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Water supply providers are facing increasing difficulty expanding their watersupply systems to satisfy growing population and industry demands. The process ofdeveloping a new water supply source or even expanding an existing source is often metwith opposition from environmental and special interest groups, and results in lengthy,expensive, and difficult litigation. The outcome in some recent expansion efforts hasbeen a directive to "do more with what you have". In these cases, water supply providersare instructed to operate beyond the safe yield of their system and rely on conservationmeasures to satisfy water supply demands during severe drought events. Operating awater supply system this close to the edge of its reliable limits requires an accuratedetermination of the safe yield and thorough knowledge of the system's performanceduring severe drought events.The authors of this paper have recently performed detailed safe yield studies forseveral large and medium-sized water supply systems. These water supply systems varyin complexity from a system with multiple reservoirs with conjunctive use of riverintakes and wells, to a simple system with a single large reservoir. The safe yieldanalyses for each of these systems involved developing a custom computer model tosimulate the daily operation of the system for a lengthy period of continuous historicalinflows, often exceeding 80 years. These site specific computer models are capable ofsimulating a variety of operating assumptions, variations in monthly demand,conservation measures, and complex regulatory restrictions. In some cases the operatingrules were dependant upon water quality variables simulated by the model.When performing safe yield studies using a daily flow model, considerable effortand skill are required to develop the inflow database, estimate evaporation losses,determine useable storage, and quantify physical transmission limitations within thesystem. The result can be a powerful tool that can be used to generate important systemstatistics, perform "what if" analyses, test proposed conservation plans, and developoperating procedures to maximize existing resources.This paper discusses the procedures for developing a daily flowmodel for a raw water supply system, with special emphasis on common oversights thatare important to avoid. Lessons learned from past analyses and the graphical presentationof complex water system statistics including safe yield are also presented. The toolsdiscussed in this paper are provided to help water supply managers "do more with whatthey have". Includes 8 references, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 13File Size: 1 file , 1.1 MB