bluuebunny/crossref_metadata_2025 huggingface dataset:
A Stochastic Model of a Fractured Rock Conditioned by Measured Information
Authors: Andersson Johan , Shapiro Allen M. , Bear Jacob
Published: February 2008

A method for the modeling of a fractured rock is developed which takes into account the uncertainty in the fracture network geometry as well as actually measured information, such as that obtained from cores. Based on certain simplifying assumptions, of which the most important are planar and independent fractures, a stochastic a priori model is formulated. The real fracture network is assumed to be a realization of this a priori model. Since measurements are performed on the real network, two different kinds of information are made available. The first kind is of deterministic nature and expresses the actual location of intercepted fractures; by inference the other part is probabilistic, given as the probability of observing a fracture intersecting the model region. This observation probability is shown to depend on the a priori model, on the geometry of the region and on the measurements only. A conditional model is formulated where each realization consists of the actually observed fractures and an additional number of stochastically generated fractures obtained by employing the probabilistic information. The number of stochastically generated fractures is a stochastic variable, the distribution of which depends on the number of fractures observed and the observation probability. Even if the rock is penetrated with only a few cores, it is possible to quantify the statistics of properties, such as the total leakage into a tunnel or the concentration of pollutants close to a waste repository. By increasing the number of cores, the uncertainty in these values is reduced. The amount of uncertainty reduction can be quantified by applying the model of the investigated domain taking into account the information from the additional measurements. As a demonstration, the proposed model is applied to a simple problem of steady state two‐dimensional flow in a vertical plane. It appears that the technique presented may serve as a powerful tool for quantifying uncertainties in flow problems and in providing guidance on how to acquire additional information of the fractured network in a given domain of fractured rock.
Instrumental Price Estimates and Residential Water Demand
Authors: Jones C. Vaughan , Morris John R.
Published: February 2008

Instrumental estimates of two price specifications, one motivated by the consumer decision problem given full information about rates and charges and the other an average price formulation, are developed to correct for measurement error when residential water sales are made at a schedule of rates, rather than at uniform prices. Annual water purchases of single‐family residences are regressed on these instrumental price estimates, family income, and household size by ordinary least squares, based on a sample of 326 observations from metropolitan Denver, Colorado, for 1976. The resulting demand estimates are robust to the price concept specified, given proportional variation in all rates and charges, and are consistent with findings in the literature. The overall price elasticity estimates range between −0.14 in a linear model to −0.44 in a log‐log model, while the estimated income elasticity varies between 0.40 and 0.55.
Competition Versus Optimal Control in Groundwater Pumping When Demand is Nonlinear
Authors: Allen Richard C. , Gisser Micha
Published: February 2008

This article considers the issue of optimal control versus no control in groundwater pumping under the assumption of a nonlinear demand function for water use. We confirm for the case of the nonlinear demand function what had been demonstrated for the case of a linear demand function: namely, if water rights are properly defined and if the storage capacity of the aquifer is relatively large, the difference between a strategy of no control and a strategy of optimal control is small and thus can be ignored for practical policy considerations. Furthermore, we demonstrate that even if simulated optimal control yields slightly better results than no control, a strategy of no control is likely to yield better results than optimal control, unless we can be sure that the estimated demand for groundwater is very close to the true demand.
Two‐Component Extreme Value Distribution for Flood Frequency Analysis
Authors: Rossi Fabio , Fiorentino Mauro , Versace Pasquale
Published: February 2008

Theoretical considerations, supported by statistical analysis of 39 annual flood series (AFS) of Italian basins, suggest that the two‐component extreme value (TCEV) distribution can be assumed as a parent flood distribution, i.e., one closely representative of the real flood experience. This distribution belongs to the family of distributions of the annual maximum of a compound Poisson process, which is a solid theoretical basis for AFS analysis. However, the two‐parameter distribution of this family, obtained on the assumption of identically distributed floods, does not account for the high variability of both observed skewness and largest order statistics, so that a significant number of observed floods qualify as outliers under this distribution. The more general TCEV distribution assumes individual floods to arise from a mixture of two exponential components. Its four parameters can be estimated by the maximum likelihood method. A regionalized TCEV distribution, with parameters representative of a set of 39 Italian AFS's, was shown to closely reproduce the observed distribution of skewness and that of the largest order statistic.
Estimation of Skewness of Hydrologic Variables
Authors: Yevjevich Vujica , Obeysekera Jayantha T. B.
Published: February 2008

Various methods of estimation of the skewness coefficient of hydrologic random variables are compared with respect to bias, variance, mean square error, and robustness. The underlying population distributions are limited to gamma (Pearson type 3) and lognormal. The simulation results show that a new skewness estimator that uses the estimated covariance between the subsample mean and the subsample variance has a lesser bias than the ordinary skewness stimators. It may be used as a surrogate when the sample size is small and population skewness large. The superior estimates of skewness resulting from the maximum likelihood estimation of parameters of the known underlying distribution and the robustness studies point to the importance of the correct inference on the type of underlying probability distribution function in hydrologic applications.
Forecasting Water Levels for Lake Chad
Authors: Guganesharajah K. , Shaw E. M.
Published: February 2008

