Preliminary report on ground water in the Salmon Falls area, Twin Falls County, Idaho

Abstract

The Salmon Falls area contains about 80,000 acres of irrigable land, of which about 30,000 acres receives some water from the distribution system of Salmon River Canal Co., Ltd. This system utilizes virtually all the available surface water. A substantial amount of surface water, estimated to be about 70,000 acre-feet annually, is lost by leakage from the reservoir and the distribution system. Some of this water could be salvaged by lining sections of the canal where excessive losses occur. Ground water has not been extensively developed in the area, but some successful irrigation wells furnished supplemental irrigation water. Recharge to the area is from precipitation on the area, seepage from peripheral streams, seepage losses from the reservoir and canal system, irrigation seepage, and ground-water underflow. Ground water leaves the area by undertow to the north and northwest, and eventually reaches the Snake River. The total mount of underflow from the area was estimated by three different methods to be 17,000, 100,000, and 170,000 acre-feet per year. The preliminary estimate of 100,000 acre-feet was derived by the inventory of recharge and is probably more accurate than the other two methods. Calculations, based on estimates of transmissibility computed from specific capacities of wells, suggest that there may be some channels or conduits of higher than average transmissibility through which a large part of the undertow leaves the area, Possibly 25 percent of the ground-water outflow could be intercepted by wells. However, in part of the area the depth to water may be excessive for economic development. Chemical analyses of 25 samples of ground water indicate that most of the water sampled is suitable for irrigation. The samples found least suitable were of water occurring at shallow depth, south and east of Hollister.