S. Martino, M. Petitta, M. Tallini
Pages: n/a - n/a
Abstract: The Gran Sasso massif is a carbonate fractured aquifer with a spring discharge of more than 18 m3 s−1. The water table has been partially drained by two motorway tunnels and an underground laboratory (UL), located into the core aquifer. Karst features have limited role below the water table, where groundwater flow is mainly regulated by the fracture network. Two paired laser extensometers (BA and BC) recorded ground deformation in the UL. Changes in deformation correlate with the seasonal recharge/discharge cycle of groundwater flow and its long-term changes. Hydrostatic conditions prevail during the recharge phases because of the low permeability of local fractures, favoring compression, and hydraulic gradient increase above the UL. Fast groundwater flow through the high-permeability fault outcropping in the UL can enhance local dilatation for short periods. Spring discharge during exhaustion periods is fed by the low-permeability fracture network, fostering hydrodynamic conditions by hydraulic gradient decrease, diminishing compression and consequently favoring dilatation. Independent support to this conceptual model comes from local tests and a numerical model which highlights the hydromechanical strain effects induced by the hydrological cycle on the jointed rock mass along BA and the role of the hydraulic gradient on the rock mass deformation.
- Issue Information
- Pages: i - vi
- Improving process representation in conceptual hydrological model
calibration using climate simulations
- Authors: Marie Minville; Dominique Cartier, Catherine Guay, Louis‐Alexandre Leclaire, Charles Audet, Sébastien Le Digabel, James Merleau
Pages: n/a - n/a
Abstract: Different sets of calibrated model parameters can yield divergent hydrological simulations which in turn can lead to different operational decisions or scientific conclusions. In order to obtain reliable hydrological results, proper calibration is therefore fundamental. This article proposes a new calibration approach for conceptual hydrological models based on the paradigm that hydrological process representation, along with the reproduction of observed streamflows, need to be taken into account when assessing the performance of a hydrological model. Several studies have shown that complementary data can be used to improve hydrological process representation and make hydrological modelling more robust. In the current study, the process of interest is actual evapotranspiration (AET). In order to obtain a more realistic representation of AET, meteorological variables and the AET mean annual cycle simulated by a Regional Climate Model (RCM) driven by reanalyses are used to impose constraints during the optimization procedure. This calibration strategy is compared to a second strategy which relies on AET derived from reference data and to the classical approach based solely on the reproduction of observed discharges. The different methodologies are applied to calibrate the lumped conceptual model HSAMI, used operationally at Hydro‐Québec, for six Canadian snow‐dominated basins with various hydrometeorological and physiographical characteristics.
- A strategy for diagnosing and interpreting hydrological model
- Authors: Seth Westra; Mark Thyer, Michael Leonard, Dmitri Kavetski, Martin Lambert
Pages: n/a - n/a
Abstract: This paper presents a strategy for diagnosing and interpreting hydrological non‐stationarity, aiming to improve hydrological models and their predictive ability under changing hydroclimatic conditions. The strategy consists of four elements: (i) detecting potential systematic errors in the calibration data; (ii) hypothesising a set of “non‐stationary” parameterisations of existing hydrological model structures, where one or more parameters vary in time as functions of selected covariates; (iii) trialing alternative stationary model structures to assess whether parameter non‐stationarity can be reduced by modifying the model structure; and (iv) selecting one or more models for prediction. The Scott Creek catchment in South Australia and the hydrological model GR4J are used to illustrate the strategy. Streamflow predictions improve significantly when the GR4J parameter describing the maximum capacity of the production store is allowed to vary in time as a combined function of: (i) an annual sinusoid; (ii) the previous 365‐day rainfall and potential evapotranspiration; and (iii) a linear trend. This improvement provides strong evidence of model non‐stationarity. Based on a range of hydrologically‐oriented diagnostics such as flow‐duration curves, the GR4J model structure was modified by introducing an additional calibration parameter that controls recession behaviour and by making actual evapotranspiration dependent only on catchment storage. Model comparison using an information‐theoretic measure (the Akaike Information Criterion) and several hydrologically oriented diagnostics shows that the GR4J modifications clearly improve predictive performance in Scott Creek catchment. Based on a comparison of 22 versions of GR4J with different representations of non‐stationarity and other modifications, the model selection approach applied in the exploratory period (used for parameter estimation) correctly identifies models that perform well in a much drier independent confirmatory period.
- Estimation of spatial covariance of log‐conductivity from
- Authors: Monica Riva; Xavier Sanchez‐Vila, Alberto Guadagnini
Pages: n/a - n/a
Abstract: We derive analytical relationships between the spatial covariance of the (natural) logarithm of hydraulic conductivity (K) and that of representative soil particle sizes and porosity. The latter quantities can be directly measured during routine sedimentological analyses of soil samples and provide a way of incorporating K estimates into groundwater flow models at a relatively modest experimental cost. Here, we rely on widely used empirical formulations requiring measurements of representative particle diameters and, in some cases, of medium porosity. We derive exact formulations relating the spatial covariance of these quantities and K and present workable approximations on the basis of perturbation methods. Our formulations provide a direct link between key geostatistical descriptors of sedimentological and hydraulic parameters of heterogeneous aquifers which can be employed in classical estimation and simulation procedures. The approach and theoretical results are tested on an extensive data set comprising 411 particle‐size curves collected at 12 boreholes in a small scale alluvial aquifer.
- What does CloudSat reveal about global land precipitation detection by
other space‐borne sensors?
- Authors: Ali Behrangi; Yudong Tian, Bjorn H. Lambrigtsen, Graeme L. Stephens
Pages: n/a - n/a
Abstract: Current orbital land precipitation products have serious shortcomings in detecting light rain and snowfall, the most frequent types of global precipitation. The missed precipitation is then propagated into the merged precipitation products that are widely used. Precipitation characteristics such as frequency and intensity and their regional distribution are expected to change in a warming climate. It is important to accurately capture those characteristics to understand and model the current state of the Earth's climate and predict future changes. In this work the precipitation detection performance of a suite of precipitation sensors, commonly used in generating the merged precipitation products, are investigated. The high sensitivity of CloudSat Cloud Profiling Radar (CPR) to liquid and frozen hydrometeors enables superior estimates of light rainfall and snowfall within 80oS‐80oN. Three years (2007–2009) of CloudSat precipitation data were collected to construct a climatology reference for guiding our analysis. In addition, auxiliary data such as infrared brightness temperature, surface air temperature, and cloud types were used for a more detailed assessment. The analysis shows that no more than 50 % of the tropical (40oS‐40oN) precipitation occurrence is captured by the current suite of precipitation measuring sensors. Poleward of 50o latitude, a combination of various factors such as an abundance of light rainfall, snowfall, shallow precipitation‐bearing clouds, and frozen surfaces, reduces the space‐based precipitation detection rate to less than 20%. This shows that for a better understanding of precipitation from space, especially at higher latitudes, there is a critical need to improve current precipitation retrieval techniques and sensors.
- Quantification of capillary trapping of gas clusters using X‐ray
- Authors: Helmut Geistlinger; Sadjad Mohammadian, Steffen Schlueter, Hans‐Joerg Vogel
Pages: n/a - n/a
Abstract: A major difficulty in modeling multiphase flow in porous media is the emergence of trapped phases. Our experiments demonstrate that gas can be trapped in either single‐pores, multipores, or in large connected networks. These large connected clusters can comprise up to eight grain volumes and can contain up to 50% of the whole trapped gas volume. About 85% of the gas volume is trapped by multipore gas clusters. This variety of possible trapped gas clusters of different shape and volume will lead to a better process understanding of bubble‐mediated mass transfer. Since multipore gas bubbles are in contact with the solid surface through ultrathin adsorbed water films the interfacial area between trapped gas clusters and intergranular capillary water is only about 80% of the total gas surface. We could derive a significant (R2 = 0.98) linear relationship between the gas‐water‐interface and gas saturation. We found no systematic dependency of the front velocity of the invading water phase in the velocity range from 0.1 to 0.6 cm/min corresponding to capillary numbers from 2 × 10−7 to 10−6. Our experimental results indicate that the capillary trapping mechanism is controlled by the local pore structure and local connectivity and not by thermodynamics, i.e., by the minimum of the Free Energy, at least in the considered velocity range. Consistent with this physical picture is our finding that the trapping frequency (= bubble‐size distribution) reflects the pore size distribution for the whole range of pore radii, i.e., the capillary trapping process is determined by statistics and not by thermodynamics.
- Floodplain ecohydrology: Climatic, anthropogenic, and local physical
controls on partitioning of water sources to riparian trees
- Authors: Michael Bliss Singer; Christopher I. Sargeant, Hervé Piégay, Jérémie Riquier, Rob J. S. Wilson, Cristina M. Evans
Pages: n/a - n/a
Abstract: Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co‐occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years.
- Ecosystem services: Challenges and opportunities for hydrologic modeling
to support decision making
- Authors: Andrew J. Guswa; Kate A. Brauman, Casey Brown, Perrine Hamel, Bonnie L. Keeler, Susan Stratton Sayre
Pages: n/a - n/a
Abstract: Ecosystem characteristics and processes provide significant value to human health and well‐being, and there is growing interest in quantifying those values. Of particular interest are water‐related ecosystem services and the incorporation of their value into local and regional decision making. This presents multiple challenges and opportunities to the hydrologic‐modeling community. To motivate advances in water‐resources research, we first present three common decision contexts that draw upon an ecosystem‐service framework: scenario analysis, payments for watershed services, and spatial planning. Within these contexts, we highlight the particular challenges to hydrologic modeling, and then present a set of opportunities that arise from ecosystem‐service decisions. The paper concludes with a set of recommendations regarding how we can prioritize our work to support decisions based on ecosystem‐service valuation.
