Comparison of morphology and flow structure at two braid-bar confluences in a large river

SZUPIANY, RICARDO; AMSLER, MARIO; PARSONS, DANIEL; BEST, JAMES; HAYDEL, ROBERT

Enschende - Holanda

Simposio; 5th IAHR Symposium on River, Coastal and Estuarine Morphodynamics – RCEM 2007; 2007

International Association of Hydraulic Research (IAHR)

ABSTRACT. This paper details the morphology and flow structure (primary and secondary currents) at two separate asymmetrical bar-confluences of the Paraná River, Argentina. The two sites occur over channel reaches ~3.8 km long and were surveyed in June 2006 with a single beam echo-sounder and an acoustic Doppler profiler (aDp). The width:depth ratios (W/D) are relatively high, providing opportunity to investigate similarities and differences between small and large scale fluvial confluences. The findings highlight that transversal distributions of the flow is critical as they combine within the confluence zone, essentially controlling the position of the scour and thus the flow structures in the downstream channel. In both confluences, and similar to studies of small confluence flows, counter rotating surface convergent flows are identified. However, the spatial extent of these secondary cells is limited to a low proportion of the total channel width. Moreover the cells are rapidly dissipated in the downstream direction. This paper details the morphology and flow structure (primary and secondary currents) at two separate asymmetrical bar-confluences of the Paraná River, Argentina. The two sites occur over channel reaches ~3.8 km long and were surveyed in June 2006 with a single beam echo-sounder and an acoustic Doppler profiler (aDp). The width:depth ratios (W/D) are relatively high, providing opportunity to investigate similarities and differences between small and large scale fluvial confluences. The findings highlight that transversal distributions of the flow is critical as they combine within the confluence zone, essentially controlling the position of the scour and thus the flow structures in the downstream channel. In both confluences, and similar to studies of small confluence flows, counter rotating surface convergent flows are identified. However, the spatial extent of these secondary cells is limited to a low proportion of the total channel width. Moreover the cells are rapidly dissipated in the downstream direction.