Residents of counties and cities near Lake Oroville and the surrounding area were evacuated yesterday amid concerns of uncontrolled releases from Lake Oroville auxiliary spillway in California, US, although the flows were later contained, the California Department of Water Resources announced.

The concern was that erosion at the head of the auxiliary spillway threatened to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville. Those potential flows could have exceeded the capacity of downstream channels. As a result, almost 200,000 people were evacuated.

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 situation at the structure however, still remains unpredictable and more updates are likely to follow.

Oroville Dam itself is sound and is a separate structure from the auxiliary spillway.