摘要:

In fully appropriated multiple‐use river basins, a major potential competitor for a share of water may be publicly sponsored appropriations to supplement low streamflows for fish, wildlife, and recreation, which generates economic values not revealed in the marketplace. Based on a survey of instream recreationists on New Mexico's Rio Chama a travel cost model is developed to identify the potential recreation demand for instream flows. A discrete optimal control model is formulated that solves for the intraseasonal allocation of reservoir releases which maximizes the yearly value of instream recreation benefits, net of values of competing uses in the basin. Results indicate that in New Mexico, reservoir releases which augment low streamflows can return gross recreation benefits in the range of $900 to $1100 per acre‐foot (ac ft) of water consumed (1 ac ft = 1.233 × 103m3). This compares to a $40/ac ft cost of using the water. Consequently, results strongly support the hypothesis of potential economic payoff from public investments in and management of instream flow reservat

ISSN:0043-1397    

DOI:10.1029/WR023i003p00381

年代:1987

数据来源: WILEY

摘要:

In periods of drought, urban water systems commonly rely on nonmarket programs to induce temporary conservation, leaving the marginal price of water unchanged; an alternative is to raise the price. Using pooled cross‐sectional and time series observations on single‐family residential customers of the Honolulu Board of Water Supply (1982), demand for water is estimated as a function of price, income, household size, rainfall, and a dummy variable denoting a water restrictions program. Short‐run elasticities suggest that an increase in marginal price of less than 40% would achieve a 10% reduction in water use, even during a drought episode. An accompanying conservation program would mitigate the necessary price increase, but only sli

ISSN:0043-1397    

DOI:10.1029/WR023i003p00393

年代:1987

数据来源: WILEY

摘要:

The problem consists in selecting the sites on the river where reservoirs and hydroelectric power plants are to be built and then determining the type and size of the projected installations. The solution obviously depends on the amount of money the utility is willing to invest, which itself is a function of what the new installations will produce. It is therefore necessary to solve the problem for all possible amounts of firm energy produced, since it is not known at the outset which production level the utility will select. This is done in the paper by a parametric mixed‐integer linear programming (MILP) method whose efficiency derives from the fact that the branch‐and‐bound algorithm for selecting the sites to be developed (and consuming most of the computer time) is solved a minimum number of times. Between the points where the MILP problem is solved, LP parametric analysis is ap

ISSN:0043-1397    

DOI:10.1029/WR023i003p00399

年代:1987

数据来源: WILEY

摘要:

Groundwater flow and contaminant transport models have been widely used for planning and design purposes in the past decade. Two of the most significant limitations for application of these models are data availability and parameter estimation. By use of a parameter identification algorithm and synthesized data, it is possible to isolate the effects of data availability and data uncertainty. This approach was implemented using the U.S. Geological Survey's method of characteristics (USGS‐MOC) model for a hypothetical aquifer. A parameter identification scheme attached to the USGS‐MOC model was used to determine unknown transmissivities and dispersivities. The study results showed that the predictive ability of the USGS‐MOC model (and, by implication, similar models) is limited unless relatively extensive and good quality data are available. For the example tested, it was found that extending the length of the observation series was more effective in improving parameter estimates and resolution of the contaminant plume prediction than adding observation wells. Further, when the boundary conditions were known, the contaminant predictions were much more sensitive to accurate estimation of transmissivity than to the estimation of dispersivities. The numerical results also showed that after a relatively short simulation period (less than 4 years), predicted contaminant concentrations could be significantly in error. This suggests the importance of integrating uncertainty analysis into the prediction of long‐term contaminant tr

ISSN:0043-1397    

DOI:10.1029/WR023i003p00408

年代:1987

数据来源: WILEY

摘要:

The southern Piedmont has undergone extensive cropland reversion during the twentieth century with row crops being replaced by forest and pasture. Ten continguous river basins with a total area of 54,020 km2had 10 to 28% of their respective areas reforested during the period 1919–1967. During the same period, water yield decreased 3 to 10 cm according to both regression and double‐mass analysis. These reductions in water yield constituted a 4 to 21% decrease in annual stream discharge and were statistically significant for a majority of the basins. The reduction of water yields by forests tends to be greater for dry years than for wet years. There was little or no relation between the degree of reforestation and reductions of water yield at the scale of this study, but when our data are included with the universe of data, the variance of our data from the overall model is much less than in the universal set. The inclusion of our results extends the range and predictive power of the universal model, giving it greater utility for water yield plann

ISSN:0043-1397    

DOI:10.1029/WR023i003p00425

年代:1987

数据来源: WILEY

摘要:

Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics‐based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics‐based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first‐order reversible sorption, Langmuir‐type kinetics and binary, homovalent ion e

ISSN:0043-1397    

DOI:10.1029/WR023i003p00438

年代:1987

数据来源: WILEY

摘要:

