bluuebunny/crossref_metadata_2025 huggingface dataset:
Network design using optimal estimation procedures
Authors: Jones D. A. , Gurney R. J. , O'Connell P. E.
Published: February 2008

A network of rain gages provides information about rainfall at only a limited number of points within a region: some procedure must then be adopted to estimate the rainfall for other chosen points and areas within the region. Methods are presented here whereby the accuracy of rainfall estimates can be quantified so that a comparison with the requirements of users of rainfall data can be made. The calculation of the accuracy of optimal estimates based on any number and configuration of gages is described. The results can be applied to the redesign of existing networks of gages by mapping the root mean square error of point interpolation, allowing the identification of those areas where new gage sites are most needed to meet some specified criterion of accuracy. Formulae are also presented which allow the accuracy of an optimal estimate of areal rainfall to be calculated for any shape of area and any configuration of gages.
Accuracy of an estuarine hydrodynamic model using smooth elements
Authors: Walters Roy A. , Cheng Ralph T.
Published: February 2008

A finite element model which uses triangular, isoparametric elements with quadratic basis functions for the two velocity components and linear basis functions for water surface elevation is used in the computation of shallow water wave motions. Specifically addressed are two common uncertainties in this class of two‐dimensional hydrodynamic models: the treatment of the boundary conditions at open boundaries and the treatment of lateral boundary conditions. The accuracy of the models is tested with a set of numerical experiments in rectangular and curvilinear channels with constant and variable depth. The results indicate that errors in velocity at the open boundary can be significant when boundary conditions for water surface elevation are specified. Methods are suggested for minimizing these errors. The results also show that continuity is better maintained within the spatial domain of interest when ‘smooth’ curve‐sided elements are used at shoreline boundaries than when piecewise linear boundaries are used. Finally, a method for network development is described which is based upon a continuity criterion to gauge accuracy. A finite element network for San Francisco Bay, California, is used as an example.
A model for optimal irrigation scheduling with saline water
Authors: Yaron D. , Bresler E. , Bielorai H. , Harpinist B.
Published: February 2008

The paper presents a dynamic programing model for optimal scheduling of irrigation with water of varying salinity levels and soil salinity parameters explicitly considered. The system underlying the model is characterized by two discrete state variables, soil moisture and the salinity level of the soil solution, which are updated on a day‐by‐day basis. Transformation functions from one state to another in response to irrigation decisions and a crop response function to soil moisture and salinity are the other elements of the model, with the objective being maximization of income derived from the irrigated crop. An application to the irrigation of sorghum in the southern semiarid area of Israel is presented and evaluated.
Thermohaline instability in anisotropie porous media
Authors: Tyvand Peder A.
Published: February 2008

The onset of thermohaline convection in a horizontal porous layer is investigated theoretically. The layer is homogeneous, anisotropic, and of infinite horizontal extent. Horizontal isotropy with respect to permeability, thermal diffusivity, and solute diffusivity is assumed. For porous media with thermally insulating solid matrices the stability diagram has the same shape as in the case of isotropy. The critical wave number is constant and equal to that of the one‐component case. For thermally conducting matrices, new features may occur: The locus of the direct mode in the stability diagram may not be a straight line, and the corresponding wave number may be nonconstant. The initiation of salt fingers is studied by linear theory. It seems that the width of salt fingers is influenced by anisotropy in the diffusivities. Anisotropy may or may not favor salt fingers, depending on a dimensionless diffusion parameter D being greater than or less than 1.
A note on capital indivisibility and the definition of marginal cost
Authors: Mann Patrick C. , Saunders Robert J. , Warford Jeremy J.
Published: February 2008

Ambiguity in the interpretation of marginal cost emerges where capital indivisibility is present. The indivisibility condition is particularly applicable to new water projects in which large capital investments are required to place a central system into full operation. Marginal cost is defined in four ways. The definitions all incorporate future costs and output only; the definitions vary in the extent to which they focus on short‐run versus long‐run allocative efficiency, and in the extent to which they attempt to minimize price fluctuations in the context of lumpy investments.
Some effects of linearizing the unsaturated soil moisture transfer diffusivity model
Authors: Hromadka T. V. , Guymon G. L.
Published: February 2008

