The 45 km-long reach of the Rhine River from Kembs to Breisach has been heavily impacted by engineering works during the last two centuries. The Kembs dam and the lateral Grand Canal d'Alsace achieved in 1959 induced significant decrease in sediment transport and diversion of most of the flow in the lateral canal so that the by-passed Old Rhine runs now a minimum flow (3% of the mean annual discharge during 300 days per year). A space-time study was conducted to understand the Old Rhine morphological response to dewatering, peak flow reduction and sediment transport interruption in particular the vegetation expansion process and its potential feedback impacts on the channel hydraulics and the sediment transport. Sets of aerial photographs integrated in a GIS environment have been used to map the extent of water bodies, gravel bars, riparian vegetation (grasslands, shrubs, trees identified by colour, texture and structure) and anthropogenic features every 10 years since the 1950s. Strong channel narrowing and associated vegetation expansion are observed until 1982. Tests conducted on the different dates underlined homogenous segments and downstream progression of the processes through time, demonstrating different patterns of adjustments. Cross-sections of 1950 and 1990 were overlaid with land use layers, demonstrating that incision and aggradation areas are spatially linked with the planform changes. From these findings, we hypothesised that vegetation encroachment modified hydraulic conditions, enabling to produce sediment transport and winnowing despite of peak flow reduction and armour layer development due to intense incision following channelization works. As a consequence, 1D hydromorphodynamical simulations were performed to quantify the mean sediment mobility along the homogeneous segments, and validate causality hypothesis. Both GIS study and 1D modelling are complementary revealing the channel and vegetation evolution and underlined the significant impact of vegetation development on the bed dynamics over decades.