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<p>Piano Key Weirs (PKWs) are classified as non-linear weirs with a long crest length within a limited width. Given the high flow capacity of these weirs for passing excess flow rate, investigation of local scour and methods for its reduction is of particular importance. To the best of our knowledge, this is the first study that employs a natural riprap layer with different gradations and lengths downstream of Type-B rectangular (RPKW) and trapezoidal (TPKW) PKWs. The riprap consists of natural stones in order to reduce environmental risks. The weirs used in this study have a constant crest length, a height of 0.20&#xa0;m, and different width ratios of inlet keys to outlet keys. Riprap layers with three different lengths (half, equal to, and one and a half times the weir height) and three different gradations were installed downstream of the weirs. The riprap acts as an armor layer, reducing the velocity of jets exiting the weir downstream and decreasing the volume of the scour hole. It also shifts the maximum scour depth farther away from the toe of the weir. This displacement of the maximum scour depth away from the toe can help reduce the risk of overturn of the weir. The most influential parameter in reducing scour in riprap-protected weirs is the ratio of the mean riprap particle diameter to its length. Scour indices indicate that the trapezoidal piano key weir with larger riprap length and coarser gradation represents the optimal condition. Moreover, the maximum scour depth increases with increasing Froude number, decreasing tailwater depth, and decreasing mean diameter of the bed particles. In this study, in which the densimetric Froude number ranged from 0.434 to 0.796, dimensional analysis together with three computational algorithms—Particle Swarm Optimization (PSO), Grey Wolf Optimizer (GWO), and a hybrid GWO-PSO algorithm (HGWPSO)—were used to predict the maximum scour depth and its distance from the weir toe. However, the highest correlation coefficient was obtained using the hybrid GWO-PSO algorithm.</p>

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Reducing local scour downstream of type B rectangular and trapezoidal piano key weirs with different riprap grain sizes and lengths

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Ali Qasim Rdhaiwi,
  • Isam Dhahir Khudhur,
  • Seyed Hamid Alavi,
  • Farnoosh A. Daneshvar,
  • Ali Khoshfetrat

摘要

Piano Key Weirs (PKWs) are classified as non-linear weirs with a long crest length within a limited width. Given the high flow capacity of these weirs for passing excess flow rate, investigation of local scour and methods for its reduction is of particular importance. To the best of our knowledge, this is the first study that employs a natural riprap layer with different gradations and lengths downstream of Type-B rectangular (RPKW) and trapezoidal (TPKW) PKWs. The riprap consists of natural stones in order to reduce environmental risks. The weirs used in this study have a constant crest length, a height of 0.20 m, and different width ratios of inlet keys to outlet keys. Riprap layers with three different lengths (half, equal to, and one and a half times the weir height) and three different gradations were installed downstream of the weirs. The riprap acts as an armor layer, reducing the velocity of jets exiting the weir downstream and decreasing the volume of the scour hole. It also shifts the maximum scour depth farther away from the toe of the weir. This displacement of the maximum scour depth away from the toe can help reduce the risk of overturn of the weir. The most influential parameter in reducing scour in riprap-protected weirs is the ratio of the mean riprap particle diameter to its length. Scour indices indicate that the trapezoidal piano key weir with larger riprap length and coarser gradation represents the optimal condition. Moreover, the maximum scour depth increases with increasing Froude number, decreasing tailwater depth, and decreasing mean diameter of the bed particles. In this study, in which the densimetric Froude number ranged from 0.434 to 0.796, dimensional analysis together with three computational algorithms—Particle Swarm Optimization (PSO), Grey Wolf Optimizer (GWO), and a hybrid GWO-PSO algorithm (HGWPSO)—were used to predict the maximum scour depth and its distance from the weir toe. However, the highest correlation coefficient was obtained using the hybrid GWO-PSO algorithm.