OFFSHORE GEOLOGICAL MAPPING AND TOPOBATHYMETRIC MONITORING OF ILLINOIS SHORELINE ENVIRONMENTS: PARAMETERIZING COASTAL RESILIENCY FOR REGIONAL STAKEHOLDER GROUPS

This presentation provides insights into an active geological monitoring and mapping program established by the Illinois State Geological Survey (ISGS), through support from the Illinois Coastal Management Program, Illinois-Indiana Sea Grant Program, and other state and federal partners. It highlights the importance of geological data collection along highly dynamic shorelines of the North American Great Lakes, which remain understudied with respect saltwater coasts. An improved understanding of how framework geology, patterns of sand transport, and lake hydrodynamics factor into coastal geomorphic change must inform efforts to promote coastal resiliency in the face of future changes in climate and human activities within the coastal zone.

Topobathymetric monitoring of shoreline environments by the ISGS has been underway since 2018 at select sites along Illinois’ ~100 km-long Lake Michigan coast, with many locations mapped at seasonal or finer temporal resolution and at cm-scale geospatial precision (in horizontal and vertical dimensions). Assessments of beach and nearshore geomorphic change, based on drone and vessel-acquired information, are supplemented with detailed geological maps of nearshore regions. These are constructed from archival geological data, information from newly acquired sediment cores and surface-grab samples, and terrestrial and marine subsurface geophysical imaging (e.g., seismic-reflection studies).

Most data-derivative geospatial layers are published through an online data clearinghouse. These include (1) delineated shoreline positions, (2) digital elevation models (topographic and topobathymetric), and (3) select geomorphic change models. To date, more than 375 beach-specific topographic and 121 bathymetric datasets have been compiled, from 2018-2024 data. These products and derivative change metrics have provided urban planners, beach managers, and other stakeholder groups up-to-date information on beach and nearshore geomorphic developments. They are also contributing to a variety of management-related research endeavors, including assessment of breakwater-chain performance at Illinois Beach State Park, where a five-year pre-construction dataset provides an unparalleled opportunity to evaluate structure performance.