- Estimating temporal changes in hydraulic head using InSAR data in the San
Luis Valley, Colorado
- Authors: Jessica A. Reeves; Rosemary Knight, Howard A. Zebker, Peter K. Kitanidis, Willem A. Schreüder
Pages: n/a - n/a
Abstract: The sustainability of the confined aquifer system in the San Luis Valley, Colorado is of utmost importance to the valley's agricultural economy. There is a dearth of hydraulic head measurements in the confined aquifer to which the current groundwater flow model can be calibrated. Here we investigate the extent to which spatially and temporally dense measurements of deformation from Interferometric Synthetic Aperture Radar (InSAR) data can be used to fill in spatial and temporal gaps in the head data set by calibrating the InSAR data with head at the monitoring well locations. We conduct this calibration at 11 wells where we expect sufficient deformation for reliable InSAR measurement, given the accepted level of uncertainty (∼1 cm). In the San Luis Valley, crop growth degrades the quality of the InSAR signal, which means that the high‐quality deformation data may not be collocated with the wells. We use kriging to estimate the deformation directly at the well locations. We find that the calibration is valid at three well locations where the seasonal magnitude of the deformation is much larger than the uncertainty of the InSAR measurement. At these well locations, we predict head prior to and within the temporal sampling window of the head measurements. We find that 59% of the InSAR‐predicted hydraulic head values agree with the measured values, within the uncertainty of the data. Given our success in extending the hydraulic head data temporally, the next step in our research is to use InSAR data to interpolate spatially between head measurements.
- Nebraska's groundwater legacy: Nitrate contamination beneath irrigated
- Authors: Mary E. Exner; Aaron J. Hirsh, Roy F. Spalding
Pages: n/a - n/a
Abstract: A 31 year record of ∼44,000 nitrate analyses in ∼11,500 irrigation wells was utilized to depict the decadal expansion of groundwater nitrate contamination (N ≥ 10 mg/L) in the irrigated corn‐growing areas of eastern and central Nebraska and analyze long‐term nitrate concentration trends in 17 management areas (MAs) subject to N fertilizer and budgeting requirements. The 1.3 M contaminated hectares were characterized by irrigation method, soil drainage, and vadose zone thickness and lithology. The areal extent and growth of contaminated groundwater in two predominately sprinkler‐irrigated areas was only ∼20% smaller beneath well‐drained silt loams with thick clayey‐silt unsaturated layers and unsaturated thicknesses >15 m (400,000 ha and 15,000 ha/yr) than beneath well and excessively well‐drained soils with very sandy vadose zones (511,000 ha and 18,600 ha/yr). Much slower expansion (3700 ha/yr) occurred in the 220,000 contaminated hectares in the central Platte valley characterized by predominately gravity irrigation on thick, well‐drained silt loams above a thin (∼5.3 m), sandy unsaturated zone. The only reversals in long‐term concentration trends occurred in two MAs (120,500 ha) within this contaminated area. Concentrations declined 0.14 and 0.20 mg N/L/yr (p 20 years of management. Average annual concentrations in 10 MAs are increasing (p
- Effective discharge in small formerly glaciated mountain streams of
British Columbia: Limitations and implications
- Authors: Marwan A. Hassan; Drew Brayshaw, Younes Alila, Edmund Andrews
Pages: n/a - n/a
Abstract: Episodic sediment supply, past glaciation, and slow responses to disturbance make small mountain streams transitional alluvial regimes in which nonequilibrium conditions are common. Bed load effective discharge in these streams is on average a low‐magnitude, high‐frequency event, but is highly variable. Using a two‐phase sediment transport model and long‐term discharge records, we distinguish between three types of streams; streams in which gravel (sediment > 8 mm diameter) moves frequently and effective discharge occurs during gravel transport (Frequently Mobile Gravel (FMG)), streams in which gravel moves infrequently but effective discharge nonetheless occurs during gravel transport (Infrequently Mobile Gravel (IMG)), and streams in which sand (sediment
- Large Rivers in the Anthropocene: Insights and tools for understanding
climatic, land use, and reservoir influences
- Authors: Helmut Habersack; Daniel Haspel, Mathias Kondolf
Pages: n/a - n/a
Abstract: Since the industrial revolution, human impacts on landscapes and river systems globally have intensified significantly. Humans nowadays artificially increase and decrease fluxes of water, sediment and nutrients on a scale far exceeding natural fluxes. Rivers integrate such changes occurring throughout their drainage basins, and thus can be considered as indicators of landscape processes and river basin “health” more broadly. This special issue brings together a set of papers that explore interactions of climate change and river processes, influences of land use changes, effects of reservoirs, as well as new approaches to sorting out the relative importance of these diverse influences on rivers and uncertainties in modeling future behavior. These papers contribute to a growing body of work demonstrating the fundamental differences between large rivers in the Anthropocene and rivers in prior time periods.
- Assessment of parametric uncertainty for groundwater reactive transport
- Authors: Xiaoqing Shi; Ming Ye, Gary P. Curtis, Geoffery L. Miller, Philip D. Meyer, Matthias Kohler, Steve Yabusaki, Jichun Wu
Pages: n/a - n/a
Abstract: The validity of using Gaussian assumptions for model residuals in uncertainty quantification of a groundwater reactive transport model was evaluated in this study. Least squares regression methods explicitly assume Gaussian residuals, and the assumption leads to Gaussian likelihood functions, model parameters, and model predictions. While the Bayesian methods do not explicitly require the Gaussian assumption, Gaussian residuals are widely used. This paper shows that the residuals of the reactive transport model are non‐Gaussian, heteroscedastic, and correlated in time; characterizing them requires using a generalized likelihood function such as the formal generalized likelihood function developed by Schoups and Vrugt (2010). For the surface complexation model considered in this study for simulating uranium reactive transport in groundwater, parametric uncertainty is quantified using the least squares regression methods and Bayesian methods with both Gaussian and formal generalized likelihood functions. While the least squares methods and Bayesian methods with Gaussian likelihood function produce similar Gaussian parameter distributions, the parameter distributions of Bayesian uncertainty quantification using the formal generalized likelihood function are non‐Gaussian. In addition, predictive performance of formal generalized likelihood function is superior to that of least squares regression and Bayesian methods with Gaussian likelihood function. The Bayesian uncertainty quantification is conducted using the differential evolution adaptive metropolis (DREAM(zs)) algorithm; as a Markov chain Monte Carlo (MCMC) method, it is a robust tool for quantifying uncertainty in groundwater reactive transport models. For the surface complexation model, the regression‐based local sensitivity analysis and Morris‐ and DREAM(ZS)‐based global sensitivity analysis yield almost identical ranking of parameter importance. The uncertainty analysis may help select appropriate likelihood functions, improve model calibration, and reduce predictive uncertainty in other groundwater reactive transport and environmental modeling.
- Hydrologic dynamics and geochemical responses within a floodplain aquifer
and hyporheic zone during Hurricane Sandy
- Authors: A.H. Sawyer; L.A. Kaplan, O. Lazareva, H.A. Michael
Pages: n/a - n/a
Abstract: Storms dominate solute export budgets from catchments and drive hydrogeochemical changes in the near‐stream environment. We captured near‐stream hydrogeochemical dynamics during an intense storm (Hurricane Sandy, October 2012), by instrumenting a riparian‐hyporheic zone transect of White Clay Creek in the Christina River Basin Critical Zone Observatory with pressure transducers, redox probes, and pore water samplers. In the floodplain aquifer, preferential vertical flow paths such as macropores facilitated rapid infiltration early in the storm. Water table rose quickly and promoted continuous groundwater discharge to the stream. Floodplain‐hillslope topography controlled post‐storm aquifer drainage rates, as the broad, western floodplain aquifer drained more slowly than the narrow, eastern floodplain aquifer adjacent to a steep hillslope. These changes in groundwater flow drove heterogeneous geochemical responses in the floodplain aquifer and hyporheic zone. Vertical infiltration in the floodplain and hyporheic exchange in the streambed increased DOC and oxygen delivery to microbially active sediments, which may have enhanced respiration. Resulting geochemical perturbations persisted from days to weeks after the storm. Our observations suggest that groundwater‐borne solute delivery to streams during storms depends on unique interactions of vertical infiltration along preferential pathways, perturbations to groundwater geochemistry, and topographically controlled drainage rates.
- An equivalent cross‐sectional basis for semidistributed hydrological
- Authors: Urooj Khan; Narendra Kumar Tuteja, Hoori Ajami, Ashish Sharma
Pages: n/a - n/a
Abstract: The computational effort associated with physically based distributed hydrological models is one of their major limitations that restrict their application in soil moisture and land surface flux simulation problems for large catchments. In this work, a new approach for reducing the computational effort associated with such models is investigated. This approach involves the formation of equivalent cross sections, designed in a manner that ensures comparable accuracy in simulating the hydrological fluxes as a fully distributed simulation. Single or multiple equivalent cross sections are formulated in each Strahler's first‐order subbasin on the basis of topographic and physiographic variables representing the entire or part of the subbasin. An unsaturated soil moisture movement model based on a two‐dimensional solution of the Richards' equation is used for simulating the soil moisture and hydrologic fluxes. The equivalent cross‐section approach and the model are validated against observed soil moisture data in a semiarid catchment and found consistent. The results indicate that the equivalent cross‐section approach is an efficient alternative for reducing the computational time of distributed hydrological modeling while maintaining reasonable accuracy in simulating hydrologic fluxes, in particular dominant fluxes such as transpiration and soil evaporation in semiarid catchments.
