2025 CSDMS meeting-058
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Using CAESAR-Lisflood to model the geomorphic recovery of a high-mountain fluvial system following an extreme sediment-charged flow
Matt Westoby,
University of Plymouth Plymouth , United Kingdom. matt.westoby@plymouth.ac.uk
High-magnitude, sediment-charged flows can leave a lasting geomorphological legacy, but their short-term impacts remain poorly understood due to observational challenges in unstable landscapes. We combined satellite remote sensing and field observations with numerical hydro-geomorphic reconstruction using CAESAR-Lisflood to model the immediate fluvial response to the 7 February 2021 ice/rock avalanche-debris flow in Chamoli district, Uttarakhand. The event deposited 10.4 ± 1.6 Mm³ of sediment within the first 30 km, in places resetting the channel to a zero-state condition. Over the subsequent 12 months, 7.0 ± 1.5 Mm³ (~67%) of the initial deposit volume was removed, mostly by monsoon river flows, resulting in a median erosion rate of 2.3 ± 1.1 m a⁻¹. Our modelling implies the presence of erosion-aggradation sediment waves moving at 0.1 to 0.3 km day⁻¹ in this initial adjustment period. Thereafter we model an exponential decline in sediment evacuation over the next decade (assuming no additional, major system shocks) and analyse CL outputs to consider the potential for sediment waves to reactivate annually. The work highlights the rapid relaxation of a high-mountain fluvial system following extreme geomorphic disturbance, with implications for water quality and downstream hydropower infrastructure.
