Saemangeum is a macrotidal zone located in southwestern Korea. Between 1992 and 2006, a series of tidal dykes 33 km in length were constructed surrounding the Mankyung and Donjin riverine estuaries and intertidal zones. The dykes lessen the tidal phase, weaken the tidal current, and lower the tidal amplitude. Their shape resembles an inequality sign that opens toward the east and can be divided into southern and northern legs, with stronger effects found in front of the southern leg. Using a finite volume coastal oceanmodel (FVCOM), we elucidate the mechanism by which these dykes modify the tide aroundSaemangeum.