Confluence of density currents over an erodible bed

Results from laboratory experiments on conservative density current confluence are reported. Hydraulic characteristics and morphodynamic consequences of the confluence of two continuous release density currents in a horizontal, 45 degrees asymmetrical junction are examined and compared to those of terrestrial subaerial river junctions. It was observed that density current confluence is markedly different than those in river junctions primarily due to the ease of the dense fluid to convect into the ambient fluid in the junction zone. Upward convection in the junction resulted in low horizontal velocity and shear stresses on the bed of the junction zone, followed by replunging to the layer of neutral buoyancy downstream of the junction where acceleration occurs. In the downstream reach was a distinctive erosional pattern similar to central scouring seen in river junctions but starting at the downstream junction point rather than at the upstream junction point. It was found that terrestrial river models match well with the density current case in terms of maximum velocity downstream of the junction, backwater effect, scour face protrusion into the downstream reach, and maximum scour orientation. Poor matching was found in terms of separation zone dimensions and shape, streamline deviation angle on the junction line, and maximum scour depth.