bluuebunny/crossref_metadata_2025 huggingface dataset:
An improved equation for estimating long‐wave radiation from the atmosphere
Authors: Satterlund Donald R.
Published: February 2008

An equation that predicts downcoming long‐wave radiation from clear skies on the basis of screen air temperature and vapor pressure has been developed. It fits measured data at extremes of temperature and humidity better than existing equations, and exhibits comparable accuracy at intermediate values.
Dense networks to measure convective rainfall in the southwestern United States
Authors: Osborn Herbert B. , Renard Kenneth G. , Simanton J. Roger
Published: February 2008

Almost all rangeland runoff in the southwestern United States results from intense short‐duration rainfall of limited‐area extent. In 1953, two southwest rangeland watersheds, the 150‐km2 Walnut Gulch and 174‐km2 Alamogordo Creek watersheds, were selected by U.S. Department of Agriculture Agricultural Research Service scientists as outdoor laboratories to measure water yield from rangeland watersheds. The networks were planned initially with gages on a 1‐mi grid, but difficulties in access resulted in more uneven networks. Because of budgetary restraints the basic networks were not completed until 1961. Gages were added after 1961, both for better estimates of rainfall on very small intensive study areas and to fill ‘gaps’ in the original network. The values of these dense rain gage networks became more apparent as the full complexity of southwestern rainfall became more apparent. Interstation correlations for storm rainfall decrease very rapidly with distance between stations. Inadequate networks can lead to significant errors in either underestimating or overestimating rainfall input as well as underestimating rainfall variability in verification of hydrologic models developed, for example, to estimate peak discharge, sediment production, or channel recharge. Finally, there are regional differences in intensities, areal extent, and duration of convective rainfall in the Southwest which require adequate sampling at several locations within the region.
A statistical approach to the inverse problem of aquifer hydrology: 2. Case study
Authors: Neuman Shlomo P. , Fogg Graham E. , Jacobson Elizabeth A.
Published: February 2008

In part 1 of this paper a new, statistically based approach to the problem of estimating patially varying aquifer transmissivities on the basis of steady state water level data was presented. Part 2 describes a case study in which the new method is applied to actual field data from the Cortaro Basin in southern Arizona. The paper does not present a perfect example of how the new inverse method should be used but only a preliminary demonstration of some of its capabilities in dealing with realistic data. The estimated transmissivities are shown to compare favorably with those obtained earlier for the same basin by an ad hoc trial‐and‐error procedure. Both sets of transmissivity values have been used successfully in conjunction with a mixed explicit‐implicit finite element model to reproduce 25 years of water level variations in the Cortaro Basin in response to pumpage during the period 1940–1965. The finite element model has revealed some important features of the local hydrogeological regime which have not been recognized previously.
Some limitations of water quality models for large lakes: A case study of Lake Ontario
Authors: Simons T. J. , Lam D. C. L.
Published: February 2008

Some of the problems encountered in the design of a predictive water quality model for a large lake are discussed with reference to Lake Ontario and within the framework of a simple dynamic phosphorus model which incorporates the essential mechanisms of complex plankton models. By fitting the model to a seasonal data base it is shown that equally satisfactory simulations are obtained with a variety of parameterizations and regardless of conditions of annual periodicity imposed on the solution. By comparison of model output with long‐term observations it is demonstrated that seasonal verification studies of dynamic models by themselves are not sufficient to diagnose the utility of such models for predicting long‐term trends. It is concluded that the uncertainty surrounding the formulation of sedimentation and nutrient regeneration, in conjunction with the sensitivity of models to assumptions regarding dynamic balance between lake concentrations and nutrient loadings, undermines the predictive capability of dynamic water quality models.
The effect of dam closure on downstream rapids
Authors: Graf William L.
Published: February 2008

The force of flowing water and the resistance of the largest boulder provide a means of evaluation of the stability of rapids in canyon rivers. Field measurements and calculations show that the closure of Flaming Gorge Dam, Utah, has had a significant effect on the stability of rapids in the canyons of the Green River in Dinosaur National Monument 68 km (42 mi) downstream from the dam. The reduction in peak flows by the dam has limited the competence of the river to move boulders deposited in the main channel by tributary processes, landslides, and prehistoric floods. Before the dam was closed, 62% of the rapids were stable, as indicated by the immobility of the largest boulder in each rapid. After the dam was closed, 93% of the rapids were stable as geomorphic/hydraulic features, though small boulders continue to move. A continuing buildup of boulders in the rapids will result from tributary contributions which are not affected by the dam.
Kinematic wave routing incorporating shock fitting
Authors: Borah Deva K. , Prasad Shyam N. , Alonso Carlos V.
Published: February 2008

