Types I, II, III, and IV Stilling Basin Performance for Stepped Chutes Applied to Embankment Dams

Abstract

Scientists at the USDA Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) conducted research on physical models of stilling basins (i.e., Types I, II, III, and IV) associated with stepped chutes to evaluate performance. Tests were conducted with naturally developing unit discharges ($0.236{\mathrm{m}}^2/\mathrm{s}\le q\le 0.930{\mathrm{m}}^2/\mathrm{s}$ ) descending a 3(H):1(V) stepped chute flume designed with 0.15-m step heights at near prototype scale and Froude numbers near the stepped chute toe ranging from $4.1\le \mathsf{F}\le 4.6$ . Data and visual observations indicated that dissipation features like floor blocks, the end sill, or a dentated end sill effectively reduced wave oscillations and lessened the impact of propagating waves downstream. The study data appear to agree with other published data for stilling basins associated with smooth chutes; thus, design engineers should have confidence in applying the US Bureau of Reclamation (USBR) stilling basin design criteria to basins associated with stepped chutes. Pressure profiles indicated positive values relative to stilling basin floor elevation along the length of all stilling basins. Additionally, pressure peaked near the basin entrance, the floor blocks, and the end sill.