Experimental Investigation the effect of slot on bed scouring in Series Triangular of Vane Attached to The Bank in 90 Degree Mild Bend

Triangular vanes attached to the bank are a new method to control erosion and help protection the bank in meandering rivers. This structure is subjected to scouring due to flow convergence at the tips of the structures. Therefore, countermeasure methods should be employed in order to prevent financial damages and life hazards. One of these methods is to use a slot. In this study, the series of triangular vanes that a parallel chord rectangular slot, with the opening of the full vane area of 10% and a ratio of a/b=4 (a and b are the length and width of the slot) the bed in which they are established position near has been used. The vanes angle is 30 degrees upstream of the bank. Experiments under different installation distances, 4, 6 and 8 times the effective vane length, hydraulic conditions are different (Froude number 0.287, 0.304, 0.322), and the clear water. In all experiments depth of flow is constant and equal to 14 cm. Then the results were compared with no slot. The results showed that the slot reduces the average depths of scour around the tips of vanes. In average, the reduce percent of the average scour depths around the tips of the structure in distances 4Le, 6Le and 8Le is equal to 9 percent, 17 percent and 18 percent respectively. The triangular vanes caused flow diversion from outer bank towards the center bend and thus the formation of thalweg. The slot reduces the maximum depth of scour thalweg. In average, the reduce percent of the maximum depth of scour thalweg in distances 4Le, 6Le and 8Le is equal to 22.6 percent, 46 percent and 30 percent respectively. The first of effective length of vanes was 1/5 flume wide. In start tests and erosion around the vanes increased the first of effective length of vanes. The slot reduces the effective length variation of vanes. In average, the reduce percent of average the effective length variation of vanes in distances 4Le, 6Le and 8Le is equal to 15.5 percent, 13.7 percent and 15.7 percent respectively.