GIS-BASED FLOOD SIMULATION FOR QUANTIFYING TERRESTRIAL RUNOFF AND SEDIMENTATION ON CORAL REEFS, BONAIRE, CARIBBEAN NETHERLAND ANTILLES

Sedimentation on coral reefs from the adjacent coast decreases a reef’s resilience to fight against disease, further increasing the reef’s susceptibility to disease. The island of Bonaire has recently seen an increase in reef diseases, such as Stony Coral Tissue Loss Disease (SCTLD), resulting in an overall decline in reef health and its diverse assemblage of corals. We investigated terrestrial runoff on Bonaire to determine the spatial distribution, accumulation, and flow rate of water into the coastal marine area. The Flood Simulator in ArcGIS Pro V3.3 was used to model water flow in a specified scene based on the terrain area, hillslope, infiltration, and the rainfall intensity and duration. Remotely sensed land cover data (2-meter spatial resolution) were incorporated into the model to account for infiltration rates, where each category was assigned specific values based on the permeability and porosity of the land cover. Natural runoff from rainfall was simulated based on 30 years of climate records to approximate the mean rainfall rates in the wet season and infrequent but large-magnitude storm events within a 24-hour period. The modeled flow velocity and discharge were mapped and then related to the sediment particle size that could be transported. Flood simulations were focused on coastal areas adjacent to three dive sites that were identified with varying concern for SCTLD, including Oil Slick Leap (SCTLD sighted), Calabas Reef (SCTLD rapidly spreading), and Invisibles (SCTLD sighted). Oil Slick Leap had the most natural terrestrial runoff and sediment input onto the reefs. In contrast, Calabas Reef and Invisibles had little direct runoff and sediment input, which are likely related to the differences in land cover, human use, and geological factors across the sites. Additional areas will be modeled to help predict which reefs are subject to runoff and sedimentation contributing to SCTLD and potentially leading to management practices and conservation efforts that combat these issues.