摘要:

A model for the optimal operating policy of a reservoir for irrigation under a multiple crops scenario using stochastic dynamic programming (SDP) is developed. Intraseasonal periods smaller than the crop growth stage durations form the decision intervals of the model to facilitate irrigation decisions in real situations. Reservoir storage, inflow to the reservoir, and the soil moisture in the irrigated area are treated as state variables. An optimal allocation process is incorporated in the model to determine the allocations to individual crops when a competition for water exists among them. The model also serves as an irrigation scheduling model in that at any given intraseason period it specifies whether irrigation is needed and, if it is, the amount of irrigation to be applied to each crop. The impact on crop yield due to water deficit and the effect of soil moisture dynamics on crop water requirements are taken into account. A linear root growth of the crop is assumed until the end of the vegetative stage, beyond which the root depth is assumed to be constant. The applicability of the model is demonstrated through a case study of an existing reservoir in India.

ISSN:0043-1397    

DOI:10.1029/91WR02360

年代:1992

数据来源: WILEY

摘要:

This study addresses regional adjustments to possible reductions in water availability which may occur with a future climate change. The study assesses potential responses of urban water suppliers to reduced water availability by examining an analogous case of reduced supply in the Denver metropolitan region. In this case the U.S. Environmental Protection Agency's veto of a large surface storage project (the Two Forks dam) prompted water providers in metropolitan Denver to take other actions to ensure adequate future water supply. In some cases, actions taken since the veto process began represent a departure from previous water provider policies. It is argued that similar institutional adjustments may occur due to climate change‐induced reductions in regional water supplies and that useful lessons may be drawn from an analysis of institutional responses to the Two Forks veto. This paper introduces what is envisioned as a long‐term assessment of regional adjustments to reduced future water suppl

ISSN:0043-1397    

DOI:10.1029/91WR02382

年代:1992

数据来源: WILEY

摘要:

Previously, soil water retention and hydraulic conductivity curves have been scaled independently with separate scale factors calculated for each curve. Here we provide a method to scale both hydraulic functions simultaneously to yield a single set of scaling factors. An algorithm was developed to scale the hydraulic data, either as a function of degree of saturationS, or normalized water content Θ. Optimization using Powell's method in combination with a Newton‐Raphson procedure resulted in one set of parameters representing the scaled mean hydraulic functions and one set of scale factors describing the variability of both the retention and conductivity relationships. We present and compare results obtained from (1) scaling water retention data only; (2) scaling hydraulic conductivity data only; (3) simultaneous scaling of soil water pressure headhand the natural logarithm of hydraulic conductivityK; and (4) simultaneous scaling of the logarithms of bothhandK. Sets of scale factors for two data sets were analyzed for distribution type and autocorrelati

ISSN:0043-1397    

DOI:10.1029/91WR02224

年代:1992

数据来源: WILEY

摘要:

A general model is presented that simulates the effect of an immobile immiscible organic liquid, as well as rate‐limited solid phase sorption, on the transport of dissolved organic contaminants in heterogeneous porous media. Specific models are developed for four cases (1) immobile immiscible liquid that resides in nonadvective domains of a heterogeneous porous medium; (2) immobile immiscible liquid that resides in the advective domain; (3) homogeneous porous media wherein mass transfer within the immiscible liquid, as well as across the liquid‐water interface, is rate limited; (4) homogeneous porous media with a single resistance to liquid‐liquid mass transfer. The performance of the homogeneous‐based, single‐resistance model was evaluated by attempting to predict a break‐through curve reported in the literature. Based on the successful prediction of the data, where values for all parameters were obtained independent of the data being simulated, it appears that the conceptual basis of the model is valid. Through a series of simulations, the effect of the immiscible liquid on retention was shown to be great, even at relatively low levels of saturation. Release of solute from residual saturation located within regions of relatively low hydraulic conductivity can be significantly rate limited, even when mass transfer between immiscible liquid and water is rapid. This has ramifications concerning the efficacy of remediation systems based on imposed hydraulic gradients (e.g., pump‐and‐treat). The model should prove useful in further investigations of the effect of immobile immiscible organic liquids on the retention and transport of organic solutes

ISSN:0043-1397    

DOI:10.1029/91WR02498

年代:1992

数据来源: WILEY

摘要:

The quasi‐linear continuous point source has been central to many studies of multidimensional flow in unsaturated soil. Immediately next to the source, however, the water pressure Ψ is positive and indefinitely large, so the quasi‐linear flow equation (limited to Ψ ≤ 0) fails in principle. We investigate whether this is a serious problem in practice. Exact analysis would be complicated and difficult, since the problem is of mixed saturated‐unsaturated flow with an unknown free boundary between the two regions. When the source strength is not too large, the saturated region is close to spherical. A simple approximate analysis follows with exterior and interior flow velocities matched on the boundary. The correction, taking into account the saturated region, shifts the quasi‐linear source a small distance above the actual source location. In practical applications the correction is usually negligibly small. Physical reasons why the approximation works well and the correction is small are indicated. In addition, these physical reasons suggest that the scope of the quasi‐linear analysis is wider than supposed hitherto. The solution in potential theory for the eccentric point source needed for the study is given in

