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The Oroville Dam made national news last weekend when nearly 200,000 downstream residents were ordered to evacuate their homes and seek refuge on higher ground. The fear at the time was that erosion on Oroville’s emergency spillway could cause the dam to fail and send a “30-foot wall of water” into surrounding communities.
This erosion occurred as a result of Lake Oroville reaching maximum capacity and overflowing its so-called “emergency spillway” which is little more than a concrete lip perched precariously above a wooded hillside. Next to this ensemble is the main spillway, a set of gates and a long concrete chute leading down to the Feather River below. At the time of the lake’s overflowing, this main spillway had already been severely damaged and the Department of Water Recourses (DWR) had reduced the flow of water down the chute in order to prevent further damage. However, the combination of this reduced outflow and continuous heavy rain swelled the lake level to over 100% of capacity. Water began flowing over the top of the emergency spillway and proceeded to eat away at the hill next to the dam. This prompted the evacuations of the downstream communities.
Fortunately the dam did not collapse as feared. The DWR increased the flow out of the main spillway (despite the damage there) and the water level in Lake Oroville was eventually lowered enough to stop the erosion of the emergency spillway. Local residents were allowed to return to their homes days later.
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The Oroville Dam Situation Explained https://t.co/VIYi1oMHHD pic.twitter.com/XvVAuTLR8F
— Erick Erickson (@EWErickson) February 19, 2017
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