摘要:

Detention reservoirs in urban drainage systems are provided for reducing the peak flows downstream of the reservoir. The flow reduction is due to the storage volume of the reservoir in which the incoming flow is temporarily stored. The relationship between the peak reduction ratio (the peak outflow discharge to the peak inflow discharge) and the relative storage ratio (maximum volume stored in the reservoir to the volume of the inflow hydrograph) is evaluated in this study. This relationship, named the efficiency function, is derived by a numerical solution of the dimensionless routing equation. Using the three‐parameter gamma distribution to represent the inflow to the reservoir, the efficiency functions can be expressed by simple linear equations. Each equation depends on a single parameter whose value is determined by the reservoir configuration (depth‐storage relationship) and the type of the outlet device (e.g., spillway or culvert). The implementation of the efficiency function is most suitable for the preliminary design stage where a large number of alternative designs can be easily tested without performing the conventional routing proced

ISSN:0043-1397    

DOI:10.1029/90WR02143

年代:1991

数据来源: WILEY

摘要:

Groundwater sources supply about 38% of all water uses in the 19 western states. Most attention has focused on withdrawals from these sources but, in recent years, concerns have been raised about the quality of groundwater. At the federal level, several laws address aspects of groundwater quality but protection of this resource has been left primarily to the states. Western state groundwater quality protection programs were comprehensively surveyed relating to six aspects: assessment of existing groundwater quality, levels of protection established, controls placed on sources of contamination, use of special management areas, coordination among the involved agencies, and program enforcement. The survey revealed several promising approaches in each of these areas in the western states which are set forth in the paper. Most of these approaches have been established in recent years, reflecting the greatly increased state attention to groundwater quality protection. It is too early to evaluate the effectiveness of particular approaches. In general the western states are taking a more active role in groundwater quality protection, and several states recently have established comprehensive programs for this purpose. Others, however, are still considering approaches to protection of groundwater quality and may find the discussion in this paper of some use.

ISSN:0043-1397    

DOI:10.1029/90WR01876

年代:1991

数据来源: WILEY

摘要:

The problem of transport of a conservative nonreactive solute in a vertical cross section of a hypothetical partially saturated, scale‐heterogeneous soil under transient water flow was analyzed here. It was assumed that locally the water flow and the solute transport can be described by the Richards' equation and by the one‐component convection dispersion equation, respectively. The simulated water content and the solute concentration distributions in the vertical cross section of the soil at different elapsed times were quantified in terms of space averages and two‐point autocorrelation functions. The time evolution of the solute plume was quantified in terms of its first two normalized spatial moments, from which the time dependence of the longitudinal and the transverse components of the solute velocity vector, and the spatial covariance tensor, were estimated. The results of this study, which are relevant to solute transport at the local or the plume scale, demonstrated the considerable variability in the solute concentration in space and time, due to the complex heterogeneity of the soil hydraulic properties in both the vertical and the horizontal directions. Consequently, the movement of the solute plume was characterized by a compression‐expansion phenomenon, attributed to the decrease in the effective solute velocity through the zones of relatively fine‐textured soil material. It was concluded that existing stochastic vadose zone transport models may be applicable to shallow depths but may fail to describe the actual spread of a solute plume when the transport takes place at relatively large depths, mainly because of the neglect of the significant vertical heterogeneity in the soil hydraulic p

ISSN:0043-1397    

DOI:10.1029/90WR02105

年代:1991

数据来源: WILEY

摘要:

