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High-tech buoys measure reservoir evaporation in Texas Posted on October 11, 2021


Andy Weinberg – Geoscientist, Texas Water Development Board

The Texas Water Development Board is putting out a series of buoys on some of the reservoirs in Texas to look at evaporation rates so we can understand how much water is lost out of the reservoirs to evaporation rather than being sent downstream for beneficial uses.

So, we’re building on some experience that other folks have had, but it's something new here in Texas. And the idea is that we're trying to get a better measurement of evaporation rates off reservoirs because evaporation takes as much water out of the lakes every year as what we use for any kind of municipal use or irrigation or anything. It's a huge amount of water that goes out with evaporation. And in the past, we've just measured it with evaporation pans. But as we get more and more stressed on our water resources here, it makes sense to get a better measurement so we can plan a little bit better for how much water we’re going to have during droughts and times when the system really gets stressed.

The buoy is a little bit different because we're basically measuring weather variables—wind speed, temperature, humidity, vapor pressure, things like that. And those all go into this big equation, the Penman-Monteith equation. And you can use all of those things to calculate what the evaporation is on hourly or daily time periods. The advantage of the buoy is we're getting measurements right on the lake, so right where it’s happening.

We've got sort of a target location for where we’re going to put the thing that we agreed to with the lake operator. Then, we'll get the mooring blocks down first so that those are set in place. They've got some marker buoys on those. And then we'll launch this thing, which goes in the middle. We have to do a little bit of assembly on the spot there where there’s an instrument cage that bolts onto the bottom of this thing. So, we've got to get that all set up off the back of the boat and bolt it together, and then send it off on its own.

It's got solar panels that provide the energy from the sun and then there's a couple of batteries that are inside. And there's an electronics enclosure in there—kind of a sealed data well that's got a data logger on a cell modem. And so it just keeps collecting data and sends information out every 15 minutes.

The data from all these buoys will be available to the public through TWDB websites—Water Data for Texas and TexMesonet.

It's a cool project for me, personally. The science is interesting, and I definitely see a benefit for everybody in Texas having better information out there.


Andy Weinberg on the importance of planning for a drought

Andy Weinberg – Geoscientist, Texas Water Development Board

"When you get a drought, then evaporation takes a lot of water out of the lakes. 2011--we got over five feet of evaporation out of reservoirs across the state. The average, statewide, our reservoirs are 20 feet deep. So, that's a quarter of the water that we have in storage is lost to evaporation in a drought year. So, it's really crucial that we know what that could look like so we can plan for it so we don't have people who are caught short."

Andy Weinberg explains where the evaporation buoys will be deployed

Andy Weinberg – Geoscientist, Texas Water Development Board

"This project was something we started up with some grant money from the Bureau of Reclamation. So, they gave us funding for four buoys. So, the idea is we get four of these out, we picked four reservoirs that are kind of across the whole state. So, we've got ones going in Lake Buchanan in Central Texas. That's where the first one's going. Lake Meredith up in the north part of the Panhandle. Red Bluff out on the New Mexico border and Choke Canyon in South Texas. So, it'll give us a pretty good geographic spread where we can look kind of across the state and get a better idea for how much the in situ measurements with the buoys differ from what we had been estimating with the pans."

This article is posted in Technology / Water Data .