Sediment patterns near a model patch of reedy emergent vegetation

24 This laboratory study describes the sediment patterns formed in a sand bed 25 around circular patches of rigid vertical cylinders, representing a patch of reedy 26 emergent vegetation. The patch diameter was much smaller than the channel 27 width. Two patch densities (solid volume fraction 3% and 10%) and two patch 28 diameters (22 and 10 cm) were considered. For flows above the threshold of 29 sediment motion, patterns of sediment erosion and deposition were observed 30 around and within the patch. Scouring within the patch was positively correlated 31 with turbulent kinetic energy in the patch. For sparse patches, sediment scoured 32 from within the patch was mostly deposited within one patch diameter 33 downstream of the patch. For dense patches, which experience greater flow 34 diversion, sediment scoured from the patch was carried farther downstream 35 before deposition along the patch centerline. Differences between the sparse and 36 dense patch patterns of deposition are explained in the context of flow diversion 37 and wake structure, which are related to a nondimensional flow blockage 38 parameter. While sediment was redistributed near the patch, observations 39 suggest that net deposition was not recorded at the reach scale. 40 41