FY 1985

Wave and current observations at the Columbia River entrance, 10–13 September, 1981

González, F.I., M.R. Mulhern, E.D. Cokelet, T.C. Kaiser, J.F.R. Gower, and J. Wallace

NOAA Tech. Memo. ERL PMEL-59, NTIS: PB85-164291/AS, 231 pp (1984)

This technical memorandum presents the results of a joint exercise undertaken by PMEL and IOS to measure waves and currents at the Columbia River Bar during 10–13 September 1981. The waves were measured in situ with a vertical accelerometer buoy (Waverider) and observed aloft with Side Looking Airborne Radar (SLAR). Drifters tracked by an independent radar system provided surface-current velocities within the river mouth. Wave refraction occurs in this area owing to depth and current gradients. Upriver of Buoy 8 waves decay on ebb and flood currents due to depth refraction away from the channel axis. During strong ebbs wave decay may be enhanced by breaking within the channel itself. Seaward of Buoy 8 waves amplify during peak ebbs and attenuate during peak floods. Most of the time the amplification and decay factors are predicted to within 20% by linear, one-dimensional theory. However, during one extreme ebb event the wave height was underpredicted by up to 50%. This was likely due to the crossing of wave crests produced by the current jet. The accurate prediction of such an event awaits the application of a two-dimensional theory for both the currents and the waves. Predictions of hazardous sea state on the Columbia River Bar could certainly be improved by implementing recent analytical and numerical advances in wave refraction-diffraction theory. This should be complemented by Bar wave-height observations made available in real-time. These would provide accurate now-casts and short-term forecasts and improve the intuition of forecasters and mariners. The observations would also provide a data base to tune the theoretical models and verify forecasts.