bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of drained and undrained response of thermally loaded repository rocks
Authors: Palciauskas V. V. , Domenico P. A.
Published: February 2008

The fluid pressure and mechanical response of a potential repository rock to heating is shown to be characterized by the isothermal parameters of the classic stress‐strain theory for a porous medium, in combination with some nonisothermal parameters describing the fluid, solid, and pore volume expansivities. The isothermal coefficients are described in terms of easily interpretable parameters by noting that the fluid response can be formulated within the limits of drained and undrained behavior. The low permeability‐high thermal conductivity environment generally considered to be ideal for nuclear waste storage would appear to favor an undrained response, at least within the isolated pores and cracks of a fractured rock medium. Several cases are presented that provide a qualitatively correct demonstration of the effects of heating in this environment. These include fluid pressure increases in excess of temperature‐induced increases in in situ stress, elastic strain and the potential for inelastic crack propagation, and porosity‐permeability augmentation. If the rocks are dry, or of a high permeability such that fluid flow takes place at constant fluid pressure, similar rock material alterations are possible. This follows from the fact that when the temperature is raised to some high value, say 80° or 90°C, and then decreased to its ambient value, the final volume of a polycrystalline substance will generally be greater than the initial one. Hence the effect of temperature is irreversible because of the differential thermal expansion of the composite mineral grains and the generation of new grain boundaries. The increase in porosity during such a heating episode is calculable and empirically related to increases in permeability.
Ecological optimality in water‐limited natural soil‐vegetation systems: 2. Tests and applications
Authors: Eagleson Peter S. , Tellers Tobin E.
Published: February 2008

The long‐term optimal climatic climax soil‐vegetation system is defined for several climates according to previous hypotheses in terms of two free parameters, effective porosity and plant water use coefficient. The free parameters are chosen by matching the predicted and observed average annual water yield. The resulting climax soil and vegetation properties are tested by comparison with independent observations of canopy density and average annual surface runoff. The climax properties are shown also to satisfy a previous hypothesis for short‐term optimization of canopy density and water use coefficient. Using these hypotheses, a relationship between average evapotranspiration and optimum vegetation canopy density is derived and is compared with additional field observations. An algorithm is suggested by which the climax soil and vegetation properties can be calculated given only the climate parameters and the soil effective porosity. Sensitivity of the climax properties to the effective porosity is explored.
A kinematic model for surface irrigation: An extension
Authors: Sherman Bernard , Singh Vijay P.
Published: February 2008

The kinematic model for surface irrigation, reported previously by Sherman and Singh (1978), is extended. Depending upon the duration of irrigation and time variability of infiltration, three cases are distinguished. Explicit solutions are obtained when infiltration is constant. When infiltration is varying in time, a numerical procedure is developed which is stable and has fast convergence. A rigorous theoretical justification is developed for computation of the depth of water at and the time history of the front wall of water advancing down an infiltrating plane or channel. A derivation is given of the continuity and momentum equations when there is lateral inflow and infiltration into the channel bed.
A model for managing sources of groundwater pollution
Authors: Gorelick Steven M.
Published: February 2008

The waste disposal capacity of a groundwater system can be maximized while maintaining water quality at specified locations by using a groundwater pollutant source management model that is based upon linear programing and numerical simulation. The decision variables of the management model are solute waste disposal rates at various facilities distributed over space. A concentration response matrix is used in the management model to describe transient solute transport and is developed using the U.S. Geological Survey solute transport simulation model. The management model was applied to a complex hypothetical groundwater system. Large‐scale management models were formulated as dual linear programing problems to reduce numerical difficulties and computation time. Linear programing problems were solved using a numerically stable, available code. Optimal solutions to problems with successively longer management time horizons indicated that disposal schedules at some sites are relatively independent of the number of disposal periods. Optimal waste disposal schedules exhibited pulsing rather than constant disposal rates. Sensitivity analysis using parametric linear programing showed that a sharp reduction in total waste disposal potential occurs if disposal rates at any site are increased beyond their optimal values.
On the climatic dependence of the IUH: A rainfall‐runoff analysis of the Nash Model and the geomorphoclimatic theory
Authors: Rodríguez‐Iturbe Ignacio , Sanabira Marcelo González , Caamaño Gabriel
Published: February 2008

