Experimental study on the effect of conjugate usage of spur dike and curved submerged vanes on the diverted discharge and the morphology changes at the entrance of intake

Intake of river is used for different purposes such as irrigation, urban water supply, industry, electricity, etc. Side intakes are used directing water from river to the flat lands. The main purpose of an intake is to ensure a constant water supply that can be adjusted to local conditions. Designers have to consider the intake level below the minimum water level of the river. A protected side intake provides a stable place in the bank of a river or lake, from where water can flow into a channel or enter the suction pipe of a pump. It is built to withstand damage by floods and to minimize problems caused by sediment. One of the issues that designers of water structures are faced is the design of sediment control facilities in the inlet of drainage and irrigation networks. In this research, conjugate usage of spur dike and curved submerged vanes was considered and the effects of spur dike length, its location and angle on the amount of discharge and the maximum depth of scour hole's in the intake inlet were investigated. In this experiment, three different deviation discharges have been studied.
Experiments were performed in a flume with 14m length and 150cm width. The side intake had 75-degree angle to the main flume, with 60cm width. In all experiments, three rows of vanes were installed in front of the inlet. Dimensions, numbers and arrangement of the vanes were designed based on the recommended values by Odgaard and Wang (1997) Material of the vanes was metallic and their shape was trapezoidal
The Spur dike was placed on the right side of the flume wall. A number of piles, with a diameter of 7 mm, were used to create a permeable spur dike. The effect of three deviation discharge 15%, 20%, and 26% were studied. And in each three discharge effects of two abutment locations, three abutment lengths and two abutment angles were observed. Time of the experiments was equal to the duration of the time in which the first stack passed from the front of the intake. Finally, the bed topography at the inlet of the intake was calculated and analyzed by surfer software. In each experiment, information of water depth in the main flume, water depth in intake channel and the maximum depth of scour hole in the inlet of intake were plotted and analyzed. Dimensional analysis was done with the basic independent variables that characterized the system and arranges them into a parsimonious functional relationship. Then the coefficients determined by statistical analysis of the experimental data. In this analysis showed the relationship between calculated and observed depth scouring with the determination coefficient of, R2 =0.758 and the mean error of, MER = 27.4%. Also the relation between calculated and observed volume scouring with the determination coefficient of, R2 =0.938 and mean error of, MER = 4.1%.
The results of experiments showed that the position, the length and the angle of spur dike had a significant impact on the diverted discharge and the maximum scour depth. After running 48 tests and considering the control experiments, with and without installing vanes, the results showed that inserting spur dike on upstream of the inlet and in the position where the width was 1.2 of the intake width, provided better results in reducing scour hole's depth. Also, it caused an increase in the amount of discharge, in comparison to the position with doubled width of the intake, on the upstream. Moreover, it was observed that spur dike with a length of 27 cm (18% blockage) had the best result in all three flow deviation. The results showed that spur dike with the angle of 75 degrees to the flow direction, was more effective than vertical spur dike. Hence, the best condition occurred when spur dike with a length of 27 cm and the angle of 75 was placed on the upstream and in the section with the width of 1.2 of intake inlet. In this condition, three diversion flows of 15%, 20% and 26% led to, 34.6%, 30% and 58.8% increasing in the percentage of intake discharge, respectively and also it respectively caused 1.9%, 26.1% and 29.5% reduction in the maximum of scour hole's depth compared to the case of a vertical spur dike.