T82 A Showcase of Undergraduate Research in Hydrogeology (Posters)

Sunday, 22 October 2017
9:00 AM - 5:30 PM
Halls 4EF

ASSESSMENT OF WAVE PROCESSES AFFECTING THE EROSION OF SPIRIT ISLAND

Paper number: T82-3
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

In 2011, The Fond du Lac Band of Lake Superior Chippewa purchased Spirit Island, located in Spirit Lake- a drowned river meander of the St. Louis River associated with the St. Louis estuary in Duluth, Minnesota. Spirit Island is sacred to the Ojibwe people because it was the sixth of their seven migration stops in the 1800s, prior to the federal government taking over the region and building five hydroelectric dams. In comparison to a herding map of the region created in 1863, a large portion of Spirit Island and surrounding wetlands has been eroded. The wetlands of Spirit Island were a prime environment for wild rice cultivation, which is of vital historical, cultural, and economic significance to the Fond du Lac tribe today.

This study attempts to determine whether water-waves are a primary control on the erosion of Spirit Island. To assess which shore faces of Spirit Island are most subjected to water-wave erosion, we used the method of Karimpour et al. (2017) for waves in fetch- and depth-limited conditions that converts wind data (fetch, water depth, velocity) to estimate wave properties (period, height) in Spirit Lake for the period 2006-2011. After applying this method to the bathymetry of Spirit Lake and correlating the results with historical maps/images, we concluded that the Eastern shore face is most subjected to erosion through wave energy.

We used flume experiments modeled on a profile of Spirit Island to study the relationship between wave properties and erosion of various grain sizes observed on Spirit Island. We measured the minimum wave frequency and amplitude required to submerge wetland environments and induce shoreline transgression. We then weighted the measured rate of sediment loss to wave climate properties calculated for Spirit Lake.

Finally, we use our computational model to evaluate different scenarios for the future of Spirit Lake. One scenario investigates the potential of sediment transport in adjacent contaminated water. The other examines the re-building of a wetland attached to Spirit Island to prevent further erosion and create habitat for wild rice reintroduction.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304156

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