Page - 57 - in Book of Full Papers - Symposium Hydro Engineering

developing “what if” scenarios and working to reinforce the decision-making processes. Initially, erosion occurring downstream of the Emergency Spillway was within expected levels. . However, on February 12, significant erosion of the rock hillside was noted to be progressing more rapidly than anticipated to the point where it was considered a threat to the Emergency Spillway. This situation prompted an immediate meeting between the Butte County Sheriff, DWR’s Acting Director, OICT management, DSOD, and FERC. Suggestions, such as increasing the FCO Spillway release to 5949 m3/s (210,000 ft3/s) to stop flow over the Emergency Spillway, had to be rejected since that would exceed downstream levee capacities, causing flooding of downstream communities. Based on the best available data, including the FCO Spillway’s current condition, Powerplant flooding potential, the potential for erosion failure of the Emergency Spillway, and continual forecasts, the DWR’s Acting Director agreed to increase FCO Spillway releases to 2832 m3/s (100,000 ft3/s). With the flow through the FCO Spillway increased to 2832 m3/s (100,000 ft3/s) February 12 at 1800 hours, the flow over the Emergency Spillway stopped several hours later. DWR maintained the FCO Spillway release at 2832 m3/s (100,000 ft3/s until February 16. On February 16, the Lake Oroville water elevation dropped low enough for the Butte County Sheriff to change the mandatory evacuation to an evacuation warning, allowing an estimated 188,000 people to return to their homes and businesses. Emergency repairs were developed and implemented, using air and ground resources. It was critical to repair the erosion damage below the Emergency Spillway in case it had to be used again. These emergency repairs to the Emergency Spillway consisted of filling erosion voids and armoring the ground surface. However, they were viewed as temporary, based on limited information, planning, and design. Fortunately, the Oroville Emergency Recovery team was onsite 24/7 and was able to collect advance-planning data and information as the damaged area was being backfilled and armored. This response effort was extremely large, yet simple in approach and had no planned stopping point set. DWR Executive management, in close coordination with DSOD and FERC, addressed terminating the Emergency Spillway repairs based on available reservoir storage, forecast, and the amount of completed temporary repair work. 57