A model for predicting the low levels in Lake Chad and a statistical model for describing the probability of the low‐level variations at various periods ahead are presented. The first model will assist in the planning of the agricultural operations one season in advance for schemes that rely on the lake water. The second provides the low levels on a probabilistic basis and can be used to measure the risk involved in selecting various abstraction levels of water from the lake during the proposed life span of the projects, and this is also a particularly useful aid in the economic and planning studies for future developments. The probabilistic model is based on the Markov chain process applied to two statistical models of the main input variable (the runoff from the River Chari); the first assuming the annual discharges to be random and the second incorporating significant cyclical components, although determined from inadequate data, and a large stochastic component.
Modeling efficient water allocation in a conjunctive use regime: The Indus Basin of Pakistan
Authors: O'Mara Gerald T. , Duloy John H.
Published: February 2008

Efficient resource use where ground‐ and surface waters are used conjunctively may require special policies to rationalize the interaction between water use by farmers and the response of the stream aquifer system. In this paper, we examine alternative policies for achieving more efficient conjunctive use in the Indus Basin of Pakistan. Using a simulation model which links the hydrology of a conjunctive stream aquifer system to an economic model of agricultural production for each of 53 regions of the basin together with a network model of the flows in river reaches, link canals, and irrigation canals, we have studied the joint effect of various canal water allocation and associated private tube well tax or subsidy policies on overall system efficiency. The results suggest that large gains in agricultural production and employment are possible, given more efficient policies.
A Comparison of Rainfall‐Runoff Modeling Techniques on Small Upland Catchments
Authors: Loague Keith M. , Freeze R. Allan
Published: February 2008

This paper reports a set of model performance calculations for three event‐based rainfall‐runoff models on three data sets involving 269 events from small upland catchments. The models include a regression model, a unit hydrograph model, and a quasi‐physically based model. The catchments are from the Washita River Experimental Watershed, Oklahoma; the Mahantango Creek Experimental Watershed, Pennsylvania; and the Hubbard Brook Experimental Forest, New Hampshire. Model performance was assessed for a verification period that is carefully distinguished from the calibration period. Performance assessment was carried out both in forecasting mode and in prediction mode. The results show surprisingly poor forecasting efficiencies for all models on all data sets. The unit hydrograph model and the quasi‐physically based model have little forecasting power; the regression model is marginally better. The performance of the models in prediction mode is better. The regression model and the unit hydrograph model showed acceptable predictive power, but the quasi‐physically based model produced acceptable predictions on only one of the three catchments. We believe that the primary barrier to the successful application of physically based models in the field lies in the scale problems that are associated with the unmeasurable spatial variability of rainfall and soil hydraulic properties. The fact that simpler, less data intensive models provided as good or better predictions than a physically based model is food for thought.
Lateral Solute Concentration Gradients in Stratified Eutrophic Lakes
Authors: Stauffer Robert E.
Published: February 2008

Lateral concentration gradients in dissolved oxygen and phosphorus were studied in the metalimnion of Lake Mendota and the hypolimnion of Green Lake, Wisconsin. Oxygen concentrations were invariably lower (by up to 4.5 mg/L) in the 3‐m interval overlying shelf sediments as compared to adjacent stations in deeper water. Conversely, phosphorus concentrations were up to 65 mg/m3 higher overlying the shelves. In Mendota, the “shelf shift,” −ΔO/ΔP, was low as compared to expectations based on Redfield's equation for the aerobic oxidation of sedimenting phytoplankton; this difference indicates a net sediment release of P under aerobic conditions, corroborating laboratory studies. For Lake Mendota a phosphorus profile at the deep hole station underestimates total lake phosphorus by circa 3% in midsummer. Because of its elongated asymmetric basin and related factors, the deep hole sampling bias is larger (circa 15%) for Green Lake. Based on lateral oxygen gradients and flux‐gradient computations, the lateral eddy diffusivity is 2 × 105 m2 day−1 in the metalimnion of Mendota and the hypolimnion of Green Lake.
Analysis of the Spatial Structure of Properties of Selected Aquifers
Authors: Hoeksema Robert J. , Kitanidis Peter K.
Published: February 2008

Data from 31 regional aquifers are analyzed to identify the horizontal spatial correlation structure of transmissivity, hydraulic conductivity, and storage coefficient. Three parameters are estimated: the variance of small‐scale variability (or nugget) and the variance and integral scale (range) of an exponential covariance function. The assumption of normality of the aforementioned geohydrologic parameters and their logarithmic transformations is also examined. Results are obtained which indicate that the logarithms of these properties generally pass normality tests.
Interannual streamflow variability in the United States based on principal components
Authors: Lins Harry F.
Published: February 2008

