bluuebunny/crossref_metadata_2025 huggingface dataset:
Some comments on testing random topology stream network models
Authors: Jarvis R. S. , Werritty A.
Published: February 2008

Various methods of classifying stream networks are examined in terms of their attendant information losses. Grouping networks according to their mean source height scores well in this respect because it retains a considerable amount of the original topologic detail present in each individual topologically distinct channel network. Stream set values determine the structural properties of the network and the degree to which a given network is ‘compact’ or ‘lineated.’ Because of difficulties in interpretation, tests of random topology hypotheses are best conducted on networks sampled at a constant magnitude. A means of comparing the topologic structure of the main stem of two or more networks is developed, based upon the absolute limits and the expectation of the parameter mean source height.
One‐dimensional simulation of aquifer system compaction near Pixley, California: 1. Constant parameters
Authors: Helm Donald C.
Published: February 2008

Aggregate one‐dimensional compaction (consolidation) of a series of aquitards in a compacting aquifer system has been simulated through use of a finite difference representation of the vertical stress distribution within an idealized aquitard. Among the parameters affecting the simulated compaction are two storage coefficients (compressibility values), one for recoverable and the other for nonrecoverable compression. These two storage coefficients introduce a transient heterogeneity within an aquitard that is generally ignored by hydrologists. A computer program with two sets of constant coefficients calculates the daily deformation due to observed changes in applied stress near Pixley, California. Although water levels fluctuate annually, no long‐term water level decline occurred near Pixley between January 1, 1959, and February 4, 1971. During this period, 3.19 ft (0.972 m) of compaction was observed. The net difference between simulated and observed compaction on February 4, 1971, was 1.3% of the observed value. Maximum deviation occurred in mid‐1964 and equaled 7% of the observed compaction.
Project evaluation during inflation
Authors: Hanke Steve H. , Carver Philip H. , Bugg Paul
Published: February 2008

Rules for correctly dealing with price and interest rate projections when one conducts benefit‐cost analysis during inflation are derived, Recommendations of the Water Resources Council and those adopted in the Water Resources Development Act of 1974 are critiqued. The use of real prices and real opportunity cost interest rates is recommended as an improvement over the present practice of employing real prices and nominal financial interest rates.
Water quality changes related to the development of anaerobic conditions during artificial recharge
Authors: Wood Warren W. , Bassett Randy L.
Published: February 2008

Artificial recharge basins or spreading sites commonly exhibit reductions in infiltration rates after prolonged periods of submergence. This loss in infiltration rate has often been shown to be associated with a large population of anaerobic or facultative anaerobic bacteria in the material underlying the basin floor. An artificial recharge experiment in a spreading basin at Lubbock, Texas, showed a significant change in the chemical quality of recharged water that was associated with the growth of anaerobic bacteria. Sulfate‐reducing bacteria reduced the sulfate concentration of the recharge water at this location by 80 mg/l. The bicarbonate concentration was increased by more than 150 mg/l, and the pH decreased 1 unit during the same time period. The change in chemical quality occurred suddenly and corresponded to a dramatic decrease in the infiltration rate in the basin. These observations on the chemical changes in recharged water make it possible to differentiate between anaerobic bacteria and other causes of reduced hydraulic conductivity in this recharge basin. The anaerobic conditions appear to start at depth and work toward the surface, thereby suggesting a process that involves adsorption of organic material and consumption of dissolved oxygen with depth.
Identification of parameters in a linear equation of groundwater flow
Authors: Nutbrown D. A.
Published: February 2008

An inductive method is presented for evaluating parameters in a two‐dimensional linear equation describing groundwater flow. The approach employs finite difference approximations, which can be simply programed for calculation by computer. Before illustrating the method, which is applicable to both stationary and time‐dependent problems, the various types of data required for evaluation in general are systematically enumerated. An assumption is introduced limiting the local variability of T, the transmissivity, and its relation to apparently similar assumptions used elsewhere is discussed. The particular aquifer chosen for illustration is the chalk of the South Downs between the rivers Adur and Ouse. The parameters are calculated on the basis of cyclic data in which annual abstraction is about 30% of the total infiltration for the year. The method gives a match to the minimum and maximum water levels during the year to within 7%.
Intervention analysis in water resources
Authors: Hipel Keith William , Lennox W. C. , Unny T. E. , McLeod Angus Ian
Published: February 2008

