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<br /> <br />. <br /> <br />002Q6<l <br /> <br />If a demand exists, segment data are used to determine which <br />reservoirs, if any, are available to meet the demand. The purpose <br />of a reservoir is to regulate natural inflow hydrology and convert <br />it to a desired outflow hydrology to meet the demands. To accom- <br />plish this in a general program requires procedures that facilitate <br />duplication of the operational policies and rules, at least in a <br />gross manner. Certain detailS are inevitably 10s~. If their <br />loss is unacceptable, special programs must be written for the <br />specific system. However, future uncertainties in water supply, <br />demands, operational policies, and project development may be <br />of greater significance. <br /> <br />. <br /> <br />When a reservoir element is encountered the first time during the <br />monthly computation cycle, the program first computes evaporation <br />for the current month. The volume at the start of the month is <br />used with the area-capacity relations to compute the corresponding <br />surface area. Evaporation rates for the month are then used to <br />compute the total evaporation volume for the month. In general, <br />a more accurate approach requires use of an average area during <br />the month. Since the ending area for the month is unknown until <br />computations are completed, an estimated value is required. <br />Computations would be carried out, the average area found and <br />compared with the estimated, and a new estimate of the average <br />area made based on these results. The entire process would then <br />be repeated until the estimated and computed areas are within a <br />desired degree of accuracy. However, this iterative approach <br />is assumed an unnecessary refinement in terms of other model <br />assumptions and inputs. <br /> <br />When the reservoir is initially encountered, any inflow is assumed <br />to raise the level of the reservoir with a portion of the water <br />entering the banks and a portion increaSing surface storage. <br />Internally, all volumes are in terms of the surface storage. <br />Indeed, flag levels, constraints, control zones, area-capacity <br />curves, etc., are in terms of surface storage. <br /> <br />In a manner similar to that for the river reach, the net effect <br />of the inputs within the reservoir are computed. Additions are <br />made directly to the reservoir and depletions removed directly <br />from it. The outlet works capacity does not apply and water <br />may be withdrawn until the reservoir is dry. If additional water <br />is required, segment data are used to determine which reservoirs, <br />if any, can be operated to meet the demand. <br /> <br />The operation of an individual reservoir is based on the demand <br />array. Three options are available: <br /> <br />. <br /> <br />(1) Make a specified release only <br /> <br />3-2 <br /> <br />(rev. 07/75) -- <br /> <br />