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<p>Stepped spillways are widely used to dissipate energy and promote flow aeration. Replacing impermeable steps with porous gabion steps introduces seepage and modifies air–water interactions, which can affect the inception of self-aeration, hydraulic resistance, and residual energy downstream. This study experimentally examined a 26.6° (1&#xa0;V:2&#xa0;H) stepped spillway (10 steps) under discharges of 25–54&#xa0;L/s by comparing a solid-step reference model with five hybrid gabion–solid arrangements and three porosity levels (37–42%). The flow regime, aeration inception point (L<sub>i</sub>), Darcy–Weisbach friction factor (f<sub>e</sub>), relative energy dissipation (ΔE/E<sub>0</sub>), and dimensionless residual head (H<sub>res</sub>/y<sub>c</sub>) were measured. Visual observations showed similar regime classifications for solid and gabion configurations; however, seepage through gabions reduced step flow depth by about 8–10% and shifted the onset of air entrainment upstream, decreasing L<sub>i</sub> by ~ 12% on average, with the largest reduction for the all-steps gabion layout. Gabion installations also increased flow resistance (e.g., average f<sub>e</sub> ≈ 0.116 versus ≈ 0.096 for the solid-step case). Energy dissipation was regime-dependent: gabion steps enhanced dissipation under low discharges (nappe flow), whereas their advantage diminished at higher discharges (skimming flow) as the porous matrix approached saturation. The best-performing gabion layout dissipated about 5% more energy and reduced H<sub>res</sub>/y<sub>c</sub> from ~ 4.65 to ~ 4.21 compared with the solid steps. These findings provide practical guidance for selecting gabion-step layouts for low-to-medium head stepped spillways, particularly under low-discharge conditions.</p>

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Hydraulic Behavior and Dissipation of Energy in Stepped Spillways with Gabion Steps

  • 期刊论文

  • 发表日期：

    2026年5月23日

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  • Rasoul Daneshfaraz,
  • Amir Ghaderi,
  • Hojjat Sadeghi,
  • Hossein Mohammadnezhad,
  • John Patrick Abraham

摘要

Stepped spillways are widely used to dissipate energy and promote flow aeration. Replacing impermeable steps with porous gabion steps introduces seepage and modifies air–water interactions, which can affect the inception of self-aeration, hydraulic resistance, and residual energy downstream. This study experimentally examined a 26.6° (1 V:2 H) stepped spillway (10 steps) under discharges of 25–54 L/s by comparing a solid-step reference model with five hybrid gabion–solid arrangements and three porosity levels (37–42%). The flow regime, aeration inception point (Li), Darcy–Weisbach friction factor (fe), relative energy dissipation (ΔE/E0), and dimensionless residual head (Hres/yc) were measured. Visual observations showed similar regime classifications for solid and gabion configurations; however, seepage through gabions reduced step flow depth by about 8–10% and shifted the onset of air entrainment upstream, decreasing Li by ~ 12% on average, with the largest reduction for the all-steps gabion layout. Gabion installations also increased flow resistance (e.g., average fe ≈ 0.116 versus ≈ 0.096 for the solid-step case). Energy dissipation was regime-dependent: gabion steps enhanced dissipation under low discharges (nappe flow), whereas their advantage diminished at higher discharges (skimming flow) as the porous matrix approached saturation. The best-performing gabion layout dissipated about 5% more energy and reduced Hres/yc from ~ 4.65 to ~ 4.21 compared with the solid steps. These findings provide practical guidance for selecting gabion-step layouts for low-to-medium head stepped spillways, particularly under low-discharge conditions.