Intervention analysis is the stochastic transfer function modeling of natural or man‐induced interventions on the mean level of a time series. The mathematics of intervention analysis is presented followed by a systematic method of analysis that is used to analyze the effect of the Aswan dam on the average annual flows of the Nile River. The analysis shows that a significant drop in the flow occurred in 1903 when the dam was brought into operation. Transfer function parameter estimates statistically describe the intervention effect while the stochastic intervention model developed can be used for forecasting and simulation. The authors maintain that the potential of intervention analysis in water resources is extensive.
The use of a dependent domain model of hysteresis in numerical soil water studies
Authors: Lees S. J. , Watson K. K.
Published: February 2008

The analysis of intermittent soil water systems requires the inclusion of a capillary hysteresis model in the space‐time simulation of the flow process. Domain models of hysteresis are reviewed, and the approach of Poulovassilis and Childs (1971) selected as the basis for a numerical hysteresis program which is able to generate primary, secondary, and higher order scanning curves. The dependence of the pore draining pressure on the pressure at the previous reversal is restricted to reversals from the boundary curves. This enables the distribution function to be approximated by a series of regularly spaced, independent domain‐type distribution diagrams, each being derived from an experimental primary curve and a set of estimated secondary scanning curves. The effectiveness of the approach is demonstrated by simulating the movement of water in a profile of #17 sand subject to intermittent infiltration‐redistribution sequences. In particular, the hysteretic path followed by the surface node is used to illustrate the generation of the necessary higher order scanning curves.
Reservoir management via reliability programing
Authors: Colorni A. , Fronza G.
Published: February 2008

The possibility of applying reliability programing for determining the monthly contract volumes to be released by a reservoir is discussed in this paper. While in standard chance constraint programing the risk of the solution is fixed a priori, here constraint reliabilities are considered as extra decision variables. Hence the optimal operation results from a compromise between profit and risk. It is shown that under quite general assumptions the reliability program enjoys a concavity property that allows the application of an efficient solution algorithm.
Numerical simulation of waste movement in steady groundwater flow systems
Authors: Pickens John F. , Lennox William C.
Published: February 2008

The finite element method based on a Galerkin technique is used to formulate the problem of simulating the two‐dimensional transient movement of conservative or nonconservative wastes in a steady state saturated groundwater flow system. The convection‐dispersion equation is solved in two ways: in the conventional Cartesian coordinate system and in a transformed coordinate system equivalent to the orthogonal curvilinear coordinate system of streamlines and normals to those lines. The two formulations produce identical results. A sensitivity analysis on the dispersion parameter ‘dispersivity’ is performed, establishing its importance in convection‐dispersion problems. Examples involving the movement of nonconservative contaminants described by distribution coefficients and examples with variable input concentration are also given. The model can be applied to environmental problems related to groundwater contamination from waste disposal sites.
A simulation model for operating a multipurpose multireservoir system
Authors: Sigvaldson O. T.
Published: February 2008

This paper describes a mathematical model used for assessing alternative policies of operation for the Trent River system in Ontario, Canada. The Trent basin is characterized by numerous reservoirs (48 were represented in the model), each with a control structure(s) in its outlet channel(s). The reservoir system is used for flood control, water supply, hydropower, and augmenting flows through the canal system during the summer period. The need for assessing alternative policies arose from growing conflicts in recent years over satisfying all of the many water‐based needs of the basin. To aid in assessing the impact of alternative policies, a simulation model was developed and applied. Every reservoir was subdivided into five storage zones (which were variable in a temporal sense). A time‐based rule curve was also prescribed to represent ideal reservoir operation. Ranges were prescribed for channel flows, which were dependent on water‐based needs. The underlying concept of the model was the functional (or mathematical) representation of the chief operator's perception of ‘Optimum’ operation and the derivation of this solution using a nested optimization submodel. ‘Penalty coefficients’ were assigned to those variables which represented deviations from ideal conditions. Different operational policies were simulated by altering relative values of these coefficients. The development and use of the model were simplified by representing the entire reservoir system in ‘capacitated network’ form and deriving optimum solutions for individual time periods with the ‘out‐of‐kilter’ algorithm. Besides being computationally efficient this algorithm simplified model development and permitted flexibility in readily using the model for a wide range of reservoir configurations and operating policies.
The concentration of dissolved solids and river flow
Authors: O'Connor Donlad J.
Published: February 2008

A general expression for the spatial and temporal distribution of conservative dissolved solids in freshwater rivers which incorporates the contribution of both the groundwater and surface water components of river flow is presented. The first part of this paper deals with the steady state conditions. With certain simplifying assumptions the correlation between concentration of dissolved solids and flow is developed for both spatially uniform and nonuniform conditions. The analysis includes the effect of both geophysical discontinuities and point sources. Examples from a number of rivers throughout the country are presented to indicate the utility of the analysis. The second part addresses the temporal variation of the dissolved solids concentration for two time scales. One describes the annual variation in concentration due to the time variable components of the river flow, and the second the variation over a semimonthly period due to a time variable point input. Applications to a variety of river conditions are also presented for the time variable analysis.
Model‐free statistical methods for water table prediction
Authors: Yakowitz Sidney
Published: February 2008

