Laboratorial investigating of the scouring extension in the range of trapezoidal and rectangular Multiple vanes to direct the flow in the rivers bends

Abstract

In this study the application of trapezoidal vanes in the river's bend as the substitute for the rectangular structures to control the erosion in the external bank has been implemented. To reach the research objective, some experiments with a number of 11 trapezoidal vanes with the angle of 30a (towards the upstream) of the distance of 56 cm under the different hyaulic conditions have been conducted. To compare the results some experiments were implemented using the rectangular vanes by the Froude number of 0. 24 and the distance of 56cm. The obtained results show that in all of the Froude numbers in the experiments by the presence of trapezoidal vanes the scouring was kept away from the outer bank and transferred to the structures' nose which is the same flume's breadth center. Also, in the downstream of the trapezoidal vanes a sediment hill is created which plays a remarkable role in external bank's restoration. In the rectangular structure the nose scouring in most of the structures extends towards the external bank. The length and the distance of the created hill in their downstream from the external bank are respectively lower and higher in trapezoidal vanes. The calculated scouring rate by the SURFER software is 56% more in the rectangular vanes than the trapezoidal ones. The dimensions of the scouring hollow around the structures increase towards the end of the bend gradually. The maximum scouring depth in the rectangular vanes is 251. 2 mm which has occurred in the structure's nose and is more about 63. 17% than the maximum scouring depth in similar experiment about the trapezoidal vanes.