Abstract The Salt River drainage basin (Star Valley) is an agricultural watershed of 829 mi2 (2150 km2) in western Wyoming. Starting in 1971, several irrigation projects were completed that converted surface irrigation systems to sprinkler irrigation systems on approximately one-half of the irrigated acres in the valley. This conversion resulted in less total water being diverted from streams for the sprinkler systems than was the case for the surface systems on the same irrigated acreage.
Salt River stream flows were hydrologically analyzed and a comparison made of the flows prior to and after conversion to sprinkler systems. A test of mean monthly flows showed that spring flows increased significantly (a = 0.05) by 58.7 percent following the conversion to sprinklers. The Salt River flows were also compared with flows of the Greys River, a nonagricultural watershed immediately adjacent to the Salt River, using the double mass analysis. This test again showed higher spring flows and also lower fall flows were evidently a consequence of irrigation practices rather than climatological factors.
Analysis of annual flood peaks was accomplished by several hydrologic and statistical tests. Included were a comparison of flood frequency distributions, a test of stationariness and a test of homogeneity. These tests revealed that flood peaks increased significantly (a = 0.05) following the conversion to sprinklers. The mean annual flood peak increased by 47.0 percent.
*The research upon which this report is based was supported by a grant from the Wyoming Water Research Center.
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