Hydrodynamic and sediment-accommodation controls on headland-beach geomorphology evaluated by statistical methods, southern Lake Erie coast

摘要

The wave- and erosion-dominated south-central Lake Erie coast is one of the most heavily human-modified shorelines of the Laurentian Great Lakes. Three prominent harbor breakwaters, installed in the early 1900s, have fragmented this sand-deprived littoral system, trapping bluff-derived sands and gravels to form harbor headland beaches. These depositional systems offer an unique opportunity to investigate littoral sedimentary dynamics from headland geomorphologic data, having served as sites of continued sand sequestration along an similar to 65 km stretch of coastline dominated by eroding coastal cliffs and bluffs. Former foreshore deposits are mapped in dip-orientation beneath modern backshore regions using ground-penetrating radar, documenting the nature of beach progradation. Chronologic control of landform succession is attained from delineated historic shoreline positions. Multiple regression analysis of established beach-growth metrics versus lake-level and ice-cover variances suggests high lake levels are more strongly associated with shoreline advance, counterintuitive to the idea that lake-level rise should promote accommodation creation. Beach-growth phases during elevated lake levels are thus likely facilitated by increased sediment influxes from sourcing bluffs, more susceptible to erosion when impacted more directly by wave action during high water levels. Ice cover plays a lesser, yet important role in headland evolution as both erosional and depositional mechanism while hard structure design dictates the overall bounds of beach form. Changes in decadal beach-progradation rates are associated with sectional changes in breakwater orientation, an intrinsic control on accommodation distribution along strike. Correlations between headland geomorphology and hydrologic regime provide insight into the coastal margin's littoral dynamics, difficult to assess directly. (C) 2017 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.