摘要:

Socioeconomic and climatological data of the major cities of the western region of Saudi Arabia have been used to develop several models to estimate the residential water usage for different kinds of houses. The developed models correlate the residential water usages with temperature, income, family size, price of water, and availability of a garden within the house. The study shows that the residential water uses in houses supplied by a public pipe network are 1.4–2 times greater than the residential water uses in houses supplied by tankers. It also shows that the price elasticities are very similar to those estimated in the United States. Income elasticities, on the other hand, are lower than those typically found in more industrialized countrie

ISSN:0043-1397    

DOI:10.1029/90WR02659

年代:1991

数据来源: WILEY

摘要:

Reservoir system simulation models are widely used to determine a system's firm water yield, average yield, or hydropower capacity. Most such models use heuristic guidelines to define the system's operating policy. Alternatively, optimization can be used within the simulation to identify a reasonable operating strategy. In this paper a theoretical justification is provided for several heuristic operating guidelines, including the widely used space rule. The guidelines are expressed as a mathematical objective function and combined with constraints on system operation to yield one‐period optimization submodels that can be used to determine releases within a simulation. Use of these one‐period optimization models improved the simulated operation of the Central Valley Project in California over the critical period of record and provided reasonable policies for other hydrologic scenar

ISSN:0043-1397    

DOI:10.1029/91WR00320

年代:1991

数据来源: WILEY

摘要:

An analog method is used to simulate a discrete transmissivity field free of the artifacts inherent in conventional multivariate Gaussian statistical generation methods. The simulated field provides a realistic model of a formation exhibiting the spatial continuity of extreme transmissivities which gives rise to barriers and preferential channels for flow. The heterogeneous transmissivity field and the corresponding steady‐state head and discharge fields are characterized in a geostatistical framework and observed spatial statistics are compared with theoretical results from the stochastic hydrogeology literature. The simulated transmissivity field exhibits a bimodal distribution and strong directional anisotropy with nested scales of heterogeneity. Despite these significant departures from standard models, the observed head covariance and head‐log‐transmissivity cross‐covariance agree well with theory. The spatial covariance of specific discharge is highly anisotropic reflecting preferential channeling in the mean direction of flow and the conservation of flux along streamlines. The effective transmissivity of the field is predicted more accurately by the spatial geometric average than by theoretical models despite the flow channeling and the anisotropy of heterogeneity. Tracer spreading, modeled by particle tracking, is non‐Fickian at displacements of up to 13.4 times the log‐transmissivity integral range because transport behavior is dominated by convection along a small number of preferential channels. The observed scale dependence of apparent longitudinal dispersivity is predicted generally well by theory. Results of this study suggest that ensemble theoretical models based on perturbation approaches can provide reasonable estimates of general flow and transport properties of single field realizations under moderate conditions of he

ISSN:0043-1397    

DOI:10.1029/90WR02705

年代:1991

数据来源: WILEY

摘要:

A numerical procedure for the determination of equivalent grid block permeability tensors for heterogeneous porous media is presented. The method entails solution of the fine scale pressure equation subject to periodic boundary conditions to yield, upon appropriate averaging of the fine scale velocity field, the coarse scale or equivalent grid block permeability. When the region over which this coarse scale permeability is computed constitutes a representative elementary volume (REV), the resulting equivalent permeability may be interpreted as the effective permeability of the region. Solution of the pressure equation on the fine scale is accomplished through the application of an accurate triangle‐based finite element numerical procedure, which allows for the modeling of geometrically complex features. The specification of periodic boundary conditions is shown to yield symmetric, positive definite equivalent permeability tensors in all cases. The method is verified through application to a periodic model problem and is then applied to the scale up of areal and cross sections with fractally generated permeability fields. The applicability and limitations of the method for these more general heterogeneity fields are discusse

ISSN:0043-1397    

DOI:10.1029/91WR00107

年代:1991

数据来源: WILEY

摘要:

Current algorithms that deduce the drainage network from a digital elevation model (DEM) represented by a regular array of surface elevations share a fault: Unless the terrain is rugged, the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation. We present a simple solution to the problem. A second difficulty is the presence of noise that creates artificial pits. We briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts. Our system has treated DEMs of nearly 9,000,000 pixels. We show how depth first search of the resulting drainage network permits segmentation of the DEM into basins by various criteria, analysis of stream‐sediment anomaly dilution profiles, improved hydrological models and other application

