CRYOGENIC WAVE TANK EXPERIMENTS EXAMINING THE EFFECTS OF NEARSHORE ICE

Shore ice effects most coastlines in high- and mid-latitude regions, shaping the coastal morphology and acting as a protective barrier to the beach while also enhancing nearshore erosion. Coastal evolution resulting from ice processes in cold climate environments has been a relatively under-studied field, to the point that it is still debated if the overall impact of shore ice is erosive or protective. Shore ice, whether continuous or variable, affects sediment entrainment and transport processes, however, predicting these effects on geomorphic change is difficult given the current lack of knowledge about coastal ice dynamics. To better understand how shore ice alters patterns and processes of sediment transport we constructed a novel cryogenic wave tank (3 x 1.2 x 0.6 m) within a walk-in freezer. Within this, we ran down-scaled simulations of the hydrodynamic processes and meteorological conditions that occurred at a site along Lake Superior during the winter of 2020-2021. Initially, as the temperature of the water in the wave tank approached freezing an icefoot formed along the beach. As the ice front continues to migrate lakeward, it appears to reach a threshold position on the shoreface where bed scour is initiated. Once this scour begins the sediment is rapidly transported offshore into deeper water. In the wave tank simulation, no onshore transport of this scoured sediment was observed under ice free conditions with the same waves, indicating the presence of the shore ice caused erosion and deposition in portions of the bed that would have otherwise been unaffected. These results provide a temporally continual sense of the sediment transport processes that occurred in-situ in Lake Superior but could not be documented by topobathymetric snapshots. Based on the wave tank observations the deep-water erosion and deposition likely transported shoreface sediment beyond the depth of closure and essentially removed them from the nearshore sediment budget.