An Experimental Study to Control Scour at River Confluence

Abstract:

The aim of present study is finding a method to control sediment erosion at river confluence. The confluences are mixture of two different flows and are common occurrences along the river. River confluences are sites of natural scour phenomenon and also influence reservoir sedimentation. The river confluence is associated with a separation zone, stagnation zone and a mixing layer along which the scour hole is observed. The eroded sediment creates potential problems by depositing at unwanted downstream locations such as barrages, weirs, check dams, reservoirs etc. As per the literature, the storage capacity of major reservoirs in India is going to be reduced nearly half of the storage capacity by 2020. Hence, an experimental study has been conducted on mobile bed (d₅₀=0.28 mm) with a confluence angle of 90^o for a discharge ratio (Q_r) of 0.5, where, Q_r is defined as the ratio between lateral flow discharge (Q_l) and main flow discharge (Q_m). Circular shape pile models of same diameter are arranged in a systematic manner with constant spacing (5 cm, 10 cm and 15 cm) to change the flow pattern for reducing scour at the confluence. Two types of pile models (8 mm ϕ and 12 mm ϕ) are used to conduct the experiments. The experimental results show that maximum scour depth at confluence is reduced by 60%. In addition, the bed profile modifications are also reported.

Keywords: Reservoir sedimentation, River confluence, Mobile bed, Scour, Vanes.

 

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