Posted on November 22, 2021
Nov. 18—City leaders have a clearer picture of the costs and construction work needed to pursue a Lake Mitchell dredging project.
Perhaps the most anticipated aspect of the preliminary dredging design that’s been underway since spring is identifying a price tag to dredge Lake Mitchell. And that number has come out to be roughly $15 million, which Mayor Bob Everson said is “within reach” for the city to take on.
“It looks promising, and it’s starting to come together. But this is preliminary designing, so none of this is concrete,” Everson said, noting the preliminary design is set to wrap up in January 2022. “It appears there will be up to 2 million cubic yards of sediment and dirt that will need to come out of the lake.”
In April, the City Council tabbed Minnesota-based Barr Engineering to complete the preliminary design at a cost of $339,000. For the past six months, city leaders have met on a bi-weekly basis with the engineering firm to receive updates on the project.
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Among the most notable findings that have resulted from the preliminary design includes the recommendation to primarily use mechanical dredging instead of hydraulic, identifying the spoil site location where the dredged sediment and dirt will be disposed and the type of water drawdown needed for dredging the lake.
Everson said the design recommends dredging most of the sediment on the lake bottom through a mechanical method, which uses more traditional construction equipment to remove the sediment and phosphorus with excavators and bulldozers, whereas hydraulic dredging removes dirt and sediment through a pipeline that discharges the sediment and phosphorus to a disposal site away from the lake with pumps.
“The best route they told us is mainly mechanical dredging with some hydraulic as well, and the mechanical dredging would require us to draw down the water with a siphon,” Everson said.
For crews to dredge the lake bottom, Everson said the water would need to be drawn down or lowered 15 to 20 feet, which would leave parts of the lake dry for a period of time.
Project leaders also indicated the majority of sediment and lake bottom material that needs to be dredged is on the west side of the lake, Everson said.
“It would likely be dry for a period of time,” Everson said, noting the lake would be dry for about a year during the project.
The city would open the mechanical dredging phase up for bids, if the project advances to that stage.
Another key piece of information that resulted from the preliminary design is identifying Firesteel Park as the spoil site where the dredged sediment and dirt would be disposed of, which could make way for the winter recreation hill that Parks and Recreation Director Nathan Powell is seeking to create by using the dredged dirt. The park is located on the southwest corner of the lake and sits on 43 acres of land.
“The winter recreation hill would come after the dredging project is done since crews will be disposing everything there until the end of
Making progress on a long-term problem
While dredging the lake to correct the long history of algae problems that have plagued the body of water has been kicked around by city leaders over the past decade, what was once a dream appears to be inching closer to becoming a reality.
Included in the 2022 budget that the City Council approved on Monday is $665,000 allocated for a final dredging design that has yet to come in front of the council since the preliminary design is still wrapping up. The council’s approval to earmark money for the final dredge design is a big indicator that a future lake dredging project is likely on the horizon.
For Powell, who is leaving his role with the city in less than a month, the progress that’s been made on restoring the city-owned lake is “exciting” for the future of Lake Mitchell. Powell said tackling the lake’s algae problem has been one of the “biggest challenges” he faced as the Parks and Recreation director, and seeing city leaders make advancements toward taking on a lake dredging project is a testament to the commitment of restoring the 600-acre body of water.
“It’s exciting for Mitchell, and we are in a good position to restore Lake Mitchell,” Powell said. “The mayor has been working hard on this since he was elected, and the council has been on board with us.”
As the lake dredging design work advances, the city is preparing to start the $1.1 million wetland project upstream along Firesteel Creek, where more than half of the phosphorus and sediment that’s a major cause of the algal blooms flows into the lake, according to previous studies.
The main goal of the wetland project is to drastically reduce the phosphorus and sediment flowing into the lake with the help of cattails planted along the wetland. While Powell is eager to advance dredging as an “in-lake” solution, he said the work that’s going to be done upstream is just as vital for the health of the body of water.
“We know that over 50% of the phosphorus comes into the lake from the Firesteel Creek, so not addressing that and doing a dredging project alone won’t be nearly as effective. You need to do both, and it’s just a great sign that both are on the table,” Powell said.