Scour depth in confluences considering tributary flow, bank slope, and post-confluence conditions

In this paper, scouring in confluences was experimentally studied considering the effects of bank slope angle (θ) of the main channel, discharge ratio (Qr) of tributary channel and densimetric Froude number (Frg3) of the post-confluence channel. The experiments were conducted using a constant confluence angle (α) equal to 90° and various bank slope angles of 45°, 60°, 75° and 90°. Applying different Qr and Frg3, the maximum effect of θ on scour depth was observed when the minor Qr was used in the tributary channel. The mildest bank slope angle caused the minimum scour depth for any given Frg3. Generally, the experiment using θ = 45° and Qr = 0.194 showed the best performance and reduced the maximum scour depth by 46%. Considering two obtained empirical relationships, it was concluded that the effect of θ on the height of the point bar is more than its effect on the scour depth. Finally, Frg3 and θ demonstrated their greatest influences on dimensionless scour depth (dse/y3) and dimensionless height of point bar (Hse/B3), respectively.