Seed-laced mulch spray bolsters against runoff

12 December 2007 | 04:16 Code : 16231 Geoscience events
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Jose Marin manned a water gun atop a truck and shot streams of a green....

  Jose Marin manned a water gun atop a truck and shot streams of a green-blue mixture 50 feet into the air across a steep, charred mountainside along state Route 76 last week. About five weeks before, the Poomacha fire scorched this section of mountains northeast of the Rincon Indian Reservation and south of PalomarMountain. That was disaster enough for those living there, but with the rainy season, Caltrans contract crews are trying to prevent the next consequence of the fires: erosion of the rising and plunging landscape bordering the winding, two-lane road. Water unchecked by foliage, such as from last week's rains, can carry away nutrient-rich top soil, block the road and clog creeks and streams and threaten aquatic life, said Jay Knapp, a Caltrans civil engineer supervising the contractors' work. The green-blue mixture, called hydromulch, is the key element in the fix, Knapp said. It's a blend of corn and water laced with indigenous weed, grass and flower seeds, including California poppy, deer weed, spreading goldenbush and purple needlegrass. The hydromulch will dry, harden and bind to the soil to prevent erosion and also set the seeds. “Once you get a couple nice long rains, we hope things will take root,” Knapp said. Friday's heavy rains ought to help seeds sprout while the hardened hydromulch captures ash and soot, Knapp said. At sections of roadways in the county that crews have not yet reached, the rain runoff, including ash and soot particles, flowed into streams that could reach lagoons and harm aquatic life, Knapp said. The rains may have been heavy enough that the runoff would be diluted and move through the lagoons and wash out to sea with little harm, Knapp said. Along denuded mountain sides, the hydromulch also lends a surprising, other-worldly look to the wilderness for those not expecting the splash of almost fluorescent green-blue over the burned land and the remaining bushes and sycamores and white oaks. The brilliant color comes from food dye added to the mix so crews know which areas have been seeded, Knapp said. After a few days, it will pale and look like a cover of moss. Pacific Restoration Group Inc. of Corona has been hired to do the work. Crews plan to cover a 10-mile stretch along Route 76 from about

Valley Center Road
, near Rincon, eastward to
Rey River Ranch Road
in about 10 days ending this week, Caltrans spokesman Edward Cartagena said. They expect to blanket about 150 acres with about 300 batches of the mix: each consisting of 12.1 pounds of seed, 1,000 pounds of fiber, 75 pounds of binding emulsion and 3,000 gallons of water. Some areas will have to be resprayed because of Friday's heavy rain and flooding, Cartagena said Monday. In about a year, growth probably will be robust, Knapp said. Without the treatment, it likely would take two years or longer for seeds to reach the area and take hold, he said. In the meantime, erosion could occur. At the base of some of the steepest sections bordering the roadway where runoff could rush, crews also placed stretches of 9-inch diameter tubes of hay bound in mesh to help channel the rainwater and sediment. At the lowest point, sandbags are piled to catch the water and any sediment and hold it there, Knapp said. Noting a spot of a particularly steep charred mountainside, Cartagena said erosion there “could actually destroy the integrity of the roadway.” Crews have completed similar work along a stretch of Interstate 15 from the south junction of
Centre City Parkway
in Escondido to state Route 56, and work is planned for more state routes. The erosion control, separate from repairs of such items as guardrails and signs the fires damaged, costs about $7.8 million, Cartagena said. It's paid for by emergency assistance money the governor approved.

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