The results of a recent study of solute transport in a hypothetical scale‐heterogeneous soil under transient unsaturated flow conditions (Russo, this issue) suggested that the time‐dependent components of the spatial covariance tensor, based on a single realization of the solute concentration in unsaturated flow, are in relatively good agreement with the components of the spatial covariance tensor, based on the ensemble‐average solute concentration derived by Dagan (1984), for solute transport under steady saturated flow. Furthermore, the asymptotic value of the longitudinal component of the dispersivity tensor λzz, estimated from the horizontally averaged solute concentration in the unsaturated flow domain, was found to be in good agreement with the asymptotic λzzderived by Dagan (1982, 1984) and Gelhar and Axness (1983) for saturated flow. These findings are explored in a general Lagrangian formulation, using small‐perturbation, first‐order approximations. The results of the analysis of the velocity field in the unsaturated flow domain of the hypothetical scale‐heterogeneous soil of Russo (this issue) suggest that there was good agreement between the result of the Lagrangian kinematic analysis and the result of the analysis of the spatial moments of the concentration distribution, in agreement with the stochastic theory of transport in saturated flow. This is explained by the finding that under unsaturated flow conditions there is an increase in the variability of the hydraulic conductivityK(and concurrently an increase in the variability of the velocityVz), accompanied by a decrease in the correlation scale ofK(and concurrently a decrease in the correlation scale ofVz) relative to the saturated conditions. The increase in the variability of the unsaturated conductivity stemmed from the variability in the water content θ and the strong nonlinear dependence ofKon θ, while the accompanying decrease in its correlation scale stemmed from the negative correlation betweenF= logKsand θ, which persisted for a relatively large separation distance in the longitudinal vertical direction. Consequently, the product between the conductivity variance and its correlation scale is of similar magnitude for both saturated and unsaturated flow regimes. The results suggest that in spite of the complexity of unsaturated flow, as compared with saturated flow, it might be amenable to a

ISSN:0043-1397    

DOI:10.1029/90WR02165

年代:1991

数据来源: WILEY

摘要:

The majority of past suspended sediment concentration modeling efforts have relied on simple regression analysis. Problems with these models, and in particular, sediment rating curves, have been gaining attention recently. It is argued here that many of the problems result from the fact that simple regression models are inappropriate for modeling fluvial systems because they fail to adequately represent the dynamic nature of fluvial processes. Transfer function models are system models which can account for the dynamic nature of fluvial systems. Single input‐single output and multiple input‐single output transfer function models for daily suspended sediment concentration are developed for two drainage basins in Iowa. Interpretation of the models with respect to hydrologic theory indicates that model form and parameter estimates can be related to drainage basin size, land use, and physiographic characterist

ISSN:0043-1397    

DOI:10.1029/90WR01607

年代:1991

数据来源: WILEY

摘要:

A perturbation solution to three‐dimensional radial flow in heterogeneous porous media is reported on; the analytical solution is in terms of the first and second moments of the gradient in the radial direction and the specific discharge in this direction. The solution requires evaluation, numerically in the case of this paper, of some rather difficult integrals which compose its basic form. By proper adjustment of the statistical anisotropy of the medium, a solution for the two‐dimensional flow problem can be emulated; the two‐dimensional solution for the mean and variance in specific discharge resembles asymptotes reported earlier by another investigator. In general, the effective hydraulic conductivity, outside a few length scales of the well itself, is found to be nearly constant and dependent upon the value selected for the statistical anisotropy factor; the variance in specific discharge behaves nearly as the inverse square of the distance from the well in all

ISSN:0043-1397    

DOI:10.1029/90WR02410

年代:1991

数据来源: WILEY

摘要:

Two indices are presented for assessing the expected responsiveness of lakes to changes in external acid inputs. The first is the ratio of the sum of acidic anion to sum of base cation equivalents (CA/CB), which is a familiar index of lake response to past inputs; the second quantity is buffer intensity (β = −dCA/dpH), which serves as an index of lakepH sensitivity to changes in current inputs. Because the indices account for both capacity and intensity ofpH buffering, the approach provides greater information on lake responsiveness to acidification than the more customary value, acid neutralizing capacity. The approach is applied to water quality data from the Environmental Protection Agency's Eastern Lake Survey and preliminary paleolimnological data from the PIRLA project (paleolimnological investigation of recent lake acidification). These applications suggest that the approach may yield a useful tool with which to evaluate existing data from sites considered for monitoring the effects of changing acid inputs on lake syste

ISSN:0043-1397    

DOI:10.1029/90WR02411

年代:1991

数据来源: WILEY

摘要:

