On the selection of design wave conditions

In the design of coastal and offshore facilities, it is customary to estima te parameters of a design sea state corresponding to a specified return per iod or annual risk, and then develop an estimate of the expected largest in dividual wave height within that sea state. It turns out that the expected largest individual wave height in a sea state with a specified return perio d may be significantly different than the maximum individual wave height wi th the same return period. The present paper serves to highlight this diffe rence. It describes for different situations the calculation of the long-te rm distribution of individual wave heights and of the maximum individual wa ve height with a specified return period. Results are presented (i) for a s pecified wave scatter diagram; (ii) for hindcast wave parameters for a sequ ence of storms or hurricanes; and (iii) for a range of parameters relating to analytical descriptions of long-term sea states. In addition, a comparis on of alternative methods of computation is made. It is found that the maxi mum individual wave height with a given return period is generally apprecia bly larger than the expected maximum individual wave height in a sea state with the same return period.