Oil spill contingency and response (OSCAR) model system: Sensitivity studies

Abstract

OSCAR, an integrated system of models and databases, has undergone a sensitivity analysis as part of a calibration and testing program. A total of 48 simulations was performed in this sensitivity study, which focused on selected parameters that may directly or indirectly influence environmental evaluations: spreading, response actions, and threshold concentration for biological effects. The main conclusions from the study are as follows: The spreading coefficient, K, is a key parameter in calculating areal coverage and mass balance. The number of particles used to represent an oil slick has a minor influence on the mass balance, to the extent that it has an influence on the simulation of response actions. In calm weather, the effectiveness of mechanical cleanup only slightly affects the total amount of oil collected, but is decisive for the rate at which oil is collected. At higher wind speeds, the total amount of oil collected becomes a strong function of effectiveness. The amount of oil that is chemically dispersed by helicopter is more dependent on the delay due to trips for refueling and refilling than on the effectiveness of the dispersant. Oil spill response actions from boats may be sensitive to the number of particles used to represent the surface slick, depending on the search strategy specified. Response from aircraft is not sensitive to particle number. In the simulations performed here, the threshold concentration for biological effects only influences the fraction of fish eggs and larvae in the interval 0 to 40 ppb-hours. The sensitivity study has shown the model to be numerically robust. The importance of specifying realistic search strategies for response vessels has also been made clear.