Picture three-and-a-half football fields with earth piled onto them — piled as tall as the Empire State Building.
That’s how much sediment flows into Tuttle Creek Lake each year. After decades of this, mud has eaten up so much space that about half of the lake near Manhattan has disappeared.
Put another way, about half of its volume for storing water is gone.
That’s why the U.S. Army Corps of Engineers and the Kansas Water Office will start a first-of-its-kind pilot test this week to try to clear out some mud.
They’ll use an underwater dredging technique that they hope will loosen some of the sediment and allow it to flow out of the dam gates and continue moving downstream in the Big Blue and Kansas rivers.
Reservoirs are filling up with mud across the country
Dams interrupt the way rivers naturally transport sand, silt and other kinds of sediment. So over the decades, manmade lakes fill up with mud. Human activity – such as tilling farmland – can also speed up how fast this happens.
As a result, reservoirs don’t last forever.
Tuttle Creek Lake was completed in 1962. As mud accumulated, the marina had to move from its original location. Boat ramps became buried under mud.
In another 25 years, the Corps of Engineers estimates that just one-quarter of the lake’s original water storage capacity will remain. In 50 years, less than 10 percent will remain.
(Tuttle’s capacity to hold back floodwater in rainy years is another matter, and that capacity remains largely intact.)
Losing so much space to store water for dry years worries not just the U.S. Army Corps of Engineers but also the state of Kansas and cities in northeast Kansas.
This lake serves more than 40% of the state’s population. Households and businesses along the Kansas River — in cities such as Topeka, Lawrence and Olathe — depend on the river for water.
In dry years, the water stored in Tuttle and other manmade lakes can be drawn upon to ensure that the river flow stays strong enough.
Testing out a new approach to dredging
Engineers will run a pilot test of what is formally called water injection dredging during a 10-day period that starts on Wednesday and continues through Saturday, Sept. 27.
Because Tuttle is such a large lake, dealing with its sediment problem through traditional dredging – if even feasible – would take large amounts of fossil fuel to transport the sediment. It would also require finding somewhere to put all that mud.
That’s why engineers want to test the idea of releasing sediment through the dam gates and letting the natural energy of the river carry it downstream.
"We are excited” to run the first test, said Laura Totten, who is managing the project at the U.S. Army Corps of Engineers Kansas City District. "This project represents a significant step forward in exploring sustainable dredging techniques.”
How does it work?
Engineers will use a barge to lower water jets into the lake and aim them at the bottom.
The spray from the water jets should loosen the mud on the bottom and cause it to swirl up a bit from the lake bed. This will create muddy, swirly water that is denser than the rest of the lake water.
Engineers hope the density difference and the force of gravity will then move the muddy water downward along the sloped bed toward the dam and out its gates.
This kind of underwater dredging isn’t new, but normally it is used to remove sediment in places where naturally occurring water movement, such as ocean tides, can help with the process. It’s not clear whether the technique will work in a lake.
What will scientists watch for during the pilot test?
It's also unclear what environmental effects the released sediment would have downstream.
The Corps of Engineers has enlisted help from scientists at Kansas State University and the U.S. Geological Survey to monitor not just the effects on the lake, but downstream in the Big Blue and Kansas rivers.
“Knowledge gained from the project will be invaluable for sediment management across the nation,” the Corps of Engineers said in a statement.
Engineers and other scientists will study whether any sediment exits through the dam and whether the water downstream shows any changes in oxygen levels, heavy metals or other content.
K-State scientists also plan to study potential effects on fish and insect larvae downstream.
The Corps of Engineers plans to carry out two more 10-day test periods next spring and summer. The total cost of the three test runs is $9.1 million. In addition to preparing and operating the barge, this amount also includes the cost of monitoring, analysis and reporting, plus preparations that took place in recent years to assess potential environmental effects.
Ultimately, the goal is to figure out whether this method has the potential to squeeze more years out of Tuttle Creek Lake at a reasonable cost — and without significant environmental impacts downstream.
Celia Llopis-Jepsen is the environment reporter for the Kansas News Service and host of the environmental podcast Up From Dust. You can follow her on Bluesky or email her at celia (at) kcur (dot) org.
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