Impacts of Coastal Structure on Coastal Bluffs in Lake Michigan: New Lessons to be learned

Session: Coastal Resilience in the Face of Change (1)

Chin Wu, University of Wisconsin-Madison, [email protected]
Nicholas Jordan, University of Wisconsin-Madison, [email protected]

Abstract

Coastal structures are commonly placed on shorelines to protect coastal infrastructure and property against bluff recession. Nevertheless, coastal structures can modify regional sediment budgets, resulting in a downcoast sediment deficit. To date, the spatial and temporal patterns of bluff recession adjacent to coastal structures have not been studied. In this talk, we will reveal how bluffs, beaches, and nearshores are impacted by nearby shore-parallel and shore-perpendicular coastal structures on Wisconsin’s Lake Michigan coast. Observations show that immediately downcoast of newly constructed shore-parallel revetments, the nearshore and bluff toe steepen dramatically, yielding abrupt changes of the coastal bluff profile within a short (1~ 5 years) period. Increased cumulative wave impact height, CWIH, caused by steepening of the nearshore and loss of beach-building processes, can accelerate undercutting of the bluff. For the downcoast of a shore-perpendicular structure, continual coastal bluff erosion and the gradual narrowing of beaches in the area are observed. The area immediately downcoast of the structure is found to maintain the form of a regional scales of headland-bay beach over a long (50~100 years) period. These results will aid coastal management and stakeholders in future planning and mitigation efforts on Wisconsin’s coast.