Pioneering dredging project targets silt buildup in Tuttle Creek Lake

John Shelley, an associate research professor at the University of Kansas, speaks at the Governor's Conference on the Future of Water about a pioneering water injection dredging project at Tuttle Creek Lake. (Photo by Morgan Chilson/Kansas Reflector)

MANHATTAN — Kansas organizations took part in a first-in-the-world project designed to move silt out of Tuttle Creek Lake in an effort to change projections showing the lake will be 75% full of silt by 2074.

The collaborative study, a project of the Kansas Water Office and the U.S. Army Corps of Engineers, plans to remove silt from the lake by using water injection dredging, which will shift silt out of the lake into the Big Blue River, said John Shelley, associate research professor at the University of Kansas, at last week’s Governor’s Conference on the Future of Water.

“​​Before the dam was built, there was about 5.3 million tons of sediment per year washing down the Big Blue River, and 5.3 million tons of sediment per year washing out of the Big Blue River,” Shelley said. “But then we built the dam and it causes this large lake, which results in 98% of the sediment being trapped in the lake. Instead of 5.3 million that used to go out, now we have about 107,000 tons of sediment per year that leave the lake.”

To put it in perspective, Shelley said to imagine taking a 1/50th slice of a jelly bean in a liter of water. That’s how much silt currently leaves Tuttle Creek Lake.

Although water injection dredging isn’t a new process, it has never been used in a lake, Shelley said.

Four basic strategies are used for managing sediment, he said: reducing the sediment coming in, redistributing sediment within the lake, routing sediment around or through the lake before it deposits, and removing it after it has deposited.

Water injection dredging is done by pumping clear water from a 120-foot barge to the bottom of the lake. Because muddy water that is stirred up is denser than the clean water, the muddy water “plunges” to the bottom of the lake and moves laterally, Shelley said.

Such a process happens naturally in some lakes and is called a density current, he said.

“The whole idea of water injection dredging is: Let’s induce a density current but do it closer to the dam so that then it can travel, and it’s close enough that it’ll travel to the dam and can be discharged downstream,” Shelley said.

The project has been in the works for several years, with preliminary work being done to test the sediment, consider what pattern the dredge should move across the lake, and consider how the Big Blue River, which the sediment is flushed to, will be affected.

This year, the project received $7.1 million in a federal grant and $2 million from the state to do the demonstration project, which began Sept. 27, Shelley said. A dredge moved in a predetermined pattern across Tuttle Creek Lake for 10 days, with 20 hours each day of active dredging. The project calls for two more 10-day dredgings to occur in the spring and summer.

Keith Gido, a Kansas State University professor, joined the project because of his expertise as a river ecologist. He and other researchers are collecting samples along the Big Blue River to measure any effects the dredging operation is having downstream.

“The dredging worked, so it moved these sediments down through the dam, and that increased the turbidity in the water, so there was a bunch of suspended sediment in the water,” he said. “As the water levels dropped, those sediments are deposited.”

Most of the sediment dropped to the river bottom but some was deposited on the shore, he said. Although many of the water samples Gido’s team took still require analysis, he said they were looking for specific issues.

“One of the things that we were concerned about was that sometimes when you have a lot of suspended sediments in the water, the oxygen concentrations will decline because there’s a lot of organic matter that’s decomposing and using up oxygen,” he said.

Lakes across the state are losing percentages of their main pools of water because silt is filling them in. This graphic, shared at a recent Kansas Governor’s Conference on the Future of Water by John Shelley, who is working on a dredging demonstration project, shows how silt is affecting lakes across the state. (Submitted: John Shelley)

Although there was a small drop in oxygen levels, Gido said, it was not near a critical value that might cause fish to die or other serious issues. When there are major storms, it’s normal for sediment to be stirred up.

“What happened was within the bounds of what we expect based on natural variability that we’ve seen due to rainstorm events and such,” he said.

Another concern was the release of sulfur oxides that make the river smell “a little funky,” Gido said. A Kansas Department of Wildlife and Parks technician told Gido that when the dredging was occurring, fishermen who were below the dam moved downstream to get away from the smell and the mud being released, but quickly moved back when it settled.

The project team, which consisted of 12 different organizations and research labs, set constraints — such as concentration limits and water quality — and determined the point where they would have stopped dredging or released more water for dilution, Shelley said. There was robust monitoring both at the lake and along the river during the dredging.

Downstream deposits on the shore of the river may be new to people who live near its banks, but it’s something that commonly happens on the Kansas River, Gido said.

If Tuttle Creek continues to lose more of its water area to silt, that would eventually cause downstream problems, too, he noted.

“A major reason the dam was built was for flood control,” Gido said. “The ability of that reservoir to control flooding is a function of how much capacity it has, right? It’s lost half of its capacity to hold water, and if it loses more, then it’s going to really compromise its ability to trap water and reduce flooding.”

Researchers will continue to assess the effects of dredging on the lake and downstream in different seasons with the upcoming 10-day sessions.

“The main point of this project — it’s not to dredge a certain volume of sediment or lower the bed level to a certain elevation,” Shelley said. “It’s really to answer questions.”

The questions are varied and include how much sediment can be moved out of the lake using water injection dredging, how much it will cost to move per cubic yard, and what are downstream impacts. The barge also moved at different speeds and patterns, so they will analyze those factors to determine what is most effective, Shelley said.

If this project can answer questions so a long-term plan could be made, then it would be successful, he said. The eventual goal would be to maintain the lake where it currently is by being able to remove the same amount of silt as comes into the lake each year.

Data is being processed and analyzed, and a webinar will be held in January to share the results of the first dredging operation, Shelley said.