Modelling the influence of vegetation on the morphodynamics of a flood event in the Allier, France

Abstract (2006)

Authors

MJ Baptist Hydraulic Structures and Flood Risk - CEG
Research Group
Hydraulic Structures and Flood Risk (CEG) (TU Delft)
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Published Date

2006

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Faculty

Civil Engineering & Geosciences

Department

Hydraulic Engineering

Research Group

Hydraulic Structures and Flood Risk

Abstract

Geophysical Research Abstracts, Vol. 8, 02516, 2006
SRef-ID: 1607-7962/gra/EGU06-A-02516
© European Geosciences Union 2006

Modelling the influence of vegetation on the
morphodynamics of a flood event in the Allier, France

M.J. Baptist
Delft University of Technology, Faculty of Civil Engineering and Geosciences, Water
Resources Section, Delft, The Netherlands (m.j.baptist@tudelft.nl)

Understanding the interactions between vegetation and the morphology of rivers is
becoming increasingly important in view of modern river management and climate
change. There is a need for predictive models for the natural response of rivers to river
rehabilitation. One way to study the effects of river rehabilitation is to study natural
reference rivers. The Allier in France is considered as a landscape reference for the
to-be-restored Border Meuse in the Netherlands. The Allier is highly dynamic, large
amounts of sand and gravel are transported during floods and its morphology changes
considerably from year to year. The riparian vegetation is characterised by pioneer
species on the low-lying dynamic point-bars, herbaceous vegetation and grass on the
higher parts and extensive softwood floodplain forests, mainly consisting of poplars,
on the older and higher floodplains. Due to the river dynamics, this river shows natural
rejuvenation of vegetation such that older forests are removed by erosion and young
pioneer vegetation can start growing on the point-bars. This model study investigates
the role of vegetation on the morphological changes of a single flood event that took
place in December 2003. A state-of-the-art 2-DH morphodynamic model was applied
in a 6 Mm2 study area. This model accounts for the effects of vegetation on the hydraulic
resistance and on the reduction of bed shear stress and subsequent bed load
sediment transport. The model results show that vegetation has a pronounced effect
on the hydrodynamics and morphodynamics. The results also reveal that this model
has only limited success in simulating the observed morphological changes. Recommendations for further model development will be made. It can be concluded that
vegetation is an important factor for the morphodynamics of gravel bed rivers, but our
knowledge is at present insufficiently advanced to accurately predict the morphological
changes in this section of the Allier.