Experimental investigation of the effects of vegetation on morphodynamics and sediment sorting

This study investigated the effects of rooted willow patches (Salix koreensis) of different densities on flow, morphodynamics and sediment sorting in a large scale outdoor laboratory experiment with natural sediments. In the experimental section with dense alternating patches flow was diverted toward unvegetated zone, creating a meandering flow pattern, whereas in the sparse patches flow was able to smoothly penetrate in the patches reducing this meandering flow pattern to a minimum due to the low drag in the vegetation zone. The thalweg of the bed was meandering shape, and was agreement with the maximum velocity pattern. As flood increased, the sandbar length increased in dense and sparse vegetation zone. At the dense vegetation zone, the bar length increased fast with time. At the low density vegetation stretch, however, the bar length was increased slowly. The bed material sorting of the bed surface in the vegetated channel was related to bed changes and flow structure changes. Downstream of dense and sparse vegetation patches, bed material size was fine at the aggradation region and coarse at the degradation region.