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Pre-storm flood releases
Planning studies are also underway to investigate the feasibility of incorporating an “Advance Release” flood management strategy into the operation of Folsom Dam and Reservoir. Using National Weather Service 5-day stream flow forecasts that warn of upcoming storms, dam operators could make releases from the reservoir before a storm arrives. The releases would create more storage space behind the dam and lower flood flows in the lower American River.

Dam operators would only use advance releases when the current flood pool and the enlarged outlet capacity could not handle the forecasted storm without significantly stressing the system.

There is a very small risk that a forecast storm may not produce as much inflow as expected, and that the reservoir may not refill to pre-advance release storage conditions. The risk is low because the Corps expects advance releases to be very rare (the 1997 event forecast would not have triggered an advance release with the enlarged outlets), and the Weather Service updates its forecasts every 6 hours, allowing dam operators to quickly adjust to new predictions.

The Corps does not currently make advance releases based on Weather Service forecasts at any of its flood control dams. As a result, the use of advance releases at Folsom Dam requires review and approval from Corps higher headquarters. Before requesting that approval, the Corps will conduct extensive modeling studies of this type of release.

In addition, the Corps will coordinate the plan with all involved agencies and organizations, and with the public. The Corps will also evaluate the environmental effects of advance releases using California Environmental Quality Act and National Environmental Quality Act criteria.

The Corps is assessing weather forecasting techniques and historical data for the Folsom Reservoir watershed. It is also simulating reservoir operations for various pre-flood conditions, including high reservoir storage at the time of the flood event, low reservoir storage, upstream reservoir storage available, and no upstream reservoir storage available.

The Folsom Dam Modification Project, when combined with the American River Common Features levee work, and the Folsom Dam Raise will give the people of Sacramento the level of flood protection they have sought since the record storms of 1986. They will finally have reduced their flood threat to less than 1 chance in 200 in any one year.



Increasing Floodwater Release Capacity

Reducing the Flood Risk