摘要:

Although the Bureau of Reclamation adopted a new mission as a water management agency, social purposes of the mission and methods of accomplishing the purposes remain undefined. A broad consensus agrees that a central feature of the agency's management program should be irrigation water conservation. This paper describes three purposes of irrigation water conservation: achieving economic efficiency of water allocation, improving environmental quality of western river systems, and satisfying outstanding Native American water claims. Five policy instruments are described as alternative methods of inducing conservation: quantity‐based regulation, price‐based regulation, transferable water use permits, conservation subsidies, and decentralization of ownership of Reclamation facilities. Two findings are: (1) price‐based regulation may not produce water conservation and (2) conservation policy instruments should be chosen with reference to their ability to achieve the purposes of federal water conservation policy. An example illustrates quantitative effects on farm income of the alternative instru

ISSN:0043-1397    

DOI:10.1029/90WR02403

年代:1991

数据来源: WILEY

摘要:

An informal analysis of readily available time series data relevant to urban water use in Tucson, Arizona, is presented as an illustration of how a management‐oriented empirical analysis, structured with general knowledge of the results of formal econometric studies, can produce useful insights for making applied price policy. Precise estimates of urban water demand price and income elasticities are not required in order to achieve conservation‐oriented goals. In the Tucson experience, annual water price increases equal to the rate of inflation plus approximately the rate of change in real per capita income would have been necessary just to maintain constant rather than increasing water use. Given the actual price policy, it is not surprising that Tucson has not achieved its mandated conservation g

ISSN:0043-1397    

DOI:10.1029/90WR02088

年代:1991

数据来源: WILEY

摘要:

This paper presents one practical method of valuing the recreational fishing benefits generated by a unit of water as it moves downstream. A cross‐sectional analysis is employed to estimate the change in individuals' fishing behavior due to a change in availability of fishery resources. A proxy for the availability of stream fishery resources is derived from the link between changes in streamflow consumption to changes in the quality of fishing downstream. The results show that marginal increases in streamflow can generate recreational benefits that exceed the marginal value of water in agriculture in some regions of the countr

ISSN:0043-1397    

DOI:10.1029/90WR02402

年代:1991

数据来源: WILEY

摘要:

Transport of reactive solute in individual fractures is investigated. Solute advection is coupled with matrix diffusion that is assumed perpendicular to the fracture plane. Fluid advection in the fracture is viewed as intersecting flow paths, whereby the advection velocity of a solute particle varies along individual streamlines. Solute mass arrival at a fixed position averaged in the direction perpendicular to the mean flow is examined. The dispersion in the solute breakthrough arises because of the different advection travel times and varying mass flux along individual streamlines. The fracture is conceptualized as a two‐dimensional porous medium with a statistically anisotropic, spatially varying transmissivity with a given correlation structure; the assumed anisotropy condition is consistent with elongated, channel‐like flow paths that have been observed in single fractures. Approximate expressions for the first two moments of solute travel time are used to illustrate the sensitivity to different correlation models for the fracture transmissivity. In particular, the finite correlation scale model, the self‐similar (fGn) model, and the channel model are considered. The expected cumulative mass arrival is more sensitive to the assumed correlation model for lower rates of matrix diffusion. The derived expression for the mass arrival can also be used for analyzing the effect of nonequilibrium sorption‐desorption reactions in single fr

ISSN:0043-1397    

DOI:10.1029/90WR01908

年代:1991

数据来源: WILEY

摘要:

Covariance analysis was used to determine the reduction in rainfall forecast and estimation variances offered by radar reflectivity data. Covariance analysis of a particular nonadvective linear physically based model indicated that the utility of the radar reflectivity data of various elevation angles is limited in mean areal rainfall predictions, even when a very small density of rain gauges exists over the region of interest and good quality radar data are used. This applies to both raw reflectivity and radar rainfall data converted through aZ‐Rrelationship. The ratio of mean areal rainfall prediction variances, defined as variance with radar data divided by variance without radar data, was found to be greater than 0.8 in most cases. On the other hand, the radar data reduced the estimated variance of the vertically integrated liquid water content considerably, even when high‐density rain gauge data were pres

ISSN:0043-1397    

DOI:10.1029/90WR02426

年代:1991

数据来源: WILEY

摘要:

