Scour Hole Profiles in Cohesive Beds Downstream of Sluice Gates

In this paper، the geometrical similarity of scour holes downstream of a sluice gate is studied experimentally. Although، nowadays a comprehensive understanding on scour of noncohesive sediments is attained، because of the complex nature of clay minerals، the scour of cohesive sediments has received less attention. 36 experiments with 12 hours run time، was carried out in a rectangular flume of 9 m length، 0. 6 m height and 0. 5 m width. Six mixtures of cohesive and noncohesive sediments with different fractions of clay minerals ranging from 10 to 40 percent were tested. The results show that the scour profiles are nonuniform across the flume width. Despite the noncohesive sediments، the scour hole in cohesive beds could not be introduced as a unique equation. Therefore، three different types of scour holes are distinguished and in each case، graphs and equations are presented to determine the shape of the hole. Also، a novel equation is proposed to calculate Bw parameter which is used to nondimensionalize the scour hole. Finally، the effect of tailwater depth is investigated.