USACE CWMS - Bighorn River Watershed

The Corps Water Management System (CWMS) includes four interrelated models to assist with water management for the basin:

- GeoHMS (Geospatial Hydrologic Modeling Extension)
- ResSIM (Reservoir System Simulation)
- RAS (River Analysis System)
- FIA (Flood Impact Analysis)

The Bighorn River is a right bank tributary of the Yellowstone River with its headwaters located near Dubois, Wyoming in the Wind River Mountain range. The Bighorn River Watershed originates on the eastern slope of the Continental Divide and starts out as the Wind River. It flows in a generally southeasterly direction towards Riverton, WY, then turns north where it flows into Boysen Reservoir.
Approximately 14 miles downstream from Boysen Dam, at the Wedding of the Rivers, Wind River becomes the Bighorn River and continues to flow north towards its confluence with the Yellowstone River northeast of Billings, MT, passing through Yellowtail Dam in the lower reach.

The drainage basin of the Bighorn River encompasses an area of about 22,900 square miles. Boysen Reservoir on the Wind River has a drainage area of approximately 7,700 square miles. The downstream Bighorn Lake formed by Yellowtail Dam has a drainage area of approximately 19,600 square miles. The topography of the basin varies greatly; ranging from mountainous terrain with peak elevations in the Wind River Range over 13,800 feet to rolling foothills and high plains with elevations near 2,700 feet at the confluence with the Yellowstone River.