- Imaging and quantification of preferential solute transport in soil
- Authors: John Koestel; Mats Larsbo
Pages: n/a - n/a
Abstract: Despite significant advances during the last decades, there are still many processes related to nonequilibrium flow and transport in macroporous soil that are far from completely understood. The use of X‐rays for imaging time‐lapse 3‐D solute transport has a large potential to help advance the knowledge in this field. We visualized the transport of potassium iodide (20 g iodide l−1 H2O) through a small undisturbed soil column (height 3.8 cm, diameter 6.8 cm) under steady state hydraulic conditions using an industrial X‐ray scanner. In addition, the electrical conductivity was measured in the effluent solution during the experiment. We attained a series of seventeen 3‐D difference images which we related to iodide concentrations using a linear calibration relationship. The solute transport through the soil mainly took place in two cylindrical macropores, by‐passing more than 90% of the bulk soil volume during the entire experiment. From these macropores the solute diffused into the surrounding soil matrix. We illustrated the properties of the investigated solute transport by comparing it to a 1‐D convective‐dispersive transport and by calculating the temporal evolution of the dilution index. We furthermore showed that the tracer diffusion from one of the macropores into the surrounding soil matrix could not be exactly fitted with the cylindrical diffusion equation. We believe that similar studies will help establish links between soil structure and solute transport processes and lead to improvements in models for solute transport through undisturbed soil.
- Stochastic modeling of fine particulate organic carbon dynamics in rivers
- Authors: J. D. Drummond; A. F. Aubeneau, A. I. Packman
Pages: n/a - n/a
Abstract: The majority of particulate organic matter standing stock in streams is
- Finite volume hydromechanical simulation in porous media
- Authors: Jan Martin Nordbotten
Pages: n/a - n/a
Abstract: Cell‐centered finite volume methods are prevailing in numerical simulation of flow in porous media. However, due to the lack of cell‐centered finite volume methods for mechanics, coupled flow and deformation is usually treated either by coupled finite‐volume‐finite element discretizations, or within a finite element setting. The former approach is unfavorable as it introduces two separate grid structures, while the latter approach loses the advantages of finite volume methods for the flow equation. Recently, we proposed a cell‐centered finite volume method for elasticity. Herein, we explore the applicability of this novel method to provide a compatible finite volume discretization for coupled hydromechanic flows in porous media. We detail in particular the issue of coupling terms, and show how this is naturally handled. Furthermore, we observe how the cell‐centered finite volume framework naturally allows for modeling fractured and fracturing porous media through internal boundary conditions. We support the discussion with a set of numerical examples: the convergence properties of the coupled scheme are first investigated; second, we illustrate the practical applicability of the method both for fractured and heterogeneous media.
- Jointly deriving NMR surface relaxivity and pore size distributions by NMR
relaxation experiments on partially desaturated rocks
- Authors: O. Mohnke; B. Hughes
Pages: n/a - n/a
Abstract: Nuclear magnetic resonance (NMR) relaxometry is a geophysical method widely used in borehole and laboratory applications to non‐destructively infer transport and storage properties of rocks and soils as it is directly sensitive to the water/oil content and pore sizes. However, for inferring pore sizes NMR relaxometry data needs to be calibrated with respect to a surface interaction parameter, surface relaxivity, which depends on the type and mineral constituents of the investigated rock. This study introduces an inexpensive and quick alternative to the classical calibration methods, e.g. mercury injection, pulsed field gradient (PFG) NMR or grain size analysis, which allows for jointly estimating NMR surface relaxivity and pore size distributions using NMR relaxometry data from partially de‐saturated rocks. Hereby, NMR relaxation experiments are performed on the fully saturated sample and on a sample partially drained at a known differential pressure. Based on these data the (capillary) pore radius distribution and surface relaxivity are derived by joint optimization of the Brownstein‐Tarr and the Young‐Laplace equation assuming parallel capillaries. Moreover, the resulting pore size distributions can be used to predict water retention curves. This inverse modeling approach – tested and validated using NMR relaxometry data measured on synthetic porous borosilicate samples with known petrophysical properties (i.e. permeability, porosity, inner surfaces, pore size distributions) – yields consistent and reproducible estimates of surface relaxivity and pore radii distributions. Also, subsequently calculated water retention curves generally correlate well with measured water retention curves.
- Reactive transport controls on sandy acid sulfate soils and impacts on
shallow groundwater quality
- Authors: S.U. Salmon; Andrew W. Rate, Zed Rengel, Steven Appleyard, Henning Prommer, Christoph Hinz
Pages: n/a - n/a
Abstract: Disturbance or drainage of potential acid sulfate soils (PASS) can result in the release of acidity and degradation of infrastructure, water resources, and the environment. Soil processes affecting shallow groundwater quality have been investigated using a numerical code that integrates (bio)geochemical processes with water, solute, and gas transport. The patterns of severe and persistent acidification (pH
- Objective extraction of channel heads from high‐resolution
- Authors: Fiona J. Clubb; Simon M. Mudd, David T. Milodowski, Martin D. Hurst, Louise J. Slater
Pages: n/a - n/a
Abstract: Fluvial landscapes are dissected by channels, and at their upstream termini are channel heads. Accurate reconstruction of the fluvial domain is fundamental to understanding runoff generation, storm hydrology, sediment transport, biogeochemical cycling, and landscape evolution. Many methods have been proposed for predicting channel head locations using topographic data, yet none have been tested against a robust field data set of mapped channel heads across multiple landscapes. In this study, four methods of channel head prediction were tested against field data from four sites with high‐resolution DEMs: slope‐area scaling relationships; two techniques based on landscape tangential curvature; and a new method presented here, which identifies the change from channel to hillslope topography along a profile using a transformed longitudinal coordinate system. Our method requires only two user‐defined parameters, determined via independent statistical analysis. Slope‐area plots are traditionally used to identify the fluvial‐hillslope transition, but we observe no clear relationship between this transition and field‐mapped channel heads. Of the four methods assessed, one of the tangential curvature methods and our new method most accurately reproduce the measured channel heads in all four field sites (Feather River CA, Mid Bailey Run OH, Indian Creek OH, Piedmont VA), with mean errors of −11, −7, 5, and −24 m and 34, 3, 12, and −58 m, respectively. Negative values indicate channel heads located upslope of those mapped in the field. Importantly, these two independent methods produce mutually consistent estimates, providing two tests of channel head locations based on independent topographic signatures.
- Uncertainty compliant design flood estimation
- Authors: A. Botto; D. Ganora, F. Laio, P. Claps
Pages: n/a - n/a
Abstract: Hydraulic infrastructures are commonly designed with reference to target values of flood peak, estimated using probabilistic techniques, such as flood frequency analysis. The application of these techniques underlies levels of uncertainty, which are sometimes quantified but normally not accounted for explicitly in the decision regarding design discharges. The present approach aims at defining a procedure which enables the definition of Uncertainty Compliant Design (UNCODE) values of flood peaks. To pursue this goal, we first demonstrate the equivalence of the Standard design based on the return period and the cost‐benefit procedure, when linear cost and damage functions are used. We then use this result to assign an expected cost to estimation errors, thus setting a framework to obtain a design flood estimator which minimizes the total expected cost. This procedure properly accounts for the uncertainty which is inherent in the frequency curve estimation. Applications of the UNCODE procedure to real cases leads to remarkable displacement of the design flood from the Standard values. UNCODE estimates are systematically larger than the Standard ones, with substantial differences (up to 55%) when large return periods or short data samples are considered.
- Calculation of wastewater effluent leakage to pristine water sources by
the weighted average of multiple tracer approach
- Authors: Guy Gasser; Irena Pankratov, Sara Elhanany, Hillel Glazman, Ovadia Lev
Pages: n/a - n/a
Abstract: A methodology used to estimate the percentage of wastewater effluent in an otherwise pristine water site is proposed on the basis of the weighted mean of the level of a consortium of indicator pollutants. This method considers the levels of uncertainty in the evaluation of each of the indicators in the site, potential effluent sources, and uncontaminated surroundings. A detailed demonstrative study was conducted on a site that is potentially subject to wastewater leakage. The research concentrated on several perched springs that are influenced to an unknown extent by agricultural communities. A comparison was made to a heavily contaminated site receiving wastewater effluent and surface water runoff. We investigated six springs in two nearby ridges where fecal contamination was detected in the past; the major sources of pollution in the area have since been diverted to a wastewater treatment system. We used chloride, acesulfame, and carbamazepine as domestic pollution tracers. Good correlation (R2 > 0.86) was observed between the mixing ratio predictions based on the two organic tracers (the slope of the linear regression was 1.05), whereas the chloride predictions differed considerably. This methodology is potentially useful, particularly for cases in which detailed hydrological modeling is unavailable but in which quantification of wastewater penetration is required. We demonstrate that the use of more than one tracer for estimation of the mixing ratio reduces the combined uncertainty level associated with the estimate and can also help to disqualify biased tracers.
- A 3‐D hydrologic transport model of a water recharge system using
carbamazepine and chloride as tracers
- Authors: Michael Rona; Guy Gasser, Ido Negev, Irena Pankratov, Sara Elhanany, Ovadia Lev, Haim Gvirtzman
Pages: n/a - n/a
Abstract: Wastewater recharge facilities are often used as a final water treatment before the discharge to the sea or before water reclamation. These facilities are often located in active aquifers that supply drinking water. Thus, leakage from the water recharge facility and gradual expansion of the underground wastewater plume are of considerable health concern. Hydrological modeling of water recharge systems are widely used as operational and predictive tools. These models rely on distributed water head monitoring and at least one chemical or physical tracer to model solutes' transport. Refractory micropollutants have proven useful in qualitative identification of pollution leakages and for quantification of pollution to a specific site near water recharge facilities. However, their usefulness as tracers for hydrological modeling is still questionable. In this article, we describe a long term, 3‐D hydraulic model of a large‐scale wastewater effluents recharge system in which a combination of chloride and a refractory micropollutant, carbamazepine is used to trace the solute transport. The combination of the two tracers provides the model with the benefits of the high specificity of the carbamazepine and the extensive historic data base that is available for chloride. The model predicts westward expansion of the pollution plume, whereas a standing front is formed at the east. These trends can be confirmed by the time trace of the carbamazepine concentrations at specific locations. We show that the combination of two tracers accounts better (at least at some locations) for the evolution of the pollution plume than a model based on chloride or carbamazepine alone.
