摘要:

This paper considers optimization models for water distribution network problems with reliability constraints. Conditions are presented for an optimal solution where each link consists of at most two pipe segments with adjacent diameters. A simple example is also given to illustrate the case where the proposed conditions do not hold and three nonconsecutive pipe diameters may be selected for a link in the optimal solution.

ISSN:0043-1397    

DOI:10.1029/92WR00283

年代:1992

数据来源: WILEY

摘要:

Recent studies have attempted econometric estimation of the effect of changing groundwater costs on various dimensions of agricultural behavior. These studies assume parametric cost values, ignoring the possibility that marginal pumping costs may be endogenous to the extent of pumping activity. Under the alternative assumption of increasing marginal pumping costs, existing estimates of various elasticities may be suspect due to specification bias. This paper investigates this possibility, modeling a pumping technology based on hydrologic principles which incorporates constant pumping costs as a limiting case. The model also allows for common pool externalities when agents pump groundwater from the same aquifer. The results of the econometric analysis strongly suggest the presence of increasing marginal pumping costs for farmers in our data sample.

ISSN:0043-1397    

DOI:10.1029/92WR00198

年代:1992

数据来源: WILEY

摘要:

Expressions for the macroscopic velocity vector and dispersion tensor for sorbing solute transport in heterogeneous porous formations whose hydrogeologic properties are repeated at intervals were derived via Taylor‐Aris‐Brenner moment analysis. An idealized three‐dimensional porous formation of infinite domain with spatially periodic retardation factor, velocity field, and microdispersion coefficients in all three directions was considered. Sorption was assumed to be governed by a linear equilibrium isotherm under local chemical equilibrium conditions. The analytical expressions presented are based on a perturbation method where all of the spatially periodic parameters employed were assumed to have “small” fluctuations. It was shown that the effective velocity vector is given by the volume‐averaged interstitial velocity vector divided by the volume‐averaged retardation factor, and the effective dispersion dyadic (second‐order tensor) is given by the volume‐averaged microdispersion dyadic divided by the volume‐averaged dimensionless retardation factor plus a dyadic expressing the increase in solute spreading caused by the spatial variabilit

ISSN:0043-1397    

DOI:10.1029/92WR00010

年代:1992

数据来源: WILEY

摘要:

Monte Carlo simulations are used to (1) investigate the accuracy of approximations that are implicit in first‐order stochastic dispersion theories and (2) identify the accuracy limits of first‐order dispersion theories in isotropic porous media. The Fickian theory of Gelhar and Axness (1983), as well as the Fickian and non‐Fickian theories of Dagan (1984) and Neuman and Zhang (1990) are investigated. All Monte Carlo simulations are in three dimensions. Confidence limits of ensemble‐averaged Monte Carlo results in isotropic porous media are established for 0.1 ≤ σY≤ 1.5. These results showed that first‐order theoretical estimates of the Eulerian velocity covariance function are quite accurate for σY<1; theoretical estimates of the non‐Fickian longitudinal dispersivity do not deviate significantly from theory for at least σY≤ 1.5; theoretical estimation of the transverse dispersivity is limited to σY<1; and, the Fickian longitudinal dispersivity is overestimated by the theory of Gelhar and Axness (1983). Of all first‐order dispersion theories, the theory of Dagan (1984) is most robust in estimating

ISSN:0043-1397    

DOI:10.1029/92WR00666

年代:1992

数据来源: WILEY

摘要:

A new technique is employed to calibrate a regional‐scale groundwater flow model to an extensive data base of undisturbed (i.e., assumed to be steady state) and transient heads. The methodology presented in this study is similar in concept to one presented by de Marsily et al. (1984) in that an adjoint sensitivity technique is coupled with a kriging algorithm to calibrate a flow model. The notable difference of the methodology presented in this paper is that it directly identifies the regions where modification of the model's kriged transmissivity or boundary pressure values will directly improve the overall fit between measured and model‐calculated heads at selected wells. At the locations identified as most sensitive to transmissivity changes, synthetic transmissivity values, referred to as pilot points, are added to the transmissivity data base and used as input for kriging the transmissivity field. An application of the methodology to data originating from approximately 10 years of regional hydrogeologic site characterization efforts that have been conducted in the Culebra dolomite at the Waste Isolation Pilot Plant in southeastern New Mexico is presen

ISSN:0043-1397    

DOI:10.1029/92WR00208

年代:1992

数据来源: WILEY

摘要:

The porosity and the autocorrelation function of the pore space are measured on thin sections of Fontainebleau sandstones. This information is used to generate artificial porous media which share these statistical properties. The Laplace equation is numerically solved to determine the formation factor, or equivalently the electrical conductivity. With no adjustable constant, the predicted formation factors were found to be in acceptable agreement with the experimental ones.

