Laboratory Study on Macro-Features of Wave Breaking Over Bars and Artificial Reefs

Abstract

Abstract : A laboratory experiment was conducted in a wave tank to examine macroscale features of wave breaking over bars and reefs. Submerged triangular- shaped obstacles representing bars and reefs were installed on a 1/30 concrete slope to cause wave breaking. Seaward and shoreward slopes of the obstacles were varied, as was the deepwater wave steepness, which resulted in 108 monochromatic wave tests and 12 irregular wave tests. Empirical expressions were determined for the wave properties investigated, which included breaker type, height, and depth; plunge, splash, and penetration distance; breaker vortex area; wave decay; wave reflection; and wave runup. Additionally, data acquired from other studies involving plane slopes were reanalyzed to determine breaker indices and plunge distance. Differences were found between wave properties on plane slopes and barred profiles. Plunging and collapsing breakers were predominate for regular waves breaking over bars and reefs, whereas spilling breakers occurred on the plane slope. The strength of return flow altered the breaking wave form. Return flow was strongest if the bars were terraced or if the seaward slope was steep, and the deepwater wave steepness was small. The position of the break point was greatly influenced by return flow, which exerted control over the breaker depth. Breaker height was found to increase in the presence of strong return flow. Plunge distance normalized by breaking wave height was found to be shorter over irregular slopes than plane slopes.