摘要:

The boundary integral equation method (BIEM) is shown to be an efficient and accurate numerical technique for solving problems of Darcy flow in porous media. The BIEM is combined with conformal transformation to the complex potential plane to solve free surface problems without iteration and with relatively few nodal points. Since the BIEM reduces the effective dimensions of the problem by one, the computer time varies approximately as the inverse square of the point spacing, whereas in finite element or finite difference methods the time varies approximately as the inverse of the fourth power of the point spacing. Two examples of the BIEM are presented herein. They are flow through an underdrained dam and a seawater intrusion problem.

ISSN:0043-1397    

DOI:10.1029/WR014i003p00385

年代:1978

数据来源: WILEY

摘要:

A two‐dimensional finite element method is used to study the problem of seepage over a sloping impermeable bed. Flow profile and seepage rates obtained from the analysis are compared with those solved from Pavlovsky's and Childs' equations. The latter equation is found to be more favorable, especially for large slopes. The effects on the flow profile due to (1) a change in the upstream and downstream conditions and (2) a sudden change in the magnitude of the slope of the impermeable bed are also investigate

ISSN:0043-1397    

DOI:10.1029/WR014i003p00391

年代:1978

数据来源: WILEY

摘要:

LetRndenote the range of cumulative sums of the net inputs to a reservoir duringntime intervals. For periodic net inputs possessing a wide variety of covariance structures, the asymptotic behavior ofRnis given by limn→∞P[Rn/γn½≤r] =FR(r), where γ is a function of the dependence and periodicity assumptions on the net inputs andFRis the cumulative distribution function of the range of a standard Brownian motion process. Analogous results hold for the adjusted range, rescaled adjusted range, and maximum deficit. (The last quantity is the storage obtained upon application of the sequent peak algorithm.) As previous authors have argued, then½behavior of the rescaled adjusted range is not inconsistent with H. E. Hurst's empirical findings if it is assumed that the so‐called Hurst phenomenon is a preasymptotic property of reservoir behavior. Useful representations for the parameter γ may be obtained for many of the net input sequences employed in hydrologic modeling, such asmth‐order autoregressive (stationary or periodic) and log autoregres

ISSN:0043-1397    

DOI:10.1029/WR014i003p00395

年代:1978

数据来源: WILEY

摘要:

The present work deals with steady phreatic flow above a thin semipervious sloping layer located at some distance below ground surface and above the water table of an underlying phreatic aquifer. Cases of both upsloping and downsloping semipervious layers are studied. A uniform recharge of constant rate and a semipervious layer of finite length are considered, either with length of flow shorter than the semipervious layer or with flow bypassing its edge. For each case, linearization is applied to the nonlinear continuity equation which governs the flow. Analytical solutions are then derived for the shape of the phreatic flow wedge, the length of the wedge, and the discharge rate. These results are compared with experimental ones obtained in a Hele‐Shaw analog. A good agreement is generally found between computed and observed results. Because of the analogy which exists between a phreatic surface and an interface in a coastal aquifer, the same results can also be applied to the steady freshwater flow above an interface in an aquifer divided into two subaquifers by a sloping semipervious laye

ISSN:0043-1397    

DOI:10.1029/WR014i003p00403

年代:1978

数据来源: WILEY

摘要:

The environmental consequences of subsurface contamination problems can be evaluated completely and effectively by fulfilling the following five requirements: (1) determining each present or future outflow boundary of contaminated groundwater, (2) providing the location/arrival time distributions, (3) providing the location/outflow quantity distributions, (4) providing these distributions for each individual chemical or biological constituent of environmental importance, and (5) using the arrival distributions to determine the quantity and concentration of each contaminant that will interface with the environment as time passes. The arrival distributions on which these requirements are based provide a reference point for communication among scientists and public decision makers by enabling complicated scientific analyses to be presented as simple summary relationships.

