Page - 34 - in Book of Full Papers - Symposium Hydro Engineering

3.5.4. 6:03 pm: Sutter County. At 6:03 pm on February 12, 2017, the Sutter County Office of Emergency Management issued the following message to people in Sutter County. “Immediate evacuation Live Oak, Yuba City, Nicholas and other communities along Feather River ordered. Evacuate on Highway 99/70 south of Highway 20 west. Do not evacuate north. A partial failure of the Oroville Dam is possible.” The county followed this first evacuation message to people in Sutter County with a subsequent message at 6:17 pm, which declared that the evacuation was ordered (or mandatory). “Immediate evacuation ordered for Live Oak, Yuba City, Nicolaus & all communities Feather River Yuba City basin. Evacuate West on Hwy 20 and/or South on Hwy 99 and Hwy 70 toward Sacramento.” 3.5.5. 6:49 pm: Yuba City. Another public evacuation message was issued which targeted the people in Yuba City—located in Sutter County. It was distributed at 6:49 pm on February 12, 2017. It was the first message issued by city officials and it followed the mandatory evacuation message distributed by the county. It contained a voluntary evacuation recommendation, and was issued by local Yuba City government. It stated the following. “City of Yuba City strongly recommends an evacuation of all residents immediately. Travel options are as follows. South on Highway 99, West on Highway 20, Highway 99 South to Highway 113, or South on George Washington to Highway 113. Do not travel on Highway 20 or Bridge Street as the bridges are closed. Do not travel North.” 3.6. PUBLIC RESPONSE At the writing of this paper, response to the public survey that we created to gather information on the response to the warnings described in previous sections was in its final stages. Some preliminary findings are described below, but these may change as the data undergo final analysis. Importantly, the survey was conducted on a representative sample of the entire population in the evacuation zone. Therefore, we have a statistical basis for generalizing the findings for people not in the sample. 3.6.1. Protective Action Initiation Response Rate Preliminary analysis of public survey responses suggests just under 70% of the population in the targeted evacuation zone actually evacuated. Table 1 lists the reasons why people did not evacuate. The primary reason for non-evacuation (33%) was that even though they were in the evacuation zone, they felt that they would be above the flood elevation. In effect, they felt they were not asked to 34