An analytical solution to the kinematic wave approximation for unsteady flow routing is presented. The model allows time‐dependent lateral inflow with piecewise spatial uniformity and can be applied to complex kinematic cascades. Kinematic shocks are considered as manifestations of higher‐order effects such as rnonoclinal flood waves, bores, etc. Within the context of kinematic approximation therefore we retain their dynamic effects by routing the discontinuities as they appear. Certain simplifying assumptions are made which permit closed form solutions and an efficient numerical algorithm, based on the method of characteristics, is employed. The resulting model, called an approximate shock‐fitting scheme, preserves the effect of the shocks without the usual computational complications and compares favorably with an implicit finite difference solution. The efficiency and accuracy of the new method are illustrated by computing a variety of unsteady flows, ranging from simple cascades to complex natural watersheds.
A simple analytical solution for horizontal absorption of water by soils for exponential soil water diffusivity
Authors: Tolikas Panagiotis K. , Tzimopoulos Christos D. , Tolikas Demetrios K.
Published: February 2008

A simple approximate analytical solution to the problem of horizontal absorption of water in unsaturated soils is presented. The soil water diffusivity is assumed to be an exponential function of soil water content, which at the boundaries is assumed to be constant. Under the assumption that the inflection point of the soil water content profile coincides with the wetting front, the infinite domain problem is reduced to a finite domain problem with one boundary at the inflection point. The soil water content at the inflection point as well as its location are calculated, and the result is employed to obtain an approximate solution to the problem. The resulting profiles are compared with others found in the existing literature. A discussion concludes this paper.
Faulting caused by groundwater level declines, San Joaquin Valley, California
Authors: Holzer Thomas L.
Published: February 2008

Approximately 230 mm of aseismic vertical offset of the land surface across the Pond‐Poso Creek fault in the San Joaquin Valley, California, probably is related to groundwater withdrawal for crop irrigation. The scarp is approximately 3.4 km long and occurs in an area where the land subsided more than 1.5 m from 1926 to 1970. Modern faulting postdates the beginning of water level declines and associated subsidence. Movement detected by precise leveling surveys from February 1977 to March 1979 was seasonal, occurring during periods of water level decline. Fault offset was greater in the year with the lower seasonal low water level. The modern movement probably is caused by localized differential compaction induced by differential water level declines across the preexisting fault.
Earth fissures and localized differential subsidence
Authors: Holzer Thomas L. , Pampeyan Earl H.
Published: February 2008

Long linear tension cracks associated with declining groundwater levels at four sites in subsiding areas in south‐central Arizona, Fremont Valley, California, and Las Vegas Valley, Nevada, occur near points of maximum convex‐upward curvature in subsidence profiles oriented perpendicular to the cracks. Profiles are based on repeated precise vertical control surveys of lines of closely spaced bench marks. Association of these fissures with zones of localized differential subsidence indicates that linear earth fissures are caused by horizontal tensile strains probably resulting from localized differential compaction. Horizontal tensile strains across the fissures at the point of maximum convex‐upward curvature, ranging from approximately 100 to 700 microstrains (0.01 to 0.07% per year), were indicated based on measurements with a tape or electronic distance meter.
A numerical inversion of the laplace transform solution to radial dispersion in a porous medium
Authors: Moench A. F. , Ogata A.
Published: February 2008

A special form of the numerical inversion of the Laplace transform described by Stehfest (1970) is applied to the transformed solution of dispersion in a radial flow system in a porous medium. The inversion is extremely simple to use because the weighting coefficients depend only on the number of terms used in the computation and not upon the transform solution as required by most numerical inversion techniques. The result obtained by use of this approximate inversion of the radial dispersion problem reproduced the curves obtained previously by Hoopes and Harleman (1967) with a finite difference scheme.
Estimation of background loadings and concentrations of phosphorus for lakes in the Puget Sound Region, Washington
Authors: Gilliom Robert J.
Published: February 2008

