Skip to content

Resolving transient dynamics of erosion, deposition and sediment transport in lahars and debris flows using field observations and LaharFlow model simulations

Jeremy Phillips1, Mark Woodhouse1, Will Downes1, Andrew Hogg2, Jake Langham3, James Walker1

  • Affiliations: 1School of Earth Sciences, University of Bristol, Bristol, UK; 2School of Mathematics, University of Bristol, Bristol, UK; 3 Department of Mathematics, University of Manchester, Manchester, UK

  • Presentation type: Talk

  • Presentation time: Tuesday 10:45 - 11:00, Room R280

  • Programme No: 3.5.2

  • Theme 3 > Session 5

Abstract

Lahars and debris flows are hazardous, concentrated, gravity-driven flows of mixtures of water, rock, and other debris entrained along their flow paths. Changes to their transported solids content through morphodynamic processes of erosion and deposition controls their rheology and basal friction, and ultimately their flow dynamics and impacts. In this study we test the capability of LaharFlow (a pragmatic dynamic shallow-layer model for lahar hazard assessment) to reproduce complex patterns of erosion and deposition preserved in a debris flow deposit, and use the model to explore the transient dynamics of sediment transport in concentrated flows. Field observations from the July 2015 Cancia debris flow (Italy) were used to identify elevation changes due to erosion and deposition over 20 m lengths along its deposit, and calibration of erosion and deposition parameters of the LaharFlow model was able to reproduce this pattern to high fidelity. Time-dependent model outputs showed that rates of erosion, deposition and flow mass flux varied along the channel during the lifetime of the flow, but the flow was consistently erosive on slopes greater than 25o and predominantly depositional on slopes less than 15o. Distinct pulses of high sediment concentration propagated downstream at approximately constant rates that were comparable to the front speed. Simulations using LaharFlow at Volcan de Fuego (Guatemala) show longitudinal profiles of sediment concentration through the flow that are consistent with previous field interpretations. Comparisons with simulations without morphodynamic processes included highlight their essential role in flow dynamics, and thus hazard and impact assessment.