Even as firefighters battle a gigantic wildfire in and around Yosemite National Park, environmental scientists are moving in this weekend to begin critical work protecting habitat and waterways before the fall rainy season beings.
Members of the federal Burned Area Emergency Response team will begin hiking the rugged Sierra Nevada terrain before embers cool as they race to identify areas at the highest risk for erosion into streams, the Tuolumne River and the Hetch Hetchy Reservoir, San Francisco's famously pure water supply.
Now the third largest fire in California history, the inferno that started Aug. 17 when a hunter's illegal fire swept out of control has burned 385 square miles of timber, meadows and sensitive wildlife habitat. It has cost $81 million to fight, and officials say it will cost tens of millions of dollars to repair the environmental damage alone.
About 5 square miles of the burned area is in the watershed of the municipal reservoir serving 2.8 million people -- the only one in a national park.
"That's 5 square miles of watershed with very steep slopes," said Alex Janicki, the Stanislaus National Forest BAER response coordinator. "We are going to need some engineering to protect them."
So far the water remains clear despite falling ash, and the city water utility has a six-month supply in reservoirs closer to the Bay Area.
The burned area represents 1 percent of the Hetch Hetchy watershed, said Tyrone Jue, spokesman for the San Francisco Public Utilities Commission. He said that because the sheer walls around the reservoir are granite with little vegetation, he believes that little stabilization work will need to be done.
However initial satellite imagery and recent visits to the burned area show that the Tuolumne Canyon above the reservoir "burned pretty hot," Janicki said.
Jue said the utility will await word from the BAER team, which will be made up of hydrologists, botanists, archeologists, biologists, geologists and soil scientists from the U.S. Forest Service, Yosemite National Park, the Natural Resource Conservation and the U.S. Geological Survey.
The team also will look at potential for erosion and mudslides across the burn area, assess what's in the path and determine what most needs protecting.