Local scour around a bridge pier in a right-angled channel confluence: an experimental study with mobile bed

Flow past a bridge pier in a right-angled channel confluence (RACC) is investigated in this experimental study. The water surface elevation and velocity profile at different time instants are measured by a point gauge and acoustic Doppler velocimetry (ADV), respectively. Additionally, the evolution of the bed is measured by a depth sensor. Effects of pier location, pier size, size of bed material, and downstream flow depth on important bed features are studied, maintaining a constant discharge ratio. It is found that the shape of the local scour hole around the pier (LSP) is unsymmetrical. Scour depth changes at different locations of the confluence: the LSP is small near the flow separation zone, and it is increased along the maximum velocity zone. The maximum scour depth attained at the pier is 81% higher than that of the LSP in a single channel, and LSP reached its peak when the pier is located at maximum velocity zone. LSP increases by 20%, when the pier size increases by 40%. LSP increases by approximately 45%, when the downstream flow depth is decreased by 45%. LSP reduces by approximately 6.8%, when the bed material size is increased by 48.5%.