Characteristics of the tidal front and particulate matter transport in an estuary limited by morphology.

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Luis P. Thomas, Beatriz M. Marino, Ricardo N. Szupiany, Mariana G. Pereyra, Francisco G. Latosinski, Marcos N. Gallo

Tuesday 30 june 2015

17:30 - 17:33h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling, Poster pitches

Parallel session: Poster pitches: 7A. Sediment - Erosion

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Measurements of flow, suspended matter transport and maximum distance travelled by the tidal front in a coastal plain estuary, located in the southeast of Buenos Aires province (Argentina) are reported. The system has shallow upper and middle sectors, while an important deep-water port is installed along the lower zone. Findings are related to the morphology, river discharge, tidal height and meteorological conditions. Salinity profiles, velocity field and backscatter intensity were obtained during tidal cycles in stations located in the last 10.5km of the estuary. The concentration, type and size of the suspended elements are determined analysing water samples, and generalized for the cross-section by means of the relationship between the backscatter intensities of two ADCPs operating at different frequencies. Under calm weather conditions, the estuary is stratified and the suspended solids consist mainly in flocs of varied sizes composed of particles of medium and very fine silt, clay and abundant organic matter. Hence, the stratified estuary behaves as a low energy system that favours the aggregation of the wash load while the settling of sediments occurs mainly on specific places of the harbour where intense dredging is needed. The results are the first of a series of long-term measurements under different hydrodynamic conditions and complement those previously obtained in the lower sector, thus contributing to the understanding of the global estuarine dynamics. The information acquired compensates for the lack of systematic measurements due to the wide range of river flow and the morphological and structural changes that occurred in the port zone, mainly in the last decades.