Levees don’t help much when the floods come strong and the crucial paragraph from this article is: “I think the community in the long term needs to be looking at an even higher level of protection -- at the 500-year level," Hess [Army Corps Regional Chief] added. "We try to do designs that are expandable to provide a higher level of protection if the community wants that. Doing a floodwall would make that difficult."
The only option providing 500 year flood protection is the Auburn Dam.
An excerpt.
Federal levee proposal wouldn't save old oaks
By Matt Weiser - Bee Staff WriterPublished 12:00 am PDT Tuesday, September 12, 2006
Federal officials have concluded that a conventional levee is the safest way to improve one of the most vulnerable points on the American River, a blow to some residents who hoped to save heritage oak trees at the site.
The U.S. Army Corps of Engineers announced Monday its preferred solution for the so-called Mayhew levee is a standard earthen embankment with a broad 3-to-1 slope along the river. Only this design, it found, can withstand high river flows without erosion and seepage.
Some residents of the Butterfield-Riviera East neighborhood wanted a steeper levee profile with a 2-to-1 slope to preserve more of the parkway. They also wanted a 700-foot concrete floodwall in one section, instead of a levee, to save three old oak trees.
The $7.2 million project is slated to begin construction next spring and be finished by December 2007. The corps presents its findings today at a community meeting at 7 p.m. at Erlewine School, 2441 Stansberry Way.
"I told my folks, 'This is a poor design,' " said John Hess, regional chief of geotechnical engineering for the corps, referring to the floodwall proposal. "This has too much risk for the community and we should not be going this way."
The 4,300-foot-long levee, along Mira Del Rio Drive near Rosemont in unincorporated Sacramento, is the only American River levee that would be overtopped if river flows reach 160,000 cubic feet per second. That is the target flow for attaining 200-year flood protection in Sacramento, together with improvements at Folsom Dam.
The current levee does not meet federal standards and does not provide even 100-year protection for the neighborhood. If the levee overtopped, estimates show flooding would be limited to about 300 nearby homes. But higher flows could cross Folsom Boulevard and then flood other parts of Sacramento.
The plan to raise the levee would contain those flows and also achieve 100-year protection for the neighborhood, saving homeowners on flood insurance.
Some residents felt a narrower levee, with a partial floodwall, could achieve the same results. The Corps of Engineers estimates this project could cost an additional $3 million, but could save three majestic oak trees near the levee that are more than 100 years old. It would also disturb less of the parkway.
Joe O'Connor, who has monitored the project for the neighborhood group and favored the floodwall option, declined to comment until he has more detail.
Stein Buer, executive director of the Sacramento Area Flood Control Agency, said the corps ruling is significant. His board and the state Reclamation Board will cast crucial votes on the project in December.
"At the staff level, we will be supporting the corps' decision," Buer said. "There's likely to be disappointment in some quarters, but I think what you'll find is that the corps has thought very carefully about this."
Hess said a floodwall could become a path for underseepage during a flood. It also presents challenges during a flood fight, because the wall limits vehicle access and it is more difficult to raise with sandbags if needed.
And in the event of overtopping, he said, the wall presents an erosion and failure risk, as seen in New Orleans after Hurricane Katrina.
"I think the community in the long term needs to be looking at an even higher level of protection -- at the 500-year level," Hess added. "We try to do designs that are expandable to provide a higher level of protection if the community wants that. Doing a floodwall would make that difficult."