Five methods are evaluated for estimating the nonlinear diffusivity coefficient in a finite element Crank‐Nicolson analog of the diffusivity model for moisture transfer in an unsaturated horizontal homogeneous soil column. The Galerkin technique is utilized for the quasi‐linear spatial discretization problem, and the commonly used Crank‐Nicolson time advancement method is used with a diffusivity coefficient update method based upon (1) a constant diffusivity coefficient for all space and time and (2) a quasi‐constant diffusivity coefficient within each element during a Crank‐Nicolson time step. In the case of constant diffusivity coefficient problems a modified capacitance matrix scheme significantly improves results over the standard finite element capacitance matrix. For nonlinear problems, five methods of estimating quasi‐constant soil water diffusivity equivalents were evaluated. These are (1) a straight line average using element endpoint water content in a diffusivity function, (2) an integration of the diffusivity constant over each element, (3) an inverse diffusivity function integration over each element, (4) an evaluation of the diffusivity coefficient as the mean parabolic value over a specified subdomain of each element, and (5) an evaluation of the diffusivity coefficient for each element at one half of the Crank‐Nicolson time step, using method 4. Both the modified and unmodified finite element capacitance matrices were used for each method considered. The unmodified finite element capacitance matrices based upon values of diffusivity coefficients evaluated as the mean parabolic value of the state variable gave the superior results.
Distribution methods for transferable discharge permits
Authors: Eheart J. Wayland , Joeres Erhard F. , David Martin H.
Published: February 2008

A mathematical model has been developed to simulate the operation of a single‐price auction of transferable discharge permits. Permits may be sold at auction by the control authority or may be given, free of charge, to the dischargers according to some agreed‐upon formula and subsequently redistributed by a similar auction. The sales method and four alternative free allocation schemes are compared through the example case of phosphorus discharge from point sources in the Wisconsin‐Lake Michigan watershed.
Real‐time forecasting with a conceptual hydrologic model: 1. Analysis of uncertainty
Authors: Kitanidis Peter K. , Bras Rafael L.
Published: February 2008

The optimal control of watershed systems requires accurate real‐time short‐term forecasts of river flows. For the first time, this paper formulates a large, nonlinear conceptual model (the National Weather Service catchment model) in a mode amenable to analysis of uncertainty and the utilization of real‐time information (measurements, forecasts, guesses) to update system states and improve streamflow predictions. The proposed methodology is based on the state space formulation of the equations describing the hydrologic model and the assumption of sources of uncertainty in the data and in the model structure. The first two moments of random variables are estimated in a computationally efficient way using on‐line linear estimation techniques. Linearization of functional relationships is performed with the uncommon but powerful multiple‐input describing function technique for the most strongly nonlinear responses and Taylor expansion for the rest. The linear feedback rule developed is based on the Kalman filter.
Unsteady sediment transport law and prediction of aggradation parameters
Authors: Soni J. P.
Published: February 2008

A general law for unsteady sediment transport in the form of a differential equation has been established. This law has been tested against the sediment transport rates obtained in the laboratory during aggradation arising from an increase in sediment supply over and above the equilibrium sediment transport capacity of the channel. Using the law, expressions for predicting the maximum depth of aggradation and length of aggradation under the above stated boundary conditions have been obtained. The agreement between values of the parameters computed from these expressions, when compared with the values observed in the laboratory and with the values obtained from the numerical model of Gessler, is very good.
A new method allowing the measurement of rapid variations of the water content in sandy porous media
Authors: Hoa N. T.
Published: February 2008

A new method allowing the measurement of rapid water content variations in sandy porous media is reported. The principle of the method is based on the variation of the factor of light transmission through a heterogeneous solid‐liquid‐air medium with water content. The transmission of light through such a medium is favored by the presence of water. The number of pores filled with water as a function of the water content being unknown, it is impossible to predict theoretically the relationship between light transmission and water content, and a calibration procedure is necessary. With proper calibration the present method compares favorably with the gamma ray absorption method.
Analysis of flow through heterogeneous random aquifers by the method of embedding matrix: 1. Steady flow
Authors: Dagan G.
Published: February 2008

The statistical structures of the hydraulic conductivity, head gradient, specific discharge, and head fields are analyzed with the aid of a simplified model consisting of a collection of spherical (in three dimensions) and cylindrical (in two dimensions) blocks of different conductivity and diameter set at random and independently in space. Results of a previous work for the effective conductivity and unbounded formations (Dagan, 1979) are recovered and given a rational derivation. The influence of the aquifer boundary and nonuniform average flows are examined for the first time. The growth of the head variance with distance from boundary in two‐dimensional flows is compared with that of the Monte Carlo simulations of Smith and Freeze (1979).
Range analysis of exchangeable normal variables
Authors: Phien Huynh Ngoc , Arbhabhirama Anat
Published: February 2008

An attempt is made in this paper to provide general equations relating the first four moments of the surplus and deficit to the first four moments of the partial sums. Equations for the expected values of the range, the products of the range, surplus, and deficit, to the partial sum over a given period are also derived. The usefulness of these equations is shown by their application to the case of exchangeable normal variables, by which some important results previously derived through complicated integrations are also obtained as special cases.
Project grant allocation process applied in sewerage planning
Authors: Hagihara Yoshimi , Hagihara Kiyoko
Published: February 2008

