Sediment Transport and Geomorphological Change in a High-Discharge Tropical Delta (Magdalena River, Colombia): Insights from a Period of Intense Change and Human Intervention (1990-2010)

There is strong indication that environmental changes and human interventions have affected freshwater discharge and sediment flux in the Magdalena River (northwestern South America) within the period from 1990 to 2010. Thus, stream flow, suspended sediment load (SSL), and riverbed dynamics were analysed in this study for estimating changes in the suspended sediment transport regime as well as of erosional/depositional patterns in different zones of the delta. It can be shown that stream flow increased at a higher rate than suspended sediment transport, promoting changes in the sediment transport regime. Erosion appeared at the mouth/frontal bar and the outlet zones and modified the sedimentary balance within the prodelta in the early 2000s. There is indication that cycles of erosion and accretion were controlled by the magnitude of fluvial discharge and riverbed scouring in the river outlet, whereas effluent diffusion and sediment dispersion were dominant in the delta front. High freshwater discharge, as buoyancy inputs, promoted the transfer of sediments from the river channel to the outer prodelta through the upper layers of the water column. Total sediment accumulation in the delta corresponded to <5% of the annual mean SSL of the Magdalena River. Overall, delta morphology remained relatively stable, experiencing a slow progradational state with highest sedimentation rates (<= 1430 mm y(-1)) in the deepest zones.