Rivers have been trained for centuries by series of transverse groynes. This generally results in damages to their ecosystems as well as in undesirable longterm morphological developments. We analyze here the possibility to train rivers in a new way by subdividing their channel in parallel channels with specific functions with longitudinal training walls. In most cases, the goal is that of obtaining one deep, regular navigation channel and one shallower channel that is able to preserve some ecological functions of the river and to contribute to convey high flow discharges. The effectiveness of longitudinal training walls in achieving this goal and their longterm effects on the river morphology have not been thoroughly investigated yet. In particular, studies that assess the stability of the parallel channels separated by the training wall are still lacking. This work studies the long-term morphological developments of river channels subdivided by one or two longitudinal walls, focusing on low-land rivers. These rivers are normally characterized by the presence of steady alternate bars, or point bars inside their bends. For this reason, the presence of these large deposits is taken into account. This is the first study dealing with the combined effects of bars and longitudinal walls. The methodology comprises both laboratory experiments and numerical simulations...

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.