Page - 89 - in Book of Full Papers - Symposium Hydro Engineering

3. KEY RECOVERY STRUCTURAL DESIGN FEATURES The Oroville Dam Spillway Incident created the need to address many areas of structural rehabilitation to facilitate the reconstruction of damaged or destroyed features of the Flood Control Outlet (FCO) Spillway chute and the Emergency Spillway. As detailed in the related situational development paper [2], the flood damage to both spillways was catastrophic. For the FCO Spillway chute, nearly 40% of the spillway chute was completely destroyed, scouring out an estimated 1.2 million m3 (1.6 million yd3) of material into the downstream Feather River channel, leaving a large hole in the foundation and a cavernous valley of eroded bedrock where once lay one of the largest spillways in the United States. Fig. 2 Oroville Dam Project Sign As shown in Fig. 2, the FCO Structure, with eight 10.21 m (33.5 ft) high radial gates, has a capacity of about 8380 m3/s (296,000 ft3/s), which has been restricted to 4200 m3/s (150,000 ft3/s) out of concern for downstream flooding. The FCO Spillway chute is 931 meters (3055 feet) long and 54.6 meters (179 feet) wide, with a steep 4:1 (horizontal:vertical) slope on the lower chute and a large energy-dissipating dentate structure at the terminal end. There is 170 meters (558 feet) of elevation change from the invert of the FCO gates to the normal water surface elevation of the diversion pool - the Feather River below the FCO Spillway chute, which is the tailwater for the powerhouse. This paper focuses on describing the repair of the FCO Spillway chute, using roller- compacted concrete (RCC), as this work was a large part of the recovery effort during the first year following the 2017 incident. Repair and recovery of the FCO Spillway chute was given the highest priority by DWR management so that the spillway would be available for the next 2017-2018 Winter Flood Season. This led to the rapid development and evaluation of recovery concepts that were constantly evolving and changing based on weekly, if not daily, interactions with the design team professionals, federal and state regulators, and eventually the construction contractor. A critical aspect of all recovery concepts was to determine the maximum work that could be accomplished within the limited timeframe, resulting in an operational FCO Spillway chute by November 1, 2017. 89