Modifying BEHI (Bank Erosion Hazard Index) to map and assess the levels of potential riverbank erosion of highly human impacted rivers: a case study for Vietnamese Mekong river system

Sedimentation and erosion of riverbanks and canals in the Mekong Delta have been longstanding issues. However, the severity and frequency of these problems are on the rise due to multiple factors, including upstream influences, climate change, rising sea levels, and human development activities. In this study, mapping riverbank erosion potential in the Vietnamese Mekong Delta is proposed to be carried out using the MK-BEHI index, which has been modified from BEHI developed by Rosgen. The MK-BEHI assesses the potential riverbank erosion by considering various factors, including: near-bank stress, bank geology, vegetation cover, bank construction, accretion/erosion rate, and bank load. Two indicators added to the index, compared to the original BEHI index, are bank construction and bank load. The index is categorized into four levels: low, medium, high, and very high, using a semi-quantitative approach. It is calculated by summing the component hazard indexes multiplied by their respective weights. The findings reveal that segments with very high potential are concentrated in certain areas, such as the segment of the Hau River flowing National Highway 91, Vam Nao River passing through My Hoi Dong, An Giang province, and the Tien River segment flowing through Sa Dec. Furthermore, numerous high-potential erosion banks have been recorded along the Tien and Hau rivers, particularly at the beginnings of the islets, curved river sections, and the Ham Luong river area encompassing Cho Lach, Mo Cay Bac, Mo Cay Nam, Thanh Phu, and Ba Tri. The aim is to provide a foundation for disaster adaptation and sustainable management.