摘要:

This paper addresses the question of similarity of runoff generation processes between catchments in the eastern wheat belt of Western Australia, and the use of dimensionless parameterizations to quantify this similarity. A spatially distributed rainfall‐runoff model, simulating runoff generation by both the infiltration excess (Horton type) and saturation excess (Dunne type) mechanisms, was developed for catchments in the region. Seven small experimental catchments, with field‐measured soil hydraulic properties and topography, were used in the study. Following on from the similarity theory developed by Sivapalan et al. (1987), a number of dimensionless similarity parameters were constructed using the field‐measured soil and topographic properties, a characteristic length scale, and a characteristic flow velocity. The objective was to determine whether the dominant runoff generation mechanism on a catchment could be reliably predicted by these similarity parameters. This was achieved through sensitivity analyses carried out with the rainfall‐runoff model. Two dimensionless parameters,K0*and ƒ*, were found to be critical for characterizing the similarity or dissimilarity of the runoff generation responses between the seven experimental catchments. Within the assumptions of the analysis, two catchments in the wheat belt region can be considered to be hydrologically similar, in terms of their runoff responses, ifK0*and ƒ* are identical in both catchments. The dominant mechanism of runoff generation on any catchment can be reliably predicted, provided that the values ofK0*and ƒ* are known. A partial quantification of the Dunne diagram (Dunne, 1978) for the wheat belt region, in terms of the infiltration excess and saturation excess mechanisms, was achieved by artificially varyingK0*and ƒ* in the rainfall‐runoff model to explore the full range of possible runoff generat

ISSN:0043-1397    

DOI:10.1029/94WR00555

年代:1994

数据来源: WILEY

摘要:

Historical and paleoflood data have become an important source of information for flood frequency analysis. A number of studies have been proposed in the literature regarding the value of historical and paleoflood information for estimating flood quantiles. These studies have been generally based on computer simulation experiments. In this paper the value of using systematic and historical/paleoflood data relative to using systematic records alone is examined analytically by comparing the asymptotic variances of flood quantiles assuming a two‐parameter general extreme value marginal distribution, type 1 and type 2 censored data, and maximum likelihood estimation method. The results of this study indicate that the value of historical and paleoflood data for estimating flood quantiles can be small or large depending on only three factors: the relative magnitudes of the length of the systematic record (N) and the length of the historical period (M); the return period (T) of the flood quantile of interest; and the return period (H) of the threshold level of perception. For instance, forN= 50,M= 50 andT= 500, the statistical gain for type 2 censoring becomes significantly larger than for type 1 censoring asHbecomes greater than 100 years. In addition, computer experiments have shown that the results regarding the statistical gain based on asymptotic considerations are valid for the usual sample size

ISSN:0043-1397    

DOI:10.1029/94WR00154

年代:1994

数据来源: WILEY

摘要:

A distributed hydrology‐vegetation model is described that includes canopy interception, evaporation, transpiration, and snow accumulation and melt, as well as runoff generation via the saturation excess mechanisms. Digital elevation data are used to model topographic controls on incoming solar radiation, air temperature, precipitation, and downslope water movement. Canopy evapotranspiration is represented via a two‐layer Penman‐Monteith formulation that incorporates local net solar radiation, surface meteorology, soil characteristics and moisture status, and species‐dependent leaf area index and stomatal resistance. Snow accumulation and ablation are modeled using an energy balance approach that includes the effects of local topography and vegetation cover. Saturated subsurface flow is modeled using a quasi three‐dimensional routing scheme. The model was applied at a 180‐m scale to the Middle Fork Flathead River basin in northwestern Montana. This 2900‐km2, snowmelt‐dominated watershed ranges in elevation from 900 to over 3000 m. The model was calibrated using 2 years of recorded precipitation and streamflow. The model was verified against 2 additional years of runoff and against advanced very high resolution radiometer based spatial snow cover data at the 1‐km2scale. Simulated discharge showed acceptable agreement with observations. The simulated areal patterns of snow cover were in general agreement with the remote sensing observations, but were lagged

