摘要:

Successful regional water resources planning involves efficiency analysis to find the system that maximizes benefits minus costs or minimizes the cost of providing a specified level of output. The required input to the financial analysis is the optimal solution for the entire project and the optimal solutions for each participant acting independently and with any subset of the total group. For annmember problem this necessitates the calculation of 2n″ ‐ 1 optimal solutions. This paper presents a reliable total enumeration procedure to solve this problem for small‐scale regional water supply systems. This procedure allows the use of realistic cost functions or detailed cost estimates to find the optimal solution, as well as to examine nonoptimal but good solu

ISSN:0043-1397    

DOI:10.1029/WR025i004p00583

年代:1989

数据来源: WILEY

摘要:

Optimization models have been used as simulation tools to mimic complex decision making processes such as real‐time reservoir system operations. A recurring difficulty in the development of optimization models for use as simulation tools is the proper specification of the objective function. A new method for calibrating the objective function of an optimization model is presented. The method is developed specifically for the quadratic program class of models, but is applicable to general nonlinear programs with polynomial objective functions. A simplified case study is used to exercise the method in calibrating a quadratic objective function of a math program used to simulate operation of the Green River Basin hydrosystem in Kentucky. Results of the case study indicate that the method may be successfully used in certain cases to determine objective function parameter values to approximate decision making processe

ISSN:0043-1397    

DOI:10.1029/WR025i004p00591

年代:1989

数据来源: WILEY

摘要:

The problems of water exclusion from, or entry into, parabolic‐cylindrical and paraboloidal cavities during steady downward unsaturated seepage are solved. Both the quasi‐linear and the full nonlinear solutions are found exactly and simply. The identical general mathematical character of the two types of solution, and the good agreement of numerical details, attest to the reliability and utility of the (very much simpler) quasi‐linear analysis. A remarkable result is that for both the parabolic cylinder and the paraboloid, the potential at the cavity wall is spatially uniform. These geometries thus constitute separatices between apically blunter ones (circular cylinder, sphere), where the potential at the wall decreases downstream, and sharper ones (wedge, cone, hyperbolic cylinder, hyperboloid), where it increases. The parabolic geometries are optimal in leaking nowhere or everywhere: blunter ones leak first at the apex and and sharper ones at a low point of the wall. Implications for the design of seepage‐excluding tunnels and underground repositories are indicated. Comparison of the present results with those for the circular cylinder and the sphere reveals the significance of two dimensionless parameters of cavity geometry: σ(=½ ακ−1, with α sorptive number andκapical total curvature); andω,

ISSN:0043-1397    

DOI:10.1029/WR025i004p00605

年代:1989

数据来源: WILEY

摘要:

A new infiltration equation, derived exactly from a recent quasi‐solution of the governing differential flow equation, is capable of expressing eleven previously published infiltration equations. On the basis of least squares fitting, the new equation in three‐parameter dimensionless form expressed each of the eleven previous equations within ±0.31% over all times. If only one parameter was retained and fitted in the dimensionless form, nine of the eleven equations were still expressed within ±2.5%. This one‐parameter dimensionless form implies the dimensional infiltration equationI= (S/A0)]1 − exp (−A0t½)] +Kt, which is therefore proposed as a realistic blend of rigor and utility for the complete range of timet(0≦t≦∞), whereIis the cumulative quality of water infiltrated,Sis the sorptivity,A0is a constant arising from the quasi‐solution, andKis the sated (satiated, near‐saturated) hydraulic conductivity. Because of its broad matching capability, this equation is deemed to hold considerable promise for describing and fitting experimental infiltration data, whether from the l

ISSN:0043-1397    

DOI:10.1029/WR025i004p00619

年代:1989

数据来源: WILEY

摘要:

Entrainment of mixed size gravel bed material was studied in nine reaches of three high‐power streams in Scotland and Norway. Paired measurements of at‐a‐point shear stress (estimated from velocity profiles) and bed load transport (by hand‐held sampler) were made. They extended to very high values (400 N m−2, 3.5 kg m−1s−1). Analyses of maximum bed load diameter, mean bed load diameter, transport rates of individual size fractions, and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size, despite strong relative size effects. Precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates. Size‐selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to

ISSN:0043-1397    

DOI:10.1029/WR025i004p00627

年代:1989

数据来源: WILEY

摘要:

Measurements in a braided reach of the proglacial White River, Washington, are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg. Analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel, but maximum bed load diameter and total gravel transport rate significantly higher, as were transport rates of given size fractions at similar shear stresses. These differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment. The influence on gravel transport of local variation in bed material size may explain the self‐sorting of “bed load sheets” described by other workers. However, in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed, which partly offsets the relative size effects on competence and cap

ISSN:0043-1397    

DOI:10.1029/WR025i004p00635

年代:1989

数据来源: WILEY

摘要:

