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Home » News/Events » The Journal » Vol. 14 Issue 1 » Restoring Floodplains at Setback Levees

Restoring Floodplains at Setback Levees

  • Irv Schiffman, River Partners Board of Directors Chair

Bear River setback levee in 2009, showing the older orchard, which has since been replaced with a riparian forest.

In recent years, River Partners has been restoring large swathes of floodplain habitat in conjunction with the construction of setback levees by the Army Corps of Engineers and the Three Rivers Levee Improvement Authority. These setback levees replace levees built years before, many of which are considered historic resources.

On California’s Feather River, for example, levee construction began in the mid-1850s to remove sediment and save cropland. Hydraulic mining washed millions of tons of silt into the riverbed, and levees were built very close to the river channel to keep water velocity high, thereby removing the sediment. To protect the extremely fertile soil of the Feather River floodplain, farmers built levees right on the riverbank to enable them to plant valuable crops as close to the river as possible.

Levees placed adjacent to rivers constrict water flows and are vulnerable to failure. Levees are also often built over incoming streams, which allows water to seep under the levee, causing a levee “boil” to form which damages the levee. Levees can be overtopped during flood events that are larger than the levee system was designed to contain. Levee failures in 1986 along the Yuba River flooded south Yuba County and caused hundreds of millions of dollars in damages. Levee failures on the Bear and Feather Rivers in 1997 caused devastating flood damages as well.

Setback levees represent a modern approach to flood control. They’re built away from the river channel, with the natural floodplain between the levee and the river. Setback levees allow the river to meander along its natural floodplain, with floodwaters spreading out and slowing down over a wide area. This increased water retention relieves pressure on narrow levees upstream while helping to lower the elevation of the river downstream. Setback levees are more resilient than traditional levees, which is even more important with threats of massive rain and flooding brought on by climate change.

Beyond their flood control benefits, setback levees provide increased opportunity for significant environmental enhancement consistent with federal and state mandates that flood reduction be combined with ecosystem restoration.

The setback levee built at the confluence of the Feather and Bear Rivers enabled River Partners to restore wildlife and habitat in the 639-acre setback area through the planting of one hundred thousand shrubs and trees. Fish have more areas in which to feed or be protected from predators on this expanded floodplain. In addition, the recharge area for groundwater is also greatly increased, providing additional benefits.

The setback levee on the Feather and Bear Rivers held up very well during last winter’s rain storms and the Oroville Dam disaster while the base of more traditional levees located close to the river showed signs of erosion.

We are now at work on the Sacramento River restoring habitat on the expanded floodplain created by the 6.8 mile Hamilton City setback levee being constructed by the Corps of Engineers. River Parters is happy to be involved in such innovative, multi-benefit levee setback projects.

The above article originally appeared in the Fall 2017 issue of the River Partners Journal.