Importance of Directional Spreading of Waves in the Nearshore Region.

摘要

Historically, monochromatic (regular) or unidirectional spectral (irregular) waves have been used in hydraulic models of coastal projects. However, real ocean waves are short-crested, having directional spreading which spreads or diffuses wave energy over many directions about a central angle of wave approach. Based on over 1000 samples of ambient and storm conditions off the North Carolina coast measured with a linear gage array, Long (1989) and Long and Oltman-Shay (1989) found a complete absence of unidirectional waves. In fact, typical directional spreading was 20 deg to 40 deg. Sand et al. (1983) measured diffracted wave energy in the lee of an entrance breakwater for unidirectional and directional irregular waves. They found larger waves for the directional cases. Kirkegaard et al. (1980) measured motions of a moored vessel near an open jetty, and found differences in response between unidirectional and directional irregular cases. During harbor modeling tests, Bowers (1987) observed significantly reduced long-period energy in the harbor when directional-spreading was present. Thus, the inclusion of directional spreading can have a significant effect on the design of coastal facilities and breakwaters. Two examples are presented to illustrate the importance of wave directional spreading. The first case study describes the effect a submerged mound of dredged material has on wave heights in the lee of the mound. The second case study discusses the effect of directional spreading on transformed wave heights just offshore of the north entrance jetty at Yaquina Bay, OR.