In this study a new approach for predicting future values of well depths on the basis of regional water table records is presented. Basically, well water level depths are viewed as random sequences, and the assumption is made that the region to be analyzed can be partitioned into several subregions of unknown geographic shapes which are statistically homogeneous in the sense that the record of each well in a fixed subregion is a different realization of the same stochastic process. Methods from clustering and time series analysis are used to find first the subregions of stochastic homogeneity and then the statistical law for the time series of the wells in a given subregion. Forecasts are made and confidence bands constructed by using the methods espoused here (in conjunction with regression techniques) on Tucson basin data. The forecasts are compared to depths actually observed, and for many wells the agreement is sufficient to make these methods appear promising.
Equity measures for exploring water quality management alternatives
Authors: Brill E. Downey , Liebman Jon C. , ReVelle Charles S.
Published: February 2008

Equity measures can be used as working tools to explore management alternatives for a water quality system. Several example measures of equity are discussed which proved useful in suggesting new management programs, in identifying critical waste dischargers, in suggesting zones for grouping dischargers, and for understanding given management programs. The example equity measures were evaluated for Delaware Estuary data by using mathematical programing.
Dupuit‐Forchheimer and potential theories for recharge from basins
Authors: Brock Richard R.
Published: February 2008

Artificial groundwater recharge from strip and square basins to an unconfined aquifer was investigated. The classical Dupuit‐Forchheimer (DF) theory and the more exact potential theory were used to determine the motion of the water table resulting from recharge. For each theory, both a linear and a nonlinear version were considered. Finite difference schemes were employed to solve the nonlinear models. Analytical solutions exist for the linear models. By comparing the results from the various theories and from experimental results in a sand model the range of validity of the theories was determined. For sufficiently shallow flows the DF theories give results that are good approximations to the potential theories. For sufficiently deep flows the potential theories must be used, particularly beneath the basin and for small times. The velocity field near a strip basin was determined from the nonlinear potential theory for both a deep and a shallow flow. Tabular results are presented that can be used to determine the rise of the water table for strip and square basins.
An evaluation of the practicality and complexity of some rainfall and runoff time series models
Authors: Delleur J. W. , Tao P. C. , Kavvas M. L.
Published: February 2008

The fundamental issue of what level of complexity is needed in stochastic models for generating or forecasting hydrologic events is studied by comparing the properties of autoregressive, moving average, and mixed models of increasing complexity for annual, monthly, weekly, and daily series. Several methods of removing seasonal nonhomogeneity of monthly series are compared, and the seasonality of monthly model coefficients is investigated. For small time increments a harmonic analysis of the coefficients is necessary to limit the number of parameters. The relative goodness of fit of several models of monthly and daily series are determined by diagnostic checks applied to the residuals, and their probability distributions are investigated. The issue of long‐range versus short‐range dependence is analyzed by comparing the statistics describing the span of dependence of several time series models. The need for compatible models for different time resolutions is discussed. The merits of the disaggregation model and its level of complexity are discussed and compared with those of other models.
Reliability, trade‐offs, and water resources development modeling with multiple crops
Authors: Dudley Norman J. , Reklis Diane M. , Burt Oscar R.
Published: February 2008

A hierarchy of models is developed to aid management and planning decisions in multicrop water resources systems located in higher latitudes of the world and featuring significant downstream requirements. A major objective is to quantify trade‐offs between systems with a high reliability of water supply but low average benefits and those of low reliability with high average but also highly variable returns. Linear programing is used to select best crop combinations for given quantities of water available over the summer, associated water usage, and revenue estimates. A simulation model predicts changes in reservoir storage resulting from inflows and releases to meet requirements of crops selected by the linear program. Interseasonal water allocation is then optimized by using dynamic programing. A method is presented for determining variance of benefits as a function of system design parameters and downstream requirements. In an application to a water resources system in Montana, downstream water requirements and penalties were found to have a large effect on high reliability‐low reliability trade‐offs.
Irrigation system operating policies for mature tea in Malawi
Authors: Palmer‐Jones Richard William
Published: February 2008

The technical specification of plant‐water relationships has led to errors in the formulation of response models for water inputs. Consequently, the optimizing procedures making use of these models may have been misleading as to both the practical water application rules recommended and the usefulness of the optimizing procedure. In this paper we show that the distribution of water within the root zone, at least for tea in Malawi, plays an important part in determining response to irrigation. This means that two or more soil moisture state variables will be necessary in the dynamic programing (DP) method of finding the optimal application policy, and this makes DP even more difficult to use in practice than has been previously indicated.
Discrete representation of storage for stochastic reservoir optimization
Authors: Klemeš V.
Published: February 2008

