Bedrock erosion in strong tidal streams

The successful design of robust marine tidal power facilities must surmount the many challenges associated with corrosion by seawater, and impacts of waves and tidal currents. Whereas useful indications of facility material survival may be obtained from laboratory testing, geological studies of potential seabed placement sites can provide useful indirect design knowledge. The north parts of the resulting map contain a fabric of rock outcrops, mostly a sequence of sandstone, siltstone, conglomerate and shale based on continuation of strata observed in the surrounding coasts. Carrying out inspections of the seabed is difficult given the extreme tidal flows, so knowledge of the rock properties is weak here, but these rock types are expected to be moderately resistant to erosion. The cross-sections reveal a small, steep near-vertical outcrop or even overhang around the edges of the train of gravel waves. The authors speculate this has developed since sea level here stabilized near its present level, perhaps around 3,400 years ago.