South Korea suffers from a high population density and stands therefore in need of agricultural and industrial land. The Koreans are seeking for solutions to solve this problem. One of the possibilities is to reclaim land from the sea. Several land-reclamation projects have already been carried out and one of the projects that is at the moment under construction is the closure of the Shiwa tidal basin. This project has been studied by the NEDECD and it appeared that the bottom protection length of 30 meter, designed by the Koreans is not sufficient according to Dutch design rules. In this thesis study, the bottom protection length has been determined according to Dutch design standards. Therefore, first a mathematical model of the region has been made to obtain the local conditions. This model is described in the sub report on the preliminary model investigation on the closure of the Shiwa tidal basin. With the model, several closure methods have been simulated. With the thus obtained local hydraulic data, the decisive D50 of the closure dam, depending on the closure method has been determined. Subsequently, the time needed for the construction of the dam has been determined with an estimation of the production capacity. With the flow velocities during every closure phase and the time during which the bottom is exposed to these flow velocities, the bottom protection length could be determined. The bottom protection length needed to avoid failure of the closure dam due to extensive scouring appeared to have a length of 15 to 300 meter. The maximum bottom protection is ten times more than the length designed by the Koreans.