San Francisco officials said they increased transfers from the city’s main source of drinking water in Yosemite National Park to other reservoirs as a fast-moving forest fire showered the lake with ash.
The fire, which had scorched an area larger than the city of Chicago, was less than two miles from the Hetch Hetchy Reservoir yesterday. The lake, about 160 miles (260 kilometers) east of San Francisco, provides 85 percent of the city’s water and generates hydroelectric power for San Francisco International Airport, San Francisco General Hospital and the city’s transit system.
The San Francisco Public Utilities Commission boosted transfers to other reservoirs to 302 million gallons a day from 275 million gallons, said Charles Sheehan, a spokesman for the agency. The commission was already moving water before the fire started because Hetch Hetchy was near capacity, he said.
“There is ash all throughout the region and there is ash at the reservoir but the condition of the water is mostly clear,” Sheehan said yesterday in a telephone interview. “Water quality has not been affected and we continue to deliver water from Hetch Hetchy.”
The ash on the surface of the reservoir had no impact on the water in the system because the intake is located at a depth of 260 feet, according to the utility. The agency said turbidity, the cloudiness of the water from suspended particles, was within normal operating parameters.
The Rim Fire grew yesterday to 161,000 acres (65,150 hectares) or 250 square miles, and was 20 percent contained, according to the California Department of Forestry and Fire Protection, known as Cal Fire. More than 3,700 personnel were fighting the blaze, which erupted Aug. 17 and threatened 4,500 structures.
The Hetch Hetchy system serves 2.6 million water customers in San Francisco and the Bay Area. Water flows from the reservoir, more than 3,000 feet above sea level in the Sierra Nevada mountains, by gravity through tunnels to San Francisco.
“This is something we typically do, transferring water from one reservoir to another and we were doing this prior to the fire,” Sheehan said. “We increased the water transfer from Hetch Hetchy but it was already ongoing.”
The Rim Fire is so far the 13th largest in the state’s history, said Dan Berlant, a Cal Fire spokesman.
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