Abstract

Urbanization alters the geomorphological attributes of rivers by increasing peak flows and reducing sediment inputs due to surface sealing and efficient stormwater systems. Attribution of geomorphological changes to urbanization has been mostly done using purely statistical tools under a regional analysis framework, which does not explicitly account for the hydrological processes by which urbanization controls river morphology. Using a process-based hourly hydrological model, we aimed to relate the observed geomorphological changes in three French rivers to the historical urbanization of their catchments over the period 1959-2018. Firstly, we applied the hydrological model to generate an hourly streamflow time series from climatic inputs by accounting for the changes in catchment imperviousness, which we estimated from historical land-cover databases. Secondly, we exploited the obtained streamflow time series to analyze the temporal evolution of the flow competence, i.e. its ability to transport sediments, with regard to the increased imperviousness of the catchments. Results show that urbanization significantly increased flow competence on the urbanized rivers, but the impact and its trend were variable from one catchment to another. This demonstrates the role of urbanization in increasing the channel instability that led to the general incision and widening observed on these rivers over the past three to four decades. Our approach shows promise in projecting the impact of changing land-use and climate on channel geomorphology.