Folscom Dam Modificiations
Folsdom Dam Raise
Folsdom Dam Bridge
In the News
After years of study, discussion,
and consensus building by the Corps, Reclamation Board, Department of
Water Resources, Sacramento Area Flood Control Agency, and the area's
political leaders, the people of Sacramento selected a major three-project
effort to reduce the flood risk that has faced the community since the
Gold Rush. These three projects, working together, are the keys
to providing more flood protection to Sacramento than any other achievable
flood control project.
American River Common Features
The American River Common Features Project includes
levee work on the Lower American River, on the east bank of the Sacramento
River upstream of its confluence with the American River, and in the Natomas
Basin. It also includes additional upstream river flow gages.
The work includes the strengthening of levees (impervious barriers placed
inside the levees, landside berms, and drainage ditches), and raising
levees at select locations. When completed, these improvements will reduce
the flood risk to about a 1 in 100 chance in any given year.
Folsom Dam Modifications
Folsom Dam’s eight low-level outlets are too
small to make full use of the downstream river capacity in the early stages
of a flood event. Releases through the existing eight outlets combined
with releases through the powerhouse are limited to approximately 35,000
cubic feet per second (cfs) until the reservoir level reaches the spillway.
At this point, the reservoir’s flood space is 40% full. The solution
is to enlarge the existing outlets and add two new outlets. This allows
for releases to reach 115,000 cfs earlier during a flood event, creates
more floodwater storage space behind the dam during the peak of a flood
event, and reduces the peak amounts of floodwater sent down the American
These improvements, when combined with the Common Features work, will
reduce the risk of downstream flood damage to a 1 in 130 chance in any
Another significant part of the Folsom Dam Modification authorization
is the development of an updated flood management plan for the Folsom
Reservoir. The plan uses the new operation capabilities created by the
dam modifications and adopts new operations criteria, based on improved
long-range weather forecasting.
The proposed update will include the potential phased releases of existing
reservoir water storage in advance of predicted major storm events. These
advance releases will be based on the Advanced Hydrologic Prediction System
of the National Weather Service, which can forecast reservoir inflows
up to 3 to 4 days prior to storm events.
If adopted, the anticipated benefit of these advance releases would be
a more adaptable flood management plan that allows the creation of additional
flood storage area behind the dam. This additional flood storage would
enable the facility to control larger flood events without downstream
flooding while allowing for more flexible dam operations.
Adding this component reduces the flood risk to a 1 in 164 chance in any
Folsom Dam Raise
When combined with the Common Features Project and
modifications to Folsom Dam’s outlet works, raising Folsom Dam 7
feet will reduce Sacramento’s flood risk to a 1 in 213 chance in
any given year.
The work involves raising the concrete section of the
dam and the associated earthen dikes 7 feet and adding larger spillway
gates. These improvements will add 95,000 acre-feet of floodwater storage
capacity to the lake’s current 977,000 acre-foot capacity.
The plan to raise Folsom Dam includes ecosystem restoration and habitat
improvements. Ecosystem restoration involves planting native riparian,
upland, wetland, and woodland vegetation; terracing riverbanks; and controlling
non-native plants at two sites totaling about 620 acres along the lower
American River. Habitat improvement involves mechanization of the temperature
control shutters at Folsom Dam to better control the water temperature
in the river for salmon and steelhead.
The Folsom Dam Raise project includes the design and construction of a
bridge over the American River near Folsom Dam.
Folsom Dam Bridge
The original plan to raise
Folsom Dam included the construction of a $36 million temporary vehicle
bridge to provide a detour for traffic that normally uses the Folsom Dam
Road to cross the American River. (For national security reasons, the
road over the dam is currently closed indefinitely.)
When Congress authorized the Corps to raise Folsom Dam in 2004, it directed
that the bridge be permanent and authorized the additional $30 million
needed for a permanent span.
The location of the bridge and its connecting road alignments are currently
under study. It will take a number of years to complete these studies
as well as the actual design and construction of the bridge and connecting
US Army Corps of Engineers
US Bureau of Reclamation
The Reclamation Board
State of California
Flood Control Agency
Placer County Water Agency
City of Folsom