Nemadji River (Minnesota / Wisconsin)

Project Status: modeling is complete

River Basin Characteristics
The Nemadji River Basin is located just south of Duluth straddling the Minnesota-Wisconsin border. Of the 433 square miles (277,400 acres) of drainage area that make up the Basin, approximately 60% of the watershed lies in Minnesota and 40% in Wisconsin. The watershed includes portions of Carleton, Pine, and Douglas Counties. 69% of the land cover within the Basin is forested lands, 18% is cropland and pasture, 11% is wetlands and lakes, and 2% are other categories. Flows from the Nemadji River enter Superior Bay at Superior, Wisconsin, and then enter Lake Superior through the Superior Entry navigation channel.

Approximately one third of the basin is comprised of glacial till and glacial lake-laid clay soils. These soils are commonly referred to as "red clay" and were formed during the last glaciation of the area some 10,000 years ago. Red clay is considered highly erodible and is prone to extensive mass wasting through "slumping" along streams and tributaries. The upland two thirds of the basin is sandy and loamy tills and glacial outwash. These soils are generally sandier and much less erodible than red clay.

Source: Executive Summary Report: Erosion and Sedimentation in the Nemadji River Basin, Nemadji River Basin Project, Natural Resources Conservation Service, U.S. Forest Service, January, 1998.

		Highly-erodible red clay is prone to mass wasting and bank slumping Forest and timber industry may have an impact on the erosion issues in the watershed 33,000 tons of sediment are dredged annually by the USACE 98% of the dredged sediment comes from erosion of the valley walls 98% of the eroded sediment is transported to the mouth of the river Dredging in mouth of river may have an impact on fishing and other recreational uses Turbidity in the river is a source of contamination

Modeling Approach
Stream bank erosion, which occurs predominantly in the red clay soil areas, was found to amount to 89% of the total sediment load delivered to the mouth of the river. As part of the NRCS' Nemadji River Basin Project (NRBP), a comprehensive sediment budget was developed and calibrated for the existing conditions based on detailed information for the Skunk Creek sub-watershed. The Skunk Creek sub-watershed consists of 6,620 acres located in Carlton County, Minnesota, within the western, central part of the Nemadji River watershed. This sediment budget has provided valuable information in developing an understanding of the sediment loading characteristics for the Nemadji River Basin. However, the sediment budget, in its present form, does not represent a tool which can be used to assess the impact of best management practices for erosion control in the watershed.

The primary objective of the Tributary Modeling project for the Nemadji River was to extend the sediment budget work of the NRBP by introducing process-based numerical models linked to GIS to describe in detail the Skunk Creek sub-watershed. The primary tasks of this project were to implement hydrologic, hydrodynamic, and sediment transport models based on the available data for Skunk Creek. These models operate within a GIS system and have provided an improved definition of the stream bank erosion processes within the watershed.
The harvesting of forested lands was also modeled to determine the effects on sedimentation. The Nemadji Sediment Transport Modeling (NSTM) system was created using ArcView GIS, MIKE11 (hydrologic model and hydrodynamic model) and a customized sediment transport model.

Project Partners
Carlton County
USDA Natural Resources Conservation Service

US Geological Survey
Baird & Associates

Wade-Trim Inc.
Dr. Mark Riedel

Use and Applications
Upon completion of the tributary model for the Nemadji River, a technology transfer workshop was held in Duluth, Minnesota, in September 2000 to train potential users of the model. At this time, the model and database were transferred to the Carlton County Soil and Water Conservation District in Duluth.

This model has since been used to assess the impacts of forest harvesting and different land use scenarios within the Nemadji River Basin, model flood predictions for storm events, and to assess plans to reduce sediment load to Lake Superior.

For more information—or to obtain a CD-ROM for advanced modeling purposes—contact:

James P. Selegean, P.E., Ph.D.
Great Lakes Hydraulics and Hydrology Office
U.S. Army Corps of Engineers
Detroit District
477 Michigan Avenue
Detroit, MI 48226
Office: (313) 226-6791
Fax: (313) 226-2398
James.P.Selegean@usace.army.mil