Interaction Between Waves, Current and Morphology Change at Tillamook Inlet

The narrow jetty configuration of Tillamook Inlet functions to constrict tidal flow, increase current speed, and prevent sediment deposition. However, the interaction of strong currents with incoming ocean waves over the inlet’s ebb shoal can amplify and complicate the wave environment at the inlet entrance. In this study, the Coastal Modeling System (CMS) was used to investigate time- and space-varying wave and current conditions affecting boating operations at Tillamook Inlet and quantify the effects of physical processes. Wave simulations with refraction, shoaling, and breaking provided estimates of wave-related parameters of interest to the navigable region at Tillamook. The simulation results showed the winter storms produced larger wave steepness and wave dissipation at the inlet complex, which were also closely associated with the bathymetry of ebb shoal. The flood currents weakened wave dissipation, while ebb currents increased wave dissipation over the ebb shoal and across the USCG recommended south passage in/out of the inlet. The effect of South Jetty shortening was localized to the immediate vicinity of the South Jetty. The calculated wave steepness and wave dissipation indicated that a south passage out of the inlet would be safer than a course straight out passing over the bar or a course turning to NW direction.