West Sacramento levees are no longer sinking as the U.S. Army Corps of Engineers Sacramento District wraps up repairs on nearly a mile of levees near the Yolo Bypass.
The repairs are part of the Corps’ West Sacramento Project, a joint effort with the West Sacramento Area Flood Control Agency and the Central Valley Flood Protection Board to improve the levees surrounding West Sacramento.
Signs of slumping, or sinking, became increasingly evident since high water saturated the levees in 2006.
The problem was a high water table, said Greg Sokolis, quality assurance representative. A high water table means the underground water is very close to the surface. In this case, it was within approximately five feet of the existing landside levee.
The Corps began necessary repairs on 2,000 feet of levee in July 2011 to restore its full flood risk reduction capability. After excavating the landside of the levee, construction crews installed a gravel drainage system in the toe, or bottom, of the levee, replacing the compacted soil before rebuilding the levee.
“The significant moisture of the high water table caused the landside levee to slump because it no longer had a solid foundation,” said Sokolis.
The solution was a gravel drain. The drain, along with a system of pumps, will funnel water seeping into the levee directly into the bypass. With the new gravel drain in place, high groundwater should no longer be a problem.
“Installing the drain will help dry out the levee foundation, so there will not be moisture to cause additional slumping in the future,” said Sokolis.
The site has also been seeded with native grasses to help prevent erosion and will be monitored until the grass grows in.
This was the second levee site along the Yolo Bypass the district has repaired in recent years.
In 2009, the Corps repaired slumping along approximately a 400-foot stretch of levee just south of the current site.
“These levees were approaching a level where they could no longer do their job,” said Beth Henderson, project manager. “Now they’re ready to continue reducing the flood risk for West Sacramento.”
Dredging Today Staff, February 2, 2012; Image: usace