Locks, dams will not prevent area flooding
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By David Heitz | Wednesday, May 21, 2008 |
Q: When forecasting the Mississippi River flood, why doesn’t the U.S. Army Corps of Engineers open the dams early to get some of the water out of the river?
— John, Cordova, Ill.
A: For starters, the Corps does not forecast floods — the National Weather Service does — but they do work closely together. When the weather service alerts the Corps to the potential for high water, the Corps deploys teams of engineers to help affected areas with flood-fighting supplies and technical information.
“Many people believe the locks and dams create, or can prevent, flooding, but it is not possible,” said Ron Fournier, Corps spokesman.
Fournier explained that the upper Mississippi River lock and dam system is known as a “slack-water” system comprised of non-navigable, movable dams. The dams are designed to maintain fixed pool levels. They are fully open during high flows.
“Each dam holds back enough water to create a navigation pool, or slack-water lake, to maintain a 9-foot navigation channel,” Fournier said. “The dam’s rollers and gates do not reach from the bed of the river to above the water line. They are only lowered into a portion of the river to assist in maintaining the 9-foot deep navigation channel.”
Once the 9-foot channel is obtained, excess water passes through the dam under the gates or rollers. In high-flow situations, the dam gates and rollers are taken completely out of the water and all the flow passes through.
The Corps does not raise dam gates in anticipation of high water because that would result in the channel depth being lost, thereby halting commercial navigation. What’s more, cities and businesses that depend on the regulated pool level for their water intake would have to cease operation.
Although raising the dam’s gates early would allow the river to flow naturally, even if all the pools behind the dams could be completely emptied (which is not possible, Fournier said, unless there are long-term, severe drought conditions), it would take only a few hours to fill the vacated space during a major flood and the river would return to its projected levels.
Fournier explained that when drawing down the river, there also are concerns about bank erosion, the effect on fish and wildlife, impacts on passenger and recreational boats and boat docks and a variety of other issues that combine to make this method of flood damage reduction ineffective.
Q: When a Davenport police officer issues a traffic ticket for speeding, why is there a “criminal surcharge” added on and an automatic “court cost” of $50, even if you don’t go to court? It used to be that you could just mail in the true cost of your fine and it was over. Now the city is determined to squeeze more money out of its citizens. I was ticketed for going 11 miles over the speed limit and it came to $89.60. Isn’t this a little excessive?
— Jimmy, Davenport
A: The surcharge and court costs are imposed by the state of Iowa, not the city, and it has been that way for a long time, said Tom Warner, the city’s acting corporation counsel.
Follow-up files
The Web address listed for the Times’ virtual tour of Quarters One was incomplete in Thursday’s editions. The video can be watched at http://videos.qctimes.com/p/video?id=1789696.
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