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 (theta) of the main channel, discharge ratio (Q(r)) of tributary channel and densimetric Froude number (Fr-g3) of the post-confluence channel. The experiments were conducted using a constant confluence angle (alpha) equal to 90 degrees and various bank slope angles of 45 degrees, 60 degrees, 75 degrees and 90 degrees. Applying different Q(r) and Fr-g3, the maximum effect of theta on scour depth was observed when the minor Q(r) was used in the tributary channel. The mildest bank slope angle caused the minimum scour depth for any given Fr-g3. Generally, the experiment using theta = 45 degrees and Q(r) = 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 theta on the height of the point bar is more than its effect on the scour depth. Finally, Fr-g3 and theta demonstrated their greatest influences on dimensionless scour depth (d(se)/y(3)) and dimensionless height of point bar (H-se/B-3), respectively.