A concept of the shallow ground-water system along the North Platte River, south-central Wyoming

Irrigation along the North Platte River in Wyoming began as early as 1875. Streams are the principal source of irrigation water with groundwater used to supplement surface-water irrigation supplies. There was concern that groundwater pumpage may have caused about 16 ft of water-level decline in an observation well over a 2-year period. Leakage or lack of leakage from surface-water diversions for irrigation probably affects groundwater levels much more than pumpage. This study includes a quantitative assessment of the groundwater system for an area of approximately 410 sq mi along the North Platte River. Inflow to groundwater in the study area was estimated to average about 15 cu ft/sec from precipitation, about 36 cu ft/sec from stream leakage and surface- water irrigation, and about 39 cu ft/sec from leakage of streams and surface-water irrigation outside the study area. Groundwater outflow from the study area was estimated to average about 90 cu ft/sec assuming steady-state conditions. (USGS)