A strange strategy is reported by the California Water Blog.
Visitors to Yosemite’s iconic Hetch Hetchy reservoir are doing a double-take. Instead of seeing the majestic backdrop of the Sierra Nevada reflected in the pristine mountain water, they are now greeted by millions of black balls that cover the surface.
After four years of record-setting drought and statewide low reservoir levels, concerns developed about evaporation losses and the drought’s effect on water quality for San Francisco’s premier water source. Plans to protect the drinking supply and reduce reservoir evaporation began in 2014, when another year of dry conditions was predicted with no end to the drought in sight.
Inspired by similar measures taken at Ivanhoe Reservoir and the Los Angeles Reservoir in Southern California, 96 million black balls were poured into Hetch Hetchy to limit sunlight penetrating the water surface. Limiting sunlight on the reservoir will reduce both evaporation and the growth of potential contaminants. Given the emergency measures required to mitigate the drought’s effects on municipal water supplies, covering the reservoir was deemed more cost-effective and easier to achieve than constructing additional treatment facilities or implementing additional water conservation actions.
Milly Pore, a spokesperson from the San Francisco PEC, explained, “We are facing long-term concerns about water quality and water supply reliability and estimated that we could save a lot of water and water quality this way.”
“It’s an eye-sore,” said Louie Swan, a recent visitor to the reservoir. “It looks like an oil slick. If this is the best we can come up with to fix water quality, we might as well take the dam down altogether.”