A model is given for sewerage planning which extends over a region controlled by a number of local governments, whereas the total grant allocated to this region is preassigned by the central government. A regional linear programing model is first set up, and using a method of decomposition, it is shown that this method itself is a decision‐making process in which information is exchanged between two levels, the central and local governments. It is shown that the aforementioned decision making process can be applied in grant allocation problems.
Phosphorus retention models for Tennessee Valley Authority reservoirs
Authors: Higgins John M. , Kim Byung R.
Published: February 2008

Data for the 18 largest Tennessee Valley Authority (TVA) reservoirs are compared with previously developed models for predicting steady state phosphorus concentrations in lakes. A plug flow model is presented for lakes and reservoirs which have significant longitudinal variation in phosphorus concentration. The results indicate that phosphorus sedimentation and retention coefficients developed for natural lakes are not directly applicable to TVA reservoirs. The apparent settling velocity of phosphorus in TVA reservoirs was substantially higher than previously reported values for natural lakes. Application of the plug flow model to Cherokee Reservoir showed good agreement with measured in‐lake phosphorus concentrations.
The use of Na/Cl ratios to trace solute sources in a semiarid zone
Authors: Magaritz Mordeckai , Nadler Arie , Koyumdjisky Hanna , Dan Joel
Published: February 2008

Rainwater interaction with soils is a major source of dissolved salts in groundwater. The transition zone between the humid and the arid area is characterized by a specific combination of reactions which do not exist elsewhere. This combination of CaCO3 dissolution and base exchange reactions affects the Na/Cl ratio, which is the quantitatively most important parameter used for tracing salinity sources of groundwater. The increase in the Na/Cl ratio in the coastal plain aquifer of Israel from north to south is related to local recharge of Na‐rich water after interaction with soils of loessial origin.
Snow surface energy exchange
Authors: Male D. H. , Granger R. J.
Published: February 2008

The release of snow in the form of melt water is important to agriculture, hydroelectric power generation, urban water supply, and flood control over a large part of the Northern Hemisphere. One of the factors governing the rate of production of melt water is the energy exchange at the snow surface. The two most important exchange processes are radiation transfer (short‐ and long‐wave) and the turbulent exchange process (sensible and latent heat transfer). The present review considers these two processes exclusively. The radiation exchange is frequently the dominant transfer process during snowmelt on the prairies, in the northern forests, and in mountainous terrain. Methods for modeling radiation on an areal basis during clear days in open areas are well advanced and agreement between calculations and measurements is good although measured data are scarce in the literature. The presence of a forest cover or cloudy skies complicates the modeling process, but relatively simple procedures have been developed in the past few years which are sufficiently accurate for many water management purposes. Sensible and latent heat transfer has been measured at a variety of sites throughout the world. When results are compared it is obvious that such factors as prevailing air mass conditions, altitude, time of year, and terrain features influence the relative importance of turbulent exchange and radiation transfer. As yet there are insufficient data to distinguish trends among these factors with any clarity although the air mass is clearly important and should be considered in future studies of the energy exchange process.
Comparison of laboratory, in situ, and rock mass measurements of the hydraulic conductivity of metamorphic rock at the Savannah River Plant near Aiken, South Carolina
Authors: Marine I. Wendell
Published: February 2008

In situ testing of exploratory wells in metamorphic rock indicates that two types of fracturing occur in the rock mass. Rock containing small openings that permit only extremely slow movement of water is termed virtually impermeable rock. Rock containing openings of sufficient size to permit transmission of water at a significantly faster rate is termed hydraulically transmissive rock. Laboratory methods are unsuitable for measuring hydraulic conductivity in hydraulically transmissive rock; however, for the virtually impermeable rock, values comparable to those of the in situ tests are obtained. The hydraulic conductivity of the rock mass over a large region is calculated by using the hydraulic gradient, porosity, and regional velocity. This velocity is determined by dividing the inferred travel distance by the age of water, which is determined by the helium content of the water. This rock mass hydraulic conductivity value is between the values measured for the two types of fractures but is closer to the measured value for the virtually impermeable rock. This relationship is attributed to the control of the regional flow rate by the virtually impermeable rock where the discrete fractures do not form a continuous open connection through the entire rock mass. Thus laboratory methods of measuring permeability in metamorphic rock are of value if they are properly applied.
Aquifer thermal energy storage: A numerical simulation of Auburn University Field Experiments
Authors: Tsang Chin Fu , Buscheck Thomas , Doughty Christine
Published: February 2008

