Page - 140 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 6 Performance of plunge pool alternative of Oroville Dam’s FCO Spillway chute 6.2. ANALYSIS OF EMERGENCY SPILLWAY To inform design decisions about the damaged hill slope downstream of the Emergency Spillway, a 2-D model of the Emergency Spillway, hill slope downstream, and part of the Feather River was developed using HEC-RAS. Terrain data were available from LiDAR obtained with drone flights by DWR following the spillway failure (and periodically thereafter, as construction progressed). The 2-D model was used to calculate water depth, velocity, and bottom shear for various flow conditions. Results were used by OER to assess the potential for future erosion and scour and to inform designers of remediation features downstream of the Emergency Spillway. Those features included a secant pile wall to prevent head cutting, armoring in key locations, and construction of a concrete apron immediately downstream of the weir. To assess the need for and to inform designers of modifications to the Emergency Spillway weir, a 3-D CFD model of the weir was developed using FLOW3D. Buttressing of the concrete monoliths was proposed to increase the factor of safety against sliding. The 3-D model showed certain configurations that would reduce the efficiency of the weir, thus reducing capacity of the spillway. This, in turn, would adversely affect the ability of the dam to pass the PMF safely. Analysis with the 3-D model led to modifications to the design. The analysis also yielded information about the flow velocity and bottom shear along the planned protection works downstream of the Emergency Spillway. 140