Characteristics of tidal channels in a mesotidal estuary of Argentina.

GINSBERG, SS; PERILLO, G.M.E.

Journal of Coastal Research

CERF

Lugar: Boca Raton; Año: 2004 vol. 20 p. 489 - 497

0749-0208

Bahía Blanca Estuary is a complex network of tidal channels, extensive tidal flats, low marshes areas and islands. The lack of a large source of sediments either from river or the shelf makes that the tidal channels of this estuary control the dispersal of sediment into the system. A 3 year study of morphodynamic equilibrium has been carried out in the tidal channels of Bahía Blanca Estuary with the aim to investigate the evolution of the system. Detailed changes in the spatial bathymetry linked to the observed flow and sediment processes to give a clearer indication of the tidal circulation in the channels. This paper discusses morphologic variability and processes of the erosion, deposition and transport of sediment, which determines the morphological evolution of the system. Current measurements showed that channels appeared to be ebb dominated with peak speeds of up to 1.2 m/s. Examination of current durations suggest that flood time dominance is about 7 hr, while ebb period is 5 hr. The cross section bathymetric is usually bimodal with two channels separated by a shallow area. The deeper channel experiences ebb-directed net, while the shallower channel, could to be influence by the net flood current. The net sediment transport into of these systems is shown to be governed more by the degree of tidal velocity asymmetry (ebb flow). In change the duration of ebb/flood-dominant periods governs the trends of erosion. Channels migration causes a shift from degradation in north sector to aggradations in south side, during adjustment. As a consequence, the estimated rate of migration is the order of 25 m yr-1.