Coastal Water Table Mapping: Incorporating Groundwater Data into Flood Inundation Forecasts

Groundwater levels in surficial coastal aquifers are dynamic and responsive to climactic conditions. Long- and short-time scale sea level changes can induce upward fluctuations in the coastal water table to the point that it can break out of the land surface, resulting in groundwater inundation. Sea-level driven groundwater inundation can compound with rainfall and coastal tidal flooding and increase flood risk to low-lying areas. In order to fully evaluate coastal flood risk, all of the hydrological processes affected by sea level must be accounted for, including groundwater inundation driven by tidal fluctuations and water table rise. The present work evaluates the importance of groundwater inundation influenced by SLR, and identifies potential hotspots (i.e. areas that have especially shallow water-tables) by analyzing and modeling a coastal water table. This project also demonstrates how this information can be incorporated into flood inundation forecasts under different SLR scenarios. The Hampton Roads region of southeast Virginia was selected as a case study to develop the groundwater inundation model, and reveal how the spatial extent and depth of flooded land increases significantly by including groundwater data.