摘要:

The contingent valuation method (CVM) and travel cost method (TCM), recommended by the federal guidelines, are applied to the problem of estimating recreational benefits in a case study of rivers in the Colorado Rocky Mountains. The primary purpose is to assess the validity of the behavioral intentions reported in CVM surveys compared to actual behavior‐based TCM analysis. Comparison of the two approaches has been limited by potential measurement problems including variation in the valuation question and model specification. This study evaluates CVM questions asking for both trip and annual values, versus TCM models of the number of trips per participant with and without adjustment for the probability of participation. Based on this case study, we cannot reject the hypothesis that recreation benefits estimated by the alternative methods are equal. Apparently, the ordinary CVM and individual TCM can provide as useful an approximation of the recreational economic welfare effects of river protection as the alternative procedure

ISSN:0043-1397    

DOI:10.1029/91WR00686

年代:1991

数据来源: WILEY

摘要:

A method of reliability improvement is proposed for water distribution networks. The ratio of expected maximum total water supplied to total water demanded is employed as a measure of reliability. A nonlinear maximum flow model is used to calculate the maximum supply of water under possible link failures and the reliability of the network. Reliability is improved by increasing pipe size. The pipe size increase is determined by considering the ratio of marginal reliability to marginal cost. The method gives a symmetric design when the network is symmetric.

ISSN:0043-1397    

DOI:10.1029/91WR00882

年代:1991

数据来源: WILEY

摘要:

The physics of the rainfall infiltration under a constant rainfall flux greater than the hydraulic conductivity at saturation are investigated and compared with those pertaining to the infiltration process under flooding. From the arguments developed theoretically the following conclusions are reached: The moisture profile prevailing at the time the soil surface becomes saturated during the rainfall process (t=T) is identical with the profile which has been developed during flooding at an earlier time at which the infiltration rate is equal to the rainfall flux (t=tc

ISSN:0043-1397    

DOI:10.1029/91WR00160

年代:1991

数据来源: WILEY

摘要:

Perforated drain tubes have, in many places, supplanted the use of drain tiles in drainage from agricultural lands, airports and the like. However, the few existent formulae for predicting drainage rates are complex and unwieldy. In this paper, a formula is derived by using a series solution of Laplace's equation and techniques of solution of dual trigonometric series, for the rate of water flow into a perforated drain tube, showing the effects of such parameters as hole size, number and spacing of holes, and drain size and depth. The formula applies to pipes perforated by small circular holes or by longitudinal slits. Recommendations for the design of perforated pipes are made, based on the delivery ratio.

ISSN:0043-1397    

DOI:10.1029/91WR00779

年代:1991

数据来源: WILEY

摘要:

Several methods of testing for multivariate trend have been discussed in the statistical and water quality literature. We review both parametric and nonparametric approaches and compare their performance using, synthetic data. A new method, based on a robust estimation and testing approach suggested by Sen and Puri, performed very well for serially independent observations. A modified version of the covariance inversion approach presented by Dietz and Killeen also performed well for serially independent observations. For serially correlated observations, the covariance eigenvalue method suggested by Lettenmaier was the best performer.

ISSN:0043-1397    

DOI:10.1029/90WR01802

年代:1991

数据来源: WILEY

摘要:

This paper provides some useful results for modeling rainfall. It extends work on the Neyman‐Scott cluster model for simulating rainfall time series. Several important properties have previously been found for the model, for example, the expectation and variance of the amount of rain captured in an arbitrary time interval (Rodriguez‐Iturbe et al., 1987a), In this paper additional properties are derived, such as the probability of an arbitrary interval of any chosen length being dry. In applications this is a desirable property to have, and is often used for fitting stochastic rainfall models to field data. The model is currently being used in rainfall time series research directed toward improving sewage systems in the United Kingdom. To illustrate the model's performance an example is given, where the model is fitted to 10 years of hourly data taken from Blackpool, Engl

ISSN:0043-1397    

DOI:10.1029/91WR00479

年代:1991

数据来源: WILEY

摘要:

