Do Trajectories Belong in Area Plans? A New Approach in California Using the Trajectory Analysis Planner (Tap II)1

Abstract

ABSTRACT The National Contingency Plan (NCP) requires that Area Contingency Plans (ACPs) be adequate to address the removal of a worst case discharge from a vessel or facility operating in or near the area. The U.S. Coast Guard took this requirement further by issuing guidance in 1992 that ACPs address response to worst case, maximum most probable, and most probable discharges. As a result, many ACPs include area-specific scenarios applying these discharge quantities. However, there remains very little guidance about including trajectories in the ACPs. For example, only three of California's six ACPs include trajectories from computer models; the remaining three contain only oil spill scenarios that incorporate committee-selected environmental conditions to help estimate where oil might go. The 2000 revision of the San Francisco Bay and Delta ACP includes a new type of trajectory using the National Oceanic and Atmospheric Administration's (NOAA's) Trajectory Analysis Planner (TAP II). TAP II is a statistical model rather than a single scenario-based deterministic model. It generates statistics that describe oil spill behavior using an ensemble modeling approach. These statistics are generated from an ensemble of thousands of possible trajectories resulting from hundreds of oil spill scenarios computed within a given location. This approach is designed specifically for planning purposes, and not response. A statistics-based approach facilitates the planning process by providing key information, including which shorelines have the highest probability of being impacted, the size of the area that might be affected, how quickly a response should be mounted, what quantity of oil could impact a shoreline location, which resources will be oiled, which assets will be affected, and the most threatening origin of possible oil discharge. The authors describe how the TAP II model employs ensemble modeling, detail its application in the 2000 version of the San Francisco Bay and Delta ACP, and discuss possibilities for future applications.