Hydraulic Performance of Circular Crested Triangular Plan Form Weirs

Abstract

Triangular labyrinth weirs are nonlinear weirs used to control and pass the required discharge with low afflux in case of limited width saving the upstream countryside and costly lands from submergence. In this paper, the hydraulic performance of circular crested triangular plan form weirs under free flow conditions is experimentally studied. In this regard, twenty-seven weir models have been fabricated and tested in a laboratory flume. These models had different vertex angles ($\theta = 45^{\circ }$, $60^{\circ }$ and $75^{\circ }$), different weir heights (${P} = 15$, 20  and 25 cm) and different crest diameters (${D} = 2.54$, 4 and 5  cm). The experimental results of all models showed that the variation of discharge coefficient (${C}_{\mathrm{d}}$) with relative head above crest (h/P) for the different values of $\theta$, P and D was a simple power equation. It was observed that the values of ${C}_{\mathrm{d}}$ decreased with the increase in h/P values for all models. An empirical power equation was obtained for the estimation of ${C}_{\mathrm{d}}$ in terms of $\theta$, h/P and h/D. The values of discharge magnification (${Q}_{{\mathrm{TC}}}/{Q}_{{\mathrm{NS}}}$) decreased with the increase in h/P values. Weirs of small vertex angle, low height and small crest diameter gave high values of discharge magnification (better performance). The best weir performance was found for a weir of $\theta = 45^{\circ }$, ${P} = 15\,\hbox {cm}$ and ${D} = 2.54\,\hbox {cm}$ (${D/P} = 0.17$) within the limitations of this study.