Seite - 28 - in Book of Full Papers - Symposium Hydro Engineering

2.3. IMPROVING ON EXISTING RESEARCH Given the limitations of the previous research, USACE, with the assistance of Drs. Mileti and Sorensen, began monitoring the nation with the goal of gathering the necessary additional information when the next large-scale emergency evacuation inevitably occurred. On February 12, that scenario occurred downstream of Oroville Dam. 3. OROVILLE EVENT OVERVIEW Based on discussions we had with locals in the Oroville area, it is clear that prior to February 2017, the public generally did not consider the consequences of an uncontrolled release of water from the Oroville Dam or its spillways. The dam was simply part of the landscape of the community that had remained virtually unchanged for nearly 50 years. 3.1. EVENT INITIATION AND EVOLUTION During the winter of 2016-2017, Northern California experienced its wettest winter in nearly a century. Record inflows from the Feather River into the Oroville Reservoir during the month of January caused employees of the California Department of Water Resources (DWR) to open the main spillway and release water at rates up to 560 m3/s (20,000 ft3/s). The release of water down the spillway was normal procedure during very wet rainy seasons and that rate of flow is far below the designed capacity of the spillway chute and downstream channel. On the afternoon of February 6, in anticipation of increased inflow from an upcoming storm, the flow from the Flood Control Outlet (FCO) Spillway was increased to 1,550 m3/s (55,000 ft3/s). The following morning, an unusual flow pattern within the FCO Spillway chute caused DWR employees to close the FCO Spillway gates to allow for inspection. The halted water flow revealed a large area of concrete slab failure and foundation erosion beneath the spillway chute. DWR began consulting with the Federal Energy Regulatory Commission (FERC) and other dam safety agencies the following day. Test flows were released down the damaged FCO Spillway to verify how much flow the spillway chute could bear. This information was important, as the area was still in the middle of a very wet season and it was likely the FCO Spillway would be needed again in the coming months. Further slab failure and foundation erosion within the spillway chute was carefully monitored and an emergency operations center (EOC) was established to oversee the spillway operations. 28