Over the last few days, the Los Angeles Department of Water and Power released 96 million black, plastic shade balls into a reservoir at the Van Norman Complex in Sylmar, which spread out in a thick layer covering every square inch of the 175-acre water surface. The 4 inch balls are weighted down with water inside to keep them in place. The balls protect the water against dust and rain, birds and wildlife, and chemical reactions caused by the sun. It is also expected to save about 300 million gallons of water from evaporating each year, enough to provide drinking water for 8,100 people for a full year.
Shade balls are also cost effective. Each ball cost only 36 cents, bringing down the entire cost of the project to less than $35 million. Covering the reservoir using traditional means would have cost the department $300 million. The balls last about 10 years, after which the Water Department expects them to be recycled and replaced.
Shade balls were first tried by Los Angles in 2008 when they covered the Ivanhoe Reservoir (some spectacular pictures in that link) with 400,000 black balls. The department detected high levels of bromate, a carcinogen that forms when bromide and chlorine react with sunlight, in the reservoir’s water. Bromide is naturally present in groundwater and chlorine is used to kill bacteria, but sunlight is the final ingredient in the potentially harmful mix. When the Department of Water Protection realized the problem, they began construction of a new underground reservoir in Griffith Park, but while the new facility was being built they had to determine a way to keep the sunlight out of the water.
They explored options such as tarps and metal coverings but they were either too expensive or will take too long to install. Then one of their in-house biologists suggested "bird balls" which are commonly used by airports to prevent birds from congregating in wet areas alongside runways.
The Los Angeles Department of Water now uses shade ball covering in four reservoirs.
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