Groundwater Flooding and Salinization Under Sea-Level Rise: Variable-Density Modeling for Coastal Communities in the East Dover Area, Delaware
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Sea-level rise is expected to increase flooding and salinization hazards along low-lying coasts. The Risks, Impacts & Strategies for Coastal Communities (RISCC) project aims to build decision support systems (DSS) for communities in South Carolina, Delaware, and Rhode Island that are disproportionately affected by sea-level rise, to support adaptation strategies for two compounding hazards: flooding and salinization. Kent and Sussex Counties (DE) face high flood exposure and high expected building loss from natural hazards, while household incomes in Kent County are relatively low. Meanwhile, continued population growth and economic development place further pressure on already stressed water resources. We developed a MODFLOW 6 variable-density flow model for the East Dover (Kent County, DE) area to simulate groundwater flooding and salinization under current and future conditions. The model builds on the SEAWAT model developed by Hingst et al. (2024). Scenarios include sea-level rise, precipitation, and pumping. Under 1 m sea-level rise relative to present MSL, simulations indicate saltwater moving inland around tidal streams, with little to no effect on the saltwater-freshwater interface elsewhere, and water tables intersecting the land surface along the marsh edge. In contrast, pumping and precipitation changes trade the two hazards against each other - changes that reduce salinization raise water tables and increase groundwater flooding, and vice versa. Simulations show that the town of Little Creek experiences both salinization and groundwater flooding, but the regional model cannot resolve the short-term dynamics that drive local impacts. We will therefore present a one-way nested child model of Little Creek, quantifying groundwater response to storm surge and extreme precipitation events and identifying which local characteristics, such as depth to water table and distance to tidal channel, control vulnerability. Finally, we will use the results of the regional model to evaluate a topographic groundwater model. The topographic model is based on surface elevation and measured groundwater and surface water levels. The numerical model will then define a minimum observation-well density required for this approach to be reliable, so it can be upscaled and used for the DSS.
Omowumi Erukubami
PhD Candidate
