Sacramento is among the most at-risk cities in America for catastrophic flooding. An aging system of dams, weirs, bypasses and levees work together to reduce flood risk for the city. But that system, just like a chain, is only as strong as its weakest link, and needs comprehensive modernization.
This year, the U.S. Army Corps of Engineers Sacramento District continued to make progress strengthening those links by fixing gaps in seepage cutoff walls in the lower American River’s levees. The Corps built more than 20 miles of seepage cutoff walls into American River levees a decade ago, but work was set aside for later—leaving gaps—where complicated encroachments exist such as utilities, power lines and bridges. Only a handful of these complex gap sites remain, with final construction slated to wrap up in 2016.
One of the fixes required building a seepage wall beneath one of Sacramento’s busiest thoroughfare, the Watt Avenue bridge. Crews worked through the night to minimize traffic disruption, and with the help of California Highway Patrol, temporarily closed up to three lanes at a time so they could maneuver the drill-rig back and forth across the bridge. To install the wall, crews cut holes in the bridge and then lowered the drill through the holes to reach the levee underneath. Using this jet grout method, the drill injects cement-like slurry into the bore holes, forming columns in the levee. In all, 40 columns of grout were installed side-by-side inside the levee to form a continuous barrier against seepage, with a dozen of those columns directly beneath the Watt Avenue bridge.
This same jet grout method and contractor were also tapped for $3.9 million of similar work inside the E.A. Fairbairn Water Treatment Plant, adjacent to California State University-Sacramento. This year’s jet grout construction at two levee sites inside the plant’s grounds is expected to be complete in January.
The third project scheduled for completion in 2013 was a $3.9 million levee project along the north bank of the American River, just east of its confluence with the Natomas East Main Drainage Canal in north Sacramento. This section, called NEMDC south, was complicated by buried utilities and an inactive railroad line. The district completed construction of 3,300 linear feet of seepage cutoff wall in October. In the coming years, two nearby smaller sections, called NEMDC north and the NEMDC extension, are in line for similar construction.
Two sites originally scheduled for 2013 are now scheduled to be completed in 2014. Fixing these lower American River levee gaps, one in Carmichael and the other in the River Park neighborhood, will complete the construction contracts awarded in September 2012, totaling more than $16.2 million.
While construction of cutoff walls in American River levees is nearly complete, and has already greatly reduced the risk of seepage, much work remains to be done in Sacramento to modernize its flood control infrastructure. The district is also working to complete a comprehensive study that investigates improvements to the flood risk reduction system throughout the city called the American River Common Features General Re-evaluation Report. A draft report, along with a recommended plan for improvements, is scheduled to be released for public comment in 2014.
Press Release, January 2, 2014