Third Chinese-German Joint Symposium on Coastal and Ocean Engineering National Cheng Kung University, Tainan November 8-16, 2006 1 Spectral wave modelling on unstructured grids with the WWM (Wind Wave Model) II: The shallow water case Ulrich Zanke and Aron Roland Institute for Hydraulic Engineering and Water Resources Management. Technical University Darmstadt, Germany roland@wb.tu-darmstadt.de Tai-Wen Hsu, Shan-Hwei Ou, Jian-Ming Liau Department of Hydraulics & Ocean Engineering National Cheng Kung University, Tainan twhsu@mail.ncku.edu.tw Abstract In the shallow water region, when the waves start to interact with the ground, resonant energy transfer within the sea state enhances till the point when the wave spectrum changes its form within some wavelengths. After this point other nonlinear processes like wave breaking, bragg-scattering, bottom-friction and near-resonant wave-wave interactions govern the evolution of the wave spectrum. Most of the coastal structures, which are matter to coastal erosion, are located in shallow water where these processes become important. One class of wave models, the so called “spectral wave models”, have the ability to hindcast the wave climate in deep and shallow water and have certain advantages in comparison with phase resolving models. In the last years these models are coupled with morphodynamic models like TIMOR (Tidal Morphodynamics) or SHYFEM (Shallow Water Hydrodynamic Finite Element Model, Umgiesser et al. (2004)) in order to investigate the morphodynamic evolution in the near shore. The WWM (Wind Wave Model; Hsu et al. (2004)) is one of these spectral wave models that have a physical formulation similar to the well known SWAN model but with the benefit that it works on unstructured meshes. In this study we will show the verification results for an alternative numerical scheme for the solution of the Wave Action Equation (WAE) in spatial space on a triangular mesh and first results of the model coupling between the SHYFEM model and the WWM for the case of the Lagoon of Venice. Introduction Especially when looking at numerical wave modelling in connection to morphodynamic modelling it becomes clear that a proper representation of the sea state in the shallow water regions for driving the morphodynamic model is very important. For such problems deterministic models like Boussinesq type models or Mild-Slope type models are still to slow because these models must resolve the certain wavelength of interest probably (at least 6 nodes) with the numerical mesh. This leads to an extreme high spatial resolution