Methods to control bed erosion at 90° river confluence: an experimental study

ABSTRACT

Confluence is a common occurrence in rivers. The convergence of flows often leads to erosion of the river bed and formation of a deep scour-hole at the confluence. In the present experimental study, vanes and circular piles are proposed as scour mitigation measures. Experiments are performed in a distorted mobile bed model (d₅₀ = 0.28 mm) with 90° confluence angle. Three different discharge ratios (Q_r = ratio of lateral to main flow discharge) of 0.33, 0.50 and 0.75 are used. Vanes (1.5 cm width and 1 mm thick) or piles (ɸ = 8 mm and 12 mm) are arranged in a row perpendicular to the lateral flow at a spacing of 5, 10 or 15 cm. Three vane angles of 15°, 30° and 60° with respect to the main flow are used. The experimental results show that scour depth (S_d) increases with an increase of Q_r. S_d reduces by 33%, 50% and 47% with vanes for Q_r = 0.33, 0.50 and 0.75, respectively. S_d reduces by 43%, 55% and 55% with 12 mm piles and by 70%, 60% and 59% with 8 mm piles, for the corresponding discharge ratios. It is observed that S_d increases with an increase of vane angle and pile diameter, but it decreases with an increase of spacing. The performance of circular piles is better than vanes in controlling bed erosion.

KEYWORDS:

• River confluence
• bed erosion
• maximum scour depth
• vanes
• piles

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study has been supported by the Department of Civil Engineering, Indian Institute of Technology Madras, India.