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On the dredge: Dane County project clears Yahara River sediment to improve water flow and prevent flooding

On the dredge: Dane County project clears Yahara River sediment to improve water flow and prevent flooding
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Being on board Dane County’s “Dragon Dredge” is like riding on a slow moving, floating vacuum cleaner.

It doesn’t go fast or far and it sucks up dirt. Sometimes a rock gets stuck in it.

Dane County purchased the $650,000 Ellicott Dredge in March as part of a five phase, multiyear and multimillion dollar effort to decrease the risk of flooding along the Yahara chain of lakes. The dredge removes built-up dirt and clay, clearing bottlenecks in the Yahara River that link the lakes.

The 42-foot-long hydraulic dredge digs through years of compacted sediment exacerbated by urban runoff. Covering 400 cubic yards in a day, the bright red teeth on the cutter head fight their way through gummy clay. The pump sucks up rocks and, occasionally, a spare log.

“You’re at the mercy of the Yahara,” said Ryan Brockner, dredge laborer. 

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John Reimer, assistant director of the county's Land & Water Resources Department, oversees the county's sediment removal project.

The idea to dredge the river to improve water flow — a unique strategy in Wisconsin — was borne out of the historic rainfall in August 2018 that hammered some areas with more than a foot of water and killed one Madison resident. The deluge caused over $154 million in damage and led to historically high lake levels.  

Dredge Map

Dane County's sediment removal project takes place in five phases and six locations. The goal is to remove sediment from choke points along the Yahara River to improve water flow and reduce flooding.

Because of the muck, the channels connecting lakes Mendota, Monona, Waubesa and Kegonsa didn’t have the capacity to push water through the chain of lakes fast enough to keep up with rainfall. 

“Water has nowhere to go but up,” said John Reimer, assistant director of the county’s Land & Water Resources Department. Flood waters rise and storm sewers back up, causing flash flooding.

Water comes into the Yahara chain of lakes faster than it goes out — taking two inches of rain over two weeks to leave the system. With the Dragon Dredge removing several feet of sediment, water will have more room and should drain through the system in about half the time.

It should also help Reimer manage lake levels and adhere to water levels set by the state Department of Natural Resources. The DNR has the statutory responsibility to regulate certain dams and create specific management requirements, which are included in the operating order issued to the owner of the dam. In this case, that owner is Dane County. 

Reimer said the goal is to minimize the frequency of flooding. Dane County has seen flooding about every 10 years, he said, with major events in 2000, 2008 and 2018.

“We (hope to) go from 10 years and extend that out to 20 years … and mitigate those impacts so they're not so frequent,” Reimer said.  

Dane County Executive Joe Parisi said the county isn’t required by state statute to do this work. Though it involves technical skills and is expensive, he said it’s necessary for Dane County to tackle. 

“We do this because someone needed to step up and take care of this because it was challenging, and it really dovetails in with a lot of our key lakes work, too,” Parisi said. “It's really the only way we're going to be able to prevent some of the future type of flooding that we saw in this last big rain event.”

McDaniel Park 2018 Flood.jpg

Lake Waubesa flooded its banks in McDaniel Park in McFarland following historic rainfall in 2018.

Lakes like bathtubs

Lakes Mendota, Monona, Waubesa, Kegonsa and Wingra form a chain of lakes connected by the Yahara River, eventually streaming into the Rock River north of Janesville.

Madison is closely linked to its five lakes. The area’s first residents built villages and farmed around the lakes. Today, the city of 269,840 — the fastest growing in the state of Wisconsin, according to the 2020 census — builds and expands its borders around the bodies of water.

A chain of lakes “is unusual but not unique,” said Emily Stanley, a University of Wisconsin-Madison professor in the Department of Integrative Biology and Center for Limnology. But a chain of lakes in an urban setting with a watershed that’s dominated by agriculture is uncommon, she said.

Stanley described the lake system like a series of bathtubs with one small outlet. Sediment that used to be topsoil accumulates in low spots in the basin and clogs the drain.

“The physical structure of the lakes and the connecting channels is not helpful,” Stanley said. “They have narrow exit points and they are harvesting water from big watersheds.”  

 The area’s flat landscape also makes it harder for water to move through the system, Reimer said, and aquatic vegetation can impede movement, too.

The county estimates that more than 8.5 million pounds of sediment enter the Yahara chain of lakes every year because of urban runoff. When all of that dirt gets stuck in the choke points between lakes, the flow of water is impeded.   

Parisi said that number makes the project’s goals more “tangible.”

“When you drive by a development (with) construction going on and you see dirt and sand all over the road, it rains and that stuff goes into the storm sewers and ends up in our lakes,” Parisi said. “It gives you a concrete example of why we should care about construction site runoff and why we should care about other types of runoff.

 “We may not always see the manifestation of it until there's a major event.”

Though this project started in response to excessive rainfall, Dane County experienced drought conditions for much of the summer. 

The 2010s were the wettest decade in the state, with 2019 as the wettest year. That year, Dane County saw excessive rainfall that prompted farmers to produce different crops and use new strategies to mitigate rainy growing seasons.  

