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Monday, June 30, 2014

Could Limiting Evaporation Help With Drought?

Water levels have dropped at Lake Travis because the drought, May 16, 2011. (Lower Colorado River Authority)

Water levels have dropped at Lake Travis because the drought, May 16, 2011. (Lower Colorado River Authority)

Most of the southwestern U.S. is in the midst of some level of drought. Parts of California, Nevada, Oklahoma and Texas are all seeing extreme drought, as rainfall and winter snowpacks have been far below average.

One of the biggest factors affecting water supplies in these hot, dry places is evaporation. Reservoirs can lose as much water to evaporation as the water that’s actually pumped out of them for drinking water.

Can anything can be done about it? From the Here & Now Contributors Network, Matt Largey of KUT explains two different approaches for limiting evaporation: a film of vegetable oil and pumping water underground.

Reporter

Transcript

ROBIN YOUNG, HOST:

General Motors could pay out more than a billion dollars to victims of crashes in GM cars that had faulty ignition switches and the company has given compensation expert, Ken Feinberg, who handled payouts after 9/11 and the Boston bombings, complete control over how that money will go out. GM admitted that its employees were negligent in warning people of the ignition switch danger, and has linked 13 deaths to the problem. Trial lawyers say there could be hundreds more victims, and today Feinberg said he's not limiting who can apply for the fund.

(SOUNDBITE OF ARCHIVED RECORDING)

KEN FEINBERG: Anybody who already settled their claim with General Motors before they knew about this cover up or this ignition switch problem, may rip up the release they signed and come back into this program.

YOUNG: Ken Feinberg also said he'll use the same formula he established in handling the 9/11 compensation fund, which calculated a person's age, earning potential and severity of the injury. The victims can either follow the formula and get a quick payment, try to justify a larger payout through an individual negotiation, or file a law suit as a last resort. Well, to the Southwest now. As you well know parts of California, Nevada, Oklahoma, and Texas are all seeing extreme drought as rainfall and winter snow packs have been way below average. One of the biggest factors, though, affecting water supplies in these hot, dry places, is evaporation. Reservoirs can lose as much water to evaporation as to the water that's actually pumped out of them for drinking water. Can anything be done? Well, maybe. From the HERE AND NOW Contributors Network, KUT's Matt Largey from Austin, Texas explains.

MATT LARGEY, BYLINE: Water can be deceiving. A lake or a reservoir might look perfectly still on a calm day, but actually it's buzzing with activity - literally. You can't see it, but the water is vibrating. Look closer - closer - closer.

DAVID MAIDMENT: Evaporation occurs because molecules that are sitting in the liquid water are vibrating against themselves.

LARGEY: That's David Maidment, from the University of Texas at Austin.

MAIDMENT: I'm a professor of civil engineering and I deal with water resources engineering and hydrology.

LARGEY: And as he was saying, water molecules...

MAIDMENT: Are vibrating against themselves.

LARGEY: And some of those molecules are picking up energy - energy from the sun - more energy from the wind across the water surface.

MAIDMENT: They acquire more energy until the point that they vibrate fast enough that they just ping off into the air.

LARGEY: And just like that, one molecule at a time, we lose billions and billions of gallons of drinkable water to evaporation.

MAIDMENT: Evaporation is a tough thing to deal with because you can't see it - very difficult to even measure. I mean, like, you can measure flow in rivers, you can measure rain coming out of the sky. Evaporation's very rarely even visible. It's like a ghost. It's like a ghostly thing - it just steals away and you can't see it, it just goes.

LARGEY: So, how do you catch a ghost? Is it possible to stop evaporation? Actually, yes.

MAIDMENT: There's really two approaches.

LARGEY: Two approaches. The first, pump the water under ground. Then it can't evaporate. But you need a bunch of space in a certain kind of aquifer to do it, and there's no guarantee that you'll get the water back once you put it down there. Then, there's that other approach.

