Tracing Morphological Transformations and Braiding Dynamics in the Himalayan Rivers of Nepal

This study quantifies multi-decadal (1990–2022) planform change and braiding behavior in three Himalayan rivers of Nepal: The Koshi, Narayani, and Karnali using a unified geospatial workflow. Multi-temporal Landsat and Sentinel-2 imagery were processed with water-detection indices (MNDWI, NDWI) to extract channel boundaries and map erosion, accretion, and persistence. High-frequency gauge records were used to derive discharge and examine functional relations between wetted-area ratio and flow, and 180 Sentinel-2 scenes (2017–2022) supported braiding-intensity (BI_T3) estimation and bar-scale assessment at sub-reach level. Results show strong river-specific contrasts: the Koshi exhibits the greatest adjustment, with only 32.5 % channel persistence and a pronounced westward lateral migration, whereas the Narayani and Karnali are comparatively stable, with 64.8 % and 54.5 % unchanged areas, respectively. Functional analyses indicate distinct sensitivities of wetted-area ratio to daily maximum discharge, and braiding intensity peaks at intermediate flows before attenuating at higher discharges. Focused sandbar analysis (2017–2022) in the Koshi reach reveals persistent bifurcation asymmetry and directional bar migration, consistent with post-monsoon redistribution of flow and sediment. By linking satellite-derived morphology to real-time discharge within a consistent, transferable framework, the study provides robust, repeatable indicators for monitoring Himalayan braided rivers and establishes a basis for comparative evaluation of planform stability and braiding across data-sparse systems.