Introduction:

Among the most important structures of water intakes, various types of Neyrpic gates can be highlighted, which are now extensively used in irrigation and drainage networks in our country. These water intake structures are designed to deliver water under non-uniform flow conditions in a way that ensures each branch canal receives its designated flow. These types of modular gates are selected for controllable water intake in canals and some diversion dams and include five types: X, XX, L, C, and CC. They are named with the index 1 or 2, respectively, depending on whether they are single-blade or double-blade, and are used at the installation site according to the required water intake rate and hydraulic conditions. The flow through these modular gates can be varied over the entire upstream level range close to the nominal value and within ±5% to ±10% of the flow. These devices control the flow through the combined weir and orifice method. In assessments conducted in the country's irrigation networks, it has been observed that the discharge from the water intake gates is not equal to the nominal discharge, and in some water intakes it is more and in some water intakes it is less than the design rate. Due to existing restrictions and the lack of specific instructions for producing these gates domestically, the specifications of the manufactured gates are different from standard gates.



Methods:

When reviewing Iranian and foreign sources to select the geometric dimensions of the structure, it was observed that most of the geometric dimensions presented in scientific sources are in complete agreement with each other, but there is a difference of opinion regarding the opening of the gate (vertical height of the blade relative to the crest of the spillway) by approximately 4 mm (the actual estimated number is 4.4 mm). Laboratory model 1, with an opening height of 90 millimeters, was constructed from the intersection point of the upstream and downstream slopes of the spillway, while laboratory model 2, also with an opening height of 90 millimeters, was prepared from the tangent line of the upper edge of the spillway and placed in testing after adhesive application, positioning the blade of the second model 4 millimeters lower compared to the first model. In fact, the total opening of the gate in the first model is 94 mm, but in the second model, the total opening of the gate is 90 mm. Also, in reviewing the available scientific sources, it was observed that there are three different methods for using the stage-discharge curve. Therefore, in this study, in order to investigate this duality in sources and determine the appropriate model, first, laboratory data were measured and stage-discharge curves were drawn for the two mentioned laboratory models, and then three different data extraction methods were used for both mentioned laboratory models. The first method is consistent with the stage-discharge curve presented by Bos (1989), the second method is a proposed method based on the design discharge point being known at the break point of the stage-discharge curve between the first and third methods, and finally the third method is consistent with the stage-discharge curve presented in other available scientific sources such as Amiri-Tokladany and Siahi (2015). In the present study, two criteria, root mean square error (RMSE) and coefficient of determination R2, were used in the Microsoft Excel software environment.



Results:

The general trend of the two stage-discharge curves for the two laboratory models is similar, but due to the larger opening of the first model (94 mm) compared to the second model (90 mm), the water flow head that leads to the onset of interference of the model blade is also different and changes from a higher head in the first model (approximately 16 mm) to a lower head in the second model (approximately 13.5 mm). In general, it is observed that by changing the angle of the gate body from horizontal (zero slope) to slopes of ±5 and ±10 degrees, the gate flow coefficient decreases and the stage-discharge curve shifts towards lower flow rates. The justification for this difference in the curves is that changing the slope angle of the flume bottom from zero to the horizon leads to a change in the slope of the spillway body and the geometric characteristics of the module gate. From comparing the stage-discharge curves of scientific sources with the results of the arranged laboratory data, it can be concluded that the second laboratory model apparently has a very good agreement with the standard curve, but the first model shows a huge difference. In fact, the first model has an opening of 94 mm and has a larger opening (4 mm) and starts the flow interference at a higher head and discharge. Also, a calculation table was created for 5 key points in the stage-discharge curve (Q, 1/1Q, 1/05Q, 0/9Q, 0/95Q) to determine the minimum root mean square error (RMSE) and the maximum coefficient of determination R2 between regression models between the six studied cases with standard data (for two laboratory models and each for three data extraction methods).



Conclusion:

Generally, the Stage-discharge curves in model 2 demonstrated better alignment with the Stage-discharge curve of the standard gate compared to model 1, which had a larger opening. The laboratory data of Model 1 were generally much higher than the design values by comparing the Stage-discharge curve for all three data extraction methods, while the laboratory data of Model 2 were generally slightly lower but close to the design values for all three methods. The result is that geometric model number 2 has been approved for constructing the geometry of the X1 type module gate, and the basis for the gate opening should be the tangent line to the curvature of the spillway. It was also observed that data extraction method 2 showed closer alignment with the experimental results, whereas method 1 indicated a significant deviation. Therefore, determining the important design points in the Stage-discharge curve using the method presented by Bos (1989) shows a significant difference with the experimental results. Additionally, the impact of changes in blade angles and upstream and downstream spillway slopes (due to the presence of slopes in the flow) on the Stage-discharge curve was investigated, and the influencing factors in these differences were discussed.