Reclamation Information Sharing Environment (RISE)

A special high-flow release from Yellowtail Dam on the Bighorn River is being considered to flush sand-size sediment from the gravel bed. Releases from Yellowtail Dam are typically in the 3,000 to 4,000 cfs range and, in the past, these flows have been sufficient to prevent sand from depositing on the gravels. However, flow releases in the past 3 to 4 years have been reduced to 1,200 to 1,500 cfs because of drought conditions and sand is thought to have accumulated in the channel. Fishery biologists and others have requested that Reclamation make a greater release to flush sand-size sediment from the gravel. The Sedimentation and River Hydraulics Group was asked to do an initial study to help determine the magnitude and duration of a special high-flow release that would be sufficient to flush sand from the gravel over a 13-mile reach of the Bighorn River downstream from Yellowtail Dam. The study approach was to review the master’s thesis by Wiley (1995) on flushing flows, perform the hydraulic modeling, determine sediment transport capacity and make future recommendations for flows and monitoring.