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The layout of the spillways is shown in Fig. 2, along with the FCO Spillway chute flow and erosion during the failure incident. The 1310.6 m (4300 ft) long FCO Spillway chute includes an unlined approach channel, a flood control outlet structure, a spillway chute, and an energy dissipater. The outlet structure has eight radial gates each 5.36 m (17 ft 7 in) wide separated by six 1.52 m (5 ft) thick piers and one central 2.44 m (8 ft) thick pier. Finally, the geometry of the outlet structure was optimized using results of 1965 physical modeling studies [4]. The FCO Spillway chute is a rectangular concrete-lined channel with a constant width 54.46 m (178 ft - 8 in). Four reinforced-concrete dentate structures at the end of the chute, the design of which is based on these same 1960s studies, dissipate the water energy. The Emergency Spillway includes an ogee section with multiple concrete monoliths of varying heights and a low-sill, broad-crested weir on natural ground. The area downstream of the Emergency Spillway was not cleared of vegetation because the expected infrequent use did not justify the potential adverse economic and aesthetic impact. Fig. 2 Photograph of Oroville, showing spillways and main dam embankment The combined spillway capacity was designed to safely pass the probable maximum flood (PMF). During this event, the design FCO Spillway chute maximum release is 8382 m3/s (296,000 ft3/s), and the design Emergency Spillway discharge is 10506 m3/s (371,016 ft3/s at reservoir pool elevation 279.5 m (917 ft). Integrated design features and operation rules were developed to control a standard project flood (SPF) inflow of 12460 m3/s (440,000 ft3/s) without using the Emergency Spillway, and with the FCO Spillway chute release limited to 4248 m3/s (150,000 ft3/s). This FCO Spillway chute release target was set to protect downstream urban and agricultural areas from potential flooding. In the 49 years since construction, the FCO Spillway chute has been used 25 of those years and the remaining 24 years the FCO spillway was not operated. Over operational period, the maximum daily release through the FCO Spillway chute equaled or exceeded 2832 m3/s (100,000 ft3’s) four times. Releases have 127