An Experimental Study on the Overbank Sedimentation in an Asymmetrical Compound Channel

Overbank sedimentation in rivers has implications in the geomorphological evolution of the river channel and in the ecosystem functions of the floodplains. The impact of suspended sediment supply on floodplain processes is still unclear because it is influenced by several factors. In this study a set of laboratory experiments were carried out in an asymmetrical compound channel to assess the dynamics of overbank sedimentation of suspended fine sediments under different: (i) width ratios (ratio between the width of the main channel and the width of the floodplain); (ii) hydraulic ratios (ratio between the water depth in the main channel and the water depth in the floodplain); and (iii) roughness-type found in the floodplain. Surface particle image velocimetry (PIV), sediment samples and suspended sediment concentration temporal records were recorded all through the experiments. The exchanges of mass of water and fine sediments between the main channel and the floodplains for the different flow scenarios considered are assessed. The width ratio has been identified as a key element for determining the coupled/uncoupled relation between the transport of sediments in the main channel and sediment deposition in the floodplains.