The geomorphoclimatic theory of the IUH is compared with the results obtained through derivation of the IUH's from a series of rainfall‐runoff experiments conducted via simulation for one basin and three different climates. The theoretical distributions of the peak and time to peak of the IUH compare very well with those obtained in the experiments. The peak and time to peak of the response hydrograph estimated through simple formulas which assume a triangular IUH also have a good agreement with the values obtained through the rainfall‐runoff model. It is shown that the uncertainty due to the variability of the IUH with the rainfall input may produce a sizable variance of estimation in the outflow hydrograph when working under the assumed nonlinear framework. The analysis is carried out with constant roughness and rectangular channels, characteristics which are taken independent of the size of the discharge.
Estimation of ARMA Models with seasonal parameters
Authors: Salas Jose D. , Boes Duane C. , Smith Ricardo A.
Published: February 2008

The Yule‐Walker equations for ARMA (p, q) models with periodic parameters are derived from which moment estimates can be obtained. Specifically, for the case of ARMA (p, 1) models, the periodic autoregressive parameters can be found by solving a system of linear equations, while the periodic moving average parameters satisfy a system of equations which can be solved iteratively. Particular examples are given and comparisons are made between the proposed moment estimates and estimates given previously.
Rainfall variation analysis and optimization of gaging systems
Authors: Shih S. F.
Published: February 2008

A general methodology is developed to compute the variance of mean rainfall using a covariance factor among rain gage stations. The relative variance, which can be reduced by increasing the density of the network, is presented as three cases; i.e., random sample method, stratified sample method without optimum allocation, and stratified sample method with optimum allocation. A special stratum‐weighted ratio is also developed for allocating the gages to the substratum. On the basis of two‐stage sampling theory, new methods are developed to decide the number of gages needed to estimate the mean rainfall with a given confidence level to achieve a specified accuracy. The stratified sample method required fewer stations to achieve the same level of statistical accuracy than the random sample method. In designing the rain gage network system, three steps are involved: (1) preliminary design, (2) allocation of the gages to substratum, and (3) improvement of the gage density according to the expected level of statistical accuracy. Three classes of low, medium, and high density of rain gage network design are recommended in accordance with the desired level of statistical accuracy. There is a nonlinear relationship between the increase in number of gages and the improvement in statistical accuracy.
Multiobjective analysis of multireservoir operations
Authors: Yeh William W‐G. , Becker Leonard
Published: February 2008

The objective of the study reported herein is to develop practical procedures for the analysis of a multiple purpose, multiple facility reservoir system to guide real time decisions concerning the optimal operation of the system. Application is made to the California Central Valley Project (CVP). The five purposes (benefits), treated as objectives here in the multiobjective optimization, include (1) hydropower production, (2) fish protection, (3) water quality maintenance, (4) water supply, and (5) recreation. The constraint method is used to develop the trade‐offs while a specially modified linear programing and dynamic programing algorithm is used for optimization. Noninferior sets can be obtained with each benefit parameterized singly and in various combinations. Two sets of monthly historical streamflows, one set corresponding to a drought year and the other set to an excess water year, are used to develop the corresponding noninferior sets. These procedures provide guidance for allocating the total benefits derived from a region's water resources and for operating the available system within all statutory, contractual, and other applicable constraints. A very high degree of decomposition of the typically large multiple purpose, multiple facility operation problem is made possible by the above technique, resulting in a rapid delineation of the noninferior policy set. The decision maker participates at various stages of the analysis and can request more or less detail with regard to the noninferior set. In our opinion, information is best presented to him via a series of two dimensional plots representing various cross sections of the noninferior set. Tabular presentations are not conducive to a good appreciation of the consequences of alternative benefit allocation policies.
Test of an equation for evaporation from bare soil
Authors: Novak M. D. , Black T. A.
Published: February 2008

An empirical equation developed by Idso et al. (1979) at Phoenix, Arizona, to calculate daily average evaporation rates during all three drying stages of a bare soil was tested using measurements made at Agassiz, British Columbia, and is discussed on the basis of available evaporation theory. The results show that their expression for potential evaporation rate did not apply at Agassiz due to differences in the advection regimes at the two locations. The Agassiz potential evaporation rate data was well represented by the Priestley‐Taylor equation with aPT (‘alpha’) = 1.27 ± 0.1. It was concluded that the Idso et al. equation for potential evaporation rate has no greater generality than the Priestley‐Taylor or other such semiempirical approaches. The concept of expressing the stage III rate as proportional to the expression for potential evaporation rate worked marginally well at a culti‐packed site and quite well at a disc‐harrowed site. It was concluded that for soils with stage III rates much greater than 50% of potential evaporation rate, more complete procedures are necessary for calculating evaporation rates during extended drying periods.
Stochastic analysis of one‐dimensional steady state unsaturated flow: A Comparison of Monte Carlo and Perturbation Methods
Authors: Andersson Johan , Shapiro Allen M
Published: February 2008

