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<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 />II <br /> <br />The runoff from Black Mesa was calculated by using the unit runoff <br /> <br /> <br />factors given in Figure 4 of the Definite Plan Report [2], which <br /> <br /> <br />relates to "Basins Similar to Those of Soap and Curecanti Creeks". <br /> <br /> <br />The values thus obtained are as follows: <br /> <br />Watershed <br /> <br />Annual Runoff <br />Cac ft.) <br />1.531 <br />412 <br />2,113 <br />5.814 <br />9.870 <br /> <br />Cottonwood Creek <br />Buckhorn Gulch <br />. Long Gulch <br />Mesa Gulch <br />Total <br /> <br />The monthly runoff values for th~ 25-year period of study are <br />given in Table 3. <br /> <br />A. Irrigation Requirements <br /> <br />The ideal diversion requirements for irrigation in the Project <br />service area were computed by USBR in the Definite Plan Report [2]. <br />The same values as given in Table 4 were applied in the operation <br />study. <br /> <br />B. Return Flows <br /> <br />The following assumptions were made to estimate usable return <br />flows from the irrigation service areas. <br /> <br />1. The return flow will be water diverted to the service area <br />minus 1.15 times the consumptive use. <br /> <br />2. Surface runoff can be considered two-thirds of total return <br /> <br /> <br />flows. the remaining one-third being the subsurface flow. <br /> <br />II-2 <br />