FLOODSETS · Flume study of flood history effects on sediment entrainment and transport in gravel-bed rivers

Floods are among the most effective geomorphic force featuring the landscape, and also one of the most hazardous natural phenomena. The timing of flood events has a major impact on fluvial morphodynamics, river management and flood protection planning, especially under a perspective of climate change, i.e. long drought periods followed by flashy intense floods. However, the effects of different sequences of events in terms of duration and magnitude – the so-called flood history – on sediment entrainment and transport are still poorly understood, thereby limiting the accuracy of predicting fluvial adjustments and the associated flood hazards. This proposal addresses the hypothesis that the condition and structure of the river bed fluctuates with flood history in a manner that can be predicted. The overall objective of the research is to quantify the influence of flood history on the mobility and transport rate of mixed sand-gravel river beds, by means of laboratory experiments. The aim is to investigate the process by which the flow field (e.g. turbulence) and the bed structure (roughness and grain exposure/protrusion) interact as a response to an imposed flood history. Multiple flood sequences will be simulated in a recirculating flume facility complemented by a state-of-the-art suite of monitoring equipment. The instrumentation will enable an integrated, high-resolution detection of both temporal and spatial dynamics of fluid flow (PIV and ADV techniques), sediment flux (bedload traps and image analysis), and bed topography adjustment (laser scanner). Once the physical processes at play will be understood, new empirical models will be developed to make incipient sediment motion and bedload rate prediction more accurate of the ones now available, being capable of including flood history effects. In order to explore how bed sediment mixture influences the flood history effects, the experiments will involve three gravel mixtures having varying proportion of sand.