ISSN:0043-1397    

DOI:10.1029/94WR00436

年代:1994

数据来源: WILEY

摘要:

Current algorithms for computing contributing areas from a rectangular grid digital elevation model (DEM) use the flow‐routing model of O'Callaghan and Mark (1984), which has two major restrictions: (1) flow which originates over a two‐dimensional pixel is treated as a point source (nondimensional) and is projected downslope by a line (one dimensional) (Moore and Grayson, 1991), and (2) the flow direction in each pixel is restricted to eight possibilities. We show that large errors in the computed contributing areas result for any terrain topography: divergent, convergent, or planar. We present a new model, called digital elevation model networks (DEMON), which avoids the above problems by representing flow in two dimensions and directed by aspect. DEMON allows computation of both contributing and dispersal areas. DEMON offers the main advantage of contour‐based models (e.g., Moore et al., 1988), the representation of varying flow width over nonplanar topography, while having the convenience of using rectangular grid

ISSN:0043-1397    

DOI:10.1029/93WR03512

年代:1994

数据来源: WILEY

摘要:

This paper describes a direct comparison of apparent ages derived from3H/3He, chlorofluorocarbons (CCl3F and CCl2F2), and85Kr measurements in shallow groundwater. Wells chosen for this study are completed in the unconfined surficial aquifers in late Cenozoic Atlantic Coastal Plain sediments of the Delmarva Peninsula, on the east coast of the United States. Most of the apparent tracer ages agree within 2 years of each other for recharge dates between 1965 and 1990. Discrepancies in apparent tracer ages usually can be explained by hydrological processes such as mixing in a discharge area. Recharge rate calculations based on apparent tracer age gradients at multilevel well locations agree with previous recharge estimates. High recharge rates on the Delmarva Peninsula result in nearly complete dissolved‐gas confinement in the groundwater. The remarkable agreement between the different tracer ages indicates negligible mixing of waters of different ages, insignificant dispersion, minimal gas loss to the atmosphere, and insignificant sorption‐desorption processes at this locat

ISSN:0043-1397    

DOI:10.1029/94WR00156

年代:1994

数据来源: WILEY

摘要:

In this paper we present seven unsaturated zone profiles of36Cl and three3H profiles from southern Australia. All profiles show single peaks corresponding to high radionuclide fallout from nuclear testing in the 1950s and 1960s. The profiles are used to estimate rates of water movement leading to recharge of the groundwater. Among these profiles is the first profile on which high concentrations of36Cl have been found below a 2‐m depth. In this profile,3H and36Cl peaks coincide. In six of the seven profiles, total36Cl fallout was found to be between 1.2 and 2.4 × 1012atoms m−2, and is of similar magnitude to that found at similar latitudes in the northern hemisphere. Comparisons of soil water fluxes estimated with3H,36Cl, and chloride are briefly discu

ISSN:0043-1397    

DOI:10.1029/94WR00161

年代:1994

数据来源: WILEY

摘要:

One way to estimate the hydrologic properties of heterogeneous geologic media is to invert well test data using multiple observation wells. Pressure transients observed during a well test are compared to the corresponding values obtained by numerically simulating the test using a mathematical model. The parameters of the mathematical model are varied and the simulation repeated until a satisfactory match to the observed pressure transients is obtained, at which point the model parameters are accepted as providing a possible representation of the hydrologic property distribution. Restricting the search to parameters that represent self‐similar (fractal) hydrologic property distributions can improve the inversion process. Far fewer parameters are needed to describe a hierarchical medium, improving the efficiency and robustness of the inversion. Additionally, each parameter set produces a hydrologic property distribution with a hierarchical structure, which mimics the multiple scales of heterogeneity often seen in natural geological media. The parameters varied during the inversion create fractal sets known as attractors, using an iterated function system (IFS). An attractor is mapped to a distribution of transmissivity and storativity in the mathematical model. Thus the IFS inverse method searches for the parameters of the IFS (typically tens of parameters) rather than the values of the hydrologic property distribution directly (typically hundreds to thousands of parameters). Application of the IFS inverse method to synthetic data shows that the method works well for simple heterogeneities. Application to field data from a sand/clay sedimentary sequence and a fractured granite produces reasonable result

