摘要:

Federal water resources projects are presently selected on the basis of the benefit‐cost ratio (BCR), which is an indicator of the economic feasibility of individual projects. From this initial feasibility test one may rank all feasible projects by descending BCR to produce a portfolio of feasible projects which maximizes the BCR within a constrained budget. The portfolio approach proposed in this study is superior to other approaches for project selection, especially when it is combined with an evaluation system to maximize net present value (NPV). Linear and integer programing techniques are combined with empirical data on Tennessee Valley Authority water resources projects to illustrate the superiority and usefulness of the portfolio approach in project selection for implementation. The portfolio approach maximizes NPV and simplifies the application of budget‐planning procedures in choosing projects when budget levels are variable or otherwise uncert

ISSN:0043-1397    

DOI:10.1029/WR012i001p00001

年代:1976

数据来源: WILEY

摘要:

Variations of models developed by E. A. Mitscherlich in the early part of this century are periodically used for estimating input‐output relationships for plants. Mitscherlich's work focused on a single variable. While these exponential models incorporate features of theoretical appeal, the procedures for quantifying the models are relatively complex when two or more independent variables are included. In fits of Mitscherlich and polynomial forms to yield‐water‐fertilizer data for corn grown under experimental conditions in Colorado and Kansas, test statistics for the polynomial forms are as good as or better than those for the more complex Mitscherlich m

ISSN:0043-1397    

DOI:10.1029/WR012i001p00006

年代:1976

数据来源: WILEY

摘要:

The commonly accepted parameters for sediment transport and resistance to flow of alluvial channels are evaluated and found to be inadequate. A resistance equationB2= [V/(gDS)½]{[(s−1)12;/(DS)½}·[(s− 1)gd¼/ω²]and a sediment transport equationC= {103[VS/ϕ(d)]− [(k)s−1)g½d)/ϕ)d)D½] [(s−1)gd¼/ω2] channels, whereBis a factor that describes the constraints that limit the response of dependent variables to changes in independent variables,Vis the mean velocity,Dis the mean depth,Sis the energy gradient,gis the acceleration of gravity,sis the specific weight of the sediment,dis the median diameter of the sediment discharge, ω is the fall velocity of a characteristic particle size, ϕ(d) has the dimensions and characteristics of a fall velocity with values found by experiment, andkis a dimensionless velocity distribution parameter. FactorCis the concentration by weight in parts per million of the transported sediment. There is no differentiation between forms of transport. Presently used equations are shown to be approximations of combinations of these two equations. The two equations describe channel behavior and sediment transport better than other equations, and they are shown to be particularly effective in describing the effects of changes of tempera

ISSN:0043-1397    

DOI:10.1029/WR012i001p00011

年代:1976

数据来源: WILEY

摘要:

This paper describes a device developed for evaluating net vapor exchanges between snow and air that minimizes many of the errors inherent in pan measurements and provides a measurement of snowmelt during the study period. It consists of (1) a cylinder for holding an ‘undisturbed’ snow core, (2) a melt collection chamber, and (3) hydraulic pistons for maintaining the snow core level with the melting snow surface.The change in weight of the snow core with time is a measure of the net vapor exchange between the air and the snow. Results are presented for seven 14‐hour days during May–June 1972 and six 24‐hour days during May–June 1973. The study site is located on sagebrush rangeland on the Reynolds Creek Experimental Watershed in southwest Idaho at an elevatio

ISSN:0043-1397    

DOI:10.1029/WR012i001p00022

年代:1976

数据来源: WILEY

摘要:

A method is presented that utilizes albedo measurements to partition the fraction of the soil surface area exhibiting energy‐limiting (potential) evaporation and the fraction exhibiting soil‐limiting evaporation to calculate actual evaporation rates during the transition phase (energy limiting to soil limiting). Since albedo is proportional to the surface water content, the change in albedo from day to day is indicative of the fraction of the soil surface that is dry and evaporating at the soil‐limiting rate. By denoting the partitioning factor as β and by using a square root of time relation with a coefficient C for the soil‐ limiting phase the evaporation rateEcfor daynafter the soil was wet is(Ec)n=βnEp+C∑i=1n(βi‐1‐βi)(n‐i+1)−1/2whereEpis the energy‐limiting rate. The Priestley‐Taylor formula was used to calculateEp. Calculated evaporation rates were compared with lysimetrically determined rates. It was concluded that this method was reliable for calculating evaporation rates during the transi

ISSN:0043-1397    

DOI:10.1029/WR012i001p00023

年代:1976

数据来源: WILEY

摘要:

