POCKETIZATION AND HARDENING OF THE SOUTHEASTERN LAKE HURON SHORELINE: IMPACTS ON BEACH MORPHOLOGY AND BLUFF RETREAT

Rising water levels and corresponding bluff retreat in Lake Michigan-Huron during the mid 1980s and late 2010s caused many landowners to erect protective shoreline infrastructure. In southeastern Lake Huron, this consisted of shoreline hardening solutions, such as rock and metal break walls, as well as structures designed to trap sand, such as groynes. 11 groynes were present along an ~25 km stretch of shoreline between Bayfield and Grand Bend in 1978, but this figure jumped to 89 by 2015. These groynes often form groyne fields, leading to the pocketization of beaches along some portions of the shoreline. The long-term impacts of these coastal engineering solutions on the sediment dynamics of southeastern Lake Huron are only beginning to materialize due to the decadal nature of water level oscillations in Lake Michigan-Huron. Previous research on engineered pocket beaches in Lake Michigan has shown that their sediment dynamics are particularly sensitive to lake level fluctuations. Field studies and analysis of air photos from between the 1950s and 2020 has shown that during the water level rise of the late 2010s, bluff retreat primarily occurred in areas south (downdrift) of groynes and on the northern side of groyne field pockets. The pocketization of parts of the southeastern Lake Huron shoreline coupled with climate change impacts such as reduced protective winter ice cover may worsen bluff retreat in specific areas during future decadal lake level rises.