Interannual modes of streamflow variation at 106 locations across the United States during the period 1931–1978 are defined by using principal components. Five statistically significant components are found to account for more than 56% of the total streamflow variance. The first principal component represents a nationwide tendency for either above‐ or below‐mean streamflow. The second component represents a north‐south opposition in departures from mean flow, and the third, an east‐west opposition. Higher‐order components (fourth and fifth) geographically depict regional patterns of opposition in the sign of streamflow departures between coastal‐continental areas and between the northern and southern plains, respectively. Analyses using spatially and temporally modified data sets indicate that the first three components (which explain 45% of the variance) are quite stable spatially, while only the first component is stable temporally. Time series analysis of principal component scores indicates that all but the fourth component are first‐order autoregressive processes, as is mean annual nationwide streamflow. The fourth component is an autoregressive (AR)(2) process. In general, the principal components of streamflow are found to exhibit more persistence over annual time scales than the mean annual flow data themselves.
Continuous Convolution With Hydrologic Data
Authors: Chapman T. G.
Published: February 2008

The integral form of the convolution equation can be used for hydrologic data sampled at equal time increments if simple functional forms are assumed for the change in the hydrologic variables between sampling points. The forms studied here are a step function, linear segment, and sliding polynomial, and algorithms are presented for convolution of all combinations of these functions. The effect of the different assumptions is demonstrated by a sample data set. These algorithms have three advantages: an appropriate functional form can be selected for the two variables to be convolved, different time increments may be used for the two variables, and the output may be calculated at any point in continuous time, not just at multiples of the sampling increments. The algorithms may also be applied to deconvolution but suffer many of the difficulties of matrix inversion techniques when the data contain errors or are derived from a system which is only approximately linear.
Transient Flow to a Large‐Diameter Well in an Aquifer With Storative Semiconfining Layers
Authors: Moench Allen F.
Published: February 2008

The Hantush theory of leaky aquifers with storge in the semiconfining layers is combined with large‐diameter well theory to produce equations that can be used in the analysis of pumped‐well and observation well data for stratified formations. Included in the equations are storage in the pumped well and a linear resistance to flow at the sand face or well bore skin. Three cases proposed by Hantush are considered. These depend upon whether the upper boundary of the overlying semiconfining layer or the lower boundary of the underlying semiconfining layer are constant head or no‐flow boundaries. Laplace transform solutions, valid for the complete time domain, are given for each of the three cases for the hydraulic head in the pumped well, the aquifer, and each of the semiconfining layers. Type cures obtained by numerical inversion are selected to illustrate the effects of well bore storage, well bore skin, and leakage. Although several dimensionless parameters are involved, these parameters tend to influence the character of different portions of the type curves, suggesting that unique matches are possible. The type curves show that well bore storage in a large‐diameter well may completely obliterate effects of leakage derived from compressible storage in semiconfining layers. For the purposes of aquifer testing, it may be possible to reduce the magnitude of well bore storage in a large‐diameter well and thus reveal the presence of leaky semiconfining layers. This may help to prevent erroneous interpretation of the well test data and incorrect evaluation of the aquifer parameters.
Moments of Catchment Storm Area
Authors: Eagleson Peter S. , Wang Qinliang
Published: February 2008

The portion of a catchment covered by a stationary rainstorm is modeled by the common area of two overlapping circles. Given that rain occurs within the catchment and conditioned by fixed storm and catchment sizes, the first two moments of the distribution of the common area are derived from purely geometrical considerations. The variance of the wetted fraction is shown to peak when the catchment size is equal to the size of the predominant storm. The conditioning on storm size is removed by assuming a probability distribution based upon the observed fractal behavior of cloud and rainstorm areas.
Estimating Total Suspended Sediment Yield With Probability Sampling
Authors: Thomas Robert B.
Published: February 2008

The “Selection At List Time” (SALT) scheme controls sampling of concentration for estimating total suspended sediment yield. The probability of taking a sample is proportional to its estimated contribution to total suspended sediment discharge. This procedure gives unbiased estimates of total suspended sediment yield and the variance of the estimate while automatically emphasizing sampling at higher flows. When applied to real data with known yield, the SALT method underestimated total suspended sediment yield by less than 1%, whereas estimates by the flow duration sediment rating curve method averaged about 51% underestimation. Implementing the SALT scheme requires obtaining samples with a pumping sampler, stage sensing device, and small battery‐powered computer.
Analysis of Well‐Aquifer Response to a Slug Test
Authors: Kabala Z. J. , Pinder G. F. , Milly P. C. D.
Published: February 2008

