River flooding can result in overbank flows, also known as flows in compound open channels. Due to the streamwise changes in the geometry and land use of the floodplains (FPs), compound channel flows (CCFs) are usually non-uniform. CCFs are investigated in a laboratory flume with a total inflow discharge injected into the main channel (MC) that exceeds the bankfull value. This results in strong spanwise exchanges of water and sediments from the MC to the FP. This study focuses on investigating the specific features of transporting and depositing fine sediments over FPs under steady, non-uniform flow conditions. The experiment begins with clear water conditions to serve as a reference. Water levels, time-averaged velocities, turbulence statistics, and large-scale coherent structure sizes are measured. Sediment-laden flows are then studied. The respective contributions of spanwise shear layer turbulence and spanwise advection by the time-averaged flow, to the deposit formation, vary both longitudinally and in relation to inflow discharge. In the downstream part of the flow, a longitudinal levee is observed, which mostly originates from the turbulent spanwise flux of sediments caused by the quasi-2D coherent structures (2DCSs) forming at the MC/FP interface. In the upstream region, the magnitude and direction of the time-averaged spanwise flow between the MC and FP dictate the location and shape of the deposit. The effect of deposits on the flow structure is quantified, and overall, deposits oppose the processes that formed them.

This data deposit gather all the data relative to this study.