A geostrophic adjustment model has been developed to describe interactions between shelf waters and an offshore current such as a western boundary current. A simple analysis demonstrates the response of coastal waters to the gradual encroachment of a western boundary current and reveals how this can lead to strong upwelling when bottom friction is taken into account. Conditions favorable to upwelling actually occur well before the western boundary current comes into direct contact with the bottom. Some aspects of the theory have been compared with laboratory experiments on interacting currents over sloping topography. The comparisons are quite favorable for relatively stable flows. However, under other conditions, baroclinic instabilities grow into large eddies which dramatically enhance exchange between the two currents. Results from the study are used to interpret documented observations of coastal encroachment by the East Australian Current and associated phytoplankton blooms. ¿ American Geophysical Union 1995