The response of a fully penetrating well to a slug test in a confined aquifer can be described by a single differential equation that is valid for any degree of damping. Although an analytical solution is not available, numerical methods are readily applied. The impact of nonlinear terms becomes significant only when the initial water level displacement is a large fraction of the effective water column height. Previously published approximate solutions for underdamped response are sometimes very accurate.
Geochemistry of Groundwater in Cretaceous Sediments of the Southeastern Coastal Plain of Eastern Mississippi and Western Alabama
Authors: Lee Roger W.
Published: February 2008

Geochemical samples of waters along two hydrologic flow paths in four Upper Cretaceous aquifers of northeastern Mississippi and western Alabama indicate similar geochemical evolution of their respective waters. The waters of the Coker, Gordo, and Eutaw‐McShan aquifers, noncalcareous sands, increase downgradient in dissolved solids and pH, and are dominated by sodium and bicarbonate ions, which generally result from a calcite dissolution‐cation exchange process. Increases in dissolved iron from oxidation reduction reactions followed by decreases in total inorganic carbon from siderite precipitation occur along the flow paths. As the total inorganic carbon increases, carbon 13 (δ13C) generally is enriched in the moving waters, indicating the addition of a predominantly heavy source of carbon, most likely dissolving calcite. In the Coker aquifer δ13C values in the waters become more negative downgradient, resulting from lignite oxidation, followed by δ13C values becoming more positive, resulting from dissolving calcite and perhaps some mixing with brines. In northeastern Mississippi the Ripley aquifer, a calcareous sand, initially contains calcium‐bicarbonate dominated water that evolves to a sodium‐ bicarbonate dominated water downgradient, primarily from the calcite dissolution‐cation exchange process. Feldspar hydrolysis to kaolinite dominates aluminosilicate reactions in the upgradient parts of the aquifers. Authigenesis of smectite clay may be occurring in the deeper, downgradient parts of the aquifers.
The Development of Multiple Seepage Faces on Layered Slopes
Authors: Rulon Jennifer J. , Rodway Ray , Freeze R. Allan
Published: February 2008

This study provides an analysis of the water table configuration and hydraulic‐head distribution in layered hillsides. A finite‐element model was used to simulate two‐dimensional, saturated‐unsaturated, steady state flow through layered slopes. A laboratory sand tank experiment was used to verify the physical foundation of the mathematical model. It is shown that layered slopes feature multiple seepage faces, perched water tables, and wedge‐shaped unsaturated zones. The hydraulic‐head distribution and water table configuration are strongly dependent on the position of the impending layers and the ratio of the hydraulic conductivity between adjacent layers. This work has geotechnical implications with regard to slope stability and the control of groundwater inflows into excavations. It has hydrogeological implications with regard to flow path analysis in contamination studies. It has geomorphological implications with respect to landform development by mass movements and surface water erosions, and to drainage network development through piping.
Hurst Behavior of Shifting Level Processes
Authors: Ballerini Rocco , Boes Duane C.
Published: February 2008

This note illustrates that certain shifting level processes possess long‐term dependence and preserve the Hurst effect for the rescaled adjusted range. Although such processes belong to a stable domain of attraction, and not that of fractional Brownian motion, they do have asymptotic behavior of the rescaled adjusted range identical to that of fractional Brownian noise; further, they are easily simulated. Other shifting level processes belonging to the same stable domain of attraction preserve the Hurst effect for the raw and adjusted ranges but not for the rescaled adjusted range.
Field Determination of the Three‐Dimensional Hydraulic Conductivity Tensor of Anisotropic Media: 1. Theory
Authors: Hsieh Paul A. , Neuman Shlomo P.
Published: February 2008

A field method is proposed for determining the three‐dimensional hydraulic conductivity tensor and specific storage of an anisotropic porous or fractured medium. The method, known as cross‐hole testing (to distinguish it from conventional single‐hole packer tests), consists of injecting fluid into (or withdrawing fluid from) packed‐off intervals in a number of boreholes and monitoring the transient head response in similar intervals in neighboring boreholes. The directions of the principal hydraulic conductivities need not be known prior to the test, and the boreholes may have arbitrary orientations (e.g., they can all be vertical). An important aspect of the proposed method is that it provides direct field information on whether it is proper to regard the medium as being uniform and anisotropic on the scale of the test. The first paper presents theoretical expressions describing transient and steady state head response in monitoring intervals of arbitrary lengths and orientations, to constant‐rate injection into (or withdrawal from) intervals having similar or different lengths and orientations. The conditions under which these intervals can be treated mathematically as points are investigated by an asymptotic analysis. The effect of planar no‐flow and constant‐head boundaries on the response is analyzed by the theory of images. The second paper describes the field methodology and shows how the proposed approach works in the case of fractured granitic rocks.
Assessment of the Instantaneous Unit Hydrograph Derived From the Theory of Topologically Random Networks
Authors: Karlinger M. R. , Troutman B. M.
Published: February 2008

