As boaters, swimmers, anglers and others splashed around in Lake Shasta this week, all around them millions of gallons of the water were disappearing into thin air through evaporation.
And not just a little bit of evaporation. The lake can lose more than 200 million gallons of water each day to evaporation during the summer.
Put into perspective, in two months during the summer, more water evaporates off Lake Shasta than all the water used by city of Redding water customers in an entire year.
“That’s a lot of water,” said Mark Williams of Martinez, who was visiting Shasta Dam this week with his family. “That would fill a few toilets.”
Even though it might seem like a lot of tiny water droplets floating into the air, getting it to stop may not be so easy.
“We’re in a hot climate. It’s totally expected,” said Don Bader, area manager for the U.S. Bureau of Reclamation, which manages Shasta Dam.
“There’s not a solution for mitigating that, that I’m aware of,” Bader said.
There may not be a solution, but there are people thinking about how to tackle evaporation on lakes.
“This is certainly a problem that the water resources engineering community has dealt with,” said Sally Thompson, an associate professor of environmental engineering at the University of California at Berkeley.
However, some of those solutions might test the public’s tolerance for what they are willing to have put in their water and what they are willing to pay to reduce evaporation, Thompson said.
Researchers and experts in atmospheric science, hydrology, land use and water management held a conference in 2015 on the problem of water evaporation on reservoirs in the West.
Researchers at the University of Colorado say evaporation in the Colorado River basin, which includes Lake Mead and Lake Powell, reaches 500 billion gallons a year — 10 percent of the river’s natural flow.
Some of the ideas floated included covering lake surfaces with thin films of organic material and using reflective plastics or lightweight shades. Reservoirs could be moved underground or moved to higher elevations to reduce evaporation, according to an article issued by the University of Colorado.
During the most recent drought, the city of Los Angeles experimented with covering a reservoir with plastic balls that floated on the water, reducing evaporation by sunlight.
The article did not mention the costs of the various proposals. Covering a 46 square-mile lake with a tarp-like material or plastic balls could be quite expensive, Thompson said.
And as for pouring a chemical onto the water to create a film to retard evaporation, that solution might not be tolerable from an environmental point of view, she said.
Bader said that when he was working at Hoover Dam on the Colorado River, someone proposed floating ping pong balls on Lake Mead to shade the water and reduce evaporation. It didn’t happen, he said.
Cost is an issue, Thompson said. After all, water isn’t free. City of Redding water users pay a basic rate of $1.357 per 748 gallons used.
When 210 million gallons of water evaporates and floats away in one day that represents about $381,000 worth of water at Redding’s retail rate.
And the bureau is in the business of selling water. Redding and many other water agencies in the North State get their water from the federal agency.
Bader said understanding evaporation levels is an important part of keeping track of how much water is coming into and going out of Lake Shasta.
Understanding evaporation on the lake begins with a pretty simple measuring process, he said. The bureau keeps a tub of water, 6 feet in diameter, near the dam.
Each morning they fill the tub with water and the following day at the same time measure how much water has evaporated. From there they multiply the amount of water loss times the surface area of the lake to arrive at how much water has evaporated.
The evaporation rate on the lake in July has varied from 313 cubic feet per second to 408 cfs.
On July 10, the lake lost 330 cfs to evaporation, or more than 215 million gallons of water. Bader said that is just a fraction of the amount of water flowing into the lake daily replacing what is lost through evaporation.
The bureau measured 3.5 billion gallons of water flowing into the lake on July 10.
“It’s hard even to get the concept of how much water that is,” Bader said.
