摘要:

The implicit stochastic model is aimed at solving the specific problem of the optimal reservoir yield when the demand is not known. The model is created to assist in the long‐term comprehensive water management planning. The presented treatment of the reservoir as a water resource for satisfying demand differs from the present practice. Knowing the character of different water demands, represented by relative demand coefficients, the implicit stochastic model provides planners with the optimal value of reservoir yield. The lack of strong and reliable economic criteria, which is common for development countries, is in this approach replaced by optimizing the reliability of satisfying water demand from the reservoir. A three‐level algorithm is proposed for the reservoir yield computation. At the first level, the simulation is used for computing the value of objective function. At the second level, computation of the seasonal reservoir operating rules is presented. The approach used for deriving the reservoir operating rules is based on the nonlinear unconstrained multivariable search of M.J.D. Powell. The third level is used for estimating the single multipurpose reservoir yield. The Fibonacci search procedure is used for the optimization of the reservoir yield at this level. The model is used in reservoir analysis for the water resources master plan of the Republic of Serbia, Yugoslavia. In this case, 49 reservoirs Were analy

ISSN:0043-1397    

DOI:10.1029/WR023i012p02159

年代:1987

数据来源: WILEY

摘要:

Irrigation organizations often place restrictions on individually arranged water sales to outside parties. It is shown that these restrictions may be consistent with efficient water use and transfers in cases where individually arranged transfers would impose detrimental spillover effects on other members of the organization. Joint optimization in the presence of spillover effects implies that organization level water trading activity will increase with an increasing market price of water and will decrease with an increase in the internal net marginal value of water. Regression analysis and other empirical evidence are found to be consistent with these implications. These results suggest that irrigation organizations engage in efficient water transfers on behalf of their members and that locally imposed restrictions on individual water transfers are not necessarily economically inefficient.

ISSN:0043-1397    

DOI:10.1029/WR023i012p02166

年代:1987

数据来源: WILEY

摘要:

A computer model using the alternating direction implicit (ADI) finite difference method to study two‐dimensional coupled soil heat and water flow with a partial surface mulch cover is developed. A new, simplified computational procedure, which has only tridiagonal matrix problems, for the ADI method is introduced. The model uses a soil surface energy balance equation to determine soil surface boundary conditions for both heat and water flow. The inputs required for the computer simulations are weather data, soil thermal and hydraulic properties, and mulch data. Numerical experiments are performed to examine the effects of soil type, mulch width, and weather conditions on soil heat and water movement. For continuous evaporation and drainage, 10‐day simulations were performed for each combination of clay, loam, and sand soil and fractions of mulch cover of 0, 0.5, 0.8, and 1.0 of the row interval width. For repetitive evaporation and infiltration, 15‐day simulations were performed. The mulch cover greatly reduces evaporation loss and the amplitude of daily soil temperature, water content, and pressure head variations. Large spatial variations in temperature and soil water content are predicted near the interface of mulch and bare soil surface. The soil hydraulic properties have important roles in controlling soil surface water content. The present model reasonably describes the soil thermal and hydrologic environments and thus can be applied successfully in soil science and groundwater hydrology and can be extended to related discip

ISSN:0043-1397    

DOI:10.1029/WR023i012p02175

年代:1987

数据来源: WILEY

摘要:

In these companion papers, a general theoretical model is presented for the description of functional relationships between relative permeabilityk, fluid saturationS, and pressurePin two‐or three‐phase (e.g., air‐water or air‐oil‐water) porous media systems subject to arbitrary saturation paths. A parametric description of hystereticS‐Prelations is developed in paper 1 which includes effects of air and oil phase occlusion or “entrapment” during imbibition. Entrapped nonwetting fluid saturations at a given point along a saturation path are linearly interpolated between endpoints of primary imbibition scanning curves using maximum trapped saturations estimated by extension of the method of Land (1968). Arbitrary order scanning curves are predicted using an empirical interpolation scheme coupled with a scaling procedure which simplifies computations and minimizes the parametric complexity of the model. All model parameters are defined in terms of measurements which may be obtained from two‐phase systems (air‐water, air‐oil, oil‐water). Extension to three‐phase systems is based on the assumption that fluid entrapment processes in three phase systems are similar to those in two‐phase systems and that wettability decreases in the

ISSN:0043-1397    

DOI:10.1029/WR023i012p02187

年代:1987

数据来源: WILEY

摘要:

A theoretical model is described for the prediction of relative permeability‐saturation (k‐S) relations in two‐phase (air‐water) and three‐phase (air‐oil‐water) porous media systems subject to arbitrary saturation paths. Integral expressions for air, water, and oil realtive permeabilities are presented which extend the nonhysteretic relative permeability model of Parker et al. (1987) to accomodate effects of pore blockage by air trapped in water and oil phases and oil trapped in the water phase. The parametric model for saturation‐pressure (S‐P) relations and fluid entrapment of paper 1 (Parker and Lenhard, this issue) is employed in the integral equations to enable derivation of closed‐form expressions for air, water, and oil relative permeabilities as functions of current fluid saturations and saturation history. Three‐phasek‐Srelations are calculated for main drainage and imbibition paths for a hypothetical soil to illustrate usage of the model and to evaluate the magnitude of fluid entrapment effects on relative permeabilities. Water permeability‐saturation relations are predicted to exhibit mild hysteretic effects except at high saturations, while hysteresis in air permeability‐saturation relations is much more pronounced. Predicted hysteresis in oil permeability is low at low water saturations but becomes quite marked as water saturation increases. Predictions ofk‐S‐Prelations for a hypothetical NAPL contamination scenario are presented using model parameters determined for a sandy soil by two methods in paper 1 (Parker and Lenhard, this issue). The results indicate that hysteresis and nonwetting fluid entrapment effects onk‐S‐Prelations may be quite substantial. Sensitivity to calibration