- Impact evaluation of the irrigation management reform in northern China
- Authors: Qiuqiong Huang
Pages: n/a - n/a
Abstract: The paper evaluates the reform in the irrigation sector in northern China, in particular, the transfer of irrigation management to water user associations or contractors from the village committee. With a set of panel data collected in randomly selected villages in northern China, a fixed effects model at the canal level with instrumental variable estimation is used to control for unobservable heterogeneity and endogeneity problem. The results show that WUAs have increased maintenance expenditures, the timeliness of water deliveries, the percent of irrigated area and the rates of fee collection. There are also improvements in irrigation systems managed by contractors but with magnitudes smaller than in the case of WUAs. WUAs or contracting, however, have limited impacts on water use and crop production. Discussions on reasons for the findings of limited impacts offer some suggestions for the next steps of the irrigation reform and call for continued research efforts to collect more data for further impact evaluations.
- Precipitation isotopes link regional climate patterns to water supply in a
tropical mountain forest, eastern Puerto Rico
- Authors: Martha A. Scholl; Sheila F. Murphy
Pages: n/a - n/a
Abstract: Like many mountainous areas in the tropics, watersheds in the Luquillo Mountains of eastern Puerto Rico have abundant rainfall and stream discharge and provide much of the water supply for the densely populated metropolitan areas nearby. Projected changes in regional temperature and atmospheric dynamics as a result of global warming suggest that water availability will be affected by changes in rainfall patterns. It is essential to understand the relative importance of different weather systems to water supply to determine how changes in rainfall patterns, interacting with geology and vegetation, will affect the water balance. To help determine the links between climate and water availability, stable isotope signatures of precipitation from different weather systems were established to identify those that are most important in maintaining streamflow and groundwater recharge. Precipitation stable isotope values in the Luquillo Mountains had a large range, from fog/cloud water with δ2H, δ18O values as high as +12 ‰, −0.73 ‰ to tropical storm rain with values as low as −127 ‰, −16.8 ‰. Temporal isotope values exhibit a reverse seasonality from those observed in higher latitude continental watersheds, with higher isotopic values in the winter and lower values in the summer. Despite the higher volume of convective and low‐pressure system rainfall, stable isotope analyses indicated that under the current rainfall regime, frequent trade ‐wind orographic showers contribute much of the groundwater recharge and stream base flow. Analysis of rain events using 20 years of 15 ‐minute resolution data at a mountain station (643 m) showed an increasing trend in rainfall amount, in agreement with increased precipitable water in the atmosphere, but differing from climate model projections of drying in the region. The mean intensity of rain events also showed an increasing trend. The determination of recharge sources from stable isotope tracers indicates that water supply will be affected if regional atmospheric dynamics change trade‐ wind orographic rainfall patterns in the Caribbean.
- Flume testing of underwater seep detection using temperature sensing on or
just below the surface of sand or gravel sediments
- Authors: F. Selker; J. S. Selker
Pages: n/a - n/a
Abstract: Temperature anomalies can identify locations of seeps of groundwater into surface waters. However, the method's sensitivity to details such as thermometer burial depth, sediment material, seep velocity, and surface water current are largely unknown. We report on a series of laboratory flume experiments in which controlled seeps under variable sediment texture, surface currents, burial depth, and temperature differentials were imposed. The focus of the study is temperature effects at the sediment surface to a few centimeters below the sediment surface, as these locations are of particular interest when using fiber‐optic distributed temperature sensors (DTS). The data demonstrate: (1) without surface water flow, seep‐related thermal anomalies were apparent in all cases, i.e., the method is feasible in such cases; (2) probe burial is helpful for fine sediment although not effective with coarse bed sediment, i.e., the method is strongly sensitive to sediment properties; (3) placing a thin rubber sheet over an unburied thermal probe increases detection of seeps in some circumstances, but not in others, and is generally not as robust as probe burial; and (4) local surface flow velocity, details of probe position and depth, and seepage velocity all influence observed temperature anomalies, limiting the opportunity to quantify seepage velocity, particularly with unburied temperature sensors. Overall, these findings suggest optimal installation would be at a well‐defined depth within fine sediment, that installation in gravel and coarser sediment is not suited to the method if there are any significant surface currents, and that more data would be required to obtain accurate estimates of seepage velocity, though a single sensor may be sufficient to identify the location of seepage.
- Valuing water quality in urban watersheds: A comparative analysis of
Johnson Creek, Oregon, and Burnt Bridge Creek, Washington
- Authors: Noelwah R. Netusil; Michael Kincaid, Heejun Chang
Pages: n/a - n/a
Abstract: This study uses the hedonic price method to investigate the effect of five water quality parameters on the sale price of single‐family residential properties in two urbanized watersheds in the Portland, Oregon‐Vancouver, Washington metropolitan area. Water quality parameters include E. coli or fecal coliform, which can affect human health, decrease water clarity and generate foul odors; pH, dissolved oxygen, and stream temperature, which can impact fish and wildlife populations; and total suspended solids, which can affect water clarity, aquatic life, and aesthetics. Properties within ¼ mile, ½, mile, one mile, or more than one mile from Johnson Creek are estimated to experience an increase in sale price of 13.71%, 7.05%, 8.18%, and 3.12%, respectively, from a one mg/L increase in dissolved oxygen levels during the dry season (May–October). Estimates for a 100 count per 100 mL increase in E. coli during the dry season are −2.81% for properties within ¼ mile of Johnson Creek, −0.86% (½ mile), −1.19% (one mile), and −0.71% (greater than one mile). Results for properties in Burnt Bridge Creek include a significantly positive effect for a one mg/L increase in dissolved oxygen levels during the dry season for properties within ½ mile (4.49%), one mile (2.95%), or greater than one mile from the creek (3.17%). Results for other water quality parameters in Burnt Bridge Creek are generally consistent with a priori expectations. Restoration efforts underway in both study areas might be cost justified based on their estimated effect on property sale prices.
- Comment on “Capabilities and limitations of tracing spatial
temperature patterns by fiber‐optic distributed temperature
sensing” by L. Rose, S. Krause, and N.J. Cassidy
- Authors: J.S. Selker; Scott Tyler, Nick vandeGiesen
Pages: n/a - n/a
- Oceanic sources of continental precipitation
- Authors: Luis Gimeno
Pages: 3647 - 3649
Abstract: In this special section, the authors have tried to address some of the many unanswered questions related to the transport of moisture from oceanic sources to the continents, including among others that of whether or not the moisture source regions have remained stationary over time, how the many changes in the intensity and position of the sources have affected the distribution of continental precipitation, and also the question of the role of the main modes of climate variability in the variability of the moisture regions.
- An efficient hybrid approach for multiobjective optimization of water
- Authors: Feifei Zheng; Angus R. Simpson, Aaron C. Zecchin
Pages: 3650 - 3671
Abstract: An efficient hybrid approach for the design of water distribution systems (WDSs) with multiple objectives is described in this paper. The objectives are the minimization of the network cost and maximization of the network resilience. A self-adaptive multiobjective differential evolution (SAMODE) algorithm has been developed, in which control parameters are automatically adapted by means of evolution instead of the presetting of fine-tuned parameter values. In the proposed method, a graph algorithm is first used to decompose a looped WDS into a shortest-distance tree (T) or forest, and chords (Ω). The original two-objective optimization problem is then approximated by a series of single-objective optimization problems of the T to be solved by nonlinear programming (NLP), thereby providing an approximate Pareto optimal front for the original whole network. Finally, the solutions at the approximate front are used to seed the SAMODE algorithm to find an improved front for the original entire network. The proposed approach is compared with two other conventional full-search optimization methods (the SAMODE algorithm and the NSGA-II) that seed the initial population with purely random solutions based on three case studies: a benchmark network and two real-world networks with multiple demand loading cases. Results show that (i) the proposed NLP-SAMODE method consistently generates better-quality Pareto fronts than the full-search methods with significantly improved efficiency; and (ii) the proposed SAMODE algorithm (no parameter tuning) exhibits better performance than the NSGA-II with calibrated parameter values in efficiently offering optimal fronts.
- Relative permeability of homogenous-wet and mixed-wet porous media as
determined by pore-scale lattice Boltzmann modeling
- Authors: C. J. Landry; Z. T. Karpyn, O. Ayala
Pages: 3672 - 3689
Abstract: We present a pore-scale study of two-phase relative permeability in homogenous-wet porous media, and porous media altered to a mixed-wet state. A Shan-Chen type multicomponent lattice Boltzmann (LB) model is employed to determine pore-scale fluid distributions and relative permeability. Mixed-wet states are created by altering the wettability of solid surfaces in contact with the nonwetting phase at the end of steady state simulation of initially homogenous-wet porous media. To ensure accurate representation of fluid-solid interfacial areas, we compare LB simulation results to experimental measurements of interfacial fluid-fluid and fluid-solid areas determined by X-ray computed microtomography imaging of water and oil distributions in bead packs. The LB simulations are found to match experimental trends observed for fluid-fluid and fluid-solid interfacial area-saturation relationships. The relative permeability of both fluids in the homogenous-wet porous media was found to decrease with a decreasing contact angle. The relative permeability of both fluids in the altered, mixed-wet porous media was found to decrease for all mixed-wet states in comparison to the initial homogenous-wet states. The nonwetting phase relative permeability decreased significantly, while the wetting phase experienced only a minor decrease. The significance of the decrease was found to be dependent on the distribution of the unaltered solid surfaces, with less dependence on the severity of alteration.
