Field based inventory of river bank erosion susceptibility model (BESI) of Raidak-II river in the Himalayan foreland basin

River bank erosion is a fluvio-hydrological hazard, and sometimes, it turns into disaster in the human-encroached river bank and flood plain. The principal objective of this study is to detect the river bank erosion potential zone using new Bank Erosion Susceptibility Index (BESI) model and spatiotemporal shifting of river Raidak-II (1980–2020). Sedimentary bank facies (SBF) analysis was conducted to identify the nature of cohesiveness of bank materials. The result showed that the maximum average lateral shifting (213.20 m) was recorded in the year 1990 (right bank), whereas the minimum average shifting (77.32 m) was measured in the year 2020 (right bank). The result also showed that the right bank of Raidak-II was mostly oscillated due to poorly sorted quaternary non-cohesive bank materials. The Bank Erosion Hazard Index (BEHI) model showed that 46.15% and 50% bank erosion sites are fallen in high-to-extreme bank erosion susceptibility zones in the years 2020 and 2022. In the case of BESI model, 69.23% and77.77% bank erosion sites are confined in high-to-extreme bank erosion susceptibility zones in the years 2020 and 2022. Therefore, BSEI model gives more precise results compared with BEHI due to three additional factors. The poorly sorted non-cohesive quaternary sediments stimulate high rate of bank erosion within Himalayan foreland basin.

河岸侵蚀是一种河流水文灾害，在人类活动侵占的河岸与洪泛平原区域，其有时会演变为灾害。本研究的核心目标为：借助新型河岸侵蚀敏感性指数（Bank Erosion Susceptibility Index，BESI）模型，分析雷达克-II河1980—2020年间的河岸侵蚀时空迁移特征，并识别河岸侵蚀潜在风险区域。本研究开展了河岸沉积相（Sedimentary bank facies，SBF）分析，以明确岸滩物质的黏结特性。研究结果显示，1990年右岸的侧向平均迁移距离达到最大值，为213.20米；而2020年右岸的侧向平均迁移距离最小，仅为77.32米。结果同时表明，雷达克-II河右岸的岸滩迁移活动最为频繁，这源于其岸滩物质为分选性较差的第四纪非黏性沉积物。河岸侵蚀危险性指数（Bank Erosion Hazard Index，BEHI）模型结果显示，2020年与2022年分别有46.15%、50%的河岸侵蚀点位处于高至极高侵蚀敏感性区域；而采用BESI模型时，2020年与2022年对应比例分别为69.23%、77.77%的侵蚀点位落入高至极高敏感性区域。由于额外纳入了三项影响因子，BESI模型的预测结果相较BEHI模型更为精准。分选性较差的非黏性第四纪沉积物，会显著加剧喜马拉雅前陆盆地内的河岸侵蚀速率。