In explicit stochastic dynamic programing optimization of storage reservoirs the ‘curse of dimensionality’ dictates the adoption of the smallest possible number of discrete states to represent the range of reservoir storage. This pressure makes it imperative to understand clearly the consequences of pushing the limit too far. It is shown that the number of storage states is subject to some absolute constraints and that it must increase linearly with the reservoir storage capacity in order that comparability of results be assured. It is demonstrated, both theoretically and with the aid of a numerical example, that a too coarse discrete storage representation can not only impede accuracy but may completely distort reality in most unexpected ways. Finally, charts are presented giving the numbers of storage states necessary to obtain stationary probabilities of reservoir emptiness and/or fullness with an error e ≤ 0.1% for log normal and normal input distributions.
Experimental and simulated transport of phosphorus through sandy soils
Authors: Mansell R. S. , Selim H. M. , Kanchanasut P. , Davidson J. M. , Fiskell J. G. A.
Published: February 2008

Reversible equilibrium adsorption‐desorption relationships were inadequate for describing the transport of orthophosphate through water‐saturated and water‐unsaturated cores from surface A1 and subsurface A2 horizons of Oldsmar fine sand. Using a kinetic model with nonlinear reversible adsorption‐desorption improved descriptions of phosphorus transport through these soils. Phosphorus effluent concentrations were described best by using an irreversible sink for chemical immobilization or precipitation with a nonlinear reversible kinetic adsorption‐desorption equation.
Water allocation and pricing for control of irrigation‐Related salinity in a river basin
Authors: Scherer Charles R.
Published: February 2008

Optimal allocation of water to sequential irrigators is considered with emphasis on downstream salinity damages caused by salt‐concentrating mechanisms inherent in irrigated agriculture. The allocation is achieved by using a dynamic programing framework with decision variables of amount diverted, land irrigated, and amount of irrigation canals lined. This framework is used to investigate a scheme whereby water is purchased and held for downstream use solely as a dilutant. The basis is established in principle for an operational, water rights market where all purchasers are financed by downstream beneficiaries. Several examples are given.
An operational approach to preserving skew in hydrologic models of long‐term persistence
Authors: Lettenmaier Dennis P. , Burges Stephen J.
Published: February 2008

Formulation of two models of long‐term persistence, fast fractional Gaussian noise (ffGn) and the first‐ order autoregressive‐first‐order moving average (Arma (1, 1)) process for a three‐parameter log normal and three‐parameter gamma distribution are given. For the three‐parameter log normal distribution the marginal probability distribution is generated exactly for both models, but the desired autocorrelation functions are distorted. Use of the three‐parameter log normal distribution requires a transformation of the lag one correlation coefficient and the Hurst coefficient for the ffGn model and of the parameters ϕ and θ for the Arma (1, 1) model. Because of the nonlinearity of the three‐parameter log normal transformation, sequences with slightly higher long‐term persistence (larger H or ϕ) must be generated in the logarithmic domain to achieve the desired model properties in the skewed domain. For the gamma distribution, the autocorrelation function is preserved exactly, but the desired marginal probability distribution is distorted. Monte Carlo tests showed that this distortion is evidenced primarily in the loss of the theoretical lower bound of the gamma distribution. This distortion is most extreme for time series having high long‐term persistence (H or ϕ) and large coefficients of variation. For operational applications, there appeared to be no clear advantage to use of either of the skewed distributions.
Simulation of two‐dimensional contaminant transport with isoparametric Hermitian finite elements
Authors: Van Genuchten Martinus T. , Pinder George F. , Frind Emil O.
Published: February 2008

A deformed isoparametric Hermitian element can be used in the simulation of two‐dimensional contaminant transport. The degree of freedom arising from the cross derivative may be eliminated in the Galerkin‐type finite element formulation, reducing the computational effort per node. Two example problems demonstrate that the Hermitian element gives results which are comparable to those obtained with the zero‐order continuous cubic element but requires 25–40% fewer degrees of freedom, depending on the geometrical description of the problem.
A new multivariate gamma distribution and its fitting to empirical streamflow data
Authors: Prékopa A. , Szántai T.
Published: February 2008

