Increasing floodwater release
Currently, the dam does not
have sufficient outlet capability to make effective releases in
preparation for one of these large storms. Releases through the
existing eight outlets combined with releases through the powerhouse
are limited to approximately 35,000 cubic feet per second (cfs).
This is less than one-third of the capacity of the American River
levees to pass floodwater. The levees can safely contain 145,000
cfs during flood operations. In order to make these large flood
releases, the reservoir must be nearly 75 percent full and the water
in the reservoir high enough to pass through the spillway gates
near the top of the dam. By that time, the flood control space behind
the dam is approximately 40 percent filled.
Enlarging the existing outlet gates and adding
two new outlets will allow for larger releases of up to 115,000
cfs earlier during a flood event. This will create additional floodwater
storage space behind the dam, which will, in turn, reduce the peak
amounts of floodwater sent down the American River. The result is
greater flood protection.
The existing eight outlet gates consist of
an upper row of four gates and a lower row of four gates. The Corps
and its partners began work in 2004. They plan to begin to enlarge
the upper row of gates and to add two new gates to this row in the
summer of 2005. The work will take approximately 6 years to complete
and will be scheduled to allow Folsom Dam to continue at its current
level of flood operation, water supply, and power service during
In 2009, operations will begin to enlarge
at least two of the lower outlet gates.
All Folsom Dam modifications are scheduled for completion in 2013.