摘要:

A stochastic model is developed for the behavior of the insecticide fenitrothion's decomposition in a New Brunswick (Canada) stagnant pond after aerial spraying. The concentrations of fenitrothion are modeled in two pond compartments: water and bottom sediments. Assuming first‐order kinetics, a mass balance equation of fenitrothion is written for each of the compartments. The deterministic model is obtained by integrating the linear system of differential equations. The stochastic model arises by considering both the initial condition in the water compartment and the input term in the sediment compartment to be stochastic, which results in a stochastic differential equation (SDE). The moment equation, derived from the Itô stochastic differential rule, provides the moment solution to the SDE. Temporal expectations and heteroscedastic variance models are thus obtained. The model is calibrated using observations obtained from fenitrothion sampling at three different locations in each of the pond's compartments. The stochastic model performs satisfactori

ISSN:0043-1397    

DOI:10.1029/WR023i007p01105

年代:1987

数据来源: WILEY

摘要:

Many authors argue that markets will (and should) become a common means of transferring water rights in the western United States. Previous studies have estimated benefits from potential transfers and identified institutional arrangements conducive to market development. However, there is little published material that describes and evaluates existing markets. This article describes five southwestern water markets and evaluates market processes using transactions data from each study area. While the evaluation is necessarily preliminary due to the limited availability of data on market transactions, the markets analyzed here appear to be relatively efficient in allocating water between municipal and agricultural uses. However, nonconsumptive use water values and third‐party impacts not specifically addressed in state laws are poorly accounted for in most areas. Trade‐offs between benefits of market activities, opportunity costs related to market transfers, and transactions costs induced by laws and institutions are identified. These trade‐offs are a key issue facing policymakers who determine the roles that market and administrative processes play in water alloc

ISSN:0043-1397    

DOI:10.1029/WR023i007p01113

年代:1987

数据来源: WILEY

摘要:

The High Plains aquifer, which underlies about 174,000 square miles (1 square mile = 2.59 km2) in the Great Plains, is the principal source of water in one of the nation's major agricultural areas. This paper examines relationships between the scale of management areas and physical factors, resulting from the lateral movement of groundwater, that limit the ability of irrigators in the High Plains to reduce their own future pumping lifts. At the scale of individual farms, irrigators have very limited ability to “bank” water in order to obtain reduced future pumping lifts. On the other hand, at the scales typical of regional management, reductions in pumpage will result primarily in reductions in water level declines within the management a

ISSN:0043-1397    

DOI:10.1029/WR023i007p01123

年代:1987

数据来源: WILEY

摘要:

A management model was defined and solved for optimal runoff water use in arid zones via microcatchment. The microcatchment layout consists of hexagons. In determining their optimal size, stochastic characteristics of the rain and runoff generation were taken into account.

ISSN:0043-1397    

DOI:10.1029/WR023i007p01131

年代:1987

数据来源: WILEY

摘要:

Rates of growth of demand, lengths of financing periods, real interest rates, and the types of facilities are shown to be important variables in evaluating the equity (or inequity) between established residents and new‐development residents when urban water and sewer facilities are expanded with public financing. Established residents pay less than the economic cost of facilities when facilities that can be efficiently expanded in an incremental manner are subject to demands that are growing at rates that are less than the real interest rate. They pay more than the economic cost when growth occurs at higher rates. When facilities are expanded at multiyear intervals with excess capacity, payments are equated to costs at lower growth rates. Similarly, increasing real costs of facilities shift that breakpoint to lower growth rates. Modest one‐time changes can be used to offset burdens on established residents when inequities do occur. Inflation has little effect on these resu

ISSN:0043-1397    

DOI:10.1029/WR023i007p01139

年代:1987

数据来源: WILEY

摘要:

Large policy studies generally involve too many alternative policies to examine each in detail. As a result, such studies often include a step in which policy options (tactics) that are clearly unattractive are screened out. The output from this step is a small list of tactics that deserve a more thorough evaluation. We describe the screening of tactics to change the movement and storage of water in the lakes and waterways of the Netherlands. This analysis was part of a larger study to help the Dutch government develop a new water management policy. The screening process for each tactic involved obtaining an upper bound on the expected annual benefits from the tactic under various assumptions about future water demands (UB) and comparing this upper bound with the tactic's annualized fixed cost (AFC). If the AFC was less than the UB, the tactic was considered promising and was retained for further analysis. If not, the tactic was screened out. Results from the screening analysis informed policy decisions that will avoid investment expenditures of hundreds of millions of dollars and will reduce agricultural damage by about $15 million/year.

