Technical assessment combined with extended cost-benefit analysis for groundwater ecosystem services restoration – An application for Grand Bahama

Abstract. A large storm surge caused by Hurricane Dorian in 2019 resulted in extensive flooding and saltwater intrusion into the aquifers of Grand Bahama Island. This caused 40 % of the island’s water supply to become brackish with no or slow recovery to date and damage of more than 70 % of mangroves and forests on Grand Bahama. Managed aquifer recharge (MAR) and reforestation were considered as nature-based solutions to mitigate the impacts of Hurricane Dorian. First, a technical assessment of MAR investigated (hydro-)geological aspects. As a result, potential locations for a MAR scheme are proposed. Further, a financial and an extended cost-benefit analysis (CBA) integrating ecosystem services (ES) assessments are conducted for proposed MAR and reforestation measures. Based on the current data availability, results indicate that the MAR scheme of rooftop rainwater harvesting is technically feasible. However, based on our first estimate with limited data, this measure will be able to provide only about 10 % of water demand in the study area and thus would not be favorable from a financial perspective. Since MAR has a range of positive aspects (including potential reduction of desalinization efforts and improvement freshwater-dependent ecosystems), we recommend reassessment with more detailed hydrogeological data. On the other hand, reforestation measures are assessed as financially profitable. The results of this study prove the technical feasibility and the added value of restoring the groundwater ecosystem on Grand Bahama, but also highlight the associated high costs.