Coastline dynamics and erosion/accretion in the estuaries of the lower Mekong Delta, Vietnam

In this study, we used Landsat satellite imagery to monitor coastline changes in critical estuaries of the lower Mekong River basin from 1989 to 2017. To delineate the shoreline dynamics, we used the automated water extraction index (AWEI) and the digital shoreline analysis system (DSAS) to calculate the rate-of-change statistics from multiple historical shoreline positions. The rate of shoreline change was assessed using linear regression (LRR) and end point rate (EPR) methods. The erosion and accretion observed in the estuaries were intermingled, with total areas of 4,732.46 and 13,471.7 ha, respectively. Erosion and accretion impacted the shoreline rates considerably at a fast pace and the erosion and accretion speeds depended on each of the five periods analyzed in this study. From 2015 to 2017, the highest erosion rate (507.78 m y-1) was recorded in the village of An Thuy in Ben Tre Province. From 2005 to 2009, the highest erosion rate (312.11 m y-1) was recorded in the village of Thoi Thuan in Ben Tre Province. The accuracy (T) of the largest erosion/accretion areas during 2005-2009 was estimated to be 87.9%, with a kappa coefficient (K) of 0.76, while the lowest overall T (78.5%) and K (0.57) were obtained for the 1989-2001 period. We calculated the total estimated erosion and accretion areas from 2017 to 2019 (estimated to be 166.14 and 1,432.29 ha, respectively), and forecasted values for 2019-2025 (235.93 and 1,126.51 ha, respectively). This study confirms that satellite imagery and statistical methods can be reliably used to analyze the shoreline changes in coastal areas, which can then support policies addressing coastal planning and development.