Racing to protect a reservoir that is a key link in Southern California's water supply, federal helicopter teams are dropping straw by the ton on slopes severely burned in October's catastrophic wildfires around Silverwood Lake in the San Bernardino Mountains.
Officials want to stabilize the slopes before heavy winter rains, which could trigger large-scale erosion of ash, silt and potentially toxic compounds into the lake.
The reservoir provides drinking water for 12 million people, said Matt Mathes, spokesman for the U.S. Forest Service in California. "There are going to be a lot of mudslides, and a lot of sediment is going to wind up in the reservoir if we're not careful."
Heavy silt and ash could choke out wildlife and reduce the reservoir's capacity, officials said. Runoff into regional water supplies could contain high concentrations of naturally occurring lead, uranium and other substances, a report by the Santa Ana Watershed Project Authority concluded.
Keeping remaining soil in place on denuded slopes would help, officials said. Slopes above some foothill neighborhoods in San Bernardino also are receiving aerial mulching.
"The timeline is to get it done before the first severe rainfall," said Ruth Wenstrom, a spokeswoman for the San Bernardino National Forest.
Pallets of rice straw are being trucked in from the Central Valley to two rough-hewn helipads. Rice straw is ideal, Wenstrom said, because it sops up moisture quickly. After the copters drop the bales, which can weigh as much as a ton, ground crews chop and spread the straw.
But mulching works only on slopes with inclines of less than 55%, meaning that many of the burned areas, which are the steepest and most erosion prone, can't be treated.
Still, the $675,000 project is the priority in the $2-million worth of emergency rehabilitation work being done since the Grand Prix and Old fires burned more than 185 square miles, including 4,500 acres of slopes that drain into the Mojave River, one fork of which drains into Silverwood Lake.
The lake, owned by the state Department of Water Resources, is a popular fishing and camping destination. Federal authorities also worry that heavy rains could cause campground sewage to overflow into the lake, said Todd Ellsworth, leader of the federal Burn Area Emergency Response team.
