Officials just lifted the Evacuation Notice for Oroville California area residents downstream of the reservoir’s spillway that threated to erode last Sunday. An Evacuation Warning is still in force. This means people can return home and businesses can resume operations but everyone must be ready to leave again at a moment’s notice. The risks could elevate and require immediate evacuation.
Since the Evacuation late Sunday afternoon, Department of Water Resources has taken the following measures to reduce the threat of erosion and lower the lake level to below the emergency spillway (ES).
- Experts investigated the eroded hole. DWR, ACOE, and FERC confirmed that no piping (movement of water beneath the concrete lip) or other erosion threatened ES.
- Water releases through the primary spillway (PS) were increased to 100,000 cfs. They’ve seen no significant erosion along east side PS where the original problem began one week ago.
- Helicopters have been dropping bags of rocks used to fortify area in front of ES against future erosion in case use becomes necessary. The area is now armored with boulders.
Current status of the lake has reduced inflows (noon - 19,000 cfs) and with outflow 100,000 cfs there is a net discharge of 80,000 cfs. The lake water level is now 887 feet and the goal is 850 feet. The coming storms are expected to have inflows far less than 100,000 cfs and DWR estimates that the 850 level can be achieved this weekend if all goes as anticipated.
Lake Oroville serves as water storage, flood control, and to generate electricity. It’s part of the larger Central Valley flood control management, as outlined in this video.
The original problem with the primary spillway is discussed in this story and comment thread.
Sunday’s evacuation notice and the situation that led to the decision was well covered here.