Numerical models for obliquely incident waves in surf and swash zones

Time-dependent numerical models are developed to predict the temporal and cross-shore variations of the free surface elevation and the cross-shore and alongshore fluid velocities in the swash and surf zones under obliquely incident waves. The assumption of shallow water with small incident angle and slow alongshore variations are made to reduce computational efforts considerably and to eliminate difficulties associated with lateral boundary conditions. These assumptions enable the models to compute the cross-shore fluid motion separately from the alongshore motion. The numerical models allow gradual alongshore variations of the bathymetry and the incident regular or irregular waves specified at the seaward boundary.; Two numerical models are developed in this study. The first model is a two-dimensional (2D) model that neglects the vertical variations of the cross-shore and alongshore velocities. As a result, this model neglects the dispersion due to the vertical variations of the horizontal velocities and predicts only the depth-averaged cross-shore and alongshore velocities. The second model is a quasi three-dimensional (3D) model that assumes a cubic profile for the horizontal velocities and includes the dispersion terms due to the vertical variations of the horizontal velocities. Two additional equations for cross-shore and alongshore momentum flux corrections are derived.; These numerical models are compared with available laboratory and field data for planar beaches. To assess the importance of the dispersion terms, both models are compared with the same data. Both models are shown to be capable of predicting the cross-shore variations of wave height, setup and runup for regular waves and root-mean-square wave height for irregular waves. For regular waves, the 2D model with the bottom friction factor calibrated previously for swash oscillations predicts the magnitude of longshore current but cannot reproduce the longshore current profile. For irregular waves, the longshore current is predicted fairly well by both models. The 3D model improves the prediction of the longshore current profile for regular waves significantly.; The 3D model is also compared with field data for a barred beach. The model underpredicts the root-mean-square wave height in the bar trough region. The field measurements of longshore currents generally indicate a broad peak in the bar trough region. Under the assumption of alongshore uniformity, the model cannot explain these broad peaks. The small alongshore variation of wave setup induced by a small alongshore variation of obliquely incident irregular waves is shown to significantly modify the driving force and longshore current profile in the bar trough region where the cross-shore gradient of the alongshore radiation stress is small. As a result, the longshore current profile in the bar trough region is sensitive to the alongshore variability. (Abstract shortened by UMI.)...