Local scouring around L-head groynes

•Extensive tests were conducted for scour around straight and L-head groynes.•A comparison was made between straight and L-head groynes.•The effect of parallel wall angle on maximum depth of scour was investigated.•Conceptual flow field in vicinity of the groyne was achieved through dye injection.

Groynes have been widely used to redirect the flow in channels and to protect eroding river banks. In general, groynes are more beneficial to aquatic habitat resources than other types of bank protection structures. One of the most important problems for designers is the estimation of maximum local scour depth in the vicinity of groynes. Due to constriction of flow area, a local velocity increased and scouring around the groyne is formed. From literatures, it can be seen that among various type of groynes, straight ones are more investigated; however, L-head groyne generally leads to larger sediment deposits between groynes, less scour at their head, and greater protection to the banks. An L-head groyne consists of parallel and perpendicular wall to flow direction. In this study, the maximum depth of scour around straight and L-head groynes is compared. Also, the effect of parallel wall angle (the angle between parallel and perpendicular walls) on maximum depth of scour was investigated and the optimal angle was determined. The results show that the maximum depth of scour around L-head groynes with parallel walls toward upstream direction is less than that of straight groynes. The distance to the thalweg line from the L-head groyne decreased compared to that of the straight groyne. The optimal angle for L-head groynes with a parallel wall in the downstream direction is found to be θ = 110° and for L-head groynes with parallel wall in the upstream direction is identified to be θ = 60°.