Evacuation orders were delivered to residents surrounding Lake Oroville at approximately 4:30pm on Sunday. DWR has been monitoring conditions at Lake Oroville’s main and auxiliary spillways around the clock for signs of erosion that could threaten the integrity of the emergency spillway and allow large, uncontrolled flows to the Feather River. To lower the lake level and thus reduce flows and the potential for erosion at the top of the emergency spillway, DWR increased flows down the main spillway’s damaged, concrete chute to 100,000 cubic feet per second. Current releases remain within the capacity of downstream channels. Oroville Dam is a separate structure from the emergency spillway and remains sound.
Based on information received from the California Department of Water
Resources (DWR) and the incident command team managing Lake Oroville, counties and cities near Lake Oroville and the surrounding area issued evacuation orders for residents. The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville. Those potential flows could exceed the capacity of downstream channels.
To avert more erosion at the top of the auxiliary spillway, DWR doubled the flow down its main spillway from 55,000 cubic feet per second (cfs) to 100,000 cfs. The next several hours will be crucial in determining whether the concrete structure at the head of the auxiliary spillway remains intact and prevents larger, uncontrolled flows.
Current flows are contained with downstream channels.
Flow over the auxiliary spillway weir began Saturday morning and has slowed
considerably. DWR officials expect that flow to stop entirely soon, which will reduce the erosion on the downstream side of the structure. Oroville Dam itself is sound and is a separate structure from the auxiliary spillway.
This is a graphic depicting the condition of other major reservoirs in California at the present time.
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