A thesis submitted in partial fulfillment of t he requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1980

The experimental characteristics of wave reflection and transmission due to submerged breakwaters located on a sloping bed are considered. The theoretical considerations are based on small amplitude wave theory in an inviscid, homogeneous and incompressible fluid. The study investigates the characteristics of reflection by measuring wave profiles at various locations and characteristics of transmission with wave records obtained at some fixed points behind the breakwater. Different types of submerged breakwaters were used in this experimental study, namely rectangular and trapezoidal. From each type, three different cross sections were adopted in the investigations by just changing the crest width and vertical height. The variations of reflection and transmission coefficients due to the change of the sloping bed and the locations where the submerged breakwater was situated were also investigated. Results from the experiments are presented as a function of the wave steepness, although this correlation may not be strongly supported by theoretical considerations. In fact, the experimental results show that the reflection and transmission coefficients are considerably dependent on wave steepness. Generally speaking, the reflection coefficients decrease when the wave steepness increases. However, from the results, the relationship of the transmission coefficient with wave steepness does not always show the same tendency as that for the reflection coefficient. This may be due to the complicated shoaling and breaking process of waves and possibly to the wave oscillation behind the submerged breakwater. For a given relative barrier dimension and relative depth, the transmission coefficient is greater for smaller wave steepness. Some of previous theoretical studies were also used to compare with the experimental results.