Flume study on hydro-morphologic changes provided by instream tree installations

Abstract

Hydro-morphologic changes provided by idealised trees composed of a root plate and a stem were studied in a sediment flume. Two tree installations were compared; floating and attached to the bed. Results from clear-water scour experiments show tunnel and shear layer scour for the floating case. For the drowned case with the root partially buried, initial scour was driven by a horseshoe vortex. When the scour reached the lower margin of the root plate, the horseshoe vortex lost coherence and tunnel scour set in. The wake flow was controlled by the scour hole as a function of the root plate size and vertical position, as well as the stem acting as a flow blockage for upwelling fluid downstream of the root plate. Scour hole dimension regulated the amount of fluid advected underneath the root and therefore the wake velocity difference. The stem exerted control on the upwelling flow and shear layers divergence from the centreline.