Avulsion distribution on rivers in the Himalayan foreland region

Abstract

Despite recent advances, we still do not have a synoptic dataset on river avulsion across a mountain foreland belt. Here we report a novel account of chronological avulsion records (for the period 1990-2019) across the Himalayan foreland region (HFR), one of the largest and most avulsion-hit areas in the world. The chronological records discerned river avulsion frequency and distribution across HFR. We identified the eastern Brahmaputra plains amongst the most avulsion-affected areas in HFR. As many as 19 tributaries across HFR have recorded avulsion events ≥ 6. Most of these avulsion-affected rivers are smaller, with hilly catchments < 500 km2. These avulsions often occurred near the proximity of the Himalayan front. Transitional reaches (and adjacent braided/meandering sections) of the tributaries have experienced higher avulsions. Observation suggests that the 1950 Assam earthquake, non-incised channels, and rapid transition in tributaries’ morphologies are decisive in the region’s frequency and distribution of river avulsions.