For lakes in watersheds that include substantial developed land the evaluation of eutrophication is facilitated by a knowledge of changes in the lake's phosphorus (P) concentrations that have occurred since development. However, background (predevelopment) concentration data do not exist for many lakes. A method for estimating background P concentrations in lakes of the Puget Sound lowland has been developed. Using a mass balance ‘Vollenweider‐type’ model, P loadings were calculated from present‐day P concentrations measured in lake water and easily measured physical characteristics for 24 lakes in undeveloped, or insignificantly developed, watersheds. From other studies, annual P loading by bulk precipitation directly on a lake's surface was estimated to be 20 kg km−2. Loading of P from forest (undeveloped) land was derived for each lake as the difference between the calculated P loading to the lake and loading by bulk precipitation. Forest land loading to each lake was converted to the annual yield (mass per unit area) of the forested portion of the watershed. The yield of P from forest land was logarithmically related to annual runoff, and the regression equation expressing this relationship explained 73% of the sample variance. By applying that regression equation to the appropriate annual runoff data the yield of P from forest land can be estimated for any lake in the study area. Loading of P from forested watershed land, calculated from forest land yield, then can be added to direct loading by bulk precipitation to estimate background P loading for each lake. By applying the mass balance model to these calculated background loadings, background total‐P concentrations can also be calculated for all lakes in the study area that have stable thermal stratification during the summer. The standard error of estimate for calculated background loadings and concentrations averages about 25% for most lakes in the area. The method presented provides reliable estimates of background (predevelopment) P loads and concentrations for Puget Sound region lakes, using data that are presently available for most lakes in the region. These estimates can be compared to present‐day P levels in developed lakes to assess the impact that land use changes have had on lake water quality.
Use and modification of a simple rainfall‐runoff model for wet tropical catchments
Authors: Higgins Roger J.
Published: February 2008

A major constraint on the application of general purpose rainfall‐runoff models is the nonavailability of data. This constraint is minimized for the case of wet tropical catchments by adopting a simple model structure which recognizes the particular characteristics of those catchments, particularly the low variability of many parameters. An exponential decay function is employed in a linear rainfall‐runoff model. Parameters of the model are seasonal. A variant of the model makes simple allowance for evaporation and base flow. It is also possible to allow for the unknown systematic difference between the observed rainfall at a point and the catchment average rainfall. In many situations, the development of specific purpose models is likely to be a viable procedure for reducing expensive and delaying data collection programs necessary to satisfy the requirements of general models.
Statistical analysis of the Brooks‐Corey and the Green‐Ampt parameters across soil textures
Authors: McCuen R. H. , Rawls W. J. , Brakensiek D. L.
Published: February 2008

Infiltration is a major component of the hydrologic cycle for most watersheds. Therefore it is important to have a method that can provide infiltration estimates for soils within ungaged watersheds. Both the analysis of variance and the multivariate analysis were used to examine whether estimated Brooks‐Corey and Green‐Ampt parameters differ singularly or collectively across soil texture classes. The analysis indicated that the parameters for the two models examined varied collectively across soil texture classes. Mean parameter values and standard errors for soil textures are presented for possible use on ungaged watersheds.
Mathematical analysis of fluid flow in porous media with general anisotropy
Authors: Falade G. K.
Published: February 2008

The fundamental solution to the unsteady state fluid flow problem in anisotropic (r, θ, Z) coordinate domain was developed. The governing equation was solved using the expedience of an appropriate coordinate transformation with the Webber integral transform. The general boundary condition was principally considered, but the solution could be extended to cover the Neuman boundary condition case without difficulty. Also, solution to the isotropic problem could be deduced as a limiting case of the derived solution.
Kinematic subsurface stormflow
Authors: Beven Keith
Published: February 2008

This paper builds on the analysis of Henderson and Wooding (1964) in comparing simplified models of subsurface stormflow for the case of a sloping soil mantle in which the hydraulic conductivity is constant throughout. It is shown that models based on a kinematic wave formulation may be good approximations for those based on the extended Dupuit‐Forchheimier assumptions for values of the nondimensional parameter λ = 4i cos θ/(K sin2θ) less than about 0.75 in terms of predicting both water table profiles and subsurface stormflow hydrographs. By using this critical value of λ the range of values of slope angle and saturated hydraulic conductivity for which the kinematic approximation is valid can be specified. A comparison is made with slope angles and hydraulic conductivities at field sites where subsurface stormflow has been shown to be an important component of catchment storm response. It is concluded that the kinematic approximation may be useful for cases of practical interest.
On the computation of Darcian velocity and mass balance in the finite element modeling of groundwater flow
Authors: Yeh Gour‐Tsyh
Published: February 2008

Darcian velocity has been conventionally calculated in the finite element modeling of groundwater flow by taking the derivatives of the computed pressure field. This results in discontinuities in the velocity field at nodal points and element boundaries. Discontinuities become enormous when the computed pressure field is far from a linear distribution. It is proposed in this paper that the finite element procedure that is used to simulate the pressure field or the moisture content field also be applied to Darcy's law with the derivatives of the computed pressure field as the load function. The problem of discontinuity is then eliminated, and the error of mass balance over the region of interest is much reduced. The reduction is from 23.8% to 2.2% by one numerical scheme and from 29.7% to –3.6% by another for a transient problem.
Modeling double aquifer flow using a comprehensive potential and distributed singularities: 2. Solution for inhomogeneous permeabilities
Authors: Strack O. D. L. , Haitjema H. M.
Published: February 2008

