This study experimentally examines the influence of various end-sill configurations on
energy dissipation and scour behavior downstream stepped spillway with a slope of
26.6°. Three sill geometries were examined: solid, partially hollow rectangular, and V
notch. Each was tested under several relative sill heights ranging from 0.20 to 0.30 and
various flow conditions represented by the upstream Froude number. Performance was
assessed in terms of energy dissipation efficiency and downstream scour
characteristics, including scour depth, scour length, and scour volume. The results show
that the sill height is the dominant parameter governing hydraulic performance.
Increasing the sill height to 0.30 consistently improved energy dissipation and reduced
scour compared with the spillway without sills. Solid sills achieved the highest energy
dissipation, with an increase of up to 25%, and also decreased the overall scour
footprint. Partially hollow sills were the most effective in reducing maximum scour depth,
achieving reductions of up to 64%. V notch sills showed moderate effectiveness that
depended strongly on the notch angle and flow intensity. Furthermore, the study yielded
a unified set of predictive equations based on nonlinear regression models. These
models effectively integrate fundamental flow parameters and discrete sill-type
variables, achieving robust predictive power (R²: 0.919–0.957). The quantitative trends
were corroborated by visual analysis of scour photographs, providing clear evidence of
how sill geometry alters erosion patterns. The findings offer practical design guidance
for optimizing stepped spillways to balance energy dissipation and scour mitigation,
thereby improving structural safety and hydraulic efficiency. |
