The mouth of the Columbia River (MCR) has a longstanding reputation of hazardous navigational conditions. This reputation has been developing since the first ship, the Columbia, traversed through the inlet in 1792. The hazardous conditions are related to the large waves and strong tidal currents that are common in the area. Tidal currents often reach 2 m/s. As large waves interact with strong tidal currents waves can steepen and break. This study investigates on the importance of wave-current interaction at the MCR. To model these conditions a two dimensional spectral model, SWAN (Simulating WAves Nearshore) (Booij, 1999), was used. SWAN simulations were completed neglecting as well as including current to make comparisons. Wave height and length were found to be influenced considerably by wave-current interaction. The SWAN simulations were also compared to both radar and insitu observations. Radar--estimated and SWAN--predicted wave direction and wave breaking were compared. SWAN-predicted wave direction and radar-observed wave direction compared well; however, poor agreement between observations and predictions occurred over a shoal in the region used to make comparisons. The source of this disagreement is unknown. Radar--observed wave breaking compared well with SWAN-predicted wave breaking in depth-limited cases; however, radar-observations indicate current induced wave breaking that SWAN does not predict. Insitu observations of wave direction and wave height both demonstrated good agreement with SWAN-predicted wave direction and wave height. Overall SWAN-predictions demonstrate good agreement with observations from both radar and insitu measurements.

As the second largest river in the U.S., the entrance to the Columbia River is home to some of the most extreme wave conditions on the Pacific Coast. Winter storms commonly generate waves 6-8 m in height, which in combination with strong tidal currents, can produce dangerous navigation conditions. To improve understanding of the wave dynamics in this complex setting, the SWAN model is applied; 2 hindcasts are conducted and an operations forecast is developed. The model is forced with offshore wave heights obtained from a buoy located in 134 m water depth (for the hindcasts) and a specialized WaveWatchIII forecast (for the forecast). In both cases tidal currents are obtained from SELFE, a circulation model of the Columbia River. The hindcasts are validated through measurements obtained from an inshore buoy located in 25 m water depth, a 4-week field experiment and remote sensing methods. The model performs best at the location of the buoy, with a normalized root-mean-squared error (NRMSE) of 11%, primarily because it is outside the area of strong tidal currents. Within the river mouth, the model is able to predict the changes in the wave field due to currents, but its performance is limited by errors in velocity estimates and strong shears in the tidal current profile. From the modeling work, it is evident that wave transformations at the mouth of the river are dominated by the tidal currents. The forecast has been operational since August 2011 and provides 45-hours of predictive wave information. In comparison with measured wave heights at the buoy, the forecast performs well, with a NRMSE of 16%. The majority of errors are caused by errors in the input conditions, since they themselves are forecasted. Additional errors arise from phase-resolved properties in the wave field that the model is unable to produce; these errors are also present in the hindcasts. Despite the limitations, this forecast provides valuable information to bar pilots since it includes the effects of the tidal currents.