Page - 130 - in Book of Full Papers - Symposium Hydro Engineering

configurations were selected, refinement of the operation policy continued (and continues as this paper is written, as full project restoration is not yet complete), with information for decision making provided by reservoir operation analyses. The reservoir operation analyses were structured to:  Assess the flood risk of removing the FCO Spillway chute so it could be reconstructed, and identify or confirm decisions about the timing of this removal and reconstruction. Based in part on this assessment, a decision was made to start construction in May 2017.  Develop an operations plan for the period of construction in 2017 that did not rely on the FCO Spillway chute and that minimized flood risk during construction. This led to drawing the reservoir down to elevation 213.4 m (700 ft) prior to the Winter Flood Season, using the powerhouse outlets.  Develop flood operations plan for the 2017-2018 Winter Flood Season to safely manage potential flood inflows with the partially reconstructed FCO Spillway chute, limiting releases through that spillway to 2832 m3/s (100,000 ft3/s). Because of the RCC invert, the maximum flow from the partially reconstructed FCO chute was limited to 2832 m3/s.  Develop flood operations plan that provides a 2018 construction season window with no reliance on the FCO Spillway chute.  Develop new flood operations plans for the period following the completely restored FCO Spillway chute. Flood operations for Lake Oroville and Oroville Dam are prescribed by the USACE, so all analyses were completed in collaboration with USACE staff, and all flood operations plans were submitted to the USACE, Federal Energy Regulatory Commission (FERC), and the State of California, Department of Water Resources, Division of Safety of Dams (DSOD) for their collective review and approval. Although flood protection and dam safety are the overriding operation objectives, operation plans also considered: water quality and environmental flow objectives, the need for water to protect endangered species, the rights of water users, and contractual commitments for water delivery by California’s SWP. The USACE HEC-ResSim application [8] and custom applications developed by DWR were used for the analyses of reservoir operations; the majority of the custom applications are spreadsheet-based. The HEC-ResSim applications were configured to simulate operations with various conditions of the reservoir outlets, including FCO Spillway configurations with reduced capacities. The simulations used various boundary conditions: (a) the historical period of record; (b) forecasts of near-term inflow provided by the NWS; and (c) statistically-derived hydrographs with flood volumes of specified exceedance probability, as developed with the hydrologic engineering analyses described below. The simulations used a daily or sub-daily time step, computing time series of pool elevation and reservoir storage, release through all Oroville Dam outlets, and discharge at downstream locations 130