Great lakes urban pocket-beach dynamics: A GIS-based analysis of infrastructure-design influences on geomorphic development

Abstract

Chicago’s lakefront beaches experienced inundation and coastal erosion when Lake Michigan’s mean annual water level rose by >1.5 m between 2013 and 2019. Understanding beach geomorphic response to this type of lake-level event is important, as future climate predictions call for a continuation of decadal oscillatory patterns. A GIS-based study of beach change was conducted along the city’s urban lakefront, where sand is embayed by groins, jetties, and revetments. Morphologic changes associated with the most recent decadal lake-level rise were evaluated in context of the surrounding infrastructure. Beach morphometrics, derived from historical aerial images and available LiDAR products, were compared against the characteristics of the fixed urban infrastructure. Overwash volumes associated with an ∼1 m-rise in lake level scaled well with beach size (R2 = 0.88), suggesting that the creation of new sediment accommodation and its spatial distribution along the urban lakefront during lake-level rise is an important control on beach morphodynamic behavior. Overwash patterns were influenced by embayment orientation and groin characteristics. Counterclockwise beach rotation of up to 21° occurred in places where shorelines were exposed to the open lake. More tightly enclosed beaches retreated more uniformly along strike due to passive inundation of terrain with lake-level rise. Our insights provide managers with useful information on key beach behavioral patterns and how they are influenced by infrastructure design, allowing for the possibility of mitigation strategies to be emplaced in anticipation of future lake-level oscillations.