A note on the amount of wave energy transmitted over nearshore sand bars

The wave energy loss as waves break on nearshore bars is an important geomorphological process as it controls the stability of the adjacent beaches and dunes. The effect is particularly important during storms as it serves to guard against severe shoreline erosion. Field measurements from Florida and Ireland of waves crossing both single and multiple bar bedforms, indicate that where bar‐breaking occurs, between 78 and 99 per cent of wave energy may be dissipated from individual waves. However, a further 20 per cent energy may reach the shore if wave frequencies increase during the reformation process. This latter effect was not noted at the multiple bar site where spilling mode breakers dominate. The level of energy dissipation is related to the time taken to cross that section of the submerged bar below the critical depth, d < 1.28H. In the field this may be approximated by the ratio of wave speed to the width of the bar breaker zone.