摘要:

Environmental policy has been explicitly expanded to consider nonpoint or dispersed sources of water pollutants. This study utilizes a national agricultural model to evaluate hypothetical policies of sediment control viewing the problem as primarily a national problem of agricultural land use. A sediment sector is added to the basic Center for Agricultural and Rural Development‐National Water Assessment model in order to test the impacts of sediment control policies on the agricultural production system. The primary function of this paper is to present the formulation of this model and a short summary analysis of some results. Specifically, costs of alternative control policies are analyzed. These costs are defined as the additional costs to agriculture of several alternative sediment control policie

ISSN:0043-1397    

DOI:10.1029/WR014i001p00001

年代:1978

数据来源: WILEY

摘要:

The imposition of recent U.S. legislative requirements (Public Law (PL) 92–500) with the 1977 and 1983–1985 water quality goals requires that water quality management plans must weigh both degree of treatment and capacity expansion questions. A planning model capable of reflecting the implications of the pollutant constraints and the scale economies of point source abatement implicit in the legislation is developed. The model captures within a mathematical programing format important characteristics of decisions associated with the time‐related water pollution control goals of PL 92–500. The model's unique features are the utilization of a biomass potential parameter as a measure of water quality and a set of heuristic procedures involving linearization of the waste treatment capacity‐removal curves. These features allow avoidance of nonconvexity problems associated with analogous models. The model also includes the usual BOD, DO, N, and P water quality measures. The model was applied in a recent planning study for the Saint John Basin

ISSN:0043-1397    

DOI:10.1029/WR014i001p00009

年代:1978

数据来源: WILEY

摘要:

There have been inconsistencies in past residential water demand studies concerning the specification of the relevant price variable. Both average and marginal price have been used. Households faced with the decision to expand (or contract) their water consumption are responsive to the additional cost (or savings) involved with this decision. The appropriate measure of this price is marginal price, not average price. Data were gathered from a large metropolitan area, Miami, Florida, to illustrate the divergence in estimation from two demand models, identically specified, except for the price variable. One utilized marginal price, the other average price. Predictions of consumption varied from 22 to 107% between the two models. The average price model significantly overestimated the response of consumption to price and income changes, a result worthy of consideration.

ISSN:0043-1397    

DOI:10.1029/WR014i001p00015

年代:1978

数据来源: WILEY

摘要:

A new multivariate gamma distribution is presented which can successfully be fitted to empirical data where the one‐dimensional marginal distributions are gamma distributions with prescribed parameters and the correlations are nonnegative. It is not intended to give explicit formulae either for the joint density or for the joint characteristic function of the random variables. Our representation of the individual gamma‐distributed random variables will be used for simulation, with the aid of which we approximate probabilities of sets in higher‐dimensional spaces. Since streamflow and other hydrological data frequently follow gamma distribution and also they are frequently stochastically dependent, our multivariate distribution and fitting technique seems to be of particular interest from the hydrological point of

ISSN:0043-1397    

DOI:10.1029/WR014i001p00019

年代:1978

数据来源: WILEY

摘要:

A numeric method for analyzing global parameter sensitivity about a fixed point in parameter space for differential equation models is presented. The method is suitable for large‐scale, multiresponse systems which may not be in steady state. By using a quadratic model, the relationship between several global response characteristics and parameter perturbations is examined. Sensitivity relationships are defined with both backward elimination regression model selection procedures and eigenvalue‐eigenvector analyses. An example of the method is given using an ecosystem model consisting of 14 coupled differential equati

ISSN:0043-1397    

DOI:10.1029/WR014i001p00025

年代:1978

数据来源: WILEY

摘要:

