Improvement in performance of the water delivery through irrigation canals of paddy fields on the basis of flow simulation in HEC-RAS

Construction of minor irrigation and drainage canals networks is vital in the infrastructure Project of Paddy Fields Development and Renovation in the North of Iran as it leads to change the conventional plot-to-plot irrigation, achieve higher productivity from limited water resources and introduce the independent irrigation and drainage management in each farm. However, according to previous studies, a great number of farmers have major problems with the existing operation of irrigation and drainage canals. Therefore, in this study, water delivery criteria were first calculated for all the farm intakes on an earth canal in Esmaelkola village of Jooybar city during irrigation season of 2015, in order to compare the existing technical performance of the system with the quantitative, reliable and valid standards. Then, after lining the canal, required structural changes to improve the performance criteria of delivery system were evaluated by simulating several alternatives of water intake andcontrol scenarios in HEC-RASmodel. The results showed that all the delivery criteria except the efficiency have considerable deviation from optimal and even moderate ones (Adequacy = 0.35, Efficiency = 0.92, Dependability = 0.98, Equity =1.18). It is dueto the poor operation and maintenance of earth canals of the distribution and intake systems of current basins. On the other hand, based on the simulation results, after lining the irrigation canals, if adequate amount of water supply is provided, when tubular intakes with variable diameter and flow control checks (weirs) are used,in addition to channel efficiency, there will be a noticeable increment in water delivery criteria especially in the last farms (Adequacy = 0.93, Efficiency = 0.92, Dependability= 0.14, Equity =0.18). The calibration and validation of the model in the cropping season of 2016 has confirmed the results of the simulation as well. Finally, construction of flow control checks (weirs) and tubular intakes, with suitable diameter depending on the water demand of the basins, is recommended for the future projects of lining canals in the current systems in addition to emphasize on studying the possibility of other options for water conveyance to the farm, such as pre-fabricated canals.