T112 Erosion: Processes, Rates, and New Measuring Techniques (Posters)

TURBIDITY IN THE MINNESOTA RIVER—COORDINATING A BASIN-WIDE STUDY

Paper number: T112-22
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

As a result of geologic and human influences, the Minnesota River supplies 85 to 90% of the sediment to Lake Pepin, a natural reservoir of the Upper Mississippi (Kelley and Nater, 2000), despite occupying only 38% of the watershed with 25% of the flow. The basin is currently infilling at ten times pre-settlement rates (Engstrom and Almendinger, 2000). This previously glaciated watershed was deeply incised as a late-glacial spillway that is now occupied by the Minnesota River. The lower 5 km of its tributaries expose 30m-bluffs of fine-grained glacial sediment as nick points move upstream. Our ability to predict river response to natural changes is complicated by recent drainage modifications that increase stream length and intensify peak flows. A comprehensive evaluation of accelerated erosion and sediment source is needed to design a river restoration strategy to meet federally mandated Clean Water Act requirements.

Investigations to estimate pre-settlement sediment loads and sources on the landscape (e.g., surface, gullies, bluffs, floodplains) are being coordinated by the Minnesota Geological Survey (MGS) and framed in regional mapping. Basin-wide studies use methods such as radionuclide tracing, cosmogenic burial dating, landscape evolution modeling, glacial mapping, and lake core analysis. MGS, in its citizen-education role, is also informing non-technical decision makers involved in the process. The MGS plans to integrate successful results to develop a cost-effective mapping approach that characterizes sediment flux in turbidity- impaired watersheds.

Engstrom, D.R. and Almendinger, J.E., 2000, Historical changes in sediment and phosphorus loading to the Upper Mississippi River: Mass-balance reconstructions from the sediments of Lake Pepin. Final Research Report, Met. Council Env. Services, 50 p. http://www.smm.org/SCWRS/researchreports/Pepin2000report.pdf

Kelley, D.W. and Nater, E.A., 2000, Source apportionment of lake bed sediments to watersheds in an Upper Mississippi basin using a chemical mass balance method. Catena (41), 277-292.