A thesis submitted in partial fulfillment of the requirements for the Degree of master of Engineering of the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M. Eng.) - Asian Institute of Technology, 1971

Where headlands are spaced along a sedimentary coast, the shoreline between the headlands will assume a crenulate shape if the most persistent or predominant waves have a resultant direction which is oblique to the headland alignment. Finally a shape is reached which is in equilibrium with the waves. This occurs when the incoming waves break simultaneously around the periphery and there is no further longshore drift. The eventual development of such an equilibrium shaped bay was studied by means of a model in which wave directions and heights were the sole variables. Thus the wave period, water depth, beach height and sedimentary material were the same throughout. The equilibrium shape of the bays, developed from an initially straight line to the fully stable state, was measured for various wave directions and heights. The curved portion of the shapes of the equilibrium coastline was then analysed by fitting the log-spiral curve. A typical prototype bay in fully developed condition, derived from investigations of hydrographic charts, was then analysed by computer to verify that diffraction and refraction combined to form the log spiral portion of the coastline.