Experimental evidences of the influence of flood magnitude and duration on the morphological evolution of a river: Initial results from the EVOFLOOD project

There is now a clear consensus that climate change will lead to an increase in the frequency and intensity of extreme rainfall events in many parts of the world, which, in turn, will lead to increased flood flows and thus flooding of large areas. Numerical simulation is one way to improve our understanding of flooding processes, especially through Global Flood Modelling (GFM). Current GFMs represent the morphology of river channels and floodplains in a very simplified way. In particular, GFM assumes that the channel morphology remains unchanged over time. However, rivers are dynamic, their morphology evolves by erosion and deposition of sediments carried by the flow. These morphological changes can radically alter the conveyance capacity of the channel and therefore the flood risk. Integrate these morphological changes in the new GFM framework is one of the main objectives of the NERC-funded EVOFLOOD project. 

Here we present the results of the experimental part of the project. We designed a controlled laboratory experiment to identify the factors controlling the morphodynamic response within river channel. In this experiment, we generate a succession of flood events characterised by different magnitudes and durations, and we quantify the evolution of the flooded area and channel width as a function of the duration, intensity and flood history. 
We find that the main parameters controlling morphological changes are flood intensity and flood history. The duration of the flood does not have a significant impact on the morphological changes because the main changes occur during the first period of the flood event. Finally, we show the importance of the upstream sediment discharge on the modification of the conveyance capacity.