摘要:

The assumption that the worst water quality occurs at the lowest streamflow may not always hold in instances involving multiple discharges and nonconservative pollutants. The additional dilution resulting from increased streamflow may be offset by adverse changes in the parameters that govern water quality and in decreased residence time, which allows the stream less time to recover from the effect of one discharge before receiving another. This paper addresses the question of whether, with multiple sources of decaying pollutants, water quality might worsen with increasing streamflow. For an isothermal uniform stream it is shown that the pattern of discharge that maximizes the derivative with respect to streamflow of critical dissolved oxygen deficit or the concentration of a substance exhibiting a first‐order decay is an infinite uniform distributed load. Whether the maximum value of the derivative is positive or negative depends on the values of the parameters that characterize the hydraulic geometry of the channel and the dependence of reaeration on flow. Theoretical results presented here indicate that for most natural streams the traditional assumption, that the lowest streamflow is the worst from a water quality perspective, will usually be valid for first‐order pollutants. Nevertheless, they also lead to the expectation that increases in impacts with increasing streamflow might occur for dissolved oxygen, especially in highly polluted and regulated streams (pollution, water quality models, rules and regulations, and manageme

ISSN:0043-1397    

DOI:10.1029/WR024i001p00001

年代:1988

数据来源: WILEY

摘要:

Mathematical expectation has traditionally been used in solving risk‐based decision making problems. However, this concept is not appropriate for decision making that affects public policy because it conceals extremes by commensurating events of different magnitudes and probabilities of occurrence. If a decision maker instead uses an expected value function in addition to a conditional expectation that captures extreme and catastrophic events, he will gain a more meaningful and more encompassing representation of the trade‐offs at hand. A theory relating conditional expectation to the statistics of extremes is developed in this paper. This expectation can now be viewed as the conditional expected risk given the occurrence of an event with a return period that equals or exceedsnyears. The theory highlights the importance of using both the conditional and the unconditional expected risk in decision making. This fact has previously been recognized in the partitioned multi‐objective risk method (PMRM), a risk analysis methodology based on the concept of conditional expectation. The theory proposed in this paper provides a formulation for analyzing the sensitivity of subjectively chosen parameters in the PMRM. This theory will also simplify the practical implementation of the m

ISSN:0043-1397    

DOI:10.1029/WR024i001p00009

年代:1988

数据来源: WILEY

摘要:

The partitioned multi‐objective risk method (PMRM) was developed for solving risk‐based multi‐objective decision making problems. Based on the premise that the expected value concept is not sufficient for proper decision making, the PMRM generates a number of conditional expected value functions (or risk functions) by partitioning the probability axis into probability ranges. The goal of partitioning the probability axis is to have better information on extreme events for decision making purposes. These conditional expectations are dependent on the chosen partitioning points. This paper analyzes how conditional expectations are sensitive to variations in partitioning. One of the risk functions is a measure of extreme and catastrophic events. By using the relationship between this particular risk function and the statistics of extremes, the sensitivity analysis is simplified. In many practical applications, it is difficult to determine which type of distribution function best represents the random process. Conditional expectations also depend on the choice of distribution, and the impact of this selection is disc

ISSN:0043-1397    

DOI:10.1029/WR024i001p00021

年代:1988

数据来源: WILEY

摘要:

A relationship between daily forest evaporation and meteorological screen data, based on an extension of a previous complementary theory approach to pasture evaporation, is proposed. The resulting formulation is tested against 800 days of a 5‐year lysimeter record for a eucalypt forest and appears to offer an alternative and plausible formulation of the relationship between the meteorological data and regional evaporatio

ISSN:0043-1397    

DOI:10.1029/WR024i001p00030

年代:1988

数据来源: WILEY

摘要:

Using data from two stations in the MAP3S acid precipitation monitoring network, some aspects of the marked point process of rainfall events are investigated and are used to illustrate some potentially useful data analytic techniques. We find no statistically significant evidence against a Poisson process model of storm arrivals, observed with a dead time corresponding to event duration. In particular, we look at the relation between amounts and the history of the process of events and the relation between events at two different stations. Events that occur close to previous events tend to have smaller than average precipitation amounts. We discuss some implications for parametric models of precipitation processes.

