Thermistor string observations of the internal wave field over the shelf off South Africa display a whitened Garrett-Munk spectrrum (log-log slopes of -1.7 to -2.0) with peaks in inertial, tidal, and high-frequency (>1 cph) bands. The vertical structure is dominated by lower-order modes, and the temporal signal is dominated by the internal tide. On propagating shoreward, the internal tide transports energy of the order of 0.04 kW m-1 onto the shelf, where it is dissipated. The resultant vertical exchange, characterized by an eddy viscosity of 10-4 m2 s-1, may maintain significant primary production in the absence of coastal upwelling. The internal tide is larger than expected, comparable with that over shelves where the forcing is twice as strong. This enhanced barotropic-baroclinic coupling is explained in terms of resonance between multiple generation sites. A linear, two-layer model is derived to investigate the enhancement due to the presence of Cape Point Valley, a submarine canyon that runs parallel to the shelf edge. Under resonant conditions the barotropic-baroclinic coupling may be 3 times as large as that in the absence of the canyon; this explains an internal tide amplitude enhancement of 70%. ¿ American Geophysical Union 1994