In chapter one, the influence of the head-loss coefficient f・u2/2g at tsunami-breakwater opening is discussed. A series of calculation with the incident tsunami profile of 1968-tsunami for Ofunato Harbor was carried out with various value of f from 0 to 3.0 and computed water level was compared with the actual record. Al though it is difficult to find out the most suitable value of f, the value of approximately 1.5 which has been adopted in our previous calculations will be regarded quite reasonable for practical purpose.
　In chapter two, one dimensional approximate method is discused by assuming an equivalent linear head loss term A・u. This method is found to be a good approximation by comparing with the previous two dimensional calculation and model experiments.
　In chapter three, the effect of permeance through rubble mound is examined by two-dimensional calculation for Ofunato Harbor and is found not to play an important role.