The Physical Model Study of the Folsom Dam Auxiliary Spillway System

Abstract

Folsom Dam, located on the American River, about 20 miles northeast of Sacramento, CA, was built in 1950 for flood control, water supply, electric power, and recreation. A new assessment of the probable maximum flood (PMF) has been made which requires the design and construction of a new outlet system to address dam safety. The new outlet system is an auxiliary spillway which includes a gated control structure, a 2%, 2000 ft long chute ending at a stepped spillway and a stilling basin downstream of the spillway. The physical model of the control structure is currently under investigation at the Utah Water Research Laboratory of the Utah State University in Logan, Utah. The focus of this physical model study was the entire auxiliary spillway system, except the control structure. This model utilized a single sluice gate across the entire width for flow control instead of a series of taintor gates, each located in a bay. A 1:26 Froude scaled model of the auxiliary spillway was built in the main channel of the St. Anthony Falls Laboratory (SAFL) to study operation of the stepped spillway and the stilling basin under varying hydraulic conditions by the control structure, headwater elevations in the reservoir and tailwater elevations. The extent of the model was from station 9+15, located 198 ft upstream of the control structure piers, to station 43+52, located 215 feet downstream of the final design of the stilling basin.