Flow and bed morphology response to the introduction of wood logs for sediment management

Summary

Submerged vanes alter sediment transport by inducing a secondary circulation without significantly compromising the conveyance capacity of the river. Here, a laboratory study is conducted to investigate whether wood logs or trunks can be used for sediment management. The effectivity of a traditional vane field is compared to set-ups with screens of stacked logs, and large individual trunks. Results indicate that all three set-ups redistribute sediment but that the trunks are least effective in inducing a secondary circulation and cause higher turbulence and drag, leading to a stronger decrease in streamwise velocity. We conclude that a field of trunks acts as a sediment trap because of a strong reduction of the streamwise velocity, without a strong secondary flow such as dominant in the other configurations. Screens of stacked logs can be successfully implemented in rivers, as they are only slightly less effective than traditional vanes. The risk of piping underneath objects and the associated scour are points of concern.