The stochastic nature of moisture content in a soil profile under steady state, unsaturated infiltration is examined, where the saturated hydraulic conductivity is taken as a stationary stochastic process. Two different techniques are employed in determining the stochastic output. These are Monte Carlo simulations and an analytic derivation from a first‐order perturbation solution. In comparing the two techniques, the liability of the perturbation expressions is investigated if the Monte Carlo results are assumed to exactly represent the stochastic nature of the moisture content. In four test examples a relatively good comparison is obtained between the results of the two techniques. The analytic nature of the perturbation solution then readily provides information concerning the general stochastic properties of the moisture content, and in this way, additional Monte Carlo runs are avoided. From this analysis it is shown that the moisture content is a stationary stochastic process at distances far from boundary regions. The distance from the boundary to regions of stationarity is dependent upon soil properties and the boundary conditions imposed.
Flow toward storage tunnels beneath a water table: 1. Two‐dimensional flow
Authors: Tal A. , Dagan G.
Published: February 2008

A system of parallel tunnels is excavated in saturated rock of low permeability for storing oil or LPG. In order to contain the product, permanent water inflow has to be maintained. In absence of recharge this flow causes a continuous drop of the water table. A numerical scheme, based on the boundary integral elements method, is used in order to determine the water table motion, the inflow to galleries, and the velocity on the perimeter. Both oil‐filled and empty galleries are considered. The shape of the galleries is maintained fixed, while the spacing and the distance to an impervious bottom is varied. An analytical approximate solution, valid for sufficiently high water table above the galleries top, is also derived. This solution is extended to the cases of vertical recharge above the free surface and LPG filled galleries. The solution of the two‐dimensional flow problem can be used in order to determine: (1) the time required for the water table to drop from its initial position to the gallery top, or to the product level, in absence of recharge; (2) the water velocity on the gallery perimeter; and (3) the total inflow to the gallery.
Why should a forecaster and a decision maker use Bayes Theorem
Authors: Krzysztofowicz Roman
Published: February 2008

Forecasts of hydrometeorologic phenomena are inherently uncertain. In practice, uncertainty is often ignored. To aid forecasters and decision makers in coping with forecast uncertainty, we investigate theoretical and exemplary answers to several fundamental questions: How to optimally use categorical and probabilistic forecasts? What opportunity losses are expected to be incurred when forecast uncertainty is ignored? Why the classical contingency analysis is suboptimal? What economic gains are to be expected from probabilistic forecasts? To illuminate the answers, analytic solutions are derived for the optimal and a nonoptimal (one that ignores forecast uncertainty) formulation of a single‐period quadratic decision problem with a categorical and probabilistic forecast of the state. The probabilistic forecast is of the type wherein the forecaster quantifies his degree of uncertainty in terms of a fixed‐probability central credible interval. Bayesian information processors for forecasts of normally distributed state variables are formulated by using conjugate families of distributions and are applied to records of daily temperature forecasts.
A note on fracture flow dispersion mechanisms in the ground
Authors: Neretnieks Ivars
Published: February 2008

Two mechanisms for spreading of a tracer pulse in fissured media are discussed: channeling and diffusion in the rock matrix. Dispersion has traditionally been treated as a random mechanism, comparable to diffusion. It is not quite clear if this is applicable to such geologic media as sparsely fissured rock or other stratified media. In this paper, two other mechanisms for dispersion are treated. One is stratified flow; the other is due to interaction with a solid material. A very idealized case of stratified flow is treated. A case is modeled where the medium flows in parallel channels. Each channel is assumed to consist of the space between two parallel plates. The flow is laminar. The various channel widths are assumed to be randomly distributed with a lognormal frequency distribution. This is a distribution which has been found experimentally in fissured crystalline rock. For this case, it is shown that an equivalent dispersion coefficient will increase with the distance between injection and observation point. For this case the normal Fickian diffusion dispersion description is not applicable if the usual assumption is made that the dispersion coefficient is constant. There are several interaction mechanisms of interest between a solute and the solid material. The one treated here is the diffusion of the solute into the porous rock matrix and sorption of the inner surfaces of the matrix. This interaction will also lead to the spreading of a tracer front, in a similar way to what other dispersion mechanisms do. It is demonstrated that if the solid material has very long extension, the dispersion due to this mechanism is so large that a Fickian dispersion coefficient cannot be evaluated without explicitly accounting for this mechanism. Attempts to evaluate Fickian dispersion coefficients by the method of moments will give values which are entirely dependent on the observation accuracy of the tail.
Evaluations of water balance models on a mixed conifer watershed
Authors: Baker Malchus B. , Rogers James J.
Published: February 2008

