Coastal Zones and Oceanography

Statement of the Problem: The growing pressure of exposure to petroleum hydrocarbons in tropical areas around the world requires novel, innovative approaches for assessing risks of hydrocarbon spills. The purpose of this study was to develop a workflow connecting a risk assessment methodology to results of spill weathering and trajectory numerical modelling, and then to emerging tropical toxicological data. Methodology: Typical incidents leading to hydrocarbon spills are prosed to be identified based on the analysis of risk profiles for the study area. The risk assessment process took into account the probabilities and consequential impacts associated with potential risk events. The rate of hydrocarbon weathering was modelled using ADIOS2 as a function of hydrocarbon properties, sea state and surface temperature. The Delft3D integrated flow and transport modelling system validated against local observations was used for assessing hydrodynamics. Spill trajectory modelling was carried out using a purpose-developed oil spill trajectory and fates model, MEDSLIK-II. Findings: The validations suggested that Delft3D-FLOW correctly propagated the tidal variations from the open boundary through the entire model domain, and accounted for variable in time and space winds. The stochastic modelling approach to spill assessments involved 100 simulation of each modelling scenario using different samples of ambient conditions each time. Three thresholds for modelling of potential entrained hydrocarbon impacts were set to 10 ppb, typical of temperate climates, and 103 ppb and 64 ppb, which are EC10 for tropical coral without and with UV impacts.  Conclusion & Significance: An inter-comparison of the respective spill impact probability maps demonstrated that appropriate thresholds may improve the predictive efficiency of spill impact assessments in the estuarine and open-ocean environments, leading to coherent contingency planning and response measures.