Validity of small-scale physical models involving breaking waves

Abstract

The presence of air bubbles entrained by the action of wave breaking can strongly influence a number of physical processes including wave impact forces on coastal structures, sediment transport and the rate of air-sea gas transfer. Due to their complex nature, laboratory facilities are commonly used to examine the influence of breaking waves on such processes and the large majority of these experiments are made in small-scale flumes filled with freshwater. In experiments involving non-breaking and hence non-aerating waves, scale effects are often unimportant. However very few authors have commented on the effect of scale on air entrainment by breaking waves, and the information available (Chanson et al., 2002; Lamarre, 1993) is contradictory. It is also noted that many researchers including Haines & Johnson (1995) and Chanson et al. (2002) have suggested that there are considerable differences in the total volume and size distribution of bubbles entrained in freshwater and seawater. It is clear therefore that in order to correctly interpret the results of laboratory tests involving breaking waves, the influence of scale on the entrainment and subsequent evolution of bubble plumes generated by breaking waves, as well as the effect of water type on the size, concentration and distribution of entrained bubbles must be understood