Lake Michigan Water Level Rise: Trends in Exposed Sand Cover at North Avenue Beach
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Description
Between 2013 and 2020, water levels in Lake Michigan rose from an all-time low to the highest levels observed in nearly four decades, inciting dramatic shoreline changes throughout the Great Lakes. These changes are particularly noticeable at North Avenue Beach (NAB) in Chicago, an artificial beach where rising waters have been addressed by dredging and the implementation of groins. Using a digital elevation model, we investigated whether sand loss was explainable by lake level change alone, or if other forces may be responsible, with particular attention given to hardened shoreline implemented north of the beach in 2016. We digitized the shoreline using spring season aerial imagery from 2012 to 2020 at the interface between wet and dry sand (east) and snapped the resulting polygons to a fixed edge (west). We then calculated beach area and related sand cover loss to water level change per the USGS station located approximately 2 miles south of the study area. Analysis reveals year-to-year loss in sand cover since 2013, with the largest single-year change occurring between 2018 and 2019. Of the six beach cells separated by groins, two cells failed over the study period, and middle cells experienced the largest individual sand losses. An inverse relationship with a slight lag exists between water level and these beach area changes. Observed sand cover loss markedly exceeded predictions based on inundation modeling. This suggests that linkages may exist between artificial shoreline modification and obstruction of sediment transport at this site.
Lake Michigan Water Level Rise: Trends in Exposed Sand Cover at North Avenue Beach
Between 2013 and 2020, water levels in Lake Michigan rose from an all-time low to the highest levels observed in nearly four decades, inciting dramatic shoreline changes throughout the Great Lakes. These changes are particularly noticeable at North Avenue Beach (NAB) in Chicago, an artificial beach where rising waters have been addressed by dredging and the implementation of groins. Using a digital elevation model, we investigated whether sand loss was explainable by lake level change alone, or if other forces may be responsible, with particular attention given to hardened shoreline implemented north of the beach in 2016. We digitized the shoreline using spring season aerial imagery from 2012 to 2020 at the interface between wet and dry sand (east) and snapped the resulting polygons to a fixed edge (west). We then calculated beach area and related sand cover loss to water level change per the USGS station located approximately 2 miles south of the study area. Analysis reveals year-to-year loss in sand cover since 2013, with the largest single-year change occurring between 2018 and 2019. Of the six beach cells separated by groins, two cells failed over the study period, and middle cells experienced the largest individual sand losses. An inverse relationship with a slight lag exists between water level and these beach area changes. Observed sand cover loss markedly exceeded predictions based on inundation modeling. This suggests that linkages may exist between artificial shoreline modification and obstruction of sediment transport at this site.