Morphological Evolution of a Nearshore Nourishment Constructed of Dredged Sediment in Southern Lake Michigan

In 2024, 49,683 m 3 of sediment was dredged from Burns Small Boat Harbor, Indiana, and placed in the adjacent nearshore in two mounds. The beneficial use of dredged sediment from navigation channels through nearshore nourishment is a common technique to cost-effectively add or retain sediment within the littoral system, particularly for sediment that is predominately sand but contains nontrivial quantities of silts or clays. This supports coastal resiliency, but sufficiently large quantities of fine-grained sediment can also generate turbidity plumes. Elevation, aerial and terrestrial imagery, hydrodynamic, sediment grain size, and turbidity data were collected before, during, and after nearshore nourishment construction to quantify erosion reduction benefits and monitor and quantify potential turbidity increases. Both mounds deflated significantly in the first 5 months after construction, with the western mound volume decreasing by 73% and the eastern mound volume decreasing by 63%. Mound positions were quite stable during the same time frame with the centroid for each mound moving <25 m. Although the mounds were a highly active source for sediment transport, relatively little change occurred in the placement area during the period with extensive shore ice in January and February. Terrestrial imagery indicated up to 17 m of beach width gain on the lee side of the nearshore nourishment, but many factors appear to have influenced morphology change. During dredging, aerial imagery indicated a visible surface turbidity plume onshore of the placement, but turbidity measurements did not substantially increase. Turbidity measurements near the placement area were less than the mean cumulative frequency distribution from the distant reference sites for more than 98% of the record. Sediment samples did not indicate a detectable influence on nearby median grain size characteristics or fine material percentage. The study highlights the coastal benefits of placing dredged sediment in the nearshore to support the beach profile.