- The variability of vertical structure of precipitation in Huaihe River
Basin of China: Implications from long-term spaceborne observations with
TRMM precipitation radar
- Authors: Qing Cao; Youcun Qi
Pages: 3690 - 3705
Abstract: The current study investigates the variability of vertical structure of precipitation in the Huaihe River Basin (HRB) of China. The precipitation characteristics have been revealed by the long-term observations of vertical profile of reflectivity (VPR) from the first spaceborne precipitation radar (PR) onboard the National Aeronautics and Space Administration (NASA)'s Tropical Rainfall Measuring Mission (TRMM) satellite. This study has statistically analyzed the latest TRMM 2A-23 and 2A-25 products (version 7, released in 2012) with ∼15 years time span (from 11 December 1997 to 19 August 2012). First, the spatial and seasonal variations of storm height and freezing level have been investigated. The results show a climatological relation connecting the storm height with the rainfall rate in HRB. Second, mean VPRs have been studied for the stratiform and convective precipitation. The VPR variability has been analyzed for different seasons and rain intensities. Third, the characteristics of rain intensification and weakening in the vertical direction have been examined by the statistical analysis of VPR slope below the melting layer. The results show that the rainfall tends to be reduced (or intensified) with the height changing downward in the light (or moderate and heavy) precipitating clouds, no matter stratiform or convection. Finally, the S-band climatological VPRs have been characterized by converting the VPR from Ku-band to S-band. Considering the wide application of national radar network for weather surveillance in China, the developed S-band climatological VPRs can be potentially applied in a VPR correction scheme to improve the ground radar-based quantitative precipitation estimation (QPE) in this river basin.
- Active-distributed temperature sensing to continuously quantify vertical
flow in boreholes
- Authors: T. Read; O. Bour, J. S. Selker, V. F. Bense, T. Le Borgne, R. Hochreutener, N. Lavenant
Pages: 3706 - 3713
Abstract: We show how a distributed borehole flowmeter can be created from armored Fiber Optic cables with the Active-Distributed Temperature Sensing (A-DTS) method. The principle is that in a flowing fluid, the difference in temperature between a heated and unheated cable is a function of the fluid velocity. We outline the physical basis of the methodology and report on the deployment of a prototype A-DTS flowmeter in a fractured rock aquifer. With this design, an increase in flow velocity from 0.01 to 0.3 m s−1 elicited a 2.5°C cooling effect. It is envisaged that with further development this method will have applications where point measurements of borehole vertical flow do not fully capture combined spatiotemporal dynamics.
- On the analysis of the medium term planform dynamics of meandering rivers
- Authors: Ronald R. Gutierrez; Jorge D. Abad
Pages: 3714 - 3733
Abstract: The continuous wavelet transform is applied to the analysis of curvature signals from both synthetic meanders and 52 realizations from 16 natural meanders ranging from class B to class G (Brice classification), thus providing information on the spatial distribution of their arc-wavelength spectrum, and therefore, representing an objective characterization of meanders. Past research has studied the meander dynamics by using the centerline (short-term frame) and the valley centerline (long-term frame). The present study introduces a medium term frame, termed the mean center (MC), which is defined as the medium term coherent wave being present in the meander planimetry for a period that is strongly governed by the occurrence of cutoff events; although in the absence of them, it is present for ∼10 to ∼30 years. The MC is obtained by using a methodology that combines the capabilities of the principal component analysis and the discrete wavelet transforms. The application of wavelet cross correlation shows that peaks in the centerline curvature are strongly correlated with those of the MC suggesting that (1) a linear relationship between them may be associated to bank processes and, (2) in all other cases, a higher nonlinear relationship may be induced by autogenic hydrodynamic processes. In freely meandering rivers, compound bends, multiple loops, and cutoff events are associated to peaks in the MC local curvature. We define the planform amplitudes as the orthogonal distance of the centerline from mean center. Planform amplitudes (orthogonal distance of the centerline from mean center) are normally distributed and ranges from 2 to 20 river mean widths.
- A Kalman filter powered by H2-matrices for quasi-continuous data
- Authors: Judith Yue Li; Sivaram Ambikasaran, Eric F. Darve, Peter K. Kitanidis
Pages: 3734 - 3749
Abstract: Continuously tracking the movement of a fluid or a plume in the subsurface is a challenge that is often encountered in applications, such as tracking a plume of injected CO2 or of a hazardous substance. Advances in monitoring techniques have made it possible to collect measurements at a high frequency while the plume moves, which has the potential advantage of providing continuous high-resolution images of fluid flow with the aid of data processing. However, the applicability of this approach is limited by the high computational cost associated with having to analyze large data sets within the time constraints imposed by real-time monitoring. Existing data assimilation methods have computational requirements that increase superlinearly with the size of the unknowns m. In this paper, we present the HiKF, a new Kalman filter (KF) variant powered by the hierarchical matrix approach that dramatically reduces the computational and storage cost of the standard KF from
O(m), while producing practically the same results. The version of HiKF that is presented here takes advantage of the so-called random walk dynamical model, which is tailored to a class of data assimilation problems in which measurements are collected quasi-continuously. The proposed method has been applied to a realistic CO2 injection model and compared with the ensemble Kalman filter (EnKF). Numerical results show that HiKF can provide estimates that are more accurate than EnKF and also demonstrate the usefulness of modeling the system dynamics as a random walk in this context.
- Detection of changes in hydrologic system memory associated with
urbanization in the Great Lakes region
- Authors: Guoxiang Yang; Laura C. Bowling
Pages: 3750 - 3763
Abstract: The change of long memory with urbanization in a regional hydrologic system was investigated using both stochastic time series models and a physically based hydrologic model. Based on observed streamflow at five USGS gauge stations in the Great Lakes region, objective fractional autoregressive integrated moving average (FARIMA) model identification and estimation procedures were used for daily streamflow. The recently improved Variable Infiltration Capacity (VIC) model with urban representation was applied to simulate the water and energy response in 16 basins in the region with various degrees of urbanization. The VIC model was driven by different years' land use/cover maps, including a year 1992 base map, and year 2010 and 2030 maps projected by the Land Transformation Model. The ability of the VIC model to capture long memory of observed daily streamflow was evaluated before applying the FARIMA model to all 16 basins. Overall, the northern portion of the domain generally has larger long-term hydrologic dependence than the southern portion. Simulated streamflow statistics show that the long memory in the hydrologic system has decreased with urbanization. In order to interpret the long memory change with urbanization from a physical point of view, spectral analysis was conducted to examine the spectrum change of soil moisture content with urbanization. The decrease in simulated streamflow long memory relates to the decreased low-frequency power and amplitude of soil moisture in the deep soil layer. The long-term response of surface water systems to urbanization should be considered by water resources and urban planners.
- What is the minimum river width for the estimation of water clarity using
medium-resolution remote sensing images'
- Authors: Dehua Zhao; Meiting Lv, Xiangxu Zou, Penghe Wang, Tangwu Yang, Shuqing An
Pages: 3764 - 3775
Abstract: Numerous studies have demonstrated the feasibility of remotely sensing water clarity of lakes, reservoirs, and larger rivers using medium-resolution spatial images. However, addressing relatively small rivers or river sections is very challenging due to the adjacency effect from the riverbanks. The objectives of this study are to quantify the minimum river width for water quality remote sensing and to validate the feasibility of using medium-resolution spatial images for estimating the Secchi disk depth (SDD). A methodology was developed to quantify the minimum river width for water quality remote sensing using high-resolution spatial images from WorldView-2 and Pléiades. Our results suggest that the influential distance of the adjacency effect from the riverbank is 17.3 m, i.e., water pixels with a distance of more than 17.3 m from the shoreline experienced a minimal disturbance from the riverbank. For the 30 m spatial resolution HJ-1A image (one of Chinese civilian satellites launched in 2008), the minimum river width is 64.6–98.5 m (the variation was determined according to the river flow direction and the pixel position relative to the shoreline). Using the sections that satisfied the minimum river width requirement, a significant estimation model was established between the spectral reflectance and the SDD (R2 = 0.94), demonstrating that the minimum river width recommended in this study is practical. This work is the first study to quantify the minimum river width for water quality remote sensing and thus provides a valuable reference for remote sensing of relatively small rivers.
- Coupled multiphase flow and poromechanics: A computational model of pore
pressure effects on fault slip and earthquake triggering
- Authors: Birendra Jha; Ruben Juanes
Pages: 3776 - 3808
Abstract: The coupling between subsurface flow and geomechanical deformation is critical in the assessment of the environmental impacts of groundwater use, underground liquid waste disposal, geologic storage of carbon dioxide, and exploitation of shale gas reserves. In particular, seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources. Here we present a new computational approach to model coupled multiphase flow and geomechanics of faulted reservoirs. We represent faults as surfaces embedded in a three-dimensional medium by using zero-thickness interface elements to accurately model fault slip under dynamically evolving fluid pressure and fault strength. We incorporate the effect of fluid pressures from multiphase flow in the mechanical stability of faults and employ a rigorous formulation of nonlinear multiphase geomechanics that is capable of handling strong capillary effects. We develop a numerical simulation tool by coupling a multiphase flow simulator with a mechanics simulator, using the unconditionally stable fixed-stress scheme for the sequential solution of two-way coupling between flow and geomechanics. We validate our modeling approach using several synthetic, but realistic, test cases that illustrate the onset and evolution of earthquakes from fluid injection and withdrawal.