This paper describes the computer simulation of two cycles of a seasonal aquifer thermal energy storage experiment recently carried out by Auburn University. The simulated production temperatures and energy recovery factors agree very well with the field data. A general description of the experiments and the numerical model used are given. Discussions are also given on the determination and choice of various parameters used in the simulations. These are followed by a detailed comparison of simulated and observed temperature distributions.
A mathematical model for consolidation in a thermoelastic aquifer due to hot water injection or pumping
Authors: Bear J. , Corapcioglu M. Y.
Published: February 2008

A mathematical model is developed for the areal distribution of fluid pressure, temperature, land subsidence, and horizontal displacements due to hot water injection into thermoelastic confined and leaky aquifers. The underlying assumption is that the aquifer is thin in relation to the horizontal distances of interest, and hence all dependent variables of interest are average (over the thickness) values. The solid matrix is assumed to be thermoelastic. Following the development of three‐dimensional conservation of mass and energy equations and equilibrium equations in terms of horizontal and vertical displacements, the mathematical model is derived by averaging the three‐dimensional model over the vertical thickness of the aquifer, subject to conditions of plane total stress. The effects of viscous dissipation and compressible work have been included in the formulation. The resulting averaged coupled equations are in terms of pore water pressure, temperature, and vertical and horizontal displacements which are functions of x, y, and t only. The equations are nonlinear and have to be solved simultaneously due to the coupling that exists among them. Equations and appropriate boundary conditions in radial coordinates have also been presented for an example of a single injecting (or pumping) well.
Some limiting forms of the poisson distribution of annual station precipitation
Authors: Eagleson Peter S.
Published: February 2008

Annual station precipitation is represented as a seasonally stationary Poisson arrival process in terms of three constituent random variables: season length, number of storms, and storm depth, and the distribution of the annual total is derived. The contribution of each constituent variable to variance of the annual total precipitation is determined, and limiting distributions of the latter are derived by letting each contribution vanish separately. In humid climates it is shown that the storm depth variability predominates, giving a distribution which is closely normal. In arid climates the number of storms controls and gives a highly skewed distribution. All cases are compared with observations.
Storm flow response to road building and partial cutting in small streams of northern California
Authors: Ziemer Robert R.
Published: February 2008

To assess the influence of road building and logging on storm flow response, a pair of watersheds were studied at Caspar Creek near Fort Bragg in northern California from 1963 to 1975. Selection cutting and tractor yarding of 85‐year‐old second‐growth redwood and Douglas‐fir forest did not significantly affect large peak streamflows. The first streamflow peaks in the fall, however, were increased about 300% after logging. These early fall storms produced small peaks, which had little, if any, hydraulic consequence. The effect of logging on peak flow was best predicted by a variable representing the percentage of the area logged divided by the sequential storm number within the year.
Mathematical model for regional land subsidence due to pumping: 2. Integrated aquifer subsidence equations for vertical and horizontal displacements
Authors: Bear Jacob , Corapcioglu M. Yavuz
Published: February 2008

A mathematical model for regional subsidence due to pumping from an aquifer is developed on the basis of Biot's work on coupled three‐dimensional consolidation. Following Biot's work on threedimensional consolidation, with coupling between mass conservation and equilibrium equations, a mathematical model for regional subsidence due to pumping from an aquifer is developed by averaging the three‐dimensional model over the thickness of the aquifer and assuming conditions of plane stress. Both (vertical) land subsidence and horizontal displacements, as functions of plane coordinates and time, can be estimated by solving the model equations for a given confined or leaky confined aquifer. An analytical solution is presented for the special case of a single well pumping from an infinite homogeneous isotropic aquifer. The solution provides estimates of changes in averaged (over the vertical) values of piezometric head, vertical subsidence, and horizontal displacement. The results indicate that under the conditions of the studied case of radial flow the solution for piezometric head is identical to the one obtained by noncoupled models. Furthermore, half the volume strain is produced by vertical subsidence while the other half by the horizontal displacement. Hence the vertical subsidence is only approximately half the value obtained in noncoupled models which neglect horizontal displacement. A numerical example demonstrates these conclusions.
Unsteady one‐dimensional settling of suspended sediment
Authors: Dhamotharan S. , Gulliver J. S. , Stefan H. G.
Published: February 2008

