FY 1979

Report on FY-78 numerical modeling in the Strait of Juan de Fuca and Puget Sound

Pease, C.H., R.J. Stewart, and J.E. Overland

NOAA Tech. Memo. ERL MESA-38, 32 pp (1979)

This report summarizes and interprets tidal current and oil spill trajectory predictions obtained from a computer model of the Straight of Juan de Fuca and regional wind fields derived from a computer model of the entire Puget Basin. These models are products of a multi-year project supported by the Puget Sound MESA program. As reported here, the models are works in progress, and a final report on their development can be expected at the end of FY-79. The meteorology of the Puget Sound Basin is discussed with respect to three dominant weather patterns which were subsequently used to run the regional meteorological model. These model results are incorporated into oil spill trajectory calculations as large scale wind fields over the Straits which are sequentially keyed by baric types for any given modeling period. A sea breeze condition was also considered and is described in the trajectory modeling section. The oceanography of the Strait of Juan de Fuca region is presented as a discussion of the dominant features, tidal and estuarine flow components, and some possible deviations from these main elements. The tide subroutines constructed for the trajectory model are based on empirical data from NOS tidal current stations and are inline functions to the trajectory model. For the trajectory simulations, the model included an empirical tidal current field, an approximate estuarine flow in the central and western Straits region, a time and space varying wind field, and the empirical "3% of wind velocity" oil spill trajectory equation. In order to provide regional coverage, tidal current velocities are interpolated in the computer model on a nominal one kilometer grid based on up to three neighboring tidal stations and anticipated channeling effects due to the bottom topography. The estuarine flow was approximated with a current field that was of uniform speed with direction determined by the local ebb tide direction. The wind field was modeled using both an observed surface wind time series from the Canadian meteorological station at Race Rocks and the large scale wind fields over the entire Straits/Puget Sound region. The principal product of the model was a series of simulated oil spill trajectories.