A new multivariate gamma distribution is presented which can successfully be fitted to empirical data where the one‐dimensional marginal distributions are gamma distributions with prescribed parameters and the correlations are nonnegative. It is not intended to give explicit formulae either for the joint density or for the joint characteristic function of the random variables. Our representation of the individual gamma‐distributed random variables will be used for simulation, with the aid of which we approximate probabilities of sets in higher‐dimensional spaces. Since streamflow and other hydrological data frequently follow gamma distribution and also they are frequently stochastically dependent, our multivariate distribution and fitting technique seems to be of particular interest from the hydrological point of view.
An approximate differential equation to describe leaky aquifer behavior during intermediate and large values of time
Authors: Rodarte Leopoldo
Published: February 2008

In analyzing a leaky aquifer for application in regional studies it is of great interest to have available simplified mathematical representations from which an analogical or digital model of the problem can be constructed. In this paper a differential equation valid for intermediate and large values of time is proposed. Also, an analytical solution corresponding to an isolated well as a test of the range of applicability of the proposed equation is obtained.
A variational inequality method applied to free surface seepage from a triangular ditch
Authors: Bruch John C. , Sloss James M.
Published: February 2008

Two‐dimensional seepage from a single triangular channel into permeable soil underlain at a finite depth by a drain has been solved by reducing the problem to a variational inequality. The results obtained consist of the location of the free surface and thus the shape of the seepage region, the velocity potential and stream function at a series of mesh points, and the seepage flow rate. The successive overrelaxation method with projection was used to solve the numerical problem. The numerical results compared very favorably with the analytical solution to the same problem.
Intertemporal allocation of irrigation water in the Mayurakshi Project (India): An application of chance‐constrained linear programing
Authors: Maji Chandi C. , Heady Earl O.
Published: February 2008

This study develops an optimal cropping pattern and a reservoir management policy for the Mayurakshi irrigation project (India). Two chance‐constrained linear programing models are formulated to account for the stochastic nature of the monthly inflows. The models also consider the increased economic opportunity offered by the introduction of new high‐yielding crop varieties. The results clearly indicate that a change in the existing cropping pattern and reservoir management policy is desirable and is consistent with the maximization of net return to the project area. The existing supply of nitrogen fertilizer in the command area is found to be inadequate to allow the best use of other resources, including irrigation water. As the probability of occurrence of a drought or a flood is kept within a limit of 10%, the crop activities in the optimal cropping pattern suffer from drought or flood conditions no more than 10% of the time. Thus the resulting cropping patterns should be preferred by the tradition‐bound farmers of the command area, who have a low risk‐bearing ability.
A fully coupled consolidation model of the subsidence of Venice
Authors: Lewis R. W. , Schrefler B.
Published: February 2008

The subsidence of Venice, a well‐known historical town in Italy, is caused by the extensive withdrawal of groundwater in its industrial area, Marghera. A fully coupled finite element consolidation model is presented to simulate the subsidence and the piezometric decline in the considered area. The model shows clearly the short time delay between changes in the withdrawal rate in Marghera and the resulting hydraulic head decline and subsidence in Venice. A comparison is also made between the coupled model and an analysis in which the flow region was analyzed separately from the subsidence calculations.
Optimization of lake hydrographic surveys
Authors: Håkanson Lars
Published: February 2008

Bathymetric maps are the source of most morphometric data used in limnological, hydrological, and sedimentological contexts. The reliability of the morphometric data will depend on the accuracy of the bathymetric map, which in turn will depend on the intensity of the hydrographic survey. The aim of this work is to analyze thoroughly the relationship between intensity of survey, aim of survey, and yield of survey and to deduce a formula which may be used to express these concepts quantitatively so that hydrographic surveys can be executed in an optimal manner. An empirical formula which may be utilized to estimate the length of contour lines of a given bathymetric map from the hypsographic curve is also introduced.
Integrated water management with reuse: A programing approach
Authors: Pingry David E. , Shaftel Timothy L.
Published: February 2008

Interest has increased recently in water recycling and reuse. The possible economic feasibility of reuse and recycling dramatically increases the complexity of designing an optimal water delivery system. In this paper we present a nonlinear model which takes into account both flow requirements and water quality. Because of the model's transshipment formulation the solution technique seems to be effective in aiding the design decisions.
Geothermal reservoir simulation: 1. Mathematical models for liquid‐ and vapor‐dominated hydrothermal systems
Authors: Faust Charles R. , Mercer James W.
Published: February 2008

Two alternative mathematical models are presented that are suitable for numerical simulation of geothermal reservoirs. The general mathematical model describes the three‐dimensional flow of single‐component water (both one and two phase) and the transport of heat in porous media. It is composed of two nonlinear partial differential equations, posed in terms of fluid pressure and enthalpy, and appropriate boundary conditions. An alternative quasi‐three‐dimensional model is derived by partial integration (in the vertical dimension) of the three‐dimensional equations. The reservoir is assumed to have good vertical communication so that vertical equilibrium (gravity segregation) between steam and water is achieved. The resulting equations, posed in terms of vertically averaged pressure and enthalpy, include effects of an inclined, variable‐thickness reservoir and mass and energy leakage to confining beds.
Models of groundwater flow in statistically homogeneous porous formations
Authors: Dagan G.
Published: February 2008

