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American River Watershed Project




American River Common Features Folsom Dam Modifications Folsom Dam Raise Folsom Dam Bridge
American River Watershed map text American River Watershed Project map
American River Watershed Project map


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.


River Channel

Folsom Dam Modifications

Outlet Before and After
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 River.

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 one year.

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 given year.



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.

Folsom Dam Raise

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 roadways.


US Army Corp of Engineers
US Army Corp of Engineers
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US Bureau of Reclamation
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The Reclamation Board
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Sacramento Area
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Placer County
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City of Folsom