California firefighters start to tame Yosemite blaze
Authorities remain concerned about threat toreservoir that supplies water to San Francisco
Firefighters in California have reported progress in containing a massive wildfire threatening Yosemite National Park and a reservoir that supplies most of San Francisco's water.
Although ash from the fire reached the Hetch Hetchy reservoir, 274 kilometres east of the city, which serves about 2.6 million people, crews said they were confident the reservoir's infrastructure could be protected. Nonetheless, city officials were busy planning how to divert water from other sources in case fallout from the blaze was to foul the Hetch Hetchy.
The so-called rim fire, the 13th largest in state history, which closed the road into one of the country's top tourist destinations, is now 20 per cent contained, the Los Angeles Times reported, quoting Yosemite fire chief Kelly Martin. That was up from 7 per cent on Sunday.
The blaze has charred nearly 65,000 hectares - including about 8,000 hectares inside the park - and destroyed at least 23 structures, the California Department of Forestry and Fire Protection said.
Crews dropped flame retardants on vulnerable areas. The fire is also threatening two groves of giant sequoia trees and historical structures in the park.
The fire is being tackled by nearly 3,700 firefighters and Highway 120, one of the main routes into Yosemite from the west, remained closed due to the fire. Meanwhile, the park said in an update on its website, "most of Yosemite National Park is not affected by the fire and is relatively smoke-free. The northern part of the park ... has some smoke. Conditions may change if winds shift."
Governor Jerry Brown has declared a state of emergency for San Francisco due to the threat to its water and electricity.
On Monday, the San Francisco Public Utilities Commission was working on contingency plans should ash and other particles from the smoke make water from the Hetch Hetchy reservoir - a source of pride among San Franciscans, who boast of its purity - unfit for consumption, said Charles Sheehan, a spokesman for the agency.
Sheehan said the city had been moving water into several closer reservoirs in its system for some time, starting before the fire, because Hetch Hetchy was full.
"We have several months of water supply locally," Sheehan said. "They are available should we need to switch over."
Smoke particles that settle on the water increase its turbidity, or cloudiness, which cannot exceed levels established by the state based on criteria from the federal Environmental Protection Agency. Sheehan said that there had been no increase in turbidity since the fire began on August 17 and that if levels started to rise, the utility would shift to alternative supplies long before standards were exceeded.
"We're continuously monitoring water quality," Sheehan said.
Water that exceeds turbidity standards would have to be filtered. But large fires in watershed areas can also create longer-term problems for water quality, scientists said.
"The bigger impact is later, when there's rain events," said Sheila Murphy, a hydrologist with the US Geological Survey in Boulder, Colorado. The rain hits the barren, ash-covered slopes, washing the ash into streams leading to reservoirs, and that can make treatment more complex and costly, Murphy said.
Additional reporting by Agence France-Presse