USBR type III stilling basin performance for steep stepped spillways

Abstract

Stepped spillways are known to have a higher energy dissipation potential when compared to a smooth invert chute of identical slope. Therefore, the length of downstream energy dissipators can be reduced. To date, little is known about the effect of the stepped profile on the stilling basin performance. Therefore, new measurements were carried out on a large-scale stepped spillway model in combination with a USBR type III stilling basin, where conventional and modified chute blocks were analysed. Pressure heads and flow depths along the basin were measured systematically for several flow rates and tailwater conditions. The results follow the recommendations by the USBR for type III basins except at the basin entrance, similarly as observed in previous studies. The conventional or modified chute blocks were found to have a minor influence on the pressure head.