Wave transformation in the nearshore zone: comparison between a Boussinesq model and field data

A numerical model based on the Boussinesq equations was developed to simulate wave transformation in the nearshore zone with emphasis on describing the effects of wave breaking. Two different formulations for estimating additional momentum due to depth-limited wave breaking, namely one proposed by Watanabe and Dibajnia [Watanabe, A., Dibajnia, M., 1988. A numerical model of wave deformation in the surf zone. Proceedings of the 21st Coastal Engineering Conference, ASCE, pp. 578-587] and another one by Schaffer et al. [Schaffer, H.A., Madsen, P.A., Deigaard, R., 1993. A Boussinesq model for waves breaking in shallow water. Coastal Engineering 20, 185-202], were incorporated and tested in the numerical wave model: Detailed, high-quality data from Duck, NC, collected during the DUCK85 and SUPERDUCK field experiments using photographic means were employed to evaluate the applicability of the Boussinesq model to surf-zone conditions. Also, comparison with the field data allowed for an assessment of how well the two formulations could describe the effects of wave breaking on the evolution of the waveform. Model simulations were compared with measured time series of water surface elevation as well as with derived statistical quantities, such as the skewness, kurtosis and root-mean-square wave height. Overall, the model results were satisfactory, although the Boussinesq model failed to accurately reproduce the strong nonlinear shoaling that occurred prior to breaking. The roller model developed by Schaffer et al. produced somewhat better agreement with the data than the model proposed by Watanabe and Dibajnia. However, the difference was small and both formulations are judged to yield acceptable results, although improvements are needed before the predictions can be used for calculating the sediment transport rate in intra-wave models. (C) 2000 Elsevier Science B.V. All rights reserved.