Several simplifying assumptions are in general required to solve analytically the set of differential equations controlling transient free surface flow to a fully penetrating gravity well. Results based on the linearization technique as well as on the delayed yield concept provide the most advanced theoretical developments to date. A review of available solutions is presented together with some complementary interpretations of their physical behavior and an analysis of the interrelations between the corresponding basic theories. If the elastic storage coefficientS8is markedly less than the specific yieldSy, the vertical fluid transport is predominant in a cylindrical zone of the water table aquifer included between two regions where flow is essentially radial and is controlled by two different Theis equations. Its boundary surfaces move in time far from the well. IfS8is of the same order of or greater thanSy, the vertical components always tend to become subordinate throughout the aquifer, which at any instant basically behaves as an artesian formation. The physical meaning of Boulton's (1955) delay index 1/α is extensively discussed. It is shown that, contrary to Neuman's (1975) conclusions, the true physical α does not vary linearly with the logarithm of the radial distancerfrom the pumping well, but it is almost linearly related to 1/rand becomes practically constant at some distance from the well (equal to twice the aquifer thickness if the medium is isotropic). An empirical delay index is also found by equating Boulton's (1963) solution and the linearized average drawdown. Its expression enables us to use the classical delayed yield solution to compute the average piezometric decline with an accuracy equal to that of the linearization approach whose final outcome is, however, more complex and needs more computational time for its numerical evaluation. The two major assumptions underlying the present solutions, which are generally more accurate than the Dupuit‐Boussinesq equation, essentially require small water table drawdowns and an aquifer of infinite areal ext

ISSN:0043-1397    

DOI:10.1029/WR012i001p00027

年代:1976

数据来源: WILEY

摘要:

Evapotranspiration from three reaches of the Gila River floodplain in Arizona was measured by the water budget during 1963–1971. Initially, the vegetation consisted of salt cedar and mesquite with densities of canopy ranging from 10 to 100%. The phreatophytes were removed from the study reaches in stages during 1967–1971. Perennial grass seed was applied but did not become established, and the postclearing vegetation was primarily annuals. Comparison of the evapotranspiration data from various reaches and comparison of data from before and after clearing required the application of an empirical equation. A consumptive use coefficient related to the description of vegetation was applied to an existing potential evapotranspiration equation based on macroclimatic observations. Initially, the vegetation description consisted of plant identification and canopy dimensions obtained by use of black and white aerial photography and ground measurements. In 1967, remote sensing in the form of color infrared aerial photography became available and densitometric interpretation was used to develop a spectral signature as the vegetation descrip

ISSN:0043-1397    

DOI:10.1029/WR012i001p00040

年代:1976

数据来源: WILEY

摘要:

A mathematical model for optimal conjunctive utilization of the groundwater quality and quantity resources of unconfined aquifers is presented. The saturated zone of the groundwater system is considered as a component of a regional waste treatment system involving a waste water treatment plant and external sources of dilution water. The model minimizes the cost associated with surface waste treatment while it maintains acceptable water quality levels throughout the aquifer. The results indicate the feasibility of secondary treatment (trickling filter) plus dilution water along with the assimilation capacity of the aquifer for waste water degradation.

ISSN:0043-1397    

DOI:10.1029/WR012i001p00047

年代:1976

数据来源: WILEY

摘要:

Summary and entire article are available on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document W‐76‐001; $1.00. Payment must accompany order.The original Boussinesq problem of the decline of a groundwater mound between parallel drains is extended to include vertical leakage and recharge and cases of freshwater lenses in confined and unconfined saline aquifers. The solution of appropriate continuity equations with some imposed restrictions by variable separation results in three distinct flow depth configurations, which can be described analytically. Transient behavior in two of these cases is nonlinear but amenable to exact solution and can be delineated in a (2μ + β, σ + μ) plane, where β and σ are leakage and recharge parameters and μ is a separation constant. It is found that similarity solutions, one of which is the original Boussinesq solution, exist for both decreasing and increasing flow depths. Active and passive influences of boundary conditions are distinguished. Solutions are applied to the evaluation of saline water intrusion in some coastal zones of Long Island

ISSN:0043-1397    

DOI:10.1029/WR012i001p00054

年代:1976

数据来源: WILEY

摘要:

The theoretical basis for the integrated finite difference method (IFDM) is presented to describe a powerful numerical technique for solving problems of groundwater flow in porous media. The method combines the advantages of an integral formulation with the simplicity of finite difference gradients and is very convenient for handling multidimensional heterogeneous systems composed of isotropic materials. Three illustrative problems are solved to demonstrate that two‐ and three‐dimensional problems are handled with equal ease. Comparison of IFDM with the well‐known finite element method (FEM) indicates that both are conceptually similar and differ mainly in the procedure adopted for measuring spatial gradients. The IFDM includes a simple criterion for local stability and an efficient explicit‐implicit iterative scheme for marching in the time domain. If such a scheme can be incorporated in a new version of FEM, it should be possible to develop an improved numerical technique that combines the inherent advantages of both

ISSN:0043-1397    

DOI:10.1029/WR012i001p00057

年代:1976

数据来源: WILEY