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I II I I I I I I I I I I I I I I I I I Section II: Water Demand Official records of water diversions from streams to irrigation systems in the Tongue Creek basin were analyzed for the years between 1975 through 19811, This period was selected because diversions during this decade more accurately reflect existing agricultural conditions than diversions in earlier years, Diversion patterns were estimated for years of low, normal and high flows, as defined in the introduction to this chapter, The year 19811 was a typical high flow year, 1975 was a normal flow year and 1981 a low flow year, Based on quantities diverted in these years, it was estimated how much water would have been diverted each year since 19111, if present agricultural conditions had prevailed, based on whether each year had high, normal or low streamflows. In Table III-I, total diversions are given, by month, for the three categories of years of low, normal and high stream flows. Table III-I was obtained by making a selection of major ditches with decrees senior to a District 110 rank of 700 and a cumulative rate greater than four cubic feet per second. These ditches were then separated according to their location, upper or lower Surface Creek, and their diversion records totaled. This total is then prorated to represent the diversions in the two areas. The data pertain to (a) the Upper Surface Creek service area including Upper Cedar Mesa, (b) the Lower Surface Creek service area, including Lower Cedar Mesa, and (c) both service areas. The following tabulation shows total annual diversions (for the November through October "water years") for all years and in years of low, normal and high stream flows, in the upper and lower service areas and in both areas combined. Values for low, normal and high flow years are sum marized from Table III-I. These values were then used for 18 low flow years, 12 normal flow years and III high flow years to obtain the all years values. III-I 0