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PRI's Environmental News Magazine

Dredging the Illinois

Air Date: Week of November 26, 1999

There is so much sediment making its way into the Illinois River that many people worry it could soon turn into a mud bog. But new dredging technology may make it possible to effectively remove large amounts of mud from the river bottom. Jonathan Ahl reports from WCBU in Peoria, Illinois.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood. The Illinois River stretches for nearly 300 miles from just outside of Chicago to the Mississippi near St. Louis. More than a million people drink from the river, and it carries more than 35 million tons in barge traffic each year. With soil erosion from farming and development along its banks, the Illinois River is in danger of clogging up with sediment. But a new technology being developed promises a more efficient way to keep the flow open and clean. From member station WCBU in Peoria, Jonathan Ahl reports.

(Sloshing water)

AHL: When farmers plow their fields near the banks of the Illinois River, or builders break ground for new developments, they kick up dirt and mud that is washed and blown into the water. That sediment is slowly turning the river into a mud flat. Mike Platt is the Director of the Heartland Water Resources Council, an environmental and conservation advocacy group based in Peoria. He says within 30 years the tide of sediment will destroy wildlife habitats and render the river useless for boating and drinking water. Mr. Platt says those aren't the only things that could go wrong with a river full of mud.

PLATT: You're talking about just a real change in the hydrology of the flow of the river. And probably, that's the most serious thing that affects us in the future, is the fact that as this thing fills up with mud and goes into trees, that you're going to have some very significant flood events.

AHL: Currently there are two ways to solve the problem of river siltation. The first is limiting agriculture and development near the river and its tributaries, making sure that less sediment gets into the river in the first place. A second is physically removing the mud from the river bottom. But that's not easy using current technologies.

(Engines)

AHL: A dredging boat is working on the section of the Illinois River where it joins with the Mackinaw, one of its major tributaries. The main boat is connected to pumps on platforms, and more than 300 yards of pipeline floating on rusted pontoons. This system of dredging is called hydraulic dredging, because there's a large amount of water taken out of the river. Kenny Brenner is a civil engineer tech for the Army Corps of Engineers, which oversees the dredging. He points to a massive iron cutter head with large teeth.

BRENNER: Right underneath and in back of the cutter head is the intake for the suction of the pipe. That's what that pump sucks water out of the river, and then therefore the suspended sediments, which the cutter head disturbs, and that's how you get the 15 percent solids and 85 percent water.

(Crunching)

AHL: A slurry of water and sediment flows through this pipeline and is shot over a levee next to the river. From there the water runs downhill through grassland and eventually gets pumped back into the river without sediment.

(Pumps)

AHL: Hydraulic dredging is a long, inefficient process. It can take weeks of dredging 24 hours a day just to remove enough sediment to add two feet of depth to the river for a stretch of a few hundred yards. And sediment is getting into the river faster than dredgers like this one can pump it out. But there is a new technology on the horizon that could drastically improve the process of removing sediment. Peoria-based Caterpillar, Incorporated, is developing a new kind of dredger. Instead of pumping out watery mud, it would scoop more solid sediment from the bottom of the river and carry it out on a conveyor belt. It's like the difference between a milkshake and a scoop of ice cream. John Marlin of the Illinois Department of Natural Resources says the material recovered by a non-hydraulic dredger has a major advantage.

MARLIN: These newer technologies are going to make it possible to move the sediment and handle it in what I would call an environmentally-friendly manner. Rather than just letting it ooze itself into backwaters, we should be able to actually form it into islands and move some of it off the floodplain for reuse by other means.

AHL: John Marlin says he's conducted studies that show crops will grow in sediment dredged from the river as well as the current topsoil. He says that would mean the topsoil that's washed into the river could be returned to the places it's needed most. But not everyone agrees that non-hydraulic dredging would solve all sediment problems.

MATHIS: We don't have enough data, I don't believe, to say we can just simply haul this stuff up and put it on the fields.

AHL: Bill Mathis is a professor of biology at Bradley University in Peoria. He says river sediment is full of pollutants like herbicides and pesticides from farm fields, and heavy metals like lead and cadmium dating back from the days when riverside industries would simply dump their waste into the river. He says that could lead to health hazards for people.

MATHIS: It's a well-known fact that some plants will take metals up. This could be a conduit to humans through the growth of various crops.

AHL: Bill Mathis says more studies need to be done before river sediment can be used for farm topsoil. But he says it's better to remove and dispose of the contaminated sediment than letting it linger on the bottom of the river. Mike Platt of the Heartland Water Resources Council says just the possibility that there is a better way to dredge has stepped up efforts to clean the river, and rejuvenated some people who until this news were resigned to the river becoming a mud bog.

PLATT: The idea of a new way to move mud is more than just about moving mud. It is about changing people's minds to believe that they can actually, actually win this thing in the long term.

AHL: Caterpillar's non-hydraulic dredger is still in the development phase, and will not likely be commercially available for a few years. But if the new machine becomes a more practical and cost-efficient way to dredge sediment, it could help much more than just the Illinois River. According to the EPA, more than several hundred million cubic yards of sediment must be dredged each year from bodies of water around the country to keep the water navigable for boats. Environmentalists say that number is much higher to keep rivers and lakes healthy and protect the wildlife they contain. For Living on Earth, I'm Jonathan Ahl in Peoria, Illinois.

 

 

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