Rim fire threatens water supply

Giant wildfire threatens San Francisco's water reservoir

August 28, 2013

"The weather is just not cooperating with us"

— Lynn Tolmachoff

The giant wildfire burning in and around Yosemite National Park struck the shores of the Hetch Hetchy Reservoir Tuesday, threatening the famously pure mountain water that feeds the taps of 2.6 million Bay Area residents. The California wildfire has grown rapidly to become one of the biggest fires in the state’s history.

Nearly 4,000 firefighters were working in Yosemite National Park as the Rim fire blackened the southern and western shores of the 117 billion-gallon Hetch Hetchy Reservoir, which provides 85 percent of San Francisco’s supply.

Last week, Gov. Jerry Brown issued a states of emergency for San Francisco, which frees up money to fight and help recover from the blaze. The state of emergency remains in place, including the City of San Francisco, because of the threat to the reservoir.

So far, despite ash raining down on it, the water quality from the reservoir is still fine. Water is drawn from 260 feet below the surface to avoid unwanted debris.

Wildfire experts say problems for San Francisco’s water agency may come later. Hetch Hetchy’s pristine waters will be vulnerable to eroding hillsides as the fire leaves behind torched soil that can’t absorb autumn rains and leveled forests that no longer anchor steep mountain slopes.

“Landslides are absolutely a concern,” said Keith Gilless, dean of the College of Natural Resources at UC Berkeley. “Trees promote stability, and if you lose the trees you may get mass movement of the soil. And if the fire is a really not one and it scorches the soil surface, the soil becomes less penetrable.”

By late Tuesday, the fire had scorched 184,000 acres- about 287 square miles. Firefighters reported making moderate progress Tuesday, estimating the blaze as 20 percent contained.

“The weather is just not cooperating with us,” said Lynn Tolmachoff, a spokeswoman for the California Department of Forestry and Fire Protections, citing gusty winds and warm temperatures.

About 4,500 structures are threatened by the fire, and at least 31 residences and 80 other structures have burned as the fire continues to grow, including 1,600 homes in Tuolomne City. Air quality north of the fire, in the Lake Tahoe basin and in the cities of Reno and Carson City, is not good.

Yosemite National Park remains open and, for the most part, the fire and smoke are heading away from the park due to southerly winds.

Officials said the cost of the firefight has swelled to more than $27 million. They said it topped $20 million by Monday.

The blaze started in a remote section of the Stanislaus National Forest in Northern California’s Sierra Nevada range Aug. 17. The fire’s cause is not known.

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