The U.S. Army Corps of Engineers Little Rock District announced this afternoon they are opening spillway gates at Norfork Dam to prevent overtopping. The corps says they are making surcharge spillway releases as the water levels continue to rise from recent heavy rainfall.
Nine spillway gates will be open half a foot releasing approximately 4,972 cubic feet per second (c.f.s.).
The total release from the spillway and hydropower units will be around 10,500 c.f.s.
The spillway release will end after the flood pool crests and recedes to elevation 579 feet per the water control plan.
According to the Corps, surcharge storage is extra storage created by operation of an overflow spillway. On a lake with a gated spillway such as Norfork, as the gates open the top of gate rises giving a bit more storage space for the flood – this operation maximizes the storage while optimizing the release. On a lake with an ungated spillway, the spillway only flows if the lake rises above the spillway. Surcharge storage is the extra volume stored in the lake due to the rise above the spillway.
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