ISSN:0043-1397    

DOI:10.1029/91WR02600

年代:1992

数据来源: WILEY

摘要:

Using concepts developed in an earlier study, a solution in Laplace transform space is obtained for transport of resident concentration in an imperfectly but yet highly stratified porous medium. The flow field, into which an instantaneous pulse of tracer is injected, is taken to be steady and mean uniform parallel to the direction of stratification. From this transform‐space solution either temporal moments can be derived by taking derivatives with respect to the Laplace parameter, or the transform‐space solution can be inverted numerically to obtain breakthrough curves for the mean concentration. When compared to an equivalent solution with a Fickian dispersive flux, these temporal moments indicate the extent to which transport in heterogeneous porous media deviates from classical Fickian behavior. The numerical inversion of the Laplace transform solution gives partial breakthrough curves for the mean concentration which have the appearance of conflicting with the derived moment information. A hypothesis is put forth which resolves this apparent conflict; this hypothesis is verified by adding a component of local dispersion to the governing transport equation. On the basis of the flux‐averaged concentration a form for the expected probability density function for the arrival time of a tracer particle is derived; arrival time moments and an arrival time cumulative distribution function are available as a consequence. Arrival time moments, as derived from the flux‐averaged concentration, do not differ significantly from the resident moments, as derived from the resident concen

ISSN:0043-1397    

DOI:10.1029/91WR02105

年代:1992

数据来源: WILEY

摘要:

Practical estimation of long‐term daily Great Lakes evaporation requires one‐dimensional (depth) models of heat storage and mixing. Conceptual models are preferable to physical models for small‐computer simulations that are multiple, continuous, and long. This paper describes a new conceptual superposition model of heat storage to extend an existing evaporation model along the lake depth. The resulting daily model is recalibrated to remotely sensed surface water temperatures and is used to illustrate anew seasonal heating and cooling cycles, heat‐temperature hysteresis, water column turnovers, and mixed‐layer developments. It is used as well to compare the vertical distribution of temperatures with independent bathythermograph data. The time occurrence structure of evaporation on the Great Lakes is investigated, and the effects of summertime initial conditions on subsequent wintertime behavior of evaporation are simulated. Impacts of perceived large‐lake thermodynamic behavior are analyzed, and suggestions are made for furth

ISSN:0043-1397    

DOI:10.1029/91WR02500

年代:1992

数据来源: WILEY

摘要:

A model of wind‐driven currents and transport of substances in unstratified water bodies is presented. The model employs a coordinate system, consisting of curvilinear functions that are orthogonal in the horizontal plane and a coordinate of “normalized depth.” The method of merging asymptotic expansions was used to obtain analytical expressions for components of current velocity as functions of wind stress and pressure anomaly gradient. The pressure anomaly was calculated using an equation that describes the influence of bottom topography, Coriolis force, inertial forces, wind friction, bottom friction and lateral fri

ISSN:0043-1397    

DOI:10.1029/91WR02024

年代:1992

数据来源: WILEY

摘要:

A new method is developed for the construction of reliable marginal confidence intervals and joint confidence regions for the parameters of nonlinear, hydrologic regression models. A parameter power transformation is combined with measures of the asymptotic bias and asymptotic skewness of maximum likelihood estimators to determine the transformation constants which cause the bias or skewness to vanish. These optimized constants are used to construct confidence intervals and regions for the transformed model parameters using linear regression theory. The resulting confidence intervals and regions can be easily mapped into the original parameter space to give close approximations to likelihood method confidence intervals and regions for the model parameters. Unlike many other approaches to parameter transformation, the procedure does not use a grid search to find the optimal transformation constants. An example involving the fitting of the Michaelis‐Menten model to velocity‐discharge data from an Australian gauging station is used to illustrate the usefulness of the methodol

ISSN:0043-1397    

DOI:10.1029/91WR02398

年代:1992

数据来源: WILEY

摘要:

Traditional multivariate data analysis techniques, such as principal components analysis (PCA), have often been used in an attempt to identify source solutions from potential mixtures, such as stream water. Artificial data, generated from conservative mixing of known source solutions in random proportions, are employed to demonstrate that PCA should be used only to determine the rank of the mixture and not to determine the composition of the source solutions. The rank of the mixture is related to the number of source solutions. Unambiguous identification of the source solution compositions from the mixture alone is impossible; thus it is necessary that potential source solutions be derived from independent measurements. In the case of stream water, possible source solutions are groundwater and soil water from different horizons. A multivariate screening procedure is presented for the evaluation of these potential source solutions.

ISSN:0043-1397    

DOI:10.1029/91WR02518

年代:1992

数据来源: WILEY