The nonparametric seasonal Kendall's test, and a related multivariate test were used to analyze 403 National Stream Quality Accounting Network (NASQAN) stations for trend for the period 1978–1987. Nominal sampling frequencies were quarterly or bimonthly. For all groups and individual constituents, trends were detected for only a minority of stations at the relatively liberal 10% significance level. The groups with the greatest percentage of trends were common ions (mostly upward) and nutrients and suspended sediment (mostly upward for total nitrogen and mostly downward for total phosphorus). In thepH and alkalinity group, the trends were dominantly upward; while this might be the result of reductions in atmospheric deposition, this hypothesis is clouded by the existence of uptrends in sulfate at many of the same stations. The trace metal analyses showed that the constituents with the greatest number of trends (dominantly downward) were arsenic and cadmium; most of the stations with downtrends were in the major population areas of the east and midwest. Additional exploratory analyses of possible relationships between trends and land use and population did not give strong evidence of possible causatio

ISSN:0043-1397    

DOI:10.1029/90WR02140

年代:1991

数据来源: WILEY

摘要:

The cumulant expansion method, used previously by Sposito and Barry (1987) to derive an ensemble average transport equation for a tracer moving in a heterogeneous aquifer, is generalized to the case of a reactive solute that can adsorb linearly and undergo first‐order decay. In the process we also generalize the Van Kampen (1987) result for the cumulant expansion of a multiplicative stochastic differential equation containing a time‐dependent sure matrix. The resulting partial differential equation exhibits terms with field‐scale coefficients that are analogous to those in the corresponding nonstochastic local‐scale transport equation. There are also new terms in the third‐ and fourth‐order spatial derivatives of the ensemble average concentration. It is demonstrated that the effective solute velocity for the aqueous concentration, not that for the total concentration (aqueous plus sorbed), is relevant for a field‐scale description of solute transport. The field‐scale effective solute velocity, dispersion coefficient, retardation factor, and first‐order decay parameters, unlike their local‐scale counterparts, are time‐dependent because of autocorrelations and cross correlations among the random local solute velocity, retardation factor, and first‐order decay constant. It is shown also that negative cross correlations between the random tracer solute velocity and the inverse of the local retardation factor may produce both enhanced dispersion and a temporal growth in the field‐scale retardation factor. These effects are possible in any heterogeneous aquifer for which a stochastic description of aquifer spatial v

ISSN:0043-1397    

DOI:10.1029/90WR01906

年代:1991

数据来源: WILEY

摘要:

The precipitation of Al in aqueous solutions can be described as a two‐step process. When acidic inorganic Al solutions (pH 4.5) were titrated with NaOH topH levels between 5.5 and 6.0, an amorphous Al(OH)3(s) phase was formed instantaneously. During the first 5 min, the apparent half time for the reduction in dissolved Al species (t1/2) was 0.162 ± 0.07 hours (n= 4). The decrease of dissolved Al species continued during the following 24 hours, but at a far slower rate (t1/2= 55.6 ± 25 hours (n= 4)). The highest precipitation rates were found in the solution of highestpH, and at approximately identicalpH, the highest rate was found in the solution of highest temperature. The dissolution of amorphous Al(OH)3(s) can also be described as a two‐step process. When the amorphous Al solutions (pH between 5.5 and 6.0) were acidified topH about 4.5 (HCl), the initial dissolution was relatively fast, but not as instantaneous as in the first step of precipitation. The apparentt1/2after 5 min was estimated to be 0.65 ± 0.12 hours (n= 4). During the first 2.67 hours (160 min) the dissolution step could be described by the equationC(t) = C0e−0.45t, i.e.,t1/2= 1.53 ± 0.60 hours (n= 20) according to which the solid Al phase should dissolve totally (97%) during 7.65 hours. However, after 24 hours of storage 40 to 50% of the original Al(OH)3(s) remained in the solid phase. This is explained by the presence of a far lower dissolution rate in a second step, i.e., the remaining Al(OH)3(s) was less soluble. The average dissolution rate for the rest of the 24‐hour period (21.33 hours) could be described by the exponential functionC(t) = C0e−0.0095t, i.e.,t1/2= 73.2 ± 23.4 hours (n= 4). This implies that a total dissolution of Al (97%) will occur after 15.3 ± 4.9 days. The implications of these findings are discussed with reference to the current geochemical models pretending to simulate and predict aluminum chemistry in soils and

ISSN:0043-1397    

DOI:10.1029/90WR02409

年代:1991

数据来源: WILEY