- Interaction between neighboring vegetation patches: Impact on flow and
- Authors: Dieter W. S. A. Meire; John M. Kondziolka, Heidi M. Nepf
Pages: 3809 - 3825
Abstract: Flow and sedimentation around patches of vegetation are important to landscape evolution, and a better understanding of these processes would facilitate more effective river restoration and wetlands engineering. In wetlands and channels, patches of vegetation are rarely isolated and neighboring patches influence one another during their development. In this experimental study, an adjacent pair of emergent vegetation patches were modeled by circular arrays of cylinders with their centers aligned in a direction that was perpendicular to the flow direction. The flow and deposition patterns behind the pair of patches were measured for two stem densities and for different patch separations (gap widths). The wake pattern immediately behind each individual patch was similar to that observed behind an isolated patch, with a velocity minimum directly behind each patch that produced a well-defined region of enhanced deposition in line with the patch. For all gap widths (Δ), the velocity on the centerline between the patches (Uc) was elevated to a peak velocity Umax that persisted over a distance Lj. Although Umax was not a function of Δ, Lj decreased with decreasing Δ. Beyond Lj, the wakes merged and Uc decayed to a local minimum. The merging of wakes and associated velocity minimum produced a local maximum in deposition downstream from and on the centerline between the patches. If this secondary region of enhanced deposition promotes new vegetation growth, the increased drag on the centerline could slow velocity between the upstream patch pair, leading to conditions favorable to their merger.
- A network-based framework for identifying potential synchronizations and
amplifications of sediment delivery in river basins
- Authors: Jonathan A. Czuba; Efi Foufoula-Georgiou
Pages: 3826 - 3851
Abstract: Long-term prediction of environmental response to natural and anthropogenic disturbances in a basin becomes highly uncertain using physically based distributed models, particularly when transport time scales range from tens to thousands of years, such as for sediment. Yet, such predictions are needed as changes in one part of a basin now might adversely affect other parts of the basin in years to come. In this paper, we propose a simplified network-based predictive framework of sedimentological response in a basin, which incorporates network topology, channel characteristics, and transport-process dynamics to perform a nonlinear process-based scaling of the river-network width function to a time-response function. We develop the process-scaling formulation for transport of mud, sand, and gravel, using simplifying assumptions including neglecting long-term storage, and apply the methodology to the Minnesota River Basin. We identify a robust bimodal distribution of the sedimentological response for sand of the basin which we attribute to specific source areas, and identify a resonant frequency of sediment supply where the disturbance of one area followed by the disturbance of another area after a certain period of time, may result in amplification of the effects of sediment inputs which would be otherwise difficult to predict. We perform a sensitivity analysis to test the robustness of the proposed formulation to model parameter uncertainty and use observations of suspended sediment at several stations in the basin to diagnose the model. The proposed framework has identified an important vulnerability of the Minnesota River Basin to spatial and temporal structuring of sediment delivery.
- Seasonal evolution of ecohydrological controls on land surface temperature
over complex terrain
- Authors: Tiantian Xiang; Enrique R. Vivoni, David J. Gochis
Pages: 3852 - 3874
Abstract: The spatiotemporal distribution of Land Surface Temperature (LST) is linked to the partitioning of the coupled surface water and energy budgets. In watersheds with a strong seasonality in precipitation and vegetation cover, the temporal evolution of LST patterns are a signature of the interactions between the land surface and atmosphere. Nevertheless, few studies have sought to understand the topographical and ecohydrological controls on LST in regions of complex terrain. Numerical watershed models, tested against spatially distributed field and remote sensing data, can aid in linking the seasonal evolution of LST to meteorology, terrain, soil, and vegetation. In this study, we use a distributed hydrologic model to explore LST patterns in a semiarid mountain basin during the transition from a dry spring to the wetter North American monsoon (NAM). By accounting for vegetation greening through remotely sensed parameters, the model reproduces LST and surface soil moisture observations derived from ground, aircraft, and satellite platforms with good accuracy at individual sites and as spatial basin patterns. Distributed simulations reveal how LST varies with elevation, slope, and aspect and the role played by the seasonal vegetation canopy in cooling the land surface and increasing the spatial variability in LST. As a result, LST is shown to track well with ecosystem-specific changes in vegetation cover, evapotranspiration, and soil moisture during the NAM. Furthermore, vegetation greening is shown to modulate the spatial heterogeneity of LST during the NAM that should be considered in subsequent atmospheric studies in regions of complex terrain.
- An integrated economic model of multiple types and uses of water
- Authors: Jonas Luckmann; Harald Grethe, Scott McDonald, Anton Orlov, Khalid Siddig
Pages: 3875 - 3892
Abstract: Water scarcity is an increasing problem in many parts of the world and the management of water has become an important issue on the political economy agenda in many countries. As water is used in most economic activities and the allocation of water is often a complex problem involving different economic agents and sectors, Computable General Equilibrium (CGE) models have been proven useful to analyze water allocation problems, although their adaptation to include water is still relatively undeveloped. This paper provides a description of an integrated water-focused CGE model (STAGE_W) that includes multiple types and uses of water, and for the first time, the reclamation of wastewater as well as the provision of brackish groundwater as separate, independent activities with specific cost structures. The insights provided by the model are illustrated with an application to the Israeli water sector assuming that freshwater resources available to the economy are cut by 50%. We analyze how the Israeli economy copes with this shock if it reduces potable water supply compared with further investments in the desalination sector. The results demonstrate that the effects on the economy are slightly negative under both scenarios. Counter intuitively, the provision of additional potable water to the economy through desalination does not substantively reduce the negative outcomes. This is mainly due to the high costs of desalination, which are currently subsidized, with the distribution of the negative welfare effect over household groups dependent on how these subsidies are financed.
- Semianalytical series solutions for three-dimensional groundwater-surface
- Authors: Ali A. Ameli; James R. Craig
Pages: 3893 - 3906
Abstract: A semianalytical grid-free series solution method is presented for modeling 3-D steady state free boundary groundwater-surface water exchange in geometrically complex stratified aquifers. Continuous solutions for pressure in the subsurface are determined semianalytically, as is the location of the water table surface. Mass balance is satisfied exactly over the entire domain except along boundaries and interfaces between layers, where errors are shown to be acceptable. The solutions are derived and demonstrated on a number of test cases and the errors are assessed and discussed. This accurate and grid-free scheme can also be a helpful tool for providing insight into lake-aquifer and stream-aquifer interactions. Here it is used to assess the impact of lake sediment geometry and properties on lake-aquifer interactions. Various combinations of lake sediment are considered and the appropriateness of the Dupuit-Forchheimer approximation for simulating lake bottom flux distribution is investigated. In addition, the method is applied to a test problem of surface seepage flows from a complex topographic surface; this test case demonstrated the method's efficacy for simulating physically realistic domains.
- Statistical framework to simulate daily rainfall series conditional on
upper-air predictor variables
- Authors: Andreas Langousis; Vassilios Kaleris
Pages: 3907 - 3932
Abstract: We propose a statistical framework to generate synthetic rainfall time series at daily resolution, conditional on predictor variables indicative of the atmospheric circulation at the mesoscale. We do so by first introducing a dimensionless measure to assess the relative influence of upper-air variables at different pressure levels on ground-level rainfall statistics, and then simulating rainfall occurrence and amount by proper conditioning on the selected atmospheric predictors. The proposed scheme for conditional rainfall simulation operates at a daily time step (avoiding discrete approaches for identification of weather states), can incorporate any possible number and combination of predictor variables, while it is capable of reproducing rainfall seasonality directly from the variation of upper-air variables, without any type of seasonal analysis or modeling. The suggested downscaling approach is tested using atmospheric data from the ERA-Interim archive and daily rainfall measurements from western Greece. The model is found to accurately reproduce several statistics of actual rainfall time series, at both annual and seasonal levels, including wet day fractions, the alternation of wet and dry intervals, the distributions of dry and wet spell lengths, the distribution of rainfall intensities in wet days, short-range dependencies present in historical rainfall records, the distribution of yearly rainfall maxima, dependencies of rainfall statistics on the observation scale, and long-term climatic features present in historical rainfall records. The suggested approach is expected to serve as a useful tool for stochastic rainfall simulation conditional on climate model outputs at a regional level, where climate change impacts and risks are assessed.
- Analysis of the impact of surface layer properties on evaporation from
porous systems using column experiments and modified definition of
- Authors: Shmuel Assouline; Kfir Narkis, Rivka Gherabli, Philippe Lefort, Marc Prat
Pages: 3933 - 3955
Abstract: The hydraulic properties of the layer at the vicinity of the soil surface have significant impact on evaporation and could be harnessed to reduce water losses. The effect of the properties of the upper layer on the evolution of phase distribution during the evaporation process is first illustrated from three-dimensional pore network simulations. This effect is then studied from experiments carried out on soil columns under laboratory conditions. Comparisons between homogeneous columns packed with coarse (sand) and fine (sandy loam) materials and heterogeneous columns packed with layers of fine overlying coarse material and coarse overlying fine material of different thicknesses are performed to assess the impact of upper layer properties on evaporation. Experiments are analyzed using the classical approach based on the numerical solution of Richards equation and semianalytical theoretical predictions. The theoretical analysis is based on the clear distinction between two drying regimes, namely, the capillary regime and the gravity-capillary regime, which are the prevailing regimes in our experiments. Simple relationships enabling to estimate the duration of stage 1 evaporation (S1) for both regimes are proposed. In particular, this led to defining the characteristic length for the gravity-capillary regime from the consideration of viscous effects at low water content differently from available expressions. The duration of S1, during which most of the water losses occur, for both the homogeneous and two-layer columns is presented and discussed. Finally, the impact of liquid films and its consequences on the soil hydraulic conductivity function are briefly discussed.
- Joint inversion of aquifer test, MRS, and TEM data
- Authors: Troels N. Vilhelmsen; Ahmad A. Behroozmand, Steen Christensen, Toke H. Nielsen
Pages: 3956 - 3975
Abstract: This paper presents two methods for joint inversion of aquifer test data, magnetic resonance sounding (MRS) data, and transient electromagnetic data acquired from a multilayer hydrogeological system. The link between the MRS model and the groundwater model is created by tying hydraulic conductivities (k) derived from MRS parameters to those of the groundwater model. Method 1 applies k estimated from MRS directly in the groundwater model, during the inversion. Method 2 on the other hand uses the petrophysical relation as a regularization constraint that only enforces k estimated for the groundwater model to be equal to MRS derived k to the extent that data can be fitted. Both methodologies can jointly calibrate parameters pertaining to the individual models as well as a parameter pertaining to the petrophysical relation. This allows the petrophysical relation to adapt to the local conditions during the inversion. The methods are tested using a synthetic data set as well as a field data set. In combination, the two case studies show that the joint methods can constrain the inversion to achieve estimates of k, decay times, and water contents for a leaky confined aquifer system. We show that the geophysical data can assist in determining otherwise insensitive k, and vice versa. Based on our experiments and results, we mainly advocate the future application of method 2 since this seems to produce the most reliable results, has a faster inversion runtime, and is applicable also for linking k of 3-D groundwater flow models to multiple MRS soundings.