Three water balance and yield models of differing degrees of complexity were evaluated using data from a mixed conifer watershed in east‐central Arizona. Statistical tests on simulated monthly flow volumes are provided with a comparison of 5‐year mean annual estimates of evapotranspiration and streamflow. One model accounts for 87% of the variation in monthly flow but produces the most bias in simulated monthly runoff volume. Another accounts for 78% of the monthly streamflow variation and produces the least bias in monthly streamflow volume. Statistics for the third model generally lie between those of the other two models.
Natural short‐circuiting of inflow to outflow through Silver Lake, New York
Authors: Englert John P. , Stewart Kenton M.
Published: February 2008

The proximity of the major inlet to the outlet of Silver Lake, New York, permits some short‐circuiting of the incoming flow. This feature, unusual to document in lakes, is verified with data which show times when the inlet and outlet waters resemble each other more than they do the lake. Rhodamine dyes and some natural inorganic chemical variables have been used as tracers to illustrate this phenomenon. The case for short‐circuiting appears less clear during some low inflows and is complicated by water level manipulation at a small dam on the outlet and withdrawal of water from the lake by communities. The significance of short‐circuiting for this eutrophic/mesotrophic lake is that some incoming nutrients from the rich agricultural watershed bypass the lake. Determinations of retention time and nutrient loading for such lakes are more complex. The governance of trophic conditions in this and similar lakes, or in parts of some lakes, may be influenced more by such incomplete mixing than generally considered.
Theory of earth tide and barometric effects in porous formations with compressible grains
Authors: Van Der Kamp G. , Gale J. E.
Published: February 2008

The general three‐dimensional equations for pore pressure, stress, and strain in a homogeneous porous medium with compressible grains are used to derive expressions for the response of fluid pressure to the stress changes due to earth tides and barometric loading effects. The analysis constitutes a generalization of earlier derivations. The formation is assumed to be of large extent laterally so that horizontal flow may be neglected. It is shown that vertical flow induced by the pore pressure changes can be analyzed by means of a diffusion equation. An expression for the specific storage coefficient is derived which is valid if horizontal deformations are negligible and which includes the effect of the compressibility of the solid grains. Measurements of earth tide and barometric effects constitute two in situ tests of bulk formation properties. Such measurements can therefore make an important contribution to the characterization of the hydraulic and elastic properties of a particular formation.
An ephemeral stream‐aquifer interaction model
Authors: Dillon P. J. , Liggett J. A.
Published: February 2008

The boundary integral equation method is applied to the interaction between an ephemeral stream and an unconfined aquifer through a semipervious streambed. The resulting two‐dimensional vertical slice model describes groundwater flow when the stream and aquifer are hydraulically disconnected or connected as well as the transition between these two states. It incorporates the Green‐Ampt equation with the hydraulically disconnected boundary conditions. The model was successfully calibrated using stream discharge and bore hydrograph data from the Little Para River recharge study, South Australia. It predicts with sufficient accuracy the inflow and outflow from the stream to the aquifer during fluctuating water levels in the stream.
Sampling frequency for water quality monitoring: Measures of effectiveness
Authors: Casey Don , Nemetz Peter N. , Uyeno Dean H.
Published: February 2008

Selecting the sampling frequency is one of the most important tasks in the design of a regulatory water quality monitoring program. This paper proposes two quantitative measures of the effectiveness of different sampling frequencies; these measures are intended to be used at the preliminary program design stage. The goal of the program is assumed to be the detection of violations of water quality standards. The first measure, M′, gives the expected proportion of violations that will be detected. The second, M″, is the ratio of the expected number of violated samples over the expected number of violations. Mathematical expressions for both statistics are developed. It is shown that by setting the average sampling interval equal to the average duration of a violation, the expected number of violated samples would equal the expected number of violations, since the errors caused by missing some violations and counting others more than once would tend to cancel out.
Conjunctive use of groundwater and surface water for irrigated agriculture: Risk aversion
Authors: Bredehoeft John D. , Young Robert A.
Published: February 2008

In examining the South Platte system in Colorado where surface water and groundwater are used conjunctively for irrigation, we find the actual installed well capacity is approximately sufficient to irrigate the entire area. This would appear to be an overinvestment in well capacity. In this paper we examine to what extent groundwater is being developed as insurance against periods of low streamflow. Using a simulation model which couples the hydrology of a conjunctive stream aquifer system to a behavioral‐economic model which incorporates farmer behavior in such a system, we have investigated the economics of an area patterned after a reach of the South Platte Valley in Colorado. The results suggest that under current economic conditions the most reasonable groundwater pumping capacity is a total capacity capable of irrigating the available acreage with groundwater. Installing sufficient well capacity to irrigate all available acreage has two benefits: (1) this capacity maximizes the expected net benefits and (2) this capacity also minimizes the variation in annual income: it reduces the variance to essentially zero. As pumping capacity is installed in a conjunctive use system, the value of flow forecasts is diminished. Poor forecasts are compensated for by pumping groundwater.
The interaction of lakes with variably saturated porous media
Authors: Winter Thomas C.
Published: February 2008

Numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space, depending on the thickness of the unsaturated zone through which infiltrating water must move. The resulting complex, transient groundwater flow systems have significant impact on contiguous surface water. In very permeable media, small, local, closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge. These have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water. The transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common. In less permeable media the same complex flow systems may occur, but the time for development and dissipation is much greater. For example, it is conceivable that small, local flow systems may exist for many months or years as a result of major recharge. Therefore directions of flow in such systems are more stable, and the effect on contiguous surface water also is more stable. The findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration, groundwater recharge, direction of seepage through the beds of surface water bodies, and complex geochemical processes related to changing directions of groundwater flow.
Multiple reservoir system screening models
Authors: Stedinger Jery R. , Sule Bola F. , Pei Daniel
Published: February 2008

Simple optimization models can be useful for identifying potentially attractive reservoir system configurations and capacities in the early stages of system design. Several families of such screening models have been developed. Their ability to identify cost‐efficient designs that meet specified draft‐reliability targets was evaluated by simulating different designs identified as potentially optimal by the various models. Chance‐constrained models, though simple, generally performed poorly; the “yield model” performed quite well on the sample three‐reservoir water‐supply problem.
The economics of irrigation with nonuniform infiltration
Authors: Feinerman E. , Letey J. , Vaux H. J.
Published: February 2008

Economic implications of nonuniform water infiltration in irrigated fields can be assessed with a simplified hydrologic balance model linked to an economic optimization model through a crop water production function. The effects of nonuniformity are derived by using two production functions that differ in terms of the sensitivity of yield to applications of water greater than that needed to achieve maximum yield. Where crop yield is sensitive to excess water, productivity and optimal levels of water application are lower in nonuniform fields than in uniform fields. If crop yield is not sensitive to excess water, outcomes depend on the price of water relative to crop income net of water costs. The conclusions, then, depend crucially on the form of the production function. An example is used to demonstrate that irrigation technology and management that increases the uniformity of infiltration may increase both productivity and the levels of agricultural water use.
Improved risk and reliability model for hydraulic structures
Authors: Lee Han‐Lin , Mays Larry W.
Published: February 2008

Improved dynamic risk and reliability models based upon conditional probability distributions are developed. The new dynamic risk model is shown to reflect more accurately the overall risk (probability of failure considering both hydrologic and hydraulic uncertainties) of a hydraulic structure. This dynamic risk model is also shown to have a close correspondence to nonparametric methods for evaluating the exceedance probability of a hydrologic event.
Real‐time forecasting and daily operation of a multireservoir system during floods by linear quadratic Gaussian control
Authors: Wasimi Saleh A. , Kitanidis Peter K.
Published: February 2008

The problem of short‐term (daily) operation of a multireservoir system during floods is examined. The problem is how to use all available real‐time information to solve the “tactical” problem of regulating reservoirs to minimize the expected value of flood damage during a relatively short operating horizon and to do so consistently with the long‐term operating strategy. A state‐space mathematical model is presented for short‐term forecasting of river flows and description of the dynamics of a multireservoir system. The model includes reduced‐order state‐space unit hydrographs to forecast storm runoff from effective rainfall and state‐space representations of linear flood routing. The optimization problem is solved in the framework of discrete‐time linear quadratic Gaussian (LQG) control. LQG control is a computationally efficient and flexible method of solving the large‐dimensional optimization problems associated with the solution of the tactical problem of short‐term operation of reservoirs. For application of the LQG control methodology the system must be represented in state‐space form with quadratic cost functions subject to linear equality constraints given by the state transition equations. The scheme was found to be suitable for operation under moderate flood conditions when capacity constraints are not likely to become binding. The methodology has been applied and tested in a real‐world case.
Organic detritus particles: Initiation of motion criteria on sand and gravel beds
Authors: Fisher John S. , Sill Ben L. , Clark Douglas F.
Published: February 2008