ISSN:0043-1397    

DOI:10.1029/92WR00059

年代:1992

数据来源: WILEY

摘要:

The linear programming gradient (LPG) method originally proposed by Alperovits and Shamir (1977) and the subsequent publications based on it are briefly reviewed. The optimal solutions obtained by different investigators for a simple two‐loop network, originally taken by Alperovits and Shamir as an illustrative example, are compared and it is shown that they are not even the local optimum solutions. The latest modification, introduced by Kessler and Shamir (1989), which incorporates the projected gradient of the objective function, is also briefly reviewed and is shown to lead to a truly local optimum solution as claimed by Kessler and Shamir. It is shown that it is preferable initially to suppress the minimum link flow constraint, necessary for reliability purposes, and introduce it later after obtaining the optimal solution for a branching configuration. The philosophy of the LPG method is analyzed. It is shown that the LPG method is inefficient, at least for optimization of the illustrative two‐loop network, as compared to a heuristic method that initially identifies logically good branching configurations for obtaining the optimal solut

ISSN:0043-1397    

DOI:10.1029/92WR00555

年代:1992

数据来源: WILEY

摘要:

Spatial and temporal variations in the composition of dissolved organic carbon (DOC) in stream and soil water of the acidified Birkenes catchment were studied during summer and autumn 1990. Hydrophobic and hydrophilic acids were the dominant fractions in the soils (dominated by podzols and peats) and brook, accounting for ∼90% of total DOC. The podzol displayed a vertical gradation of DOC fractions, with hydrophobic acids dominating in the O horizon (∼65%) and hydrophilic acids dominating in the E and B horizons (∼60%). In the bogs, hydrophilic acids were the dominant fraction at all depths. Temporal variations in the relative contributions of the various DOC fractions were most pronounced in the podzol O horizon and the brook during successive autumn rainstorms, and small in the mineral soils and bogs. In the brook, DOC increases at peak discharge were dominated by hydrophilic acids. If stream water was assumed to be a conservative mixture of water from the podzol O and B horizons and from the deeper layers in the bog surrounding the stream, 92% of the variability in the concentration of hydrophobic and hydrophilic acids in the stream could be explained. This mixing analysis suggested that base flow largely originated in the deeper layers of the bogs, while peak flow was primarily made up of B horizon (∼50–65%) and O horizon (∼35

ISSN:0043-1397    

DOI:10.1029/92WR00056

年代:1992

数据来源: WILEY

摘要:

The hydrology of a small karst drainage basin in Jamaica, the Martha Brae River basin, was examined using stable isotopes. Variations in the isotopic composition of the groundwaters sampled and their positions relative to the local meteoric water line on a δD/δ18O diagram permitted the identification of two distinct groundwater types. The isotopic data also provided evidence that the most productive portion of the aquifer is divided by a major fault, which impedes groundwater flow. Information regarding the mechanisms and elevation of recharge was inferred from the δD versus δ18O relationships and differences in isotopic composition, respectiv

ISSN:0043-1397    

DOI:10.1029/91WR02519

年代:1992

数据来源: WILEY

摘要:

Evaporation from Williams Lake, computed by the energy budget method for the five open‐water seasons of 1982–1986, varied from a maximum seasonal rate of 0.282 cm/d in 1983 to a minimum seasonal rate of 0.219 cm/d in 1982. The pattern of monthly values of evaporation is not consistent from year to year. The normally expected pattern of low evaporation values in May, followed by increasing values in June to maximum values in July is true for only 3 of the 5 years. Comparison of annual evaporation calculated by the energy budget and mass transfer methods indicates that energy budget values varied from 13% greater to 11% less than mass transfer values. Furthermore, there is no seasonal bias in the pattern. Large differences exist in the magnitude of energy fluxes to and from Williams Lake. By far the greatest energy fluxes, having magnitudes of hundreds of watts per square meter, are incoming solar radiation, incoming atmospheric radiation, and outgoing long‐wave radiation emitted by the lake water. The least energy fluxes are related to advection, which generally have magnitudes less than 5

ISSN:0043-1397    

DOI:10.1029/92WR00553

年代:1992

数据来源: WILEY