Most natural porous formations display significant variations in space of permeability K and storativity S. Such formations are regarded as random structures characterized by the permeability frequency distribution and its autocorrelation. With the aid of three basic length scales (l, microscale; £, integral scale of K autocorrelation; and L, length scale of space change of average K) a classification of aquifers is suggested. A similar classification is proposed for the flow regimes. The study is limited to statistically homogeneous or slowly varying formations (£ ≪ L) and to uniform or slowly varying (in space and time) flows. In the section dealing with steady flows, effective permeability, as well as variances of head gradient, specific discharge, and head, is computed for one‐, two‐, and three‐dimensional flows. Bounds and an estimate of the effective permeability in terms of a log normal permeability distribution are given. The computations are based on physical, simplified models of formation structure. It is shown that the head variance is grossly overestimated for one‐dimensional flow through blocks ‘in series,’ and the same is true for specific discharge for layers ‘in parallel.’ The two‐ and three‐dimensional variances are much lower and are close to each other. The unsteady flow is analyzed with the aid of the relaxation time needed for blocks of different K, S to adapt to the environment. For flows which change slowly and uniformly the effective permeability is that derived for steady uniform flows, and the effective storativity is equal to the S arithmetic mean. The head gradient variance computed with the aid of some physical models is compared with that of steady uniform flow, and it is shown that for sufficiently slow time changes the flow field can be considered momentarily uniform. The various results are employed to estimate effective properties, as well as fluctuations of the head and specific discharge, in aquifers, with possible applications to prediction, the inverse problem, and hydrodynamic dispersion.
Climatological estimates of lake evaporation
Authors: Morton F. I.
Published: February 2008

A model for estimating areal evaporation and transpiration is modified slightly to provide estimates of annual lake evaporation from monthly observations of temperature, humidity, and sunshine duration (or radiation) in the land environment. The model estimates tend to be higher than the more conventional estimates in humid areas and lower in arid areas, with the latter tendency particularly noticeable in the case of Lake Nasser on the Nile River. However, the results agree very well with comparable water budget estimates for Lake Hefner in Oklahoma, the Salton Sea and Silver Lake in California, Pyramid and Winnemucca lakes in Nevada, Lake Ontario on the border between New York and Ontario, and Dauphin Lake in Manitoba. They also compare reasonably well with energy budget estimates of the evaporation from Lake Mead on the border between Arizona and Nevada when the net inflow of heat is taken into account. A technique that provides such realistic results over a wide range of depths and environments with readily available data should prove very useful in water resource or environmental impact studies. Examples of such uses are provided by maps of Canada and the southeastern United States that show average annual values of the lake evaporation, and average annual values of the difference between the evaporation from a projected reservoir, and the combined evaporation and transpiration from the area before flooding.
Estimation of the pore size distribution from the moisture characteristic
Authors: D'Hollander E. H.
Published: February 2008

Most pF curves are shaped as cumulative distribution functions. From this observation, restricted to nonshrinking or swelling soils, a close relationship is established between the moisture characteristic and the pore size distribution, based on an empirical law relating the pore suction to a characteristic size referred to as the effective pore radius. For many soils showing a moisture characteristic similar to a normal cumulative distribution function, the derived pore size distribution is log normal. In this case, a direct identification technique is developed, yielding the parameters of the density function from the experimental pF‐θ relationship. Practical applications demonstrate the validity of this probabilistic model, which gives good agreement with morphometric pore size data, available in the literature. The model also gives rise to an analytical expression for the pF curve in terms of two structural parameters of the porous system, the mean and the standard deviation of the effective pore radius.
Effects of in‐transit water on groundwater mounds beneath circular and rectangular recharge areas
Authors: Ortiz N. V. , Zachmann D. W. , McWhorter D. B. , Sunada D. K.
Published: February 2008

Analytical solutions, accounting for the reduction in storage capacity caused by in‐transit water, are presented for the growth of groundwater mounds in an unconfined aquifer in response to uniform deep percolation from a rectangular and circular recharging area. The solution for the circular case was obtained by integrating the solution for the analogous case of heat flow in a composite cylindrical region with respect to time. In the rectangular case the solution was obtained by a product of two functions representing the solution for the instantaneous addition of a recharge slug over a long strip and integrating with respect to time. The aquifer is homogeneous, isotropic, infinite in areal extent, and resting on a horizontal impermeable base. Dimensionless curves are presented to afford a relatively simple means for the analysis of the growth of groundwater mounds.
Solution of linearized boussinesq equation with stochastic boundaries and recharge
Authors: Sagar Budhi
Published: February 2008

