Wave-driven circulation across the coral reef at Bamburi Lagoon, Kenya

Sea level, current and wave measurements were carried out within and outside an open-ended bar reef lagoon on the East African coast. The oceanic tides in this area are semidiurnal with a tidal range varying from 3 m at spring to 1 m at neap. Reef submergence relative to the mean sea level is 0.7 m. Waves with significant wave height of typically 0.5 m and periods of 8–10 s continuously break on the reef-top and on the reef-edge during most of the tidal cycle. This results in a wave set-up on the reef-top and a lagoon-ward flow across the reef. The set-up drives a time-dependent circulation, which is larger during neap tide when the reef is moderately submerged, than during spring tide. The wave driven circulation, though small compared to the tidally driven circulation, is still important because it hinders inflow of polluted water from tidal creeks that enter the ocean north and south of the lagoon itself.