Unintended coastal transformation from small-scale infrastructure and land use change.

This study investigates the impact of small-scale coastal development on beach material changes along the Ban Khlong Wan (BKW) coastline in the Mid-Gulf of Thailand, a site of legal disputes between local communities and government agencies over environmental impacts. We applied shoreline change analysis, high-resolution LiDAR observations, beach material characterization, and land use change assessment to understand the causes of beach transformation. Contrary to prior reports attributing the transition from sandy to muddy conditions to coastal protection structures, our findings reveal the coastline remained predominantly sandy until 2002, with shoreline shifts averaging less than ± 1 m/year. The construction of a fishery pier and hard structures (2004-2008) disrupted longshore sediment transport, leading to sand accumulation updrift and sediment deficits downdrift. This, combined with increased muddy inputs from upstream land use change, particularly the conversion of 100 ha of natural wetland into aquaculture ponds, contributed to mudflat formation. While detached breakwaters and seawalls aided in shoreline stabilization, they were not the primary cause of the transformation. Rather, the shift from alongshore sandy to riverine muddy sediment supply was the key driver. These findings highlight the need for integrated coastal management that considers the interactions between infrastructure, sediment processes, and land use change to mitigate degradation and support sustainable development of small-scale coastal projects.