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Rejecting Rip Rap

The high cost of using hardscape to repair a washed out bank along Moraga Creek recently nudged the East Bay Regional Park District into experimenting with a softer and cheaper approach.

The district initially planned to repair the the 150-feet of damaged creek bank along the popular Lafayette-Moraga Trail with traditional stabilization materials: riprap and concrete. But soil bioengineering, or using plants and plant parts to stabilize banks, turned out to be a bargain in comparison - $35,000 versus $125,000.

Although some engineers are still nervous about soil bioengineering, the park district's Larry Jinkins, a civil engineer with a background in forestry, says riprap's increasing cost, lack of habitat values and aesthetics, and the fact that it can be difficult to work with, convinced him to try willows instead. Jinkins and his crew created willow "poles" (long, thick cuttings with lateral branches removed) from vegetation already growing along the creek, then pounded them two feet into the soil along the bank just before last winter's rains began. The poles have since sprouted and stabilized the washed-out bank, holding fast in the winter storms. At the toe of the bank, workers installed a coir "log" (roll of coconut hull erosion control fabric), and on the upper bank, a mat of the fabric.

The park district's conversion to such greener techniques hasn't stopped with this project. Jinkins has also used soil bioengineering to stabilize failing banks on sections of Dry Creek in Hayward and in the Black Diamond Mines area, where he was concerned about the damage riprap might do to red-legged frog habitat.

In some areas, the district is replacing culverts with articulated concrete blocks, which allow more of the stream to be open. "We're tired of cleaning out culverts, plus they block the free movement of critters up and downstream" says Jinkins. Jinkins is also beginning to use these low-flow-type crossings to replace culverts in more remote areas where people "don't mind getting a little water in their boots." It's likely that the district will expand its use of such solutions. "We've got an enormous backlog of projects - $31 million in deferred maintenance," he says. "Many of them are amenable to our new environment-enhancing technologies."

Contact: Larry Jinkins (510)544-2561

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