A commercial tow pushing a fleet of barges is a common sight for residents in rivertowns along the Mississippi River. However, what happens out of sight to allow that commercial traffic is not so common.
The U.S. Army Corps of Engineers is charged with maintaining a channel in the river that is 9 feet deep and wide enough for barges to navigate.
In many places that is easy. The river is naturally wider and deeper than the shipping industry requires, so nothing needs to be done. But in other places, the Corps must constantly monitor the navigation channel.
“It’s called the Nine-foot Channel Project,” said Paul Machajewski, dredged materials manager for USACE, “but we dredge to 12 feet. We maintain the straightaways about 300 feet wide, but when you go around a corner, the barges need more room, so we will go 500 feet or wider on the bends, so they can get around the corner.”
One spot that has to be dredged every year is near Reads Landing, Minn.
“The majority of the sedimentation that is occurring here is because of the Chippewa River,” Machajewski said. “It is a younger river than the Mississippi. It is steeper and still digging the bottom, so that is what is bringing in most of the sedimentation.”
When the dredge boat, the Goetz, is at Read’s Landing, the crew works around the clock, according to Machajewski, who has worked for the Corps of Engineers for 30 years. There are 30 people on board, and they work 12-hours shifts. Two 12-person crews alternate with an additional six-person crew that overlaps both of the other crews.
On a recent stop at Read’s Landing, the Goetz removed “somewhere around 60,000 cubic yards of sand,” Machejewski said. “They do about 1,000 yards an hour, which is about 100 dump truck loads if you are trying to visualize that.”
Because the actual dredging happens underwater, it is difficult to picture what is happening, but Patrick Loch, public affairs specialist with the Corps of Engineers, offered a description.
“The first mate described it that the cutter head is like a blender,” Loch said. “It is attached to a vacuum, and it mixes the sand with water like a slurry , and using the pipes, it shoots it up and over the hill. At one point, he had the pipeline stretched out almost a mile. We have bulldozers up there making sure that it goes where we want it.”
Most of the sediment coming into Lake Pepin from the Chippewa River ends up being piled on an island near Read’s Landing. That island was identified as a good placement in the 1970s and the agreement was that other locations inland from the river would also be identified.
“They didn’t do that,” Machajewski said. “It is not that easy. Our challenge now is to find those upland places. We used to just put the sand along the banklines everywhere we went, but there were environmental impacts to wetlands and other habitats were being affected.”
Col. Karl Jansen, commander of the USACE St. Paul District, said, “We are exploring what is the plan for the next 20 to 40 years, because ideally we are identifying ways to manage sediment that stand for a long time which ultimately saves money. We want to find ways to manage the sediment that are efficient and cost effective for the taxpayer, but also publicly acceptable.”
Machajewski’s job is to “find a home for that big pile of sand.” he said. Much of it can be recycled for other uses such as contractors using it for general fill for projects, transportation crews using it for road construction, or winter road maintenance crews using it to mix with salt.
“A lot of this sand will go up to the Lake Pepin project,” Machajewski said. “There is a need for this sand up there, and this is a win-win for everyone.”