Model experiments on overtopping amount of irregular waves have been performed in order to study the efficiency of various low crest types of seawalls. The following models are used in the experiments; block mounted seawall, vertical seawall of slit caisson,seawall of a stepped or smooth slope, and seawall with permiable detached breakwater.
　By formulating Goda's figures for the estimation of wave over-topping rate over vertical type seawall, it has become easy to calculate the overtopping rate and the crest height of the seawall under the conditions given. The relationship between the overtopping rate and the crest height of seawall is clarified by the formula and the experiments, and the degree of reduction of the crest height has been estimated for the above various types of seawalls, by comparing the overtopping rates between the vertical type and the above types of seawall.