A one‐dimensional, unsteady numerical model for the prediction of the vertical distribution of suspended sediment concentration and rate of suspended sediment deposition in water stirred uniformly has been developed. The model is derived from the convective‐diffusive transport equation and uses a fully implicit, exponential finite difference scheme. The model is unconditionally stable regardless of vertical diffusivities and particle fall velocities. Such a model has not previously been given in the sedimentation literature and is of interest for theory and applications. A generic study of vertical suspended sediment profiles and trap efficiencies has been made. The results, presented in dimensionless form, cover Peclet numbers Vh/D from zero to infinity. V is the particle fall velocity, h is the water depth, and D is the mean vertical exchange coefficient. In studies of suspended sediment behavior the parameters V and D are often unknown or not well determined. The generic results generated show what kind of variations in suspended sediment concentrations and trap efficiencies can be expected with different values of V and D. Sediment deposition is shown to occur through downward frontal movement when Vh/D is large (≥ 20) and through columnar precipitation when Vh/D is small (≤ 0.2). Residence time is shown theoretically to be far more important for estimates of sediment deposition rate than turbulence. This is in agreement with empirical findings for reservoir trap efficiency.
Seasonal reversals of groundwater flow around lakes and the relevance to stagnation points and lake budgets
Authors: Anderson Mary P. , Munter James A.
Published: February 2008

Several researchers have observed seasonal reversals in the direction of groundwater flow around lakes. If these reversals are prolonged and are accompanied by the formation of a stagnation point, they may have a significant effect on a lake's water and nutrient budgets. The formation of a stagnation point at a flow‐through lake (i.e., a lake that receives groundwater through part of the lake basin and recharges the groundwater system over the rest of the lake basin) is accomplished by the formation of a groundwater mound on the downgradient side of the lake. In this paper the seasonal formation of a stagnation point at Snake Lake, Wisconsin, is investigated with the aid of two‐dimensional transient computer models applied in cross section and areally. The analysis demonstrates the potential for the seasonal formation of a stagnation point at a flow‐through lake and provides some insight into the transient development of the stagnation point.
Mass transport: 3. Role of hydraulic conductivity data in prediction
Authors: Smith Leslie , Schwartz Franklin W.
Published: February 2008

Spatial variations in hydraulic conductivity play a critical role in controlling contaminant transport in groundwater flow systems. A stochastic analysis of mass transport is carried out to investigate various relationships between the number of hydraulic conductivity measurements available to characterize that heterogeneity and the resulting uncertainty in transport predictions. Uncertainties arise both from the unknown spatial variation in hydraulic conductivity and in estimating the parameters of the probability distribution for hydraulic conductivity. The simultations are based on limited sampling of hydraulic conductivity values from a series of hypothetical field sites. Results are interpreted in light of the uncertainty in determining seepage velocities within the flow system. The simulations indicate that considerable hydraulic conductivity data may be necessary to obtain a reasonable degree of confidence in predictions of site behavior. For the sample grids considered, the hydraulic conductivity data do not go far toward reducing the uncertainty in the groundwater velocity. The data seem most effective in locally influencing the mean velocity and constraining the variability in the velocity at the measurement points. A complex dependence is observed between the uncertainty in the velocity field and the hydraulic conductivity measurements. Transport predictions are sensitive to the arrangement of the heterogeneities inferred from the data set. Results of this study suggest that given a moderate number of data points, the unknown patterns of spatial variation in hydraulic conductivity are a more important source of uncertainty than errors in estimating the mean and standard deviation of the hydraulic conductivity distribution.
A model of discontinuous measurement error and its effects on the probability distribution of flood discharge measurements
Authors: Potter Kenneth W. , Walker John F.
Published: February 2008

Above a given threshold an indirect method is usually used to estimate flood discharges. This results in a significant increase in the standard deviation of the measurement error, a phenomenon which the authors have termed discontinuous measurement error. An error model reveals that the coefficients of variation, skewness, and kurtosis of the distribution of the measured flood discharges are significantly higher than the corresponding coefficients of the parent flood distribution. This bias has important implications with regard to flood frequency analysis.
Increasing hydrogen ion activity of water in two reservoirs supplying the San Francisco Bay Area, California
Authors: McColl J. G.
Published: February 2008

The hydrogen ion activity (H+) of water in two Sierra Nevada reservoirs (Pardee and Hetch Hetchy) that supply the San Francisco Bay area has been increasing with time over the period 1954–1979. This conclusion is based on weekly measurements ofpH at the two reservoirs and is supported by measurements of alkalinity which decreased at Pardee over the period 1944–1979. Based on linear models, the rate of the increasing (H+) was the same at both reservoirs, and (H+) varied concomitantly from year to year, suggesting a common, general cause. Mean monthly variation in (H+) corresponded to mean monthly variation in atmospheric pollution from a nine‐county area around San Francisco Bay. The most likely cause of the increasing (H+) of reservoir waters is NOx from automobile exhausts primarily from the San Francisco Bay area.
Estimation of accumulation parameters for urban runoff quality modeling
Authors: Alley William M. , Smith Peter E.
Published: February 2008

