Observations and computational multi-phase modelling in tropical river settings show complex channel changes downstream from rainfall-triggered landslides

Panici, D., Bennett, G., Boothroyd, R. J. , Abancó, C., Williams, R. D. , Tan, F. and Matera, M. (2024) Observations and computational multi-phase modelling in tropical river settings show complex channel changes downstream from rainfall-triggered landslides. Earth Surface Processes and Landforms, (doi: 10.1002/esp.5841) (Early Online Publication)

Abstract

Alluvial river channels respond to changes in sediment supply by adjusting their geometry. Landslide sediment delivery and geomorphic response of river channels during floods are poorly understood and rarely examined in tropical settings. We investigate the impact of landslides on channel geomorphic changes during an extreme typhoon-induced flood event in the Philippines, specifically the complex geomorphic response of the Antamok River to Typhoon Mangkhut in September 2018, which triggered >500 landslides in the Ambalanga catchment. The catchment has a legacy of anthropogenic modifications, such as extensive small-scale (artisanal) mining and tailings storage facilities (TSFs) from large-scale mining activities. We use a novel mix of mapping and computational modelling approaches to test the hypothesis that landslide sediment delivery is a major control on channel geomorphic change. Pre- and post-event imagery show that the overall active channel area increased by 35.9% and the mean active channel width increased by 9.1 m. Spatially, we find no clear relationship between landslide sediment input or unit stream power and channel width geomorphic change, with longitudinal changes in active channel width complicated by TSFs. Multi-phase modelling using r.avaflow revealed how landslide sediment delivery and TSFs interacted with the flow to generate the observed patterns of channel change. The model simulated channel incision in the upper parts of the catchment (up to 0.78 m) and deposition in the TSFs (up to 1.73 m). Our findings demonstrate that well-established methods (e.g., stream power threshold) fail to fully explain channel width geomorphic changes, particularly for anthropogenically altered catchments. Integrating techniques, such as landslide mapping and multi-phase computational modelling improves understanding of sediment supply's role in channel width change during extreme events. Numerical simulations also demonstrate that conventional assumptions of increased erosion and deposition with rising flow discharge are inaccurate with large sediment input, highlighting instead the effectiveness of multi-phase models.

• Item Type: Articles
• Additional Information: Department of Science and Technology, Philippines; Natural Environment Research Council, Grant/Award Numbers: EP/X527749/1, NE/S003312, NE/S003371, NE/W006871/1; Newton Fund, Grant/Award Numbers: X527749, W006871.
• Status: Early Online Publication
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Williams, Professor Richard and Boothroyd, Dr Richard
• Authors: Panici, D., Bennett, G., Boothroyd, R. J., Abancó, C., Williams, R. D., Tan, F., and Matera, M.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Earth Surface Processes and Landforms
• Publisher: Wiley
• ISSN: 0197-9337
• ISSN (Online): 1096-9837
• Published Online: 10 April 2024
• Copyright Holders: Copyright © 2024 The Authors
• First Published: First published in Earth Surface Processes and Landforms 2024
• Publisher Policy: Reproduced under a Creative Commons licence