An instantaneous unit hydrograph (iuh) based on the theory of topologically random networks (topological iuh) is evaluated in terms of sets of basin characteristics and hydraulic parameters. Hydrographs were computed using two linear routing methods for each of two drainage basins in the southeastern United States and are the basis of comparison for the topological iuh's. Elements in the sets of basin characteristics for the topological iuh's are the number of first‐order streams only, (N), or the nuber of sources together with the number of channel links in the topological diameter (N, D); the hydraulic parameters are values of the celerity and diffusivity constant. Sensitivity analyses indicate that the mean celerity of the internal links in the network is the critical hydraulic parameter for determining the shape of the topological iuh, while the diffusivity constant has minimal effect on the topological iuh. Asymptotic results (source‐only) indicate the number of sources need not be large to approximate the topological iuh with the Weibull probability density function.
An Overview of the Law of Groundwater Management
Authors: Tarlock A. Dan
Published: February 2008

Groundwater management law has evolved in this century from a simple rule of capture to a variety of rules that require sharing among claimants, both within and outside of groundwater basins. Courts and legislatures have modified the law of groundwater in response to aquifer depletion. Most of the change has occurred in the Far West, but eastern states are now modifying their law as shortages and use conflicts intensify. Arizona, Colorado, and New Mexico have developed the most sophisticated conservation regimes that attempt to limit groundwater use to improve methods of extraction and to move water to higher valued uses. Other large groundwater using states are also implementing or considering similar conservation regimes. Groundwater conservation is encouraged by a recent Supreme Court decision that holds that groundwater is subject to the negative commerce clause. The decision has the effect of forcing states to justify conservation regimes that block out‐of‐state and perhaps in‐state access to the resource.
The State as a Participant in Water Markets: Appropriate Roles for Congress and the Courts
Authors: DuMars Charles T.
Published: February 2008

The Supreme Court has ruled that water is a commodity in commerce the same as coal and oil and gas. It has held further that automatic state ownership of the resource because the water is within a state's boundaries is a legal fiction. This ruling will require substantial readjustment by the states including possible acquisition of water by the states in the water market the same as any private water right holder. If the state becomes the owner of water resources, it may lease those water resources for use within the state and at the same time preserve sufficient control over the resource to continue to function as a viable political entity in the federal system. The proper role of the Supreme Court in evaluating state attempts at ownership of their water resources should be to support the states in this effort and to protect the states from efforts by Congress to preclude such state ownership.
Risk Costs for New Dams: Economic Analysis and Effects of Monitoring
Authors: Paté‐Cornell M. Elisabeth , Tagaras George
Published: February 2008

This paper presents new developments and illustrations of the introduction of risk and costs in cost‐benefit analysis for new dams. The emphasis is on a method of evaluation of the risk costs based on the structure of the local economy. Costs to agricultural property as well as residential, commercial, industrial, and public property are studied in detail. Of particular interest is the case of sequential dam failure and the evaluation of the risk costs attributable to a new dam upstream from an existing one. Three real cases are presented as illustrations of the method: the Auburn Dam, the Dickey‐Lincoln School Project, and the Teton Dam, which failed in 1976. This last case provides a calibration tool for the estimation of loss ratios. For these three projects, the risk‐modified benefit‐cost ratios are computed to assess the effect of the risk on the economic performance of the project. The role of a warning system provided by systematic monitoring of the dam is analyzed: by reducing the risk costs, the warning system attenuates their effect on the benefit‐cost ratio. The precursors, however, can be missed or misinterpreted: monitoring does not guarantee that the risks to human life can be reduced to zero. This study shows, in particular, that it is critical to consider the risk costs in the decision to build a new dam when the flood area is large and densely populated.
Fundamental Problems in the Stochastic Convection‐Dispersion Model of Solute Transport in Aquifers and Field Soils
Authors: Sposito Garrison , Jury William A. , Gupta Vijay K.
Published: February 2008

The stochastic convection‐dispersion equation (CDE) and its application to field scale subsurface solute transport are investigated with respect to their physical and mathematical foundations. It is shown that even the best‐developed stochastic CDE models involve physical approximations and mathematical assumptions which stand in need of much more rigorous theoretical study and detailed field experimentation. The stochastic convection‐dispersion model does not yet resolve clearly the mathematical conditions necessary in order to relate the mean solute concentration calculated with a field scale stochastic CDE to measured values of the solute concentration determined in a single field experiment. The “scale effect” in respect to solute dispersion coefficients has been studied only under conditions in which results of little predictive value can be obtained. Without the clarification of these and other fundamental issues raised in the present paper, it seems prudent to conclude that additional theoretical research on field scale solute dispersion is needed and that the stochastic convection‐dispersion model does not yet warrant unqualified use as a quantitative predictive tool in the management of solute movement in aquifers and field soils.
Stochastic Modeling of the Space‐Time Structure of Atmospheric Chemical Deposition
Authors: Egbert Gary D. , Lettenmaier Dennis P.
Published: February 2008

