Behavior of long-period waves in the nearshore region

The behavior of coexisting free and bound long wave fields in the nearshore region under extreme, moderately extreme and normal sea state is investigated. A separation technique coupling water surface and velocity, or pressure and velocity measured at two stations is developed using Hilbert transform. The surf beats generated due to the breaking of short-wave groups and the incident long waves coming from the offshore are determined using the separation technique. The incident and reflected velocity fields are also separated. The numerically simulated results by Radiation Stress Model (RSM) are compared with the field data. Both the field and numerical data indicate that a significant part of the long wave energy within the frequency band considered in this study is contributed by the surf beats generated due to the wave breaking. The results indicate that during extreme sea state, the incident long wave field is governed by the forced long waves. However, a significant presence of free long wave is observed in the incident long wave field when the typhoon is far away from the site as well as under normal sea state. The scatter plots of the incident, reflected, and measured wave fields reveal that even in the directional wave field, the proposed separation technique can separate incident and reflected wave fields quite satisfactorily. Comparison of the simulated results and field data indicates that the RSM can be used to simulate long waves in the nearshore regions.