The technique presented in the first part of this paper is generalized to the case of inhomogeneous permeabilities. The aquifer system is subdivided into regions of homogeneous permeability with discontinuities of the permeability occurring across the boundaries of these regions. The potentials are discontinuous across the common boundaries, which are represented as polygons. Line doublets are used to create the discontinuities in the potentials without violating the condition of continuity of flow. The strengths of the line doublets are determined from the condition that the head is continuous across the boundaries of the subregions. The method is validated against exact solutions, and some applications are discussed. The modeling of inhomogeneities by the use of line doublets is presented for a Dupuit‐Forchheimer analysis but is equally well applicable to problems of three‐dimensional flow and two‐dimensional flow in the vertical plane. The potential to be used for the latter applications equals the permeability times the head.
regulating corrosive water
Authors: Anderson Robert , Berry Donna
Published: February 2008

This paper examines an EPA proposal to regulate the corrosivity of drinking water in a benefit‐cost framework. The principal benefits from reducing corrosivity include improvements in health and lower maintenance expenditures for water supply systems and households. Despite considerable uncertainty over the magnitude of these benefits, treatment seems warranted, with the possible exception of very small systems.
Nile water for Sinai: Framework for analysis
Authors: Guariso Giorgio , Whittington Dale , Zikri Baligh Shindi , Mancy Khalil Hosny
Published: February 2008

The current plans of the Egyptian government call for a massive expansion of irrigated land, approximately 1.8 million additional hectares by the year 2000. The Egyptian Ministry of Irrigation presently intends to construct the Salaam, or Peace, Canal for the delivery of Nile water to the new reclamation areas in the Eastern Delta and Sinai. There are two primary objectives in transporting water to Sinai: (1) economic: to reclaim land to increase agricultural production and (2) political: to settle Sinai and establish a larger, permanent Egyptian presence. In this paper a multiobjective programing model is formulated and solved in order to examine the trade‐offs between the economic and political objectives and to study their interrelationships with such variables as water quantity, water quality, water transport costs, crop rotations, and irrigation technology. The results illustrate that the high costs of water transport to Sinai will require the use of modern, water‐efficient irrigation technologies, as well as entail substantial economic sacrifices if the political objectives associated with agricultural settlements in Sinai are to be achieved through the use of intensive, year‐round cultivation such as that practiced in the Nile Valley. The analysis also shows that the entire array of decisions to be made regarding the reclamation efforts (e.g., routes for the canals, site selection, irrigation technology) may be sensitive to the value of water in the rest of the country, a point largely ignored in the official plans.
Optimal control of reservoir discharge quality through selective withdrawal
Authors: Fontane Darrell G. , Labadie John W. , Loftis Bruce
Published: February 2008

A methodology combining simulation and optimization techniques is presented for determining optimal operational guidelines for selective withdrawal structures to meet downstream water temperature objectives. The goal is to develop operating rules that take into account anticipation of future critical temperature conditions that could occur. A one‐dimensional reservoir thermal simulation model developed by the U.S. Army Engineer Waterways Experiment Station is used to simulate the thermal stratification cycle of a reservoir. The thermal stratification model is interfaced with a new method of formulating dynamic programing problems called objective‐space dynamic programing to develop the optimal operation for each decision period. An advantage of the approach is that the thermal simulation model is retained in its original form rather than having to be restructured to fit explicitly into the optimizing model. An objective function related to release temperature deviations from desired target levels is minimized over a portion of the stratification cycle. Application to a case study shows the potential for improved system performance using the dynamic programing technique, as compared to the normal myopic period by period operation.
Possible use of active microwave remote sensing data for prediction of regional evaporation by Numerical simulation of soil water movement in the unsaturated zone
Authors: Bernard R. , Vauclin M. , Vidal‐Madjar D.
Published: February 2008

This paper presents a methodology for estimating bare soil evaporation from microwave radar data. The classical Richards’ equation is solved numerically by using soil moisture values estimated from simulated radar data as the upper boundary condition. It is shown that a sampling period of 3 days for the radar data permits a good estimation of evaporation for a clay soil with relatively low hydraulic conductivity values. However, for a sandy soil with higher hydraulic conductivity values the sampling period must be shorter, particularly for wet conditions which occur after rain events. The possibility of extending the local transfer model to the field scale, matching the expected observed scale from airborne or satellite radar, is investigated. We show that this can be done when the spatial heterogeneities of the field can be scaled through similar media concept.
Robustness of water resources systems
Authors: Hashimoto Tsuyoshi , Loucks Daniel P. , Stedinger Jery R.
Published: February 2008

