Geology, erosion history, and mitigation strategies applied to Great Lakes coastal bluffs: An examination of the Allegan County, Michigan, dewatering demonstration site
Published:January 01, 2013
Ronald B. Chase, James P. Selegean, 2013. "Geology, erosion history, and mitigation strategies applied to Great Lakes coastal bluffs: An examination of the Allegan County, Michigan, dewatering demonstration site", Insights into the Michigan Basin, Robb Gillespie
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The Great Lakes coast contains numerous unstable bluffs underlain by heterogeneous glacial materials consisting of till, sand, and gravel layers, and lacustrine clays. Many of the bluffs are steeper than their equilibrium angles and typically move as slow earth slides or occasional rapid slumps. Such movements develop largely where interlayered sand and clay contain perched groundwater that acts to reduce effective stress during winter months when perched potentiometric surface elevations rise because water cannot discharge through frozen soil. Aerial photograph records dating back to 1938 show that bluffs recede in amphitheater-like depressions followed by "catch up" where headlands between amphitheaters are attacked by other forms of erosion. This bluff recession is particularly pronounced during stages of high lake levels.
The erosion control experiment described herein has been designed to determine the manner in which groundwater activity influences the causes and mechanisms of mass wasting on the Great Lakes coasts. Three dewatering demonstration sites were selected, monitored electronically for virtually all movement and cause relationships, and dewatered to demonstrate a potential mitigation strategy other than construction of wave barriers.
Erosion activity and dewatering effects were carefully monitored for three seasonal cycles. Results show that (1) dewatering greatly reduces ground displacements during winter months, and (2) bluff movements are almost perfectly timed to, or lag slightly after, the hours when potentiometric surfaces near the bluff face reach their highest elevations during freezing (greatest soil pore pressure) or their greatest rates of surficial discharge (soon after thaw).
This field guide project was supported by grants from the U.S. Army Research Office, Terrestrial Sciences Program (Grant 3467-GS) from 1996 to 1999 and the U.S. Army Engineer Research and Development Center (ERDC) from 2000 to 2007, and 2012, through U.S. Senate Bill 227 (National Shoreline Erosion Control Development and Demonstration Program), with support from Western Michigan University (WMU). Additional personnel involved were Alan E. Kehew, Co-PIand, WMU graduate students William Montgomery, Rennie Kaunda, Mark Worrall, Gregory Young, William Bush, and Amanda Brotz. Well and monitoring instrument positions were chosen by R. Chase and designed by Ronald L. Erickson and James P. Selegean, U.S. Army Engineer District, Detroit, Michigan. Well constructions and instrument installations were done by STS Consultants, Chicago, Illinois. This huge project was very smoothly administered by M. Eileen Glynn and William R. Curtis, ERDC, Vicksburg, Mississippi.
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Insights into the Michigan Basin
This guidebook volume is a compilation of field excursions offered at the 47th annual meeting of the North-Central Section of the Geological Society of America, held in Kalamazoo, Michigan, May 2013. These field trips examine a wide range of geological time intervals and topics, from Silurian salt, to Cretaceous cosmic impact, to newly interpreted Mississippian–Pennsylvanian Michigan stratigraphy, to Quaternary glacial landscape formation, sand dune development, and present-day coastal bluff stability/erosion issues. Trips geographically range throughout southern Michigan and northern Indiana from Detroit, Michigan, in the east to the Kentland Quarry in Indiana to the west.
Early depositional events within the Michigan Basin are examined deep underground in the Detroit Salt Mine (trip leaders: W.B. Harrison III and E.Z. Manos [onsite leader]). This salt mine has been in operation for more than 100 years, and extends for miles beneath the city of Detroit.
Kentland Quarry, located in northwest Indiana, is the site of a Cretaceous-aged meteorite impact (trip leader: J.C. Weber). This site allows for surface examination of a similar style impact event that occurred in now buried Ordovician-age (Trenton) rocks located in Cass County, (southwest) Michigan.
Mississippian-aged fluvial deposits have been traditionally classified as the youngest bedrock exposed in Michigan. These rocks crop out in the center of the Michigan Basin near Grand Ledge, Michigan (trip leaders: N.B.H. Venable, D.A. Barnes, D.B. Westjohn, and P.J. Voice). Younger, more recently identified, Pennsylvanian rocks will be the subject of a related core workshop at the Michigan Geological Repository for Research and Education (MGRRE) in Kalamazoo (workshop leaders: S. Towne, W.B. Harrison, and D.B. Westjohn).
The regional, surficial geology of southwest Michigan is highlighted by three field trips. The first trip details the glacial landforms and sedimentary features formed by the differing dynamics of the Michigan and Saginaw lobes of the Laurentide Ice Sheet (trip leaders: A.E. Kehew, A.L. Kozlowski, B.C. Bird, and J.M. Esch). The two other trips follow along the Lake Michigan eastern shoreline and examine development of sand dune complexes (trip leader: E. Hansen) and present-day, coastal bluff stability and erosion issues (trip leaders: R.B. Chase and J.P. Selegean).
- Allegan County Michigan
- clastic sediments
- coastal environment
- erosion control
- erosion features
- field trips
- glacial features
- Great Lakes
- ground water
- lake-level changes
- landform evolution
- Michigan Lower Peninsula
- North America
- potentiometric surface
- United States