| Résumé | Extreme wave conditions at coastal structures located offshore of natural coastlines and the zone of wave breaking are influenced by the deepwater wave conditions, the coastal bathymetry between deepwater and the structure, and the ongoing growth, generation and decay of waves across the coastal shelf. At locations where the coastal shelf is relatively flat, the gradually reducing water depths can limit the significant and maximum wave heights and crest elevations that may be encountered. If a coastal structure is located in deeper water than the bathymetry of approaching waves, for example port or navigation structures located in dredged channels or basins, coastal engineers need to consider wave conditions in the shallower approach waters and the transformation and propagation of waves across the dredged area. The directional characteristics of wave spectra in this situation can have a significant impact on extreme wave conditions that occur within the dredged basin.
Forristall (2004) concluded that for shallow water with a flat seabed, the commonly adopted wave breaking coefficient (H/depth) of 0.78 was unrealistic and that wave breaking coefficients that large could not be observed in many physical model data sets. Forristall (2004) also concluded based on the information available at that time, that it was uncertain if Nelson’s(1994) depth limiting breaking coefficient of 0.55 was realistic for conditions other than the relatively broad and flat reef conditions examined in that paper.
This paper presents insights into extreme wave conditions for gently sloping natural seabed profiles and also within a dredged basin, for directional seas which occur within the direct path of severe storms; for example, tropical cyclones. The random nature of directional seas has a significant influence on the observed maximum wave heights on the natural seabed and within a dredged basin. Data from a large 3D physical model, in conjunction with numerical modelling and literature, has been used to gain insight for practitioners into maximum wave heights for directional seas in finite water depth. |
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