By using the method of eigenfunction expansion a solution to the linearized Boussinesq equation with stochastic initial conditions, boundaries, and recharge is obtained. The solution is obtained explicitly in the form of two expressions, one for the expected value of the dependent variable and the other for its covariance. The inclusion of both the Neumann and the Dirichlet boundary conditions is considered. It is found that the expected value of the dependent variable is the same as the solution of the deterministic problem with expected values of the input stochastic quantities. An example of the use of the solution is presented. From the result of the example it is seen that the initial condition contributes a major portion to the standard deviation of the dependent variable.
Calculation of aquifer parameters from sparse data
Authors: Birtles A. B. , Morel E. H.
Published: February 2008

Automatic methods used for the calibration of regional groundwater models are notoriously sensitive to inadequacies in hydrological data used to determine the groundwater regime. The situation is often aggravated by errors introduced by manual interpolation to give estimates of piezometric head between observation boreholes, particularly in areas where these are sparse or locally nonexistent. In this paper a new technique is proposed for the automatic interpolation of groundwater level data that are scattered thinly over a regional aquifer system and the simultaneous determination of transmissivity and storage coefficient distributions. The method makes full use of all available information, and it is consistent with the two‐dimensional groundwater flow equations. Results are given to illustrate the success achieved by the method in a practical application.
Perspective on ‘Delayed yield’
Authors: Neuman Shlomo P.
Published: February 2008

The phenomenon of ‘delayed yield’ has received wide attention in the literature during recent years. Considerable work has been devoted to the development of physically based mathematical models capable of successfully reproducing observed aquifer behavior. As a result of this effort, there appears to be at present a consensus of opinion among the main contributors to the theory of delayed yield as to an acceptable physical and mathematical interpretation of this phenomenon. In spite of this apparent consensus of opinion, there is still a considerable amount of controversy in the literature about some fundamental aspects of unconfined well hydraulics. The outstanding issues concern the physical assumptions underlying various delayed yield models, changes in the flow regime of an unconfined aquifer as a function of radial distance from the pumping well, the relationship between Boulton's α and other physical characteristics of the aquifer, the validity of conditions required in order to represent unconfined flow by integrodifferential equations, and the behavior of unconfined aquifers at large values of time. The present paper offers a perspective from the author's viewpoint on these and other related issues.
A nonparametric Markov Model for daily river flow
Authors: Yakowitz Sidney J.
Published: February 2008

This paper presents to an audience of research hydrologists what is believed to be a significant new development in time series modeling. The model class is the class of (not necessarily finite state) Markov chains. The basic advantage of this class is that in comparison to parametric models (such as autoregressive moving average) it is a very rich class, and the value of the statistical method described herein is that, as proven elsewhere, it provides convergence over this large class. The technique is applied to Cheyenne River data, and discussion is provided on how to incorporate prior statistical and geological information into the model. Also, comparisons are made between the nonparametric Markov analysis provided here and the currently popular streamflow models and statistical techniques.
Probability weighted moments: Definition and relation to parameters of several distributions expressable in inverse form
Authors: Greenwood J. Arthur , Landwehr J. Maciunas , Matalas N. C. , Wallis J. R.
Published: February 2008

Distributions whose inverse forms are explicitly defined, such as Tukey's lambda, may present problems in deriving their parameters by more conventional means. Probability weighted moments are introduced and shown to be potentially useful in expressing the parameters of these distributions.
Daytime energy exchange and evaporation from a wooded swamp
Authors: Munro D. S.
Published: February 2008

Hourly values of daytime energy balance components were obtained for 5 days in late summer at a wooded swamp in southern Ontario. Bowen ratio estimates of the energy used in evaporation were compared with values obtained from the equilibrium form of the combination model. Agreement between the two methods was found to be poor for hourly values but better in the case of daytime totals, where the proportion of Bowen ratio to equilibrium estimates varied from 0.7 to 1.04. The results did not support the use of a potential evaporation formula despite an apparently nonlimiting supply of moisture in the soil.
Modeling groundwater flow fields containing point singularities: Streamlines, travel times, and breakthrough curves
Authors: Charbeneau Randall J. , Street Robert L.
Published: February 2008

