EFFECTS OF BED DISCORDANCE ON FLOW DYNAMICS AT OPEN-CHANNEL CONFLUENCES

Although a discordance in bed elevation between mainstream and tributa ry channels is a common feature of most river confluences, this height differential is largely ignored in many models of junction flow dynam ics. Here we present new laboratory flume data that demonstrate the si gnificant influence of bed discordance on flow at an acute angled conf luence. A difference in bed height between mainstream and tributary ch annels is shown to obliterate flow deflection at the bed and create a distortion of the mixing layer between the flows, resulting in fluid u pwelling at the downstream junction corner. This upwelling is responsi ble for the absence of a flow separation zone near the bed at the down stream junction corner and the lack of a zone of marked flow accelerat ion in the postconfluence channel. These experiments reveal complex fl ow fields generated by bed discordance and suggest the need for major revisions to current models of river channel confluence flow dynamics and their application to sediment routing at these sites.