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

Thesis (M.Eng.) - Asian Institute of Technology, 1991

When a structure is placed on an erodible bed and is subjected to a current or wave field, scour will most likely occur around the structure. It is very difficult to predict this scour, because the scouring process is more complicated than the normal transport process. Both erosion and sedimentation processes are involved in the movement and transportation of sediment on the seabed which is mainly due to the wave action. Three different types of structures, namely, vertical, inclined and stepped face seawall were tested in this study for comparative study of scour in front of them. An attempt is made to determine the beach profile response due to the presence of various types of structures placed at various positions in response to normally incident wave attack. Throughout the experiments the water depth, beach slope and wave direction were kept constant. It is found from the laboratory experiments that extensive scour occur at the toe of vertical type seawall, minimum scour occur at the toe of stepped face seawall. Further it was observed that storm wave with high wave steepness erode the sandy beach and accumulate in the offshore zone causing shoreline retrogression. It was also found that scour depth is directly related to run up height, reflection coefficient, wave steepness, sand size and above all characteristics of waves.