A multivariate space‐time stochastic model suitable for the analysis of weekly atmospheric chemistry wet deposition measurements is described. The model is hierarchical, with weekly ion concentration fields represented as the sum of a persistent long‐term mean field, and yearly and weekly variation fields. A simple method of moments estimation scheme is proposed which exploits the hierarchical nature of the model to separate spatial structure at weekly, yearly, and persistent time scales. Estimation of both isotropic and anisotropic covariance functions are considered. The model was applied to precipitation, sulfate concentration, and pH measurements made in the Northeastern United States during 1980–1981. While significant spatial correlation was found at weekly and longer (long‐term mean) time scales, there was little or no temporal correlation. The observed spatial correlation was substantially anisotropic, particularly for precipitation and sulfate concentration fields. The anisotropy, as well as correlation length scales, showed strong seasonal variations. Substantial differences were apparent in the spatial structure of pH and sulfate, with sulfate more closely linked to precipitation. An application of a multivariate version of the model showed that the spatial structure of the sulfate fields is not due solely to the spatial structure of the precipitation fields.
Water Discharge and Suspended Sediment Concentrations in the Amazon River: 1982–1984
Authors: Richey Jeffrey E. , Meade Robert H. , Salati Eneas , Devol Allan H. , Nordin Carl F. , Santos Umberto Dos
Published: February 2008

An equal‐width‐increment procedure was developed to measure water discharge and the suspended sediment load of the Amazon River and its principal tributaries. A variable speed hydraulic winch deploys an instrument array of a sounding weight, Price current meter, and collapsible bag sampler by lowering it from the surface to the bottom and back at a constant velocity. Eighteen verticals are taken at main stem stations (fewer on tributaries), with positioning determined by shipboard observation with a sextant monitoring angles from a three‐marker baseline on the shore. Confidence intervals (95%) for discharge and the fluxes of fine (< 0.063 mm) and coarse (> 0.063 mm) suspended sediments were 5%, 10%, and 20%, respectively. Water discharge varied from 31,700 m3/s to 69,700 m3/s upriver at Vargem Grande and from 91,700 m3/s to 203,000 m3/s downriver at Obidos. Concentrations of fine suspended sediments generally decreased downstream from 220–490 mg/L at Vargem Grande to 110–250 mg/L at Sao Jose do Amatari. Large concentrations of fines at high water in the Rio Madeira of 590–770 mg/L increased downstream concentrations of fines in the Amazon. Coarse suspended sediments had some of the same distribution and transport patterns as the fines but with only 20–30% of the concentration.
On Binary Time Series Obtained From Continuous Time Point Processes Describing Rainfall
Authors: Guttorp Peter
Published: February 2008

Recent work on modeling rainfall occurrence has used continuous time point process models. In many cases the available data is not sufficiently precise to properly fit such a model. For example, if only occurrence or nonoccurrence of precipitation is given daily, a more appropriate model would be a binary time series. In this work we relate some parameters of the time series thus obtained to parameters of the underlying (but not observed) continuous time process. We carry out the details for several models proposed in the literature, such as the Neyman‐Scott Poisson cluster process and the Smith‐Karr renewal Cox process. An application of the theory is illustrated on some Washington State rainfall data.
A Frequency Domain Analysis of Groundwater Quality Fluctuations: Interpretation of Field Data
Authors: Duffy Christopher J. , Gelhar Lynn W.
Published: February 2008

Environmental tracer or pollution patterns in groundwater have been regarded as a qualitative means of studying complex or large‐scale hydrogeologic systems. However, questions have arisen as to whether the “natural state” analog has quantitative value, such as for the estimation of transport or aquifer parameters. In this paper we demonstrate the application of spectral analysis and frequency domain methods to temporal tracer patterns for the physical interpretation of transient environmental tracers in a variety of hydrologic settings. Three case studies are examined where the source of environmental tracer is represented as a stochastic process. Process and parameter estimation is performed by comparison of the theoretical transfer function and phase spectrum. The most important result of this paper is that different source configurations (nonpoint, point, etc.) and different groundwater flow patterns produce unique frequency response characteristics for solutes within each system. It is this feature which allows us to make inference about the governing physical processes and parameters.
Urban Water Balance: 1. A Model for Daily Totals
Authors: Grimmond C. S. B. , Oke T. R. , Steyn D. G.
Published: February 2008

