The Raft River basin, mostly in south-central Idaho and partly in Utah, is a drainage basin of approximately 1,510 square miles. Much arable land in the basin lacks water for irrigation, and the potentially irrigable acreage far exceeds the amount that could be irrigated with the 140,000 acre-feet estimated annual water yield. Therefore, the amount of uncommitted water that could be intercepted and used within the basin is the limiting factor in further development of agriculture irrigated with water derived from within the basin; Water for additional irrigation might be obtained by pumping more ground water, but only if large additional ground-water storage depletion can be tolerated. Alternatively, supplemental water might be imported.
The Raft River basin is an area of rugged mountain ranges, aggraded alluvial plains, and intermontane valleys. Topography and geologic structure strongly influence the climate and hydrology. The Raft River rises in the Goose Creek Range of northwestern Utah and flows generally northeastward and northward, joining the Snake River in the backwater of Lake Walcott.
The climate ranges from cool subhumid in the mountains to semiarid on the floor of the Raft River valley. Precipitation ranges from less than l0 inches on the valley floor to more than 30 inches at some places in the mountains. Rainfall is light during the growing season of about 100 days, and irrigation is necessary for most cultivated crops.
About 87,000 acres of land was irrigated in the 1960's, on the average, and most of that is in the lower Raft River valley. Nearly all usable surface water in the basin is diverted for irrigation and as of 1966 less than 20,000 acres were irrigated exclusively with surface water. Most stock, farm, and domestic water is from wells. Irrigation with ground water is Widely practiced and about 69,000 acres were irrigated partly or wholly with ground water in, 1966. In 1963 the valley was closed to further issuance of permits to appropriate ground-water because of declining water levels.
Geologic structure, lithology, and physiographic history control the surface-drainage pattern as well as the occurrence and movement of ground water. The principal water-bearing formations are the Salt Lake Formation of Pliocene age, consisting mainly of weakly consolidated sandy sediments and some layers of volcanic rock; the Raft Formation of Pleistocene age consisting of sand and gravel, lake sediments, and thin beds of silt and clay; and alluvial deposits of Holocene age that form aquifers beneath the bottom lands of the valleys. Good yields from wells, ranging upward to several thousand gallons a minute, are obtained from the water-bearing formations. Basalt lavas of the Snake River Group yield water where they occur below the water table of the valley. A few wells that penetrate limestone obtain substantial supplies from crevices.
Thickness of the composite aquifer ranges from 0 to more than 1,500 feet. Transmissivity of the composite aquifer is estimated to vary from about 10,000 gpd/ft (gallons per day per foot) along the basin margins to more than 450,000 gpd/ft. Permeability of the water-bearing deposits is highly variable, but is estimated to average about 300 gpd/ft2 for the basin as a whole.
The ground-water storage capacity of the basin is large; in the lower Raft Rive subbasin alone, the upper 200 feet of saturated deposits contain an estimated 9,000,000 acre-feet of water. The average specific yield of the shallow deposits is estimated to be 20 percent.
The water yield of the Raft River basin is estimated to average about 140,000 acre-feet per year as compared to 183,600 acre-feet estimated by Nace and others (1961) and 320,000 acre-feet estimated by Mundorff and Sisco (1963). Surface outflow of the Raft River to the Snake River now amounts to only about 1,900 acre-feet per year, a decline of about 15,000 acre-feet a year from the estimated original average outflow prior to ir
Additional Publication Details
USGS Numbered Series
The Raft River Basin, Idaho-Utah as of 1966: A reappraisal of the water resources and effects of ground-water development
United States, Dept. of the Interior, Geological Survey, Water Resources Division,