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Delavan Lake dredging clears natural filter

An aerial map of the Delavan Inlet, created by HDR Engineering of Springfield, IL, is courtesy of Ryan Simons' blog.

October 12, 2011 | 07:44 AM
DELAVAN — Cleaner, clearer water in Delavan Lake should result from the Delavan Inlet Dredging Project, which is scheduled to be completed this month.

Started in July, the $1.46 million project, removed thousands of pounds of silt and sediment that had built up in and along a 3,000-foot section of the Delavan Lake Inlet, a 210-acre wetland that filters topsoil, fertilizer and sediment from the water that flows into the lake.

Successful completion of the project is expected to restore the inlet's ability to filter out eroded topsoil and nutrients that now enter the lake through Jackson Creek. It will also restore boating access into the inlet area and the lake, said Ryan Simons, chairman of the Delavan Town Board.

In 2008, the Delavan Town Lake Committee took the initiative and spearheaded the effort to renovate and rebuild three of the primary features of the 1989 lake rehabilitation project.

Most of the project cost of $1.46 million is being paid by the town of Delavan, The town's share is $1.34 million in local taxes, with the city of Delavan contributing $125,000 and the Wisconsin Waterway Commission contributing $100,000.

The town of Delavan is bearing most of the cost because most of the inlet is within the town, Simons said. A small part is along Lake Lawn Resort, which is in the city of Delavan, and the city has contributed a portion of the costs as well, he said.

Town of Delavan officials and the town's lake committee worked with area residents, local organizations, the city of Delavan, the Wisconsin Department of Natural Resources, and the Wisconsin Waterways Commission to make the project a reality. The town is currently working to reinstitute a comprehensive water quality monitoring program to systematically check lake water quality.

While the project price tag is high, the price of not doing the dredging would be even higher, Simons said.

"This is something we need to do," Simons said of the dredging. "It will be paid for through borrowing."

Some room tax money was also used to help pay for the work, he said.

And in 10 to 15 years, it's a project the town will have to do again

In 2005, a study conducted by the Fiscal and Economic Research Group at the University of Wisconsin-Whitewater found that Delavan Lake generates about $77 million in local spending annually, along with 812 jobs and $17 million in direct labor income.

The researchers found that business and property values are directly tied to Delavan Lake's water quality. If water quality decreases, business and property values also tend to decrease.

As water quality increases, so do business and property values.

Delavan Lake is one of the top five fishing lakes in Wisconsin, and the town wants to keep it that way, Simons said.

"Hopefully, through increased activity on the lake, it will help allay costs," he said.

Most of Delavan Lake's water, about 68 percent of it, comes from the narrow inlet on the northeast side of the lake, and through the 3,000-foot channel leading to it. The inlet and the channel drain the 26,600-acre Delavan Lake watershed.

Delavan Lake is 2,072 acres, about 60 feet at its deepest, and is both fed and drained by Jackson Creek, a tributary of Turtle Creek.

Over time, the inlet had become clogged with so much sediment that it lost about 56 percent of its natural storage capacity and became less effective at cleansing the water flowing into the lake.

The dredging project will remove as much as 50 percent of the sediment and phosphorus entering from Jackson Creek. About 34,522 cubic yards of sediment has already been scraped from the two sedimentation ponds.

When the project is completed, about 900 truckloads of sediment containing 40.8 tons of phosphorus will have been removed. Before the dredging, about 7,000 pounds of phosphorus had entered the lake through the inlet every year.

The previous two projects were:

n The removal of 3,000 cubic yards of sediment from Brown's Channel, a small tributary. The $150,000 project was completed in winter 2006.

n Reconstruction of the Mound Road sedimentation ponds, a 140-acre wetland with two man-made sedimentation ponds. The 4- to 5-foot-deep ponds were excavated in 1992. By 2002, the ponds were more than 40 percent filled with sediment and no longer functional. To renew the ponds, they needed to be dredged and deepened to 10 feet. The project was wrapped up in 2009.

HDR Engineering of Springfield, Ill., designed the project and is managing the dredging and dewatering of the spoils.

HDR's design was researched and planned to assure that the lake would be provided physical and ecological benefits, such as reduced phosphorus, improved recreational access, better fishing, and overall improvements in water quality.

JND Thomas of Riverdale, Calif., and Daytona Beach, Fla. is the main contractor for the project. The company was awarded the contract after a thorough review of its credentials. The firm specializes in providing water-borne environmental and commercial work.

Keith Ayers, dredging supervisor for JND Thomas at Delavan Lake, said, barring bad weather, the project should wrap up by the middle of October.

Dredged sediments are dewatered, and water is returned to the lake and the phosphorous-rich spoils are landfilled.

The firm has eight full-time employees on site, working in two shifts until the project is completed.

Progress can be followed on the internet at www.townofdelevan.com/inlet-dredge-project.

This is the continuation of a lake restoration project that started in 1989.

In the late 1980s, Delavan Lake turned into an algae soup by mid-summer that discouraged swimming, clogged boat motors and killed off game fish. Farm and residential development around the lake poured nutrient-rich runoff into the watershed and into the lake. Those nutrients fed the algae blooms.

In 1989, communities around Delavan Lake, with the Wisconsin Department of Natural Resources and the U.S. Geological Survey, began a three-year, $7 million project to clean up Delavan Lake.

The project included drawing down lake levels to kill off undesireable fish populations and building ponds to help capture sediment coming from Jackson Creek.

A dam was built to further control inflow and the bottom of the lake was treated to bind up phosphorous sediments and keep them from feeding any more algae blooms.

The lake was then restocked with game fish. It was one of the nation's largest lake rehabilitation projects, and it appeared to be successful.

Over the years, Delavan Lake's health has been measured using a TSI rating, or Trophic State Index, which is used by the U.S. Environmental Protection Agency.

A "good" TSI reading of 0-60, means that the lake has enough nutrients for adequate plant life, but also has enough oxygen to support game fish and other aquatic species.

The U.S. Environmental Protection Agency uses a TSI scale to rate a lake's phosphorus concentrations, chlorophyll levels and water clarity.

Phosporus is a nutrient that encourages elevated algae growth. Chlorophyll is an indirect measure of the amount of plant life in the lake.

Delavan Lake's TSI readings had been declining since the early 1990s, but has remained relatively constant since 2007.

The inlet dredging, the third of these projects, is designed to keep the TSI rating in the 55 range and possibly improve it even more.

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