Preliminary Analysis of Morphology Change, Waves, and Currents for Navigation at Tillamook Inlet, Oregon
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS COASTAL AND HYDRAULICS LAB
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This report documents preliminary investigations of morphologic change and numerical modeling of wave and current conditions that affect entrance channel navigation at Tillamook Inlet, Oregon. It is believed that unfavorable conditions are caused by a combination of three primary factors a large ebb shoal, the Pacific coast high-energy wave climate, and a narrow dual-jetty entrance that forms a high current environment. A limited analysis of two bathymetry surveys for representative summer and winter months in 2005 and 2010 indicated that the geometry of ebb shoal outside the entrance of the inlet has been changing, exhibiting an asymmetric orientation relative to the entrance in 2005 which became symmetric by 2010. The historical morphologic evolution of the ebb shoal was evaluated in an attempt to determine possible relationships between the ebb shoal changes and changes to waves and currents in the entrance channel at Tillamook. The numerical modeling analysis was limited to one selected summer month and one winter month, with the sole purpose being the investigation of potential relationships between the geometry shape, footprint, and elevation of the ebb shoal and local wave and current conditions during these two selected months. Results indicated that both the geometry of ebb shoal and the entrance jetties together influence the magnitude of waves and currents at the inlet area through the entrance channel and over the shoal. The two jetties forming the narrow inlet entrance played a critical role in the evolution of the ebb shoal, controlling the spatial variation and severity of waves and currents at the entrance and over the ebb shoal. Wave conditions at Tillamook Inlet may be improved by changing the geometry of the ebb shoal or jetties or both.
- Physical and Dynamic Oceanography