This paper presents the analysis and calculation of wave attenuation when waves travel on sand bed, sand ripple bed and muddy bed, respectively. The study shows that (1) dissipation of wave energy due to bottom percolation may be neglected on sand bed; (2) wave attenuation due to the friction of sand ripples is one order more than that of flat sand bed and (3) the energy loss of waves propagating on muddy bed is the largest. Then, equivalent coefficients of friction are calculated in order to compare with the solution by bottom-friction model. Wave attenuation are also computed by Bingham-model and the principle of conservation of wave energy flux on very mild, muddy slope. The results coincide well to the wave information from Lian Yungang Wave Observation Station. Theoretical prediction proves that the equivalent coefficients of friction strongly rely on water depth, the shallower the water depth is, the more the equivalent coefficients of friction are.
Offshore and coastal areas are where people frequently engage various kinds of human activities, for examples, port building, sea wall construction, installation of oil drilling platform and seashore power station, etc, When designing structures placed in shallow water, the design wave height always takes the critical wave height--breaking wave height. The critical wave height adopted in Chinese Code is determined by Goda's method, which is widely used in many countries. This method is based on the study of regular waves on bottom slope i >/1/50. The maximum wave height is 0.78 times of water depth. On this slope, wave attenuation may be neglected because wave travels from deep water to shallow water only in a short distance and the energy toss is small.