Advanced Geomorphology Class Helps Carleton Assess Spring Creek Storm Damage
By Mary Savina
In late June 1998, a severe thunderstorm affected much of the Cannon River watershed, including Spring Creek, which runs through the Carleton campus. Abutments of the Highway 19 bridge over the Creek were damaged, destroying part of the roadway and causing a semi-trailer to get stuck. Further upstream, a few houses were flooded, banks were eroded and an enormous amount of sediment was moved. By late January, the College was beginning to consider a protracted and expensive project to "repair" eroding streambanks on College property upstream of Lyman Lakes. On the basis of a quick walk-through in February, I doubted that eroding stream banks were a major future source of sediment to the lakes. Working out the details was a perfect project for the thirteen-student Advanced Geomorphology class in the spring, which was to focus on watershed analysis and a long-term monitoring network for Spring Creek.
|Rebecca Fallon '99 takes a GPS reading during the Spring Creek storm damage assessment.
Here is a short list of our accomplishments during the course:
- We added information to the GIS database for Spring Creek watershed. (Joanna Reuter (Carleton '00) and Miriam Krause (Pomona '00) created the GIS during a 1998 Keck project). This GIS has been made available to the City of Northfield and to the public, through the Northfield Library through an ENTS concentration capstone project. The GIS is accessible on the web at http://gis.carleton.edu/
- We presented to Carleton's Facilities office and its consulting civil engineer and landscape architect the results of our study on streambank erosion on the College's part of Spring Creek including recommendations about bank stabilization and reports on flood effects of 1998.
- We completed a preliminary monitoring plan for lower Spring Creek, including choosing sites for weirs and other permanent installations, devising plans for bank erosion and pond sedimentation studies, and continued biological monitoring.
- We completed a preliminary biological survey of aquatic invertebrates that shows that part of the Creek (between Second Street and Wall St. Road) has stable riffles and pools and that the riffles, in particular, show high biological diversity.
- We completed a preliminary water chemistry survey of Spring Creek to show the sources of water and develop hypotheses of how surface and ground water sources interact.
The high point of the class was the presentation to college officials on June 4, 1999 that focused on the stream banks. Students prepared a map showing areas of eroding stream banks, including the five sites (of 35 total) that we felt should be stabilized. All 35 bank sites are described in a database accessible through the GIS. We determined that the 1998 storm was highly unusual in the recent record in the amount of coarse sediment (mostly sand) that was transported into Upper Lyman Lake. We also found that vegetation on the Spring Creek floodplain slowed the floodwaters, allowing even more sediment to be deposited on the floodplain and preventing additional erosion. We concluded that the reach of Spring Creek on the campus above the Second Street bridge into the Arb is a healthy biological community, with stable riffles and pools and that disturbance along this reach should be minimized.
We were also able to suggest specific remediation measures for the relatively few banks that we believe need to be stabilized.
Dennis Easley, the Superintendent of Grounds, said this about the presentation: "I thought the work and the presentations by the students were done exceptionally well. They were thorough and informative. The College often talks about educational opportunities in the Arb, but in Facilities we rarely see anything that is useful to us. This was certainly a profound exception to that perception. Thanks for bringing it all together."
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