INVESTIGATING LARGE LANDSLIDES ALONG THE ONTONAGON RIVER IN THE UPPER PENINSULA OF MICHIGAN

Landslide susceptibility mapping and early warning are critical for landslide risk reduction. However, landslide susceptibility modeling has to be well informed by the specific failure types and triggers unique to each climate and geomorphology. This research explains the creation of a landslide susceptibility model in a Northern climate with atypical landslide conditions for riverbank erosion-triggered landslides. The study site (Ontonagon River basin) is situated in northern Michigan on the southern shore of Lake Superior and receives an average of 4.8 m of snowfall annually, accompanied by a strong warming trend and rain in the spring. Undercutting of the steep riverbanks causes large failures which continuously threaten bridges and a nearby hydroelectric plant. A landslide database was mapped in this investigation using aerial imagery from 1992 to 2016. Landslide triggering factors were interpreted using temperature, cumulative precipitation, and river discharge data, demonstrating that river discharge is the primary predictor of landslides despite the source being either rainfall or snowmelt. A preliminary threshold was then created to determine the discharge characteristics likely to cause failures. A susceptibility map was created for the river system using a combination of Scoops3D with logistic regression, improving overall accuracy to 93%. Furthermore, Scoops3D proved valuable in constraining the model to failures of engineering significance (large volume and impact) and kinematic possibility. The threshold-susceptibility scheme is thus a powerful tool for assessing comprehensive slope stability along river channels.