The Synergistic Effect of Trapezoidal Geometry and Lateral Slope in Piano Key Spillways

Articles in Press

Document Type : Research Paper

Author

Department of Civil Engineering, Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran.

Abstract

Piano key weirs (PKWs) are efficient hydraulic structures for flood control and water management because they increase the effective crest length within a limited footprint. Nevertheless, the geometric optimization of these structures remains an important research topic. This study experimentally investigates the synergistic effect of combining trapezoidal geometry with a global sidewall slope in Type-A PKWs. Four physical models, including rectangular and trapezoidal weirs with and without a 5° sidewall inclination, were tested in a 15-m laboratory flume. The results showed that for upstream head ratios \left(H/P\right)greater than 0.12, more than 75% of the crest length becomes engaged in the flow, and the discharge coefficient of sloped models increases noticeably. In addition, the sloped trapezoidal PKW (TPKW5) exhibited, on average, a 13% higher discharge coefficient than the sloped rectangular PKW (RPKW5), with a relative error lower than ±2%, indicating a genuine synergistic interaction between the two geometric parameters. Moreover, the discharge efficiency of TPKW5 was about 5% higher than that of RPKW5. These findings suggest that the combined use of a trapezoidal planform and a global sidewall slope can be an effective strategy and intelligent combination for designing low-head spillways with superior hydraulic performance.

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Main Subjects

Iranian Journal of Soil and Water Research

Articles in Press, Accepted Manuscript
Available Online from 31 May 2026

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