摘要:

This work examines some conditions under which contaminant transport in fractured porous rocks can be described by an equivalent porous medium (single continuum) model. For this purpose, a two‐dimensional mathematical and numerical model for flow and contaminant transport was developed. The model allows for contaminant transport by advection, diffusion, and dispersion in both fractures and porous blocks. Concentration distributions were calculated for different flow conditions and medium properties. The resulting S‐shaped breakthrough curves, characteristic of ordinary porous media, indicated the possibility of regarding the fractured porous medium as a single (equivalent) continuum. The results were compared to an existing analytical solution for contaminant movement in ordinary porous media. Analysis showed that within the range of considered parameter values, and except for the region close to the source, a single continuum model is sufficient for modelling the movement of contaminants. In such cases, application of the equivalent porous medium model is an actual field situation requires knowledge of the “equivalent” porosity and the equivalent coefficient of dispersion appearing in the governing transport equation. In practice, these coefficients must be determined by analysis of breakthrough curves obtained from fiel

ISSN:0043-1397    

DOI:10.1029/WR024i008p01225

年代:1988

数据来源: WILEY

摘要:

The main objective of this paper is to investigate the properties of multivariate periodic autoregressive moving average (ARMA)(l, 1) processes. Such properties include the covariance structure, the parameter space, and estimation. The parameter space of such periodic processes is derived by aggregation (for instance, monthly models will aggregate to annual models). In particular, the parameter space and estimation are analyzed for contemporaneous ARMA (CARMA) models. It is shown that in general, the aggregation of a multivariate periodic ARMA(1, 1) model leads to a stationary multivariate ARMA(1, 1) model. However, not always a periodic CARMA(1, 1) model aggregates into a stationary CARMA(1, 1) model. Furthermore, it is shown that in estimating the aggregated model parameters, the method based on the periodic model and corresponding parameters, is superior to that based on the aggregated series.

ISSN:0043-1397    

DOI:10.1029/WR024i008p01237

年代:1988

数据来源: WILEY

摘要:

Groundwater contamination by nonaqueous liquids such as organic solvents and petroleum hydrocarbons frequently occurs as a result of surface spills, tank leaks, and improper disposal practices. This first of two papers examines the physics governing the emplacement and movement of a separate phase in porous media, the role of sorption, and the conditions necessary to mobilize a separate phase. The movement of the separate phase is controlled by capillary forces, and ganglia displacement by groundwater is not possible under reasonable hydraulic gradients. In addition, because of mass transfer limitations in liquid phase dissolution, groundwater extraction at contaminated sites is shown to be ineffective in removing the nonaqueous contaminant within a reasonable time frame. Therefore other means of mobilizing the trapped second phase are needed, steam displacement is proposed and steam front propagation through contaminated porous media is evaluated. The results of laboratory experiments supporting some of these analytical results are presented in the second paper (Hunt et al., this issue).

ISSN:0043-1397    

DOI:10.1029/WR024i008p01247

年代:1988

数据来源: WILEY

摘要:

An analysis of the movement of nonaqueous liquids such as organic solvents and gasoline in part 1 (Hunt et al., this issue) showed that separate phase liquids are not completely displaced by groundwater flow under typical pumping conditions and that removal of the compounds by dissolution is mass transfer limited. Steam displacement was proposed as a more efficient cleanup strategy for separate phase organic liquids present in porous media. This paper presents the results of a series of laboratory sand column experiments designed to confirm the theoretical analyses presented in part 1 (Hunt et al., this issue). Experiments with trichloroethylene, a benzene‐toluene mixture, and a commercial gasoline, showed that water flow at rates as high as 15 m d−1could not displace the separate phase liquids when present in a sand matrix in quantities corresponding to a column average saturation of 2.5%. Steam injection, on the other hand, displaced the contaminants as a separate phase just ahead of the steam front, producing a concentrated, small‐volume waste stream. Analysis of the laboratory data consisting of pressure gradients, temperature profiles, and water flow velocities shows that the laboratory results are consistent with the theoretical predictions. Moreover, computations of energy requirements show that steam displacement of separate phase contaminants is economically attra

ISSN:0043-1397    

DOI:10.1029/WR024i008p01259

年代:1988

数据来源: WILEY

摘要:

