justnorth posted on March 26, 2007 05:19 :: 1790 Views
The risk of flooding is high statewide in coming weeks because of the prolonged drought in the north and the threat of rain on partially frozen ground in the south, state dam safety officials say. They warn owners and operators of Wisconsin’s 3,800 dams to take steps now to try to prevent problems before water levels rise.
The National Oceanic and Atmospheric Administration (NOAA), which is sponsoring 2007 National Flood Safety Awareness Week, March 19-23 [http://www.floodsafety.noaa.gov] (exit JustNorth), has predicted that portions southern Wisconsin along with eastern South Dakota, eastern Iowa, southeastern Minnesota, and northern Illinois are currently at heightened risk of flooding.
“There’s a high risk of flooding across the state and we’re urging dam owners and operators to check now to make sure their dam gates and control structures are operational before the rivers come up,” says Meg Galloway, Wisconsin’s chief dam safety engineer and leader of the Department of Natural Resources dam safety and floodplain section. Owners and operators need to monitor their dams and operations and be ready to kick off the emergency action plan that large dams are required to have in place, she added.
The combination of rain and melting snow on frozen ground in the south will mean much more runoff than normal during warmer weather when the ground’s not frozen.
“While the rainfall amount predicted is fairly moderate the amount of runoff it produces because the ground is frozen will take people by surprise. They should take preventive measures like they would for a large downpour in summer,” she says.
In northwestern Wisconsin, the flooding risk stems from the same drought conditions that have spurred wildfire warnings already this year. Many dammed northern waterways are vulnerable to more flooding than usual because little or no water has been flowing through dam control structures to keep them from freezing. There’s an increased chance at this time of year that many of the control structures are plugged with ice, according to Bill Sturtevant, a dam safety engineer based in Madison.
“A lot of those dams haven’t seen water for a few years. If we get a big slug of water and their control structures are plugged up with ice or debris, water will rise in the impoundment and the dam could overtop or be overly stressed.”
Sturtevant says that if either condition occurs, the dam is at risk of failing which could cause downstream flooding.
Dam owners and operators should make sure their control structures are able to operate as intended.
They can also use grappling hooks to break up the ice jams, and melt ice by the dams to prevent ice jams. As ice starts to break up and move, it can result in ice jams that can act as dams that can flood low lying area and also send a rush of water downstream when they break up.
FOR MORE INFORMATION CONTACT: Meg Galloway (608) 266-7014; Bill Sturtevant (608) 266-8033
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