Last year, Dane County released its Climate Action Plan, which included newly published climate modeling by UW-Madison scientists that showed southern Wisconsin will continue to get hotter and wetter over time. It’s likely that large precipitation events will increase in frequency and intensity, according to the modeling.

“It’s going to happen again,” Reimer said of flooding.

['We can't wait': Madison leaders pledge urgency following climate change report]

Dredge video screenshot

The second phase of the county's sediment removal project, happening now, will dredge the 11 miles between Lake Waubesa and Lower Mud Lake.

‘Trial by fire’ in water

The sediment removal project, which will cost the county an estimated $15 million, will take place in five phases and six locations along the Yahara River, which is channeled from Lake Mendota through the Isthmus and southeast through lakes Monona, Waubesa and Kegonsa.

For the inaugural phase, dredging occurred between lakes Monona and Waubesa. In the second phase, happening now, the dredge is working the 11 miles between Waubesa and Lower Mud Lake, which borders McFarland.

Reimer said he has fielded many phone calls from neighbors requesting information on the project and that, overall, people have supported it.

“Usually in lake levels, it's either too high or too low or I can never make anyone happy, but at least with this project, I'm getting a lot of positive feedback,” he said.

Don and Denise Peterson have owned their McFarland home, located across from where the dredge is currently working, for 17 years. They said the noise of the dredge has faded into the background and that they have become used to looking at it from their home.

“I look at it as short-term pain for long-term gain,” Don Peterson said.

The second half of this second phase will take place between Lake Kegonsa and Highway B, likely starting in the spring of 2022. The third phase will involve dredging the Yahara River between Lower Mud Lake and Lake Kegonsa with the final two phases covering stretches of the Yahara River from Highway B to Stoughton and lakes Mendota to Monona. 

Ideally, Reimer said the project would start at the bottom of the chain with Lake Kegonsa and work upward. But the phases were planned to keep the project moving efficiently.

There was pre-existing dredge work and data for the area of Phase 1 that made it a natural place to start. Later phases involve a cultural fishing area that is important to the Ho-Chunk Nation, which involves greater planning not to disturb, and a whitewater park under development in Stoughton.  

In July, the blue Dragon Dredge was working on the Yahara River in McFarland upstream of Mud Lake. It sat in the water near Sleepy Hollow Road and near the backyards of some riverfront homes, where many homeowners had to use sandbags to keep rising water at bay in 2018.

Sun umbrellas repurposed from a landfill flanked the sides of the dredge and offered the operators some shade while they were on the deck and outside of the control room. The dredge includes a GPS monitoring system that shows the terrain on the bottom of the river. A gauge for vacuum pressure shows the operators when to slow down.

Jaime Salazar, lead dredge operator, said the team flew a drone before starting work to map out the dredge’s path through the river. 

When it’s running, the cutter head sweeps back and forth across the river bottom, excavating sediment for the pump to obtain. Long stakes, or spuds, at the back end hold the dredge in place. Winches and cables on the outside of the dredge are used to swing the machine in an arc.

The work is slow and methodical.

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Dane County hired four permanent, full-time employees to operate the Dragon Dredge and several limited-term workers for extra help as needed.

“You can only handle so much every pass,” Brockner said.   

Brockner said it’s also been “trial by fire.” 

Though Dane County is in its second phase of the project, this is the first time county employees have operated the dredge themselves. The county paid Dredgit Corporation $3.25 million in 2019 to complete the first phase of the project, the dredging between Monona and Waubesa.  

This type of dredging work is specialized, making it more difficult to find a contractor and delaying the start of the first phase. Reimer said the county conducted two rounds of a contractor search before settling on the Texas-based Dredgit Corporation — the only application.

“It took us quite a bit of time to move it forward,” Reimer said. “This is an important topic in flooding that we want to get it done as timely as we can.”   

Parisi said they learned that owning the dredge would put the county in the "driver's seat."

“In order to control our own destiny and the timing and to be as effective and efficient as possible and to move this along as quickly as possible, we decided it was in our best interest to engage in the majority of the work ourselves,” Parisi said.

A beginner’s dredge

Ellicott’s Series 370 Dragon Dredge is advertised as ideal for first-time owners due to its simple design. It’s also easy to transport and can be assembled on site.

Steve Miller, the domestic sales manager for Ellicott Dredges, said the Maryland-based company, which has manufacturing plants in Baltimore and New Richmond, Wisconsin, primarily focuses on small- to medium-sized, portable dredges.

“That’s exactly what Dane County needed for... flood control and to establish flood capacity in these lakes,” Miller said. 

Miller agreed that owning the dredge will make the project more efficient. Contracting involves acquiring necessary permits and funding that can take awhile.

Owning the equipment is more sustainable, he said, because the county can run the program each year and in smaller segments — and respond to emergencies. If a big rainstorm flushes sediment into an area that was just dredged, the county has the machine to do it again.

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Ryan Brockner and Jamie Salazar, sitting, operate the Dragon Dredge on the Yahara River in McFarland.

If maintained properly, the dredge can last between 20 and 30 years, especially in freshwater, Miller said.  

