LAUSR

Despite the extensive application of check and offtake structures in irrigation canals, their periodic assessment is generally not included in water management plans, especially in Iran. This issue would be more important when there are many problems in water distribution in irrigation projects. In this study the performance and operating status of different hydraulic structures in the Varamin irrigation scheme were evaluated using a precise flowmeter. Results show that Neyrpic modules have an error in range of 8 to 83% and these structures, on average, delivered 22% more water. The discharge coefficient of duckbill weirs has changed considerably as well and they are not able to regulate the water level appropriately, because of ageing and physical destruction. The results showed that to achieve an acceptable performance of Neyrpic modules in this scheme it is essential to perform some physical modifications, such as cleaning and sealing the gates, removing sediment around the gates, replacing old gates and continuous inspection of infrastructure. A series of measurements to estimate water losses during the conveyance process show that the conveyance efficiency for each 1000 m length of main, secondary and tertiary canals are respectively 95.0, 91.5 and 89.3%. Consequently to achieve a suitable water distribution pattern, preventive maintenance should be considered. © 2018 John Wiley & Sons, Ltd. key words: conveyance efficiency; hydraulic sensitivity; Neyrpic modules; performance assessment; water level regulation Received 24 December 2017; Revised 11 September 2018; Accepted 12 September 2018