EFFECTS OF PERMEABILITY ON RIVER-BED FORMATION USING SUBMERGED SPUR-DIKE GROUPS

Continuous submerged groynes can be used to create diverse riverbed configuration. However, scour holes were too large to make groynes unstable in case of impermeable and rigid structures. In order to reduce the scour depth, we used permeable and flexible groynes, that is, gabions. Model groynes with various characteristics were set on a laboratory open channel and velocity distributions and bed configurations were measured. The permeability and embedding effects were investigated experimentally. Three groynes were laid on movable sand bed without embedding. The permeability is necessary to prevent sinking of groynes and can reduce front scour drastically. The third groyne was folded at halfway because of the head sinking by erosion. The permeability decreases the velocity behind groynes and changes the flow structures slightly, but the bed configurations created by groynes were very similar to those of rigid, impermeable and embedded groynes.