When water resource systems investments are made there is little assurance that the predicted performance will coincide with the actual performance. Robustness is proposed as a measure of the likelihood that the actual cost of a proposed project will not exceed some fraction of the minimum possible cost of a system designed for the actual conditions that occur in the future. The robustness criterion is illustrated by its application to the planning of water supply systems in southwestern Sweden.
Simulation of solute transport using a transfer function model
Authors: Jury William A.
Published: February 2008

A transfer function model is proposed for simulating solute transport under natural field conditions where substantial variability exists in water transport properties. This approach makes no attempt to describe the variability through a deterministic model but merely measures the distribution of solute travel times from the soil surface to a reference depth. Using this distribution function, it is possible to simulate the average solute concentrations at any depth and time for arbitrary solute inputs or water application variability. Equivalently, the model may be used to predict the probability of extremely long or short travel times for a mobile chemical. In this paper several illustrative calculations are performed for which analytic solutions are possible. In a companion paper (Jury et al., this issue) a field test of the model is reported.
Cost allocation in water resources development
Authors: Young H. P. , Okada N. , Hashimoto T.
Published: February 2008

Different methods for allocating the joint costs of water supply projects among users are compared on the basis of certain commonsense principles of equity. We contrast the separable costs‐remaining benefits (SCRB) method with simple proportional allocation schemes and more sophisticated methods from cooperative game theory, including the Shapley value and variants of the core. Advantages and disadvantages of the methods in practice are examined using a regional water supply system in Sweden. It is argued that these principles provide a useful framework for choosing intelligently among methods. The appropriateness of a method depends on the context, especially on the reliability of information about costs and demands. The conclusion is that there is no one best method, although from a normative standpoint the SCRB method may be one of the worst.
A univariate versus a multivariate parameter distribution in a stochastic‐conceptual analysis of unsaturated flow
Authors: Russo David , Bresler Eshel
Published: February 2008

Solutions of stochastic‐conceptual flow problems obtained by utilizing a single stochastic parameter, the scaling factor α, are compared with solutions obtained by using multivariate parameter distribution. Two cases of one‐dimensional vertical flow are analyzed: (1) piston flow of solute under steady uniform surface water recharge and (2) transient water flow when uniform recharge rate is applied on the surface. Under steady vertical infiltration, expressing the variabilty of the hydraulic conductivity function K(θ) by the single stochastic‐variate α gives essentially the same results as the case when the variability in K(θ) is expressed by three stochastic variates. The agreement between the simulated average solute concentration profiles obtained by the two methods is improved as the recharge rate increases and a larger portion of the field is under ponding conditions. Similar results are found for the simulated potential runoff. For the case of the transient flow of water the variability in K(θ), as well as the variability in the soil water retentivity function h(θ), is expressed by a scaling factor α obtained from hydraulic conductivity data. Using α as the only stochastic variate resulted in mean water content (θ) profiles which are in a relatively good agreement with the mean θ profiles obtained when expressing the variability of K(θ) and h(θ) by five stochastic variates. The agreement between the distributions of the θ profiles obtained by the two methods, is rather poor. This agreement, as well as the agreement between the distributions of the depth of the wetting fronts, calculated by the two methods, are only slightly improved by using α as water content dependent stochastic variate. The results suggest that the scaling factor α, as a single stochastic variate, can be successfully used for stochastic analysis of water and solute flows under steady and transient infiltration conditions.
Management model for power production from a geothermal field: 1. Hot water reservoir and power plant model
Authors: Maddock Thomas , Mercer James W. , Faust Charles R.
Published: February 2008

A management model is developed that determines the optimum economic recoverability of a particular hot‐water geothermal reservoir undergoing exploitation for electric power generation. The management model integrates a physical model of the reservoir that predicts the areas of pressure decline due to withdrawals, and pressure rise due to reinjection of spent fluid, with a model of a two‐stage steam turbine power plant that determines the quantity of electricity generated for a rate of hot‐water extraction. Capital costs, variable costs and annual fixed costs are obtained for the reservoir development, extraction and reinjection, the transmission system, and the power plant. Revenues are determined for electrical power production. Application of the management model to a simplified, yet realistic example reservoir demonstrates that the methodology developed in this report can be used for analyzing the management of an integrated geothermal reservoir power plant system. For the example reservoir, 12 potential sites are developed, five for extraction wells and seven for injection wells. The wells on these sites are used to develop up to 27 MW of electrical power over a 20‐year time interval.
Comparison of techniques for estimating annual lake evaporation using climatological data
Authors: Andersen M. E. , Jobson H. E.
Published: February 2008

