The rainy season is upon us and that means it’s time for the Sacramento District of U.S. Army Corps of Engineers to stop all of its levee work around the Sacramento and American rivers.
“We can’t work on levees in the wintertime because of runoff,” says Tom Karvonen, project manager for Sacramento River Bank Protection Project (SRBPP). “When it’s raining it’s impossible to do the storm water protection required to keep soils from running in the river.”
Karvonen, whose district is currently working on about eight projects or roughly 450,000 lineal-ft of levee improvements around the Sacramento River basin, says his present concern is the construction of a setback levee along South River Road in West Sacramento.
Known as River Mouth 57-2, the project includes a new levee that will be set back 250 ft from the old existing levee. The new structure will be 15 ft high, 2,200 ft long, and have up to a 75-ft-deep seepage cutoff wall in its center to strengthen the levee and help prevent water from leaking through or under.
“River Mouth 57 – 2 is unique because most of our sites are rock and erosion repair, but on this project we had the opportunity to do a set-back levee,” says Karvonen. “This type of levee takes some of the pressure off the river because it increases the width of the flood plain, and at same time allows for natural vegetation to develop and recapture some of the flood plain.”
He says the project is challenging because of different soil conditions such as clay and sand that can affect water flow. “We want to make sure that under-seepage and through-seepage is addressed in all levee repairs, and that is something we’ve gained a greater understanding of over last 10 or 15 years,” he says.
Construction on the site is currently shut down for the winter, but the existing levee remains in place to protect against any risk of flood from rain. The $3 million project is a joint effort between the Corps and the Central Valley Flood Protection Board. San Francisco-based Yerba Buena Engineering and Construction is the contractor. Work is scheduled to complete in fall of 2014.
Karvonen says the new levee is up and the main construction is complete on the project and when work resumes in spring they will conduct tests to address any mitigation requirements, along with any under- seepage and through-seepage issues that might arise.
This is the second time the project will be carried over through the rainy season. In 2011, wet weather conditions and high water levels delayed levee construction until September, which was too far into the construction season to be finished before winter flood and environmental preservation deadlines.
The SRBPP is a continuing construction project authorized by Section 203 of the Flood Control Act of 1960. The purpose of this project is to provide protection to the existing levee and flood control facilities of the Sacramento River Flood Control Project (SRFCP). To date, work has been carried out in two phases, with a total of about 837,000 feet of bank stabilization.