Performance of Long Throated Flume and Modification of Broad Crested Weir to Improve the Measurement Accuracy

The discharge measurement at the delivery points is one of the most important issues that the irrigation network managers were dealing with during the last decade for improving water management and irrigation efficiency. Doroodzan Irrigation and Drainage Network, similar to other irrigation networks of Iran, was faced with the problem of measuring instruments, not being accurate with the lack of calibration. In this regard, one of the Doroodzan canals, Ordibehesht, was selected for the first time in Iran, in order to install long throated flumes structure during 2011.
In this research, the structures installed in tertiary canals T15, T19, and T20 were surveyed. The measurements were made during the 2011-2012 irrigation season. The S4 Micro Moline was used in order to measure velocity and discharge. For each structure (T15, T19, and T20), measurement procedure was repeated at least three times. Consequently, the discharge was also measured for individual head and the Q-h tables and diagrams were prepared. The Win-Flume model was applied for (hydraulic) designing, calibration, solving the equations, and consequently deriving the Q-h equation and drawing the diagram and comparing the surveying data and the equation reports. The results showed that the model was capable of solving, reporting and comparison. The error of measurement at minimum discharge (12 to 21 percent) is larger than the estimation made by the model (6 to 9 percent). Therefore, the plan of the structure, especially the crest, was changed to fix the problem. The proposed plan of the structure (Mixed Crest) is designed by using the Win-Flume and it is more accurate and requires less submergence protection than the last one.