ABSTRACT

Confluence of river channels plays a significant role in channel avulsion, flood plain evolution and dynamics of the fluvial system. The principal objectives of the present study are (i) to analyze the direction and degree of confluence shifting through the recent past (1955–2020) by applying geospatial techniques and (ii) to find out the probable causes of confluence dynamics of the Raidak river system within quaternary geological sites of a Himalayan foreland basin in West Bengal, India, applying fluvio-geomorphological and sedimentary bank facies. Modified Normalized Difference Water Index method is also used. The result shows that the Raidak-Sankosh confluence (RSC) shifted by 9.94 km of the total distance between 1955 and 2020, whereas Raidak-I-Torsa confluence (RTC) has shifted 4.29 km overall distance during the same period. Both confluences were shifted toward the south and south-east directions. Total erosion and accretion area at the proximity of RSC and RTC has been registered as 40.1 sq km and 47.57 sq km and 39.67 sq km and 37.99 sq km, respectively, for the 65-year period. The key factors of confluence dynamics are regular flood events and channel avulsion, non-cohesive bank materials and huge channel bed sedimentation with multiple bars.

摘要

河道合流在河道撕裂、洪泛区演化和河流系统动力学中起着重要作用。本研究的主要目标是 (i) 通过应用地理空间技术分析近期（1955-2020 年）汇流变化的方向和程度，以及 (ii) 找出 Raidak 河汇流动力学的可能原因印度西孟加拉邦喜马拉雅前陆盆地第四纪地质遗址内的系统，应用河流地貌和沉积滩相。还使用了改进的归一化差异水指数方法。结果表明，Raidak-Sankosh 汇流点 (RSC) 在 1955 年至 2020 年期间移动了 9.94 公里的总距离，而 Raidak-I-Torsa 汇流点 (RTC) 在同一时期移动了 4.29 公里的总距离。两个汇合点都向南和东南方向移动。在 65 年期间，RSC 和 RTC 附近的总侵蚀和增生面积分别为 40.1 平方公里和 47.57 平方公里以及 39.67 平方公里和 37.99 平方公里。汇流动力学的关键因素是定期的洪水事件和河道撕裂、非粘性堤岸材料和具有多条堤坝的巨大河床沉积。