Breaker bar morphodynamics under erosive and accretive wave conditions in large-scale experiments

Abstract

Differences between breaker bar evolution under high energy (erosive) and subsequent mild energy (accretive) wave conditions are studied based on three data sets from large-scale morphodynamic experiments. Under erosive wave conditions, a clear linear relationship between the height and the cross-shore location of the breaker bar is observed. The similar cross-shore shape of the sediment transport magnitudes underlines the similarity of the bar evolution under erosive wave conditions. Under the subsequent accretive wave conditions, two major evolution patterns are observed during onshore migration (decaying or non-decaying breaker bar). In the presented data, the feedback between the wave conditions and the beach morphology determines if a bar decays during onshore migration. This feedback involves that the wave breaking location depends on the morphology and on the wave conditions resulting in differences in sediment transport patterns between the two types of onshore bar migration. A comparison against numerous other experimental beach profile data sets strongly supports the linear relationship between bar height and bar location under erosive wave conditions. For accretive wave conditions, the number of comparable data sets is very limited. The comparison underlines that breaker bar evolution under accretive wave conditions cannot be condensed to a single pattern as under erosive wave conditions.