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spillway gate sill is at Elevation 248.0 m ft (813.6), and the crest of the emergency spillway overflow structure is at Elevation 274.6 m (901 ft). Fig. 1 Overview of Oroville Dam facility prior to the February 2017 incident 2.2. SERVICE SPILLWAY The service spillway is located on the right abutment of the main dam. It consists of an unlined approach channel, a gated headworks structure, and a concrete-lined chute extending to just above the Feather River channel. The headworks structure has a total of eight top-seal radial gates. The upstream sill elevation of the service spillway headworks is at Elevation 248.0 m (813.6 ft) and the tops of the radial gates (in the closed position) are at approximately Elevation 258.2 m (847 ft). The chute downstream of the headworks structure is about 54.6 m (179 ft) wide and just over 914 m (3,000 ft) long, with a drop of about 152 m (500 ft). The first 305 m (1,000 ft) of the service spillway chute downstream of the headworks slopes at about 5⅔ percent, after which the chute transitions through a vertical curve to a much steeper slope of about 24.5 percent for the last 443.5 m (1,455 ft). Four large, reinforced concrete “dentate” blocks are located at the downstream end of the chute, to disperse the spillway flow and dissipate energy as the flow enters the river. 148