摘要:

Residential water demand is studied with microdata and with allowance for (1) seasonal differences in price elasticity, (2) a dynamic adjustment process, (3) a marginal price specification, (4) cross‐price effects between peak and off‐peak demand, and (5) the inclusion of a detailed set of household demographic variables including accurate measures of age distribution and household income. The findings are that the peak (summer) price elasticity of demand is more than twice the off‐peak elasticity; cross price effects are important at the 5% level of significance; variables measuring household income, property value, related property features, and age distribution are simultaneously significant; and finally, peak period adjustment rates are found to be less than off‐pea

ISSN:0043-1397    

DOI:10.1029/92WR01082

年代:1992

数据来源: WILEY

摘要:

Allocation of water between instream uses such as recreation and consumptive uses such as irrigation is an important public policy issue in the western United States. One basis for identifying appropriate levels of instream flows is maximization of net economic benefits. A general framework for estimating the recreational value of instream flows was developed and applied to Montana's Big Hole and Bitterroot rivers. The paper also provides a synthesis of methods for interpreting covariate effects in dichotomous choice contingent valuation models. Precision of the estimates is examined through a simulation approach. The marginal recreational value of instream flow in these rivers is in the range of $50 per acre foot (1 acre foot equals 1233.5 m3) for recreation at low‐flow levels plus $25 per acre foot for downstream hydroelectric generation. These values indicate that at some flow levels, gains may be achieved on the study rivers by reallocating water from consumptive to instream use

ISSN:0043-1397    

DOI:10.1029/92WR01188

年代:1992

数据来源: WILEY

摘要:

This paper explores the similarities of digital elevation maps (DEMs) of natural river basins and optimal channel network (OCN) configurations obtained minimizing the total rate of energy expenditure in the system as a whole and in its parts. Striking similarities are observed for natural and optimal networks in their fractal aggregation structure and in certain multifractal structures found to be characteristic of river basins. Our results suggest, upon critical assessment of the reliability of the identification of the attractor of the underlying dynamics implied by our optimality concepts, that fractal structures are indeed possibly a product of least energy dissipation. Power laws emerging in the description of the distribution of aggregated quantities from both DEMs and OCNs suggest a link with the framework of self‐organized criticality in the dynamics of natural channel network formation. Also, the geomorphological description of OCNs reveals surprising analogies with well‐known empirical or experimental results, A comparison of Peano's basins with OCNs suggests that nature seems to reject the type of strict self‐similarity exhibited by Peano's construct in favor of different shapes implying statistical self‐similarity not only because of chance acting through random conditions but also because of necessity as reflected by least energy expenditure conside

ISSN:0043-1397    

DOI:10.1029/92WR00801

年代:1992

数据来源: WILEY

摘要:

Streams with acidic sulfate compositions (pH less than 3.5) are naturally generated in the alpine Geneva Creek Basin of the southern Rocky Mountains, an area underlain by Proterozoic metamorphic and igneous rocks that are intruded by Tertiary felsic stocks with associated pyritic alteration. These naturally acidic waters are similar in composition to more familiar man‐made acid mine waters or to surface waters acidified by sulfate precipitation. Detailed study of the stream compositions has revealed the principal reactions driving the weathering process and was used to estimate the relative effects of snowpack ionic input versus the solute contribution from acid attack in soil zones and groundwater. In the Geneva Creek Basin, atmospheric sources of solute represent a minor component to the stream water composition, except for chloride, which can be used to determine the fraction of contribution. The weathering process is a balance between oxidation of sulfides, dissolution of silicates, formation of the clay minerals vermiculite, kaolinite, and smectite, carbonate neutralization, and precipitation of ferric and aluminum oxyhydroxides and aluminum sulfate. The chemical analyses of snow samples, multiple samples of water from Geneva Creek and its tributaries, and the composition of primary and secondary minerals identified in the basin serve as input to a mass balance geochemical model, which facilitates the interpretation of the principal geochemical processe

ISSN:0043-1397    

DOI:10.1029/92WR01101

年代:1992

数据来源: WILEY

摘要:

This paper discusses the results of numerical analysis of dispersion of passive solutes in two‐dimensional heterogeneous porous formations. Statistics of flow and transport variables, the accuracy and the role of approximations implicit in existing first‐order theories, and the convergence of computational results are investigated. The results suggest that quite different rates of convergence with Monte Carlo runs hold for different spatial moments and that over 1000 realizations are required to stabilize second moments even for relatively mild heterogeneity (σY2<1.6). This has implications for the extent of the spatial domain for single‐realization numerical studies of the same type. A comparison of the variance of plumes with the results of linear theories (0.05<σY2<1.6) shows an unexpectedly broad validity field for the theoretical solution obtained from a suitable linearization of flow and transport. Reformulation of the same problem linearizing in turn the flow or the transport equations shows opposite deviations from the linear theory. The interesting consequence is that the errors induced by linearizations in the flow or the transport equations have different signs, and their effects on the moments of dispersing plumes are compensating, thereby yielding consistent formulations. Unexpected features of the statistics of probability distributions of longitudinal and transverse velocities and travel times are also computed and di

ISSN:0043-1397    

DOI:10.1029/92WR00578

年代:1992

数据来源: WILEY

摘要:

