摘要:

Two generalized dynamic reliability models (integrating both hydrologic and hydraulic uncertainties) based on binomial and Poisson distributions are developed for evaluating flow conveyance reliability of hydraulic structures. The two generalized models correct the deficiencies of dynamic reliability models developed previously. Relative performance of the generalized models and two conventional reliability models were examined. It is found that the total risk is significantly underestimated by the conventional approaches when hydraulic uncertainty is moderate or large.

ISSN:0043-1397    

DOI:10.1029/WR021i010p01463

年代:1985

数据来源: WILEY

摘要:

Four different cost allocation methods are compared which allocate the joint costs of water resource projects among its participants on the basis of separable and nonseparable costs: the egalitarian nonseparable cost (ENSC) method, the separable costs remaining benefits (SCRB) method, the minimum costs remaining savings method, and a new method, the so‐called nonseparable cost gap method, which is derived from the τ value, a game theoretical concept. All these methods, except the ENSC method, can be described with the aid of lower and upper bounds for the core of the involved cost game. For convex cost games, these three methods use the same bounds for the core and hence coincide, but their cost allocation not necessarily belongs to the core. For a second class of cost games the so‐called one‐convex cost games, all methods, except the SCRB method, coincide, and their cost allocation turns out to be the center of gravity of the core of the involved cos

ISSN:0043-1397    

DOI:10.1029/WR021i010p01469

年代:1985

数据来源: WILEY

摘要:

Nonlinear optimization models are presented for the optimal operation of an unconfined aquifer system. The aquifer's response equations are developed using finite difference methods, quasilinearization, and matrix calculus. The optimization model, which is structured as a discrete time optimal control problem, identifies the optimal pumping pattern necessary to satisfy an exogenous water demand. A quasilinearization optimization algorithm and projected Lagrangian methods are used for the solution of the planning model. Example problems are presented which demonstrate the viability of the approach for nonlinear, nonconvex groundwater management problems.

ISSN:0043-1397    

DOI:10.1029/WR021i010p01476

年代:1985

数据来源: WILEY

摘要:

The average annual water balance of savanna vegetation systems is modeled as an interactive competition between trees and grass for water and energy. Ecological optimality hypotheses are introduced which allow specification of the woodland canopy density, the grass canopy density, and the plant (water use) coefficients of both tree and grass under conditions of natural equilibrium. Only one tree‐grass equilibrium state is found and is shown to agree well with the observed state of savanna in Sudan and the Transvaal. This state is stable with respect to perturbations of vegetation canopy density, but is metastable with respect to shifts in climate. Two other equilibrium states exist as vegetation monocultures, i.e., grassland and forest, but both are shown to be unstable with respect to perturbations of vegetation densit

ISSN:0043-1397    

DOI:10.1029/WR021i010p01483

年代:1985

数据来源: WILEY

摘要:

The free boundary value problem of steady groundwater flow in an unconfined aquifer with accretion is solved by numerical methods in an exemplary situation. New formulas, which improve the results of the commonly used Dupuit‐Forchheimer theory, are given for the dependence of the height of the phreatic surface on the accretion rate. In this way it is shown that simple formulas, which describe the flow of groundwater in a more accurate way than the classical ones, can be derived with the help of modern mathematical technique

ISSN:0043-1397    

DOI:10.1029/WR021i010p01494

年代:1985

数据来源: WILEY

摘要:

Tracer tests are the most reliable field methods for obtaining information describing advection and dispersion in aquifers. This paper describes the design and performance of single‐well tracer tests utilizing multilevel observation wells at a field site near Mobile, Alabama. In a given observation well, a total of 7 sampling zones were isolated using inflatable packers and silicone rubber plugs. All instrumentation was contained within a removable insert that extended from the well bottom to the land surface. Each sampling zone contained an electrical conductivity probe and was connected to the surface with two lengths of vacuum tubing. When combined with peristaltic pumps, the tubing allowed mixing of the sampling zone contents as well as water sample collection. A total of 5 experiments were performed using bromide as a conservative tracer. Results showed that the sampling zones were well isolated and that sampling zone mixing was necessary to achieve results that were independent of probe placement within a given zone. Both electrical conductivity and bromide concentration breakthrough curves indicated the presence of a high horizontal permeability zone in the bottom third of the aquifer, although the concentration data were considered the more accurate and reliable. Permeability values based on tracer travel times from the injection‐recovery well to the multilevel observation well varied by a factor of 4 over the aquifer thickness. Such results are reasonably consistent with permeability trends inferred during thermal energy storage experiments performed previously at the same s