A three‐dimensional theory is described for field‐scale Fickian dispersion in anisotropic porous media due to the spatial variability of hydraulic conductivities. The study relies partly on earlier work by the authors the attributes of which are briefly reviewed. It leads to results which differ in important ways from earlier theoretical conclusions about dispersion in anisotropic media. We express the dispersion tensorDas the sum of a local component d and a field‐scale component Δ. The local component is assumed to be independent of velocity (which is most appropriate if it represents molecular diffusion) and its principal terms are taken to act parallel and normal to the mean velocity vectorμ. The field‐scale component is written asαμ, whereαis a dispersivity tensor and μ= |μ|. We show that at large Peclet numbersP, the dispersivity tensor reduces to a single principal component parallel to the mean velocity, regardless of howμis oriented. This result, valid for arbitrary covariance functions of log‐hydraulic conductivity, differs from that of L. W. Gelhar and C. L. Axness (1983), according to whom the asymptotic dispersivity tensor may possess more than one nonzero eigen value. They calculate the direction of the largest principal dispersivity to be offset from the mean velocity toward the direction of least spatial correlation (or away from the stratification in typical layered media). We show that this principal dispersivity is offset in the opposite direction at small and intermediate Peclet numbers but rotates toward the mean velocity asPincreases. The largest eigen value is constant and dominated by field‐scale velocity fluctuations at largePvalues. The other two eigen values diminish asymptotically in proportion toP−1and are controlled by d as well as by field‐scale differential convection. The range of small Peclet numbers has not been previously investigated under anisotropic conditions yet is of much importance for transport in low‐permeability rocks or soils. We show that at lowPvalues all three principal dispersivities are proportional toPand thus Δ is proportional to μ2(a phenomenon reminiscent of Taylor diffusion). When the mean velocity is inclined to the axes of anisotropy, the eigen values of Δ are neither parallel nor normal toμ. However, sinceDis dominated bydat small Peclet numbers, the principal dispersion coefficients are asymptotically (as P→0) parallel and normal to the mean velocity just like whenPis large; their maximum deviation from these direction

ISSN:0043-1397    

DOI:10.1029/WR023i003p00453

年代:1987

数据来源: WILEY

摘要:

On the basis of a review of recent theoretical and experimental studies of flow through fractured rocks, we have studied the fluid flow and solute transport in a tight fractured medium in terms of flow through channels of variable aperture. The channels are characterized by an aperture density distribution and a spatial correlation length. Aperture profiles along the channels are statistically generated and compared to laboratory measurements of fracture surfaces. Calculated tracer transport between two points in the fractured media is by way of a number of such channels. Tracer breakthrough curves display features that correspond well with recent data by Moreno et al., which lends support to the validity of our model. Calculated pressure profiles along the channels suggest possible measurements that may be useful in identifying the geometrical characteristics of the channels. Finally, predictions were made for tracer breakthrough curves in the case of single fractures under various degrees of normal stress. These suggest possible laboratory experiments which may be performed to validate this conceptual model.

ISSN:0043-1397    

DOI:10.1029/WR023i003p00467

年代:1987

数据来源: WILEY

摘要:

A model is proposed which estimates the probability of the flow in a river exceeding a given discharge during a period of 1 month conditional on the catchment wetness at the start of the month. The model is fitted to data selected on the basis of a rainfall threshold. It assumes a Weibull distribution of flows conditional on rainfall and catchment wetness. The model is applied to the River Browney and the River Aire in the north of England. Base flow in the river is used as a measure of catchment wetness. Extreme value distributions are fitted to the rainfall and base flow data independently, and a Poisson distribution is assumed for the number of exceedances above the rainfall threshold in each month. The results from these catchments show that the antecedent catchment conditions significantly affect the flood risk.

ISSN:0043-1397    

DOI:10.1029/WR023i003p00481

年代:1987

数据来源: WILEY

摘要:

The arrangement of tributaries in dendritic channel networks is controlled in part by the relationship between the spatial requirements of the tributaries and the availability of space. An investigation of 6105 tributaries in four dendritic networks reveals that the arrangement of tributaries of different sizes along subbasin main streams is influenced by two constraints on the availability of space on the acute side (inside) of the main streams. The first constraint arises from the tendency for semidivide angles (between the main stream and adjacent divides) at subbasin outlets to be larger on the obtuse (outside) than on the acute side of the main stream. This constraint not only causes a higher proportion of large tributaries than small ones to form on the obtuse side of subbasin main streams near their outlets but favors the development of large tributaries on the obtuse side farther upstream than small ones. The second constraint is imposed by the tendency for subbasin main streams to curve upstream. This constraint affects tributaries that are almost as large as the subbasin main stream they join and, like the first constraint, it favors the formation of large tributaries on the obtuse side farther upstream than small ones.

ISSN:0043-1397    

DOI:10.1029/WR023i003p00489

年代:1987

数据来源: WILEY