Many recently developed watershed models utilize accumulation and washoff equations to simulate the quality of runofffrom urban impervious areas. These models often have been calibrated by trial and error and with little understanding of model sensitivity to the various parameters. Methodologies for estimating best fit values of the washoff parameters commonly used in these models have been presented previously. In this paper, parameter identification techniques for estimating the accumulation parameters from measured runoff quality data are presented along with a sensitivity analysis of the parameters. Results from application of the techniques and the sensitivity analysis suggest a need for data quantifying the magnitude and identifying the shape of constituent accumulation curves. An exponential accumulation curve is shown to be more general than the linear accumulation curves used in most urban runoff quality models. When determining accumulation rates, attention needs to be given to the effects of residual amounts of constituents remaining after the previous period of storm runoff or street sweeping.
Consequences and responsibilities in drought forecasting: The case of Yakima, 1977
Authors: Glantz Michael H.
Published: February 2008

This study is concerned with the impact of an actual forecast of total water supply available (TWSA) made by the Bureau of Reclamation for irrigators in the Yakima Valley (Washington). Estimates of TWSA (legally calculated by combining natural flow estimates, water storage, and other sources, i.e., return flow) were issued in February 1977, suggesting that less than half of the long‐term average water supply would be available for the coming irrigation season. The Bureau allocated the estimated TWSA as follows: those with nonproratable (senior) water rights were to get 98% of their normal water allocation, while those with proratable (junior) rights were to receive about 6%. The TWSA estimate and subsequent water allocations prompted irrigation districts, as well as individual farmers and federal, state, and local government agencies, to take a variety of measures they might not otherwise have taken. By May 1977 the Bureau realized that there was more water in the system than they had expected and that some of their assumptions had in fact distorted their projections of TWSA. Many farmers took legal action against the Bureau to recover costs they claimed were incurred by their responses to the erroneous water supply projections. This study raises questions about societal responses to seasonal water supply estimates and about the benefits to society of good forecasts as well as the costs of erroneous ones. It also raises the issue of who, if anyone, should bear the responsibility for the societal implications of such forecasts.
Use of mathematical models to generate alternative solutions to water resources planning problems
Authors: Chang Shoou‐Yuh , Brill E. Downey , Hopkins Lewis D.
Published: February 2008

An optimization model is generally not a perfect representation of a complex real world planning problem. Optimization models, however, can be used to generate alternatives that are good and different so that analysts and decision makers can examine a wide range of alternatives to gain insight and understanding. Modeling to generate alternatives (MGA) techniques have been designed to serve this purpose. This paper provides a preliminary assessment of the capabilities of the Hop, Skip, Jump (HSJ) method, a random method, and a branch and bound/screening (BBS) method for generating good and different alternative solutions. These three methods are illustrated using an example water resources planning problem represented by a mixed integer programing model. Each method yields sets of alternatives that are different from each other, but for each method the alternatives are different in different ways. Given that all three methods are efficient, it may be most fruitful to use more than one method and thereby to consider alternatives that are not only different, but different in different ways.
Permeability of fractured rock: Effect of fracture size and data uncertainties
Authors: Sagar Budhi , Runchal Akshai
Published: February 2008

Equations are derived for equivalent Darcy permeability of a fracture system that consists of nonextensive fractures having arbitrary orientations with respect to the rock block considered. It is shown that in the case of nonextensive fractures, one cannot proceed to the limiting process where the volume of the bounding rock block can be reduced to an arbitrarily small value. Therefore, the dimensions of the block along with the dimensions of the fractures appear in the equations for the nine components of permeability. This leads to a situation where the equivalent permeability matrix is not only nonsymmetric, but also it does not follow the tensorial rules of axis rotation. This leads to the conclusion that, in the case of nonextensive fractures, the equivalent permeability cannot be defined as a characteristic intrinsic property of the medium as is possible in the case of porous medium or in a fractured medium that has extensive fractures. To analyze the effect of uncertainties in the field data on the estimation of equivalent permeability, a ‘second‐order’ statistical analysis is proposed. The method is quite general and can be used to analyze the propagation of parameter uncertainties in models. A numerical example using preliminary fracture data from the Columbia River basalt in Washington State is presented. The mean and standard deviation of the equivalent permeability of a 5×5 m block is estimated. Assuming that each component of the equivalent permeability has log normal distribution, the probability of their assuming values different from the mean is found to be significant. This points out the uncertainty that would be inherent in the flow simulation, if the mean value of permeability is used.
Ecological optimality in water‐limited natural soil‐vegetation systems: 1. Theory and hypothesis
Authors: Eagleson Peter S.
Published: February 2008

