HGS Research Highlight - Topographic control on groundwater salinization due to ocean surge inundation

Authors: Xuan Yu, Jie Yang, Thomas Graf, Mohammad Koneshloo, Michael A. O'Neal, Holly A. Michael

Ocean surges introduce saltwater to coastal aquifers and threaten fresh groundwater resources. Topography controls the spatial and temporal dynamics of surge inundation processes, which leads to variable depths of saltwater inundation and heterogeneous infiltration. Our study explored the impact of coastal landforms (e.g. ponds, dunes, barrier island, and channels) by simulating surface water flow over synthetic and real-world topographies, and associated subsurface flow to systematically assess the impact on surge-introduced salinization of coastal aquifers.

Schematic illustration of the ocean surge-introduced saltwater infiltration at the surface of a coastal aquifer.

To examine topographic control on groundwater salinization, we modeled a theoretical overwash event and variable-density groundwater flow and salt transport in 3D using the fully coupled surface and subsurface numerical simulator, HydroGeoSphere. The model simulates the coastal aquifer as an integrated system considering overland flow, coupled surface and subsurface exchange, variably saturated flow, and variable-density groundwater flow.

The video shows the modeled overland flow and subsurface salinization during and after ocean surge.

This study suggests that topographic connectivity promoting overland flow controls the volume of aquifer that is salinized. In contrast, the amount of water that can be stored in surface depressions determines the amount of infiltrated seawater and the time for the saltwater to flush out of the aquifer. It is found that topography has a significant impact on groundwater salinization due to ocean surge overwash, with important implications for coastal land management and groundwater vulnerability assessment.

The complete manuscript has been published by Water Resources Research