Experimental and Numerical Analysis of Infragravity Waves in a Dissipative Beach
Monday, 15 December 2014
For experimental analysis of infragravity waves in a dissipative beach we carried out a field campaign. A crosshore array of pressure sensors, located outside the surf zone and inside the surf zone, was used. These sensors measured for 12 hours continuously with a rate of 1 Hz by 3 days. A Fourier analysis was applied to the free surface data to identify infragravity energy. A FIR filter was applied to obtain the infragravity signal along the array of pressure sensors; we found an increase in the height of the infragravity wave as it approaches to the coast of almost 50%. The evolution of the infragravity wave signal was analyzed outside and inside the surf zone for the biggest wave event recorded in the field campaign, finding a significant increase in the height of the infragravity wave. Finally, using a wavelet analysis we observed that as the infragravity wave was approaching to the coast, the energy within the infragravity frequencies increase for lower frequencies. For the numerical analysis of infragravity waves in the dissipative beach, we use the SWASH model that is a non-hydrostatic model which phase-resolves the free surface and fluid motions throughout the water column. The model was validated (Willmott index of 95% of agreement between the simulated and measured time series) with data from the experimental array of pressure sensors. We ran the model by changing the boundary condition to analyze the swash oscillation in the selected beach. We found that the model was able to predict the swash oscillation and confirms that in a dissipative beach the energy in the swash zone was dominated by the infragravity energy. These results help to understand the role of infragravity regime in coastal flooding processes and morphological changes in natural beaches.