Abstract
The confidence interval for R-year return wave height is examined for the design of coastal structures. It is, however, a relative discussion whether it is wide or narrow. Even when we have just a short record of extreme wave height, there is no restriction to estimate a wave height of a longer return period, though it is accompanied with a very large interval. Engineers have been bothered with a problem: how much wide interval is no worth being considered. As a solution we introduce newly the degree of experience for the estimation of occurrence intensity of extremewave height.