Stable isotopes, major elements, trace elements, and noble gases in groundwater from northern Mali permit a reconstruction of the paleohydrology of the Sahelian and sub‐Saharan regions of west Africa. Major floods of the Niger River during the more humid episodes of the Holocene, probably associated with northward migration of the interior river delta (flood zone), were responsible for groundwater recharge. A marine aerosol input, somewhat modified by rock‐water interaction, dominates the groundwater chemistry. Stable isotope compositions distinguish the Saharan zone groundwater from waters recharged in the Sahelian zone south of the Azaouad ridge. Carbon 14 dating shows that whereas the latter are modem, the Saharan zone was recharged in the Early to Middle Holocene. Noble gas contents suggest that recharge north of Azaouad occurred under cooler climatic conditions than presently prev

ISSN:0043-1397    

DOI:10.1029/90WR01703

年代:1991

数据来源: WILEY

摘要:

Two mass balance equations were used to model the transfer of dissolved chemicals from the soil solution to the surface runoff water and transport of these chemicals to the field outlet end. One mass balance equation is written for the chemicals dissolved in the overland water, and the other for the chemicals within the soil profile. The chemical input into the surface runoff water is by the rate‐limited convective mass transfer process. Two time scales are isolated: the slow time scale represents the diffusion‐based mass transfer process and the fast time scale represents the convective transport of dissolved chemicals by overland flow. Scaling the mass balance equations for the slow time scale yields a small parameter, which multiplies the time derivative of the mass balance equation written for the overland flow, providing a singular perturbation problem. By using the method of matched asymptotic expansion, an inner and outer problem is formulated and solved for each order of approximation. A single composite expansion, uniformly valid over the entire domain, is derived analytically. This approximated solution was compared with an exact analytical solution for the case in which chemicals are initially uniformly distributed throughout a semi‐infinite soil profile. The time scale method was then used to solve a more complicated problem in which chemicals are initially distributed within a certain soil surface layer of a semi‐infinite soil

ISSN:0043-1397    

DOI:10.1029/90WR01784

年代:1991

数据来源: WILEY

摘要:

Regional scale latent heat flux (LE) was estimated from rawinsonde soundings of the planetary boundary layer (PBL) over the Konza tailgrass prairie in July 1986. Two approaches were used to calculate LE: similarity theory and an algebraic solution of a conservation equation for water vapor in the PBL. Nine of the soundings were complete. However, the latter five soundings only recovered data for every sixth possible level. The results were compared with estimates made by an array of nine Bowen Ratio surface stations. Similarity theory, using vertically averaged values, produced estimates that were reasonably close to the surface values. However, the use of values at the top of the PBL resulted in large overestimation of the evaporation fluxes. When complete soundings were available, the conservation equation yielded estimates which agreed very well with surface values. The agreement was reduced for incomplete soundings. This is likely related to the sensitivity of the equation to uncertainties in the height of the inversion. Overall, the conservation equation produced estimates in closest agreement with the surface stations. The results suggest that adequate vertical resolution of measured profiles is important for proper estimation of regional surface fluxes.

ISSN:0043-1397    

DOI:10.1029/90WR02407

年代:1991

数据来源: WILEY

摘要:

This paper presents an integral equation technique for solving stochastic boundary value problems in groundwater flow. The aquifer considered has deterministic hydraulic conductivity but is subject to random boundary condition and domain recharge. Using the distribution of fictitious sources and dipoles, stochastic integral equations for the mean and covariance of head and flux are derived. An iterative boundary element technique is applied for numerical solution. Two one‐dimensional examples are examined and compared with exact solution. A two‐dimensional problem is then presen

ISSN:0043-1397    

DOI:10.1029/90WR02168

年代:1991

数据来源: WILEY

摘要:

A new formulation is proposed for the estimation of transmissivity in confined aquifers based on head measurements. This formulation consists of a formulation which minimizes a weighted residual norm of the gradient of the measured and observed head. The weighting is the square of the estimated transmissivity. We show by theoretical analysis and numerical experimentation the improved global convergence properties and characteristics of stability under head measurement uncertainty exhibited by the new formulation. We conclude that the new formulation may be superior to conventional head residual formulations or may be useful as an added term to conventional formulations. The formulation is further demonstrated by a field scale application to the Friuli Aquifer in Italy.

ISSN:0043-1397    

DOI:10.1029/90WR02141

年代:1991

数据来源: WILEY