Mean annual evaporation estimates were determined for 30 lakes by use of a numerical model (Morton, 1979) and by use of an evaporation map prepared by the U.S. Weather Service (Kohler et al., 1959). These estimates were compared to the reported value of evaporation determined from measurements on each lake. Various lengths of observation and methods of measurement were used among the 30 lakes. The evaporation map provides annual evaporation estimates which are more consistent with observations than those determined by use of the numerical model. The map cannot provide monthly estimates, however, and is only available for the contiguous United States. The numerical model can provide monthly estimates for shallow lakes and is based on monthly observations of temperature, humidity, and sunshine duration.
Annual and monthly reservoir operating rules generated by deterministic optimization
Authors: Karamouz Mohammad , Houck Mark H.
Published: February 2008

The development of general reservoir system operating rules by deterministic optimization is investigated in this paper. An algorithm that cycles through a deterministic dynamic program, a regression analysis, and a simulation model is proposed and tested for 48 cases: annual operating rules are determined for 12 cases, and monthly operating rules are determined for 36 cases. The algorithm is easy to use, and each component of the algorithm is relatively simple. The results of using the algorithm for the 48 cases demonstrate the significant value of the algorithm in selecting reservoir operating rules.
Use of atmospheric fluorocarbons F‐11 and F‐12 to determine the diffusion parameters of the unsaturated zone in the Southern High Plains of Texas
Authors: Weeks Edwin P. , Earp Douglas E. , Thompson Glenn M.
Published: February 2008

Two stable, entirely man‐made fluorocarbon gases, trichlorofluoromethane (F‐1l) and dichlorodifluoromethane (F‐12), have been released into the atmosphere during the past 40 years as a consequence of their widespread commercial use. Production data for these compounds are well documented, and atmospheric buildup can be reconstructed on the basis of published release estimates. On‐site measurements of F‐1l and F‐12 concentrations in soil air within unconsolidated sedimentary deposits were made using gas chromatography at four sites in the Southern High Plains of Texas. Measurable concentrations of both gases were found at depths as great as 43.9 m. An analytical model and a finite‐difference model (both based on molecular‐diffusion theory) were used to assess the on‐site results. For the analytical model, effects of porosity, tortuosity, gas‐liquid partitioning, and sorption were tested as part of a lumped diffusion coefficient parameter. In the finite‐difference model, effects of porosity, tortuosity, and gas‐liquid partitioning were treated separately for individual layers, and sorption was treated as a single uniform parameter. Tortuosity values determined using the in situ measurement of F‐1l and F‐12 concentrations and the subsequent numerical modeling of results agree closely with values calculated using published theoretical and empirical relationships. These results thus confirm that the procedures for estimating tortuosity developed from theoretical considerations or by laboratory techniques are useful for predicting the transport of gases through even very thick and heterogeneous unsaturated zones. Such confirmation has not previously been available.
Chemical transport in a fissured rock: Verification of a numerical model
Authors: Rasmuson A. , Narasimhan T. N. , Neretnieks I.
Published: February 2008

Numerical models for simulating chemical transport in fissured rocks constitute powerful tools for evaluating the acceptability of geological nuclear waste repositories. Due to the very long‐term, high toxicity of some nuclear waste products, the models are required to predict, in certain cases, the spatial and temporal distribution of chemical concentration less than 0.001% of the concentration released from the repository. Whether numerical models can provide such accuracies is a major question addressed in the present work. To this end we have verified a numerical model, TRUMP, which solves the advective diffusion equation in general three dimensions, with or without decay and source terms. The method is based on an integrated finite difference approach. The model was verified against known analytic solution of the one‐dimensional advection‐diffusion problem, as well as the problem of advection‐diffusion in a system of parallel fractures separated by spherical particles. The studies show that as long as the magnitude of advectance is equal to or less than that of conductance for the closed surface bounding any volume element in the region (that is, numerical Peclet number <2), the numerical method can indeed match the analytic solution within errors of ±10−3% or less. The realistic input parameters used in the sample calculations suggest that such a range of Peclet numbers is indeed likely to characterize deep groundwater systems in granitic and ancient argillaceous systems. Thus TRUMP in its present form does provide a viable tool for use in nuclear waste evaluation studies. A sensitivity analysis based on the analytic solution suggests that the errors in prediction introduced due to uncertainties in input parameters are likely to be larger than the computational inaccuracies introduced by the numerical model. Currently, a disadvantage in the TRUMP model is that the iterative method of solving the set of simultaneous equations is rather slow when time constants vary widely over the flow region. Although the iterative solution may be very desirable for large three‐dimensional problems in order to minimize computer storage, it seems desirable to use a direct solver technique in conjunction with the mixed explicit‐implicit approach whenever possible. Work in this direction is in progress.
Daily operation of a multipurpose reservoir system
Authors: Yazicigil Hasan , Houck Mark H. , Toebes Gerrit H.
Published: February 2008

