Geospatial and fluvio-geomorphological investigation of confluence dynamics of river Raidak within Himalayan foreland basin, India

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.

KEYWORDS:

• Confluence
• Channel Avulsion
• Quaternary
• Geospatial
• Himalayan foreland basin

Acknowledgments

The authors are acknowledged to the Central Water Commission, Govt. of India (CWC, Govt. of India), Jalpaiguri, for providing flood season discharge data of river Raidak, Raidak-I, Torsa and Sankosh. Authors are thankful to the GSI and CGWB for providing Geological and Geomorphological map of the study area. Authors are also highly thankful to the USGS for supplying satellite images and earthquake data of the study area.

Data availability statement

The data that support the findings of this study are available on request from the corresponding author, [B. B.] upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).