The solution space of an approximate statistical‐dynamic model of the average annual water balance is explored with respect to the hydrologic parameters of both soil and vegetation. Within the accuracy of this model it is shown that water‐limited natural vegetation systems are in stable equilibrium with their climatic and pedologic environments when the canopy density and species act to minimize average water demand stress. Theory shows a climatic limit to this equilibrium above which it is hypothesized that ecological pressure is toward maximization of biomass productivity. It is further hypothesized that natural soil‐vegetation systems will develop gradually and synergistically, through vegetation‐induced changes in soil structure, toward a set of hydraulic soil properties for which the minimum stress canopy density of a given species is maximum in a given climate. Using these hypotheses, only the soil effective porosity need be known to determine the optimum soil and vegetation parameters in a given climate.
A case study of a chemical spill: Polychlorinated biphenyls (PCBs): 2. Hydrogeological conditions and contaminant migration
Authors: Schwartz Franklin W. , Cherry John A. , Roberts J. Russell
Published: February 2008

The purpose of the second paper in this pair is to describe the hydrogeology and to account for the observed patterns of PCB contamination at the Federal Pioneer site in Regina, Canada. Six major hydrostratigraphic units were identified from detailed test drilling and sampling. From the surface downward these are a thin surface fill, the Regina clay, the Condie silt, the till zone, the interglacial silt, and the Regina aquifer system. This latter unit is an important source of potable groundwater. At present the nearest wells are hundreds of meters from the site. The permanent water table is situated below the Condie silt in sandy glacial till. An active perched groundwater system has developed within the thin fill layer beneath the floor of the plant. The extensive lateral flow of groundwater in this zone has contributed significantly to the spreading of PCBs at the site. The PCBs have also moved downward through fractures in the Regina clay and in the upper part of the Condie silt. It can be expected that capillary forces will halt the downward movement of Inerteen 70‐30® as fractures narrow or stop. However, the possible existence of fractures connecting the contaminated zone to the Regina aquifer system or the potential for transport as a dissolved phase in the groundwaters may permit PCBs migrate downward to the aquifer or to flow laterally off‐site. The most significant hazard represented by the spill is the potential for contamination of future water supply wells that may be placed near the site or aquifer contamination that could result if future drilling provides pathways for contaminants through poorly sealed wells or test holes.
Saltwater encroachment in an aquifer: A case study
Authors: Gupta A. Das , Yapa Poojitha N. D. D.
Published: February 2008

An approach considering both analytical and numerical models for assessing the saltwater encroachment phenomenon in an aquifer is found to be quite efficient in field situation with limited information on salt concentration and parametric variations. A case study of saltwater encroachment in Bangkok, Thailand, illustrates the use of this approach in identifying the sources of contaminating water and in evaluating the effectiveness of the water quality monitoring network.
An approach to optimizing reservoir operation for downstream aquatic resources
Authors: Sale Michael J. , Brill E. Downey , Herricks Edwin E.
Published: February 2008

The issue of instream flow maintenance for downstream aquatic resources is a relatively new environmental quality consideration required in planning water resources projects. A mathematical programing methodology is proposed to examine the relationship between biological instream flow needs (IFN) and more traditional water project objectives, such as water yield, flood control, reservoir recreation, or economic efficiency. This optimization approach combines the linear decision rule (LDR) modeling technique with an objective function representing the value of reservoir releases to downstream fisheries. The IFN performance objective is based on an index of physical habitat conditions called weighted usable area (WUA) which has been developed by the U.S. Fish and Wildlife Service. Data from a multipurpose reservoir in central Illinois have been used to demonstrate the application of the nonlinear programing model and a heuristic solution algorithm employing piecewise linearization of the habitat objective functions and linear programing.
Conjunctive multibasin management: An optimal control approach
Authors: Noel Jay E. , Howitt Richard E.
Published: February 2008

The economic effects of conjunctive management of ground and surface water supplies for irrigation are formulated as an optimal control model. An empirical hydroeconomic model is estimated for the Yolo County district in California. Two alternative solution methodologies (analytic Riccatti and mathematical programing) are applied and compared. Results show the economic potential for interbasin transfers and the impact of increased electricity prices on optimal groundwater management.
Analysis of the effect of changing discharge on channel morphology and instream uses in a Braided River, Ohau River, New Zealand
Authors: Mosley M. Paul
Published: February 2008

