154
Jorge L6pez Laborde· Gustavo J. Nagy
and tides). According to their results, the turbidity frontal area was divided into different regions:
1. a northern area where the principal forcing is the river discharge,
2. a southern area, close to the Argentinean coast, where the tidal and meridional wind
effects are more significant, and
3. Samborombon Bay and Punta Rasa areas, where only local wind effects are significant.
7.4
Synthesis
Hydrodynamics of the Rio de la Plata is controlled by the discharge of Uruguay River
(average flow rate 4700 m3 S-1 at Hervidero Gauging Station) and Parana-Paraguay
Rivers (average flow rate 15400 m3 S-1 at Rosario Gauging Station and 17000 m3 S-1 at
Corrientes Gauging Station). Together these rivers produce a combined annual average discharge (1960-1980) between 20 000 and 23 000 m3 S-I, with minimum and maximum values of 10800 and 30600 m3s- 1 (Mazio and Martinez 1989). Recent data reveals a significant average flow rate increase.
The Uruguay River receives the discharge of Parana Bravo across from Nueva
Palmira, the discharge of Sauce River across from Punta Gorda and the discharge of
Parana Guazu River across from Carmelo. Most of the discharge occurs to the southeast, in the direction of Colonia, by the Sistema Fluvial Norte; however this discharge
can shift to the South, in the direction of Playa Honda, along the existing navigation
channels (Canal de las Palmas and Pozos de Barca Grande).
In the upper Rio de la Plata, bottom morphology appears similar to a braided fluvial pattern. The Parana River delta front shows a differential lineal growth (10.62 to
30.02 m ye 1 ). Both have been interpreted as the consequence of the dynamic balance
between the subaqueous delta advance and the Uruguay River discharge, causing sediment redistribution (Cavallotto 1987; Parker and Lopez Laborde 1988, 1989).
In the vicinity of Colonia, the Banco Grande de Ortiz produces a concentration of
flows along Barra del Farallon, while over Canal Norte, along the Uruguayan coast, a
slow and gentle current occurs. Therefore, in the middle Rio de la Plata the larger flows
occurs against the Argentinean coast, along Gran Hoya del Canal Intermedio.
Two facies associations of bottom sediments have been distinguished in this area
(Parker et al. 1985):
1. along the northern coast, sands and silty sands, grade to silty sands and silts in the
Banco Grande de Ortiz and to silts, clayey silts and even silty clays in the outer river;
2. along the southern coast, sandy silts and silts grade to silty clays.
Near Oyarvide, due to the influence of Arquimedes and Ingles banks, the main
current rotates and divides into two branches: a northern one, along the Uruguayan
coast, and a southern one. Bottom morphology (greater depths at Canal Oriental) and
Coriolis force are responsible for the greater flow concentration along the northern
branch, whereas at Samborombon Bay currents are negligible.
The outer Rio de la Plata is an area of complicated current patterns due to tidal
amplitude and phase differences along the river mouth transverse section. Winds blow-
Jorge L6pez Laborde· Gustavo J. Nagy
and tides). According to their results, the turbidity frontal area was divided into different regions:
1. a northern area where the principal forcing is the river discharge,
2. a southern area, close to the Argentinean coast, where the tidal and meridional wind
effects are more significant, and
3. Samborombon Bay and Punta Rasa areas, where only local wind effects are significant.
7.4
Synthesis
Hydrodynamics of the Rio de la Plata is controlled by the discharge of Uruguay River
(average flow rate 4700 m3 S-1 at Hervidero Gauging Station) and Parana-Paraguay
Rivers (average flow rate 15400 m3 S-1 at Rosario Gauging Station and 17000 m3 S-1 at
Corrientes Gauging Station). Together these rivers produce a combined annual average discharge (1960-1980) between 20 000 and 23 000 m3 S-I, with minimum and maximum values of 10800 and 30600 m3s- 1 (Mazio and Martinez 1989). Recent data reveals a significant average flow rate increase.
The Uruguay River receives the discharge of Parana Bravo across from Nueva
Palmira, the discharge of Sauce River across from Punta Gorda and the discharge of
Parana Guazu River across from Carmelo. Most of the discharge occurs to the southeast, in the direction of Colonia, by the Sistema Fluvial Norte; however this discharge
can shift to the South, in the direction of Playa Honda, along the existing navigation
channels (Canal de las Palmas and Pozos de Barca Grande).
In the upper Rio de la Plata, bottom morphology appears similar to a braided fluvial pattern. The Parana River delta front shows a differential lineal growth (10.62 to
30.02 m ye 1 ). Both have been interpreted as the consequence of the dynamic balance
between the subaqueous delta advance and the Uruguay River discharge, causing sediment redistribution (Cavallotto 1987; Parker and Lopez Laborde 1988, 1989).
In the vicinity of Colonia, the Banco Grande de Ortiz produces a concentration of
flows along Barra del Farallon, while over Canal Norte, along the Uruguayan coast, a
slow and gentle current occurs. Therefore, in the middle Rio de la Plata the larger flows
occurs against the Argentinean coast, along Gran Hoya del Canal Intermedio.
Two facies associations of bottom sediments have been distinguished in this area
(Parker et al. 1985):
1. along the northern coast, sands and silty sands, grade to silty sands and silts in the
Banco Grande de Ortiz and to silts, clayey silts and even silty clays in the outer river;
2. along the southern coast, sandy silts and silts grade to silty clays.
Near Oyarvide, due to the influence of Arquimedes and Ingles banks, the main
current rotates and divides into two branches: a northern one, along the Uruguayan
coast, and a southern one. Bottom morphology (greater depths at Canal Oriental) and
Coriolis force are responsible for the greater flow concentration along the northern
branch, whereas at Samborombon Bay currents are negligible.
The outer Rio de la Plata is an area of complicated current patterns due to tidal
amplitude and phase differences along the river mouth transverse section. Winds blow-