In the work of Charbeneau and Street (1979) a method was presented for modeling steady state groundwater flow fields containing injection and extraction wells. The Galerkin finite element method was used with greatly improved accuracy of the simulation near wells achieved by removing the singular behavior of the flow with an analytic solution for the near‐well zone, solving the nonsingular problem, and combining the results. In the present paper, methods for exploiting the improved hydraulic head solution are presented. Velocity fields are derived through differentiation of the head solution combined with smoothing and averaging. The velocity fields are used for generating systems of streamlines and determining times of travel to points of interest (including breakthrough curves for a nondispersive contaminant). The method is compared with analytical results for a single injection‐extraction well pair.
Stochastic analysis of steady state groundwater flow in a bounded domain: 2. Two‐dimensional simulations
Authors: Smith Leslie , Freeze R. Allan
Published: February 2008

A stochastic analysis of two‐dimensional steady state groundwater flow in a bounded domain is carried out by using Monte Carlo techniques. The flow domain is divided into a set of square blocks. A nearest‐neighbor stochastic process model is used to generate a multilateral spatial dependence between hydraulic conductivity values in the block system. Both statistically isotropic and statistically anisotropic autocorrelation functions are considered. This model leads to a realistic representation of the spatial variations in hydraulic conductivity in a discrete block medium. Results of the simulations provide estimates of the output distributions in hydraulic head. The probability distribution for hydraulic head must be interpreted in terms of the spatial variation of the expected head gradients, the standard deviation in the hydraulic conductivity distribution, the ratio of the integral scales of the autocorrelation function for conductivity to the distance between boundaries on the flow domain, and the arrangement of statistically homogeneous units within the flow domain. The standard deviation in hydraulic head increases with an increase in either the standard deviation in hydraulic conductivity or the strength of the correlation between neighboring conductivity values. The standard deviations in hydraulic head are approximately halved when a uniform, bounded, two‐dimensional flow field is reduced to one‐dimensional form. The uncertainties in the predicted hydraulic head values are strongly influenced by the presence of a spatial trend in the mean hydraulic conductivity. In evaluating the concept of an effective conductivity for a heterogeneous medium, both the nature of the spatial heterogeneities in hydraulic conductivity and the flow system operating within the flow domain must be considered.
Linear decision rule in reservoir design and management: 6. Incorporation of economic efficiency benefits and hydroelectric energy generation
Authors: Houck Mark H. , Cohon Jared L. , ReVelle Charles S.
Published: February 2008

The linear decision rule (LDR) model introduced by ReVelle et al. (1969) is extended to include multiple uses of a reservoir system with an objective of economic efficiency. A method of incorporating hydroelectric energy production within the LDR model is presented and the water supply uses of the reservoir system are evaluated and reformulated. The extended LDR model is shown to be well within the limits of computational feasibility for large (10 or more facilities) reservoir systems with conflicting uses and an objective of maximizing net economic efficiency benefits.
Flood risks and the willingness to purchase flood insurance
Authors: Karlinger M .R. , Attanasi E. D.
Published: February 2008

Computer simulation experiments were conducted to determine the effects of alternative sources of uncertainty on the willingness to pay for flood insurance. Two alternative insurance protection schemes were investigated: coinsurance and fixed coverage. The question investigated here is to what extent does the insurance scheme influence how purchasers respond to flood risks? Floods were assumed to be log normally distributed and the effects on the purchase of insurance of uncertainties in the parameters of the distribution were explored using response surface analysis. Results indicate that fixed coverage insurance provisions shift most of the uncertainty in the physical parameters governing natural disaster occurrences away from the insuree and onto the insurer. The results also show that the form of the damage function has little effect on the demand for flood insurance.
A logical approach to the design storm concept
Authors: Packman J. C. , Kidd C. H. R.
Published: February 2008

Flood estimation using isolated event simulation models requires selection of a suitable combination of design storm and antecedent conditions. Current practice in storm drainage design is to adopt arbitrarily a storm duration, profile, and catchment wetness and to assume that the return periods of rainfall depth and flood peak are equal. This paper describes how sensitivity analysis may be used to examine the relationship between rainfall and flood return periods and, thereby, to determine systematically a suitable set of design inputs which give a peak runoff of the required return period. This process permits this particular model to be used with confidence in design as well as in simulation.
Distribution‐free methods for estimating flood and streamflow exceedance probabilities by correlation
Authors: Cooper David M. , Clarke Robin T.
Published: February 2008

This paper deals with the problem in which it is necessary to infer the probabilistic characteristics of a streamflow variableyt(e.g., annual peak discharge, or accumulated streamflow during some time interval) given a correlated longer recordxt(e.g., annual peak discharge at a gaging site with longer record; rainfall during the same time interval). In particular, it is necessary to estimate probabilities of the formP(y≥y0) for givenY0. Conventional methods make assumptions about the joint probability distribution ofxtandyt; the methods developed in this paper require no such assumption, being distribution free. Estimates ofP(y≥Y0) are also obtained by Bayesian methods.