Alternatives to Concrete Creek Banks Show Promise

Although limited to 1,500 feet along one creek, an experiment with environmentally friendly alternatives to concrete showed promise in preventing erosion--despite this year’s torrential winter runoff, officials say.

The Ventura County Resource Conservation District, an agency dedicated to preventing erosion of agricultural land, launched an experimental project to show landowners there are softer alternatives to traditional riprap-and-concrete structures to keep banks from washing away.

After the recent heavy rains, the results are in: The experimental techniques, suitable only for relatively small channels, worked.

The project area is a 1,500-foot stretch of creek running through a Long Canyon lemon orchard off Stockton Road, about five miles west of Moorpark.

District employees laid giant mats of woven fabric over soil planted with native grasses and flowering plants, which grow through the protective layer of material. Fifteen types of mats, blankets, plastic webbing--some of them biodegradable, and of varying widths--were installed.

“We’ve been holding our breath,” said Peggy Rose, district project manager. “When we started this project, we didn’t realize it would be an El Nino winter.”

The grasses have a dense root structure that binds to the soil, and coverings were anchored to the soil with giant metal staples. The most lightweight method employed a straw covering and the most weather-resistant method used small cement slabs spaced so grass could grow between them.

Standing in the now dry channel, decked with 2-foot-high green grass and purple lupine, Rose described the creek bed before the project as “a mess.” Trees were falling into the channel and banks were ineffectively lined with sheet-metal walls.

The channel’s 20-foot depth, its steep grade, and its almost vertical sides contributed to increased water velocity and erosion.

To slow the water, workers brought in tons of soil to reshape the channel. Its banks were re-formed into a gentler slope. Along its length, the floor was raised and graded to resemble an elongated staircase. The configuration, sometimes called “check dams,” consists of small sections of grouted rock separating flat stretches of the creek floor.

Rose pointed to sections of the bank left untouched to show a before-and-after contrast. Water draining from the orchards cut deep gullies in the bank walls, and raging creek flows took out bathtub-sized portions of soil in some places.

“It’s a world of difference,” Rose said, emphasizing that these methods won’t get landowners in trouble with the state Department of Fish and Game or the U.S. Army Corps of Engineers, regulatory agencies charged with protecting waterways and wetlands habitat.

The environmentally sensitive techniques actually create habitat, according to Peter Brand, a watershed restoration manager with the California Coastal Conservancy, which contributed part of the $350,000 cost of Rose’s demonstration project.

Indeed, birds, ladybugs, bees and other insects are already living in and benefiting from the flourishing flora.

Brand also likes the price tag of the methods.

“It’s affordable and farmers can do it themselves with their own labor,” Brand said. “They can’t wait for the government to find the money to solve these kinds of problems.”

As effective as they are in the 40-foot-wide test channel, mat-and-grass stabilization methods would not work in larger channels with faster-moving water. Calleguas Creek’s main stem, from the Ventura Freeway to the ocean, is completely washed out after heavy rains, Rose said, and would not benefit from “soft” flood-management practices.

Brand added that it may be wise to widen those types of waterways to give flood waters “more room to move,” and that building structures or laying roads to the edge of the flood plain is not a good idea.

Taking a look at the entire Calleguas watershed, of which the Long Canyon drainage is a part, Brand said erosion upstream causes flooding downstream and the best place to start solving problems is in the upper watershed.

Rose said she is scheduling tours of the project site and plans to host slide presentations and workshops for landowners and agency officials. Those interested can call the Ventura County Resource Conservation District at 386-4685 for more information.