Journal of Water Resources Planning and Management

In the absence of an alternative means of wastewater disposal, wastewater reclamation projects involving the use of reclaimed water for irrigation require facilities for seasonally storing the reclaimed water. Surface reservoirs represent one means of providing this seasonal storage. Constructing surface reservoirs, though, can be economically prohibitive. A second option for reclaimed water seasonal storage is the use of ground‐water aquifers. Regulatory restrictions and public health concerns are significant constraints to the recharge of treated wastewater into domestically used ground‐water aquifers. Where basins not subject to these constraints are available, however, ground‐water aquifers offer the potential for providing an economical means of seasonally storing reclaimed wastewater. An example reclaimed water irrigation project in southern California is presented for which the use of a small, isolated ground‐water basin for seasonally storing reclaimed water has been approved. For this southern California project, the use of a ground‐water basin for storing reclaimed water during times of minimal irrigation demand is resulting in a significant reduction in the overall capital costs of required wastewater reclamation facilities.

Simulation, screening, and optimization procedures are developed and used conjunctively to analyze multipurpose water development opportunities for a complex river system. The general model is capable of generating an information base for water‐development planning; evaluating physical and economic efficiencies of alternative water uses; and analyzing the economic and environmental tradeoffs, as well as the financing and policy issues associated with water development alternatives. The general model consists of three components: 'simulation, screening, and optimization, but this paper focuses on the simulation component. The simulation consists of a water‐use and economic algorithm capable of simulating water uses and losses, and calculating system costs and benefits for water development alternatives. The simulation model also generates input data for the multi‐objective optimization model.

Designing programs to control pollutant discharges into streams is easier if the areas of water quality degradation from adjacent discharges do not overlap, so that each discharge may be treated as a single entity. Conservative pollutants accumulate in a stream but decaying pollutants from one source may be of insignificant concentration at the point where the next downstream source is introduced. There may be greater overlap of areas of degraded water quality at high streamflows than at low ones. In assessing whether discharges may be treated separately, all streamflow conditions should be considered. This paper develops and presents a simple set of techniques based on dimensionless variables that may be used to determine whether adjacent discharges of nonconservative pollutants may be regarded as independent. The application of these techniques is demonstrated for an example problem. It is shown, for example, that for dissolved oxygen (DO) deficit, if the reaeration coefficient exceeds the decay coefficient and the residence time between adjacent dischargers is greater than 10 times the reciprocal of the decay coefficient, there is no significant overlap between adjacent dischargers at any streamflow.

This paper reports the development and application of a modeling package for the real‐time operation of Feitsui and Shihmen Reservoirs in the Tanshui River Basin, Taiwan, the Republic of China. The modeling package consists of a 10‐day (the traditional reservoir operation period in Taiwan) streamflow forecast model, a rule‐curve‐based simulation model, and an optimization model. Given a forecasted streamflow sequence for the entire year, the simulation model is first used to determine whether a severe shortage of water is expected. Using the simulation results as an initial feasible operating policy and an appropriate objective function (which is different for periods with and without an anticipated shortage), a dynamic‐programming‐based optimization model is then used to determine an improved operating policy. At the end of each 10‐day period, the streamflow forecast is updated using a Kalman filter technique and the observed streamflow during the period, and the simulation and optimization models will be rerun for the remaining periods of the year. The cycle repeats until the last period is reached. Tested with actual operational records and a hypothetical condition, the models are shown to be capable of producing improved 10‐day operating rules for the present reservoir system. The entire modeling system was run on a VAX 8650 and an IBM‐AT compatible personal computer (PC). The execution time for a 1‐yr (36 10‐day periods) operation is less than 5 min on the VAX 8650, and about 45 min on the PC.

This paper presents the results of the application of a procedure to assist in planning for the rehabilitation of a water distribution system. The procedure is applied to New York City and incorporates the costs of replacing water mains and those of repairing main breaks to determine least‐cost planning strategies. Results show that New York's current policy of replacing main segments that have had two or more breaks is the least‐cost approach on a city‐wide basis. However, application of slightly different strategies to different pipe diameters and to different boroughs can yield slightly lower costs. Results of the procedure are sensitive to the discount rate and the costs associated with main breaks. Results show that delaying replacement of mains beyond an optimal time yields higher total costs. Several of the results can be generalized and are applicable to distribution • systems of other utilities: (1) Smaller diameter mains should be replaced more frequently, given all other factors are the same; (2) reasonable, least‐cost strategies can be approached even with uncertain input parameter values; (3) knowledge of costs associated with breaks is very important; and (4) in addition to cost, the resulting physical integrity of the system is very important.

Saudi Arabia is an arid country with the potenial for acute water shortage. The demand for water has grown substantially against a scarce and dwindling water supply. This growing imbalance has been met mainly by increasing water supply, while water‐demand management has been overlooked. The critical issue is how to reconcile the rapidly rising demand with scarce and depletable resources. This paper demonstrates and emphasizes the need and the urgency of adopting conservation and water‐demand management programs to achieve an acceptable balance between water needs and availability. There is considerable scope for improving the efficiency of water use in various sectors. The government of Saudi Arabia must shift its emphasis from supply development to demand management to avoid wasteful, inefficient uses of critical and nonrenewable water resources. The paper describes the country's water resources, discusses some problems and their implications of water use, and suggests some possible conservation measures with more emphasis on the agricultural sector, the largest and most inefficient user of water.

A comprehensive procedure for simultaneously relating storm rainfalls of a range of frequencies to runoff hydrographs of the same frequencies is suggested. Hypothetical storm rainfall is developed from published rainfall frequency data and then related directly to runoff peaks and volumes of corresponding frequencies obtained from recorded runoff. The vexing questions of what rainfall patterns to use to define a storm of a specified frequency and what ground conditions to use for converting the rain to runoff of the same frequency are answered in the model calibration process. Using the same criteria in application as in calibration eliminates some major uncertainties. The primary reason for relating rainfall to runoff is to compute flood hydrographs for conditions and locations other than those for which adequate runoff records are available. Once sound relationships are developed where good runoff data are available, such relationships can be used to assess flood potential for other basin conditions and management plans, as well as for other locations.

Reallocation of storage may increase a reservoir's capability to satisfy municipal and industrial water‐supply demands. The reallocation, however, simultaneously may decrease the reservoir's capability to satisfy competing demands. I developed a PC‐based reservoir‐operation simulator to provide information about such trade‐offs. The simulator accounts for: (1) Gain and loss of water in the reservoir; (2) gain and loss of water between the reservoir and a downstream demand point and (3) loss of water at the downstream point. The user controls the sequence of data preparation and simulation with a set of menus. The user “fills in the blanks” in data‐entry screens to define system characteristics, storage allocation, and hydrologic inputs. I designed the output specifically for the PC, and included the capability to write files that may be read by spreadsheet and graphical‐display programs. This state‐of‐the‐art interface expedites the edit‐simulate‐evaluate cycle, permitting the civil engineer to search for solutions to water‐use problems, rather than for solutions to computer‐use problems.

A decision support system for the water‐quality management of the Tejo estuary, named Hypertejo, is presented. Hypertejo is based on a chain of data bases, dispersion, nonpoint pollution, and regional water‐quality management models. Due to large running times of some of the models, making their interactive use impossible, Hypertejo was designed as a synthesis of the interconnected data bases and models. This synthesis was achieved by applying descriptive statistics and transfer function concepts. The system, implemented using HyperCard, provides answers to questions posed by three levels of users: member of the government, mayor, and technical manager. Hypertejo implementation for a pilot zone in the estuary is used to illustrate the potential applications of similar systems in water‐quality management studies.