ISSN:0043-1397    

DOI:10.1029/WR023i012p02197

年代:1987

数据来源: WILEY

摘要:

The saturated hydraulic conductivityKsof sediments in the vadose zone is an important parameter in predicting the seepage rates of water and contaminants. The borehole permeameter is an in situ technique to test a relatively large sample size at any depth. Solutions are presented which account for the effects of unsaturated flow. These solutions are derived from a regression analysis of results of numerical simulations in which unsaturated hydraulic conductivity is represented by one or two parameters. The results of a borehole permeameter test in a uniform sand are compared with field ponding tests and air entry permeameter tests. The regression‐based solutions for the borehole permeameter which account for capillarity provide very good agreement with other permeameter results. Depending upon the approach used to solve the borehole problemKsvalues determined by methods which neglected and included capillary effects varied by a factor of only about two for the soil teste

ISSN:0043-1397    

DOI:10.1029/WR023i012p02207

年代:1987

数据来源: WILEY

摘要:

Groundwater chemistry was monitored during a test of the feasibility of long‐term (180‐day) aquifer thermal energy storage. From a source well 92,100 m3of groundwater was pumped, heated (110°C), and injected into the aquifer consisting primarily of quartz sandstone, with lesser amounts of dolomite, feldspar, and clay minerals. Softening the water prior to heating effectively prevented mineral precipitation in the heat exchanger and injection well. Recovered water was saturated with respect to quartz, dolomite, and calcite, which indicates that quartz, dolomite, and calcite dissolved during aquifer storage. Loss of sodium in the aquifer is thought to result from mixing of ambient groundwater (up to 27%) with heated, injection water. Upon subsequent cycles, softening requirements are expected to decrease, and less mineral dissolution is expected to occur during aquifer storage, resulting in negligible changes in the hydraulic characteristics of the aqu

ISSN:0043-1397    

DOI:10.1029/WR023i012p02215

年代:1987

数据来源: WILEY

摘要:

A chance‐constrained stochastic programming model is developed for water quality optimization. It determines the least cost allocation of waste treatment plant biochemical oxygen demand (BOD) removal efficiencies, subject to probabilistic restrictions on maximum allowable instream dissolved oxygen deficit. The new model extends well beyond traditional approaches that assume streamflow is the sole random variable. In addition to streamflow, other random variables in the model are initial in‐stream BOD level and dissolved oxygen (DO) deficit; waste outfall flow rates, BOD levels and DO deficits; deoxygenationk1, reaerationk2, and sedimentation‐scour ratek3coefficients of the Streeter‐Phelps DO sag model; photosynthetic input‐benthic depletion ratesAi, and nonpoint source BOD input ratePifor the Camp‐Dobbins extensions to the Streeter‐Phelps model. These random variables appear in more highly aggregated terms which in turn form part of the probabilistic constraints of the water quality optimization model. Stochastic simulation procedures for estimating the probability density functions and covariances of these aggregated terms are discussed. A new chance‐constrained programming variant, imbedded chance constraints, is presented along with an example application. In effect, this method imbeds a chance constraint within a chance constraint in a manner which is loosely associated with the distribution‐free method of chance‐constrained programming. It permits the selection of nonexpected value realizations of the mean and variance estimates employed in the deterministic equivalents of traditional chance‐constrained models. As well, it provides a convenient mechanism for generating constraint probability response surfaces. A joint chance‐constrained formulation is also presented which illustrates the possibility for prescription of an overall system reliability level, rather than reach‐by‐r

ISSN:0043-1397    

DOI:10.1029/WR023i012p02227

年代:1987

数据来源: WILEY

摘要:

Since the 1950s there has been continuing interest in the problem of joining the intermediate‐time series solution for one‐dimensional infiltration and the large time traveling wave solution. In practical field terms, however, observational errors, and errors produced by minor heterogeneities and nonuniformities of initial moisture content, will be far larger than the errors of even the crudest joining technique. The practical problem thus warrants only the minimum number of parameters and maximum simplicity. For soils which are initially relatively dry, two parameters suffice, and these are ideally taken as the physically meaningful and measurable sorptivitySand hydraulic conductivityK1. Polynomial fractions are unsuitable; piecewise representation is simple and adequate for most purposes, but a technique using the Knight infiltration solution of Burgers’ equation gives greater accuracy. It is well suited when a continuous representation and/or accuracy is de

ISSN:0043-1397    

DOI:10.1029/WR023i012p02239

年代:1987

数据来源: WILEY

摘要:

Given the discharge of a reactive material to the land surface, the fraction of the contaminant which reaches the underlying aquifer is uncertain due to variations in the rate of precipitation and infiltration. A stochastic conceptual framework is developed to estimate this variation. The framework relates the pollutant leachate fraction to the long‐term rate of infiltration and derives the probability of a given leacheate fraction from the probability of obtaining the associated infiltration rate. Application of the methodology is illustrated for the case where cumulative infiltration is represented by a compound Poisson process and pollutant fate is determined for one‐dimensional advective‐dispersive transport with linear equilibrium adsorption and first‐order chemical decay. The derived probability model for this case compares favorably to results from Monte Carlo simulations of a numerical transport model. Applications and limitations of the methodology with more sophisticated transport, reaction, and stochastic infiltration models are con

ISSN:0043-1397    

DOI:10.1029/WR023i012p02246

年代:1987

数据来源: WILEY