Laboratory experiments were used to extend the application of the Shields entrainment function to both organic sediments and inorganic sediments overpassing a bed composed of particles of a different size. A total of 89 flume experiments were conducted to simulate organic sediment motion over sand and gravel stream beds. Although the study emphasis was on organic particles, some of the test included inorganic sediments. The bed particle diameters ranged from 0.7 × 10−3m to 22 × 10−3m, while the organic particle diameters ranged from 0.56 × 10−3m to 7.45 × 10−3m. A visual technique was used to determine the initiation of motion. The laboratory results were used to derive a modified Shields relationship which includes both the transported and bed particle characteristics. This modified Shields function predicts the initiation of motion of both organic and inorganic particles overpassing beds whose composition is significantly different than these particles. These results have direct application to the prediction of incipient motion of organic and inorganic detritus particles in streams and estuaries.
Measurement of Evaporation by a Vapor Budget Technique
Authors: Sill B. L. , Fowler J. E. , Lagarenne W. R.
Published: February 2008

A vapor budget method for measuring evaporation from lakes is described. The technique involves measuring the upwind and downwind horizontal water vapor flux in the atmosphere for air that passes over an exposed water body. The difference in the two fluxes is shown to be equal to the surface evaporation. Instrumentation used to measure the required vertical profiles of horizontal velocity and water vapor density is also described. The method is applied on a small pond (57 × 57 m) in southern California, and measurements are compared with hourly water budget values of evaporation. Despite the short fetch, which limits the thickness of the vapor layer, comparison of the vapor budget values and those obtained by the water budget method is favorable. Results from a limited number of measurements on a larger lake (with a 600‐m fetch) are also presented. It is estimated that at the present state of development, the vapor budget method is accurate to approximately 20% for small‐ to medium‐sized lakes.
Perturbation Analysis of Nearly Horizontal Flows in Leaky Aquifers
Authors: Lafe Olurinde , Oladeji Olaniyi
Published: February 2008

A perturbation method is used to analyze the equations governing flows in two aquifers separated by a semipervious stratum. The upper aquifer is phreatic (unconfined), while the lower one is semiconfined. The nearly horizontal flow approximation produces a coupled system of equations for both aquifers which, in particular, is nonlinear for the phreatic region. A parameter perturbation technique is shown as a convenient way of linearizing and uncoupling the equations. Analytical solutions of the perturbed equations for two simple problems are presented.
Aquifer Reclamation Design: The Use of Contaminant Transport Simulation Combined With Nonlinear Programing
Authors: Gorelick Steven M. , Voss Clifford I. , Gill Philip E. , Murray Walter , Saunders Michael A. , Wright Margaret H.
Published: February 2008

A simulation‐management methodology is demonstrated for the rehabilitation of aquifers that have been subjected to chemical contamination. Finite element groundwater flow and contaminant transport simulation are combined with nonlinear optimization. The model is capable of determining well locations plus pumping and injection rates for groundwater quality control. Examples demonstrate linear or nonlinear objective functions subject to linear and nonlinear simulation and water management constraints. Restrictions can be placed on hydraulic heads, stresses, and gradients, in addition to contaminant concentrations and fluxes. These restrictions can be distributed over space and time. Three design strategies are demonstrated for an aquifer that is polluted by a constant contaminant source: they are pumping for contaminant removal, water injection for in‐ground dilution, and a pumping, treatment, and injection cycle. A transient model designs either contaminant plume interception or in‐ground dilution so that water quality standards are met. The method is not limited to these cases. It is generally applicable to the optimization of many types of distributed parameter systems.
The Operational Significance of the Continuum Hypothesis in the Theory of Water Movement Through Soils and Aquifers
Authors: Baveye Philippe , Sposito Garrison
Published: February 2008

The operational meaning of the representative elementary volume (REV) concept, on which current foundational theories of water movement through porous media are based, is analyzed critically. It is concluded that the REV concept as applied to real porous media is both unnecessarily restrictive and experimentally unverifiable. In its place a relativist concept is proposed in which macroscopic physical variables are defined as convolution products of microscopic properties of a porous medium with weighting functions that represent the appropriate measuring instruments. The effects of resolution and precision differences among experimental measuring devices, now recognized as critical in the assessment of spatial variability in the properties of soils and aquifers, can be incorporated naturally within the relativist concept but are excluded a priori in the REV concept. The relativist point of view, unlike the REV concept, has a clear operational meaning and, in principle, extends theoretical validity to all local measurements made on porous media. It is sufficient mathematically to derive conventional macroscopic balance equations for mass and linear momentum as well as a differential equation for the isothermal transport of water through an unsaturated, anisotropic, deformable soil or aquifer.
Molecular Dynamics and Statistical Mechanics of Water Near an Uncharged Silicate Surface
Authors: Mulla David J. , Cushman John H. , Low Philip F.
Published: February 2008

