Water resources of Walworth County, South Dakota

The water resources of Walworth County, South Dakota are for the most part undeveloped. In 1978, only about 10,000 acre-feet of water was used for irrigation, stock, domestic, and public supplies; most of this water came form Lake Oahe on the Missouri River, and was used for irrigation. The lake stores about 22 million acre-feet of water; the average annual flow of the Missouri River is about 16 million acre-feet. Tributary streams normally are dry at least 10 months per year. Average annual net surface runoff from the county is 7,900 acre-feet. At least 99 percent of the precipitation per year is lost by evapotranspiration. An estimated 1.2 million acre-feet of water is stored in eight aquifers in the glacial drift. The water generally is suitable for irrigation, stock, and domestic use. It is estimated that more than 55 million acre-feet of water is stored in nine aquifers in the bedrock. These aquifers are in the Dakota Formation, Inyan Kara Group, Sundance and Minnelusa Formations, Madison Group, Devonian strata, and Stony Mountain, Red River, and Deadwood Formations. The water is slightly to very saline and, at best, is suitable for livestock and marginally acceptable for domestic supplies. (USGS)