摘要:

Successive linear programming, an optimal control algorithm, and a combination of linear programming and dynamic programming (LP‐DP) are employed to optimize the operation of multireservoir hydrosystems given a deterministic inflow forecast. The algorithm maximize the value of energy produced at on‐peak and off‐peak rates, plus the estimated value of water remaining in storage at the end of the 12‐month planning period. The LP‐DP algorithm is clearly dominated: it takes longer to find a solution and produces significantly less hydropower than the other two procedures. Successive linear programming (SLP) appears to find the global maximum and is easily implemented. For simple systems the optimal control algorithm finds the optimum in about one fifth the time required by SLP but is harder to implement. Computing costs for a two‐reservoir, 12‐month deterministic problem averaged about seven cents per run using optimal control and 37 cents using successive linea

ISSN:0043-1397    

DOI:10.1029/WR021i001p00001

年代:1985

数据来源: WILEY

摘要:

A multiphase approach to the modeling of aquifer contamination by organic compounds is developed. This approach makes it possible to describe the simultaneous transport of a chemical contaminant in three physical forms: as a nonaqueous phase, as a soluble component of an aqueous phase, and as a mobile fraction of a gas phase. The contaminant may be composed of, at most, two distinct components, one of which may be volatile and slightly water soluble and the other of which is both nonvolatile and insoluble in water. Equations which describe this complex system are derived from basic conservation of mass principles by the application of volume averaging techniques and the incorporation of various constitutive relations and approximations. Effects of matrix and fluid compressibilities, gravity, phase composition, interphase mass exchange, capillarity, diffusion, and dispersion are all considered. The resulting mathematical model consists of a system of three nonlinear partial differential equations subject to two equilibrium constraints. These equations relate five unknowns: two capillary pressures and three mass fractions.

ISSN:0043-1397    

DOI:10.1029/WR021i001p00011

年代:1985

数据来源: WILEY

摘要:

A system of equations, derived in part 1 of this paper, which describes the multiphase migration of an organic contaminant in the subsurface is presented. Although this system is not amenable to solution by analytical means, an approximate solution can be sought by a finite difference discretization of the governing equations. A one‐dimensional, implicit numerical model is developed in this manner. To handle the solution of the resultant system of nonlinear algebraic equations, a Newton‐Raphson iteration scheme is employed. In order to apply the finite difference model to a specific problem a number of parameters must be evaluated. These include three‐phase relative permeabilities, saturation‐pressure relations, partition coefficients, and mixture densities and viscosities. As a demonstration of the model's applicability, the migration of a two‐component hydrocarbon mixture in a soil column is simulated. A mass balance is performed, and convergence of the iteration scheme as well as convergence of the difference scheme in space and time are examined heur

ISSN:0043-1397    

DOI:10.1029/WR021i001p00019

年代:1985

数据来源: WILEY

摘要:

Most alpine and subalpine lakes of the Sierra Nevada (California) are very dilute, weakly buffered calcium bicarbonate waters. Seventy‐three lakes selected to lie in basins representative of Sierran bedrocks were sampled in the summers of 1981 and 1982 and have a median alkalinity of 50 μeq 1−1(range 5–1137) and apH of 7 (range 5.7–9.4). The alkalinity of Sierran lakes cannot be predicted from altitude, basin area, or lake area. The concentrations of sulfate, calcium, or alkalinity in lake waters are positively correlated with the percent areal coverage of volcanic or calcareous rocks in the basins. The lakes are not acidified but are extremely sensitive to increases in acidity of atmospheric preci

ISSN:0043-1397    

DOI:10.1029/WR021i001p00027

年代:1985

数据来源: WILEY

摘要:

Infiltration phenomena in swelling soils were investigated theoretically. The approach taken consisted of applying both the approximate analytical techniques developed by J.‐Y. Parlange and co‐workers and conventional finite difference numerical methods to study the generalized Richards equation for one‐dimensional infiltration in a swelling soil. Equations were derived for the ponding time and the post‐ponding infiltration rate that are generalizations of the Parlange‐Smith model expressions for rigid soils. Ponding times for swelling soils were shown to be shorter than those for nonswelling analogs, and post‐ponding infiltration rates in swelling soils were shown to approach zero instead of becoming equal to the hydraulic conductivity, as in rigid soils. These results were confirmed, both qualitatively and quantitatively, with the numerical model, which also provided instantaneous moisture profiles and surface swelling predictions in agreement with field observations. A three‐parameter infiltration equation proposed recently by J.‐Y. Parlange et al. (1982) was generalized to describe swelling soils and shown to be in good agreement with published laboratory and field data. It appears that the generalized analytical model equations developed can be employed conveniently in hydrologic applications which do not require high accuracy

ISSN:0043-1397    

DOI:10.1029/WR021i001p00033

年代:1985

数据来源: WILEY

摘要:

