Army Corp survey could lead to Lake Koshkonong dredging

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Saturday, April 3, 2010
— Residents on Lake Koshkonong this week might have seen a cabin-topped johnboat waddling across the lake's choppy water.

The vessel, which belongs to the U.S. Army Corps of Engineers' Rock Island, Ill., District, is a survey boat equipped with sonar mapping equipment.

"People have asked us if we were out here searching for bodies," Ray Frana, an Army Corps technician on the boat, said Friday.

Frana and his partner, Army Corps technician Terry "Sam" Hoover, weren't searching for bodies. They were mapping the topography of Lake Koshkonong's silt-laden bottom.

The work is the first field activity in a multi-agency study of silting and erosion at Lake Koshkonong, a shallow, 10,500-acre impoundment of the Rock River east of Edgerton.

The study could lead to a $2 million to $5 million plan to dredge areas of Lake Koshkonong. The plan, which officials said could span five or more years, would include use of dredged material to build islands to shelter bays and coves on the lake.

"It's kind of like reshaping the lake in some respects. It's kind of like landscaping," Army Corps project manager Stephen Russell said.

Russell said the islands would serve as windbreaks to control wave chop and shoreline erosion, while enhancing fish hatcheries and migratory bird habitat at the lake.

Dredging would improve lake access for boats, officials said.

"This project would truly benefit all lake users, from recreational boaters to sportsmen and other user groups," Rock-Koshkonong Lake District Chairman Brian Christianson said.

The Army Corps and the Wisconsin Department of Natural Resources, together with lake district officials have spent the last four months planning the lake depth and dredging study.

The study, approved March 12, is funded through state matching funds and an Army Corps grant awarded to the lake district last year.

"This (study) will let us put boots on the ground and shovels in the lake, finally," Christianson said.

Although Christianson said funds for dredging haven't been secured, pending public response and permitting, a pilot project for the first dredge and island construction could start in spring 2011.

Koshkonong's underwater topography hasn't been measured since the 1970s. The Army Corps couldn't give exact numbers on the lake depth, but Frana said measurements of the lake's central channel vary from 5 to 7 feet.

He said the lake's bays and coves seem to have depths 3 feet shallower than areas near the channel.

Christianson said shore erosion and silting are worst in a cove by Vinnie Ha Ha, a lakefront neighborhood near Koshkonong Mounds golf course.

"Residents there have asked the lake district to dedicate money for dredging. They're getting a lot of erosion there. For them, they want to be able to use their piers and get their boats to deeper waters," he said.

Some piers extend nearly 300 feet into the water.

"We'd like to put an end to that," Christianson said.

Officials acknowledged some lakefront residents could be worried that manmade islands would spoil their view of the lake.

"We recognize that a lot of people want to see across the lake. We'd want to continue that," Russell said.

Russell said the islands would be minimal in size. He said they'd be topped with silt for plant cover, and likely would be ringed with riprap to keep sediments from washing away.

"They'd just be something to break up wave fetch," he said.

Christianson said residents might have heard rumors dredging would create an avenue for high-speed boat traffic in the lake's central channel.

"A lot of people think we're going to dredge right down the middle of the lake and then put in a huge island in the middle. That's not what's going to happen," he said.

Christianson said during dredging projects, recreational access to parts of the lake would be interrupted. Pending studies, he said officials wouldn't know how much dredging could be necessary or where islands might be built.

"It's kind of like remodeling a house. We won't know until we tear down the walls, so to speak," Christianson said.

In coming months, the lake district will seek input on the dredging plan through public hearings with residents and user groups, Christianson said.

He said the first of those hearings could come in late April.

Last updated: 1:42 pm Thursday, December 13, 2012

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