Evaluation of a New Method for Calculating Discharge in Oblique Linear Weirs

Document Type : Research Paper


1 Ph.D. Candidate, Department of Water Science and Engineering, Faculty of Agriculture and Natural Resources, Islamic Azad University Ahwaz, Ahwaz, Iran.

2 Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

3 Assistant Professor, Department of Offshore Structures, Faculty of Marine Engineering, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran.


Sharp crested weirs are one of the most important structures in the river intake and are the most common instruments for measuring the intensity of flow in open channels, which are widely used in water transmission systems and irrigation and drainage canals to regulate water levels and floods. One of the types of sharp crested weirs is angular weir, in which by increasing the effective length of the crown, more discharge is allowed to pass with less head, resulting a higher efficiency and consequently a reduction in irrigation system costs. In this study, 165 existing laboratory data obtained from two flumes with widths of 0.5 and 0.52 m and with seven ratios of weir length to flume width (L/B) of 1.14 and 3.86 and six weir crown heights of 0.10 m to 0.506 m were used in free flow conditions. In this study, the critical depth of flow passage over the weir crown was used to calculate the flow rate. Also, a new function was developed to calculate the flow rate directly and without the need for flow coefficient by presenting the geometric coefficient of the weir, including all the geometric characteristics of the structure. The results of this study showed that by increasing the height of the crown, the flow head and the weir angle relative to the flow horizon increase. The results also showed that the new relationship with R2 = 0.9984 has high accuracy for measuring critical depth and flow rate.


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