Leveraging Remote Sensing for Exploring Climatic and Hydro-Geomorphic Linkages to Flooding: A Case of Bagmati River in Central Nepal

Rivers are dynamic systems that evolve in response to different geologic, hydrologic, climatic, and anthropogenic factors. This study utilized over three decades of remote sensing imagery to quantify river planform dynamics of the Bagmati River in central Nepal. It maps the spatiotemporal changes in the active river channel extent and lateral migration rates from 1990 to 2022, revealing an alarming decline in total river channel area by about 65% as compared to the historic extent. Lateral migration rates of the river channel varied significantly along the reach ranging between 2 and 40 m per year (m/yr). Intra-annual analysis of the erosion and accretion areas from river masks before and after the monsoon season revealed a stronger correlation between peak annual flow and accretion area in the study reach. Further exploration of a flood event in July 2019 using Sentinel-1 radar imagery revealed that the inundated area followed the historic channel extent, and multi-day precipitation event had a major contribution to triggering floods in the Bagmati. This study highlights the invaluable role of satellite remote sensing in studying river planform dynamics, which helps devise informed approaches for flood mitigation, erosion control, and myriads of other crucial endeavours to safeguard the population in the vicinity.