An Efficient Hydrodynamic Modelling System for Predicting Geomorphological Processes due to Flash Floods.

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Qiuhua Liang, Jingming Hou, Luke Smith

Tuesday 30 june 2015

11:30 - 11:45h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 5A. Sediment - Erosion

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An Efficient Hydrodynamic Modelling System for Predicting Geomorphological Processes due to Flash Floods Qiuhua Liang; Jingming Hou; Luke S Smith School of Civil Engineering, Newcastle University, UK Recent studies have shown that UK summer flash floods triggered by intense rainfall are likely to become more frequent and severe (Kendon et al. 2014) and this is borne out by the evidence of more reported events in recent years. Commonly happening in certain small and medium-sized catchments, flash floods are typically characterised by short response times and high flow velocities, and sometimes, accompanied by landslides and debris flows. The high kinetic potential of the flood waves may erode, transport, and deposit large quantities of sediment as they move downstream and subsequently cause active geomorphological changes. It is crucial to better understand and hence simulate the hydro-geomorphological processes in order to more reliably predict this type of flood events for risk management and forecasting practices. Currently, few computer models are able to reliably simulate at a field scale the rainfall-runoff and resulting geomorphological processes during a flash flood event. Accurate simulation of a flash flood event requires a shock-capturing hydrodynamic model to represent the violent flow features, beyond the capability of simplified hydraulic/hydrological models. In this work, a shock-capturing finite volume Godunov-type model solving the two-dimensional shallow water equations is adopted and coupled with a sediment transport model to describe bed evolution during a flood event. The morphological evolution is evaluated according to the relation between the rate and capacity of the total-load sediment transport (i.e. suspended load and bed load). Finally the coupled modelling system is implemented on graphics processing units (GPU) in order to substantially improve the computational efficiency for field-scale applications. The performance of the new hydro-geomorphological modelling system is demonstrated by reproducing laboratory tests and finally applying it to simulate the geomorphological changes in a reach of River Coquet, Northumberland, UK, under flood conditions. References: Kendon JE, Roberts NM, Fowler HJ, Roberts MJ, Chan SC, Senior CA (2014) Heavier summer downpours with climate change revealed by weather forecast resolution model. Nature Climate Change, DOI: 10.1038/NCLIMATE2258.