When Mother Nature overhydrates Northeastern Oklahoma, as it did this past spring, the water only has so many places to go. To compensate, the U.S. Army Corps of Engineers Tulsa District operates a complex network of flood storage reservoirs, including Lake Tenkiller.
It all begins with the Corps' hydrology division, which monitors forecasts, water elevations and other factors to prevent a flow of water that is too large for the Arkansas River in Van Buren, Arkansas. There are 13 major flood storage reservoirs upstream of Van Buren, which forces the Corps to monitor the whole connection of water throughout the region - not just Tenkiller. Therefore, releases from Tenkiller always factor in the situation downstream.
"Our hydrology department are the ones that let us know on how much water we need to release," said Lee Wall, power plant specialist at Tenkiller Lake. "They tell us how much and we'll decide the gate."
Tenkiller has 10 spill gates called "Tainter" gates, five auxiliary Tainter gates, and two sluice gates. The sluice gates are an alternative to underground water flow, using a penstock to deliver water to hydro turbines and sewerage systems. The Tainter gates are use in the lock and dam to release water.
"We start with the sluice gates and then, depending really on how much they want released, we go to our main Tainter gates," said Wall. "If they want us to release too much, we have to use the Tainter gates. This flood we had last time, everything came out of the sluice gates."
TAPER is a real-time decision support tool used by Corps staff. The system simulates the river and reservoir network to determine how much water should be released from Tenkiller to avoid downstream flooding. The TAPER system also uses rules to prevent flows at Van Buren from reaching above the regulated level, which varies seasonally.
Because the string of water resources is all connected together, the Corps can only release so much water at certain times.
"Our situation at Tenkiller in particular was kind of strange this year," said Dennis Covey, lake manager. "We really didn't receive a whole lot of rainfall, but we were holding back water because of all those other lakes that did [receive rain], were having to release. Then we ended up getting some rain toward the end, which bumped us up at a faster rate to where we actually had to start releasing."
There is also a threshold for how much water can be released at a time.
Wall said Tenkiller's maximum downstream capacity is 15,000 cubic feet of water per second. For comparison, the lake was releasing water through a sluice gate on Tuesday, Aug. 6, at only 800 cubic feet per second, said Wall. By 5 p.m., according to the Corps website, there was a reservoir release of 2,300 cubic feet per second.
"Once it goes over 15,000, we break the banks and start flooding areas a little bit," said Wall. "So we always try to keep our releases at less than 15,000. They know what the elevation is and they know how much the banks can hold. Downstream, according to what's going on, if it rises up above a certain elevation and then we're dumping into it, then we can topple the banks that way, too. So they have to keep track of everything that's going on around us."
The spring flood that wiped out homes and put cities underwater along the Arkansas caused two barges to break loose from the Port of Muskogee and eventually run into Webbers Falls Lock and Dam 16.
The event had thousands of Oklahomans wondering if the structure would survive. It did, and so did the barges, but they're still stuck and obstructing a couple of gates at the dam.
In another example of the chain reaction that occurs with water networks, Covey said Tenkiller is not releasing as much water as it would be, because of the situation lingering at Webbers Falls. He added that the contractor to remove the barges hasn't been able to do so because of the high amount of water, but "right now is when they can."
"It's allowing us to go down very slowly, but we would be releasing more if the barges wouldn't have hit the dam and we weren't trying to get those out," he said.
"Those barges are keeping us from closing, I believe, two gates at lock 16, so we need to be able to operate those gates in order to operate like we're supposed to."
The 13 large flood water reservoirs amount up to 7.6 million acre-feet. And with a large territory to cover and so much water to control, it takes an entity like the Corps to keep an eye on all of Oklahoma's upstream water sources, to better protect the downstream infrastructures.
Covey, who has worked at four different lakes, said it's common for people become upset when the lake they live on or near is not releasing water - especially if the water levels are so high that recreational use becomes difficult or impossible.
"All this water has to go somewhere and it all goes down the same pike, which is the Arkansas River," said Covey. "So we have to monitor the whole system, not just your lake."