ISSN:0043-1397    

DOI:10.1029/94WR00585

年代:1994

数据来源: WILEY

摘要:

On March 13, 1991, construction of the entrance tunnel to the Äspö Hard Rock Laboratory opened a vertical fracture zone at a depth of 70 m. This provides an opportunity to study geochemical changes resulting from shallow water inflow into a crystalline bedrock aquifer as anticipated during construction and operation of a deep repository for spent nuclear fuel. Chloride ion is a natural conservative tracer for mixing between the dilute ([Cl−]<10 mg L−1) shallow groundwater and the saline ([Cl−] = 5000 mg L−1) native groundwater of the fracture zone. A sharp dilution front, corresponding to 80% dilution of the native groundwater, indicated arrival of shallow groundwater in the entrance tunnel after 3 weeks. In spite of this large input of shallow water, the fracture zone remains predominantly anoxic. Major element hydrochemistry and carbon and oxygen stable isotope data indicate large inputs of alkalinity and biogenic CO2(g). Input of organic carbon with shallow groundwater provides a possible energy and carbon source for anaerobic respiration. There is no evidence for sulfate reduction, and Fe(III) oxyhydroxide fracture minerals are the only other dominant electron acceptor

ISSN:0043-1397    

DOI:10.1029/94WR00155

年代:1994

数据来源: WILEY

摘要:

Models of solute transport in fractured geologic media that are based on the discrete network approach require that a method be adopted for transferring mass through each fracture intersection. The two usual models for mass partitioning between the outflow branches of crossing fractures assume either stream tube routing or complete mixing. A mathematical analysis of two‐dimensional, laminar flow through the intersection of two orthogonal fractures with smooth walls is carried out to examine the mixing process. Mixing ratios are expressed in terms of a local Peclet number (Pe= υr/D), where υ is an average fluid velocity within the fracture intersection,ris the radius of the fracture intersection, andDis the diffusion coefficient. As a general observation the concept of complete mixing within a fracture intersection does not properly represent the mass transfer process at any value of the Peclet number. A mixing ratio equivalent to complete mixing may be observed, but only for particular flow geometries and in a limited range of the Peclet number. Stream tube routing models provide a good approximation for Peclet numbers greater than 1; and in some cases this limit may be as low as 10−2. The actual value of the lower limit depends upon the geometry of the bounding streamline that separates the flow into the two outflow fractures, in relation to the fracture through which solute enters the intersection. There is a range in the Peclet number, of roughly 3 orders of magnitude, where the extent of mixing is dependent upon the value ofPewithin the interse

ISSN:0043-1397    

DOI:10.1029/94WR00432

年代:1994

数据来源: WILEY

摘要:

The concentration variance, i.e., mean squared concentration fluctuations, undergoes mean advection, a local dispersive flux, and a macrodispersive flux due to a correlation between squared concentration perturbations and velocity perturbations. The products of the macrodispersion coefficient and the squared gradient of the mean concentration field determine the rate of production of concentration variance. The rate of dissipation of concentration variance is determined by the product of the local dispersion coefficient and the mean squared gradient of the concentration perturbation field. Variance dissipation is represented as a first‐order decay with the decay coefficient equal to twice the sum of the local dispersion coefficient divided by the squared concentration microscale. The concentration microscale, estimated for an advection‐dominated log hydraulic conductivity microscale, is an increasing function of the log conductivity microscale. Thus the larger the log conductivity microscale is, the slower is the rate of dissipation of concentration fluctuations by local dispersion and vice versa. The wave number squared dependence of fluctuation dissipation requires intensive sampling to realistically model the log conductivity spectrum and its microscale, which determines the rate of dissipation of concentration fluctuations by the action of local dispersion. There is no mechanism of destroying concentration fluctuations without the action of local dispers

ISSN:0043-1397    

DOI:10.1029/94WR00076

年代:1994

数据来源: WILEY