Comparative analysis of hydraulic performance of oblique and triangular labyrinth weirs with equal crest length: An experimental investigation

Abstract

Optimizing discharge capacity while maintaining low upstream water levels remains a challenge in hydraulic engineering, especially in constrained channels such as urban waterways, valleys, and flood-prone corridors. Oblique and triangular labyrinth weirs have been developed to increase effective crest length without widening the channel; however, the lack of direct experimental comparison under identical geometric conditions still leads to uncertainty in practical design selection. This study presents an experimental investigation and comparative performance analysis of an oblique and a triangular labyrinth weir with equal crest length (100 cm) under controlled laboratory conditions. The models, constructed from 10 mm acrylic sheets, were tested under steady free-flow conditions in a laboratory flume measuring 16.00 m × 0.50 m × 0.40 m. Discharge and upstream head were systematically measured to evaluate the discharge coefficient as a function of normalized head. The results showed that both nonlinear weirs outperformed a conventional linear weir (maximum discharge coefficient of 0.62), with the oblique weir achieving the highest performance with a peak discharge coefficient of 0.70, followed by the triangular labyrinth weir (0.66). At an equivalent upstream head of approximately 0.025 m, the oblique weir conveyed approximately 10–12% higher discharge than the labyrinth weir and 35–40% higher than the linear weir. The oblique weir outperformed the others due to reduced contraction, better flow alignment, and lower energy losses. In contrast, the triangular labyrinth weir suffered from nappe interference at higher heads, reducing efficiency. Overall, the oblique weir performed better and was more practical.