MAIDMENT: That's called a monolayer.

LARGEY: A what?

MAIDMENT: Monolayer.

LARGEY: Monolayer?

MOSHE ALAMARO: A monolayer is a material which is extracted from vegetable oil.

LARGEY: Moshe Alamaro is a researcher at MIT in Cambridge, Massachusetts. And he's done a lot of work with monolayers. As he was saying, it comes from vegetable oil.

ALAMARO: And when you place it on water, the material spread spontaneously and create a film a width of which is literally one molecule.

LARGEY: One molecule thick. mono - layer. And the monolayer, it acts as kind of a lid, floating on the surface to keep the water molecules from pinging off into the air to keep them from evaporating. A one molecule thick it's almost imperceptible.

ALAMARO: You cannot see it, you cannot smell it, you cannot taste it. You don't see anything.

LARGEY: You can drive a boat through it, swim in it. Monolayer gets torn...

ALAMARO: But after a few minutes, the monolayer cover repair itself spontaneously.

LARGEY: But what about saving water? Alamaro claims a monolayer on a reservoir can reduce evaporation by 75 percent.

ALAMARO: In California and Texas, the evaporation suppression on existing reservoir can add 4 million acre foot capacity per year.

LARGEY: That's about as much water as 4 million households use in a year. You might be asking, really? Has it been tested? Well, the idea of monolayers has actually been around for decades. In fact, almost 50 years ago...

PAUL RODMAN: Back in 1966.

LARGEY: Back when Paul Rodman was a grad student at Oklahoma State.

RODMAN: We used it on Lake Hefner, 2500 acres -the water supply for the city of Oklahoma City.

LARGEY: They put them on a layer of this reservoir to test how much it would reduce evaporation, if at all. And, it did. Sort of.

RODMAN: Whenever they were able to keep the lake surface covered, the evaporation reduction was 40 to 60 percent.

LARGEY: 40 to 60 percent. That could save a ton of water. But about that first part of what he said...

RODMAN: Whenever they were able to keep the lake surface covered...

LARGEY: Keeping the lake surface covered - that was the problem.

ALAMARO: What happened is, once the monolayer was placed on the reservoir, the wind was pushing the film down wind, exposing most of the area of the reservoir to evaporation.

LARGEY: Evaporation is one thing, but how do you stop the wind?

RODMAN: That was a fatal flaw effectively as far as discontinuance eventually of that research.

LARGEY: The monolayer had met its match.

RODMAN: Eventually it was dropped and has been dropped now for 45 years or something like that. That's a long time.

LARGEY: Until Moshe Alamaro and some other scientists picked it back up. And he thinks they've solved the monolayer's fatal flaw.

ALAMARO: To make long story short, we place skimmers along the perimeter of the reservoir.

LARGEY: The monolayer gets pushed to one side, sucked up by those skimmers, and pumped back to the other side. It drifts to one side, gets sucked up, and pumped back. Repeat. Essentially, a monolayer conveyor belt.

ALAMARO: We found that moving monolayer is effective as monolayer in rest, up to 30 miles per hour wind speed.

LARGEY: Of course, and here's the thing, it hasn't been tested on a large scale. So far, the system has only been tested in a lab. And David Maidment says it's here - the testing - that things gets really tricky.

MAIDMENT: You know, it's not like you can just put this on a pond outside your back yard, or something, because it's the sheer force of the wind on a large surface of water that's really the issue that has to be tested, and you can't do that on a small area.

LARGEY: Alamaro tried to test his system in Texas last year, but he says it got bogged down in red tape. Now he's working on a plan to test his monolayers on a reservoir outside San Francisco and given the extreme drought now gripping California, if any place could stand to save a little extra water, it would be there. For HERE AND NOW, I'm Matt Largey. Transcript provided by NPR, Copyright NPR.


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Robin Young and Jeremy Hobson host Here & Now, a live two-hour production of NPR and WBUR Boston.

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