Morphologic and sediment transport adjustments around an artificial point constriction in a large meandering river (Bermejo River, Argentina)

RAMONELL, CARLOS; MONTAGNINI, MARÍA DANIELA; PEREZ, MELINA; AMSLER, MARIO; ORFEO, OSCAR

Enschende - Holanda

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

International Association of Hydraulic Research (IAHR)

ABSTRACT. The Bermejo River is one of the lowland rivers with more specific solid discharges in the world. For the last 60 years, mean maximum rates of meander channel shift of 600 m/year were recorded around Lavalle Bridge. The bridge was built in a cut-off formed straight reach of the river. The reach downstream the bridge remained straight to nowadays, lengthening from 4 km to 8 km during the eighties, when large floods occurred. The meander growth at the upstream reach prompted the breaching of the bridge. We suggest that the opposite river behavior around the bridge could be related with a disequilibrium in the sediment transport. The bridge acts like a dam during the high water levels promoting sedimentation in the upstream reach, and channelized bed-lowering downstream. During low water stages, the upper reach slope would exceed the limit necessary to convey the water and sediment input and meandering became the mechanism to decrease the energy excess. The Bermejo River is one of the lowland rivers with more specific solid discharges in the world. For the last 60 years, mean maximum rates of meander channel shift of 600 m/year were recorded around Lavalle Bridge. The bridge was built in a cut-off formed straight reach of the river. The reach downstream the bridge remained straight to nowadays, lengthening from 4 km to 8 km during the eighties, when large floods occurred. The meander growth at the upstream reach prompted the breaching of the bridge. We suggest that the opposite river behavior around the bridge could be related with a disequilibrium in the sediment transport. The bridge acts like a dam during the high water levels promoting sedimentation in the upstream reach, and channelized bed-lowering downstream. During low water stages, the upper reach slope would exceed the limit necessary to convey the water and sediment input and meandering became the mechanism to decrease the energy excess.