Validation of a Stochastic Boussinesq Model for Wave Spectra Transformation in the Surf Zone

This thesis presents a field validation of a stochastic, nonlinear wave shoaling model based on a third-order closure Boussinesq equations (Herbers and Burton, 1997). The model predicts the evolution of directionally spread waves propagating over an alongshore uniform beach. The model consists of a coupled set of evolution equations for the wave spectrum and bispectrum that incorporates linear shoaling and refraction effects and nonlinear energy exchanges in near-resonant triad interactions. Dissipation due to breaking is approximated using an empirical quasi-linear damping function and a relaxation to Gaussian statistics. The model was verified with field data from five alongshore instrument arrays deployed near Duck, North Carolina from August to December 1997 as part of the SandyDuck experiment. The predicted shoaling evolution of the frequency-directional wave spectra shows the expected development of harmonic peaks through triad interactions. The predicted harmonic spectral levels and direction are in good agreement with the observed spectra, but the predicted directional spread is biased low inside the surf zone. The significant wave height predictions are generally in good agreement with observations. The model tends to overshoal the waves outside the surf zone and slightly overdissipate wave energy inside the surf zone. Infragravity wave growth, sea surface skewness and asymmetry are predicted fairly accurately by the model.Naval Postgraduate School Monterey CA is the author of 'Validation of a Stochastic Boussinesq Model for Wave Spectra Transformation in the Surf Zone', published 2001 under ISBN 9781423550839 and ISBN 1423550838.