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Geomorphic evolution of the Le Sueur River, Minnesota, USA, and implications for current sediment loading

By
Karen B Gran
Karen B Gran
Department of Geological Sciences, University of Minnesota, Duluth, 1114 Kirby Dr., Duluth, Minnesota, 55812, USA
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Patrick Belmont
Patrick Belmont
National Center for Earth-surface Dynamics, St. Anthony Falls Lab, 2 Third Ave. SE, Minneapolis, Minnesota 55414, USA
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Stephanie S Day
Stephanie S Day
National Center for Earth-surface Dynamics, St. Anthony Falls Lab, 2 Third Ave. SE, Minneapolis, Minnesota 55414, USA, and Department of Geology and Geophysics, University of Minnesota, Twin Cities, 310 Pillsbury Dr. SE, Minneapolis, Minnesota 55455, USA
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Carrie Jennings
Carrie Jennings
Department of Geology and Geophysics, University of Minnesota, Twin Cities, 310 Pillsbury Dr. SE, Minneapolis, Minnesota 55455, USA, and Minnesota Geological Survey, 2642 University Ave. W, St. Paul, Minnesota 55114, USA
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Andrea Johnson
Andrea Johnson
Department of Geological Sciences, University of Minnesota, Duluth, 1114 Kirby Dr., Duluth, Minnesota, 55812, USA
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Lesley Perg
Lesley Perg
National Center for Earth-surface Dynamics, St. Anthony Falls Lab, 2 Third Ave. SE, Minneapolis, Minnesota 55414, USA, and Department of Geology and Geophysics, University of Minnesota, Twin Cities, 310 Pillsbury Dr. SE, Minneapolis, Minnesota 55455, USA
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Peter R Wilcock
Peter R Wilcock
National Center for Earth-surface Dynamics, St. Anthony Falls Lab, 2 Third Ave. SE, Minneapolis, Minnesota 55414, USA, and Department of Geography and Environmental Engineering, Johns Hopkins University, 3400 North Charles St., Ames Hall 313, Baltimore, Maryland, 21218, USA
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Published:
May 01, 2009

There is clear evidence that the Minnesota River is the major sediment source for Lake Pepin and that the Le Sueur River is a major source to the Minnesota River. Turbidity levels are high enough to require management actions. We take advantage of the well-constrained Holocene history of the Le Sueur basin and use a combination of remote sensing, field, and stream gauge observations to constrain the contributions of different sediment sources to the Le Sueur River. Understanding the type, location, and magnitude of sediment sources is essential for unraveling the Holocene development of the basin as well as for guiding management decisions about investments to reduce sediment loads.

Rapid base-level fall at the outlet of the Le Sueur River 11,500 yr B.P. triggered up to 70 m of channel incision at the mouth. Slope-area analyses of river longitudinal profiles show that knickpoints have migrated 30–35 km upstream on all three major branches of the river, eroding 1.2–2.6 × 109 Mg of sediment from the lower valleys in the process. The knick zones separate the basin into an upper watershed, receiving sediment primarily from uplands and streambanks, and a lower, incised zone, which receives additional sediment from high bluffs and ravines. Stream gauges installed above and below knick zones show dramatic increases in sediment loading above that expected from increases in drainage area, indicating substantial inputs from bluffs and ravines.

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GSA Special Papers

Management and Restoration of Fluvial Systems with Broad Historical Changes and Human Impacts

L. Allan James
L. Allan James
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Sara L. Rathburn
Sara L. Rathburn
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G. Richard Whittecar
G. Richard Whittecar
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Geological Society of America
Volume
451
ISBN print:
9780813724515
Publication date:
May 01, 2009

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