Properties such as the swelling, mass transfer, and porosity in aqueous colloidal systems and natural soils are thought to vary in magnitude depending upon the extent of surface‐induced perturbation in the water near silicate surfaces (vicinal water). Any satisfactory theoretical understanding of the interrelation between the perturbations in vicinal water and the properties of colloidal systems must involve the statistical mechanical analysis of an appropriate molecular model for the vicinal water. We have conducted a preliminary molecular dynamics simulation in order to elucidate the effects of an uncharged silicate surface on the structure and dynamics of vicinal water. Statistical mechanics were used to interpret position and velocity trajectories computed in the molecular dynamics simulation. The results of our simulation indicate that the vicinal water differs substantially from bulk water over appreciable distances for the static orientation of molecular dipole moments and the rate of relaxation of these moments and substantially over smaller distances for hydrogen bonding patterns and the rate of self‐diffusion. No significant differences between the radial distribution functions of vicinal and bulk water are evident. Because vicinal water may be perturbed to large distances from a clay surface, one must take extreme care in deriving transport equations in saturated and unsaturated media which are high in clay. We may conclude that a satisfactory derivation of the solute transport equations in systems high in colloids and having low water content does not exist.
Economic Results of Simulated Changes in Pakistan's Irrigation System
Authors: Johnson Sam H. , Reuss John O.
Published: February 2008

An integrative simulation model is used to simulate alternative water management systems for the Punjab, the largest state in Pakistan. Results from the model indicate that current canal closure schedules severely restrict economic returns from possible cropping systems. Closure during February, or in April after wheat harvest, increases possible returns by $20–$30 per hectare. Demand systems, while strongly advocated by numerous consultants, are not as economically productive as are present continuous flow systems. Only after per hectare water allocation is increased by more than 1.5 times do demand systems provide a higher per hectare economic return.
Microwave Measurements of Moisture Distributions in the Upper Soil Profile
Authors: Sadeghi A. M. , Hancock G. D. , Waite W. P. , Scott H. D. , Rand J. A.
Published: February 2008

Laboratory and field experiments were conducted to investigate the ability of microwave remote sensing systems to detect the moisture status of a silt loam soil exhibiting abrupt changes in moisture content near the surface. Laboratory soil profiles were prepared with a discontinuous moisture boundary in the subsurface. Reflectivity measurements of these profiles were made with a bistatic reflectometer operating over the frequency ranges of 1–2 and 4–8 GHz (wavelength ranges of 30–15 and 7.5–3.75 cm, respectively). These measurements exhibited a well‐developed coherent interference pattern in good agreement with a simple two‐layer reflectivity model. Field measurements of bare soil surfaces were conducted for initially saturated profiles and continued for extended periods of drying. During drying, coherent interference patterns similar to those observed in the laboratory were detected. These appear to be due to steep moisture gradients occurring between drying layers near the surface. The field results were modeled by a five‐segment linear moisture profile with one or two steep segments and a multilayer reflectivity program. Agreement between model and field response over the frequency range was used to estimate the depth of drying layers within the soil. These depths were monitored over the second and third drying cycles. Formation of the drying layers under field conditions appears to be influenced by drying time, tillage, and evaporative demand. In any case, it appears that the coherent effects caused by nonuniform moisture profiles may substantially affect the reflectivity of even rough soil surfaces.
A Stochastic Optimization Model for Real‐Time Operation of Reservoirs Using Uncertain Forecasts
Authors: Datta Bithin , Houck Mark H.
Published: February 2008

A real‐time operation model primarily useful for daily operation of reservoirs is developed. This model is based on a chance constraint formulation and assumes a particular form of the linear decision rule. It uses the conditional distribution function (CDF) of actual streamflows conditioned on the forecasted values. These CDF's are constructed by incorporating the statistical properties of forecast errors for different time steps. The objective considered is the minimization of weighted probable deviations from storage and release targets. These weights are surrogates for the actual loss functions, and the probable deviations are functions of the reliability levels specified in the model. With the use of target values for release and storage, this model is capable of using a release policy that is a subset of a seasonal policy and overcomes the myopic (short‐sighted) nature of operation. Simulation of actual operation, using this model for a hypothetical reservoir, demonstrates the feasibility and efficiency of this approach. This model is shown to be applicable for a system of reservoirs. The restrictions associated with the use of a linear decision rule are shown to be invalid for this model.
A Linear Analysis of Thermal Effects on Evaporation From Soil
Authors: Milly P. C. D.
Published: February 2008