ISSN:0043-1397    

DOI:10.1029/WR021i010p01497

年代:1985

数据来源: WILEY

摘要:

An experimental field study of the alkalinity and major ion budgets of Bickford watershed in central Massachusetts indicates that organic acid production by the ecosystem contributes measurably to surface water acidification. Applying the concepts of alkalinity, electroneutrality of solutions, and mass balance, organic acids were found to comprise 20% of all strong acid sources on one subcatchment annually, a value half as large as the measured bulk mineral acid deposition. Inorganic cation to anion ratios in Provencial Brook varied between 1.0 in winter and 1.6 during summer, suggesting the presence of up to 100 μeq/L of unmeasured charge from organic anions during the growing season. Base titrations and ultraviolet photooxidation experiments confirmed the existence of lowpKa(3.5–5.0) acidic functional groups. A positive linear relationship between dissolved organic carbon (DOC) and anion deficit for a group of surface and groundwater samples indicates the DOC contains about 7.5 meq carboxylic groups per gram C. Biological factors related to both upland and wetland carbon metabolism apparently control this natural acidification phenomenon, which has not been documented on other watersheds in the northeastern United States for which annual alkalinity budgets have been determin

ISSN:0043-1397    

DOI:10.1029/WR021i010p01503

年代:1985

数据来源: WILEY

摘要:

Nearly instantaneous melting of snow and ice by the March 19, 1982, eruption of Mount St. Helens released a 4 × 106m3flood of water from the crater that was converted to a lahar (volcanic debris flow) through erosion and incorporation of sediment by the time it reached the base of the volcano. Over the next 81 km that it traveled down the Toutle River, the flood wave was progressively diluted through several mechanisms. A transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater, when the total sediment concentration had decreased to about 78% by weight (57% by volume). The hyperconcentrated lahar‐runout flood wave, transporting immense quantities of sand in suspension, continued to experience progressive downstream dilution. Although turbulence was significantly dampened by the extremely high suspended load, very large standing waves and antidune waves were observed. The hyperconcentrated lahar‐runout flow deposited an unusual, faintly stratified, coarse sand which locally contained small, isolated gravel lenses. Very similar deposits in the Quaternary stratigraphy of Mount St. Helens and other Cascades volcanoes suggest that lahars may be more frequent than previously recogn

ISSN:0043-1397    

DOI:10.1029/WR021i010p01511

年代:1985

数据来源: WILEY

摘要:

Computational efficiency and computer memory requirements for four methods of minimizing functions were compared for four test nonlinear‐regression steady state groundwater flow problems. The fastest methods were the Marquardt and quasi‐linearization methods, which required almost identical computer times and numbers of iterations; the next fastest was the quasi‐Newton method, and last was the Fletcher‐Reeves method, which did not converge in 100 iterations for two of the problems. The fastest method per iteration was the Fletcher‐Reeves method, and this was followed closely by the quasi‐Newton method. The Marquardt and quasi‐linearization methods were slower. For all four methods the speed per iteration was directly related to the number of parameters in the model. However, this effect was much more pronounced for the Marquardt and quasi‐linearization methods than for the other two. Hence the quasi‐Newton (and perhaps Fletcher‐Reeves) method might be more efficient than either the Marquardt or quasi‐linearization methods if the number of parameters in a particular model were large, although this remains to be proven. The Marquardt method required somewhat less central memory than the quasi‐linearization metilod for three of the four problems. For all four problems the quasi‐Newton method required roughly two thirds to three quarters of the memory required by the Marquardt method, and the Fletcher‐Reeves method required slightly less memory than the quasi‐Newton method. Memory requirements were not excessiv

ISSN:0043-1397    

DOI:10.1029/WR021i010p01525

年代:1985

数据来源: WILEY

摘要:

To determine the soil water diffusivity,D(θ), by the horizontal infiltration method of R. R. Bruce and A. Klute (1956) the slope of the water distribution curve and the area under the curve must be evaluated. Experimental data often exhibit scatter, thus making the evaluation of the slope difficult. In this paper a rapid, simple method is described that introduces an empirical function that by linear least squares regression yields a curve that fits water distribution data for a wide range of soil textures. The function is differentiable, and its integral is easily calculated with a numerical technique available on programmable scientific calculators. The proposed method produces estimates ofD(θ)that reach expected large values near water saturation. This result offers a clear advantage over other simple methods that assume an exponential relation betweenDandθand thus describeD(θ)adequately only over the middle range of water conte

ISSN:0043-1397    

DOI:10.1029/WR021i010p01539

年代:1985

数据来源: WILEY