摘要:

A general methodology to evaluate the economic feasibility of dual water systems is presented. In a first step, a static analysis (evaluation at a single point in time) is developed. The analysis requires the evaluation of consumers' and producer's surpluses from water use and the capital cost of the dual (outdoor) system. The analysis is then extended to a dynamic approach where the water demand increases with time (as a result of a population increase) and where the dual system is allowed to expand. The model determines whether construction of a dual system represents a net benefit, and if so, what is the best time to initiate the system (corresponding to maximization of social welfare). Conditions under which an analytic solution is possible are discussed and results of an application are summarized (including sensitivity to different parameters). The analysis allows identification of key parameters influencing attractiveness of dual water systems.

ISSN:0043-1397    

DOI:10.1029/WR023i010p01807

年代:1987

数据来源: WILEY

摘要:

We clarify the implication, with respect to self‐similarity, of the facts that the probability of rain tends to increase with the size of the area of observation and that the distribution of rain rate contains an atom at zero. These properties observed in precipitation processes lead to subtle difficulties which are not compatible with self‐similar

ISSN:0043-1397    

DOI:10.1029/WR023i010p01816

年代:1987

数据来源: WILEY

摘要:

Two algorithms that improve upon the sequent‐peak procedure for reservoir capacity calculation are presented. The first incorporates storage‐dependent losses (like evaporation losses) exactly as the standard linear programming formulation does. The second extends the first so as to enable designing with less than maximum reliability even when allowable shortfall in any failure year is also specified. Together, the algorithms provide a more accurate, flexible and yet fast method of calculating the storage capacity requirement in preliminary screening and optimization mod

ISSN:0043-1397    

DOI:10.1029/WR023i010p01819

年代:1987

数据来源: WILEY

摘要:

The water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by Earth tide dilatation of the aquifer. Because a finite amount of time is needed for water to flow into and out of the well, there exists a phase shift (or time lag) between the tidal dilatation of the aquifer and the water level response in the well. We derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity, storage coefficient, well radius, and the period of the harmonic disturbance. This solution is rather insensitive to the storage coefficient. Thus if the phase shift is known for a harmonic disturbance, the transmissivity can be calculated given a rough estimate of the storage coefficient. Theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying, as in the case of Earth tides. This opens the possibility of estimating aquifer transmissivity from water level records that show Earth tide fluctuations. A case study, using data from a site near Parkfield, California, is presented to illustrate application of the theory. Phase shifts of theO1(25.82‐hour period) andM2(12.42‐hour period) tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure. A brief error analysis suggests that the computedO1phase shift is subject to large uncertainty, while the computedM2phase shift is substantially more accurate. Based on an assumed storage coefficient range of 10−4to 10−6, the estimated transmissivity range is 8 × 10−6to 2 × 10−5m2/s. While hydraulic tests have not been performed to validate these estimates, the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to

ISSN:0043-1397    

DOI:10.1029/WR023i010p01824

年代:1987

数据来源: WILEY

摘要:

The amount and distribution of liquid water are important for assessing the mechanical strength, meltwater generation, and meltwater transmission in snow. Liquid water also has a profound effect on the performance of active and passive remote sensing systems operating in the microwave and millimeter wave region of the electromagnetic spectrum. New methods of measuring liquid water have been reported which show considerable promise. Our purpose is to address the question of measurement equivalence by comparing the three direct methods of freezing calorimetry, alcohol calorimetry, and dilution and by comparing the precision of a calibrated capacitance probe with one of the direct methods. All comparisons were made in a laboratory cold room with snow having a mass liquid water content of 0–14 mkg per 100 mkg of snow. The comparisons show that the methods are equivalent with an uncertainty of ±1.8 mkg per 100 mkg of snow. However, the operational achievement of equivalence is strongly dependent on a variety of factors such as sample size, mixing of snow and working fluid, and operator ski

ISSN:0043-1397    

DOI:10.1029/WR023i010p01833

年代:1987

数据来源: WILEY

摘要:

Characteristics and moment estimators of temporal rainfall models such as Poisson rectangular pulse (PRP), Neyman‐Scott white noise (NSWN), and Neyman‐Scott rectangular pulse (NSRP) are investigated. It is shown that PRP and NSWN have a correlation structure like that of an autoregressive moving average (ARMA) (1,1) model whereas the NSRP has a dependence structure like that of an ARMA (2, 2). The admissible regions of lag‐1 and lag‐2 autocorrelations are derived to demonstrate that in general they are more restricted than their ARMA counterparts. An additional property denoted as variance ratio, which is intimately related to the scale of fluctuation of a process, is defined and used for model comparison. The bias and mean square error properties of the moment estimators are investigated with emphasis on the NSWN model, for which it is suggested that the temporal scaleT, defined by βT= 1, provides the most efficient estimators of the parameters. Parameter β defines the arrival of rain bursts relative to the origin of storm systems. All three models are fitted to an extensive data set covering hourly precipitation data at 38 stations in northeastern Colorado. The correlation and variance ratio plots are used to select the appropriate model for each month. However, it is shown that the diurnal periodicity of storm occurrence is predominant during the summer months, which is a characteristic not built into any of the temporal models

