Hindcast modeling of short waves at the mouth of the Columbia River estuary

The region around the mouth of the Columbia River estuary is subject to high waves, which augmented by the presence of offshore shoals and tidal currents, lead to strong wave focusing near the mouth of the estuary. The large waves are a navigational hazard and a possible mechanism for sediment transport in this region. Hindcast modeling of wave propagation has been done to assess the ability of two numerical models (SWAN and REF/DIF S) to simulate waves in this region. Both models account for wave refraction and strong wave-current interactions, but while SWAN accounts for locally generated wind waves, REF/DIF S accounts for diffraction effects. Nearshore currents have been obtained from a regional circulation model (ELCIRC) that incorporates tidal, fluvial and atmospheric forcings. Measured field data from an offshore NOAA buoy (located approximately 20 km west of the mouth of the estuary) are used as input conditions for the models. Initial results comparing the two models for a test case were presented at the Ocean Sciences 2004 meeting, where significant differences between the two model results were observed. In this study the models have been compared against data from an extensive field exercise carried out by the Coastal Hydraulics Laboratory of USACE (Special thanks to Hans R. Moritz of USACE for discussions on this data set). The field gauges were placed at four locations around the mouth of the estuary for prolonged periods between 1997 and 1999. This study is limited to local wave propagation processes within a 40x40 km grid around the mouth of the estuary.