Effect of Sill Arrangement on Maximum Scour Depth Downstream of Abruptly Enlarged Stilling Basins

Scour downstream (DS) of hydraulic structures (HS) may endanger the safety of the structures if the necessary precuations are not considered during the design stage. Normally, different measures produce different effects on reducing the maximum scour depth DS of HS. One of the important HSs is the abruptly enlarged (or sudden expanding) stilling basins. In this paper, the effects of different arrangements of sills inside an abruptly enlarged stilling basin will be discussed. An experimental program was conducted to investigate the effects of continuous end sill, one asymmetric side side, double staggered asymmetric side sills, symmetric side sills, central sill and continuous central sill. The flow patterns were observed and the maximum scour depths were recorded. The results revealed that in most of the cases the flow patterns are asymmetric resulting in asymmetric scours. The reduction in the maximum scour depth depends on the type of arrangement of the used sill and on the flow conditions represented by Froude number. Both of the central sill with limited width and continuous central sill improved the flow patterns towards symmetric type and yielded minimized maaximum scour depth with preference to the continuous sill.