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Aurora Looks to Approve Mastodon Lake Dredging

Posted on December 1, 2020

The Aurora City Council is set to approve dredging of Mastodon Lake on the East Side that would help drainage and water quality and ease flooding.

Aldermen also are looking to improve a change in floodplain mapping that would allow about 100 properties – some residential and some business – to be taken out of the lake’s floodplain, meaning they would no longer have to pay to carry federal flood insurance.

Both items have been placed on the City Council’s consent agenda for Tuesday, meaning they are likely to be approved.

The floodplain map revision would be done by HR Green Inc., of Yorkville, with a $39,750 contract. The same company would do final engineering for a Dredging and Shoreline Restoration project. The contract for that would be $176,350.

The dredging project is estimated at a total of $2.8 million. The city has applied for a state grant of $550,000 to put toward the project. City officials said they expect to hear about the grant in February 2021.

The engineering design is expected to take between eight and nine months, so Mark Phipps, of the city’s Public Works Department, estimated construction on the dredging and shoreline restoration would not start until the fall of 2021. The dredging and shoreline restoration would make the lake deeper in some places while creating more shoreline.

The city proposes to greatly improve the lake’s water quality with the dredging, as well as improve aeration and water circulation. The lake water has gotten so shallow – between 2 and 4 feet – that it has caused much algae and other aquatic growth, Phipps said.

Along the new shoreline, HR Green proposes planting vegetation and creating outcroppings. They even propose some fountains to help with aerating the water, Phipps said.

Both the dredging and shoreline restoration, as well as the revision of the floodplain map, were part of a Mastodon Lake master plan developed by HR Green. The lake was first excavated in the 1930s as part of the building of Phillips Park.

The excavation is a famous part of Aurora history because it unearthed historic mastodon bones, giving the lake its name. The bones unearthed remain on display at the Phillips Park Visitors Center.

With the lake deepened, it would allow for better drainage, including for the Phillips Park Golf Course, city officials said. It also means lowering and lessening the floodplain, which is what would allow numerous properties to be taken off the floodplain map, Phipps said.

In addition, HR Green now has more precise ways of measuring the floodplain, which was first mapped by the fledgling Federal Emergency Management Agency, or FEMA, in the 1960s and 1970s. Phipps said because flood maps were done in a hurry and without much attention to detail and precision, they included more properties in the floodplain than should be there.

He said in most cases, floodplain is not developed, and when development occurs, private entities come along and pay to have more precise measurements about what needs to be in the floodplain and what does not.

It is unusual to have a situation like this, with areas that have been in a floodplain for a while. That’s why the city can take on the cost of remapping the floodplain, he added.

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