Effect of the number of rows, height and arrangement of submerged vanes in flushing of dam reservoir

Background and objectives: Pressurized flushing is one of the common methods in sediment flushing of dam reservoirs. In this method, sediments settled in the reservoir are released out of the dam together with water flow using the bottom outlet. For increasing the performance of pressurized flushing, it is attempted to fall down water level to minimum height of operation. Also, in the previous researches, the performance of different hydraulic and structural methods was evaluated in order to increase the pressurized flushing. Researchers have always tried to recognize the process of flushing and effective parameters and therefore, propose efficient procedures to increase the performance of flushing. Aim of this study is to investigate experimentally the effect of the number of rows, height and arrangement of submerged vanes in the enhancement of flushing reservoir.
Materials and methods: To carry out the experiments of this research, a physical model including sediment reservoir, settling basins and water supplied tank was used. Submerged vanes were set up in front of bottom outlet with two heights (HV/D>1 HV/D<1) and different number of rows (one, two, three rows). In tests, in addition to the parallel arrangement, the flushing performance of new type of submerged vanes arrangement as titled radial arrangement was investigated in three depth of water level (HW=20, 30, 40 cm). Sediment particles was made of sand washed with 0.51 mm diameter. The tests were run with constant discharge equal to 2L/s for an hour and at the end of each experiment, weight of flushed sediment was determined.
Results: Results showed that with decreasing the raw number of vanes in parallel arrangement, the performance of sediment flushing was increased. On the other hand, one-raw submerged vanes (double vanes) with relative height HV/D=0.5 and 2 have the best flushing performance with 173 and 231 percentages respectively compared with control model. Also, submerged vanes with relative height HV/D=2 have better performance than ones with relative height HV/D=0.5. The radial arrangement of vanes increased effectively the flushing performance. So that the flushing performance of submerged vanes relative height HV/D=0.5 and 2 increased about 11.33 and 4.1 times compared with the control model. In the radial arrangement, the flushing performance of vanes with relative height HV/D= 2 were less than ones with relative height HV/D=0.5 because of focusing the approaching inflow on the back of the side vanes.
Conclusion: Radial arrangement could increase the flushing intensity (especially with increasing the water depth of reservoirs). This condition is a relative advantage for flushing. In the other words, the flushing operation has more efficiency in the full condition of dam reservoirs and it is not necessary to fall down the water level of reservoir.