USING LIDAR FOR MAPPING COASTAL GEOMORPHOLOGICAL CHANGES DUE TO MINING TAILINGS MIGRATING ALONG THE LAKE SUPERIOR SHORE AT GRAND TRAVERSE BAY, MI

We use multiple year bathymetric and terrestrial LiDAR and MSS data to map geomorphic changes due to stamp sand (the basaltic waste by-product of copper milling operations) migrating along the east side of the Keweenaw Peninsula, MI. About 22.7MMT of stamp sand was dumped into Lake Superior from two stamp-mills operating at Gay, MI from 1901-1932. A fraction (about 16%) remains there; about 30% migrated along the beach due to beach drift, and most of the remainder winnowed into Lake Superior. Erosion of the waste pile continues at present. Beach and longshore drift of tailings from the source pile affected the entire coastal area 8km southward to a breakwall at the Traverse River. At the breakwall the stamp sand beach has accumulated to approximately 100 meters width (the original natural sand beach was about 5-10 meters wide) and accumulated vertically up to 7 meters thick and 1-2m height above the structure. Stamp sand overtops the breakwall during storms and accumulates in the Traverse River Harbor of Refuge, nearly blocking it off completely. Stamp sand along this area has also negatively affected a critical Lake Trout breeding area (Buffalo Reef) and nearly wiped out benthic invertebrate communities. Additionally, stamp sand has damaged recreational properties, dammed river mouths, and damaged coastal wetlands. With the influx and migration of coarse, angular stamp sand onto natural quartz sand beaches, a new, steep beach profile developed (11% vs. 4% on the natural sand beach), which consequently allowed storm waves to breach the storm ridge and flood across 100m+ of the accreted stamp sand. Recreational properties were damaged by the flooding on the stamp sand beach north of the breakwall, but there was no damage to properties along the natural sand beach south of the breakwall. We compare the beach and littoral geomorphology of stamp sand and natural sand beaches with LiDAR profiles and elevation models. Dynamics and form of approaching waves along stamp sand (reflective) and natural sand (dissipative) beaches are also compared.