Reduction of scour using a combination of riprap and bed sill

Abstract

Providing the most effective solution for protection of the bed downstream of hydraulic structures constitutes an important field of research. In addition, for safe and cost-effective designs, it is important to be able to predict the maximum scour depth downstream of hydraulic structures. The study reported in this paper examined the effectiveness of two types of countermeasures – a bed sill and riprap – to reduce the maximum scour depth adjacent to horizontal rigid aprons. For tests with the bed sill located downstream of the apron, two distinct scour holes were formed upstream and downstream of the sill, with respective maximum scour depths of ds1and ds2. The results show that a bed sill can reduce ds1and ds2by up to 23% and 47%, respectively, compared with the maximum scour depth for the no-sill condition. However, when the erodible bed between the apron and the bed sill was replaced by riprap, ds1and ds2decreased by up to 53% and 90% respectively. Variations of the other characteristic scour hole lengths, including the maximum extension of the scour hole and the maximum height of the mound, were also studied and an attempt was made to examine any geometrical similarities in the scour hole profiles under different conditions.