ISSN:0043-1397    

DOI:10.1029/90WR02658

年代:1991

数据来源: WILEY

摘要:

In crop simulation models the water subroutine computes evaporation and transpiration separately. This property allows a greater confidence in the simulation of the early crop stages in terms of water requirements. In the present article the authors suggest a semiempirical model of the drying stage of soil evaporation that can be easily integrated into various crop models. The model is based on a physical approach, yet it depends solely on permanent soil properties and on some key data on the local climate. The basic theory relies upon the mass balance of a dry surface layer of varying thickness. After successive assumptions on the main limiting factors of the drying process, the authors demonstrate that this process can be described by one equation relating actual to potential evaporation. The advantage of this formula comes from its introducing just one synthetic parameter that can be expressed as the product of two components: a climatic one and a pedological one. When compared with experimental data, the results of the model show that the order of magnitude of the evaporative process is respected, which is required for crop models.

ISSN:0043-1397    

DOI:10.1029/91WR00075

年代:1991

数据来源: WILEY

摘要:

The solution via dynamic programming (DP) of a reservoir optimal control problem is often computationally prohibitive when the proper description of the inflow process leads to a system model having several state variables and/or when a sufficiently dense state discretization is required to achieve numerical accuracy. Thus, to simplify, the inflow correlation is usually neglected and/or a coarse state discretization is adopted. However, these simplifications may significantly affect the reliability of the solution of the optimization problem. Nowadays, the availability of very powerful computers based on innovative architectures (vector and parallel machines), even in the domain of personal computers (transputer architectures), stimulates the reformulation of the standard dynamic programming algorithm in a form able to exploit these new machine architectures. The reformulated DP algorithm and new machines enable faster and less costly solution of optimization problems involving a system model having two state variables (storage and previous period inflow, then taking into account the inflow correlation) and a number of states (of the order of 104) such as to guarantee a high numerical accuracy.

ISSN:0043-1397    

DOI:10.1029/90WR02766

年代:1991

数据来源: WILEY

摘要:

A proof is given that the reciprocity principle applies to Darcian flow in a network of heterogeneous branches with either no‐flow or fixed‐head boundary conditions. Formulae are obtained for the Laplace transform of the drawdown in the special case of homogeneous branches; this provides a new method for accurately solving some flow problems in netwo

ISSN:0043-1397    

DOI:10.1029/91WR00258

年代:1991

数据来源: WILEY

摘要:

Regional daily evaporation was estimated by means of continuous measurements of the available energy flux at the surface and one or more instantaneous determinations of the evaporative fraction (EF). The data were obtained during the First ISLSCP Field Experiment (FIFE) in northeastern Kansas. EF, which is the ratio of the latent heat flux and the available energy flux, was assumed to be constant during the daylight hours; thus it was determined from only a few instantaneous surface flux values calculated on the basis of radiosonde profiles in the surface layer, together with remotely sensed surface temperature. Comparison of 23 estimated and measured daytime evaporation values showed good correlation (r= 0.97), although the evaporation was underestimated by about 5% on average. In the estimation of daily evaporation, nighttime evaporation must also be considered; measurements by means of the eddy correlation method showed that on average it accounted for some 8% of the total daily evaporation.

ISSN:0043-1397    

DOI:10.1029/90WR02706

年代:1991

数据来源: WILEY

摘要:

Analytical solutions describing the transient soil water pressure distributions during one‐dimensional, vertical infiltration toward the water table through homogeneous and two‐layer soils are derived. Exponential functional formsK=Kseαψand θ = θr+ (θs− θr)eαψare used to represent the hydraulic conductivity and pressure relation and the soil water release curve. Steady state profiles are used as initial conditions. Hydraulic behavior of the soils during wetting and drainage processes is discussed in terms of the pressure head and moisture content profiles and temporal variation of the specific discharge. The solutions provide a reliable means of comparing the accuracy of various numerical methods, especially in very dry

ISSN:0043-1397    

DOI:10.1029/90WR02772

年代:1991

数据来源: WILEY