Page - 31 - in Book of Full Papers - Symposium Hydro Engineering

acknowledge that this would cause additional erosion along the FCO Spillway chute, but would possibly alleviate the risk that the Emergency Spillway would fail. During the discussion at the EOC, a DWR dam safety official entered the room and estimated that erosion was moving toward the Emergency Spillway at a rate of approximately 9-10 m (30 ft) per hour. At that moment, the erosion was approximately 9-10 m (30 ft) from the base of the Emergency Spillway. The official recommended an evacuation of the downstream communities in case the Emergency Spillway was to fail. Everyone present began talking loudly amongst themselves until the Sheriff took control of the room. He asked, “Can anyone here give me a reason not to evacuate?” The room went silent. He made the decision to evacuate at approximately 3:50 pm. An Emergency Action Plan (EAP) had been prepared for Oroville Dam shortly after it was built. An inundation map plan that showed the areas that would be inundated if the entire dam were to fail was included as a part of the EAP. However, a map estimating the flood extents of an Emergency Spillway failure did not exist. The Sheriff, with the assistance of DWR dam safety officials, made a conservative estimate on the areas to evacuate within Butte County based on the available maps. The Sheriff also called the Sheriffs of Yuba and Sutter Counties located downstream. He quickly related that he was evacuating the potential inundation areas along the Feather River within Butte County and that they should do the same in their respective counties. 3.4. COMMUNICATION OF EVACUATION DECISION TO SAFETY OFFICIALS DWR communicated with a variety of organizations about the situation at Oroville Dam beginning on February 8, 2017. They also distributed the following evacuation decision message to 161 organizational contacts, including safety and emergency managers (159 were reached), on February 12, 2017 at 4:10 pm. That message stated: “This is an evacuation order. Immediate evacuation from the low levels of Oroville and areas downstream is ordered. A hazardous situation is developing with the Oroville Dam auxiliary spillway. Operation of the auxiliary spillway had led to severe erosion that could lead to a failure of the structure. Failure of the auxiliary spillway structure will result in an uncontrolled release of floodwaters from Lake Oroville. In response to this developing situation, DWR is increasing water releases to 100,000 cubic feet per second. Immediate evacuation from low levels of Oroville and areas downstream is ordered. This is NOT A Drill. This is NOT A Drill. This is NOT A Drill.” 31