Page - 32 - in Book of Full Papers - Symposium Hydro Engineering

3.5. CHRONOLOGY OF FIRST PUBLIC EVACUATION MESSAGES Five first public evacuation messages were subsequently issued to people in different at risk geo-political areas. These were: (1) Butte County, which contains the City of Oroville, (2) the National Weather Service to people in Butte, Sutter, and Yuba Counties, (3) Sutter County, (4) Yuba City, which is the largest city in Sutter County, and (5) Yuba County, which contains the City of Marysville. Fig. 3 illustrates the location of these communities in relation to Oroville Dam. We catalogued first evacuation messages for different subpopulations because their timing was central to our efforts to examine warning decision-making, diffusion, and protective action initiation. The five first public evacuation messages follow. Fig. 3 Areas Receiving Evacuation Orders Downstream of Oroville Dam (Source: United States Geological Service) 3.5.1. 4:21 pm: Butte County. The Butte County Sheriff’s Office sent the first public evacuation message to the public of Butte County at 4:21 pm on February 12, 2017. It stated the following. “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 has lead 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 the low levels of 32