Evaporation of water from a soil surface is a complex process that can be strongly tied to the distribution of temperature in the soil. One way of examining this coupling is through linearization and analytic solution of the partial differential equations and boundary conditions that govern the distributions of moisture and temperature. The solution for a step change in temperature and matric head at the surface of a soil that is initially isothermal and uniformly wetted suggests that evaporation can be calculated accurately by neglecting the dependence of moisture content on temperature, even when the associated “thermal liquid flux” is the largest moisture flux immediately beneath the soil surface. The resulting error decreases with the hydrothermal diffusivity ratio η, which is the ratio of soil moisture diffusivity to soil thermal diffusivity, and increases with the thermal liquid force ratio ξ, which is proportional to the poorly understood temperature coefficient of matric head. In contrast, the solution for diurnally varying evaporation from a relatively dry soil shows that the relative error induced by neglecting vapor diffusion due to thermally induced vapor concentration gradients is approximately equal to the relative magnitude of the neglected flux itself. This error is roughly equal to ση½, where the thermal vapor force ratio σ; is the ratio of characteristic thermal to isothermal driving forces. Furthermore, when ση½ is large, the daytime switches from a time of maximum evaporation to a time of minimum. This behavior is not reproduced if the thermal vapor flux is ignored.
On the Treatment of Evapotranspiration, Soil Moisture Accounting, and Aquifer Recharge in Monthly Water Balance Models
Authors: Alley William M.
Published: February 2008

Several two‐ to six‐parameter regional water balance models are examined by using 50‐year records of monthly streamflow at 10 sites in New Jersey. These models include variants of the Thornthwaite‐Mather model, the Palmer model, and the more recent Thomas abcd model. Prediction errors are relatively similar among the models. However, simulated values of state variables such as soil moisture storage differ substantially among the models, and fitted parameter values for different models sometimes indicated an entirely different type of basin response to precipitation. Some problems in parameter identification are noted, including difficulties in identifying an appropriate time lag factor for the Thornthwaite‐Mather‐type model for basins with little groundwater storage, very high correlations between upper and lower storages in the Palmer‐type model, and large sensitivity of parameter a of the abcd model to bias in estimates of precipitation and potential evapotranspiration. Modifications to the threshold concept of the Thornthwaite‐Mather model were statistically valid for the six stations in northern New Jersey. The abcd model resulted in a simulated seasonal cycle of groundwater levels similar to fluctuations observed in nearby wells but with greater persistence. These results suggest that extreme caution should be used in attaching physical significance to model parameters and in using the state variables of the models in indices of drought and basin productivity.
Short‐Term, Single, Multiple‐Purpose Reservoir Operation: Importance of Loss Functions and Forecast Errors
Authors: Datta Bithin , Burges Stephen J.
Published: February 2008

Short‐term operation policy for multipurpose reservoirs can be derived from an optimization model with the objective of minimizing short‐term losses (opportunity costs). Construction of such loss functions requires the definition of target values for the decision variables, assessment of reliabilities with which inflows can be predicted, and an explicit statement of operational objectives. Formulation and evaluation of a model is complicated by the uncertainties inherent in the prediction of future streamflows and by controversies about the criteria of evaluation. We discuss these issues and illustrate some of our arguments with simple numerical experiments. A series of synthetic short‐term forecasted values (which satisfy a specified distribution of forecast errors) is used to examine operation of a single reservoir. The quality of forecasted values is represented by the mean and variance of these errors or the coefficient of prediction (Cp). The objective function of the operation model is assumed to be the best possible tradeoff between probable deviations from two operation targets: release and storage volume. Reservoir release was effected according to the solution of the optimization model conditioned upon the forecasted streamflow volumes for a given time increment. The storage volume was then corrected to reflect actual streamflow for the forecasted period. This became the initial storage for the next forecast period. Actual losses, deviations between actual and forecasted losses, the variance of storage and release volumes, and operational performance measures, including reliability, resiliency, and vulnerability, were found to be sensitive to the relative importance given to deviations from release or storage targets and the quality of forecasts. The performance of an operation policy based on a model that uses predicted streamflows as deterministic inputs cannot be correlated directly with the shape of the assumed loss function.
Controllability conditions for reservoir flood control systems with applications
Authors: Mariën Jan L.
Published: February 2008

A number of theoretical results are presented concerning the necessary and sufficient conditions under which there exists a regulation for a multireservoir flood control system with given deterministic inflows such that no flooding occurs at a flood damage center situated downstream. These so‐called controllability conditions have a very simple form for a large variety of multireservoir systems; they can be reduced to the existence of a no‐flood control for a number of simple single reservoirs associated with the original system. It is then suggested how these findings can be used as an aid in the planning and operation of structural flood control systems. A practical example is given with numerical results that are impossible to obtain without the use of the theoretical findings on controllability.