Effects of river morphological change on inundation modelling during extreme flood sequences .

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Mingfu Guan, Nigel Wright, Andrew Sleigh

Tuesday 30 june 2015

11:45 - 12:00h 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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Flooding modelling has generally concentrated on clear-water simulation without the incorporation of morphological change. However, field evidence shows that extreme floods can cause significant changes in the river channel. Increasingly attention has been paid to the influences of morphological changes within floods. Yet, the significance of morphological changes on inundation modelling is still unclear and debated in the research community. A sequence of floods might result in much more severe channel adjustments which will influence flood dynamics more significantly. Existing studies have left largely unexplored the effects of cumulative morphological changes on inundation modelling during extreme flood sequences. To extend knowledge in this field, this study explores how morphological changes affect flood hydraulics during a sequence of extreme floods and how the channel adjustments resulting from an event influence the hydrodynamics of the next event. A recently updated 2D hydro-morphodynamic model is used to simulate a series of hypothesised scenarios with and without river morphological change within a sequence of glacial outburst floods in southern Iceland. The full-scale river channel is 9 km long with width varying from 100m to 500m. The results show that the river morphological changes have much more significant impacts on flood dynamics during the later flood of the sequence; thus, the necessity to consider a sequence of events is demonstrated. The assumption of unchanging of river morphology during inundation modelling might be open to question.