Seepage found in levees

The state is finding some leaky spots in the ring of embankments that protect Marysville from flooding, the Marysville Levee Commission heard Tuesday.

Potential for underseepage — the flow of water under a levee — has been found at nearly all the locations the state Department of Water Resources evaluated, said Larry Dacus, an engineer with MBK Engineers, of Sacramento. He gave a report of the preliminary results from the state study.

"There are some underseepage issues out there," said Dacus.

Seepage refers to the flow of water through or under a levee. Too much of it can undermine the earthen embankment and cause it to fail during a flood.

In an interview, Dacus said about 70 percent of the Marysville levees will probably need some kind of work to fix seepage problems.

While that does not mean the levees will fail — they have withstood a number of floods despite the problems —it does mean the trouble spots would have to be repaired to meet new standards for levees.

New slurry walls would be the most likely fix because development rules out other options that would require too much land to be purchased.

More information is coming out on Marysville and other areas as part of a $35 million Department of Water Resources study of levees protecting urban areas.

Contractors for the DWR have drilled 61 holes in the top of Marysville levees and taken core samples in what is possibly the most extensive study to date. Eight electronic devices, called piezometers, have been installed to monitor water flow.

The next phase of work has started in which crews are taking core samples from the levee toe to verify the early results. A final report is expected by September or October of this year.

There are no estimates yet of how much it would cost to fix Marysville's levees to bring them up to the goal of protection against a 200-year flood, which has a 0.5 percent chance of occurring in any given year.

"It does give us some better preliminary information on the scope of work so we can start looking at some of the dollars," said David Lamon, the city services director.

The issues that have been found so far may not be new — a previous examination of the levees as part of an earlier Yuba Basin Project found about the same magnitude of problems in the 7.6-mile ring of levees surrounding the city.

State studies have also been examining Marysville levees for stability, erosion, settling and seismic analysis. The most serious problems so far, aside from seepage, are from possible erosion along the section that borders the Yuba River.

An examination of the patrol road to Hallwood, or spur levee, has found it is not high enough to block a 200-year flood, is not well maintained, and has seepage problems.

Contact Appeal-Democrat reporter John Dickey at 749-4711 or jdickey@appealdemocrat.com.