Scour around Spur Dike in Sand-Gravel Mixture Bed

Scour is the main cause of failure for spur dike. The accurate prediction of scour around spur dike is essential to design a spur dike. The present study focuses on the maximum scour depth in equilibrium condition and parameters, which influence it in a sand-gravel mixture bed. Outcomes of the present experimental study showed that the non-dimensional maximum equilibrium scour depth increases with critical velocity ratio (U/U-ca), water depth-armour particle ratio (h/d(a)), Froude number for sediment mixture (F-rsm), water depth-spur dike length ratio (h/l), and decreases with increase in armour particle-spur dike length ratio (d(a)/l). The maximum scour depth is proportional to dimensionless parameters of U/U-ca, h/d(a), F-rsm, h/l, but the scour depth is inverse proportional to d(a)/l. Scour around spur dike in a sand-gravel mixture is mainly influenced by the property of the sediment mixture. The scour increases with decrease in non-uniformity of the sediment mixture. A non-linear empirical equation is proposed to estimate the maximum scour depth at an upstream nose of rectangular spur dike with a maximum error of 15%. The sensitivity analysis indicates that the maximum non-dimensional equilibrium scour depth depends on F-rsm, followed by the secondary sensible parameters d(a)/l, h/l, and h/d(a).