Morphological response to the installation of detached breakwaters along the Cigu coast of Tainan, Taiwan

Coastal landforms represent a state of equilibrium between natural forces and geological resistance. Any hard structures constructed can interfere with the natural processes of the coastal system and initiate a series of reactions. This study investigates the morphologic changes after the installation of a group of eleven detached breakwaters at the Cigu coast of Tainan, Taiwan. Multi-temporal satellite images and aerial photographs, along with field data of beach profiles, are used to analyze the sequential landform changes before and after the construction of these engineering structures. During the late 1990s, the shoreline of the Ding-tou-er Barrier had retreated after a couple of typhoon events, and the coastal hazard prevention agency decided to install detached breakwaters to prevent further erosion. Due to the installation of detached breakwaters, the nearby shores, especially the down-drift side of the coast, experienced rapid erosion either during or after the construction. Only the four detached breakwaters at the most northern end had salients that formed on their back sides. The others yielded no sand accumulation at all. Moreover, the sand accumulates on the back side of the detached breakwaters at such a fast rate that vegetation cannot grow or expand. Thus, the bare surface sand became the source of wind-blown sand that moved over the dike during the winter season. These wind-blown sand first buried the road and large numbers of spare tetrapods, then encroached the nearby aqua-cultural ponds.