“Once you dredge these lakes down you’ve increased that capacity. Now the rainwater has a place to go and now you’re going to mitigate the damage to the town and to your infrastructure,” Miller said. “You’ve given the county this capacity to mitigate these major rain events. That cuts down on your storm damage costs.”

Dane County hired four permanent, full-time employees to operate the dredge plus several limited-term workers for extra help as needed. Ellicott sent trainers to get the new dredge operators acquainted with the machinery operation, safety protocols and maintenance.

“It’s all new to us,” said Brockner, who was in his second week of dredging.

[Local execs: Dane County growth highlights housing, transportation needs]

Where does the dirt go?

If a dredge is like a vacuum, then the dirt has to be emptied somewhere. 

The sediment slurry sucked up in the Dragon Dredge is pumped through about a mile of pipe into a large pond, or dewatering basin, that was built off of Highway 51 across from the Babcock Park boat launch.

“Seeing the whole process come together is exciting,” said Brockner, the dredge operator who helped build the basin.

At the base of the dewatering site, the sound of water rushing through the pipe can be heard while walking along the length of it. The surface of the manmade pond is still until water gushes through the pipe on one end of the site. A small rowboat is docked at the other end.

The sediment settles out of the water and then the water is pumped back into the river. Each week, the county makes sure the water meets standards outlined by the Wisconsin Department of Natural Resources. 

So far in the second phase, Reimer conservatively estimates the dredge has removed more than 5,000 cubic yards of sediment. The first phase removed 35,000 cubic yards, and he estimates an additional 5,000 cubic yards of debris and rocks that are too heavy to remove with a hydraulic dredge will be removed this fall using an excavator on a barge. 

All of the sediment left after the water is pumped back into the river can be dried and used for road construction, like the state’s upcoming project to improve Highway 51.

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The sediment sucked up in the Dragon Dredge gets pumped through about a mile of pipe into a large dewatering basin. The manmade pond was built off of Highway 51 across from the Babcock Park boat launch.

A matter of inches

The goal with the dredging is to have more days for lake levels to fall between the summer minimum and maximum range — a difference of six inches. In dry weather, Reimer said the county targets keeping the lake levels in the middle of the range to allow for three inches before exceeding the summer maximum.  

Recently, the lakes exceeded the summer maximum because the area received over two inches of rain between July 7 and July 10. The lake will rise two inches and then the watershed — the area of land that drains water into the lakes  — brings additional water into the lake, which increases its levels.

When lake levels are at risk of getting too low or too high, the county adjusts the dams. For example, when Monona and Waubesa are above maximum, Babcock Dam is completely open. When Lake Kegonsa is in the summer range, the dam is only partially open.   

“Once we see forecasts of rain we will be proactive to open the dams to deliver as much water as possible,” Reimer said.

Recently, Monona and Waubesa’s water levels have been closer together. On Aug. 17, there was about two inches of difference between the two. Normally, there’s a difference of between four and six inches. In the 2018 flood, Reimer said they were separated by eight inches.

“The closer their water levels means the less of a constriction between the lakes to release the water,” Reimer said.

To notice water level reductions across the entire system, Reimer said water flow from Lake Waubesa needs to be improved.

Effects on habitat

Apart from influencing water flow, the sediment removal project will also have an effect on existing habitats. Dredging disturbs what is living in the river.

“There is going to be some collateral damage,” Stanley said.

But the habitats that will likely be disturbed are completely buried in legacy sediment, Stanley said. 

“These are not always lovely, natural habitats to begin with, and they're doing this phased approach, so they’re not going to be hitting the system brutally hard all at once,” Stanley said.

Reimer believes the area will be improved for wildlife when the project is complete. The area between Babcock Dam and Lower Mud Lake, in particular, is a significant fish refuge area where fish spawn or migrate.

“What we want to do is not only dredge but dredge it in a way that we can put rock back down or we can put that habitat down so the fishery is restored or even enhanced,” Reimer said. “It's going to be deeper, it's colder, and the water depth is greater, so you can support more fish.”

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A fish-eating duck named the common merganser, floats along the dredging pipes on on the Yahara River in McFarland.

Dredging a river to improve water flow is a unique approach in Wisconsin. When Reimer researched strategies, he found that no other municipal or county government was doing this type of work in the state. According to the DNR, no other dredging projects are being conducted at this “magnitude.”

Nationwide, he found more dredging work done in coastal environments and in ports and harbors to improve shipping.

“Here for flooding, I didn't really find too much that counties, municipalities were taking this on,” Reimer said. “We're pretty unique.”

Miller, Ellicott’s domestic sales manager, pointed to programs doing similar dredging operations outside of the state. For example, Ohio’s Department of Natural Resources invested in dredging to improve water quality and aid navigation into ports. 

“Dane County is far from the first or will be the last. They certainly were very proactive,” Miller said. “What's really impressive was how they saw a need, they saw a challenge and how quickly they responded to it.”

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Abigail Becker joined The Capital Times in 2016, where she primarily covers city and county government. She previously worked for the Wisconsin Center for Investigative Journalism and the Wisconsin State Journal.

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