Sediment transport and geomorphological adjustments in a high discharge tropical delta (Magdalena river, Colombia): insights of a period of intense change and human intervention (1990-2010).

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Juan Camilo Restrepo, Kerstin Schrottke, Andrés Orejarena, Juan Carlos Ortíz, Aldemar Higgins, Luís Otero, Leonardo Marriaga, Camille Traini

Friday 3 july 2015

9:00 - 9:15h at Antarctica (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) Morphodynamics of estuaries and coastal areas

Parallel session: 14A. Sediment - Coast

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The Magdalena River in northwestern South America provides the largest supply of freshwater (205.1 km3 yr-1) and the greatest amount of suspended sediment (142.6 x10 6 t yr-1) to the Caribbean Sea. The river mouth has been intervened since 1930 to allow shipping into the port of Barranquilla. In the last two decades, the watershed also has undergone severe human interventions. Furthermore, in 2000, a shift in its hydrological patterns appeared. The response of the Magdalena delta to these stressors remains unclear. Therefore, data of streamflow, suspended sediment and riverbed dynamics from 1990 to 2000 were analysed in this study to estimate changes in the suspended sediment transport regime and related processes as well as erosional/depositional patterns in critical zones of the delta. It can be shown, that the streamflow increased at a higher rate than suspended sediment transport, promoting changes in the sediment transport regime between the 1990s and the 2000s. These changes led to erosion of the mouth/frontal bar and outlet zones and modified the erosional/accretionary balance in the prodelta, in the early 2000s. Erosional/sedimentary cycles were controlled by the magnitude of fluvial discharges and river bed scouring in the river outlet, whilst effluent diffusion and sediment dispersion were dominants in the delta front. High freshwater discharges, as buoyancy inputs, promoted the transfer of sediments from the river channel to the outer prodelta through the upper layers of the water column. The total sediment accumulation in the delta corresponded to <5% of the annual mean SSL of the Magdalena River. In general, the morphology of the delta remained relatively stable; it experienced a slow progradational state. Higher sedimentation rates (_1430 mm yr-1) appeared in the deeper zones.