An optimization model that may be used by reservoir system operators to improve daily, real‐time operations and to evolve better long‐term operating guidelines is developed and tested. The four multipurpose reservoirs in the Green River Basin (GRB) of Kentucky are used as a case study. The GRB Operation Optimization Model (GRBOOM) is a linear program constructed to imitate the decision‐ making process that results in actual reservoir release decisions. The model is easily modifiable and very flexible, which allows sensitivity analysis and experimentation with new operating guidelines. This experimentation should permit the operators to evolve improved operating policies. The inputs to the model are data that are readily available, and the outputs may be presented in easily interpreted graphical form.
Recharge from an ephemeral stream following wetting front arrival to water table
Authors: Abdulrazzak Mohamed J. , Morel‐Seytoux Hubert J.
Published: February 2008

After the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table, the rate of recharge, which is also that of infiltration, is affected by the development of a groundwater mound. The effect is practically immediate if the water content behind the wetting front is close to saturation. An approximate analytical solution is developed in that case, which predicts the time dependence of the recharge rate. Comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations. As long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2.5, the analytical solution is essentially exact. Under most field conditions these ratios are largely exceeded. Consequently, the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications.
The effect of certain restrictions imposed on the interarrival times of flood events on the Poisson distribution used for modeling flood counts
Authors: Ashkar Fahim , Rousselle Jean
Published: February 2008

In the application of partial duration series models of flood analysis it is occasionally observed that successive exceedances are correlated. To reduce this correlation, some investigators tend to impose certain restrictions on the interarrival times of flood events in order that these events will not occur close together in bunches. We show analytically how such restrictions interfere with the underlying hypotheses of the Poisson process commonly used to model flood counts, and we caution against imposing restrictions that may render this simple and appealing model inapplicable.
Estimating a regional flood frequency distribution
Authors: Stedinger Jery R.
Published: February 2008

When floods at different sites are assumed to arise from the same distribution except for scale (U.S. Geological Survey's Index Flood Method), one can attempt to identify the dimensionless flood‐flow frequency distribution by normalizing small samples by each sample's sample mean. Unfortunately, the resultant curve may be a poor description of the true dimensionless flood distribution. This problem can be overcome by working with the logarithms of the peak flow values and using unbiased moment or probability weighted moment estimators. However, the correlation among concurrent flood flows in a region is shown to place severe limits the accuracy with which a distribution's moments can be estimated with many such correlated records.
Analytical solutions for rectangular aquifers with third‐kind (Cauchy) boundary conditions
Authors: Corapcioglu M. Yavuz , Borekci Osman , Haridas Ajit
Published: February 2008

Closed form analytical solutions for the drawdown due to a single well pumping at a constant rate from a rectangular aquifer with third‐kind (Cauchy) boundary conditions are obtained by employing the finite Fourier integral transforms. Three illustrative examples are considered and the solutions are generated at the spatial and temporal locations of interest.
Transferable Discharge Permit Trading Under Varying Stream Conditions: A simulation of multiperiod permit market performance on the Fox River, Wisconsin
Authors: O'Neil William B.
Published: February 2008

The state of Wisconsin has recently established the legislative basis for what may be the first, operating water‐pollution permit market in the United States. The efficient properties of such markets have been discussed widely in the theoretical literature, but little empirical work has been published regarding the potential cost savings attainable in specific situations. This paper describes part of the empirical analysis that supported the creation of a transferable discharge permit (TDP) market on the Fox River in Wisconsin. A multiperiod water quality planning model is developed to illustrate the performance of a TDP market under conditions of varying stream flow and temperature. The model is applied to the case of the Fox River and is used to compare the cost of achieving target water quality levels under conventional regulatory rules with the cost associated with operation of a TDP market. In addition to the cost estimates, the simulation of market performance yields information on the probable pattern of trading that may occur in the Fox River TDP market.
A geostatistical approach to the inverse problem in groundwater modeling (steady state) and one‐dimensional simulations
Authors: Kitanidis Peter K. , Vomvoris Efstratios G.
Published: February 2008

The problem of estimating Hydrogeologic parameters, in particular, permeability, from input‐output measurements is reexamined in a geostatistical framework. The field of the unknown parameters is represented as a ‘random field’ and the estimation procedure consists of two main steps. First, the structure of the parameter field is identified, i.e., mathematical representations of the variogram and the trend are selected and their parameters are established by using all available information, including measurements of hydraulic head and permeability. Second, linear estimation theory is applied to provide minimum variance and unbiased point estimates of hydrogeologic parameters (‘kriging’). Structure identification is achieved iteratively in three substeps: structure selection, maximum likelihood estimation, and model validation and diagnostic checking. The methodology was extensively tested through simulations on a simple one‐dimensional case. The results are remarkably stable and well behaved. The estimated field is smooth, while small‐scale variability is statistically described. As the quality of measurements improves, the procedure reproduces more features of the original field. The results are also shown to be rather insensitive to deviations from assumptions about the geostatistical structure of the field.
Runoff prediction errors and bias in parameter estimation induced by spatial variability of precipitation
Authors: Troutman Brent M.
Published: February 2008

