Scour pattern at zero-degree confluent channels

Confluences are essential nodes in natural and artificial networks of open channels, where the merging of flows creates a complex flow and scour pattern. The present study is an experimental investigation on the zero-degree confluence of rigid and mobile bed channels. Excessive scouring at the confluence of the channels leads to the failure of the common wall and floor of the rigid channel. Experimental studies show that primarily two scour holes develop, one at the confluence point of the channels and a second downstream of the rigid (primary) channel. Results are presented for scour patterns and maximum scour depth for varied ratio of the discharge in the primary channel and total discharge and for varied tailwater depth. Experiments were also carried out for three length of the solid apron provided in the primary channel beyond the divide wall to examine the effect of the apron on the flow and scour pattern. Scour holes formed downstream of the primary channel and at the confluence point decreases with an increase in tailwater depth and solid apron length but increases with an increase in the ratio of discharge in the primary channel and total discharge. One scour hole formed at the confluence of the two channels and another hole formed downstream of the primary channel. The scour hole formed at the confluence was extending in the secondary channel. Equations are developed to compute the maximum scour depths of the two scour holes and extension of the scour hole in the mobile (secondary) channel. Sensitivity analysis shows that the Densimetric Froude number of flow downstream of the confluence is the most sensitive parameter that affects maximum scour depth of the scour holes and extension of scour hole in the secondary channel.