Evaluating the Effect of the Discharge Control Valve Implementation in Tape Irrigation Systems

Water shortage is the main challenge for agriculture in arid and semi-arid regions. Therefore, improving water productivity using different methods such as implementing pressurized irrigation systems is necessary. In these systems the both efficiency and distribution coefficients are vital. The purpose of this study is to investigate the performance of flow control valves in regulating the volume of water delivered in the field and saving water consumption. A flow control valve is recommanded to deliver an almost constant flow for different pressure ranges.

In this study, the performance of automatic flow control valves to adjust the water delivered in the field was investigated. For this purpose, two valves with flow rates of 5 and 10 Ls-1 were installed on a farm equipped with a drip irrigation system to evaluate the effect of the valves in a field condition. The farm is located in Mahdiabad of Takestan. The area of this field is about 12 ha. Also, EPANET software is used to model the irrigation system in different scenarios. This software can simulate the behavior of water flows in pressurized networks. To model the irrigation system, the specifications of the reservoir, water transmission lines, manifold pipes, and laterals including the length, diameter of the pipes, and elevation, were applied as the input characteristics of the program. Numerical models need to be calibrated to check the correspondence between the measured and simulated parameters. To compare the values measured and simulated by the EPANET model, statistical indices of root mean square error (RMSE), mean absolute error (MBE), and error percentage (NRMSE) were used.

Firstly, the current condition of the farm was evaluated. The results showed the water discharges were 6.4 and 12.35 L s-1 for plots B and F on-farm, respectively. These discharges were 28% and 25.3% higher than the designed discharges for parts B and F, respectively. As a result, water consumption was increased and its surplus was wasted as deep percolation or surface runoff. Then the flow control valves were installed in the suitable places. After installing the flow control valves, the water delivery condition was re-evaluated. Discharges of B and F plots were 4.86 and 9.96 L s-1, respectively. EPANET software was applied to simulate the flow in the irrigation system. The results showed that the flow control valves could be used successfully to deliver an accurate volume of water to the plots and they could compensate the effect of changes in pool water height or ruptures of irrigation tapes. By investigating the effect of changing the height of the pool water, it was found that increasing the height of the water in the pool would result in increasing the irrigation system discharge. However, by installing the flow control valve, water delivery remained almost constant by changing the water height in the pool. Additionally, by examining the performance of the valve during rupture or dislocation of the irrigation tapes, the flow through the tested irrigation fields increased. However, with the use of flow control valves, due to the structural mechanism of them, the flow rate did not exceed from the designed values. Also, the results showed that a dislocation or leakage in the irrigation tapes reduced the pressure and increased the amount of flow consumed by the irrigation system. However, the numerical modeling results showed that with the installation of the automatic control valve, the flow rate of the irrigation tapes remained in a suitable range.

Conclusion                                                              

Flow control valves regulate discharge irrespective of the pressure fluctuations. Experiments were performed to identify the ability of a discharge control valve to improve water distribution uniformity in an actual field condition. Field measurements revealed the successful application of the control valves on a farm scale. Also, numerical results indicated that the flow control valves could be used effectively to increase the flow uniformity inthe cases of the water height fluctuations in the reservoir pools or  ruptures of the irrigation tapes. In general, it was found that the flow control valve was a good choice to increase the water efficiency and uniformity in the field conditions. Numerical simulations could determine the suitable locations of the valves and their discharge characteristics.