Minnesota Water Resources Conference - Water Resources Center ...

Concurrent Sessions III 3:15–4:45
Track D: Sediment Loading
BOOK OF ABSTRACTS
Tuesday, Monday, October 27 23
Sediment loading in the LeSueur River Basin
Stephanie Day, University of Minnesota, dayxx196@umn.edu; Patrick Belmont, University of Minnesota; Karen Gran, University
of Minnesota; Carrie Jennings, Minnesota Geological Survey; Andrea Johnson, University of Minnesota
The LeSueur River is the largest contributor of sediment to the Minnesota River system. There are a many
features within the LeSueur Basin which may contribute sediment, including, bluffs, banks, ravines, uplands,
and tile drains. We have employed a variety of techniques to constrain the sediment contribution from each of
these potential sources. These techniques include side scanning LiDAR to survey bluffs and banks, repetitive
sediment sampling in the river and ravines, repeat surveys in the main stem channels, as well as in ditches
and ravines, sediment sampling of active channel alluvium for cosmogenic nuclide analysis as an indicator of
sediment provenance, grain size distributions, and optically stimulated luminescence (OSL) dating.
The LeSueur River cuts through a series of glacial tills, blanketed throughout much of the basin by a thin
mantle of glaciolacustrine sediment. The river was formed after a rapid incision of what is today the Minnesota
River, due to an outburst flood of Glacial Lake Agassiz 11,500 years before present. This incision caused two
knickpoints to propagate upstream forming the LeSueur River. As a result the lower 35 km of each of the three
main branches of the LeSueur are highly incised, contain slopes of 0.002, and have developed large bluffs and
ravines, both of which feed the main channel with sediment.
Preliminary results of bluff and bank erosion indicate that the erosive potential varies widely for each individual
feature. Most variation is probably due to the sediment composition and stratigraphy of the bluff. Turbidity
measurements on the main stems demonstrate substantial seasonality in sediment export from the system.
The highest sediment flux accompanies spring thaw, when the agricultural uplands are typically bare earth and
tilled and bluffs and ravines are most susceptible to slumping as they thaw. High sediment loads continue until
a ground cover is formed on the agricultural uplands, which functions to physically trap sediment and greatly
reduce flow in the river due to the high evapotranspiration rates.
Wild Rice River Sediment Budget
Jonathan Petersen, U.S. Army Corps of Engineers, jonathan.w.petersen@usace.army.mil; Jon Hendrickson, U.S. Army Corps of
Engineers, and Rebecca Soileau, U.S. Army Corps of Engineers
In-stream sources and sinks of sediment, sediment transport capacity, and geomorphic characteristics in the
lower 90 miles of the Wild Rice River, the lower 35 miles of the South Branch Wild Rice River, and the lower 7
miles of Marsh Creek were estimated. Information used included modern and historic cross sections, aerial
photographs, past studies and research, and data from USGS gages. Techniques and tools used included
geomorphic analysis, field reconnaissance, sediment sampling and analysis, aerial photo analysis, river cross
section surveys, and hydraulic modeling. Analysis was done by 5 mile river reach. Hydraulic modeling was
completed with the sediment transport capacity function in HEC-RAS. The focus of the sediment budget was
determining sediment sources from bank and watershed erosion to the flood control projects and planned
ecosystem restoration project.
Minnesota Water Resources Conference, October 27–28, 20078 34