Spatial variability of precipitation causes inflated mean squared errors of prediction in precipitation‐runoff modeling. One component of these larger errors is a bias, which often takes the form of over‐prediction for large events and underprediction for small events. This problem is examined using an assumed stochastic structure for the spatial behavior of rainfall together with a form of the Green‐Ampt infiltration equation for prediction of storm runoff volume. The stochastic rainfall model incorporates the nonstationarity and spatial correlation exhibited by actual rainfall. The bias in runoff prediction causes parameter estimates obtained by least squares calibration to be asymptotically biased. The magnitude and direction of the bias depends on the interaction between the runoff prediction bias and the sensitivity of predicted runoff to changes in parameter values. Numerous climatic and hydrologic factors exercise an influence on this interaction.
A theoretical explanation of solute dispersion in saturated porous media at the Darcy Scale
Authors: Bhattacharya R. N. , Gupta Vijay K.
Published: February 2008

The transport of a nonreactive dilute solute in saturated porous media is explained at three distinct space‐time scales. These are the kinetic, microscopic, and Darcy scales. The transition from one scale to the next higher scale, i.e., from the kinetic to the microscopic to the Darcy, is a consequence of the central limit theorem of probability theory. At the microscopic scale, the solid and the liquid phases together form a heterogeneous continuum. The microscopic solute concentration is governed by a parabolic equation with spatially varying drift and diffusion coefficients. The so‐called dispersion phenomenon at the Darcy scale is shown to appear in the transition from the microscopic to the Darcy scale. In the computation of the dispersion coefficients, the Peclet number appears naturally as a dimensionless parameter. For large Peclet numbers the coefficients of dispersion at the Darcy scale are shown to be linear in the liquid convective velocity. A general expression is obtained which gives the order of magnitude of the dispersion coefficient for all Peclet numbers within the Darcy regime of the liquid convective velocities. This expression shows that for very small Peclet numbers, only the molecular diffusion provides the dominant contribution, whereas for intermediate values of Peclet numbers, both the liquid convection and the molecular diffusion contribute to the dispersion coefficients; in this range the dispersion coefficients are not linear in the liquid convective velocity. These findings are well supported by existing experimental observations. These theoretical insights into dispersion at the Darcy scale are also important in explaining the so‐called macrodispersion and the scale effect at field scales.
Meltwater movement in a deep snowpack: 1. Field observations
Authors: Jordan Peter
Published: February 2008

The flow of meltwater through a snowpack can be described by Darcy's law, and by a set of equations relating conductivity, capillary pressure, and liquid water content which are similar to the equations governing unsaturated groundwater flow. Field observations were conducted which were designed to test the applicability of the unsaturated flow equations to the description of meltwater movement at the scale of a small watershed. Simple instrumentation was used to measure capillary pressure and meltwater flux rates; this was supplemented with energy and water balance measurements for the study watershed. Observations of surface snowmelt, meltwater flux, and streamflow for the snowmelt period confirm the nature of meltwater flow as described by the unsaturated flow equations, and illustrate the controlling influence of snowpack hydraulics on the streamflow hydrograph. Observed speeds of the meltwater wave front in the snowpack average about 0.22 m h−1 and capillary pressures and kinematic wave speeds observed are comparable to those reported in other deep‐snow environments. The difficulty of obtaining reliable liquid water content measurements is identified as a major limitation in the determination of hydraulic properties of the snowpack.
A methodology for evaluation of flood forecast‐response systems: 3. Case studies
Authors: Krzysztofowicz Roman , Davis Donald R.
Published: February 2008

Case studies are reported to illustrate a methodology for evaluation of the performance of flood forecast‐response (FFR) systems. The methodology concerns specifically the economic evaluation of the effectiveness of riverine flood forecasts as a means of reducing property damage. The case studies include the evaluation of the FFR systems in three communities: Milton, Pennsylvania; Victoria, Texas; and Columbus, Mississippi. The first study is reported in greater detail, and then a comparative analysis of all three systems is presented. Also, an example is given of evaluation of the economic worth of flood forecasts from the viewpoint of an individual decision maker. The capability of the methodology as a decision aid is illustrated in the context of several planning problems, such as the determination of the economic benefit of an improvement in the forecast system (e.g., installation of weather radar) or in the response system (e.g., increased community preparedness for floods), the development of an optimal response strategy, etc.