Identifying Riverbank Erosion Hotspots along the Mekong River in Cambodia and Vietnamese Mekong Delta Using Google Earth Engine and Satellite Images

Abstract:

Riverbank erosion is one among several natural hazards that affect the livelihood of people and the development of the countries in the Lower Mekong Basin. It causes problems on resettlement, substantial damages to properties and public infrastructure as well as fish habitats. In 2019, 402 people in Cambodia were relocated due to riverbank erosion according to data from the National Committee for Disaster Management. In 2011, Vietnam lost 60.54 ha of land which cost around $1.5 million according to the Mekong River Commission. This study aims to identify riverbank erosion hotspots along the Mekong River in Cambodia and the Vietnamese Mekong Delta. Riverbank erosion hotspot is defined as an area subjected to substantial and frequent erosion coincides with an area of high exposure. A riverbank erosion monitoring tool is first developed by using satellite images (Landsat and Sentinel-2) in Google Earth Engine. Sentinel images have a better spatial resolution of 10 m as compared to Landsat images with a spatial resolution of 30 m; however, Landsat has a longer record of data compared to Sentinel-2. Long-term historical morphological change maps from 1984 up to the present are created. The changes are analyzed using linear regression. To improve the accuracy of the tool, different water indices (NDVI, NDWI, and MNDWI) are applied. The results are validated with Google Earth application. The maps of riverbank erosion are then overlaid with landuse map using GIS (Geographic Information System) software to develop the riverbank erosion hotspot map. Preliminary results show that riverbanks have eroded up to more than 1 km at some segments along the Mekong River within the last twenty years. In Cambodia, Koah Soutin and Ruessei Srok have high average erosion rates of 34 m/year and 63 m/year, respectively. The erosion rate of the island is even higher. In the Mekong Delta, Sa Dec is the most eroded segment with an erosion rate of around 50 m/year. Most of the eroded areas are farmland and rural residential area. This study provides an efficient tool for identifying riverbank erosion hotpots of a large river. The riverbank hotspots maps would be useful information for policymakers to develop an efficient and viable mitigation and response measures to improve the sustainable livelihood of the affected people in both countries.