US Army Corps of Engineers
South Pacific Division

Sacramento District’s Hamilton City project combines flood management with ecosystem restoration

Published July 24, 2019
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Thousands of native plantings were installed as part of the revegetation portion of the project. Overall, construction of approximately 6.8 miles of setback levee combined with the plantings will create more than 1,500 acres of riparian habitat for birds and critters along the Sacramento River in Hamilton City, Calif. (U.S. Army photo by Tyler Stalker/Released)

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The current, degraded levee known as the “J levee,” separates privately owned orchards (left) and natural floodplain (right) near Hamilton City, Calif., April 14, 2011. A mature elderberry plant on the far right is home to the valley elderberry longhorn beetle, which has been listed as a federally threatened species since 1980. (U.S. Army Photo by Todd Plain/Released)

The Hamilton City Flood Damage Reduction and Ecosystem Restoration project is the first of its kind in the nation and earned the U.S. Army Corps of Engineers Sacramento District an American Society of Civil Engineers award for Small Flood Management Project of the Year.

Approximately 90 miles north of Sacramento, Hamilton City sits in a low lying area behind a bend in the Sacramento River. For years, the town’s only defense has been the J levee – an un-engineered earthen levee built in 1904 – which provides such minimal benefit that there’s about a 10 percent chance of flooding every year.

The town has long been at risk. There’s been five recorded instances when flood fighting prevented major flooding. The town was evacuated six times during a 15-year period between 1983 and 1998. And portions of the town did, in fact, flood in 1974.

For years the small town of roughly 2,000 people pursued federal help, hoping to secure a Corps of Engineers federal project to build a new levee system. However, the combination of the town’s small size and the cost of a federal flood risk management project dwarfing the value of nearby property and structures made it nearly impossible to justify a project that warranted federal participation.

That didn’t stop the community from continuing its pursuit to replace the aging J levee.   

Approximately 30 years after beginning to look for opportunities to reduce Hamilton City’s flood risk, the solution came about in a first-of-its-kind project that aligned flood risk management with ecosystem restoration.

The formation of strong partnerships led to a willingness to work together on a multipurpose project. The community wanted to create flood relief for the people of Hamilton City; The Nature Conservancy wanted to find a way to restore native habitat; Area farmers wanted to reduce damages from flows that scoured their property along the edge of the river. The Hamilton City Flood Damage Reduction and Ecosystem Restoration project was able to address these problems with one solution.

 “The Hamilton City Flood Damage Reduction and Ecosystem Restoration project focused on measures that provide both flood risk reduction and ecosystem restoration benefits, establishing a restored riparian corridor along the Sacramento River,” said Bryon Lake, Hamilton City Project Manager.

The project, authorized in the Water Resources Development Act of 2007, will cost approximately $91 million to build 6.8 miles of setback levees and restore nearly 1,500 acres of riparian habitat, reconnecting the floodplain to the Sacramento River.

Rather than build up levees along the river, setback levees are placed further from the river and have a better foundation, allowing the river to expand more naturally during times of increased water flows. Setback levees also create space to allow for more habitat within the floodway.

“The key feature is the setback levee. Building a new levee on sound foundation significantly reduces risk of flooding to the community,” said Alicia Kirchner, Sacramento District’s Deputy Engineer for Programs and project Management. “Building that same new levee set back from the Sacramento River creates space to restore native floodplain habitat and more natural floodplain function. One feature, yielding two types of benefits resulted in a project that had funding priority.”

During any substantial increase in river flows, the river will now widen into the restored floodplain channel rather than flow over, or through the levee, spilling into the town.

Another benefit is that riparian habitat now has connectivity up and down the river, providing wildlife increased native riparian habitat. The first phase of the project was completed five months ahead of schedule, and area wildlife has already benefitted from the restoration.

“This project is special. Everyone came together at the right time and place, and it is an example of the best that collaborative project planning has to offer,” said Kirchner.