Hydrodynamic and Trajectory Modeling of the August 11, 2006 M/t Solar 1 Oil Spill in Guimaras, Central Philippines with Validation Using Envisat Asar Data

Oil spill patterns detected from Envisat ASAR images were integrated with hydrodynamic and oil spill trajectory models for the purposes of understanding the August 11, 2006 M/T Solar 1 oil spill, and to evaluate the accuracy of the oil spill patterns simulated by an oil trajectory model. The oil spill incident event that occurred a few kilometers southwest of Guimaras Island in Panay Gulf and Iloilo Guimaras Strait (PG-IGS), Central Philippines, is considered to be the worst oil-related environmental disaster the Philippines has experienced. A three-dimensional, windand tide-driven hydrodynamic model of the PG-IGS coastal zone was developed using the Environmental Fluid Dynamics Code (EFDC) to ascertain water circulation patterns. The simulated currents by the EFDC model were used as inputs to an oil spill trajectory model based on the General NOAA Operational Modeling Environment (GNOME) that provided continuous simulation of the transport of spilled oil from its source to the nearby coastal communities. The oil trajectories simulated by the GNOME model were validated by comparing it to oil spill patterns detected from Envisat Advanced Synthetic Aperture Radar (ASAR) images of the oil spill incident. The use of sea surface currents simulated by the EFDC-based hydrodynamic model was vital in explaining the trend, shape, and direction of the observed oil slicks from the Envisat ASAR images. Conversely, the use of Envisat ASAR images for oil spill pattern validation provides an easier and direct assessment of the GNOME-based oil trajectory model's performance. The comparison between model-simulated oil spill patterns and the patterns mapped from Envisat ASAR images showed that in general, the simulated slick patterns differ in location, shape and extent to those detected from the SAR images. It appears from the results of actual-versussimulated oil spill patterns that improvement is needed in the EFDC and GNOME models, most especially in their data inputs. While the oil spill patterns simulated by the GNOME model differs at some aspects from the actual patterns, the results highlighted the usefulness of the model for oil spill trajectory analysis and its use for oil spill response in the future once improvements to the model have been considered.