ISSN:0043-1397    

DOI:10.1029/WR024i001p00035

年代:1988

数据来源: WILEY

摘要:

Dynamic features of the flow in a 180° constant‐radius, recirculating laboratory channel are studied. The width‐depth ratio and radius‐width ratio of the channel are 16 and 5.4, respectively, and the sediment is sand with median grain diameter and geometric standard deviation of 0.3 mm and 1.45, respectively. The particle densimetric Froude number is 6.5. Individual components of the momentum equation are measured, and their relative effect on the momentum balance is evaluated. It is found that flow accelerations, notably downstream acceleration of the downstream and cross‐stream velocity components, induced as a result of change in channel curvature at the entrance to the bend have a significant effect on the flow processes in this bend. The cross‐stream velocity gradients are relatively insignificant. The curvature change affects the flow and bed topography in a manner similar to that in which a driving force affects an underdamped oscillating system. The findings are used for an evaluation of available bend f

ISSN:0043-1397    

DOI:10.1029/WR024i001p00045

年代:1988

数据来源: WILEY

摘要:

When water of one chemical composition is displaced by water of another, there is a change in composition at any point within the flow system which may occur more or less rapidly, depending on both the hydraulics and chemistry of the system. For many applications it is possible to decouple the hydraulic and chemical analyses, and later combine them for prediction of effluent compositions from well fields or concentration histories at observation wells. When an advection‐reaction model is used, the displacement problem is described mathematically as a Riemann problem. In this paper the Riemann problem is solved for the ternary exchange system using the method of characteristics. The pattern of composition changes is found to follow the right eigenvector paths in composition space, and the eigenvalues provide composition‐dependent retardation functions. The hydraulics is treated fairly generally and allows one to consider steady uniform or nonuniform flow fields or stochastic flow models. Both laboratory and field applictions are presen

ISSN:0043-1397    

DOI:10.1029/WR024i001p00057

年代:1988

数据来源: WILEY

摘要:

In‐lake alkalinity generation (IAG) is important in regulation of alkalinity in lakes with long residence times, particularly seepage lakes. An IAG model based on input/output modeling concepts is presented that describes budgets for each ion involved in alkalinity regulation by a single differential equation that includes inputs, outputs, and a first‐order sink term. These equations are linked to an alkalinity balance equation that includes inputs, outputs, IAG (by sulfate and nitrate reduction), and internal alkalinity consumption (by ammonium assimilation). Calibration using published lake budgets shows that rate constants are generally similar among soft water lakes (kSO4≈ 0.5 m/yr;kNO3≈ 1.3 yr−1;kNH4≈ 1.5 yr−1). Sensitivity analysis shows that predicted alkalinity is sensitive to water/residence time, but less sensitive to modest changes in rate constants. The model reflects the homeostatic nature of internal alkalinity generation, in which internal alkalinity production increases with increasing acid input and decreases with decreasing acid inputs of

ISSN:0043-1397    

DOI:10.1029/WR024i001p00065

年代:1988

数据来源: WILEY

摘要:

A significant retardation of radionuclides transported by flowing water from an underground repository can be expected if the nuclides are able to diffuse into the water filled micropores in the rock. This diffusion into the pores will also increase the surface available to interactions between the nuclides in the groundwater and the rock material, such as sorption. To calculate the retardation, it is necessary to know the sorption properties and the diffusivities in the rock matrix for the radionuclides. Diffusion experiments with cesium and strontium in biotite gneiss samples have been performed. Both the transport of strontium and cesium through rock samples and the concentration profiles of cesium and strontium inside rock samples have been determined. The result shows that diffusion of cesium and strontium occurs in the rock material. A diffusion model has been used to evaluate the diffusivity. Both pore diffusion and surface diffusion had to be included in the model to give good agreement with the experimental data. If surface diffusion is not included in the model, the effective pore diffusivity that gives the best fit to the experimental data is found to be higher than expected from earlier measurements of iodide diffusion in the same type of rock material. This indicates that the diffusion of cesium and strontium (sorbing components) in rock material is caused by both pore diffusion and surface diffusion acting in parallel.

ISSN:0043-1397    

DOI:10.1029/WR024i001p00075

年代:1988

数据来源: WILEY

摘要:

The concept of time stability as defined by Vachaud et al. (1985) is expanded to include general linear transformations in time and to account for the occurrence of spatial scale dependency. Time stability is described as the temporal persistence of a spatial pattern and is evaluated using correlation analysis of successive measurement dates. Spatial coherency analysis is suggested as a method for examining the temporal persistence of a spatial pattern as a function of spatial scale. Spatial coherency analysis was used to examine the temporal persistence of soil water storage (0–1.7 m) measured every 10 m in a 720‐m‐long transect for drying and recharge events. Soil water recharge altered the spatial pattern of water storage at small scales which was significantly related to surface (topographic) curvature. Drying did not alter the spatial pattern of soil water storage. The study supports the concept that soil water storage at a point is the product of hydrologic processes operating at different spatial scales. The analysis can be used to relate the spatial scale of processes to independent fa

ISSN:0043-1397    

DOI:10.1029/WR024i001p00085

年代:1988

数据来源: WILEY