Experimental study on the formation of alternate bars with fixed and loose banks

CARRASCO-MILIAN A; VIONNET CA; VALENTINE EM

Santa Fe

Simposio; RCEM 2009 - Sixth International Symposium on River, Coastal and Estuarine Morphodynamics; 2009

FICH - UNL

Free or alternate bars exert a significant effect on the flow resistance and sediment transport patterns governing the evolution of alluvial, low-gradient rivers. The initiation of alternate bars responds to an intrinsic instability mechanism arising from the interaction of the turbulent flow with the underlying erodible bed interface. Though much knowledge has been gained about alternate bars from earlier flume studies, the vast majority of the available experimental data were mostly obtained from experiments with loose beds and non-erodible banks. Consequently, a comparative experimental study between loose and fixed banks under identical slope, water discharge and sediment flux will help to clarify if the formation of alternate bars is indeed the preferred evolving spatial scale of the problem, delaying the lateral migration of the stream for much longer time scales. To that aim, a comparative set of experiments was carried out in a straight channel available at the Department of Civil Engineering and Geosciences at the University of Newcastle (UK), analyzing the differences between loose and fixed banks under identical bed slope, water discharge and sediment flux. The aim was to clarify if the formation of alternate bars is indeed the preferred evolving spatial scale of the problem, delaying the lateral migration of the streambed for much longer time scales.