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<br />21 <br /> <br />Water use per acre <br /> <br />Since 1922 the I. B. & W. C. has published in their <br /> <br />armual reports: the diversions from Rio Grande in U. S. below Falcon Dam, culti- <br /> <br />vated acreages, and annual rainfall over area. A tabulation of these data is <br /> <br />presented as table 13 (p. 22). This table shows an average armual diversion of <br /> <br />1.83 acre-feet per acre and an armual rainfall of 2.02 feet, or a total of 3.85 <br /> <br />feet of water over the area. The diversion figures are reliable but the culti- <br /> <br />vated acreages are subject to error and probably are high. Although the rainfall <br /> <br />is greater than the diversions, it often does not occur at proper time to be of <br /> <br />much help. This means that the 1.83 acre-feet per acre is low and the 2.02 feet <br /> <br />of rain is high, so far as benefits are concerned. <br /> <br />During the eight years 1922-29 ample water for all diverters was in river <br /> <br />almost at all times, and several million acre-feet was flowing into the Gulf each <br /> <br />year. The water used during these eight years averaged 2.36 acre-feet per year; <br /> <br />this represents the water used by Valley farmers when they could get about all <br /> <br />they wanted. <br /> <br />Water balance All U. S. storage is in Falcon Reservoir, and releases are <br /> <br />made upon request of the Special Water Master office. In addition to controlled <br /> <br />releases from Falcon, water is added to river from two other sources: (1) runoff <br /> <br />caused by rainfall below Falcon Dam (principally in Mexico) providing "free" water <br /> <br />that may be diverted in U. S.; and (2) return flow from irrigated lands on both <br /> <br />sides of river, supplied by underground drainage, plus, mBlfbe, some natural under- <br /> <br />ground flow. The total flow is reduced by evaporation, and, mBlfbe, seepage into <br /> <br />ground-water aquifers. What is left in the river is either diverted or wastes into <br /> <br />the Gulf. <br /> <br />All water released from Falcon has been on request, to meet need of diverters, <br /> <br />except flood water was spilled from first of October 1958 through March 1959, as <br /> <br />storage exceeded conservation pool limit. <br /> <br />U. S. releases, diversions, percent diverted, and flow to Gulf annually since <br /> <br />.,", r r ,. '44 <br />'..,f ~) "'..- ~'... ~ <br />