Cadwell Creek in west central Massachusetts, like many New England watersheds, is underlain by crystalline metamorphic bedrock with glacial till serving as the main unconfined aquifer. Groundwater hydrology and chemistry were monitored in a network of 10 wells. Low air‐equilibrated pH (lpar;4.7–5.4), low alkalinity (near 0 mg L−1CaCO3), and low conductivity (23–34 μmhos) occur in the groundwater in the downstream parts of the watershed where hydraulic gradients are steep and groundwater residence times are short (about 3 months). On the other hand, the headwater areas are typified by low hydraulic gradients and slower groundwater velocities, with correspondingly higher air‐equilibrated groundwater pH (7.0–7.4), alkalinity up to 26 mg L−1, and higher conductivity (32–71 μmhos). Therefore even in this supposedly acid‐sensitive terrain, groundwater is neutralized if mineral‐water contact time is sufficiently long (here ∼1 year). Because some 70% of Cadwell Creek base flow originates as shallow groundwater in the lower reaches of the watershed, the stream is very acidic most of the year. Only during late summer, when deeper base flow from headwater sources prevails, does thepH and alkalinity of the strea

ISSN:0043-1397    

DOI:10.1029/WR025i004p00644

年代:1989

数据来源: WILEY

摘要:

Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and calcite‐saturated fresh groundwater can produce a water that is undersaturated with respect to calcite. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for calcite dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of calcite. The amount of dissolution varies within a mixing zone, depending on the properties, physical dimensions, and boundary conditions of the aquifer system. Nearly all of the dissolution occurs in the fresher side of the mixing zone, with the maximum dissolution occurring in water that is fresher than that predicted solely by geochemical reaction models. The greatest porosity and permeability development occur at the toe and at the top of the mixing zone. If permeability increases as porosity increases, asymmetry in the dissolution causes the mixing zone to migrate landward over time. Dissolution rates indicated by the model show that this mechanism can produce significant increases in porosity and permeability over time spans on the order of tens of thousands of years. Given the comparatively long span of geologic time, this process may be largely responsible for porosity and permeability development observed in those carbonate rocks through which a freshwater‐saltwater mixing zone had at one time migra

ISSN:0043-1397    

DOI:10.1029/WR025i004p00655

年代:1989

数据来源: WILEY

摘要:

Intracell flow is important in modeling cells that contain both sources and sinks. Special attention is needed if recharge through the water table is a source. One method of modeling multiple sources and sinks is to determine the net recharge per cell. For example, for a model cell containing both a sink and recharge through the water table, the amount of recharge should be reduced by the ratio of the area of influence of the sink within the cell to the area of the cell. The reduction is the intercepted portion of the recharge. In a multilayer model this amount is further reduced by a proportion factor, which is a function of the depth of the flow lines from the water table boundary to the internal sink. A gaining section of a stream is a typical sink. The aquifer contribution to a gaining stream can be conceptualized as having two parts; the first part is the intercepted lateral flow from the water table and the second is the flow across the streambed due to differences in head between the water level in the stream and the aquifer below. The amount intercepted is a function of the geometry of the cell, but the amount due to difference in head across the stream bed is largely independent of cell geometry. A discharging well can intercept recharge through the water table within a model cell. The net recharge to the cell would be reduced in proportion to the area of influence of the well within the cell. The area of influence generally changes with time. Thus the amount of intercepted recharge and net recharge may not be constant with time. During periods when the well is not discharging there will be no intercepted recharge even though the area of influence from previous pumping may still exist. The reduction of net recharge per cell due to internal interception of flow will result in a model‐calculated mass balance less than the prototype. Additionally the “effective transmissivity” along the intercell flow paths may be altered when flow paths are occupied by intercepted rec

ISSN:0043-1397    

DOI:10.1029/WR025i004p00669

年代:1989

数据来源: WILEY

摘要:

Intercepted intracell flow, especially if cell includes water table recharge and a stream ((sink), can result in significant model error if not accounted for. A procedure utilizing net flow per cell (Fn) that accounts for intercepted intracell flow can be used for both steady state and transient simulations. Germane to the procedure is the determination of the ratio of area of influence of the interior sink to the area of the cell (Ai/Ac).Aiis the area in which water table recharge has the potential to be intercepted by the sink. DeterminingAi/Acrequires either a detailed water table map or observation of stream conditions within the cell. A proportioning parameterM, which is equal to 1 or slightly less and is a function of cell geometry, is used to determine how much of the water that has potential for interception is intercepted by the sink within the cell. Also germane to the procedure is the determination of the flow across the streambed (Fs), which is not directly a function of cell size, due to difference in head between the water level in the stream and the potentiometric surface of the aquifer underlying the streambed. The use ofFnfor steady state simulations allows simulation of water levels without utilizing head‐dependent or constant head boundary conditions which tend to constrain the model‐calculated water levels, an undesirable result if a comparison of measured and calculated water levels is being made. Transient simulations of streams usually utilize a head‐dependent boundary condition and a leakance value to model a stream. Leakance values for each model cell can be determined from a steady state simulation, which used the net flow per cell procedure. For transient simulation,Fnwould not includeFs. Also, for transient simulation it is necessary to checkFnat different time intervals becauseMandAi/Acare not constant and change with time. The procedure was used successfully in two different models of the aquifer system in the Ozarks. The use ofFnwas essential to the two model studies because most model cells in both models contained water table recharge and multiple

ISSN:0043-1397    

DOI:10.1029/WR025i004p00677

年代:1989

数据来源: WILEY