Role of vegetation on river bank accretion

Abstract

There is rising awareness of the need to include the effects of vegetation in studies dealing with the morphological response of rivers. Vegetation growth on river banks and floodplains alters the river bed topography, reduces the bank erosion rates and enhances the development of new floodplains through river bank accretion. The role of riparian vegetation on river morphology is examined in this thesis, with particular attention to its effects on bank accretion, focusing on lowland streams in temperate climates. The work is based on the combination of extensive literature review, small- and large-scale laboratory experiments, field observations and numerical simulations in order to overcome the shortcomings of single approaches. The results of the study demonstrated that vegetation is essential for the accretion of river banks in non-clay dominated environments, highlighting the role of the colonization of new deposits by plants, which is strongly influenced by the hydrologic regime. Vegetation establishment plays a key role on the stabilization of the channel-width and on the vertical accretion of both levees and floodplains. The vertical accretion and channel incision induced by colonizing plants showed that vegetation colonization increases the amplitude and length of the bars in the main channel, affecting the final river planform. The outcomes of this research emphasize the relevance of considering the effects of vegetation on the river management and on the designing, planning and maintenance programs of restoration projects. To advance in the understanding of the dynamics of river banks, future research is also recommended on quantifying of the role of root systems and fine sediments on the reinforcement and consolidation processes of soils.