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releasing water to control the Lake Oroville reservoir level in accordance with the prescribed operations plan. During this operation, the FCO spillway suffered a catastrophic failure of the lower chute area eventually resulting in the loss of approximately 427 m (1400 ft) of the lower chute, including the scour of more than 1.2 million m3 (1.6 million yd3 of soil and rock materials. On February 11, 2017, the Emergency Spillway (Fig. 1) was used for the first time since the project was completed in 1968. During this operation, significant erosion and scour caused by the Emergency Spillway overflow led authorities to fear for the safety of the spillway structures, resulting in the activation of the Emergency Action Plan and evacuation of about 188,000 persons from downstream communities. Fig. 1 Flood Control Outlet (FCO) Structure and Emergency Spillway, March 2011 This paper is part of a series developed by the State of California, Department of Water Resources (DWR) to describe the Oroville Dam Spillway Incident - Emergency Response and Recovery. including lessons learned and key design features to allow the Oroville Dam FCO Spillway chute to be able to pass expected annual flood flows by the next wet-year cycle, starting by November 1, 2017. This paper presents the roller-compacted-concrete portion of the reconstructed spillway design that was intended to be used for replacing the eroded foundation of the FCO Spillway chute and as a buttress and apron for the rehabilitated Emergency Spillway. Through a series of design and project management decisions, the 87