Water resources of the Wind River Indian Reservation, Wyoming

Comprehensive information about the water resources on the Wind River Indian Reservation, west-central Wyoming is needed to manage the existing water uses and develop future water supplies for Shoshone and Northern Arapahoe Tribal members and others who live on or near the reservation. As a result, the U.S. Geological Survey, in cooperation with the Shoshone Tribe and the Northern Arapahoe Tribe, conducted a comprehensive study of the water resources of the reservation. Rocks from all geologic periods except those of Silurian age are present on the reservation. Ground water, as well as springs, are present in many of these geologic units. These units provide water for public-supply, domestic, agricultural, and industrial uses, and are a potential source of water for irrigation on the reservation. At least 507 wells are completed in deposits of Quaternary age on the reservation, and most of these wells are less than 50 feet deep. Median yields from wells completed in different deposits of Quaternary age ranged from 6 to 20 gallons per minute. The Wind River Formation of Tertiary age is the major source of drinking water for domestic and public-supply uses. Most of the 608 wells in this formation are completed in permeable, lenticular, and discontinuous sandstone deposits. Inventoried well depths ranged from 37 to 994 feet, with a median depth of 190 feet. Yields ranged from about 0.1 to 350 gallons per minute, with a median yield of 20 gallons per minute. One hundred and thirteen wells are completed in five Mesozoic and three Paleozoic age geologic units. Wells completed in the Mesozoic units are usually less than 150 feet deep. Median yields ranged from 5 gallons per minute for the Cody Shale of Cretaceous age to 55 gallons per minute for the Nugget Sandstone of Jurassic (?) and Triassic (?) age. The Paleozoic units consist of the Tensleep Sandstone of Pennsylvanian age and the Madison Limestone of Mississippian age and these two units are potentially the most productive water-yielding geologic units on the reservation, with estimated yields of as much as 1,000 gallons per minute. Streams provide most of the water for irrigation, which is the largest water use on the reservation. Sixty active or inactive U.S. Geological Survey streamflow-gaging stations are located on perennial, intermittent, and ephemeral streams on or near the reservation. Statistical summaries of streamflow data for 24 gaging stations with 10 or more years of daily discharge records indicate that low-flow, high-flow, and flow-duration characteristics of streams on the reservation are extremely variable. Average annual runoff was 122 to 1,150 acre-feet per square mile on streams with gaging stations. The chemical quality of ground water on the reservation is variable. In water sampled from the Little Wind River and Popo Agie River flood-plain alluvium near the mountains, dissolved-solids concentrations generally were less than 400 mg/L (milligrams per liter), and ionic compositions were dominated by calcium and bicarbonate. With increasing distance from the mountains, dissolved-solids concentrations ranged from about 600 to about 750 mg/L, and ionic composition consisted of a mixture of calcium, magnesium, and sodium cations with mostly sulfate anions. These changes in the chemical quality of water downgradient could be caused by lithologic changes in the flood-plain alluvium, a