The water balance provides a framework through which to study the interactions between the elements of the hydrologic cycle. This paper presents a simple model for evaluating the components of the urban water balance based on standard climate data and easily obtained parameters to describe the site. The time scale can be varied from 1 day to at least 1 year depending on the availability of appropriate input data and the form of the evapotranspiration submodel chosen. The evapotranspiration model proposed is of the combination type with modifications to allow for application to the suburban environment. An important methodological concept throughout the model is the recognition that a suburban area can be subdivided into three discrete surface types for hydroclimate purposes (impervious, pervious unirrigated, and pervious irrigated). Presented in this paper is an outline of the model, sensitivity analyses, and information for its implementation.
A Discrete Conceptualization of a Volterra Series Model for Surface Runoff
Authors: Napiórkowski Jaroslaw J. , Kundzewicz Zbigniew W.
Published: February 2008

The Volterra series rainfall‐runoff model used to be regarded as a nonlinear black box with no correspondence between the physical prototype and the model parameters. However, as was outlined in earlier contributions by Napiórkowski and coauthors (J. J. Napiórkowski, 1978, 1983; J. J. Napiórkowski and W. G. Strupczewski, 1979, 1981; J. J. Napiórkowski and P. O'Kane, 1984), the output signal of a cascade of identical nonlinear reservoirs can be approximately expressed in the form of a Volterra series model. This offers obvious advantages in the process of identification due to the parsimony of parameters. The conceptualization of the Volterra series model performed in the present study is based on a state space formulation within the discrete framework justified in view of the inherently discrete problems that we are forced to deal with in practice. The methodology presented is tested on data from the catchment of the Cache River in southern Illinois.
Existence Values and Normative Economics: Implications for Valuing Water Resources
Authors: Brookshire David S. , Eubanks Larry S. , Sorg Cindy F.
Published: February 2008

The definitional issues and conceptual framework of existence value are explored. It is argued that existence value may have two components (1) an economic component that is consistent with utility maximizing behavior and (2) an ethical component that is inconsistent with normative benefit‐cost assumptions. Issues as how to appropriately include a measure of existence value within a utility maximizing framework are also explored. Difficult conceptual problems arise out of this discussion. Caution is suggested to the water resources analyst in including existence value within an economic framework.
A natural gradient experiment on solute transport in a sand aquifer: Spatial variability of hydraulic conductivity and its role in the dispersion process
Authors: Sudicky E. A.
Published: February 2008

The spatial variability of hydraulic conductivity at the site of a long‐term tracer test performed in the Borden aquifer was examined in great detail by conducting permeability measurements on a series of cores taken along two cross sections, one along and the other transverse to the mean flow direction. Along the two cross sections, a regular‐spaced grid of hydraulic conductivity data with 0.05 m vertical and 1.0 m horizontal spatial discretization revealed that the aquifer is comprised of numerous thin, discontinuous lenses of contrasting hydraulic conductivity. Estimation of the three‐dimensional covariance structure of the aquifer from the log‐transformed data indicates that an exponential covariance model with a variance equal to 0.29, an isotropic horizontal correlation length equal to about 2.8 m, and a vertical correlation length equal to 0.12 m is representative. A value for the longitudinal macrodispersivity calculated from these statistical parameters using three‐dimensional stochastic transport theory developed by L. W. Gelhar and C. L. Axness (1983) is about 0.6 m. For the vertically averaged case, the two‐dimensional theory developed by G. Dagan (1982, 1984) yields a longitudinal djspersivity equal to 0.45 m. Use of the estimated statistical parameters describing the ln (K) variability in Dagan's transient equations closely predicted the observed longitudinal and horizontal transverse spread of the tracer with time. Weak vertical and horizontal dispersion that is controlled essentially by local‐scale dispersion was obtained from the analysis. Because the dispersion predicted independently from the statistical description of the Borden aquifer is consistent with the spread of the injected tracer, it is felt that the theory holds promise for providing meaningful estimates of effective transport parameters in other complex‐structured aquifers.
A note on nonlinear storage routing
Authors: Koussis Antonis D. , Osborne B. J.
Published: February 2008

Parameter estimates for a conceptual, nonlinear storage routing model are derived on the basis of wave theory. An iterative solution scheme for the nonlinear storage routing model is analyzed with respect to its convergence and is compared in an application to quasi‐nonlinear and to linear storage routing schemes of the Muskingum type. The comparison shows that a noniterative, quasi nonlinear scheme is an excellent substitute for the fully nonlinear storage algorithm.
Dilettantism in hydrology: Transition or destiny?
Authors: Klemeš V.
Published: February 2008

