Morphological change assessment from intertidal to river-dominated zones using multiple-satellite imagery: A case study of the Vietnamese Mekong Delta

Understanding river bank and shoreline dynamics is important for ecological conservation, livelihood stabilization, water resources management and hazard mitigation, but this is always a difficult task because the river and coastal morphology is influenced by both natural processes and human activities. The Vietnamese Mekong Delta with its dense population of 17 million people and a complex river system under the impacts of both natural and artificial drivers was chosen as a case study to understand erosion and accretion mechanisms of deltas. Sedimentation plays a critical role in sustaining the livelihoods of population, biodiversity, and food production, but long-term and large-scale sediment dynamics studies on huge sediment starvation due to dams and sand mining were limited. Remote sensing data analysis with the cloud-computing-based Google Earth Engine for the period from 1989 to 2014 has exhibited that both regional and local drivers and hydrological characteristics of each region were responsible for river bank erosion and accretion. In the river-dominated zone, the levels of erosion and accretion are from medium rates (1–5 m/year) to high rates (> 5 m/year), and erosion processes commonly occur along the Mekong River branch (Tien River). In the tidal-dominated zone, the river banks were quite stable, and erosion processes with medium levels mainly occurred at river segments near estuaries, except for the Ba Lai estuary. In the coastal zone, erosion and sedimentation alternatively took place at a rapid rate. The main erosion mechanisms were toe-scour and lower slope erosion in the river-dominated zone, the tidal fluctuation-related soil collapses in the tidal-dominated zone, and monsoon-influenced erosion in the coastal zone. Engineering or alternative solutions should be chosen appropriately to maximize the efficiency of protection for each region, while more monitoring programs are required to provide more reliable data to study erosion and sedimentation processes.