Experimental study on the effects of the shapes and arrays of submerged impermeable plates on turbidity current characteristics

Background and objectives: Nowadays, dams are one of the most important structures to store surface water. Turbidity currents are usually the reason of sediment transport and deposition in deep reservoirs. As the turbidity current is completely stopped in the middle regions of the reservoir, sediment deposition reduces near the dam wall and as a result the main tasks of the dam are not disrupted. So, it is important to study the phenomenon. Roughening up or using obstacle the bed is a technique for changing the turbidity current hydraulics or reducing of its velocity. Some researches have been studied at this field, however, it is necessary to evaluate the effect of submerged impermeable plates on turbidity currents.
Materials and methods: In the present research, the head velocity and height of the turbidity current head were studied on the bed with submerged impermeable plates. For this purpose an experimental, flume with 30cm width, 10m length and 46cm height was used. The turbidity current was entered into the flume with concentration of 20 g.l-1 with 1 and 2 percent bed slopes and concentration of 40 g.l-1 with 1 and 2 percent bed slopes. Impermeable plates which came into two different areas (16 and 36 cm2) in five shapes (Square, rectangular, triangle, rhombus and trapezius) were located across the current. Also, square impermeable plates were placed as five arrays (parallel, plaid, converge, diverge and Z-shape) with an area of 16 cm2.
Results: Flow velocity was measured in 6 sections with distance 50cm and the height of head in 21 sections with distance 15cm. Then, non-dimensional graphs of velocity, height, Froude number and Richardson number of turbidity current head were drawn by using the data which obtained by Buckingham dimensional analysis method. Dimensionless velocity during the installation significantly decreased due to collision turbidity current to with plates. Also, the height of turbidity current head in the along of flow path indicated that plates gradually reduced the height of head at the beginning of the route. Height of turbidity current head was increased and the current path Froude number was decreased at the end of the path.
Conclusion: Results showed that the development velocity of the turbidity current reduced between 25-48 percent proportion to smooth bed in the condition of plate’s installation with different shapes and also the height of head reduced between 5.1-18.4 percent. Also, development velocity was reduced between 11.2-45.1 percent and the height of head was reduced between 0.4-18.4 percent in different arrays. Converge array in the concentration of 20 g.l-1 and Parallel array in the concentration of 40 g.l-1 were determined as the best array. By changing the area of plates from 16 to 36 cm2 between different shapes, the shape of rhombus with 22.2 percent, showed the greatest effect in reducing velocity.