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River Dams Won’t Prevent Floods

June 15, 2008

By Frank Schultz, The Janesville Gazette, Wis.

Jun. 15–Photo Gallery

Flooding photos

Beauty among the flooding, Riverside Park 6/13/08

Severe storms and flooding have caused problems locally and statewide. If you have been affected, we want your photos. Send us your photo.

To view a gallery of photos of the flooding taken by Gazette photographers, click here.

View Gallery

JANESVILLE — The Rock River soon will be flowing over land that has been river-free for 100 years or more.

What’s going on, and why can’t we do anything about it?

First the background: Heavy rains across the southern half of the state have saturated the Rock River in Wisconsin, covering hundreds of square miles.

The river is expected to reach a record high level at Janesville on Wednesday.

But all those dams on the river will keep the water in check, right?

Nope.

How about Lake Koshkonong, won’t it absorb the water?

No. Sorry.

Truth is, those dams are not designed to hold vast amounts of water, and Lake Koshkonong already is full, said a Sue Josheff, a DNR civil engineer responsible for the lower Rock River basin.

The rule for anything that holds water, be it a wetland or a huge reservoir, is that once it’s full, it’s full, said Kenneth Potter, civil and environmental engineering professor at UW-Madison.

It’s a bit more complicated than that, Potter said, but in essence, that’s the situation all along the river.

Wetlands can absorb floodwaters, up to a point. So wouldn’t we be better off with more wetlands and fewer dams?

“Wetlands are useful,” Potter said, “but when you get this kind of rainfall, you just better not be in the floodplain.”

Potter said recent rains were unusual in that they were so intense over such a wide area. And they came after much of the land already was saturated.

The water behind dams such as the Centerway Dam in Janesville already is flooding low-lying areas. There’s no other place for it to go, Josheff said.

Wisconsin, with about 3,800 dams, has very few that are designed for flood control, Josheff said.

Most dams were built to create millponds and drive water wheels. Janesville’s Monterey Dam is one of those.

Others were built or converted to produce electricity. The dam in Beloit and the Centerway Dam in Janesville still produce electricity. The Indianford Dam used to.

The Monterey Dam, owned and operated by the city of Janesville, keeps the river high as it flows through the city, so it keeps the river looking better than if it trickled through a muddy channel in the summertime.

But other than that, the dam doesn’t serve any purpose, said Jack Messer, director of public works.

Private businesses or municipalities operate most dams, Josheff said. The DNR regulates some of them, giving operators a range of water level they must maintain. The federal government regulates the hydropower generators.

During floods such as this, the DNR tells operators to open the gates as wide as possible and let the river run as freely as it can, Josheff said.

The DNR has been monitoring river levels and offering advice to operators and emergency government officials as needed as flooding progressed across the state recently, she said.

The silver lining to this rain cloud is that the Rock River is big, and it flows over rather flat land. It reacts slowly.

Smaller streams, such as the Sugar River, will give rise to flash floods with localized thunderstorms.

The Rock has a huge drainage area, or watershed. Recent rains oversaturated most of that watershed, and now, days later, the effect is being felt downstream.

“The nice thing about the Rock, from your viewpoint, is that it’s not flashy,” Potter said.

And that means cities such as Janesville have time to plan.

“I think this is a good test for the city,” Potter said.

Climate experts are saying more intense weather is part of global climate change, although it would be difficult to pin any one event on global warming, Potter said.

However, it’s prudent to plan for more intense weather such as this, Potter said.

City officials should learn from this incident, he said, and ask themselves what they can do to prepare for future events, maybe ones with even higher water.

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Copyright (c) 2008, The Janesville Gazette, Wis.

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