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amenable to direct measurement. Theoretical and indirect methods of estimating con- , ' sumptive use m~st be relied upon in the tributary areas. t'n the New Mexico portion of the Gila River Basin, the annual consumptive use of water is r~ported by the New Mexico I n- terstate Stream Commission, pursuant to arti- cle VII of the Match 9, 1964, decree of the United States Supreme Court in Arizona v. California, et a/. ' Agriculture: About 85 percent of the con- sumptive use in t~e tributary area to the Col- orado River main~tream is for irrigated agricul- ture. The annual (rrigated acreage and crops grown within eachj reporting area were esti- mated principally :from information in the yearly State Agriclj/ture Statistics. Irrigated pasture and some minor crops not reported by the statistics were\estimated from informa- tion in the 1969 O!lnsus of Agriculture, sup- porting informatioil from framework studies, and various other Iqcal reports including county, farm-agent intervieWs. In essence, the county data from t~e statistics were dis- aggregated into the( reporting areas and sub- areas for computatibnal purposes. The Blaney-Criddle emp;irical formula was utilized to compute the ann~al rate of crop consump- tion use. The formula is based on the assump- tion of a full water supply, among other things, and results i~ a theoretical water re- quirement rather th~n actual use. Seasonal crop consumptive uS;e factors' "K" for the lower elevation deserlt areas were selected from Technical Bulletin 1~9 "Consumptive Use of Water by Crops in Arizona," issued September 1965 by the University of Arizona and the U.S. Department of 19riculture. In the higher areas, season<\1 factors from the Soil Conservation Service jTechnical Release No. 21 were utilized. Effective precipitation, that amount of rainfall which satisfies a portion of consumptive use, is a:ccounted for by criteria developed for this area by Wayne D. Criddle, former Utah State En4ineer. Among the many variables affecti(1g the actual use of wa- ter, the most importar1t is individual farm water supply and its nianagement. There is no adequate method to a<ljust computed annual requirements to actual water use over broad areas. . Past studies of the incidental consumptive use of water associated with irrigation (water surfaces and vegetative areas on rights-of- way for canals, laterals, drains, roads, etc.) suggest that this use may be accounted for by adding 10 to 20 percent of the computed crop consumptive use. A factor of 15 percent is used herein to represent this use. In the heavily irrigated central Arizona area of the Gila River Basin, in-transit water may some- times be considered a depletion. In-transit water is potential ground water recharge which, due to declining water tables, intercep- tion by impervious beds (perched water), etc., is presently irrecoverable. Although this water is not truly consumed, it is not avail- able for use. This temporary loss of water has not been included in this report because of the lack of pertinent information to estimate its present magnitude. Evaporation from Reservoirs, Lakes, and Stockponds: Adequate data are available at most of the major reservoirs in the tributaries to estimate annual lake evaporation. Monthly net evaporation rates were derived from nearby climatic stations recording pan evaporation and precipitation. Stockpond evaporation was taken directly from framework study support- ing data which were prepared by the Soil Conservation Service. I n addition to major re- servoirs and stockponds, there are many other reservoirs about which I ittle information exists. For the most part, these reservoirs are small and are used for a number of joint pur- poses. Using available listings of these im- poundments and other data. a total average surface area and a representative evaporative loss were estimated. No attempt was made to vary these losses or those from stockponds on a year-by-year basis. Municipal and Industrial: The base for estimat- ing municipal and industrial uses is the urban and rural population within the report- ing areas. Preparation of annual population estimates was guided by the 1970 Census, and various State and county statistical reviews and reports which include popUlation esti- ~ ~ -j . ~ ,,' j ,. :..:: ~ 13 ~ .~ 1 I