Manhattan, KS— Tuttle Creek Lake sits like a shrunken version of its former self.
Take the abandoned campground: Drinking water stopped reaching its pipes as the reservoir filled with mud. Several boat ramps now lead only to dirt.
Locals remember waterskiing in these areas, before so much silt filled it in and cut the lake’s surface in half.
Decade by decade, it happened gradually but inevitably. A mind-boggling amount of dirt settles in Tuttle Creek reservoir each year.
“If something is not done, then there won’t be water during major drought periods,” said John Shelley, a senior hydraulic engineer and sedimentation specialist at the U.S. Army Corps of Engineers. “There just won’t be water.”
The situation threatens drinking water for hundreds of thousands of northeast Kansans in the cities and towns along the Kansas River. All of the reservoirs in the Kansas River Basin face similar problems — not just Tuttle Creek, but Clinton, Perry, Kanopolis and Milford lakes, too.
At Tuttle alone, the equivalent of three-and-a-half football fields piled with soil as high as the Empire State Building has settled in the lake every year since 1962.
So this reservoir will soon become the site of a world’s first.
Starting next year, the Corps of Engineers will pelt the lakebed with Jacuzzi-like water jets to try to move some mud and release it downstream.
The stirred-up mud will hopefully slide down the sloped, underwater lake bed, toward low exit gates on the dam. The moving mud might even build momentum that pulls more silt with it as it rushes downhill.
One scientist likens the idea — a new twist on older technology — to triggering an avalanche of snow down a mountainside. But he says no one knows how well the plan will work, if at all.
“If Kansas were to prove this as a successful concept,” said Admin Husic, a professor of water resources engineering at the University of Kansas Department of Civil Environmental and Architectural Engineering, “it would be a big jump forward.”
Engineers trying to save shrinking reservoirs in other states would take note, but some biologists fret about the idea’s potential effects on the Kansas River.
“I hear a lot of conversations about water quantity,” said Amy Burgin, a scientist at the Kansas Biological Survey and Center for Ecological Research, “and less about how this might impact the water quality.”
Burgin is also a professor at the University of Kansas Department of Ecology and Evolutionary Biology.
Lakes, rivers and wetlands all connect, she said, affecting myriad living things.
“Rivers are not pipes,” she said. “They’re active biological communities.”
Let gravity do the work
Regular old dredging uses lots of diesel because machinery and pipes do the heavy lifting.
Blades and hoses cut up the lake bed and suck up the mud, often onto barges. The sediment gets transported someplace on land for dumping.
About $20 million cleared out three years’ worth of sedimentation.
“It’s been more than three years now,” Shelley said, “So it’s more than filled in, for sure.”
The new approach to be tested at Tuttle Creek Lake aims to let gravity do much of the work.
The Tuttle lake bed slopes toward the dam, which has gates at the bottom. If engineers can get silt to slide downhill, helped by the laws of physics, they can open the gates to let it out.
The Corps will hire contractors to rig up boats with pipes that can pump water down to the lakebed, creating something like low-pressure Jacuzzi jets.
They’ll use that to fluff up the mud. Once the mud swirls up into the water, the water will become heavy and potentially tumble down the underwater slope toward the dam. Again, imagine an avalanche, just with mud and underwater.
Called water injection dredging, the technique of loosening mud this way has been used in ports and marinas around the world.
But those are the kind of places where water already moves — offering currents that can help carry the loosened load. In a relatively static lake, will the stuff really move?
“The best-case scenario would be that the amount of sediment leaving (the dam) is the same amount as what’s coming in” through gradual sedimentation, Husic said.
That’s the ultimate dream. If the results of this pilot project were to suggest that engineers can achieve a long-term balance, that would make Tuttle Creek Lake sustainable. The half of Tuttle that still remains could exist many generations into the future.
But don’t break out the champagne yet.
In a worst-case scenario, the approach won’t have any effect. That is, a plume of mud will fluff up and swirl around in the water, only to settle back in more or less the same place, without sliding downhill.
Or maybe teeny amounts of mud will make it to the exit, but not enough to make a difference.
The Corps and Kansas expect to spend about $6 million combined to find out.
How taming our rivers backfired
If vast amounts of silt do spill through the gates, it’s unclear how it will affect the Kansas River.
On paper, the idea can look good.
Landscape erosion is natural. Rivers carry silt and eventually that silt reaches the ocean. This is how things worked since time immemorial.
But when a river reaches a dam, the silt stops moving and sinks to the bottom. The water exiting on the other side runs unnaturally clear.
This change takes a large-scale toll in Kansas and across the U.S., which has tens of thousands of dams. Ninety-eight percent of the country’s 3 million miles of rivers and streams is tamed by human infrastructure, The Nature Conservancy says, leading to fish and mollusk declines and hurting commercial fisheries.
Particularly dramatic evidence lies on the coast in the Gulf of Mexico. There, as Pulitzer-prize-winning science writer Elizabeth Kolbert documents, the nation’s decisions to micromanage the Mississippi River with flood walls, levees and other feats of engineering cost Louisiana two football fields worth of land every three hours by preventing silt from replenishing the shoreline as it once did.
In today’s heavily transformed waterways, many fish and critters that evolved to live in cyclically muddy waters now struggle.
All that churning, clear water leaving dams has other effects, too. Kansas streams and rivers would be less destructive to rapidly eroding banks if they had more silt in them.
To be clear, erosion is a serious problem along Kansas waterways for reasons beyond the dammed silt. The rivers run straighter and faster than before federal engineers got involved. And agriculture has destroyed much of the landscape’s native vegetation to grow crops right up to the water’s edge.
