Optimization of surface irrigation by low-cost water management

Surface irrigation is the most common method of irrigation. over 80% of agricultural lands in Iran are irrigated by this method. Generally, this technique, has lower investment and energy requirements than pressurized irrigation methods. Many efforts are applied to improve the economic output of water use and to preserve the environment in Iran. Modifying the design and management parameters at the farm level, can improve the performance of irrigation systems. The main objective of this study, is to optimize surface irrigation efficiency, with low-cost tools, using a simulation model.

The study areas were selected fields of Molla-Sani region in Khuzestan province, located in southwest of Iran. Field experiments were carried out in two fields, irrigated using a surface irrigation system. Three irrigation events and three plots (as repeats) were applied per field. Experiments were conducted on the three borders of 150 m length, 7 m width, and 0.125 % slope, in Field 1, and on three borders of 200 m in length, 7 m width, and 0.1 % slope, in Field 2. The inflow rates of 25 and 35 L/s were applied in the fields 1 and 2. Inflow rate was checked using a W.S.C flume. The borders were divided into parts of 10 m distances to measure the advance and recession times. The best combination of parameters was determined with the simulation model. The objective function (OF) including the application efficiency and the distribution uniformity was applied to optimize the irrigation performance.

This study showed that, based on simulation model, changing the inflow rate, has no effect on the best value of objective function. The optimal inflow rate and cut-off time are recommended as 35 L/s and 30 min in a border with length of 50 m, in the Field 1, and, the best performance in the Field 2, are obtained from the inflow rate of 20 L/s and the cut-off time of 48 min and length of 50 m. Field experiments showed that, the difference of infiltration rates, were not significant, during this study. Based on the data obtained from three events, in both fields, and analyzed via the simulation model, the average NRMSE (Normalized Root Mean Square Error) index values for the evaluation of the advance curves were 12.7, 12.5, and 11.6%, while of the recession curves were 6.9, 6.8, and 6.6%.

The pressurized irrigation has the high investment and energy requirements than surface irrigation. Furthermore, the evaporation rate is much, in the research region. Because of the inflow rate and cutoff time are the most effective parameters in improving irrigation, thus, in this region, prediction and selection of the optimum combination of cut-off time and inflow rate are the low-cost tools to improve the surface irrigation performance compared to modifying length and slope in border irrigation or transform of surface to pressurized system, in the farm level.