A simple lumped parameter stochastic model for optimal water management in a stream‐connected aquifer system is examined. The physical system is represented by a linear reservoir model, and a conditional probability approach is used to estimate the effect of parameter variability. A drawdown correction is used to incorporate the local drawdown of the wells and is a crucial part of the model. A management analysis is carried out by using a linear decision rule to minimize the expected value of the discounted costs with appropriate chance constraints, and the resulting nonlinear optimization problem is solved iteratively by using a standard linear programing package. In order to evaluate the limitations of the lumped parameter model in a management context, the results of the management technique are compared with results from Maddock (1974) who used a distributed representation of the aquifer. The conclusions of this analysis indicate that stochastic effects are not very important in arriving at an operating policy but are important in determining the expected cos

ISSN:0043-1397    

DOI:10.1029/WR014i001p00030

年代:1978

数据来源: WILEY

摘要:

In analyzing a leaky aquifer for application in regional studies it is of great interest to have available simplified mathematical representations from which an analogical or digital model of the problem can be constructed. In this paper a differential equation valid for intermediate and large values of time is proposed. Also, an analytical solution corresponding to an isolated well as a test of the range of applicability of the proposed equation is obtained.

ISSN:0043-1397    

DOI:10.1029/WR014i001p00039

年代:1978

数据来源: WILEY

摘要:

The unidimensional form of the thermal energy conservation principle as a quasi‐linear partial differential equation (PDE) has been shown accurate for point temperature forecasts on completely mixed streams and river‐run reservoir systems. Two methods of solution are presented which lead to a unique solution. Yet this nonrandom solution is contrary to the behavior of nature, and so a philosophic change is introduced. From the PDE subsidiary differential system a stochastic differential equation (SDE) is obtained with random forcing function from the meteorologic and forebay‐depth analyses. With random initial conditions (time‐averaged components of the in situ water temperature vector) the SDE is then recast as a random nonlinear Volterra integral equation (RIE). Then a solution to the random‐initial‐conditions RIE (fixed points of the expectations), by the so‐called dishonest method (Keller, 1962), is compared with a solution obtained by repetitively solving the PDE as a random equation (expectations of the fixed points). Of course, these solutions, obtained by ‘dishonest and honest’ methods, are not necessarily unique, but they may be sufficiently close in some sense. Hence proper interpretation and use of this RIE model would enable water resource planners economically to determine stream temperatures in probability during critical climatic or river flow conditions. And then intelligent planning and scheduling could avoid some catastrophic aquatic event which might occur as a result of extreme w

ISSN:0043-1397    

DOI:10.1029/WR014i001p00045

年代:1978

数据来源: WILEY

摘要:

Numerical solutions of differential equations should be checked for the conditions of consistency, convergence, and stability. The implicit solutions that satisfy these conditions are sometimes found to be oscillatory about the true solutions. The reasons for these oscillations are explained. A method to derive criteria for nonoscillatory solutions of a nonlinear partial differential equation is outlined. These criteria for modified Richards' equation are presented, and their physical significances are explained.

ISSN:0043-1397    

DOI:10.1029/WR014i001p00052

年代:1978

数据来源: WILEY

摘要:

An estimateFˆof a water resource system's performance, when it is derived by simulation using synthetic streamflow sequences, is subject to at least three errors: first, model errors, arising from the approximation to the ‘true’ streamflow mechanism which the model represents; second, sampling errors in the model parameters θ when they are calculated from the historic records; and third, errors introduced by the Monte Carlo calculation from whichFˆis derived. This paper presents some observations on the effects of the first two types of error on the estimateFˆbut concentrates on the application of variance reduction techniques to the derivation of Monte Carlo estimatesFˆfor given θ. These techniques are, first, the use of control variates and, second, the use of antithetic variates, and their application is illustrated by using some hypothetical examples of the calculation of probabilities of extreme hydrological events and of the calculation of reliability measures for a much oversimplified storage system. Considerable reduction in the variance ofFˆresulted from the application of the control variate method; the reduction in VarFˆresulting from the use of antithetic variates was much less but still probably worth the small additional programing effort required. It is concluded that the promise of the control variate method suggests that it should be applied to assist in the efficient simulation of more realistic water resource systems than the trivial ones considered in

ISSN:0043-1397    

DOI:10.1029/WR014i001p00055

年代:1978

数据来源: WILEY