Proceedings of 2013 IAHR World Congress ABSTRACT: In the present paper, a Boussinesq model by with improved dispersion and weakly nonlinear characteristics is improved to simulate wave breaking in two horizontal dimensions. Both spilling and plunging breakers were taken into consideration. The model so far has been proven capable of simulating accurately wave propagation and breaking due to bathymetric changes in one horizontal dimension. A fourth-order predictor-corrector numerical scheme was employed to simplify the numerical implementation. The wave breaking due to variations in water depth was simulated, through the eddy viscosity breaking model. In the improved model the Boussinesq equations become simpler and the quality of the output was increased through a stable and efficient computational code. The model was verified against regular and random wave propagation. The results were as compared against one dimensional experimental data and software MIKE21 BW, including plunging breaking monochromatic waves. The proposed model was also checked against two-dimensional experimental results for breaking and nonbreaking monochromatic waves. The model results are in general quite acceptable for both one-and two-dimensional wave propagation in shallow water. KEY WORDS: Two-dimensional models, Boussinesq, Wave breaking, Eddy viscosity. 1 INTRODUCTION The study and quantification of wave processes in the offshore region as well as in shallower waters and the surf zone is considered as the most fundamental element not only for the design of technical works, but also for the understanding of the phenomena that occur within the coastal zone. Waves that propagate towards the shore are subject to many deformations attributed to shoaling and refraction, because of bathymetric changes, diffraction and reflection, due to interaction with obstacles, etc. Scientists have developed a large array of theories and models to describe the wave transformation, among which, Boussinesq-type wave models have a prominent position, being accurate in simulating wave propagation especially in shallow water regions. The most recent models are capable of precise simulation of highly nonlinear and fully dispersive wave characteristics. However, extra care should be taken when dealing with those models because they usually do not account for wave breaking and the resulting energy dissipation. Wave breaking is the most significant process in the surf zone and a complete model must be able to measure the contribution of this phenomenon. Many attempts have been made in order to incorporate wave breaking formulations, the earliest successful of which is considered the surface roller model proposed as a concept by Svendsen (1984) and implemented by the study of Schäffer et al. (1993). This approach incorporated an extra term in momentum conservation equation linked to the surface roller thickness, which was related to the front slope of the wave form. Madsen et al. (1997a) expanded the surface-roller approach in a two-horizontal dimension concept and dealt with irregular wave conditions (1997b). Wave Breaking Simulation by a Boussinesq Model in Two Horizontal Dimensions Efstratios N. Fonias Postgraduate Student, National Technical University of Athens, School of Civil Engineering, 15780, Zografos, Greece. Email: stratos.fonias@gmail.com Constantine D. Memos, Professor, National Technical University of Athens, School of Civil Engineering, 15780, Zografos, Greece. E-mail: memos@hydro.ntua.gr Theofanis V. Karambas, Associate Professor, Aristotle University of Thessaloniki, Department of Civil Engineering, 54006, Thessaloniki, Greece. E-mail: karambas@civil.auth.gr