Coos Bay Inlet, located on the south central coast of Oregon, provides tidal flow to two estuary systems: Coos River to the north and South Slough to the south. The upper reaches of South Slough constitute a National Marine Sanctuary, administered by the National Oceanographic and Atmospheric Administration. Charleston Harbor is located at the entrance into South Slough and is affected by continual shoaling problems within the harbor entrance channel. A two-dimensional numerical tidal model (WIFM) was used to investigate the tidal hydrodynamics of the inlet complex. Due to the nature of the complex geometry of the Coos Bay area, it was necessary to develop a capability of computing the tidal regime on a variable grid system. The primary objective of this study was to apply WIFM to the Coos Bay-South Slough complex to predict quantitatively the hydrodynamics (exclusive of sediment transport and wave action) of the tidal flow in the system and hence draw a comparison between existing conditions and alternate improvement plan conditions.