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Oroville-Federal Flood Control Operating Criteria

For federal projects, or as a condition of federal cost sharing on other projects, USACE (U.S. Army Corps of Engineers) prescribes rules for operating reservoir space dedicated to flood control.

By mid-October each year, Lake Oroville storage must be reduced to a specified level within the range of a maximum flood control pool of 750,000 acre-feet and a minimum flood control pool of 375,000 acre-feet. The allowable level within the range is recalculated each day, using an index that reflects the wetness of the watershed and the likelihood of heavy runoff from any incoming storms. As a wet season, such as in 1997-98, progresses the allowable storage tends to coincide with the maximum flood control pool.

When high inflows occur, water is temporarily held in the flood reservation as necessary to maintain reservoir releases within prescribed limits that are designed to prevent downstream damage. The downstream flow limits set by the USACE for Lake Oroville are 150,000 cfs north of Honcut Creek, 180,000 cfs above the mouth of the Yuba River, and 320,000 cfs south of the Bear River.

While water is being stored to maintain releases within target levels, reservoir storage may exceed the level allowable under the flood operating criteria, a condition known as "encroachment" into the required flood reservation. The USACE criteria recognize that such encroachment will occur and establish release criteria for such conditions.

Reservoir operators must balance the conflicting objectives of controlling the current flood event and preparing for a possible future one: the encroachment is eliminated when downstream conditions permit.

Text taken from the California Water Plan Update, Bulletin 160-98.