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<p>Stepped weirs are widely used in hydraulic engineering for passive energy dissipation and downstream erosion control. However, their hydraulic efficiency often declines significantly at high discharges when shifting into the skimming flow regime. While introducing perforations along the steps offers a promising passive geometric modification, prior studies have focused primarily on overall energy dissipation, leaving the localized, regime dependent behavior poorly understood. This study experimentally investigates the energy dissipation efficiency of a 45° stepped weir (<i>P</i> = 30&#xa0;cm, L = 30&#xa0;cm, 6 steps) utilizing a novel flow regime based framework categorized by the downstream Froude number (Fr1). A non perforated configuration (H01) served as the baseline, and 12 distinct perforated configurations were evaluated across a matrix of 4 perforation ratios (Ø = 0.33, 0.50, 0.66, 1.00) containing up to 24 jet holes (d = 1&#xa0;cm). Steady flow rates were tested across five precise discharges ranging from 7.85 to 16.83&#xa0;L/s (q* = 0.05 to 0.11) to capture fully developed turbulent conditions (2.6 × 10<sup>4</sup> ≥ Re ≤ 5.6 × 10<sup>4</sup>). The results demonstrate that perforation efficiency is strongly non-linear and governed inherently by the prevailing hydraulic regime. Under low Froude number conditions (Fr1 ≤ 2.466), limited and uniformly distributed perforations (Ø = 1.00 at low flow intensity) provided highly consistent enhancement, yielding mean energy dissipation improvements of 10–11% relative to the baseline. Peak efficiency occurred at an optimal intermediate discharge intensity of q* = 0.08 (approx. 11.2&#xa0;L/s), where the fully perforated arrangement achieved a maximum relative improvement of 21.4%. Conversely, operating above a critical threshold of q* = 0.09 under highly supercritical skimming flow (Fr1 &gt; 2.799) triggered a hydraulic performance collapse. In this zone, excessive flow volume bypassed the step faces through internal routing, acting as low-friction flow outlets and causing negative efficiency improvements down to -10.6%. These findings establish a clear upper boundary for effective perforation, proving that geometric modifications must be tailored to specific flow conditions. When optimized for predictable seasonal flow regimes, these passive configurations offer a sustainable alternative for small-to-medium scale embankment spillways, significantly mitigating downstream scour potential while reducing structural material volume and long-term basin maintenance costs.</p>

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Sustainable Energy Dissipation in Perforated Stepped Weirs: A Flow-Regime-Based Experimental Study

  • 期刊论文

  • 发表日期：

    2026年6月20日

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  • Nashwan K. Alomari,
  • Ahmed Y. Mohammed,
  • Thaer Hashem

摘要

Stepped weirs are widely used in hydraulic engineering for passive energy dissipation and downstream erosion control. However, their hydraulic efficiency often declines significantly at high discharges when shifting into the skimming flow regime. While introducing perforations along the steps offers a promising passive geometric modification, prior studies have focused primarily on overall energy dissipation, leaving the localized, regime dependent behavior poorly understood. This study experimentally investigates the energy dissipation efficiency of a 45° stepped weir (P = 30 cm, L = 30 cm, 6 steps) utilizing a novel flow regime based framework categorized by the downstream Froude number (Fr1). A non perforated configuration (H01) served as the baseline, and 12 distinct perforated configurations were evaluated across a matrix of 4 perforation ratios (Ø = 0.33, 0.50, 0.66, 1.00) containing up to 24 jet holes (d = 1 cm). Steady flow rates were tested across five precise discharges ranging from 7.85 to 16.83 L/s (q* = 0.05 to 0.11) to capture fully developed turbulent conditions (2.6 × 104 ≥ Re ≤ 5.6 × 104). The results demonstrate that perforation efficiency is strongly non-linear and governed inherently by the prevailing hydraulic regime. Under low Froude number conditions (Fr1 ≤ 2.466), limited and uniformly distributed perforations (Ø = 1.00 at low flow intensity) provided highly consistent enhancement, yielding mean energy dissipation improvements of 10–11% relative to the baseline. Peak efficiency occurred at an optimal intermediate discharge intensity of q* = 0.08 (approx. 11.2 L/s), where the fully perforated arrangement achieved a maximum relative improvement of 21.4%. Conversely, operating above a critical threshold of q* = 0.09 under highly supercritical skimming flow (Fr1 > 2.799) triggered a hydraulic performance collapse. In this zone, excessive flow volume bypassed the step faces through internal routing, acting as low-friction flow outlets and causing negative efficiency improvements down to -10.6%. These findings establish a clear upper boundary for effective perforation, proving that geometric modifications must be tailored to specific flow conditions. When optimized for predictable seasonal flow regimes, these passive configurations offer a sustainable alternative for small-to-medium scale embankment spillways, significantly mitigating downstream scour potential while reducing structural material volume and long-term basin maintenance costs.