عنوان مقاله [English]
The objective of this study is to evaluate Avan modern irrigation network with an area of 10985 ha. The main district’s water inputs (irrigation, precipitation and canal releases) and outputs (actual evapotranspiration of crops, outflow surface drainage and canal seepage) were measured or estimated during the hydrological years of 2006 to 2009. The district-level irrigation performance was poor (mean value of seasonal irrigation consumptive use coefficient-ICUC in the studied years were equal 37%), due to the low distribution (66%) and on-farm (53%) efficiencies for the 1385-88 irrigation seasons. Thus, despite the high volume of applied irrigation water, the actual district ET was 19% lower than the maximum achievable ET, indicating that the water-stressed crops yielded below their maximums. By using neoclassical approach, it was shown that the values of net (0.83) and effective efficiencies (0.68) were more than classical efficiency (0.53) in surface irrigation systems. The results obtained in this study showed that effective efficiency has suitable expression about irrigation management and method at farm scale, whereas net efficiency only considers the concept of reuse of beneficial losses on spatial scale larger than the field. Potential reductions in water allocation were analyzed for three ICUC values (65, 75, and 85%) and two scenarios of modernization (I and II). In scenario I, where the aim was to achieve maximum ET and crop yields, water allocation could be reduced from 34.8 to 50.2% of the current allocation. In scenario II, where the aim was to achieve the maximum conservation of water under the actual ET and crop yields, reductions in water allocation would be much higher than current allocation (47.4 - 59.8%). Thus, significant volumes of water could be conserved in the rehabilitation of this district by increasing the distribution efficiency and, in particular, the on-farm irrigation efficiency.