摘要:

This paper presents a methodology to obtain optimal reservoir operation policies for a large‐ scale reservoir system. The model yields medium‐term (one‐year‐ahead) optimal release policies that allow the planning of activities within the current water year, with the possibility of updating preplanned activities to account for uncertain events that affect the state of the system. River flows are characterized as a multivariate autoregressive process and are forecasted using maximum likelihood estimators. The solution method is a sequential dynamic decomposition algorithm that keeps computational requirements and dimensionality problems at low levels. The model maximizes the system annual energy generation while satisfying constraints imposed on the operation of the reservoir network. Several alternative versions of the model are also presented, which can be used under different assumptions. The model is applied to a large‐scale multireservoir system, the northern portion of the California Central Valley Project. The optimal release policies show a potential increase in the system total annual energy with respect to heuristic schedules current

ISSN:0043-1397    

DOI:10.1029/WR021i005p00619

年代:1985

数据来源: WILEY

摘要:

A quadratic optimization model is applied to a large‐scale reservoir system to obtain operation schedules. The model has the minimum possible dimensionality, treats spillage and penstock releases as decision variables and takes advantage of system‐dependent features to reduce the size of the decision space. An efficient and stable quadratic programming active set algorithm is used to solve for the optimal release policies. The stability and convergence of the solution algorithm are ensured by the factorization of the reduced Hessian matrix and the accurate computation of the Lagrange multipliers. The quadratic model is compared with a simplified linear model and it is found that optimal release schedules are robust to the choice of model, both yielding an increase of nearly 27% in the total annual energy production with respect to conventional operation procedures, although the quadratic model is more flexible and of general applicability. The adequate fulfillment of other system functions such as flood control and water supply is guaranteed via constraints on storage and spillage variab

ISSN:0043-1397    

DOI:10.1029/WR021i005p00631

年代:1985

数据来源: WILEY

摘要:

A heuristic linear programming‐based procedure has been developed for the least cost layout and design of water distribution networks. The methodology is capable of analyzing a wide range of demand pattern and pipe failure combinations. Hydraulic consistency is ensured throughout the procedure through the use of the Hardy‐Cross network solver technique. The procedure can also be extended for use in the expansion or reinforcement of existing network systems. While the techniques used to reduce the size of the constraint set to enable the procedure to handle a wide range of loading conditions do not guarantee global optimality, a pragmatic “reasonable” optimum is achieved. The method is demonstrated by application to the design of a new network and the expansion of an existing network. In the expansion of the existing network problem the solution obtained was less expensive than any previously published s

ISSN:0043-1397    

DOI:10.1029/WR021i005p00642

年代:1985

数据来源: WILEY

摘要:

A general contaminant transport simulation technique based on a Galerkin finite element representation in space and an alternating direction time‐stepping scheme is developed. The formulation, which is in terms of natural coordinates following the principal directions of hydraulic conductivity of the medium, decouples the spatial components of the equations, leading to tridiagonal matrices. The numerical accuracy can be easily controlled in each principal direction through the well‐established Peclet and Courant numbers. Results are found to be comparable to those from the classic finite element scheme, but the cost of computation is generally much less because the computational effort varies only linearly with the grid size. The technique is thus well suited for transport simulations with complex layered anisotropic groundwater systems requiring large and detailed gr

ISSN:0043-1397    

DOI:10.1029/WR021i005p00653

年代:1985

数据来源: WILEY

摘要:

A condensed version of the Valencia‐Schaake disaggregation model is developed which describes the distribution of monthly streamflow sequences using a set of coupled univariate regression models rather than a multivariate time series formulation. The condensed model has fewer parameters and is convenient for generating flow sequences which incorporate the intrinsic variability of streamflows and the uncertainty in the parameters of the annual and monthly streamflow models. The impact of parameter uncertainty on derived relationships between reservoir capacity and reservoir performance statistics is illustrated using required reservoir capacity (calculated with the sequent peak algorithm), system reliability, and the average total shortfall. Modeled sequences describe flows in the Rappahannock River in Virginia and the Boise River in Idaho. For high‐reliability systems the results show that streamflow generation procedures which ignore model parameter uncertainty can grossly underestimate reservoir system failure rates and the severity of likely shortages, even if based on a 50‐year r

ISSN:0043-1397    

DOI:10.1029/WR021i005p00665

年代:1985

数据来源: WILEY

摘要:

This study deals with the definition and measurement of the dispersive properties of a stratified aquifer based on the single‐well tracer test. Knowledge of such dispersive properties are of fundamental importance to the evaluation, analysis, and simulation of contaminant migration in groundwater, a subject of great interest in recent years. In the single‐well test, tracer is pumped into the formation for a period of time and then pumped out. Concentration data are obtained from the injection‐withdrawal well and from one or more sampling‐observation wells which may be multilevel. Our analysis of such a test is based on a Lagrangian‐Eulerian numerical model which considers the depth‐dependent advection in the radial direction and local hydrodynamic dispersion in the vertical and radial directions. Results show that the movement of an injected tracer in a stratified aquifer may be accurately simulated without resorting to the use of a scale‐dependent, full aquifer dispersivity if the flow field is known in sufficient detail. When the advection process is simulated accurately, the values of local dispersivity will be small, constant, and on the order of those measured in the field or laboratory at individual levels in the aquifer. The full‐aquifer breakthrough curves measured in observation wells in a single‐well test in a stratified aquifer are determined by the hydraulic conductivity profile in the region between the injection‐withdrawal well and the observation well if the travel distance between these wells is typical of most test geometries. However, the relative concentration versus time data recorded at the injection‐withdrawal well during the withdrawal phase is primarily a measure of mixing in the aquifer due to local dispersion which has taken place during the experiment. The amount of mixing will depend on both the hydraulic conductivity distribution in the aquifer and the size of the experiment. As the experiment scale increases, the effects of local vertical dispersion will become larger compared to the effects of local radial dispersion. Local vertical dispersion will cause a solute traveling in a high‐conductivity layer in an aquifer to migrate into adjacent low‐conductivity layers where its movement will be relatively slow in comparison. In the initial design of a tracer test it is important to have some idea of the type of nonhomogeneity with which one is dealing. More information of a broad nature concerning the types or classifications of nonhomogeneities that exist in natural aquifers would be very useful. Future resear

ISSN:0043-1397    

DOI:10.1029/WR021i005p00676

年代:1985

数据来源: WILEY

摘要:

Modeling of seasonal hydrologic time series often requires the identification of periodic functions of its basic parameters such as the mean, standard deviation, and autocorrelation coefficients. The consequences of incorrect estimation of harmonics on dependence models of the stochastic component are investigated. The underremoval of harmonics in the periodic mean introduces four additional terms in the inferred autoregressive moving average model of stochastic component for each underestimated harmonic. Overremoval has a small effect on the dependence structure. In both cases, however, the total number of parameters to be estimated increases. The underremoval of harmonics in the periodic standard deviation decreases the values of autocorrelation coefficients of the stochastic component, whereas the overremoval may increase them. In the case of the periodic standard deviations the effect on model identification of stochastic component appears to be minimal. The neglect of periodicity in the auto‐ correlation coefficients can lead to erroneous stationary models of the stochastic componen

ISSN:0043-1397    

DOI:10.1029/WR021i005p00685

年代:1985

数据来源: WILEY

摘要:

Interannual modes of streamflow variation at 106 locations across the United States during the period 1931–1978 are defined by using principal components. Five statistically significant components are found to account for more than 56% of the total streamflow variance. The first principal component represents a nationwide tendency for either above‐ or below‐mean streamflow. The second component represents a north‐south opposition in departures from mean flow, and the third, an east‐west opposition. Higher‐order components (fourth and fifth) geographically depict regional patterns of opposition in the sign of streamflow departures between coastal‐continental areas and between the northern and southern plains, respectively. Analyses using spatially and temporally modified data sets indicate that the first three components (which explain 45% of the variance) are quite stable spatially, while only the first component is stable temporally. Time series analysis of principal component scores indicates that all but the fourth component are first‐order autoregressive processes, as is mean annual nationwide streamflow. The fourth component is an autoregressive (AR)(2) process. In general, the principal components of streamflow are found to exhibit more persistence over annual time scales than the mean annual flow

ISSN:0043-1397    

DOI:10.1029/WR021i005p00691

年代:1985

数据来源: WILEY

摘要:

The only practical means of forecasting spring and summer runoff in remote high mountain basins such as the upper Indus in Pakistan is from preseason snow cover on satellite images. Previous studies have shown that regression coefficients of runoff on snow cover differ between basins in magnitude and sign. A conceptual analysis explains this, identifies the glaciological and snowpack variables that control annual variation in meltwater runoff, and forms the basis of a parametric forecasting model that is successfully applied to contrasting tributaries of the upper Indus, despite very crude parameter values. It incorporates the uncertainty due to possible nonaverage summer weather. Suggestions are made about additional remote sensing and ground reconnaissance investigations that could improve forecasting capability in this and similar regions.

ISSN:0043-1397    

DOI:10.1029/WR021i005p00702

年代:1985

数据来源: WILEY

摘要:

Two‐dimensional infiltration in a soil containing regularly spaced, water‐filled, vertical cracks is determined by a finite difference numerical solution of the saturated‐unsaturated flow equations for selected soil hydraulic characteristics. The equivalent Green‐Ampt model gives results which correspond well with finite difference solutions. Differences in cumulative infiltration and infiltration rates, expressed as percentages of the corresponding finite difference results, typically vary up to about 4%. When the crack spacing‐depth ratio and the magnitude of the moisture potential at the wetting front are both small, calculations predict that wetted tongues moving away from adjacent cracks interact to temporarily enclose an unwetted pocket, an event coinciding with a sudden drop in the infiltration rate and the breakdown of the corresponding Green‐Ampt

ISSN:0043-1397    

DOI:10.1029/WR021i005p00709

年代:1985

数据来源: WILEY