- Stochastic calibration and learning in nonstationary hydroeconomic models
- Authors: M. P. Maneta; R. Howitt
Pages: 3976 - 3993
Abstract: Concern about water scarcity and adverse climate events over agricultural regions has motivated a number of efforts to develop operational integrated hydroeconomic models to guide adaptation and optimal use of water. Once calibrated, these models are used for water management and analysis assuming they remain valid under future conditions. In this paper, we present and demonstrate a methodology that permits the recursive calibration of economic models of agricultural production from noisy but frequently available data. We use a standard economic calibration approach, namely positive mathematical programming, integrated in a data assimilation algorithm based on the ensemble Kalman filter equations to identify the economic model parameters. A moving average kernel ensures that new and past information on agricultural activity are blended during the calibration process, avoiding loss of information and overcalibration for the conditions of a single year. A regularization constraint akin to the standard Tikhonov regularization is included in the filter to ensure its stability even in the presence of parameters with low sensitivity to observations. The results show that the implementation of the PMP methodology within a data assimilation framework based on the enKF equations is an effective method to calibrate models of agricultural production even with noisy information. The recursive nature of the method incorporates new information as an added value to the known previous observations of agricultural activity without the need to store historical information. The robustness of the method opens the door to the use of new remote sensing algorithms for operational water management.
- The vertical variability of hyporheic fluxes inferred from riverbed
- Authors: Roger H. Cranswick; Peter G. Cook, Margaret Shanafield, Sebastien Lamontagne
Pages: 3994 - 4010
Abstract: We present detailed profiles of vertical water flux from the surface to 1.2 m beneath the Haughton River in the tropical northeast of Australia. A 1-D numerical model is used to estimate vertical flux based on raw temperature time series observations from within downwelling, upwelling, neutral, and convergent sections of the hyporheic zone. A Monte Carlo analysis is used to derive error bounds for the fluxes based on temperature measurement error and uncertainty in effective thermal diffusivity. Vertical fluxes ranged from 5.7 m d−1 (downward) to −0.2 m d−1 (upward) with the lowest relative errors for values between 0.3 and 6 m d−1. Our 1-D approach provides a useful alternative to 1-D analytical and other solutions because it does not incorporate errors associated with simplified boundary conditions or assumptions of purely vertical flow, hydraulic parameter values, or hydraulic conditions. To validate the ability of this 1-D approach to represent the vertical fluxes of 2-D flow fields, we compare our model with two simple 2-D flow fields using a commercial numerical model. These comparisons showed that: (1) the 1-D vertical flux was equivalent to the mean vertical component of flux irrespective of a changing horizontal flux; and (2) the subsurface temperature data inherently has a “spatial footprint” when the vertical flux profiles vary spatially. Thus, the mean vertical flux within a 2-D flow field can be estimated accurately without requiring the flow to be purely vertical. The temperature-derived 1-D vertical flux represents the integrated vertical component of flux along the flow path intersecting the observation point.
- A fast nonparametric spatio-temporal regression scheme for generalized
Pareto distributed heavy precipitation
- Authors: P. Naveau; A. Toreti, I. Smith, E. Xoplaki
Pages: 4011 - 4017
Abstract: Analyzing the behavior of heavy precipitation, high temperatures, and extremes of other environmental variables has become an important research topic both for hydrologists and climatologists. Extreme value theory provides a well-developed mathematical foundation to statistically model excesses above a high threshold. Practitioners often assume that those excesses approximately follow a generalized Pareto distribution. To infer the two parameters of this distribution, a variety of estimations has been proposed and studied. Among them, maximum likelihood estimation offers an elegant way to include covariates, but imposing an explicit form on the parameters dependence. When analyzing large data sets, this procedure can be too slow and sometimes produce aberrant values due to optimization problems. To overcome these drawbacks, a method based on probability weighted moments and Kernel regression is proposed, tested, and applied to a Swiss daily precipitation data set. The method is implemented as a freely available R package.
- First-order based cumulative distribution function for solute
concentration in heterogeneous aquifers: Theoretical analysis and
implications for human health risk assessment
- Authors: F. P. J. Barros; A. Fiori
Pages: 4018 - 4037
Abstract: Quantifying the uncertainty of solute concentration in heterogeneous aquifers is an important step in both human health and ecological risk analysis. The need for a probabilistic representation of transport is justified by the incomplete characterization of the subsurface. We derive the one-point concentration cumulative distribution function (CDF) while taking into account the spatial statistical structure of the hydraulic conductivity, space dimensionality, the injection source size, the Péclet number, and the sampling volume at the monitoring location. The CDF is application oriented and derived at first order in the log-conductivity variance. We illustrate how several key parameters control the shape of the concentration CDF. The CDF shape is important since it reflects both uncertainty and the dilution state of the plume. The transition from a bimodal to a unimodal CDF is examined and results are further supported by analyzing the concentration coefficient of variation. Results indicate the significance of the statistical anisotropy ratio (i.e., the ratio between the hydraulic conductivity correlation scales) in determining the CDF shape. The importance of the sampling volume in the tails of the concentration CDF and a comparison between the proposed model with the β-CDF approach (i.e., beta distribution) are also shown. Finally, we illustrate how the framework could be used in applications by evaluating the human health risk CDF. Our results are formally valid for low to moderate heterogeneous aquifers and source sizes small as compared to the hydraulic conductivity correlation length. The proposed approach can serve as a benchmark tool for other methods.
- Quantifying the influence of deep soil moisture on ecosystem albedo: The
role of vegetation
- Authors: Zulia Mayari Sanchez-Mejia; Shirley Anne Papuga, Jessica Blaine Swetish, Willem Jan Dirk van Leeuwen, Daphne Szutu, Kyle Hartfield
Pages: 4038 - 4053
Abstract: As changes in precipitation dynamics continue to alter the water availability in dryland ecosystems, understanding the feedbacks between the vegetation and the hydrologic cycle and their influence on the climate system is critically important. We designed a field campaign to examine the influence of two-layer soil moisture control on bare and canopy albedo dynamics in a semiarid shrubland ecosystem. We conducted this campaign during 2011 and 2012 within the tower footprint of the Santa Rita Creosote Ameriflux site. Albedo field measurements fell into one of four Cases within a two-layer soil moisture framework based on permutations of whether the shallow and deep soil layers were wet or dry. Using these Cases, we identified differences in how shallow and deep soil moisture influence canopy and bare albedo. Then, by varying the number of canopy and bare patches within a gridded framework, we explore the influence of vegetation and soil moisture on ecosystem albedo. Our results highlight the importance of deep soil moisture in land surface-atmosphere interactions through its influence on aboveground vegetation characteristics. For instance, we show how green-up of the vegetation is triggered by deep soil moisture, and link deep soil moisture to a decrease in canopy albedo. Understanding relationships between vegetation and deep soil moisture will provide important insights into feedbacks between the hydrologic cycle and the climate system.
- Global-scale analysis on future changes in flow regimes using Gini and
Lorenz asymmetry coefficients
- Authors: Yoshimitsu Masaki; Naota Hanasaki, Kiyoshi Takahashi, Yasuaki Hijioka
Pages: 4054 - 4078
Abstract: By introducing two scalar quantities, namely, the Gini and Lorenz asymmetry coefficients, we examined their characteristics and applicability to the global analysis of changes in river flow regimes under future climate change. First, by applying these coefficients to river discharge data, we showed that various types of flow-duration curves can be interpreted quantitatively in terms of the seasonal inequality in the discharge (i.e., the unevenness of the temporal distribution of river discharge). Their statistical characteristics, based on five theoretical distribution functions frequently used in hydrological analysis, were also shown. Next we used these coefficients to evaluate the seasonal inequality of major global rivers using the global hydrological model H08 for four 30 year time spans (1960–1989, 2010–2039, 2040–2069, and 2070–2099) under four climate-change scenarios. We used ensembles of hydrological simulation results with five general circulation models. From the analysis of the Gini coefficient, future changes in seasonal inequality show a contrasting geographical pattern: a decreasing trend at high northern latitudes and an increasing trend in most other areas. The Lorenz asymmetry coefficient shows large changes at high northern latitudes, attributable to major shifts in the flow regime accompanied by different snow-melting properties under different future climate scenarios. Although a flow-duration curve is a pictorial representation of river discharge suitable for one specific site, by depicting the geographical distribution of these two coefficients along river channels, different characteristics of flow-duration curves at different sites can be detected, even within the same river basin.
- Groundwater flow to a pumping well in a sloping fault zone unconfined
- Authors: Ching-Sheng Huang; Shaw-Yang Yang, Hund-Der Yeh
Pages: 4079 - 4094
Abstract: This study develops a mathematical model for simulating the hydraulic head distribution in response to pumping in a sloping fault zone aquifer under a water table boundary condition. A two-dimensional equation with a sink term representing the pumping is used for describing the head distribution in the aquifer. In addition, a first-order free surface equation is adopted to represent the change in water table at the outcrop. The analytical solution of the model, derived by the Laplace and finite Fourier cosine transforms, is expressed in terms of a double series. A finite difference solution within a deformable grid framework is developed to assess the solution obtained by specifying the free surface equation at the outcrop. Based on the analytical solution, we have found that the model's prediction tends to overestimate drawdown in a late pumping period. The temporal head distribution is independent of the aquifer slope if the water table change is small, and exhibits a double-humped shape due to the effect of the free surface. The temporal drawdown predicted from the analytical solution is further compared with those measured from a pumping test conducted in northern Portugal.
