On October 6th, 2016, VLAWMO Board member Marty Long (North Oaks) took a helicopter tour with the US Army Corps of Engineers and MNDOT over the convergence of the Mississippi and Minnesota Rivers in Saint Paul, also known as Bdote in Native Dakota history. Outside of Marty’s role as a Board member of VLAWMO, he works in the businesses of mulch, compost, and soil.
What was the tour for?
The purpose of the tour was to learn about river dredging, shoreline management, and land uses along the rivers.
While sedimentation is a regular part of any large river, the Mississippi experiences more sedimentation than its historical amount because of erosion and runoff from the landscape. This has a number of implications on the health of the river, but also creates a need for ongoing dredging to keep commercial channels open for navigation. As sediment such as sand flows downstream, it gathers in sand ‘spits’ that create shallow spots in the river. The Army Corps of Engineers maintains a depth of 9’ along the marked navigation channels that run through Saint Paul.
What happens to material dredged from the river?
Pictured is the confluence of the Minnesota and Mississippi rivers. The main channel (location) produces a clean, course material with little silt and clay. Rapid water flow over time creates this sand by breaking down larger rocks upstream, and moving course material down the riverbed. This course material is put into soils that are used for drainage and soil structure projects across the state.
Slower moving shorelines produce material heavy in clay and silt, which are high in organics such as nitrogen and phosphorus. When dredged, this material is used in potting soils.
What should we do about sedimentation?
As seen in the photo gallery, the Minnesota River (left or bottom) converges with the Mississippi (right or top). The differences in land use are apparent with the muddy, turbid water of the Minnesota River contrasting to that of the Mississippi. Before reaching the Twin Cities, the Minnesota runs through many agricultural areas while the Mississippi does not. An ongoing effort between farmers and the Minnesota Pollution Control Agency strives to support agriculture while reducing runoff – buffer strips, economic planning, and conservation drainage are some examples of strategies in place to find solutions that work for people and water quality. Dredging plays an important role in valuable uses to our rivers, but reducing sedimentation reduces the amount of material that’s suspended in the water column, thus reducing the need for dredging. Another example of an issue needing sediment reduction is further South on the Mississippi on Lake Pepin.
Outside of agriculture, promoting perennial, native vegetation in yards, parks, or schools helps reduce Stormwater runoff that eventually finds its way to rivers. Small initiatives such as raingardens and shoreline restorations can add up to make a big difference in sedimentation.
Visit the State of the River Report for more information on issues facing the Mississippi today, and see the Agricultural Drainage Management Coalition for more on drainage practices.
What’s that big green machine?
Pictured in the gallery below is the McCloskey screener for sorting dredged material. It produces a quality, clean dirt and compost material to be shipped out across the State. See one in action here.
Is that a water treatment plant?
The Metropolitan Wastewater Treatment Plant is located on the Mississippi River and was part of the flyover tour. It’s the largest wastewater treatment facility in Minnesota, and one of the largest in the nation, treating an average of 215 million gallons of waste water every day before it gets put back into the Mississippi. Learn more here.