Page - 44 - in Book of Full Papers - Symposium Hydro Engineering

2. OROVILLE DAM FACILITY The Oroville Dam facility design was initially proposed in 1953 and was modified a number of times based on new requirements and scaled physical model studies, with construction being complete in 1968. The Oroville Dam and its major appurtenant facilities consist of a main dam (Oroville Dam), two saddle dams (Bidwell Saddle Dam and Parish Saddle Dam), two spillways (FCO Spillway and Emergency Spillway), the Hyatt Powerplant (Powerplant), and the River Valve Outlet. The main embankment is a zoned earthfill at 234.7 m (770 ft) high and a crest length of 2110 m (6920 ft). Bidwell Saddle Dam is located at the end of the Bidwell Bar Canyon arm of Lake Oroville and has two embankments. The combined length of the Bidwell Saddle Dam is 409 m (1340 ft) and the maximum embankment height is 14.3 M (47 ft). Parish Camp Saddle Dam is an embankment with a maximum height of 8.2 m (27 ft) and is 79.9 m (260 ft) long. Oroville Dam’s two spillways include a Flood Control Outlet (FCO) structure and an Emergency Spillway. They are configured as two separate structures right (north) of the main dam’s right abutment. The function of the FCO structure is to provide flood protection to the downstream communities. Flows are regulated through the FCO structure, thus routing storms and river inflows through the reservoir storage. The FCO structure has three main components: a Flood Control Outlet, a 1310 m (4300 ft) long FCO Spillway chute, and an energy dissipater. The FCO structure was sized to control the “standard project flood” peak inflow of 12460 m3/s (440,000 ft3/s) without using the Emergency Spillway. During the standard project flood routing, the maximum flow through the FCO structure was set at 4248 m3/s (150,000 ft3/s) due to downstream levee capacity. This upper limit of release was set to protect local and downstream urban and agricultural areas from flooding. However, during the estimated Probable Maximum Flood (PMF) events, the FCO structure was designed to release a maximum of 8283 m3/s (296,000 ft3/s). The FCO Spillway chute is a rectangular, reinforced- concrete open-channel chute. The profile of this lined chute closely follows the original natural terrain. This minimized the excavation as well as the disturbances of the underlying rock due to blasting. The FCO Spillway chute was founded on varying degrees of weathered rock. Four dentate structures were placed at the end of the chute to dissipate excess energy. From the end of the dentates, the flow releases into the Feather River. The purpose of the Emergency Spillway is to discharge extreme floods to prevent overtopping of the Oroville Dam embankment. The Emergency Spillway consists of two sections; an ogee section and a low-sill weir. The ogee section consists of multiple concrete monoliths founded on bedrock with varying heights. The tallest monolith has a height of about 15.9 m (50 ft) from the original ground and excavated into rock. The low-sill weir is a broad-crested concrete weir also founded on rock. The Emergency Spillway was sized such that during a PMF event, the spillway would be able to release a maximum flow of 10,506 m3/s (371,016 ft3/s) when the reservoir elevation is at 297.5 m (917 ft). The natural topography downstream of the Emergency Spillway was designed to convey the Emergency Spillway flows to the river. The area downstream 44