Sebewaing River (Michigan)

Project Status: modeling is complete

River Basin Characteristics
The Sebewaing River is a tributary to the Saginaw Bay on Lake Huron and discharges at Sebewaing Harbor (a Federal Navigation Harbor). The Sebewaing River watershed covers 66,000 acres and is split between Huron and Tuscola counties.

Land use within the basin is predominantly agricultural, but contains several small villages. Watershed soils are mainly loams and loamy sand near the lakeshore and contain more clay further inland. The Sebewaing River is heavily channelized and tile-drained for agricultural purposes. It is believed that agricultural ditch maintenance over time may have led to steep banks, causing instability and bank erosion. Sources of sediment include erosion from agricultural fields and drains as well as from ice damage to the river banks during the spring thaw.

Dredging occurs in Sebewaing Harbor for navigation purposes and to avoid flooding in commercial and residential areas near the harbor. On average, 14,700 cubic yards of sediment have been dredged from the harbor each year from 1966 to 1996. Two nearby confined disposal facilities (CDFs) have been filled with this material, making the storage of future dredge spoils an issue for the watershed.

		Saginaw Bay is a federally designated Area of Concern (AOC) Watershed is 90% agricultural Agricultural ditch management may lead to instability and erosion Sebewaing River is heavily channelized and till-drained for agricultural purposes

Modeling Approach
The Corps developed a hydrologic Soil and Water Assessment Tool (SWAT) model as well a GIS interface called AVSWAT. AVSWAT will allow users to evaluate scenarios and predict outcomes from hypothetical changes in land use, development or watershed management practices. The SWAT model, along with dredge records, may be used to
partition the sediment budget into individual sediment sources, including erosion from cropland and from within the drainage network. The model also takes into account information from local practitioners and residents on sediment sources, drains, types of crops being grown, tillage practices, water table management practices and historic conditions.

In addition, a custom-designed Channel Stability Tool (CST) was also developed for the watershed. The CST is an easy to use, GIS-based interface
that allows for the interactive determination of how various ditch and riparian management activities affect stream bank and stream channel stability.

Modeling for the Sebewaing River project was completed in October 2007, along with a training workshop for state and local partners to learn to utilize the modeling tool for various planning scenarios.

Use and Applications
A comprehensive sediment budget was created with the data from this model, allowing stakeholders to quantify various sediment sources within the watershed. The riparian buffer analysis highlighted areas where riparian buffer zones would potentially be most useful if installed and streamside management will protect stream bank stability.

The Channel Stability Tool (CST) gives stakeholders the capability to analyze and choose the best fit ditch management practices. This tool shows the potential consequences, such as erosion or sedimentation, of various ditch management practices, while accounting for gravitational forces, stream bank cohesive forces and root tensile strength of individual plant species. Together, the parts of this tributary model will allow stakeholders to manage and protect the Sebewaing River and watershed.

Project Partners
Baird & Associates
Huron County Drain Commission
Michigan Department of Environmental Quality
Michigan Department of Natural Resources
Sebewaing Inter-county Drain Commission

Tuscola County Drain Commission

Tuscola County Soil & Water Conservation District

Village of Sebewaing

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