Field observations and numerical modeling of swash motions at an engineered embayed beach under moderate to energetic conditions

Abstract

Wave run-up is a key factor for the assessment of coastal flood risk during large swell events. The behavior of swash motions along embayed beaches is strongly influenced by particular features such as rocky headlands, irregular morphology, or tides, that have not received much attention in the past. In the present paper, swash motions along an engineered embayed beach were investigated under moderate to energetic wave conditions through field observations and numerical computations. Using pressure sensors and video-derived run-up data a Boussinesq-type nearshore wave model was found to capture the relevant wave transformation and swash zone processes reasonably well. The tidal water level variations were found to have a significant impact on the overall swash amplitudes and to condition the respective role of short- and long-wave components to the swash motions. In the studied configuration, the tidal level rise was shown to cause a transition from a very dissipative to a reflective or intermediate beach configuration depending on incident wave energy. Moreover, swash amplitudes were observed to vary significantly alongshore with differences of up to a factor of 2.2. Numerical results suggest that both the foreshore slope and the sub-tidal morphology play a key-role in the alongshore swash distribution.