Damutu Bay in eastern Zhejiang, China has abundant tidal flat resources for years of silt deposition in the wide open seas, making it an ideal place for mudflat reclamation. In this study we set up a two-dimensional hydrodynamic and sediment transport model based on Mike 21 FM to investigate changes in suspended sediment concentration (SSC) after reclaiming to 1 m and 3 m depth contours in the seas. The model results are compared temporally and spatially to field observations in December, 2011 and August, 2012 of water levels, current velocities, and SSC, and indicate a strong data-model agreement. This study shows the sensitivity of the system to changes in SSC and suggests that a large-scale tidal flat reclamation could reduce SSC by 15∼20% on average in Damutu seas which would influence physical and biological processes particularly in the intertidal areas around the bay.