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<br />OD1813 <br /> <br />_ Irrigations in which the net quantity of water (difference <br />between return flow and diversions), number of acres irri- <br />gated, and the salt pickup rate per acre per month are <br />specified. <br /> <br />_ Variable exports in which the export quantity depends on the <br />availability of water in the reservoirs, either as spills or <br />water in excess of a specified level. <br /> <br />Program inputs include the system configuration; reservoir charac- <br />teristics, parameters, initial conditions, evaporation rates, and <br />operating criteria; upstream and downstream boundary values; water <br />use inputs; and run and output options. Output includes printed <br />and cathode ray tube (CRT) plots of results at various river loca- <br />tions and reservoirs. Initial input data, detailed month-by-month <br />results, and a concise summary for the entire run including simple <br />descriptive statistics can be printed. In addition, the user can <br />request the program to make extensive logical checks of all the <br />input data. <br /> <br />River Basin System Configuration <br /> <br />The portion of the Colorado River Basin from the four stations upstream <br />of Lake Powell to Imperial Dam (Figure l) is conceptualized for model- <br />ing purposes to the configuration shown in Figure 2. This configura- <br />tion represents the final one used for the runs whose results are <br />described in this memorandum. Initial attempts at modeling, which <br />only sought to provide an overall or gross picture, simplified the <br />system by eliminating operation of Lakes Mohave and Havasu. These <br />early attempts, in which these stretches were treated as river reaches <br />rather than reservoirs, were unsuccessful. <br /> <br />Hodel nodes correspond to a geographical location on the river. They <br />are chosen to coincide with existing gaging stations, to locate points <br />at which model output is desired, to delimit portions of the river <br />system such as reservoirs or river reaches, and to subdivide lengths <br />of the river to obtain the desired resolution for water use inputs. <br />Elements are defined as the portion of the river system between geo- <br />graphically adj acent nodes. The only exception is upstream boundary <br />elements which have no upstream node. Five types of elements are <br />permitted: Upstream boundaries, downstream boundary, river reach, <br />junction, and reservoir. <br /> <br />Both water and salt are introduced at the upstream boundary elements. <br />Desired flows at the downstream boundary are specified as target val- <br />ues which mayor may not be met. River reach elements are assumed to <br />have no storage properties and merely route flows from the upstream <br /> <br />3 <br />