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Show 18 - Area occupied Annual use Basin by phreatophytes (acre-feet) 8. Lower San Simon-GilaRiver 12,500 00,000 9. Duncan 1,800 9,400 TOTAL 72,000 - 82,000 275,000 - 350,000 Question VII. Of the total amount of precipitation on the combined watershed, what is the best estimate in acre-feet of the amount* returned to the atmosphere by (a) evaporation and (b) transpiration ? Preparation of an accurate answer to this question would require additional basic research regarding precipitation, runoff, diversion of surface flow for irrigation, recharge; research regarding evaporation from water surfaces, from wetted sand in stream bottoms, from irrigated lands, from the land surface immediately following rains, from mountain snows during the winter and during spring melt; and research regarding use of water by plants, both those using perennial water and desert plants using near-surface water immediately following rains. Many of these data are not available. It is tentatively estimated that 37,500,000 acre-feet of the total precipitation falling on the drainage basin of the Gila River upstream from Gillespie Dam is lost by evapo-transpiration. Question VIII. How many pumps are now operated in this basin for the purpose of withdrawing water from the underground by: (a) Individuals for agricultural or domestic use? (b) Industrial plants? (c) Municipalities ? The following tabulation is based on counts by the U. S. Geological Survey of irrigation pumping plants operated in |