Deluges Would Threaten Reservoir

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.

At 3,350 feet, Silverwood is the highest reservoir in the State Water Project and is home to trout, largemouth bass, catfish and bluegill. It attracts waterfowl, raptors and songbirds. Canada geese and an occasional bald eagle also can be seen.

As for any project in the remaining wild lands of the Southland, mulching is a delicate balancing act. Helicopters were ordered to steer clear of the Mojave River fork edge because it is home to the endangered arroyo toad.

But protecting Silverwood Lake is critically important, said Jill Wicke of the Metropolitan Water District, because it helps funnel water from the northern part of the state through the California Aqueduct eastern branch to heavily urban southern parts.

“It’s the way we get state project water through the east part of our system, and it feeds four of our five treatment plants” in Yorba Linda, Riverside, Temecula and Laverne.

While the 78,000-acre-foot reservoir is small compared to others -- basically “a wide spot in the pipeline,” in the words of Wicke -- there currently is no other way to get the water through the eastern branch of the California Aqueduct to Los Angeles-area water districts.

The Metropolitan Water District, which imports water from the aqueduct and from the Colorado River, has the capacity at its treatment plants to handle any additional toxic substances, Wicke said. But smaller districts that get water directly from Silverwood or other sources in the burned areas could be harder hit, she and federal officials said.

Crews began mulching around the reservoir on Nov. 20 and will continue until mid-December unless winds or rain prevent it.

“We’ve had two nice slow, steady rains so far,” Wenstrom said. They were actually helpful because they helped seeds sprout. Tiny shoots appearing on the slopes eventually could help anchor the soil, unless a knockout rainstorm hits before the mulching is done.

“Mother Nature still holds all the cards,” Wicke said.