The Hydrogeology of Curaçao: an electrical resistivity study

Abstract

Worldwide, coral reef health is declining rapidly due to both global stressors (climate change) and local stressors (pollution). Reef maintenance on Curaçao focusses on reducing local stressors including terrestrial pollution. One f low path for terrestrial pollution is via submarine groundwater discharge (SGD). Yet, on the island of Curaçao these hotspots of submarine groundwater discharge have not yet been located, let stand quantified. With this research we aimed to increase our understanding of groundwater flow on the island. This will serve as a foothold for future SGD research. To do so, we have conducted 9 electrical resistivity tomography (ERT) measurements to understand (1) the heterogeneity of the lava formation, the main aquifer, (2) the saltwater-fresh water interface at the coast, and (3) the groundwater flow at geological interfaces. To assist in the interpretation of the data we measured groundwater levels and the discharge of Hato spring, in addition to observing local geological outcrops. We discovered that the lava formation is a very heterogenous aquifer due to variety in degree of weathering of the pillow basalt. As a result of the heterogenous permeability, the extent of seawater intrusion in the coastal lava formation is strongly variable. Yet, the lava formation does form a better barrier for sea-fresh water mixing than the limestone terraces. The midden formation (sedimentary rock) forms a thin aquifer near the surface. And, at the interface of lava and midden formation, the groundwater flow is hampered. As a result, the groundwater is confined within the lava formation until the lava formations reservoir “overflows”. The same occurs at the interface of the lava formation and the diorite intrusion. The next step in SGD research is quantifying the seaward groundwater flux where the lava formation is in direct contact with the sea or limestone formation. Here seaward groundwater flow is not hampered by the midden formation or the intrusion and thus forms hotspots of Submarine (polluted) Groundwater Discharge.