摘要:

Fundamental shifts in water allocation and management are occurring throughout the West. Changing public values have reversed our historic preference for supply augmentation through the construction of new storage systems and replaced it with one for the reallocation of existing supplies. The emerging reallocation era will be characterized by the better management of existing supplies to serve both traditional and new user communities. Reallocation can be accomplished in three ways: (1) the rededication of unallocated or unused blocks of stored water on federal and state reservoirs, (2) the voluntary transfer of existing water rights, and (3) the redefinition of existing rights by judicial decisions and legislation which trim consumptive entitlements. We currently lack a coherent water allocation principle to replace the equation of conservation with storage and maximum consumption, but we are simultaneously trying to reduce the transaction costs of transfers and to impose a number of ad hoc state and federal restraints on water transfers to accommodate the previously neglected claims of nontraditional water users and other interested parties. These new laws can greatly increase the costs of transfers and make them politically unattractive. The expanded recognition of traditional and new third party rights could produce a new riparianism in the West. This would overturn the law of prior appropriation which has thrived because it was premised on the severance of the right to use water from its source and allowed water to be allocated to new demands. In contrast, the common law of riparian rights confines water rights to landowners in the watershed of a stream. From the beginning, western courts rejected the watershed limitation, but many recent transfer restraints modify the law of prior appropriation and reintroduce the principle of watershed protection rule in the form of a premise that river systems should be managed on an ecosystem basis. Emerging new watershed rules could make all transfers presumptively suspect.

ISSN:0043-1397    

DOI:10.1029/91WR00369

年代:1991

数据来源: WILEY

摘要:

Automated extraction of geometry for hydraulic routing from digital elevation models (DEM) is a procedure that must be easily accomplished for widespread application of distributed hydraulically based rainfall excess‐runoff models. One‐dimensional kinematic routing on a regular grid DEM is difficult due to flow division and convergence. Two‐dimensional kinematic routing on a triangular irregular network (TIN) surmounts many of these difficulties. Because TIN DEMs typically require far fewer points to represent topography than regular grid DEMs, substantial computational economy is also realized. One‐dimensional routing using vector contour data overcomes the grid‐based routing disadvantages but often requires several orders of magnitude more storage points than a TIN. The methodology presented in this paper represents a compromise between slightly increased computational complexity and the economy of TIN topographic representation. We take the unique approach of subdividing each topographic triangle (TIN facet) into a set of coplanar triangular finite elements, performing routing on a single facet and then routing the resulting excess hydrograph to downstream facets and channels via upstream boundary conditions. Results indicate that shock conditions are readily handled, computed depths match analytic results to within ±3% and volume balances are typically within 1%. This modeling system illustrates the viability of kinematic routing over a TIN DEM derived directly from digital ma

ISSN:0043-1397    

DOI:10.1029/91WR00224

年代:1991

数据来源: WILEY

摘要:

Chaos analysis has altered the way we view natural systems. Complex or random‐appearing phenomena may be chaotic and thus deterministic, rather than random. In this study, we used the Grassberger‐Procaccia algorithm (GPA) to evaluate a runoff time series from a second‐order catchment in southwestern Idaho for chaotic dynamics. GPA can identify the presence of low‐dimensional chaotic dynamics for experimental time series. A daily runoff record, 8800 days in length, was examined. We found no evidence of chaotic dynamics in snowmelt runoff. Snowmelt runoff measured at a daily time step has a large number of degrees of freedom, which is characteristic of a random rather than chaotic process. These results suggest that the random‐appearing behavior of snowmelt runoff is generated from the complex interactions of many factors, rather than low‐dimensional chaot

ISSN:0043-1397    

DOI:10.1029/91WR00225

年代:1991

数据来源: WILEY

摘要:

This paper presents some new results for the transfer and extension of information at sites with short hydrological records. The results refer particularly to the transfer and extension of annual flood data. The methods described make use of incomplete or “censored” data such as may be supplied by people living near a river or from records collected for nonhydrological purposes, and they constitute extensions to methods already described in the literature. For two specific censoring configurations, the gain in information is assessed analytically; it is shown that, under certain conditions, the gain in information can be substantial, but in general the gain is small, particularly where scale parameters are estimated. For other configurations of censored data, an analytical formulation is not possible, and integrals are given from which information gain may be assessed by numerical calculation. Another result extends the use of flood peaks exceeding some threshold value (“peaks over a threshold,” POTs); probabilistic models of flood frequency using POTs are, in effect, fitted using censored data. The value of the results presented in the paper is likely to be restricted by assumptions about the probabilistic structure of flood sequences: in one case that their distribution (at different sites) is bivariate lognormal, and, for the POT model, that floods occur as a Poisson process with POTs exponentially distributed. The results show, in strictly qualitative terms, the circumstances in which information might be gained by the use of censored data at two sites, and how large (or small) the gains m

ISSN:0043-1397    

DOI:10.1029/90WR02660

年代:1991

数据来源: WILEY

摘要:

