The impact of hurricane Dorian on freshwater resources of Grand Bahama island.

Abstract:

On September 1, 2019, Hurricane Dorian hit the northernmost islands of the Bahamas as a Category 5 storm with surge exceeding 20 ft. The storm's impact was catastrophic, especially in Grand Bahama, resulting in extensive flooding that contaminated the groundwater resources with saltwater. Given the fact that groundwater, in the form of freshwater lenses (FWLs), is the sole source of drinking water on the island, it is very important to assess how quickly the resource can recover from this disturbance. The goal of this work is to understand how the rate of recovery of FWLs is impacted by climatological characteristics and human activities.

A field campaign was conducted on the island between January and October 2020. Soil cores at various depths and surficial samples at various locations were collected monthly to determine the distribution of salt within the soil profile. Groundwater samples were collected at 16 wells within the inundated area at the three main wellfields of the island on a weekly basis. In-situ measurements of electrical conductivity, total dissolved solids, salinity, temperature and water levels were collected using portable meters. Despite the flushing induced by the precipitation during the wet summer season, preliminary results show that almost a year after the flooding event, salinity levels remain elevated on both soil water and groundwater, indicating a slow aquifer recovery.

The collected data provided the foundation for building a robust three-dimensional, density dependent model using SEAWAT that simulates the saltwater intrusion process in the FWL system and predicts the seawater intrusion extent, its temporal dynamics and the flushing process. Investigation of the impact of climatic and anthropogenic activities on FWL recovery is expected to advance our understanding of the vulnerability of FWLs in current and future climate and assist local authorities in decision making and planning while strengthening the resilience of groundwater resources in remote islands.

Acknowledgment: This material is based upon work supported by the National Science Foundation under Grant No. 2015311. The authors would like to thank Grand Bahama Utility Company (GBUC) for their support.