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<br />":)l,~r.:l <br />UtJ. 0,)'1 <br /> <br />The common period of record begins with water year 1906. After flow <br />records were adjusted to natural conditions, any missing data in the <br />records were filled in using multiple regression techniques, where <br />possible. <br /> <br />5.3.1 Upper Basin <br /> <br />Natural flows and natural salt are computed for all streamflow <br />gauging stations in the Upper Basin. The monthly flow and salt <br />values for both the actual flow and intervening flow stations are <br />based on these natural flows and natural salt. <br /> <br />Natura 1 Flow <br /> <br />The basic equation used to determine natural flows for a given month <br />. at a given streamflow station is: <br /> <br />Natural flow = historical flow + crop consumptive use + reservoir <br />regulation + exports + M&I depletions + incidental depletion <br />imports <br /> <br />Not every term of the equation, of course, was applicable at every <br />station. The historical flow was gauged flow as recorded by the <br />USGS. The other terms are described as follows. <br /> <br />i <br />, <br /> <br />Monthly crop consumptive use was calculated by the modified <br />Blaney-Criddle method. The area.upstream of the stream gauge was <br />broken into subareas and the irrigation consumptive use for each <br />subarea was calculated based on recorded crop distribution patterns, <br />growing seasons, and climate. Irrigation consumptive use values for <br />all subareas above a gauge were added, to arrive at a monthly total <br />irrigation consumptive use value for the particular station. Care <br />was taken to be consistent with earlier studies such as the 1948 <br />Final Report of the Engineering Advisory Committee and the 1971 Upper <br />Colorado Regi on Comprehensive Framework Study. <br /> <br />Reservoir regulation was analyzed in three parts: monthly change in <br />surface storage, monthly change in bank storage, and monthly evapora- <br />tion. The changes in these factors were added algebraically for each <br />reservoir on a monthly basis. Monthly reservoir regulation values <br />for all reservoirs upstream of the station were then totaled to com- <br />pute the reservoir regulation for that station. <br /> <br />i <br /> <br />Monthly flows for out-of-basin exports were obtained from the USGS <br />and irrigation districts. The export term is the monthly sum of all <br />export flows out of the basin, upstream of the station. <br /> <br />Municipal and industrial or M&1 is primarily municipal use and ther- <br />mal powerplant use upstream of the station. It was determined from <br />diversion records and records of powerplant uses. The monthly values <br />were calculated by dividing the annual values by twelve. Refinements <br />are being investigated that would more realistically relate the <br />monthly values to actual use patterns. <br /> <br />19 <br />