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Project stabilized Indianford Dam

INDIANFORD — The weakest part of a dam is often the ground it’s anchored in.

That was the case when water bypassed a dam to carve a new channel that emptied Lake Delton recently, and that was the fear of Rock County officials last week at the Indianford Dam.

Indianford’s dam is on the Rock River, downstream from Lake Koshkonong. It helps stabilize the lake’s level.

These days, water pours freely through the dam, but the lake is well above flood stage. So there’s a lot of water pressure on the dam and the land around it.

County and Koshkonong Lake District officials became concerned last week that the water could rise and erode the saturated land between the dam and the nearby bridge, and that could lead to a Lake Delton-style breach.

Concerns were raised June 12 by the dam’s maintenance contractor, who lives nearby, said Brian Christianson, chairman of the lake district board.

The district owns the dam, but the county owns the parkland on either side. Both entities agreed they needed to do something.

In the space of six hours Friday, workers built dikes on either side of the dam, said Rock County Public Works Director Ben Coopman.

Meanwhile, rumors circulated that the dam had failed, which brought people to the site to see the “damage,” Christianson said.

“But what they see is several hundred tons of rock there that is protecting our shoreline, and I know we did the right thing,” Christianson said.

A layer of plastic sheeting was covered with gravel, and then many loads of large stones were brought in to make a wall. More gravel was poured on the rocks, and the sheeting was then pulled up over the top, with gravel to weigh it down.

Sandbags would have worked, too, but that would have taken thousands of bags and many more hours, Coopman said.

Their concerns’ were real. Water was covering lower parts of the dike Tuesday, Coopman said.

A rough estimate of the cost of the work is $30,000.

So far, the dike is holding well, but “we’re not out of the woods yet,” Coopman said.

If the water did cut a new channel, Lake Koshkonong would drop much lower than anyone wants, Coopman said.

And, of course, a lot of water would course downstream to Janesville and points south.

Coopman said the county has been lucky to have few such problems. The next biggest project was replacing a washed-out, 5-foot diameter culvert on County KK in Lima Township, probably costing $12,000 to $10,000.