Oil Spill Modeling Lessons Learned over Four Decades of Catastrophic Spills

ABSTRACT Oil spill modeling developed tremendously over the past four decades, from simple floating particle trajectories of the 1979 Ixtoc spill to four-dimensional oil trajectory and fate models coupled with biological exposure, toxicity, and population models begun in the late 1980s to early 1990s, spurred by the Exxon Valdez, other major spills at that time and the Oil Pollution Oct of 1990. While many of the basic concepts and algorithms were developed in the 1990s, advances in computer hardware/software, as well as modeling techniques, have allowed for much better resolution of the needed model inputs, computations and outputs. Data availability and assimilation has greatly improved the performance of meteorological, hydrodynamic and ice (metocean) models, which are critical inputs to oil spill modeling. While large oil spills are traumatic events adversely impacting the environment and socioeconomic interests, they provide opportunities for process studies, model development and validation due to resources supporting the efforts and collections of needed data. Among other lessons, the Ixtoc spill modeling demonstrated the need for comprehensive, time-varying winds and currents from metocean models as input. In modeling the Exxon Valdez, spatially and temporally (hourly) varying winds driven by mountainous terrain, as well as coastal currents, were highly influential to the trajectory and fate of the oil. Measurement data was needed to drive modeling as the existing metocean models were not sufficiently accurate to account for observed oil movements. Other large spills in 1989 were in estuaries and coastal areas where oil movements were primarily driven by river and tidal currents, for which hydrodynamic models were reliable. The 1996 North Cape oil spill was the first for which water column exposure and effects modeling could be verified with field data. The Erika and Prestige spill trajectories were largely driven by the ships' movements while releasing oil and the winds. In modeling the Deepwater Horizon spill, metocean models were able to predict observed surface oil movements for several days and in terms of general overall direction. However, the modeled deepwater plume moved in various directions depending upon the hydrodynamic model used as input, highlighting the need for more accuracy in ocean models below surface waters. Recent developments in instrumentation, remote sensing, and data assimilation should improve both deepwater and surface trajectories. This combined with advancements in toxicity modeling and supporting data will facilitate confidence in biological effects modeling results. Described research and monitoring needs are based on modeling lessons learned.