Insufficient seawater circulation in harbors due to construction of coastal structures nearby causes seawater pollution problems. To solve such problems, a seawater exchange breakwater (SEB) was constructed at Jumunjin Harbor on Korea's eastern coast. The SEB is composed of a semicircular overtopping seawall on the north side of the offshore breakwater and 6 circular conduits through rubble-mound breakwater (existing case; CASE 0). Additional counter-measures, CASE 1 and CASE 2, work to improve water quality are examined here. A seawater exchange system including pipeline with 781.9 meters in length and 1.5 meters in diameter is linked to 3 conduits of the existing ones, and is set along the berthing areas of the harbor. Moreover, two outlets are placed at the areas vulnerable to seawater circulation in 2 cases. Incident waves top over the overtopping seawall and waves are partially transmitted. The variation of water level in the overtopping seawall is assumed to be the water level outside the reservoir if the water level is higher than the wall crest level. The instantaneous flow velocity is approximated by Manning's empirical formula for flow in the pipe with assumption of uniformity. This system induces residual current into the harbor which improves the water quality inside the harbor. The outflow at each outlet for each case is calculated and compared with the existing case. When the actual discharge is 11,833m3/day, the coefficient of correlation is measured Cq=0.11. The seawater exchange rates in the harbor concerned three cases including the existing case were computed using KU-SUS modeling system. The modeling system results indicate that CASE 2 is more efficient for water quality inside the harbor.
Harbors are enclosed by breakwater except the entrance waterway so that wave and current penetrate into the harbor. If the harbor entrance is narrow and the tidal range at the site is small, water quality problems may arise.