Hydraulic conductivity data are frequently summarized using mathematical functions that quantify the relationship between water content (θ) and hydraulic conductivity (K(θ)). This study was done to determine the effects of the choice of theK(θ) function and to determine if field data from layered profiles could be summarized using only one parameter per depth. ThreeK(θ) functions together with a matching factor were fitted to hydraulic conductivity data from a field plot. The functions wereKm(θ/θm)1/β,Km[(θm−θc)/(θ−θc)]1/n,andKmexp {α(θ−θm)}, where α, β,n,Km, θc, and θm,are parameters to be estimated. For each function, two methods were considered. Method 1 fitted a different value to α, β,n, andKmfor each depth while maintaining θcat a fixed value. All hydraulic conductivity functions fit data from a Muir silt loam equally well, as evidenced by the coefficient of linearity (r2) values greater than 0.72, mean square error (MSE) values less than 0.97, and coefficient of variation (CV) values less than 50%. The fitting was accomplished using ln {K} as the dependent variable. Method 2 fitted values by depth only to Km, and all other parameters were held constant. The hydraulic conductivity functions performed equally well, withr2values greater than 0.60, MSE values less than 1.2, andCVvalues of 50% or less. When some loss of precision can be tolerated, the number of parameters required to summarize data from a l

ISSN:0043-1397    

DOI:10.1029/WR024i008p01271

年代:1988

数据来源: WILEY

摘要:

A method is presented for locating wells in a monitoring network under conditions of uncertainty. The method couples the use of a simulation model of contaminant transport and a facility location model. The Monte Carlo technique is used with the simulation model to translate uncertainty in the simulation model parameters into uncertainty in the contaminant concentration distribution. The simulation model determines which well locations would detect a given realization of a contaminant plume with a concentration above a specified limit. The facility location model is then used to select a fixed number of well locations so that a maximum number of such plume realizations are detected. The selected well network maximizes the probability of detection. The method is applied to an example problem. Although the technique is computationally intensive, the results indicate that practical problems are tractable.

ISSN:0043-1397    

DOI:10.1029/WR024i008p01277

年代:1988

数据来源: WILEY

摘要:

Multivariate analysis of grid cell landscape data and of daily rainfall and streamflow data is used to locate mesoscale catchments of the Hunter valley, Australia, in multidimensional spaces which define landscape, rainfall, and streamflow indices for each catchment. Multiple regression equations are developed and validated for predicting indices of streamflow from those of landscape and rainfall. This methodology provides a basis for using landscape and rainfall data to locate gauged and ungauged catchments in a common space in which proximity between catchments predicts similarity of streamflow.

ISSN:0043-1397    

DOI:10.1029/WR024i008p01283

年代:1988

数据来源: WILEY

摘要:

Most hydrochemical models employ immeasurable or “artificial” parameters that need to be estimated from calibration data. A methodology is presented here for the automatic calibration of artificial parameters, which improves parameter identifiability through increasing the information available for determining the parameter values. Instead of calibrating the model using only one signal (e.g., the hydrograph), multiple signals (e.g., chemical signals as well as the hydrograph) are considered simultaneously. Either a simple least squares or a weighted least squares objective function may be used. The methodology is applied to the hydrologic module of the Birkenes hydrochemical model using artificial data. From a wide range of starting points, a gradient search optimization technique is able to consistently locate the correct parameter values uniformly better when using two signals (the hydrograph and a conservative tracer) than when only one signal (the hydrograph) is u

ISSN:0043-1397    

DOI:10.1029/WR024i008p01299

年代:1988

数据来源: WILEY

摘要:

A revision of the Birkenes model of streamwater acidification has been attempted to incorporate additional chemical and hydrologic information gained in the last 6 years since its original construction. The first stage of this effort has been an analysis of the hydrologic submodel with the goal of extending it to predict concentrations of a conservative tracer in streamwater. An objective calibration of the model indicated that the model is overparameterized. Only one passive store is identifiabile, not two as currently contained in the model and the routing between the two reservoirs is not determined by the data. Inclusion of the conservative tracer improved the identifiability of the dimensional parameters, but had little effect on the rate or routing parameters. If the hydrologic structure is to be determined from the hydrograph and conservative tracer alone, it must be simplified to eliminate unidentifiable parameters. The validity of using more complex rainfall‐runoff models in hydrochemical models which seek to test chemical mechanisms is called into question by this analysi

ISSN:0043-1397    

DOI:10.1029/WR024i008p01308

年代:1988

数据来源: WILEY

摘要:

Ever since Mandelbrot (1975, 1983) coined the term, there has been speculation that river networks are fractals. Here we report analyses done on river networks to determine their fractal structure. We find that the network as a whole, although composed of nearly linear members, is practically space filling with fractal dimension near 2. The empirical results are backed by a theoretical analysis based on long‐standing hydrologic concepts describing the geometric similarity of river networks. These results advance our understanding of the geometry and composition of river network

ISSN:0043-1397    

DOI:10.1029/WR024i008p01317

年代:1988

数据来源: WILEY