a. ashraf sadraddini

Imperfect knowledge due to unpredictable climatic conditions leads to uncertainty in decision making in agriculture. Therefore, a probabilistic analysis of the various possibilities besides increasing flexibility in decision-making can also enhance the reliability of decisions. Using Tabriz Synoptic station’s data, the values ofthe crop (TriticumAestivum L.) evapotranspiration and effective rainfall in mid to late season in the study area (Tabriz plain) were estimated. Analyzing the effective rainfall and crop evapotranspiration as probabilistic variables, a reliable method for estimating the irrigation water requirement was described using the “probability distributionfunctions”.By examining 12 different probability distribution function, it was found that the log normal distribution function achieves the best results for the monthly precipitation data with values greater than 30 mm, but there is no unique probability distribution function for evapotranspiration data.This method can also provide a general formula for calculations of irrigation water requirement with different probability levelsduringthe growing season. Results showed thatthe reported values of irrigation requirement in the NETWAT program that is atthe 50 % probability level andused in most of irrigation projects in Iran, were different the calculated values in this study.According to similar reports in different researches, the represented method is recommended for more precise estimation of irrigation water requirements (with different probabilities) especially in critical situations (with high evapotranspiration and low rainfall values) or for crops that are sensitive to water stress in 80% probabilitylevelor higher.

In this research، five-drip irrigation systems were selected in Sattarkhan Channels Network and technical performances of them were evaluated. In each system one manifold was randomly selected and four located lateral pipes، at the beginning، one-third، two thirds and end of each manifold were selected. By considering the same proportionality، four apple trees were identified a long each lateral pipe. Emitter discharges of two drippers at each of these trees، pressure at the beginning and at the end of the lateral pipes were measured in the all selected manifold pipes. Also، the minimum lateral inlet pressure at each manifold was identified by measuring the flow pressure of the all lateral inlets. Results showed that the water Emission Uniformities of the systems (EUs) were within the range of 48. 1 to 82. 8 percent and the systems performances based on this index were classified poor to good. Potential application efficiencies of the low quarter of the systems (PELQs) were varied from 43. 3 to 74. 5 percent. So that، only the irrigation system at one of the farms had relatively good performance and the systems'' performances in the other farms were poor. Application efficiencies of low quarter of the systems (AELQs) were in the range of 52. 7 to 80 percent. Based on AELQs index، only one system had good performance while the performances of the others were poor. In general، the reasons for the low system performances were pointed as inappropriate distribution of pressure، high-pressure difference in the systems، the unsuitable irrigation water depth، low skills of irrigators and poor operation management of the systems.

Determination of hydraulic head loss is one of the most important components of designing drip irrigation systems. For having an optimized water distribution in drippers, it is necessary that head loss in each section should be in predetermined range. In recent years, fluent software has been used greatly in hydraulic science and fluid mechanics for evaluation of different flow regimes. The mentioned software has fantastic capabilities andits advantages have been proved in solving different fluid problems, mass and heat transfer. In the current study we tried to simulate hydraulic behavior of water flow in drip irrigation manifolds. Thus, three manifolds with same 18 meter length and outer diameter of 32, 40 and 50 millimeters which have 8 outlets with 2 meter intervals have been set. Validation of mentioned model has been done by comparing its result with observed values, measured in laboratory and computed results by Darcy Weisbach formula. In these experiments, pressure distribution was measured in three manifolds with different diameters and inlet pressure of 0.8, 1.0 and 1.2 bar using digital piezometer. Results showed that fluent software and Darcy Weisbach formula by having maximum relative error of 1.1268 and 0.5720 and correlation coefficient of 0.99959 and 0.99993, respectively in comparison of measured head loss are suitable models for simulation of water flow in manifolds and also are the appropriate and accurate methods in hydraulic simulation of water flow in drip irrigation systems.