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
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.
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.