Wind-driven circulation in a shallow bay or harbor is greatly influenced by bottom bathymetry. As a result, the wind-induced flushing time of the system can be significantly reduced by a deep channel dredged along the prevailing wind direction. In Koombana Bay, on the coast of southwest Australia, there exists a navigation channel of this type. Its effective flushing of the bay is studied here by current meter and drogue deployments, the use of HF radar to measure surface transport, amd simulations with idealized long-basin models and two-dimensional and three-dimensional numerical models. ¿American Geophysical Union 1987