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<br />Ou1165 <br /> <br />~ <br /> <br />The following tabulations for calendar year 1986 show final records of <br />diversions of water from the mainstream of the Colorado River, return flow of <br />such water to the mainstream and consumptive use of such water by water user <br />agencies which have contracts with the United States. The records were <br />furnished by the U.S. Geological Survey, International Boundary and Water <br />Commission, Bureau of Indian Affairs, Bureau of Reclamation (RGclamaticn), <br />National Park Service, Fish and Wildlife Service, and water user agencies. <br />Diversions to All-American Canal and Gila Gravity Main Canal at Imperial Dam <br />were assign~d to each user based on deliveries to each user at its turnout from <br />the canal and a prorated amount of the conveyance loss from the canal. The <br />loss proration was based on the quantity delivered to each user and the length <br />of the canal through which it was carried. <br /> <br />- <br /> <br />The tables also show estimRtes of water use by water users other than those <br />_ wnich have contIa~with the United States. Records of quantities of water <br />pumped by permittees under the Lower Colorado River Land Use Program and by <br />others are incomplete or not available. Consequently, estimates of pump age <br />from the mainstream, from both the river and the wells, are shown for each <br />State. Pumping from the underground was considered from only those weIls <br />located in the flood plain of the Colorado River between the toes of the slopes <br />on either side of the valley. Supplemental sheets are enclosed which show the <br />estimates of water pumped by each diverter between Davis Dam and the <br />International Boundary. <br /> <br />The estimate of diversion by pumping during 1986 was made by two basic <br />methods: (1) For most electric pumps, diversion was computed on a monthly basis <br />from power records and a "kilowatthour per acre-foot factortf that was <br />determined by discharge measurement; (2) For pumps other than electric, a <br />consumptive use factor of 6 acre-feet per irrigated acre per year was used. <br />Irrigated acres were determined by field inventory during the year made with <br />the aid of aerial photographs and orthophotomaps which were taken during May- <br />August 1976. <br /> <br />. <br /> <br />There are undetermined amounts of unmeasured return flow reaching the Colorado <br />River by means of underground flow from aquifers underlying water user areas. <br />Also, the return flow to Lake Mead from Las Vegas Wash contains some ground <br />water-originated return flow mixed with Colorado River return flow. A Task <br />Force on Unmeasured Return Flows to the Lower Colorado River, consisting of <br />State and Federal members, was organized during 1970 to provide advice and <br />guidance to Reclamation and the U.S. Geological Survey which are jointly <br />conducting a program to determine the location and amounts of such unmeasured <br />return flows. Studies to determine unmeasured return flows are continuing, and <br />when these quantities are determined in a mutually acceptable manner, sueh <br />amounts are anticipated to be credited to the affected users and States in <br />making the ultimate annual consumptive use computations. The tabulations for <br />calendar year 1986 do include acceptable determinations of the appropriate <br />Colorado River return flows accruing to Lake Mead from Las Vegas Wash for the <br />State of Nevada and a portion of the flows from the Yuma Mesa Division for the <br />State of Arizona. <br /> <br />5 <br /> <br />r, <br />