MORPHOLOGICAL CHANGES ON A HIGHLY REGULATED ESTUARY ? THE PATH TO SILTATION IN THE MAGDALENA RIVER MOUTH (COLOMBIA, SOUTH AMERICA)

Código

PAP069

Autores

Carolina Consuegra, Andres Orejarena, Humberto Llinás, Javier Pérez, Juan Camilo Restrepo Lopez

Tema

PROCESSOS HIDROSSEDIMENTOLÓGICOS E MORFOLÓGICOS: FLUVIAIS, LACUSTRES E COSTEIROS

Resumo

The Magdalena River mouth (Colombia,South America) has undergone major physical changes after a variety of engineering infrastructures built since 1936. Currently, the river mouth is controlled by two long jetties, contraction groynes, a training wall and regular dredging, leading to a minimum depth of 9.15 m in the deep channel. These manmade structures inhibit the morphological responses to changes in fluvial inputs (freshwater and sediments). Moreover, the Magdalena River mouth can be classified as turbid. Consequently, the Magdalena Rivermouthprovides an illustrative example for analyzing siltation processes in systems where interact the low capacity of morphological response against environmental changes and an active sediment transport regime. Riverbed dynamics along the final reach of the river mouth were analyzedfor estimating changes in the erosional/depositional balance as well as to determine patterns of morphological adjustments. The subaqueous part of the delta appeared to be sensitive to changes in suspended sediment load. Such changes led to erosion of the river mouthzone in the early 2000s, whereas sedimentation was the dominant processes between 2004 and 2011. Since then, the river mouth has undergone a succession of erosion/sedimentation cycles, although sedimentation has been the predominant process.Changesin the longitudinal profile along the deep channel also reflects these patterns and highlight a sort of morphological stability despite the steady efforts of deepening this channel.The average rates of sedimentation (37 -822 mm yr-1) were of a comparable magnitude with rates reported from deltas experiencing severe sediment turnover. These response patterns reflect the spatial differences in hydro-sedimentary processes. In the river mouth, the cycles of erosion and accretion are controlled by the balance between fluvial discharge and saltwater intrusion. Consequently, mixing and vertical stratification, which in turn promote turbidity maximum zone formation, play a major role within siltation processes in the Magdalena River mouth.