sea floor geometry
determines where waves break relative to the shore
profile geometry
maximum waver erosion occurs where the sea floor profile causes waves to gain height in the foreshore and break at the shoreline
if the sea floor slopes gradually surf will occur seaward of the shoreline
if the sea floor slopes steeply, surf may not form and the swell will contact the headlands
planimetric geometry: wave refraction
waves conform to the sea bottom topography, that is, decelerate first opposite the headlands and bend around them into the bays
wave energy is concentrated on headlands and diverges in the bays
wave refraction also generates a longshore drift of water and sediment from the breaking waves at the headlands to the lower water in the adjacent bays
erosion on headlands and deposition in bays causes coastlines to become less irregular over geologic time