Bottom pressure characteristics in a stilling basin downstream of a stepped spillway for two different chute slopes

In the last decades numerous stepped spillways were built, mostly on the downstream face of roller compacted concrete (RCC) dams. Stilling basins are often used as an energy dissipater. Although the hydraulics of stepped chutes was extensively investigated in the last decades, only fragmentary information is available on the hydraulic characteristics of stilling basins preceded by stepped chutes. Therefore, an experimental Campaign was performed on a large-scale physical model of a stepped chute with adjustable slope terminating in a plain stilling basin, to study the effect of stepped chute approach flows on the hydraulic features in the basin. Experiments were conducted for two chute slopes and various discharges. Results on the basin flow features as tailwater depths, dynamic bottom pressures as well as roller and jump length characteristics are presented and discussed, focusing on the effect of stepped chute slope on the basin bottom pressure characteristics. The results show that increasing the chute slope from 30º to 50º pronounces the bottom mean, fluctuating and extreme pressures up to approximately one tailwater depth downstream of the jump toe. For 50° sloping stepped chutes, the extreme pressure coefficients reached up to about 3 times the values reported in literature for smooth chutes.