Use of water by phreatophytes in 2000‐Foot channel between Granite Reef and Gillespie dams, Maricopa County, Arizona

Abstract

The following is a summary of data obtained in a study of transpiration by phreatophytes in the channels of the Salt and Gila Rivers, between Granite Reef and Gillespie dams, Maricopa County, Arizona. The study was made in the spring of 1950 by the U. S. Geological Survey in cooperation with the Corps of Engineers, United States Army. The kind and amount of phreatophyte growth was mapped in the area covered by a proposed flood‐control channel, 2000 ft wide, extending between the two dams. Most of the mapping was done from the air, using recent aerial photos. Transpiration by the phreatophytes was computed using the results of the mapping combined with water‐use factors developed by experimental work done by the Geological Survey in Safford Valley, Arizona, during 1943 and 1944. Estimates of future phreatophyte use and of the amount of water that might be saved by clearing and maintaining the channel area were based on extensions of water‐level graphs to include the next 50 years, and on the experimental work at Safford. The estimates were as follows: (1) total estimated transpiration from ground water at time of investigation ‐ 29,000 ac ft per year; (2) estimated average transpiration from ground water, within the channel area, during period 1950–1999 (a) without Colorado River water ‐ 22,200 ac ft per year, (b) with Colorado River water in 1960 ‐ 29,900 ac ft per year; (3) estimated average water saving effected by channel clearing, 1950–1999 (a) without Colorado River water ‐ 16,600 ac ft per year, (b) with Colorado River water in 1960 ‐ 22,400 ac ft per year.