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Updated 10/16/07.
Project Title
An Integrated Sediment Budget for the Le Sueur River Basin, Minnesota
Project Overview
Objective
The goal of this project is to develop an integrated sediment budget for the Le Sueur River basin in southern Minnesota. The Le Sueur River is one of the most substantial contributors of sediment to the Minnesota River and to Lake Pepin on the Mississippi River. Significant stretches of the Le Sueur and Minnesota Rivers are impaired for turbidity under the Clean Water Act, and the Minnesota River contributes 85-90% of the suspended sediment that is in Lake Pepin, which is also impaired for turbidity.
Sediment budget
We will ultimately develop a model of sediment fluxes being contributed from uplands (primarily agricultural fields), gullies and ravines, eroding bluffs and channel banks, and river terraces and floodplains. In this way, we are developing a spatially-integrated sediment budget. In addition, our sediment budget will integrate multiple timescales, from decades to seasonal cycles and even the variability generated within a given storm event. Study area
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This hillshade relief image shows the modest topography of the Le Sueur uplands and the incised channel near the mouth. LIDAR coverage is available for Blue Earth County, here shown in lighter grey. |
Sampling strategy and experimental design
Field campaign
Modeling efforts
Social science efforts - economic valuation and impacts of watershed restoration
Context and Potential Impacts of the Research
Practical application of the sediment budget
Our sediment budget will inform the Minnesota Pollution Control Agency’s (MPCA) development of a Total Maximum Daily (sediment) Load requirement for the Le Sueur River, which will guide development and management decisions throughout the basin.
Why does MPCA need such an elaborate study to help determine the maximum sediment load allowable if the Clean Water Act has already established a turbidity standard? Essentially, this is a case of "one size does NOT fit all." The national Clean Water Act standard, enforced by the Environmental Protection Agency (EPA), does not necessarily work for the geologic setting of the Le Sueur River. Here’s why: The MPCA is charged with limiting the amount of sediment pollution in Minnesota’s waterways. The term "sediment pollution" refers to an excessive concentration of sediment that is contributed to the river as a result of human activity. But in the Le Sueur River, the sediment load of silt and clay, which determines the turbidity (a measure of how murky the water is as a result of the sediment), was very high long before human settlement of the area. High, natural turbidity in the Le Sueur River is primarily due to two factors: 1) the easily eroded glacial material (dominated by silt and clay) that covers the top 20 to 150 meters below the land surface and 2) active vertical river incision, initiated in the Minnesota river (~ 12,000 years ago), that is now propagating upstream from the mouth of the Le Sueur River. Although we have evidence that erosion rates have very likely increased since human settlement, the Clean Water Act standard may be lower than the natural turbidity level of the Le Sueur River. Thus, instead of asking "how can we reduce the sediment load to EPA standards?" (which are likely below the natural sediment yield of the Le Sueur River), the question becomes "what is a reasonable sediment load we should seek to attain?"
Primary research questions:
What proportion of sediment is being derived from uplands, ravines, high bluffs, and streambanks, respectively?
How have agricultural tile drains affected hydrology, and what are the implications for sediment transport?
What role does knickpoint migration play in bluff erosion and ravine development?
How does the Le Sueur River interact with its floodplain to temporarily store sediment?
What is the economic value of the Le Sueur River ecosystem (i.e., how much do people care about this problem)?
Why NCED?
The MPCA selected NCED for several reasons. Among those reasons, and most importantly, NCED has a reputation for interdisciplinary collaboration and is able to combine field observation with numerical and analog modeling. In addition, NCED has the advantage of being based in Minnesota, with the ability to pull resources from across the country.
Researchers
External Cooperative Groups
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