Optimal conjunctive use of aqua-agriculture reservoir and irrigation canal for paddy fields (case study: Tajan irrigation network, Iran)

Aqua-agriculture reservoirs have been used as one of the main resources for supplying water to paddy fields, particularly under water shortage conditions. In this study, a simulation–optimization model for conjunctive use of irrigation canals and aqua-agriculture reservoir was developed in order to maximize rainwater harvesting while minimizing water withdrawal from irrigation canal. The simulation and optimization processes were done based on water balance and using genetic algorithm, respectively. The model was run for dry (2014), normal (2013) and wet (2012) years for Zarrin-Kola aqua-agriculture reservoir, located in Juybar, north of Iran. According to the results, in wet, normal and dry years, 37.4, 29.9 and 12.1% of precipitation at the reservoir upstream were transformed to runoff, respectively. The results depicted that the volume of overflow from the reservoir in wet and normal years was 0.45 and 0.13 times greater than reservoir maximum capacity, respectively. Therefore, the amount of withdrawn water from irrigation canals should be decreased or the capacity of the reservoir could be increased as much as overflowed water in wet year. Increasing the area of cultivation fields or planting second crops can be considered as the other management practices for water optimum usage. However, there was deficit irrigation in dry year and withdrawing water from canal was not capable to address the total water demand. According to the results of the considered scenarios, it can be concluded that under drought conditions, deficit irrigation or decreasing cultivation area could be considered as efficient management approaches. If deficit irrigation is not carried out (i.e., full irrigation), the area of cultivation fields irrigated by the reservoir should be decreased from 620 to 424 ha.