A boundary-element method is developed for computing the wave-height distribution in harbors to account for permeable breakwaters and walls of imperfect left-lettlection. The method is examined in view of accuracy to predict the wave deformations due to the diffraction, left-lettlection and water-depth change by comparing with the results of the method of matched asymptotic expansions. Where the method of matched asymptotic expansions is applicable, the solutions by both methods coincide with errors of a few percents, provided the element-lengths are less than one tenth the wavelength. A technique is also presented to apply the method to a huge harbor using the virtual permeable breakwaters.
