Fluidodynamic processes related to the sediments transport in the estuary of the Quequen Grande River, Argentina

PEREYRA, MARIANA G.; LASTRA, GABRIELA; MARINO, BEATRIZ M; THOMAS, LUIS P

Santa Fe

Congreso; RCEM 09 6th Symposium on River, Coastal and Estuarine Morhodynamics,; 2009

IARH International Association on Hydraulic Engineering and Research

The measurements obtained during a field work carried out in the last 3 km of the estuary of the Quequén Grande River, located southeast of Buenos Aires Province (Argentina), are analyzed and some interesting fluid-dynamics processes related to the movement of the sediments in the studied zone are identified.The river presents a meandering pattern which ends in the sea through a microtidal coastal-plain primary estuary with semidiurnal tides and whose morphology is substantially modified by the continuous dredging that provides deep water conditions for the harbour activities. Thus, a 12 m depth is kept throughout the last 2 km whereas further upstream the thalweg has a depth of 3-4 m, giving place to an artificial step that separates the estuary in two parts affected by the tide in different way. Such an abrupt variation of the depth induces particular local flows and reduced circulation zones. The system is partly mixed from the step to the estuary head located 15 km upstream, while in the last 2 km the water column is highly stratified with an upper 1-2 m layer of fresh water and a halocline developed that reaches salinities of about 34 being homogeneous down to the bottom.The three components of the water velocity were measured; information about the suspended sediments was obtained by means of the reflected acoustic signal (backscatter) of an ADCP; the salinity, temperature and suspended sediments distributions as function of the local depth were determined employing a CTD, while water and sediments samples were taken in six stations where the surface pH and dissolved oxygen level were also measured. The measurements made after the occurrence of the “sudestada” (a strong local wind from the south that blows for several days) that generated more intense currents than usual due to the higher tide level, and the turbidity currents above the estuary bottom produced by the ships movements, resulted of special and practical interest to our study.