Control of Bed Erosion at 60° River Confluence Using Vanes and Piles

TLDR: In this article, the authors used a distorted model with a non-uniform sediment of mean particle size d¯¯ 50672 ǫ = 0.28mm with a confluence angle of 60°.

Abstract: River confluences have complex hydrodynamics than ambient flows due to different flow characteristics of the two merging flows. Secondary circulation develops due to merging of two flows which leads to bed erosion. The eroded sediment gets deposited at various locations in the downstream of the confluence. It is reported in the literature that major reservoirs in India will lose 50% storage capacity by 2020 and reservoirs all over the world lose storage capacity by as much as 5% every year. In view of controlling bed erosion at the confluence, vane and circular pile models are used as scour mitigation structures and experimental results are presented. Experiments are performed in a distorted model with a non-uniform sediment of mean particle size d 50  = 0.28 mm with a confluence angle of 60°. Two different discharge ratios (Q r = ratio of lateral flow discharge to main flow discharge) of 0.5 and 0.75 are used with a constant flow depth (H m) of 5 cm in the main channel. Vanes of width 0.3H m (1.5 cm), thickness of 1 mm are placed at 15°, 30° and 60° vane angles with respect to main flow. Circular pile models of 8 and 12 mm diameter are also used. Two different spacing of 2H m and 3H m (10 and 15 cm) between the vanes or piles are used to perform the experiments. For Q r = 0.5 and 0.75 using vanes, scour depth reduces by 25 and 34%, respectively. When circular pile models of 8 and 12 mm are used, the scour depth reduces by 25, 38 and 27, 43%, for Q r = 0.5 and 0.75, respectively. The scour depth decreases with an increase of vane angle and pile diameter, but increases with an increase of spacing. Therefore, piles have better performance over vanes in reducing scour at the confluence.