A practical new field method is proposed to evaluate hydraulic conductivity in partially saturated media near a water impoundment. The new method is an inverse procedure which utilizes a flow net constructed from the steady state total hydraulic head distribution around the water source. In the vicinity of constant head sources and downstream along any stream tube, wetness and conductivity generally decrease. Knowing the stream tube geometry and hydraulic gradient from the flow net, Darcy's law is used to determine unsaturated hydraulic conductivities within the stream tube relative to some segment of the stream tube where conductivity is known. This approach was used successfully to predict the unsaturated hydraulic conductivity which was input to two variably saturated numerical models, utilizing total hydraulic head fields generated by the models. This procedure is also applied to pressure head and water content data collected in the field surrounding a constant head borehole infiltration test originally designed to determine only saturated hydraulic conductivity above the water table. For practical purposes the new procedure compares very favorably with (1) results of a field experiment to obtain unsaturated hydraulic conductivity in situ using the instantaneous profile method and (2) values of unsaturated conductivity calculated from field and laboratory measurements of water content and pressure head.

ISSN:0043-1397    

DOI:10.1029/WR021i001p00045

年代:1985

数据来源: WILEY

摘要:

Quantitative predictions of the effects of acid deposition onterrestrial and aquatic systems require physically based, process‐oriented models of catchment soil water and streamwater chemistry. A desirable characteristic of such models is that they include terms to describe the important phenomena controlling a system's chemical response to acidic deposition, yet be restricted in complexity so that they can be implemented on diverse systems with a minimum of a priori data. We present an assessment of a conceptual model of soil water and streamwater chemistry based on soil cation exchange, dissolution of aluminum hydroxide, and solution of carbon dioxide, all processes that occur in catchment soils and that have rapid equilibration times. The model is constructed using an “average” or lumped representation of these spatially distributed catchment processes. The adequacy of the model is assessed by applying it to 3 years of soil water and streamwater chemistry data from White Oak Run, Virginia, a second‐order stream in the Shenandoah National Park. Soil properties predicted by the model are in good agreement with presently available measurements of those soil properties. The success of the model suggests that lumped representations of complex and spatially distributed chemical reactions in soils can efficiently describe the gross chemical behavior of whole catchments (e.g.,pH, alkalinity, and major ionic concentrations in surface waters). Further assessment of the adequacy of this conceptual approach will require more detailed empirical knowledge of the soil processes being modeled, particularly soil cation exchange and the variability of soil CO2partial pr

ISSN:0043-1397    

DOI:10.1029/WR021i001p00051

年代:1985

数据来源: WILEY

摘要:

The inverse problem is defined here as follows: determine the transmissivity at varius points, given the shape and boundary of the aquifer and recharge intensity and given a set of measured log‐transmissivityYand headHvalues at a few points. The log‐transmissivity distribution is regarded as a realization of a random function of normal and stationary unconditional probability density function (pdf). The solution of the inverse problem is the conditional normal pdf ofY, conditioned on measuredHandY, which is expressed in terms of the unconditional joint pdf ofYandH. The problem is reduced to determining the unconditional head‐log‐transmissivity covariance and head variogram for a selectedYcovariance which depends on a few unknown parameters. This is achieved by solving a first‐order approximation of the flow equations. The method is illustrated for an exponentialYcovariance, and the effect of head and transmissivity measurements upon the reduction of uncertainty ofYis investigated systematically. It is shown that measurement ofHhas a lesser impact than those ofY, but a judicious combination may lead to significant reduction of the predicted variance ofY. Possible applications to real aquifers are

ISSN:0043-1397    

DOI:10.1029/WR021i001p00065

年代:1985

数据来源: WILEY

摘要:

In this paper we develop maximum likelihood procedures for parameter estimation and model selection that apply to a large class of point process models that have been used to model rainfall occurrences, including Cox processes, Neyman‐Scott processes, and renewal processes. The statistical inference procedures are based on the stochastic intensity λ(t) = lims→0,s>0(1/s)E[N(t + s) −N(t)|N(u),u

ISSN:0043-1397    

DOI:10.1029/WR021i001p00073

年代:1985

数据来源: WILEY

摘要:

Let {Yj} represent periodically sampled river discharge values. For simplicity, say that a flood occurs at epochn+ 1 if, for some fixedT, Yn+1>T. Assume that at epochn, the decision maker must decide whether or not to issue a flood warning, this decision being based on the past flow record {Yj}j≤n. Finally, assume that costs have been assigned to the two types of mistakes: the “false alarm” event, and the event that a flood occurs when no warning was issued. It is argued that outside the Gaussian assumption, standard time series methodology is inappropriate for the flood warning problem. The purpose of this paper is to relate recent progress based on alternate principles. A nonparametric inference procedure is described which converges to the optimal decision function for the flood warning problem as the length of the historical record increases for any stationary G2‐ergodic Markov process. Under additional assumptions, rates can be established and shown to be optimal in a certain sense. The new methodology is compared with autoregressive moving average predictors on simulated and river fl

ISSN:0043-1397    

DOI:10.1029/WR021i001p00081

年代:1985

数据来源: WILEY