Appendix is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document W91–004; $2.50. Payment must accompany order.By using analytical solutions to the problem of one‐ and two‐dimensional linearized unsteady infiltration from a strip source in a soil with saturated hydraulic conductivity varying exponentially in space, explicit criteria for the validity of the one‐dimensional approximation are derived, in terms of parameters describing the soil type, the uniformity of the infiltrating source at the surface, and the soil heterogeneity. Numerical solutions for the linearized infiltration problem are developed for any variation of hydraulic conductivity in space. Extensive simulations suggest that for a sizable strip source and moderate variation of hydraulic conductivity, a set of independent neighboring soil columns represents well the multidimensional infiltration problem. The possibility of defining sufficient parameters controlling the accuracy of the one‐dimensional approximation is

ISSN:0043-1397    

DOI:10.1029/91WR00330

年代:1991

数据来源: WILEY

摘要:

Appendix is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document W91‐003; $2.50. Payment must accompany order.The problem of unsteady multidimensional infiltration in heterogeneous soils is approached analytically. By assuming that the hydraulic conductivity is an exponential function of the soil matric potential and a linear function of the soil moisture, the governing flow equation is linearized for a special variation of the saturated hydraulic conductivity in space. By using integral transform methods, analytical solutions to the one‐ and two‐dimensional flow problem are derived and shown to be generalized versions of known results for homogeneous soils. The development aims at obtaining quantitative criteria for the validity of the one‐dimensional approximation, which is commonly used in hydrologic appli

ISSN:0043-1397    

DOI:10.1029/91WR00331

年代:1991

数据来源: WILEY

摘要:

This perturbation analysis of divergence/convergence effects on hillslope infiltration and downslope unsaturated flow indicates that, in general, these effects are unimportant for usual hillslope topography. Only where the radius of the contour is less than about 10 times the characteristic infiltration lengthlgrav(or 10 times the sorptive length) need the perturbation be taken into account. This result opens up a considerable extension of applicability of the analysis of infiltration on planar hillslopes to embrace slopes with curved contours, such as ridge noses and hollows.

ISSN:0043-1397    

DOI:10.1029/91WR00098

年代:1991

数据来源: WILEY

摘要:

The solution of the nonlinear unsaturated flow equation is given for a problem of infiltration (and associated subsurface flows) into concave and convex topographies made up of homogeneous isotropic soil with uniform initial moisture content. The analysis embraces concave and convex surfaces which are parts of the surfaces of circular cylinders and spheres. We thus model concave and convex slopes (of both ridges and isolated hills), valley bottoms and hollows, and ridgecrests and hillcrests. The major geometrical influence on the flow processes is the slope angle. Only when σ−1(σ = surface total curvature) is less than about 10 times the characteristic infiltration lengthlgrav(or 10 times the sorptive length) does the perturbation due to surface curvature need to be taken into account. Accordingly, the earlier analysis of infiltration on planar hillslopes has wide applicability to slopes with surface curvat

ISSN:0043-1397    

DOI:10.1029/91WR00129

年代:1991

数据来源: WILEY

摘要:

A two‐dimensional finite difference model to study the simultaneous movement of a dense, nonaqueous phase liquid and water in heterogeneous porous media is developed. A distinctive feature of the solution is that the primary variables solved for, wetting phase pressure and wetting phase saturation, are both existent throughout the solution domain regardless of whether the nonwetting phase is present. This eliminates the need to specify small, fictitious saturations of nonwetting fluid ahead of the advancing front where only wetting fluid is present, as is often required in conventional simulators. The model is therefore well suited for the simulation of ground water contamination problems involving the advance of immiscible liquids into previously uncontaminated groundwater systems. The finite difference equations are solved fully implicitly using Newton‐Raphson iteration. In order to minimize computer storage and execution time a Dupont‐Kendall‐Rachford iterative solver utilizing Orthomin acceleration has been incorporated. The numerical model is verified against an exact analytical solution which incorporates fully the effects of both relative permeability and capillary pressure. The model is validated through comparison to a parallel‐plate laboratory experiment involving the infiltration of tetrachloroethylene into a heterogeneous

ISSN:0043-1397    

DOI:10.1029/91WR00266

年代:1991

数据来源: WILEY

摘要:

The migration of a dense, nonaqueous phase liquid through heterogeneous porous media is examined using numerical simulation. Laboratory measurements of capillary pressure‐saturation curves were performed on samples obtained from a sand aquifer and scaled to permeability to provide a data base of model input parameters. Numerical simulations incorporating 25,200 finite difference cells are carried out in a spatially correlated, random permeability field to illustrate the influence of fluid properties on the migration of a nonwetting liquid below the water table. The simulation results are characterized by spatial moments to reflect the relative degrees of lateral spreading exhibited by the migrating nonwetting body in the presence of lenses of differing permeability. In addition, numerical simulations were performed in a solution domain containing a single lens of lower permeability material in order to examine the local‐scale sensitivity to porous media and fluid properties. The results of the study show the migration of a nonwetting liquid to be extremely sensitive to subtle variations in the capillary properties of the porous medium and to be influenced strongly by the fluid physical propert

ISSN:0043-1397    

DOI:10.1029/91WR00267

年代:1991

数据来源: WILEY