Seabed-wave resonance and sand bar growth

Abstract

The interaction of surface water waves with undulating sea-bed topography is of fundamental importance to coastal engineersand sedimentologists. For example, wave reflection from submerged bars on beaches may provide a mechanism for protecting the beach from further wave attack. Additionally the interaction of surface water waves with other tidally or wave generated bedforms, such as sandwaves on offshore banks, may modify wave climates on adjacent coastlines. While there have been numerous studies of the interaction of sea waves with engineering structures, such as breakwaters, piers, and jetties, there have been comparatively few investigations of wave interactions with naturally occurring bedforms. Predictions have recently been made of the amount of wave energy reflected as a result of resonant interactions between surface water waves and undulating sea-bed topography but with no supporting experimental proof. I describe here preliminary results from what are believed to be the first published laboratory measurements of resonant interactions between surface water waves and submerged bars which show that significant and large amounts of wave energy may be reflected and that these reflections are brought about by resonant interactions between surface-water waves and the bedforms. In particular, at resonance, incident surface water wavelengths are approximately twice the bedform wavelengths. These results have implications not only in terms of wave reflection from naturally occurring bedforms, say bars on beaches, but also for sediment transport processes in general.