ISSN:0043-1397    

DOI:10.1029/WR014i003p00409

年代:1978

数据来源: WILEY

摘要:

A steady two‐dimensional flow system is used to demonstrate the application of location/arrival time and location/outflow quantity curves in determining the environmental consequences of groundwater contamination. The subsurface geologic and hydrologie evaluations needed to obtain the arrival results involve a sequence of four phases: system identification, new potential determination, flow system kinematics, and contaminant transport analysis. Once these phases are completed, they are effectively summarized and easily used to evaluate environmental consequences through the arrival distribution

ISSN:0043-1397    

DOI:10.1029/WR014i003p00416

年代:1978

数据来源: WILEY

摘要:

The versatility of the new contaminant arrival distributions for determining environmental consequences of subsurface pollution problems is demonstrated through application to a field example involving land drainage in heterogeneous porous materials. Though the four phases of the hydrologic evaluations are complicated because of the material heterogeneity encountered in the field problem, the arrival distributions still effectively summarize the minimal amount of data required to determine the environmental implications. These arrival distributions yield a single graph or tabular set of data giving the consequences of the subsurface pollution problems. Accordingly, public control authorities would be well advised to request that the results of subsurface pollution investigations be provided in the form of arrival distributions and the resulting simpler summary curve or tabulation. Such an objective is most easily accomplished through compliance with the requirements presented by Nelson (1978a) for assuring a complete subsurface evaluation.

ISSN:0043-1397    

DOI:10.1029/WR014i003p00429

年代:1978

数据来源: WILEY

摘要:

The versatility of the new contaminant arrival distributions for determining environmental consequences of subsurface pollution problems is demonstrated through application to a transient flow system. Though some of the four phases of the hydrologic evaluations are more complicated because of the time dependence of the flow and input contaminant concentrations, the arrival distributions still effectively summarize the data required to determine the environmental implications. These arrival distributions yield two graphs or tabular sets of data giving the consequences of the subsurface pollution problems in a simple and direct form. Accordingly, the public control authorities would be able to use these results to choose alternatives or to initiate corrective actions, depending on the indicated environmental consequences.

ISSN:0043-1397    

DOI:10.1029/WR014i003p00441

年代:1978

数据来源: WILEY

摘要:

Sensitivity analysis is the study of a system's response to various disturbances. In this study, disturbances of aquifer parameters are considered. In the simulation of an aquifer the investigator must establish tolerances within which the parameters of the physical system may vary without appreciably affecting the model results. By means of a first‐order sensitivity formalism it is shown how to evaluate the perturbed hydraulic head for a small change in aquifer parameter. An expression for the sensitivity coefficient is obtained in this study by taking the partial derivative of the flow equation with respect to a particular parameter. The sensitivity coefficient is evaluated either analytically or by numerical techniques for some common models. The sensitivity formalism is applied to the Theis equation to study the general behavior of sensitivity coefficients and to determine the range of validity of the first‐order sensitivity formalism. The formalism is also applied to one‐ and two‐dimensional numerical models to see the effect of barrier and constant head boundaries. The perturbed hydraulic head is obtained for a change of transmissivity (T) and storage coefficient (S) by applying the first‐order sensitivity formalism. This procedure should be a valuable tool in calibrating models or establishing tolerances on T and S for a given acceptable error in hydraulic head. In general, a ±20% deviation inTorSmay be handled adequately by the first‐order formalism discussed

ISSN:0043-1397    

DOI:10.1029/WR014i003p00451

年代:1978

数据来源: WILEY

摘要:

Infiltration during a rainfall event can be divided into two distinct stages: a stage with surface ponding and a stage without surface ponding. Few of the infiltration models in current use are suitable to describe infiltration for both stages. In this paper the Green and Ampt equation was applied to determine the time that separates these two stages so that infiltration for the different stages can be treated separately. To obtain an integrated form of the Green and Ampt equation, it is traditionally assumed that the cumulative infiltration is zero at the time when surface ponding starts. But in a rainfall event the cumulative infiltration equals the water infiltrated into the soil profile prior to the ponding time, which is usually not zero. Therefore a modification in the traditional Green and Ampt equation is needed to describe infiltration during a rainfall event. It is shown in this paper that this modification is equivalent to a shift of the time scale by an amount which is referred to as the pseudotime by the author. The modified version of the Green and Ampt equation was applied to determine rainfall excess and to predict total runoff for three major storms recorded by the Agricultural Research Service from 1957 to 1959 on a watershed near Oxford, Mississippi. A comparison of the prediction and the measured total runoff appeared to be promising.

ISSN:0043-1397    

DOI:10.1029/WR014i003p00461

年代:1978

数据来源: WILEY