Sustainable coastal zone planning based on historical coastline changes: A model from case study in Tainan, Taiwan

Coastal regions are threatened by natural processes, such as erosion driven by storm surge and the effect of jetties, as well as by human behavior. This study outlines a management framework based on an analysis of a case study dataset of long-term coastal change in southwestern Taiwan. Specifically, the coastal structure of Taiwan's largest lagoon, Cigu, was analyzed over a 300-year-long period. A series of satellite-derived images between 1974 and 2015 were assessed. The dataset was integrated with a geographic information system (GIS). The results revealed that human activities, including the construction of hard structures along the coastline and along an upstream reservoir, altered the balance of sediment transmission and resulted in the retreat and erosion of barrier sandbars along the coast. A lagoon evolution model revealed that the Cigu Lagoon may disappear in the future. Furthermore, the coastline will continue to retreat because harbor dykes and offshore breakwaters stop sediment transportation to the downdrift. Soft erosion mitigation is suggested as an immediate approach. However, recovering the sediment budget from reservoirs and dykes could be a long-term solution. In principle, the best coastal environmental protection plan from the national involves delaying urbanization and preserving unexploited coastal wetlands.