Recovery of urban Great Lakes beaches after lake-level rise: The roles of infrastructure, sand supply, and management activities

Managing beaches along urban waterfront corridors of the North American Great Lakes is challenging, as already complex lacustrine hydro-, littoral sand-supply, and coastal morphodynamics are impacted by shoreline and offshore infrastructure in ways not yet fully understood. This paper addresses the legacy controls of geomorphic developments and changes in sand volume within lakefront embayments, during high decadal base water-level conditions, on subsequent beach-recovery dynamics, during lake-level fall. Showcased are insights from annual topobathymetric assessments from 2021 through 2024, over which time Lake Michigan's base water level fell by ∼ 1 m from its 2020 highstand. Data from ongoing geological monitoring activities were supplemented with federal datasets, which provided information on 2012–2020 sand volumetric changes across urban lakefront embayments with ∼ 1.5 m of lake-level rise. Beach geomorphic developments with 2020–2024 interannual lake-level fall are shown to have been influenced by the legacy of preceding morphodynamic and sand-sequestration patterns. Unlike the shared lake-level and storm histories, these parameters are beach-specific. While all Chicago beach shorelines retreated and experienced overwash into backshore regions during lake-level rise, shoreline advance and foredune re-establishment with lake-level fall have been influenced by preceding sand volumetric changes. This has implications for coastal managers, who must develop site-specific mitigation plans that take intrinsic controls of lakefront structures and time-varying sand-transport patterns on beach morphodynamics into account. The re-establishment of ecologically important foredune areas within urban beaches is of particular interest, given that the urban lakefront of Chicago has recently hosted nesting pairs of the endangered Great Lakes piping plover.