Current pattern analysis for oil-spills a case study using San Francisco Bay

Abstract

During oil-spill events the movement and spreading of the pollutant is of critical interest to responders and there are always demands for forecasts of the future position of the oil. For floating portions of the spilled oil that are constrained to remain on the surface, the two-dimensional kinematics of the flow patterns can be used to identify locations for flotsam collection. In areas where there are strong "flow convergencies" a Lagrangian view shows the surface water moving towards a common region. As a result, the concentrations of floating material will increase where convergence zones are found. In coastal communities these areas are typically referred to as "tidal rips" or "rips". In some regions these convergence zones are persistent enough to have common names associated with them. The convergence zones are always areas for flotsam collection. A high-resolution now-casting numerical model has been implemented for San Francisco Bay to assist oil-spill prevention and response. Thirty-six hours of now-casting highresolution numerical model results are available centered around the present time. The current patterns from these model results can be further analyzed to provide information that identifies areas of strong convergence. Results of this kinematic analysis can be used to identify likely collection areas for floating oil and to provide location maps for the effective placement of recovery equipment. Convergence zones are typically associated with barotropic flow over large bathymetry variations or density fronts at interfaces where oceanic and fresh water mix. These analysis techniques were further developed and tested in San Francisco Bay to strengthen local oil-spill response planning activities. During an actual spill caused by the Cape Mohican in San Francisco Bay (late October 1996), the planning response for clean up efforts and the development of insights on the movement of oil patches were enhanced by the results of the current pattern analysis.

The Coastal Dynamics of Heterogeneous Sedimentary Environments: Numerical Modeling of Hydrodynamics and Mass Transport in Estuaries

“…This is not problematic, however, because the hydrodynamics in South Basin are dominantly local and not subject to annually variable factors like freshwater inflow from the Sacramento-San Joaquin delta. The effect of large-scale circulation on drifter trajectories will be seen to be dominated by tidal flow as suggested in previous work (Galt, Cheng et al 1997).…”

“…5.18 indicates the main channel as well as areas where tidal currents impact the coast. This result is slightly different from that of Galt et al (1997) (Fig. 5.19) because they used a barotropic model and assumed the oil was limited to the surface.…”

“…The distribution reveals the effects of convergence caused by the tidal flow moving from shallow to deep water. This type of convergence occurs in SFB along the deep channel in South Bay (Galt, Cheng et al 1997). Thus, the pattern in Fig.…”

“…. 30, 1996 from the TRIM2D circulation model on a 250 m grid (Galt, Cheng et al 1997). The approximate source of the oil is indicated by the red square.…”