FY 1979

Waves at the Columbia River entrance

Overland, J.E. (ed.)

In Report of a Workshop held at Seattle, WA, 19 April, 1978, NOAA Special Report, ERL/PMEL, 97 pp (1979)

During the past two and a half centuries more than 200 major disasters have occurred at the entrance to the Columbia River. On May 4, 1880, an entire fleet of small fishing boats was caught in gale force winds and was unable to return to port. Since the construction of jetties and the development of modern methods of weather prediction and analysis, the toll of ships and lives has diminished dramatically. However, breaking waves caused by the strong ebb tide current have continued to precipitate hundreds of search and rescue missions a year. For example, on September 13, 1976, the Pearl-C, a charter fishing boat, sank while being towed across the Columbia River Bar. Two persons were rescued, one person was reported drowned, and seven others, including the vessel's skipper, were never found. As a result of a thorough investigation of the accident by the National Transportation and Safety Board (see Appendix G), NOAA was asked "to develop an oceanographic measurement system to measure, process and report those sea conditions which are important to the safe navigation of boats crossing the Columbia River Bar." To address this challenge the Pacific Marine Environmental Laboratory (PMEL) and the Seattle Weather Service Forecast Office jointly sponsored a workshop of wave conditions at the Columbia River entrance on 19 April 1978. The morning session reviewed the need of various user agencies for information, including the U. S. Army Corps of Engineers, U. S. Coast Guard, and the Weather Service, and summarized past and ongoing projects by individual investigators. Present services of the Portland Weather Service Forecast Office were outlined. The afternoon was reserved for an open forum to define critical areas for technique development. This report provides the workshop presentations and several longer papers included as appendices that serve as supporting documents for the discussions. The conclusions and recommendations of the workshop are summarized as follows:

• The Coast Guard emphasized the need for measurement and communication to the public. The bar generally does not look nearly so rough from the seaward side as from the other side, so the mariners need to know what they will encounter and whether to cross the bar or wait for the slack tide.
• The Army Corps of Engineers is concerned with rational guidelines for channel and jetty design. A present project is to deepen the entrance channel. Tradeoffs represent possible savings of millions of dollars.
• Almost no data have been collected to validate hypotheses of wave breaking at the Columbia. The Columbia River Bar pilots indicated that 4-s waves will spill break for a distance of several miles. As this occurs in 50-ft depth, it implies that breaking is associated with the spatial variation of the effluent jet of the river/ebb current rather than shoaling. Investigation should be made of breaking mechanisms caused by wave/current interaction using idealized analytical and numerical computations. Additional insight will be gained from aircraft, coastal radar, SeaSat-A satellite imaging. These studies can serve as a guidance to bar forecasting.
• Several speakers emphasized the importance of developing empirical techniques for relating offshore waves to bar conditions based upon the upcoming waverider program of the Corps of Engineers and PMEL.
• It is important to intercompare the waverider measurements with the present seismometer system.
• Weather Service elements indicated a lack of utility of the National Meteorological Center wave guidance package when applied to coastal problems. Present reliance is upon a semi-automated single-point model developed by Enfield at Oregon State University.
• It is important that the deep-water forecast provide spectral information, since destructive waves at different bars along the west coast occur in response to different ranges of offshore wave period.