Interaction between channel junction and bridge pier on flow characteristics

Abstract

Considering many bridge piers that destroyed every year due to scouring, flow behavior around these obstructions was one of the interests of engineers in recent years. This phenomenon has usually been studied in straight channels and has rarely studied at channel confluences. To accomplish this, after calibrating SSIIM1 model for a 90° channel junction, the effect of circular bridge pier at two positions after channel confluence (x/w = −1.5 and x/w = −3, x = distance from upstream corner of junction in flow direction, w = main channel width) on flow pattern were conducted. The results indicated that bridge pier caused backwater rise by 4.1% at upstream of channel confluence compared to without bridge pier case. Water surface profile of main channel reduced in two steps. First step was due to reduction of effective width of main channel because of tributary channel inflow and the second one was due to flow contraction near bridge pier while in the absence of bridge pier it only had one step. Also the results showed that longitudinal velocity decreased at upstream sections of bridge pier. At the centerline of the section corresponding to downstream corner of junction for (x/w = −1.5) and (x/w = −3) these reductions were 25.4% and 16.3% respectively. Keywords: Bridge pier, Channel confluence, SSIIM1