Investigating the Performance of Drip Irrigation Systems in Urban Green Spaces (Case Study: El Baghi Forest Park, Tabriz)

Investigating the Performance of Drip Irrigation Systems in Urban Green Spaces (Case Study: El Baghi Forest Park, Tabriz)

Abstract
Background and Objectives

Drip irrigation is a more reliable solution for using water resources because it distributes water efficiently. Providing the water required by plants with appropriate efficiency and uniformity, and requiring less manpower is one of the most important goals of designing drip irrigation systems. In recent years, with the decreasing trend of water resources in Iran, many forest parks and urban green spaces have also been equipped with drip irrigation systems. After drip irrigation is selected as a solution for the optimal use of water resources and implemented, special attention should be paid to the efficiency of such systems' operation. In such circumstances, evaluating and monitoring these systems is an undeniable necessity. The present study was conducted to evaluate drip irrigation implemented in six blocks in the El Baghi Forest Park of Tabriz in the northwest of Iran with an area of 180 hectares. This park is located in the Urmia Lake basin, which is facing a severe water crisis as the lake is drying up. Increasing irrigation efficiency and water productivity in this basin, especially in the agricultural sector, which accounts for 93% of water consumption, is essential.
Methodology
An experimental design was implemented to assess the performance of the drip irrigation system under study by selecting the three plots from each irrigation block, resulting in a total of 18 plots. The selection of these plots was determined based on the topography of the area and their proximity to the main branch of each block. Within each selected plot, four lateral pipes were chosen at specific positions along the manifold: at the beginning, at one-third, and two-thirds of the distance from the start to the end of the manifold, as well as at the manifold's endpoint. Four trees were identified along each lateral pipe, maintaining a consistent distance ratio. Pressure measurements were conducted at the inlet of all lateral pipes within each plot, and the lateral with the minimum inlet pressure (denoted as Minimum Lateral Inlet Pressure, MLIP) was identified. The flow rate of two drippers was measured for each of the selected trees. Additionally, the water pressure at the beginning of the four selected lateral pipes was recorded under operating conditions. To facilitate this, a pressure gauge was connected to the inlet of each lateral pipe via a tee junction, and the pressure was recorded during operation. The pressure at the end of each lateral pipe was also measured by removing the end fitting and attaching the pressure gauge directly to the pipe’s endpoint. Consequently, for each selected manifold, a total of eight pressure measurements (at the beginning and end of the lateral pipes) and 32 water volume measurements (corresponding to 16 trees) were obtained at the outlet points. Subsequently, the following parameters were calculated for each section: the average dripper flow rate, the minimum inlet pressure to the lateral pipe (MLIP), the discharge correction factor (DCF), and the efficiency reduction factor (ERF). In conjunction with relevant equations, these parameters were then utilized to derive the evaluation criteria for the drip irrigation system design under investigation.
Findings
The results showed that the uniformity of water distribution in plots (EUm) was between 91.9% and 97.6% and in units (EUs) between 79 and 93 percent, the potential efficiency of the lower quartile in plots (PELQm) was between 82.7 and 87.8 percent and in blocks (PELQs) between 71% and 83.6%, and the actual efficiency of the lower quartile (AELQs) in blocks was also between 78% and 91%. Plot D33 with EUm, PELQm, and AELQs equal to 91.9%, 82.7%, and 87% respectively was the weakest plot in terms of performance, and plot C104 was the best plot with EUm, PELQm, and AELQs equal to 91.9%, 82.7%, and 87% respectively. Finally, the entire system was evaluated as good with average EUs, PELQs, and AELQs equal to 85.10%, 84.30%, and 84.38%.
Conclusion
In the present study, the drip irrigation system implemented in El Baghi Park with relatively light soil and hilly-slope topography was evaluated. The water volume required by the trees and the calculated applied volume showed that almost all units were irrigated sufficiently. After collecting the information from the field measurements using the SCS method, evaluation factors such as EU, AELQ, and PELQ were calculated as evaluation criteria. The evaluation results showed that the irrigation blocks in this system are in a relatively good to good performance condition. According to the results of the performance evaluation indicators and field surveys, the main problems of the system were: pressure difference in the system, clogging of drippers and their manipulation, lack of proper and timely filtration washing, improper repair of pipes and fittings when needed, and poor operation management.