SPUR FAILURE IN RIVER ENGINEERING

Spurs are river engineering elements used to protect river banks from erosion and to concentrate flow to the river axis. Today, spurs are also employed for promoting environmental conditions along a river bank. These elements are characterized by a large variety of geometrical parameters, of which none is definitely fixed. Based on a preliminary study that identified optimum spur arrangements in a straight river reach the present research project adds to the protection of spurs by riprap. The first two spurs are demonstrated to require a suitable riprap for promoting nearly uniform scour conditions along the entire spur reach. This research investigated the effects of a variety of parameters on spur flow, notably spur length, spur spacing, spur height plus the diameter and the number of riprap rows, along with the main hydraulic and granulometric parameters. Design equations were established based on a large experimental campaign to predict riprap failure in terms of the previous set of variables. The failure modes are described along with a novel failure mechanism. The paper ends with a set of limitations allowing for the application of these results in river engineering.