One of the longest coastal dyke in the world has been constructed in Saenangeum area in the southwest of Korean Peninsula (center location at 126.5E and 35.8N). A 33km-long dyke system connecting a few islands separates the open ocean from the landward water of 401 km2 area that is planned for reclamation as a part of coastal development. The water quality of the lake is vulnerable to be degraded due to low mixing rate. Opening and closing operation of two water gates provides water exchange between the lake and coastal water. An optimized operation of flow control is definitely