State agencies like the Kansas Water Office and Kansas Forest Service work with farmers willing to replant riverbanks with native vegetation.
Picture buffer zones 70 feet wide and packed with willows, cottonwoods, switchgrass and wild plums that create formidable root systems to help hold soil in place.
Andy Klein, of the Kansas Forest Service, works on some of the fastest-eroding stream banks across Kansas, where rivers swallow whole rows of crops.
One farmer told him, “I wish we could have done this project 15 years ago, because I’ve lost about 15 acres of cropland,” he recalled.
Some scientists say those efforts help, but the Corps would do better to release dammed-up silt if possible.
Ideally, that would do three things: Help the reservoir’s shrinking capacity, benefit downstream ecosystems that need silt, and ease the erosion along some downstream banks.
“Restoring sediment continuity would be a huge benefit from the Kansas River all the way down to the Gulf of Mexico,” said Heidi Mehl, who directs water and agriculture programs for The Nature Conservancy in Kansas. “So much sediment is being held back.”
The Corp’s idea might work at other reservoirs, too, but only those with exit gates at the base of the dam. Redmond doesn’t have them.
Can engineering solve problems it created?
Yet Burgin, the KU ecologist, says biological and chemical realities make it impossible to predict whether water injection dredging — the avalanche-triggering-Jacuzzi idea — would help or hurt the Kansas River.
First, natural turbidity is cyclical. Spring rains bring more silt than summertime does.
Burgin wants to know whether the water injection dredging will mimic seasonal patterns.
She also wants to know how much mud will enter the Kansas River. Some silt is just dandy for filter-feeding mussels, for example. But too much could smother them — a bad outcome for raccoons and other creatures that eat them, too.
Finally, she warns, the sediment could carry chemicals that washed off of farm fields over the years. Fertilizers, herbicides, insecticides.
Whereas now, she said, any chemicals at the bottom of the lake are “somewhat stable.”
“They don’t get disturbed very much,” she said. “Not very many organisms live down there because there’s not very much oxygen.”
Once the mud is on the move, exposed to more oxygen, plants and animals, chemicals could transform. Nitrates could fertilize the river.
“There’s so many variables,” she said. “It’s not necessarily a simple matter of testing what’s in the sediment.”
Shelley, at the Corps of Engineers, says his agency has tested the sediment extensively for weed killers and other pesticides, metals and nutrients.
“Everything has shown that there’s nothing of concern,” he said. “We’re pretty confident in that.”
U.S. Geological Survey testing got similar results, he said.
The Corps also says the pilot project that starts next year will involve several short-run tests, with monitoring downstream to see what happens.
“If there are any impacts that are positive or that are negative,” he said, “they’re just going to be short-lived.”
If results are promising, the Corps could then conduct further work to figure out how to potentially use the technique longer term in sync with natural cycles and ecological factors.
This video from the Kansas Water Office shows how shooting water into mud causes it to lift and swirl.
In recent decades, the Corps launched a national partnership with The Nature Conservancy to tweak dam discharges in order to better mimic natural river cycles.
Shutting gates too suddenly, for example, kills mussels that can’t move fast enough to retreat when water levels fall unnaturally fast.
Mehl wants the Corps to apply that same thinking to its potential sediment releases.
For example, water injection dredging may prove only to release the finest of silt, she said. She wants monitoring and modeling to understand where it will end up and how to adjust the water flow to avoid problems.
“A large slug of fine sediment can really choke fish habitat and suffocate their eggs,” she said.
Droughts and floods
Tuttle only stores half as much water as it used to. Combined with the other shrinking reservoirs in the Kansas River basin, that makes cities nervous.
About 800,000 people rely on the Kansas River for drinking water.
Mike Lawless is president of the board of the Kansas River Water Assurance District and deputy director of public works for Lawrence.
The district includes 14 entities, from industries like Evergy and water suppliers such as Lawrence, Olathe and Topeka. Its board supports the pilot project.
“We know that we have to do something,” he said, “to prolong the life of the reservoirs.”
The district pays for storage capacity in Tuttle Creek, Perry and Milford lakes to lean on in times of serious drought, such as in 2012, one of the driest years on record.
A spokeswoman for Topeka said the city worries that releasing sediment into the Kaw could cause murkiness, taste or odor issues that would “put stress on the water treatment process.”
But the city is prepared.
Reservoirs also serve another function: Preventing floods. The dams along the Kansas River can accommodate more volume than their everyday water levels. When torrential rains pound northeastern Kansas, the reservoirs swell and the Corps releases the water gradually.
But as the lakes continue filling with mud, this cuts into flood capacity, too.
When the U.S. dammed its rivers, the fact that they would gradually fill with mud wasn’t lost on the engineers. Solving the problem was simply left to later generations.
“To my knowledge, there’s not a single dam in the country that had a sediment management plan for what to do” eventually, Shelley said. “There’s a growing recognition that something needs to be done.”
The Nature Conservancy worries the increasingly urgent situation will lead to building new dams in parts of the country.
“Which would mean new valleys flooded,” Mehl said. “Lands and towns lost.”
That prospect would exact steep fiscal, societal and environmental prices.
For better or for worse, Kansas may not have that option. That ups the stakes to hold onto the region’s existing reservoirs.
“We don’t have any more big valleys that we can impound,” said Ted Harris, a research professor at the Kansas Biological Survey. “We’re stuck with the reservoirs that we have.”
Celia Llopis-Jepsen covers the environment for the Kansas News Service. You can follow her on Twitter @celia_LJ or email her at celia (at) kcur (dot) org.
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