Numerical Investigation on the Influence of Shoreline on Infragravity Waves

Infragravity gravity (IG) waves are low-frequency surface gravity waves with frequencies below wind-generated short waves, typically between 0.004 and 0.033 Hz, generated primarily as a result of non-linear energy transfer from short waves in the nearshore region. These long-period waves play an important role in the nearshore hydrodynamics, wave run-up and harbour sieches. Detailed numerical simulations using the fully non-linear Boussinesq wave model FUNWAVE-TVD are carried out in this study to understand the cross-shore variation of infragravity energy and the influence of the shoreline on the dissipation and reflection of IG waves. The IG wave energy increases in the shoaling zone and then continues increasing further shoreward and reaches a maximum value near the shoreline. At the shoreline, part of the IG wave is reflected seaward. Infragravity wave energy and reflection characteristics are quantified using spectral analysis of free surface elevations and energy flux estimates. The influence of shoreline configuration on IG wave dynamics is examined by comparing a natural beach profile with an armoured shoreline representing a vertical structure such as a seawall or dike. The presence of a hard coastal structure alters the reflection characteristics and energy distribution when compared to a gently sloping beach.