Anthropogenic and hydrodynamic drivers of shoreline change in the Vietnamese Mekong Delta (2009-2023)

Abstract

ABSTRACT The Vietnamese Mekong Delta (VMD), a region of immense ecological and economic importance, faces unprecedented environmental pressures. This study provides a comprehensive analysis of shoreline dynamics along the VMD coast of Vinh Long province, focusing on the segment between the Co Chien and Bassac River mouths from 2009 to 2023. Utilizing a multi-temporal remote sensing approach with satellite imagery, shoreline changes were quantified to investigate the interplay of natural and anthropogenic drivers. Shorelines were extracted using an automated histogram thresholding method and standardized to the mean sea level (MSL) datum, enabling robust inter-annual comparisons. Results reveal a dominant erosional trend, with approximately 72.6% of the coastline experiencing retreat at a mean rate of -5.7 ± 6.9 m per year. To isolate coastal engineering impacts, the analysis specifically compared pre-2014 and post-2014 periods, marking the completion of the Duyen Hai Thermal Power Plant breakwater system and the Quan Chanh Bo canal groins. Pre-2014 changes were characterized by widespread erosion, primarily attributed to significant reductions in sediment supply from the Mekong River. In contrast, post-2014 shorelines exhibited a classic structural impact pattern: pronounced accretion in the northern section and accelerated erosion in the southern section. This pattern is strongly modulated by monsoonal seasons, with the energetic Northeast monsoon driving dominant southwestward longshore sediment transport, causing a larger sediment supply deficit along the southern shoreline. This research underscores the coast’s critical vulnerability to regional sediment deficits, locally exacerbated by engineering works, providing a scientific basis for sustainable coastal management.