Constant discharges of 26.5, 56.7, 105, 240, and 507 m3s−1 were released down the Ohau River from Ohau A power station, and measurements of water depths and mean velocities made along cross sections in a braided section of the channel. Frequency distributions of water depth and velocity are presented both singly and jointly for each discharge; the methods used provide much more information on the changing character of the river than is provided by conventional hydraulic geometry relations. As discharge increases, existing channels become wider, deeper, and faster and frequently merge to become a single larger channel. However, additional channels are generated with the same characteristics as those existing at lower discharges, and the total number of channels at a cross‐section remains constant. Hence the increase of water surface area tends to be by addition of faster, deeper water to a constant area of shallow, slow water (whose location in the river bed changes). This process has the major implication for instream uses such as salmonid spawning in that the area suitable for these uses may remain constant over a wide range of flows. In some respects, then, the braided river is morphologically more stable than a single‐thread river.
The permeability of a melting snow cover
Authors: Colbeck S. C. , Anderson Eric A.
Published: February 2008

Data from snow lysimeters in California and Vermont are used to find the saturated permeability of a melting snow cover in the range of 10–40 × 10−10 m2 depending on snow density. The unsaturated permeability increases as about the third power of liquid saturation. The gravity flow theory is shown to be an accurate representation of meltwater drainage from snow covers in two diverse areas even though the snow covers are treated as homogeneous units. The variation of saturated permeability with snow density occurs about as predicted by Shimizu's formula for dry snow, although ice layers decrease the permeability somewhat.
Synthetic streamflow generation: 1. Model verification and validation
Authors: Stedinger Jery R. , Taylor Marshall R.
Published: February 2008

A part of the streamflow construction and simulation process is the verification that a stochastic streamflow model reproduces those statistics which by design it should reproduce; the use of unbiased statistics is shown to be advantageous in this exercise. In addition, if a model reproduces statistics not used in the model‐parameter estimation process, its credibility is further enhanced. These concepts are illustrated, and the performance of a wide range of monthly streamflow models are compared using data for the upper Delaware River basin in New York State.
The Mediterranean heat storage and Israeli precipitation
Authors: Tzvetkov E. , Assaf G.
Published: February 2008

The Mediterranean winter storms are intensified by the thermal gradient between the warm sea and intrusions of cold continental air masses. The thermal gradient reflects atmospheric conditions as well as the seasonal heat which is stored in the upper sea. Atmospheric conditions are difficult to predict, yet the heat storage can be measured in the beginning of the winter season. A fair correlation (R = 0.55) was found between the heat storage in the southeast Mediterranean and winter precipitation, and remarkable correlation (R = 0.9) was found between heat storage depletion and precipitation. This allows us to consider the upper heat storage as an index for weather predictions. Small heat storage is associated with annual precipitation which does not exceed the average. Large heat storage will precede winters which are not dryer than the average.
Pore velocity estimation uncertainties
Authors: Devary J. L. , Doctor P. G.
Published: February 2008

Geostatistical data analysis techniques were used to stochastically model the spatial variability of groundwater pore velocity in a potential waste repository site. Kriging algorithms were applied to Hanford Reservation data to estimate hydraulic conductivities, hydraulic head gradients, and pore velocities. A first‐order Taylor series expansion for pore velocity was used to statistically combine hydraulic conductivity, hydraulic head gradient, and effective porosity surfaces and uncertainties to characterize the pore velocity uncertainty. Use of these techniques permits the estimation of pore velocity uncertainties when pore velocity measurements do not exist. Large pore velocity estimation uncertainties were found to be located in the region where the hydraulic head gradient relative uncertainty was maximal.
Paleohydrology of southwestern Texas
Authors: Kochel R. Craig , Baker Victor R. , Patton Peter C.
Published: February 2008

Current statistical methods may be unable to accurately predict recurrence intervals of rare, large‐magnitude floods, especially in semiarid regions having positively skewed annual flood distributions, great hydrologic variability, and widely spaced gaging stations. Current approaches rely on historical data, but catastrophic floods may have recurrence intervals far greater than the length of historical records. In the lower Pecos and Devils Rivers of southwestern Texas, paleoflood discharge and frequency estimates are extended over 10,000 years by the study of slack‐water flood sediments. Slack‐water deposits are typically fine‐grained sand and silt that accumulate during floods in areas where current velocity is reduced, i.e., in back‐flooded tributary mouths, channel expansions, downstream from bedrock spurs and/or slump blocks, and in shallow caves along bedrock walls. Radiocarbon dating of organic detritus in slack‐water deposits establishes the flood chronology while paleoflood discharges can be estimated by slope‐area techniques. Paleoflood information extracted from slack‐water sediments can greatly extend flood records. These floods may be weighted like historical data in log Pearson type 3 calculations of flood frequency. Our morphostratigraphic approach combines recorded data with geomorphic evidence to derive estimates of flood frequency. This technique offers an inexpensive and rapid way to assess catastrophic flood risk.