Do longshore bars shelter the shore?

In most past theories on Bragg reflection of waves by a finite patch of rig id bars, only outgoing waves are allowed on the transmission side, simulati ng the effect of an idealized shoreline where all the incident wave energy is consumed by breaking. In these theories the amplitudes of both the incid ent and reflected waves are found to decrease monotonically over the bar pa tch in the shoreward direction. This result has motivated the idea of artif icially constructing bars to protect a beach from incident waves. However, some numerical calculations have suggested that this tendency does not alwa ys hold when there is some reflection from the shore. We show here that wit h finite reflection by the shoreline the spatial distribution of wave energ y over the patch can indeed be reversed, indicating that the mechanism can increase the hazards to the beach. The phase relation between the bars and the shoreline reflection is found to be the key to this qualitative change of wave response.