The unsatisfactory state of hydrology is, in the final analysis, the result of the dichotomy between the theoretical recognition of hydrology as a science in its own right and the practical impossibility of studying it as a primary discipline but only as an appendage of hydraulic engineering, geography, geology, etc. As a consequence, the perspectives of hydrologists tend to be heavily biased in the direction of their nonhydrologic primary disciplines and their hydrologic backgrounds have wide gaps which breed a large variety of misconceptions. This state of affairs often paralyzes hydrologists' ability to differentiate between hydrology and water management, hydrology and statistics, facts and assumptions, science and convenience, etc., with consequent dangers both to scientific development of hydrology and to its practical utility. The danger increases with the proliferation of computerized “hydrologic” models whose cheaply arranged ability to fit data is presented as proof of their soundness and as a justification for using them for user‐attractive but hydrologically indefensible extrapolations. These points are illustrated, among other things, by discussion of flood frequency analysis. The paper concludes with some thoughts concerning minimum standards for the testing of hydrologic simulation models that would ensure at least a modest level of credibility, and with a few suggestions for ingredients of a long‐term cure that can prevent hydrology from joining alchemy and astrology in the annals of dilettantism.
A mixed gamma ARMA(1, 1) Model for river flow time series
Authors: Sim C. H.
Published: February 2008

In this paper we consider a time series model which can easily be used for simulating stationary river flow sequences with high skewness and the long‐term correlation structure of an ARMA(1, 1) model. The model is fitted to monthly streamflows taken from a river in Malaysia. The simulated data bear a close resemblance to the historical sequence in terms of the mean, variance, skewness, and autocorrelation coefficients.
Changes in the chemical composition of drinking water after well infiltration in an unconsolidated sandy aquifer
Authors: van Beek C. G. E. M. , Puffelen Van J.
Published: February 2008

Upon well recharge of aerobic water into an anaerobic aquifer a number of redox and dissolution reactions occur. In these redox reactions sulfides and organic material are oxidized by oxygen and nitrate present in the recharge water. Acid, produced during these redox reactions, is neutralized by calcium carbonate present in the aquifer and by the hydrogen carbonate‐carbon dioxide equilibrium. Sulfides, organic material, and calcium carbonate are present in finite quantities in the aquifer. Therefore these processes will terminate after some time, and an aerobic zone will spread around the recharge well. These geohydrochemical reactions have major consequences for a system consisting of separate recharge and discharge wells with respect to the clogging of the discharge wells and to the treatment of the abstracted water to drinking water.
Unsaturated flow in a centrifugal field: Measurement of hydraulic conductivity and testing of Darcy's Law
Authors: Nimmo J. R. , Rubin J. , Hammermeister D. P.
Published: February 2008

A method has been developed to establish steady state flow of water in an unsaturated soil sample spinning in a centrifuge. Theoretical analysis predicts moisture conditions in the sample that depend strongly on soil type and certain operating parameters. For Oakley sand, measurements of flux, water content, and matric potential during and after centrifugation verify that steady state flow can be achieved. Experiments have confirmed the theoretical prediction of a nearly uniform moisture distribution for this medium and have demonstrated that the flow can be effectively one‐dimensional. The method was used for steady state measurements of hydraulic conductivity K for relatively dry soil, giving values as low as 7.6 × 10−11 m/s with data obtained in a few hours. Darcy's law was tested by measuring K for different centrifugal driving forces but with the same water content. For the sand at a bulk density of 1.82 Mg/m3 and 27% saturation, results were consistent with Darcy's law for K equal to 5.22 × 10−10 m/s and forces ranging from 216 to 1650 times normal gravity.
Evaluation of a “Reliability programming” reservoir model
Authors: Strycharczyk Jerzy B. , Stedinger Jery R.
Published: February 2008

A recent series of papers presented a “reliability programming” formulation of reservoir design and operating problems. The algorithms employ a chance‐constrained formulation of reservoir operating constraints and system objectives, but avoid the use of linear decision rules. Examination of the reliability programming formulation of the reservoir management problem reveals that the reservoir model employs a very restrictive operating policy. In a numerical example the reliability programming model's constraints overestimated reservoir capacity requirements by an order of magnitude. The basic reliability programming formulation of reservoir management issues is also questioned.
Numerical estimation of effective permeability in sand‐shale formations
Authors: Desbarats Alexandre J.
Published: February 2008

A numerical approach is used to estimate effective permeability in sand‐shale formations under steady state uniform flow conditions. Permeability is modeled as a binary, second‐order stationary random function taking on two possible values Kss and Ksh in sandstone and shale, respectively. This model is realistic since experience with sandstone reservoirs has shown that randomly dispersed low‐permeability shales are the single dominant heterogeneity affecting flow behavior. The cases of both spatially correlated and uncorrelated permeabilities are considered. For the case of spatially correlated permeability, an autocovariance model was fitted to data from the Assakao fluvial sandstone which outcrops in the Tassili region of the central Sahara. The turning bands method was used to simulate the spatially correlated permeabilities of blocks discretizing the flow field. Effective permeability was found to depend on the shale volume fraction, the spatial covariance structure, and the dimensionality of the flow system. Existing analytical methods for estimating effective permeability in a two‐phase medium are found to be inaccurate when compared to numerical results or unapplicable to stratified environments. In addition to providing a check of analytical work, the numerical approach is found to be a useful tool for exploring the effects of reservoir heterogeneity on flow behavior in a qualitative sense.