- Development of an integrated modeling approach for identifying multilevel
non-point-source priority management areas at the watershed scale
- Authors: Lei Chen; Yucen Zhong, Guoyuan Wei, Yanpeng Cai, Zhenyao Shen
Pages: 4095 - 4109
Abstract: The identification of priority management areas (PMAs) at the large-basin scale is notably complex because of the random nature of watershed processes, which complicates the application of traditional deterministic PMAs. In this study, a multilevel PMA (ML-PMA) framework is designed as a new tool to pinpoint these sensitive areas, within a basin, that contribute the most to water quality deterioration. The main advantage of the ML-PMA framework is the wide availability of its supplementary tools and its complete framework, which integrates both watershed and river processes in addressing PMAs at the watershed scale. The watershed model, stream model, and a Markov chain approach are integrated to depict the dynamics of watershed processes and various water quality statutes. Based on the results of this study, the river migration process is vital for water quality degradation in the river network and significantly influenced the final PMA map. In addition, the proposed ML-PMA framework considers the impact of climatic conditions and hydrological properties and allows for a more cost-effective allocation of PMAs among different years. In the authors' view, the connectivity of PMAs in terms of flux distribution and propagation downstream on which the ML-PMA is based makes the ML-PMA framework particularly interesting for watershed non-point-source pollution control.
- IDA: An implicit, parallelizable method for calculating drainage area
- Authors: Alan Richardson; Christopher N. Hill, J. Taylor Perron
Pages: 4110 - 4130
Abstract: Models of landscape evolution or hydrological processes typically depend on the accurate determination of upslope drainage area from digital elevation data, but such calculations can be very computationally demanding when applied to high-resolution topographic data. To overcome this limitation, we propose calculating drainage area in an implicit, iterative manner using linear solvers. The basis of this method is a recasting of the flow routing problem as a sparse system of linear equations, which can be solved using established computational techniques. This approach is highly parallelizable, enabling data to be spread over multiple computer processors. Good scalability is exhibited, rendering it suitable for contemporary high-performance computing architectures with many processors, such as graphics processing units (GPUs). In addition, the iterative nature of the computational algorithms we use to solve the linear system creates the possibility of accelerating the solution by providing an initial guess, making the method well suited to iterative calculations such as numerical landscape evolution models. We compare this method with a previously proposed parallel drainage area algorithm and present several examples illustrating its advantages, including a continent-scale flow routing calculation at 3 arc sec resolution, improvements to models of fluvial sediment yield, and acceleration of drainage area calculations in a landscape evolution model. We additionally describe a modification that allows the method to be used for parallel basin delineation.
- The terms of turbulent kinetic energy budget within random arrays of
- Authors: Ana M. Ricardo; Katinka Koll, Mário J. Franca, Anton J. Schleiss, Rui M. L. Ferreira
Pages: 4131 - 4148
Abstract: This article is aimed at quantifying and discussing the relative magnitude of key terms of the equation of conservation of turbulent kinetic energy (TKE) in the inter-stem space of a flow within arrays of vertical cylinders simulating plant stems of emergent and rigid vegetation. The spatial distribution of turbulent quantities and mean flow variables are influenced by two fundamental space scales, the diameter of the stems and the local stem areal number-density. Both may vary considerably since the areal distribution of plant stems in natural systems is generally not homogeneous; they are often arranged in alternating sparse and dense patches. The magnitude of the terms of the budget of TKE in the inter-stem space has seldom been quantified experimentally and is currently not well known. This work addresses this research need. New databases, consisting of three-component LDA velocity series and two-component PIV velocity maps, obtained in carefully controlled laboratory conditions, were used to calculate the terms of the TKE budget. The physical system comprises random arrays of rigid and emergent cylinders with longitudinally varying areal number-density. It is verified that the main source of TKE is vortex shedding from individual cylinders. The rates of production and dissipation are not in equilibrium. Regions with negative production, a previously unreported feature, are identified. Turbulent transport is particularly important along the von Kármán vortex street. Convective rate of change of TKE and pressure diffusion are most relevant in the vicinity of the cylinders.
- Modeling substrate-bacteria-grazer interactions coupled to substrate
transport in groundwater
- Authors: Bijendra M. Bajracharya; Chuanhe Lu, Olaf A. Cirpka
Pages: 4149 - 4162
Abstract: Models of microbial dynamics coupled to solute transport in aquifers typically require the introduction of a bacterial capacity term to prevent excessive microbial growth close to substrate-injection boundaries. The factors controlling this carrying capacity, however, are not fully understood. In this study, we propose that grazers or bacteriophages may control the density of bacterial biomass in continuously fed porous media. We conceptualize the flow-through porous medium as a series of retentostats, in which the dissolved substrate is advected with water flow whereas the biomasses of bacteria and grazers are considered essentially immobile. We first model a single retentostat with Monod kinetics of bacterial growth and a second-order grazing law, which shows that the system oscillates but approaches a stable steady state with nonzero concentrations of substrate, bacteria, and grazers. The steady state concentration of the bacteria biomass is independent of the substrate concentration in the inflow. When coupling several retentostats in a series to mimic a groundwater column, the steady state bacteria concentrations thus remain at a constant level over a significant travel distance. The one-dimensional reactive transport model also accounts for substrate dispersion and a random walk of grazers influenced by the bacteria concentration. These dispersive-diffusive terms affect the oscillations until steady state is reached, but hardly the steady state value itself. We conclude that grazing, or infection by bacteriophages, is a possible explanation of the maximum biomass concentration frequently needed in bioreactive transport models. Its value depends on parameters related to the grazers or bacteriophages and is independent of bacterial growth parameters or substrate concentration, provided that there is enough substrate to sustain bacteria and grazers.
- CO2 injectivity in saline aquifers: The impact of non-Darcy flow, phase
miscibility, and gas compressibility
- Authors: Ana Mijic; Tara C. LaForce, Ann H. Muggeridge
Pages: 4163 - 4185
Abstract: A key aspect of CO2 storage is the injection rate into the subsurface, which is limited by the pressure at which formation starts to fracture. Hence, it is vital to assess all of the relevant processes that may contribute to the pressure increase in the aquifer during CO2 injection. Building on an existing analytical solution for immiscible and spatially varying non-Darcy flow, this paper presents a mathematical model that accounts for combined effects of non-Darcy flow, phase miscibility, and gas compressibility in radial two-phase displacements. Results show that in low-permeability formations when CO2 is injected at high rates, non-Darcy simulations forecast better displacement efficiency compared to flow under Darcy conditions. This will have a positive effect on the formation CO2 storage capacity. This, however, comes at the cost of increased well pressures. More favorable estimations of the pressure buildup are obtained when CO2 compressibility is taken into account because reservoir pressures are reduced due to the change in the gas phase properties. Also, non-Darcy flow results in a significant reduction in halite precipitation in the near-well region, with a positive effect on CO2 injectivity. In the examples shown, non-Darcy flow conditions may lead to significantly different pressure and saturation distributions in the near-well region, with potentially important implications for CO2 injectivity.
- Improved flow velocity estimates from moving-boat ADCP measurements
- Authors: B. Vermeulen; M. G. Sassi, A. J. F. Hoitink
Pages: 4186 - 4196
Abstract: Acoustic Doppler current profilers (ADCPs) are the current standard for flow measurements in large-scale open water systems. Existing techniques to process vessel-mounted ADCP data assume homogeneous or linearly changing flow between the acoustic beams. This assumption is likely to fail but is nevertheless widely applied. We introduce a new methodology that abandons the standard assumption of uniform flow in the area between the beams and evaluate the drawbacks of the standard approach. The proposed method strongly reduces the extent over which homogeneity is assumed. The method is applied to two field sites: a mildly curved bend near a junction featuring a typical bend flow and a sharply curved bend that features a more complex sheared flow. In both cases, differences are found between the proposed method and the conventional method. The proposed technique yields different results for secondary flow patterns compared with the conventional method. The velocity components estimated with the conventional method can differ over 0.2 m/s in regions of strong shear. We investigate the number of repeat transects necessary to isolate the mean flow velocity vector from the raw ADCP signal, discarding the influences of noise, positioning and projection errors, and turbulence. Results show that several repeat transects are necessary. The minimum number of repeat measurements needed for robust mean velocity estimates is reduced when applying the proposed method.
- A multimodel data assimilation framework via the ensemble Kalman filter
- Authors: Liang Xue; Dongxiao Zhang
Pages: 4197 - 4219
Abstract: The ensemble Kalman filter (EnKF) is a widely used data assimilation method that has the capacity to sequentially update system parameters and states as new observations become available. One noticeable feature of the EnKF is that it not only can provide real-time updates of model parameters and state variables, but also can give the uncertainty associated with them in each assimilation step. The natural system is open and complex, rendering it prone to multiple interpretations and mathematical descriptions. In this paper, a multimodel data assimilation method is proposed by embedding the EnKF into the Bayesian model averaging framework to account for the uncertainty stemming from the model itself. An illustrative example, considering both hydrogeological and groundwater flow uncertainties, is employed to demonstrate the proposed multimodel data assimilation approach via the EnKF. Results show that statistical bias and uncertainty underestimation can occur when the data assimilation process relies on a single postulated model. The posterior model weight can adjust itself dynamically in time according to its consistency with observations. The performances of log conductivity estimation and head prediction are compared to the standard EnKF method based on the postulated single model and the proposed multimodel EnKF method. Comparisons show that the multimodel EnKF performs better in terms of statistical measures, such as log score and coverage, when sufficient observations have been assimilated in this case.