Mapping Future Coastal Groundwater Flooding and Impacted Infrastructure Using a Hybrid Analytical–Geospatial Approach

ABSTRACT Surface flooding from rising sea levels is widely recognised as a coastal threat, but coastal subsurface (groundwater) flooding is often overlooked. Coastal water table rise due to sea‐level rise can accelerate contaminant flow from onsite wastewater treatment systems (OWTS), decrease roadway performance, corrode below‐ground infrastructure, and intensify surface flooding. The few related, existing studies were primarily local, leaving important gaps for regional coastal risk assessments. In this study, we employed analytical solutions for coastal water table rise within a new geospatial framework to facilitate risk assessments at larger scales relevant for governance. An ArcGIS toolbox was developed to classify coastal aquifers as recharge or topography limited and perform the analytical calculations along a regional coastline using publicly available geospatial datasets. The analysis was conducted for Nova Scotia (~10 000 km shoreline), an Atlantic Canadian province characterised by high relative sea‐level rise and reliance on private wells and OWTS. Results highlight coastal regions expected to experience shallow groundwater and possessing potentially vulnerable infrastructure (water table depth < 1.5 m) before and after (year 2099) projected sea‐level rise. The model revealed that the most southwestern county (Yarmouth) will experience the highest percent of coastal land with groundwater flooding before (5.7%) and after (7.1%) sea‐level rise. Because of differences in coastal infrastructure distribution, the Bay of Fundy (Annapolis County) coastline had the highest fraction of potentially compromised OWTS and roadways (up to 12.8%), while the highest relative increase in potentially compromised OWTS by 2099 was in the southeast (+115%, Shelburne County). This novel hybrid analytical–geospatial approach serves as a first‐order assessment and can be used to prioritise localities for further site‐specific research and inform targeted coastal development policies.