ISSN:0043-1397    

DOI:10.1029/WR023i010p01837

年代:1987

数据来源: WILEY

摘要:

Variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful. Typically, only cases involving wide transition zones have been simulated with variable density transport models, possibly because of inaccuracies in the modeling approaches used. The major components of a successful approach are threefold. First, functionally consistent approximation of terms involved in fluid velocity calculations is necessary. In the case of Galerkin finite element methodology, a significant modification is required to the standard approach in order to achieve consistency. Second, the simulator must be verified in a particular series of tests. The usual tests using Henry's problem for verification of density‐dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces. Third, adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity. The effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern Oahu, Hawaii. The transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed. Simulation of this common situation with an inconsistent approximation gives grossly incorrect results, while simulation with a consistent model provides a robust tool for analysis of system hydrolog

ISSN:0043-1397    

DOI:10.1029/WR023i010p01851

年代:1987

数据来源: WILEY

摘要:

The convection‐dispersion equation (CDE) developed byDagan[1984] to predict the ensemble‐average concentration of a conservative solute in groundwater has been used successfully to interpret recent tracer experiments in a sand aquifer at the Borden site in Canada. This successful application encouraged further investigation of the Dagan model in respect to its physical basis and predictive characteristics. It is shown in the present paper, which deals with the first topic, that the Dagan model CDE can be derived through an extension of the cumulant expansion technique applied previously byChu and Sposito[1980] to develop a mean CDE for solute transport in homogeneous porous media. This technique also leads directly to the mean CDE developed byGelhar and Axness[1983] as an asymptotic (large time) limit and to model dispersion coefficients derived byMather on and de Marsily[1980] andGüven and MoIz[1986]. The Dagan CDE then is considered in detail in respect to which conceptualization of the solute concentration, resident or flux, the model may utilize in predictive applications. General mathematical expressions relating the two conceptualizations are derived for an arbitrary solute transport problem and then are applied to the Dagan model for point and prism source inputs. Finally, the Dagan model is interpreted physically using data from the recent tracer experiments ofRoberts and Mackay[1986] at the Borden site. It is shown that model predictions of resident and flux concentrations are numerically indistinguishable on any time scale over which field solute concentration measurements typically are made. The model prediction of dispersion coefficients, on the other hand, leads to dramatic differences in predicted plume behavior depending on whether finite time expressions or their asymptotic limits are used. According to the Dagan model, the asymptotic transverse dispersion coefficient cannot replace the time‐dependent coefficient on any realistic time scale for solute movement at the Borde

ISSN:0043-1397    

DOI:10.1029/WR023i010p01867

年代:1987

数据来源: WILEY

摘要:

How to predict flow through a network of discrete fractures in a three‐dimensional domain is investigated. Fractures are modeled as circular discs of arbitrary size, orientation, transmissivity, and location. A fracture network is characterized by the statistical distributions of these quantities. Fracture traces observed on a wall form the basis for estimates of mean fracture radius, fracture orientation parameters, and fracture density. Fracture trace lengths are estimated with the scanline method and from areal sampling on circular regions. The traces observed on the wall can also be used to condition the network. This trace conditioning is achieved by forcing the network generator to always reproduce the observed traces. Conditioning might be a means of decreasing the variability of the fracture networks. A numerical simulation model has been developed which is capable of generating a fracture network of desired statistical properties and solving for the steady state flow. On each fracture disc the flow is discretized with the boundary element method. A series of hypothetical examples are analyzed. These examples consist of sets of Monte‐Carlo simulations of flow through a series of networks generated from the same statistical distributions. The examples lead to the following conclusions. Large fractures and high fracture density implies good connectivity in the networks. A high fracture density implies a small variance in the flow through the network. Trace conditioning decreases estimation variance only when the fracture network consists of large fractures. Fracture statistics can be estimated reasonably well from fracture traces observed on a w

ISSN:0043-1397    

DOI:10.1029/WR023i010p01876

年代:1987

数据来源: WILEY

摘要:

Using a modified flux gradient technique, transmetalimnetic oxygen transport was evaluated in Lakes Mendota and Delavan, two eutrophic Wisconsin basins featuring moderate depth (17

ISSN:0043-1397    

DOI:10.1029/WR023i010p01887

年代:1987

数据来源: WILEY