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<br />3-2 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />which represent streams, inflows (natural runoff), reservoirs and diversions <br />that exist in the basin. The model simulates the amount of water flowing in <br />each link (stream reach) and the amount of water contained in each reservoir <br />while taking account of consumptive use by various water users. This is done <br />on a monthly basis for each year being modeled. The selection of the years <br />used in the modeling is discussed in the following section. <br /> <br />3.3 STUDY PERIOD HYDROLOGY <br /> <br />The first steps in developing the basin model were to select the <br />historical period to be studied and to compute virgin flows (flows which would <br />have occurred without the effects of stream regulation or diversions) for that <br />study peri od. The study period consi sted of 384 consecut i ve months from <br />October 1952 through September 1983. This period was selected because it is <br />statistically similar to the total period of record for three key streamflow <br />gaging stations in the basin and includes a variety of hydrologic conditions. <br />Nearly all the significant dry years in the period of record were included in <br />the selected study period. <br /> <br />Separate data files of monthly virgin flows were derived for 59 locations <br />in the basin. Virgin flows at gaged sites were derived from historical flow <br />records corrected for upstream reservoir operations, basin imports and <br />exports, and irrigation depletions. Historical irrigation depletions were <br />estimated from climatic data, consumptive use calculations, diversion records, <br />and detailed operating studies of selected ditches. Virgin flows at ungaged <br />sites were developed from virgin flows at gaged sites corrected for area and <br />elevation differences. <br /> <br />3.4 REPRESENTATION OF WATER RIGHTS <br /> <br />Gunnison basin water rights are represented in the model in one of two <br />ways. "Se 1 ect" water rights whi ch significantly i nfl uence ri ver <br />administration or which transfer water from one sub-basin to another are <br />