The tidal flooding/drying process in the Satilla River Estuary was examined using an unstructured-grid finite-volume coastal ocean model (FVCOM). Driven by tidal forcing at the open boundary and river discharge at the upstream end, FVCOM produced realistic tidal flushing in this estuarine tidal-creek intertidal salt-marsh complex, amplitudes and phases of the tidal wave, and salinity observed at mooring sites and along hydrographic transects. The model-predicted residual flow field is characterized by multiscale eddies in the main channel, which are verified by ship-towed ADCP measurements. To examine the impact of complex coastal geometry on water exchange in an estuarine tidal-creek salt-marsh system, FVCOM was compared with our previous structured-grid finite difference Satilla River Estuary model (ECOM-si). The results suggest that by failing to resolve the complex coastal geometry of tidal creeks, barriers and islands, a model can generate unrealistic flow and water exchange and thus predict the wrong dynamics for this estuary. A mass-conservative unstructured-grid model is required to accurately and efficiently simulate tidal flow and flushing in a complex geometrically controlled estuarine dynamical system.