Document Type : Original Article
Authors
Abstract
In most of the countries in the world, even in the developed countries, surface irrigation is still one of the important irrigation methods in irrigated agriculture. It is estimated that more than 90 percent of the irrigated lands are irrigated with surface irrigation methods. Since determination of optimum field’s dimensions, including slope, inflow rate, and irrigation time, play an important role in enhancement of application efficiency and reduction of projects costs. Therefore, this research was conducted in the Ramshir irrigation and drainage network in the Khuzestan province (namely Velayate plan) with the objectives of determining fields’ dimensions, design and management parameters of border irrigation with closed-end regime and for achieving higher application efficiency and distribution uniformity. Using water advance and recession measurements along the border length and use of a comprehensive surface irrigation model, that is to say, WinSRFR-3.1 model, the soil infiltration parameters of the area were determined. Hence, the model was calibrated and the parameters of the best fitted infiltration equation, based on the Kostiakov-Lewis equation, was determined. Also by using the simulation part of the model, the dimensions and other design and management parameters of border irrigation, with closed-end regime cultivated with wheat crop, was determined. Based on results and with regards to proper application efficiency and distribution uniformity, the border design alternative of 7 m wide, 200 m length, and slopes of 0.005 to 0.001 m/m was a proper alternative for all ranges of selected inflow discharges (10-20 lit/s) and net irrigation depths of 50 to 90 mm. However, based on results, the design alternative of 200 m border length and longitudinal slope of 0.0005 m/m is the best alternative with regards to higher application efficiency. Moreover, the longitudinal slope of 0.0005 m/m is an ideal slope for all combinations of design alternatives with fair application efficiencies. Basically, the border length of 300 m and higher are not a suitable option for all selected slopes and low inflow rates of less than 10 lit/s. Finally, in the Ramshir irrigation and drainage network, if the field’s dimensions together with the other design and management parameters is set properly, achieving high application efficiency, even higher than 70 percent, in the border irrigation for many design alternatives is easily possible.
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