Carrivick, JL

Guan, M

Sleigh, PA

Stanies, K

Wright, NG

White Rose Research Online

This is a repository copy of A layer-based morphodynamic model for unsteady outburst geomorphic floods: application in real world events.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/81337/Version: Accepted VersionProceedings Paper:Guan, M, Wright, NG, Sleigh, PA et al. (2 more authors) (2013) A layer-based morphodynamic model for unsteady outburst geomorphic floods: application in real world events. In: Parsons, DR, Ashworth, PJ, Best, JL and Simpson, CJ, (eds.) Proceedings of the 10th International Conference on Fluvial Sedimentology (2013). 10th International Conference on Fluvial Sedimentology, 14-19 July 2013, Leeds, UK. , 130 - 131. eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. ICFS10LEEDS, UK 14-19 JULY 2013 000130A layer-based morphodynamic model for unsteady outburst geomorphic floods:application in real world eventsM.F.Guan1, N.G. Wright1, P.A. Sleigh1, J.L. Carrivick2and K. Staines21School of Civil Engineering, University of Leeds, Leeds, UK. cnmg@leeds.ac.uk, N.G.Wright@leeds.ac.uk, P.A.Sleigh@leeds.ac.uk2School of Geography, University of Leeds, Leeds, UK. J.L.Carrivick@leeds.ac.uk, gykehs@leeds.ac.uk1. IntroductionOutburst floods generally comprise advancing intensewater waves which can induce considerable geomorphicchange rapidly. Therefore, the exploration andinvestigation of such floods cannot be limited to waterflow itself, but must also consider flow-inducedsediment transport. However, many numerical modelsdo consider the flow as clear water, neglecting sedimenttransport processes. Although this treatment simplifiesthe numerical model, it must be open to question interms of understanding real flood behaviours. In recentyears, investigations on sediment transport in transientoutburst floods are increasingly carried out; however,the understanding of how sediment load transports andinteracts with water in flood propagation is stillambiguous and scarce. The aim of this project is todevelop a layer-based morphodynamic model, and thento understand more of fluvial hydraulics and sediment-flow interactions in large scale outburst floods.2. Layer-based model frameworkFor bedload dominant sheet flow, sediment generallyaccumulates and transports at the bottom, while floodwater propagates as an agent of sediment in the upperlayer. Therefore, based on that consideration, a layer-based concept model is adopted here (see Fig.1).Accordingly, the model system is governed by: mass andmomentum conservation of the whole mixture flow, aswell as mass conservation of sediment at bottom layer.The proposed model system is primarily composed of acombination of the following modules: Hydrodynamic module: governed by 2D shallow waterequation with consideration of sediment effects. Sediment transport module: controlling the sedimentmass conservation. Morphological evolution module: for updating the bedelevation after erosion and deposition.Figure 1: schematic drawing of the layer-basedconceptual model3. Results and discussions3.1 Model validationThe proposed model was validated by a series ofexperimental works, involving: (1) dam break flow overmovable bed of sand and PVC particles; (2) sedimentaggradation in the transcritical flow (3) dam breach dueto flow overtopping; (4) dam break flow over movablebed channel with a sudden enlargement; etc. Thesecases are well reproduced by the layer-based numericalmodel.3.2 Application to volcano-induced GLOFThe layer-based model is applied to simulate a largescale volcano-induced glacial outburst flood occurred atSólheimajökull, Iceland in 1999. Fig.2 shows the waterdepth at 2 hours with and without sediment and thedistribution of sediment erosion and deposition after 6hours. Therein, the erosion and deposition primarilyoccur in the main channel with eroded volume of7.3×105m3and deposit volume of around 4.6×105m3.Further, through the comparisons and analysis betweenthe simulations of flood with and without incorporationof sediment, it is found that sediment accelerates theflood propagation but decreases the water level at mostcross sections. As for the effects of sediment size, thesensitivity is analysed by inputting three differentsediment sizes as: mixed diameter, d50=40mm andd50=80mm. It was found that (1) sediment grain sizedoes not have significant influence on hydrodynamicprocess; but (2) it directly decides the features andextent of geomorphic change caused by the flood.Figure 2: water depth with and without sediment at 2hours and the distribution of erosion and depositionICFS10LEEDS, UK 14-19 JULY 2013 0001314. ConclusionsA novel layer-based morphodynamic model is proposedfor rapid geomorphic floods. The model fully considersthe hydraulic and sedimentary factors and it is validatedby a series of experiments with good performances. Inlarge scale flooding, sediment transport has significanteffects on hydraulic features and rapid geomorphicchange. Therefore, understanding the effects clearlyand predicting the flood accurately are very importantfor flood risk management and flood hazard mitigation.AcknowledgmentsThe first author would like to thank the ChinaScholarship Council (CSC) and the School of CivilEngineering at University of Leeds for their financialsupport for his PhD studies.ReferencesCarrivick J.L., Manville V., Graettinger A., and Cronin,S.J.(2010) Coupled fluid dynamics-sedimenttransport modelling of a Crater Lake break-out lahar:Mt. Ruapehu, New Zealand. Journal of Hydrology,388, 399-413.Carrivick J.L.(2010) Dam break-Outburst floodpropagation and transient hydraulics: A geosciencesperspective. Journal of Hydrology, 380, 338-355.Russell A.J., Tweed F.S., Roberts M.J., Harris T.D.,Gudmundsson M.T., Knudsen O. and Marren P.M.(2010) An unusual jökulhlaup resulting fromsubglacial volcanism, Sólheimajökull, Iceland.Quaternary Science Reviews, 29, 1362-1381.

A layer-based morphodynamic model for unsteady outburst geomorphic floods: application in real world events

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A layer-based morphodynamic model for unsteady outburst geomorphic floods: application in real world events

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