A Shady Plan to Save Scarce Water

Aug. 18, 2015
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What’s black and floats, and has 96 million moving parts?

Los Angeles is experimenting with “shade balls” in the Los Angeles Reservoir. The floating high-density polyethylene (HDPE) balls—colored black to make them more resistant to degradation from UV radiation—are intended to slow evaporation from the 3.3-billion-gallon reservoir. They are also supposed to slow the growth of algae and protect water quality. You can see a video here of some of them being released.

What’s black and floats, and has 96 million moving parts? Los Angeles is experimenting with “shade balls” in the Los Angeles Reservoir. The floating high-density polyethylene (HDPE) balls—colored black to make them more resistant to degradation from UV radiation—are intended to slow evaporation from the 3.3-billion-gallon reservoir. They are also supposed to slow the growth of algae and protect water quality. You can see a video here of some of them being released. [text_ad] About 96 million of the 4-inch-diameter balls are being released into the reservoir, which has a surface area of 175 acres. The total cost of the project is about $34.5 million, and the effort is expected to prevent 300 million gallons of water per year from evaporating. The overall benefits are expected to save $250 million a year, the city says. Many of us who’ve been following the issue of plastic debris in the oceans and lakes might balk at the idea of deliberately putting so much plastic into the water, especially because the balls are expected to last about 10 years and then begin to break down into smaller pieces—although presumably the city can remove them before then. The HDPE is approved for contact with drinking water—it’s the same material milk jugs are made of—and the city says nothing will leach into the water. At least one biologist, who was not involved with the project, has questioned the project’s effectiveness: “I don’t believe that in the long run this provides a good strategy in protecting the water. I believe that this will increase evaporations due to a greater surface area as well as providing a great place for bacteria to have a nice environment to grow protected from UV light that kills it. This system will require greater levels of water treatment that in the long run will require more money to ensure public safety,” Nathan Krekula says in this article. One alternative the city considered to slow evaporation was to put a protective cover over the reservoir—which would have had to be done in sections, given its size—but that would have come with a price tag of about $300 million. The shade balls have been used on a smaller scale in other reservoirs and are based on the concept of “bird balls” sometimes used in open waters near airports to discourage waterfowl activity, thus reducing the risk of bird strikes.

About 96 million of the 4-inch-diameter balls are being released into the reservoir, which has a surface area of 175 acres. The total cost of the project is about $34.5 million, and the effort is expected to prevent 300 million gallons of water per year from evaporating. The overall benefits are expected to save $250 million a year, the city says.

Many of us who’ve been following the issue of plastic debris in the oceans and lakes might balk at the idea of deliberately putting so much plastic into the water, especially because the balls are expected to last about 10 years and then begin to break down into smaller pieces—although presumably the city can remove them before then.

The HDPE is approved for contact with drinking water—it’s the same material milk jugs are made of—and the city says nothing will leach into the water. At least one biologist, who was not involved with the project, has questioned the project’s effectiveness: “I don’t believe that in the long run this provides a good strategy in protecting the water. I believe that this will increase evaporations due to a greater surface area as well as providing a great place for bacteria to have a nice environment to grow protected from UV light that kills it. This system will require greater levels of water treatment that in the long run will require more money to ensure public safety,” Nathan Krekula says in this article.

One alternative the city considered to slow evaporation was to put a protective cover over the reservoir—which would have had to be done in sections, given its size—but that would have come with a price tag of about $300 million.

The shade balls have been used on a smaller scale in other reservoirs and are based on the concept of “bird balls” sometimes used in open waters near airports to discourage waterfowl activity, thus reducing the risk of bird strikes.
About the Author

Janice Kaspersen

Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.