Flow structure, bed morphology and contaminated sediment transport at the confluences of pipe and channel

The confluence between a pipe and an open channel is a common pattern. This study analyses the flow characteristics of pipe and channel confluences by examining the bed morphology and turbulent structure. A general process-response model of the hydro-morpho-sedimentary processes is proposed. The study also investigates the transport of contaminated sediment carried in the drainage pipe at the discharge outlet. The bed morphology at the confluence of the pipe and channel is characterized by a scour hole at the pipe outlet, a scour hole bar and a deposition zone. Above the scour hole and deposition zone, the inner shear layer exists with intense turbulence and low velocities between them. Contaminated sediments accumulate on the inner side of the channel, with coarser particles (D-50 > 2.28 x 10(-4) m) near the pipe outlet and finer particles carried downstream. The findings of this study could be helpful to pollutant transport management in natural confluences.