The Influence of Weir Crest Alignment Patterns on the Discharge through Rectangular Sharp-Crested Weirs

Abstract

This research aimed to study the influence of weir crest alignment on the discharge through the rectangular sharp-crested weirs by the creating of hydraulic model to simulate the flow in open channel through rectangular sharp-crested weirs. The obtained from the study was analyzed and for the comparison between the actual discharge (QA) and the theoretical discharge (QT) through the rectangular sharp-crested weirs for different heights of water level above the weir crest (h). The model of sharp-crested weir in this study was constructed from the thin plastic sheets with smooth surface which having constant crest length (L). There are 6 patterns of weir crest in different values of θ which is the angle between the weir crests at the center-line of channel flow section when observing from the downstream side i.e. 30°, 60°, 90°, 120°, 150° and 180°. From the study of the flow behavior through rectangular sharp-crested weirs for different values of h, it was found that the values of QA are totally less than the values of QT for all 6 patterns of weir crest alignments since the energy loss of flow through the sharp-crested weir is commonly ignored in the analysis of theoretical discharge. To obtain the theoretical discharge through sharp-crested weir which close to the actual value, the determination of discharge coefficients of rectangular sharp-crested weir (CR) were performed and it was found that CR is proportional to θ by which CR = 0 . 584, 0 . 602, 0 . 665, 0 . 69 8 , 0.719 and 0.757 for θ = 30°, 60°, 90°, 120°, 150° and 180°, respectively.