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<br /> <br />o 020 4 9' <br /> <br />. <br /> <br />IDMD(I)=2 - A specified release is made in a manner identi- <br />cal to that for IDMD(I)=l, but in addition <br />further releases are permitted to meet down- <br />stream demands. <br /> <br />Demands occur when the upstream flow in a river reach is less <br />than the net depletion. The difference represents a demand <br />for water that has not been met. Similarly, if depletions in <br />a reservoir exceed the 'total water in storage or target flows <br />at the downstream boundary are not met, a demand exists. <br /> <br />The demand array is time dependent requiring monthly values. <br />A single annual cycle can be used, or values can be changed <br />for each year. It is also noted that the demand array per- <br />tains to releases of water from storage and not to flows. <br />Thus, flows may be routed through a reservoir even though <br />IDMD(I)=l. <br /> <br />Reservoir Inputs - Segment Data (Card Type 4-1) <br /> <br />. <br /> <br />Whenever a demand exists, the program uses segment data to <br />determine which reservoirs are normally available to make <br />releases to meet the demands. Segment data includes a segment <br />number, the number of reservoirs available*, and the element <br />numbers of the available reservoirs. It is noted that the <br />term normally available is used because even though the <br />segment data specifies a given reservoir, capacity restric- <br />tions or the value specified by the demand array may prevent <br />releases. Finally, the percent of the demand to be released <br />from each reservoir is also included on the segment card <br />and used when the release rule code is set to 1 (see <br />following subsection). <br /> <br />Segment numbers, ISEG, for use with each element are specified <br />on the element data Card 3-1. They are only meaningful for <br />river reaches, reservoirs, and the downstream boundary. They <br />are ignored for upstream boundaries and junctions. Segments <br />are numbered starting at one going up to the maximum. Figure 2 <br />illustrates the segment concept for a hypothetical river basin. <br />As shown, more than one element may reference the same segment. <br /> <br />* Availability involves both physical (reservoir must be upstream), <br />and political or legal (operation policy and water rights must <br />permit drafts to be made on the reservoir). <br /> <br />. <br /> <br />2-7 <br /> <br />