A new method valid for highly dispersive and highly nonlinear water waves interacting with a rapidly varying bathymetry has recently been developed. It is based on truncated series solutions to the Laplace equation combined with the exact boundary conditions at the free surface and at the sea bottom. We consider the method to belong to the Boussinesq-type family of methods although it is formulated as six coupled equations involving up to fifth-derivative operators. As a result, linear and nonlinear wave characteristics are very accurate up to wave numbers as high as kh=30, while the vertical variation of the velocity field is applicable for kh up to 12. This presentation will concentrate on

the following achievements: a) Velocity profiles in highly nonlinear shallow water and deep water waves; b) Investigation of crescent wave patterns; c) Investigation of class III Bragg scattering. First, velocity profiles in highly nonlinear waves are computed in deep water as well as in shallow water. The results are verified against streamfunction theory and against Tanakas solitary wave solution. With the established range of applicability,

the method has an obvious potential for computing the velocity field in highly nonlinear irregular wave fields, which makes it an attractive tool for design purposes. Next, a numerical study of crescent (or horseshoe) water wave patterns is presented. These patterns arise from the instability of steep deep-water waves to three-dimensional disturbances. We focus on the development of the most unstable stationary L2 pattern, discuss the growth rate and the physical processes. Next, we investigate the development of oscillating crescent patterns which no longer propagate in quasi-steady form, but emerge and disappear repeatedly. Quantitative estimates for the oscillation period are given based on a stability analysis following McLean (1982). Finally, we study the interaction of nonlinear waves with an undular sea bottom. As a result we observe class III Bragg scattering, which involves three surface wave numbers and one bottom wave number. Reflection occurs as a sub-harmonic resonance, while transmission occurs as a super-harmonic resonance. The growth rate of the Bragg scatter as well as the location of the resonance depends on the nonlinearity of the incoming wave. A downshift/upshift of resonance is observed for reflection/transmission and in order to explain this we develop a new third order theory for bichromatic waves.