Sill height and downstream slope of a long-throated weir changes effect on the accuracy of flow discharge coefficient and energy depreciation in trapezoidal canals

Discharge measurement is the basis of accurate water distribution and proper management of Irrigation networks operation. In order to exploit Irrigation networks properly, it is required to measure water discharge in different points of network. Long-throated flumes are hydraulic structures that measure the flow enjoying low sensitivity to submergence, high accuracy, and low costs. One of important issue in the design of long-throated flumes is determination of sill height and downstream slope. The hydraulic of a long-throated flume is similar to a Broad-crested weir. In this research, the effect of geometric factors on the structure measured discharge has been investigated. Eight physical model of long-throated flume with constant upstream slope, four different downstream slopes and with two sill heights of 10 and 20 cm were examined. The dimensions of long-throated physical models were designed by WinFlume Software and built from PVC. The models were installed within a flume with 60cm wide, followed by discharge measurement. The comparison of measured discharge using triangular weir with the results of WinFlume indicated the accuracy of this model in discharge measurement. The percentage of error average in measured discharge and theoretical discharge is 2.4 in a 20-cm step and 8.2 in a 10-cm step.

Keywords:

Long-throated flume , Discharge , Sill height , Downstream slope