Equations commonly used to estimate soil freeze‐thaw depths in nonpermafrost and permafrost terrain (Stefan/St. Paul equations) are combined with a daily snowpack/soil water balance model to investigate the effects of soil freezing and thawing on water balance components and the effects of climate, soil, vegetation, and topography on freeze‐thaw regimes. Sensitivity analysis indicates that soil moisture has a dominant influence on soil freezing and thawing, with distinctive effects offall soil moisture contents versus spring and summer inputs after partial soil thawing. The combined models displayed reasonable but sometimes surprising responses to specific sensitivity experiments involving temperature change, vegetation change, and topographic change. Attempts to reproduce measured freeze‐thaw regimes as reported in the literature were generally successful but limited by the short data record on most sites. An improved understanding and modeling of surface/air temperature relationships for unmodified and modified landscapes is identified as a critical

ISSN:0043-1397    

DOI:10.1029/92WR00983

年代:1992

数据来源: WILEY

摘要:

Assessments of resources at risk to anthropogenic pollution require extensive environmental monitoring. In addition, such assessments are required to have a long‐term monitoring component in order to evaluate not only the status but also the trend of the resources at risk to ecological stresses. There is a need to identify statistical methodologies that would provide effective and cost‐saving environmental monitoring designs, since such monitoring surveys are very expensive. In this paper the purely sequential, accelerated sequential, and three‐stage procedures are evaluated as effective fixed‐precision sampling procedures for environmental monitoring. Current monitoring designs utilize a sampling methodology where each resource is assigned a population inclusion probability, with the intent of describing the distribution of the whole population of resources at risk to anthropogenic environmental stresses. This study assumes that existing designs accurately describe the population distribution. A simultaneous fixed‐precision estimation procedure is developed as an efficient method of estimating practically relevant percentiles of the cumulative distribution function, using water quality data from the Eastern Lake Survey as a lake population distribution. Accelerated sequential and three‐stage procedures are shown to be better alternatives to the purely sequential procedure, requiring fewer sampling operations without any substantial loss of efficiency. Depending upon the precision required, all procedures showed potential reductions in sample size by as much as 60%. These types of designs for environmental monitoring are expected to be advantageous in national monitoring efforts directed toward the assessment of the status and trends of various ecological

ISSN:0043-1397    

DOI:10.1029/92WR00916

年代:1992

数据来源: WILEY

摘要:

The use of Chlorofluorocarbons (CFCs) as an age‐dating tool and tracer in shallow groundwaters has been investigated. New methodology for field sampling and preserving groundwaters containing parts per trillion concentrations of the CFCs, F‐1l and F‐12, is presented. Samples are analyzed by purge‐and‐trap gas chromatography with an electron capture detector. Physical and chemical processes that can alter natural concentrations (air‐water equilibrium) of CFCs were investigated to assess dating uncertainties. CFC model recharge ages appear to be defined within 2 years under optimum conditions. The method was applied to central Oklahoma to demonstrate the usefulness of CFCs as (1) an age‐dating tool of shallow groundwaters, (2) a tracer of sewage effluent in surface and shallow groundwaters, and (3) a tracer of shallow groundwater. Results of dating indicate two primary recharge periods in central Oklahoma over the past 45 years that correspond to the wet periods 1945–196

ISSN:0043-1397    

DOI:10.1029/92WR01263

年代:1992

数据来源: WILEY

摘要:

Simulations of transient, unsaturated vertical flow in different initially dry homogeneous soils using Richards' equation suggest that, for a relatively coarse numerical grid, there is no universal weighting scheme to estimate interblock conductivities capable of giving an accurate resolution of the resulting steep wetting fronts, except for the scheme associated with the Kirchhoff transformation (KT). The principal drawback of KT is that it can hardly be applied to heterogeneous soils. A new asymptotic weighting (AW) scheme, based on the asymptotic behavior of the hydraulic conductivity function in the vicinity of residual saturation, is proposed. Numerical tests demonstrate that the AW scheme describes wetting fronts in homogeneous soils nearly as accurately as a scheme based on KT. Applicability and robustness of the AW scheme for simulating water infiltration into heterogeneous soils having substantial vertical variation of hydraulic properties are also demonstrated. Extension of the proposed scheme to higher dimensions is straightforward.

ISSN:0043-1397    

DOI:10.1029/92WR00914

年代:1992

数据来源: WILEY

摘要:

Solute transport studies frequently rely on numerical solutions of the classical advection‐diffusion equation. Unfortunately, solutions obtained with traditional finite difference and finite element techniques typically exhibit spurious damping or oscillation when advection dominates. Recently developed variants of these techniques such as the finite analytic method (Chen and Li, 1979; Chen and Chen, 1984) and the optimal test function method (Celia et al., 1989a, b, c) perform well for steady state problems. Extensions of these methods to the transient case have, however, not been successful, primarily because of inadequate approximations of the temporal derivative. The new numerical method proposed in this paper avoids this difficulty by taking the Laplace transform of the transient equation. The transformed expression behaves like a steady state advection‐diffusion equation with a first‐order decay term. This expression can be solved with either the finite analytic or optimal test function method and the time dependence recovered with an efficient inverse Laplace transform algorithm. The result is an accurate and robust transient solution which performs well over a very wide range of Peclet numbers. We demonstrate this approach by applying the finite analytic method to a Laplace transformed one‐dimensional model problem. A comparison with other competing techniques shows that good approximations are required in both space and time in order to obtain accurate solutions to advection‐dominated problems. A good space approximation combined with a poor temporal approximation (or vice versa) does not give satisfactory results. The method we propose provides a balanced space‐time approximation which works very well for one‐dimensional problems. Extensions to multiple dimensions are conceptually straightforward and brie

ISSN:0043-1397    

DOI:10.1029/92WR01009

年代:1992

数据来源: WILEY