ISSN:0043-1397    

DOI:10.1029/WR023i007p01145

年代:1987

数据来源: WILEY

摘要:

An intraseasonal irrigation scheduling problem is dealt with via extended linear quadratic (ELQ) control. The ELQ control is well‐suited for constrained multidimensional problems and provides openloop feedback control rules over the control horizon. A conceptual model is developed to describe the dynamics of water allocation and salt movement in the root zone of a crop. Moisture stress and osmotic stress are combined to obtain the integrated inhibitory effect of salinity on transpiration. For the intraseasonal model to be effective against perennial salt accumulation in the root zone, it should be able to yield control laws which will lead to favorable root zone conditions at the end of an irrigation season, thus avoiding any significant leaching prior to the next growing season. This long‐term aspect of salinity control is handled via probabilistic state constraints which impose desired salinity and moisture levels with desired confidence level. The ELQ control is employed in a case study of expected net benefit maximization over an irrigation season of corn in Fort Morgan, Colorado. The results, in general, correspond well with expected irrigation schedules under different conditions and provide valuable information on both short‐ and long‐term aspects of irrigation control under saline conditions. The ELQ control, being an analytic iterative solution scheme with theoretically guaranteed fast convergence, has a distinct computational advantage over state‐of‐the‐a

ISSN:0043-1397    

DOI:10.1029/WR023i007p01153

年代:1987

数据来源: WILEY

摘要:

To date optimization models for groundwater quality management give no assurance that water quality standards will be met. This is in part because they ignore errors in hydraulic heads, flows, and solute concentrations due to flow and transport model parameter uncertainty. Here we explicitly incorporate parameter estimation and estimate uncertainties into a model for the optimal design of an aquifer remediation scheme. Parameter uncertainty is incorporated into the decision‐making process. The objective is to identify the best remediation strategies (well site selection and pumping‐recharge rates) so that water quality standards are met at a specified reliability level. The procedure couples three methods: (1) a finite element flow and transport simulation model combined with nonlinear least squares multiple regression for simultaneous flow and transport parameter estimation; (2) first‐order first‐ and second‐moment analysis to transfer the information about the effects of parameter uncertainty to the management model; and (3) nonlinear chance‐constrained stochastic optimization combined with flow and transport simulation for optimal decision making. This joint approach enables one to estimate unknown aquifer parameters, quantify the uncertainty of the parameter estimates, simulate flow and transport responses, and automatically account for parameter uncertainty in the decision‐making process through the simulation management model. Results show that remediation requirements can increase dramatically due to parameter uncertainty. Risk‐averse design solutions automatically provide insurance by “overdesigning” the strategy relative to the risk‐neutral case. The approach is fairly general and is applicable to a variety of groundwater management problems. The influence on design solutions of the reliability level and verification of the underlying statistical assumptions of the first‐order analysis are explored in a sensitivity study and 2000 Monte Carlo si

ISSN:0043-1397    

DOI:10.1029/WR023i007p01162

年代:1987

数据来源: WILEY

摘要:

The stream function concept is introduced to the analysis of hydrodynamic dispersion in porous media. The governing partial differential equation for the stream function for two‐dimensional flow under steady state water and solute transport conditions in an isotropic porous medium is derived. For a uniform seepage velocity, the corresponding differential equation is obtained as a special case. The equation for axially symmetric solute transport case is also derived. It is shown that the isoconcentration curves and the hydrodynamic dispersion stream lines are not orthogonal to each other. For the uniform seepage velocity field case, general solutions are presented for concentration distribution and hydrodynamic dispersion stream function (HDSF) for strip sources having variable concentration distributions. Special solutions are presented for concentration, HDSF, and convective‐dispersive flux components for a strip source having constant concentration. The concept of hydrodynamic dispersion bounding streamline separating the solute transport zone from the other zones is also introduced. The methodology of the HDSF concepts and the solutions for some idealized cases can be applied for contaminant plume analysis, computer model validation, and other hydrogeological stud

ISSN:0043-1397    

DOI:10.1029/WR023i007p01175

年代:1987

数据来源: WILEY

摘要:

The study is a continuation and extension of a previous work (Dagan, 1985a) whose aim was to identify the values of the log‐transmissivityYfor steady flow. The common basic assumptions are thatYis a normal and stationary random space function, the aquifer is unbounded, and a first‐order approximation of the flow equation is adopted. The expected value of the water headH, as well as theYunconditional autocovariance, are supposed to have analytical expressions which depend on a parameters vector θ. The proposed solution of the inverse problem consists of identifying θ with the aid of the model and of the measurements ofYandHand subsequently computing the statistical moments ofYconditioned on the same data, The additional features of the present study are (1) incorporation of a constant, but random, effective recharge and its identification and (2) accounting for the fact that θ estimation is associated with some uncertainty, whereas before θ was assumed to be identified with certainty. Analytical expressions are derived for theYandHcovariances for an exponential autocovariance ofY. Paper 2 (Rubin and Dagan, this issue) of the study illustrates the applications of the method to a real‐

ISSN:0043-1397    

DOI:10.1029/WR023i007p01185

年代:1987

数据来源: WILEY