Abstract
The HIROI formula, which estimates the wave forces, has been used in breakwater design for many years. As far as the authors know, significant wave height has been used for the HIROI formula in the past. The time when the formula was presented, however, was long before emergence of the concept of significant wave height. We verified the process of derivation of the formula by tracing back to the paper in which Dr. HIROI first presented the formula, studied the changes in wave height used for the formula and investigated the history of changes in the shape of breakwaters.
As a result, we found that the highest wave height must be used for the HIROI formula, and that changes in breakwater structure existed behind the use of significant wave height in the formula.