Estimates of “macropore” soil water phenomena are calculated from a simple stochastic model of infiltration. Probability density functions (pdf) for cumulative infiltration (I), infiltration rate (I′), and infiltrating‐water flux (ν) are proposed. Cumulative infiltration is defined here as the maximum quantity of water the soil can accept from unponded water supplied at a given location on the soil surface. Similarly, infiltration rate is defined as the maximum rate at which unponded water can enter the soil. The pdfs for cumulative infiltration (fI) and infiltration rate (fI′) are derived by assuming that the saturated hydraulic conductivity (Ks) is a lognormal‐distributed random variable. The actual infiltrating‐water flux will depend onI′, rainfall rate (R0), slope, and surface roughness. For a flat and smooth soil surface the pdf for infiltrating‐water fluxfνis derived fromfI′, by assuming that water failing to infiltrate into portions of the soil with lower infiltration rates will flow over the soil surface, eventually being accepted by areas with higher infiltration rates. The pdffνpredicts that macropore soil water flow phenomena will become more pronounced as the rainfall rate approaches the mean infiltration rate, when macropore flux predicted byfν, is many times the rainfall rate. These results indicate that stochastic description of soil hydraulic properties shows promise in describing macropore soil water phenomena. Models of the field‐scale effects of macropore soil water flow should include infiltration rate variability and runoff contributions t

ISSN:0043-1397    

DOI:10.1029/91WR00588

年代:1991

数据来源: WILEY

摘要:

A simulation experiment is used to test the stochastic theory of unsaturated flow proposed by Mantoglou and Gelhar (1987a, b, c). Tension means and variances derived from this theory are compared to tension distributions obtained from a detailed three‐dimensional model developed by Ababou (1988). The synthetically generated unsaturated hydraulic conductivity functions used in the detailed model vary significantly over relatively small distances. Results from a simulated infiltration event indicate that the stochastic theory's predictions reproduce the overall trend of the heterogeneous tension distribution. Deviations from the predicted mean generally lie within confidence intervals derived from the predicted variance. The stochastic theory predicts less vertical moisture movement and somewhat more horizontal spreading than a comparable deterministic analysis. This reflects the fact that the effective hydraulic conductivity function used in the stochastic approach is anisotropic. The magnitude of this anisotropy increases with increasing tensio

ISSN:0043-1397    

DOI:10.1029/91WR00762

年代:1991

数据来源: WILEY

摘要:

Exact and relatively simple analysis is possible for one hysteretic redistribution process, that in long horizontal columns with the two parts,xθ4). The operative moisture potential is the primary drying potential forx0, θ4≥ θ ≥ θ2. The operative moisture diffusivity is the primary drying diffusivity forx0. The drying diffusivity is greater than the wetting diffusivity near θ = θ1and less near θ = θ2Solutions are found for illustrative examples corresponding to four values ofH, the relative magnitude of the hysteresis loop. The resorptivityR, the total wet‐to‐dry exchange of water acrossx= 0 in reduced form, is analogous to the sorptivitySin absorption and infiltration. For the calculated examples,Ris about one third ofSfor the corresponding absorption process and varies only mildly withH. Nonhysteretic calculations may thus give reasonable estimates ofRfor horizontal hysteretic redistribution, though they cannot give details such as the moisture jump atx= 0, Desorption moisture profiles forx0 are relatively steep, and the penetration depth small. It follows that in experiments the initially wet section of the column should be made some 5–10 times long

ISSN:0043-1397    

DOI:10.1029/91WR00780

年代:1991

数据来源: WILEY

摘要:

Four new algorithms are presented to cost‐effectively delineate displacement fronts and capture zones via particle tracking in complex flow fields. These algorithms include methods of (1) defining path lines using “mixed distance and time particle tracking”; (2) computing displacement fronts and capture zones using “dynamic particle allocation front tracking” allowing insertion/deletion of particles to optimize front definition; (3) obtaining accurate breakthrough curves by using simultaneous “mass redistribution,” reallocating particle mass among particles defining the displacement front; and (4) determining production well breakthrough curves using “optimized sorting algorithms” when backward tracking to map capture zones. Examples are shown for capture zones and aquifer remediation applications. Comparisons are made to conventional algorithms. Results show that the number of particles required to define displacement fronts and breakthrough curve is a function of time, position, and How field complexity. Dynamic front tracking results in significant savings of storage and computational expense, even for relatively simple velocity fields. A corresponding increase in the accuracy of breakthrough c

ISSN:0043-1397    

DOI:10.1029/91WR00720

年代:1991

数据来源: WILEY