Experimental study on the effects of longitudinal training walls

Recent developments in river training include the replacement of series of transverse groynes by a longitudinal training wall. The idea is to obtain higher flood conveyance capacity during peak discharges and maintain the navigation channel at low flows. This new type of interventions creates a (near-bank) side channel parallel to the main (navigation) channel, splitting water discharge and sediment transport between the two channels. However, it is not clear yet whether the two-channel system is stable, i.e. both channels tend to remain open, and whether the intervention will meet the objectives, particularly considering the long term morphological adaptations. This study examines the stability of two-channel systems created by longitudinal training walls in low-land rivers with a bed topography characterized by alternate bars. Based on the results of preliminary numerical simulations, showing high risk of system instability with the closure of one of the two channels, this study concentrates on experimental tests. The work is on-going and the preliminary results suggest that the position of a training wall related to a near-bank bar plays an important role on the stability of the system. Further work will be carried out with more extensive experimental investigations to carefully verify the long-term effects of a longitudinal training wall in a river with alternate bars, starting at different locations related to a bar.