COASTAL SUBSURFACE MONITORING PROGRAM FOR SOUTHEAST FLORIDA

A $10M Congressional Appropriation motivated by the 2021 Champlain Tower collapse in Surfside, Florida, supports monitoring of shallow soil and groundwater conditions that may affect infrastructure. Following the collapse, there was a recognition that data on the subsurface and its water dynamics and chemistry at the appropriate locations and scales that might have been relevant to understanding the collapse were not available.

Unlike the typical focus of regional coastal groundwater monitoring to warn of potential saltwater intrusion impacts on drinking water supplies, this study emphasizes detection of near-shore freshwater lens geometries and their dynamics, the penetration of ocean/bay water level fluctuations into the subsurface, unsaturated zone and water table dynamics under large precipitation events, and corrosion risk in dense urban areas with high-value infrastructure.

The original project vision included 16 paired transects of ten 100-m spacing stations monitoring water potential, water content, electrical conductivity, and corrosion parameters at 5 depths from the surface to the permanent water table. A Monitoring Technology Advisory Panel met in June 2023 to review plans and offer suggestions for improving the monitoring program. Key recommendations were to proceed stepwise, by focusing on collecting available geotechnical and geological data, collecting new electrical resistivity data, completing new borings at candidate sites, and installing monitoring wells prior to establishing more intensive monitoring systems. In parallel to additional characterization, the Panel recommended developing a high resolution density-dependent groundwater flow model using existing model results for boundary conditions. To optimize monitoring system placement, it was recommended to catalog buried infrastructure susceptible to saltwater intrusion and to review adjacent soil conditions, particularly near infrastructure that has already been identified for implementation of corrosion mitigation.

The monitoring program will provide data and analyses that establish existing conditions, document change as sea levels rise, and provide early warning of changing subsurface conditions that permit coastal managers, utilities, municipalities, and building officials to plan, adapt, and avoid potentially catastrophic infrastructure failures.