An evaluation for exchange of water mass through breakwater with openings is proposed on the basis of the results of hydraulic experiments and numerical simulations. Wave and flow experiments were carried out in hydraulic channel. Three type of breakwater with openings were tested as follow. 1) The caisson with openings at lower part 2) The caisson with openings at the joint part of breakwater 3) The perforated slit caisson with openings at lower part. Hydraulic conductivity was affected by the ratio of the openings with total area of the wall. The 3-D flow numerical simulations(CADMAS-SURF/3D) revealed that the water mass exchanged coefficient can be evaluated. The results of hydraulic experiment show good agreement with numerical simulations.
