Laboratory investigation of the effect of river widening and installation of submerged vanes simultaneously on bed load transport

Submerged vanes technique has been used for strengthening river bed, protection of river banks, decreasing erosion in the river bend, preventing penetration of river bed sediments to intake structures, correcting river cross section in the adjacent bridge bases. In the present research using an experimental model by changing different parameters related to submerged vanes, the way of transferring bed load was examined in a separate section.
The objective of this research is examination of the effect of submerged vanes on load convey in a separate section. For this purpose, the middle part of the flume was considered for creating separated and broadened section. From the beginning of the flume 0.7 meter with original width of the flume was considered as slowing down current for establishing a uniform current. After that, two glass boxes with 4 meters length, 0.075 meters width were used for decreasing flume width in higher part of the experimental cross section. Then 1.5 meter length with original width of flume was considered as experimental cross section. From the end of the experimental section to the end of the flume, the conditions of the upstream canal were repeated. After finishing experiment, the rate of sediment progression is recorded in experimental section. Also after finishing experiment, the experimental section is drained and using laser meter device in a 5×3 matrix, the topography of the sediments in experimental section is set. In these experiments, dimensions, angle, arrangement and length distance of submerged vanes change and its effect on vane performance were examined.
Examining the effect of vane dimensions on how to transfer bed load indicated that by increasing submerged vane dimensions, submerged vane performance parameter is also increased. So that it increased from 10 to 46 percent with increasing the dimensionless length from 0.19 to 0.38 in dimensionless height of 0.31. By increasing the ratio of the dimensionless length, the width distance between vanes is decreased and causes increase in effect domain of whirling currents and this causes whirling movement of sediments around submerged vanes and not forming sediment beds. This causes dispersion and accumulation of sediments around submerged plane and decreases the speed of transferring bed load. For detecting vane performance in different arrangements, eight experiments were conducted. submerged vane performance parameter was higher than zero in all arrangements indicates decreasing bed load transfer and also decreasing bed load progression distance in experimental cross section relation to the observing state. the more number of vanes in Z and parallel arrangement and influence of vortex flows cause that sediment transport velocity is decreased. Generally, experiment parameter varies between 7 to 25 percent. For detecting the effect of installation angle on submerged vanes performance, experiments included six angles. Results indicated that all of the installation angles have positive performance and the submerged vanes in 90 degrees in relation to approaching current showed the highest performance than other installation angles of submerged vanes that was 23 percent.
In general, we can conclude that installation of submerged vanes in experimental phase causes change in progression velocity of sediments and change in sediment distribution pattern. Also the results indicated that increasing dimensions of submerged vanes causes decrease of sediment transfer and increase of sediment accumulation around the first row vanes. According to the results of arrangements, in convergent arrangement with 30 degrees to approaching current, the submerged vanes indicated the best performance. Also chess arrangement because of its rather high width distance in double rows of the vanes has not satisfactory performance.