CHAPTER 8 . Physical Characteristics and Processes of the Rio de la Plata Estuary
(1965,1966); Urien (1966,1967,1972); Lopez Laborde (1987a,b); Depretis and Griffin
(1968). A brief description of the main morphological features is presented here.
The upper region is characterized by shallow areas, 1-4 m deep (Playa Honda and
Great Ortiz Bank) separated from the coasts by channels 5-8 m deep (North Channel
System, west part of the Oriental Channel and the Intermediate Channel). The Barra del
Indio is a wide and gentle bar extending from the Argentinean coast between Punta
Indio and Punta Piedras to the northeast. It has a slightly convex surface with a depth of
6.5-7 m. It borders the Maritime Channel to the east, a wide depression which separates
the Barra and the SamborombOn Bay from the Alto Maritimo (Cavallotto 1987; CARP 1989).
The Maritime Channel, the Samborombon Bay, the Alto Maritimo and the east part
of the Oriental Channel are the main characteristics of the lower estuary. The Maritime Channel has a depth of 12-14 m increasing to the south where it reaches 20 m.
The Oriental Channel runs along the Uruguayan coast and is the deepest chann,el in
the estuary: it is 25 m deep off Punta del Este. Alto Maritimo is a plain formed by the
Bank Arquimedes, English Bank and the Bank Rouen (Cavallotto 1987; CARP 1989).
Bank Arquimedes and the English Bank are stable areas, 6-8 m deep, and with approximate surface areas of 45-350 km2, respectively. They act to divide the river flow,
separating the east part of Oriental Channel and the Maritime Channel (Urien 1967;
CARP 1989). The Bank Rouen is 30 km south of them, has a north-south orientation,
covers an approximate area of 700 km2, and is 10-12 m deep. The other major feature
in the outer region is the Samborombon Bay, a shallow area with depth ranging from
2-10 m, which extends from the north at Punta Piedras to the south at Punta Rasa.
The suspended sediment concentration in the Rio de la Plata water varies from
100-300 mg 1-1 (Urien 1967; CARP 1989). The estimated average annual suspended
sediment load is 79.8 x 106 t yr' (Urien 1972).
8.2.2
Climatology
The atmospheric general circulation in the region is controlled by the influence of the
quasi-permanent South Pacific and South Atlantic high pressure systems. Southwestward circulation associated with the South Atlantic high advects warm, moist air from
subtropical regions. Cold anticyclones over southern Argentina periodically (particularly in winter) drive cold maritime air masses from the Southwestern Atlantic over
the littoral area. The Rio de la Plata is located within one of the most cyclogenetic areas
in the Southern Hemisphere (Taljaard 1967). The highest frequency of occurrence is
in winter. A recent, comprehensive review of possible mechanisms that produce this
cyclogenesis is given by Seluchi (1995). An important feature in this region is the presence of upper air troughs, usually associated with frontal systems approaching the
region with southwest-northeast trajectories, that interact with subtropical air masses
over northeastern Argentina, northern Uruguay and southern Brazil. This interaction
produces cyclogenesis resulting in strong winds over 30 m S-1 from the southeast in
extreme events, and storms affecting the area for several days. This phenomenon is
called "sudestada" and is responsible for disastrous flooding in the littoral of the Rio
de la Plata. Statistics of the wind field (Servicio Meteorologico Nacional (SMN) 1982),
based on 10 years of data from the weather station Ponton Pnicticos Recalada, located
in the outer estuary (Fig. 8.1), show that the winds generally range from southwest-
(1965,1966); Urien (1966,1967,1972); Lopez Laborde (1987a,b); Depretis and Griffin
(1968). A brief description of the main morphological features is presented here.
The upper region is characterized by shallow areas, 1-4 m deep (Playa Honda and
Great Ortiz Bank) separated from the coasts by channels 5-8 m deep (North Channel
System, west part of the Oriental Channel and the Intermediate Channel). The Barra del
Indio is a wide and gentle bar extending from the Argentinean coast between Punta
Indio and Punta Piedras to the northeast. It has a slightly convex surface with a depth of
6.5-7 m. It borders the Maritime Channel to the east, a wide depression which separates
the Barra and the SamborombOn Bay from the Alto Maritimo (Cavallotto 1987; CARP 1989).
The Maritime Channel, the Samborombon Bay, the Alto Maritimo and the east part
of the Oriental Channel are the main characteristics of the lower estuary. The Maritime Channel has a depth of 12-14 m increasing to the south where it reaches 20 m.
The Oriental Channel runs along the Uruguayan coast and is the deepest chann,el in
the estuary: it is 25 m deep off Punta del Este. Alto Maritimo is a plain formed by the
Bank Arquimedes, English Bank and the Bank Rouen (Cavallotto 1987; CARP 1989).
Bank Arquimedes and the English Bank are stable areas, 6-8 m deep, and with approximate surface areas of 45-350 km2, respectively. They act to divide the river flow,
separating the east part of Oriental Channel and the Maritime Channel (Urien 1967;
CARP 1989). The Bank Rouen is 30 km south of them, has a north-south orientation,
covers an approximate area of 700 km2, and is 10-12 m deep. The other major feature
in the outer region is the Samborombon Bay, a shallow area with depth ranging from
2-10 m, which extends from the north at Punta Piedras to the south at Punta Rasa.
The suspended sediment concentration in the Rio de la Plata water varies from
100-300 mg 1-1 (Urien 1967; CARP 1989). The estimated average annual suspended
sediment load is 79.8 x 106 t yr' (Urien 1972).
8.2.2
Climatology
The atmospheric general circulation in the region is controlled by the influence of the
quasi-permanent South Pacific and South Atlantic high pressure systems. Southwestward circulation associated with the South Atlantic high advects warm, moist air from
subtropical regions. Cold anticyclones over southern Argentina periodically (particularly in winter) drive cold maritime air masses from the Southwestern Atlantic over
the littoral area. The Rio de la Plata is located within one of the most cyclogenetic areas
in the Southern Hemisphere (Taljaard 1967). The highest frequency of occurrence is
in winter. A recent, comprehensive review of possible mechanisms that produce this
cyclogenesis is given by Seluchi (1995). An important feature in this region is the presence of upper air troughs, usually associated with frontal systems approaching the
region with southwest-northeast trajectories, that interact with subtropical air masses
over northeastern Argentina, northern Uruguay and southern Brazil. This interaction
produces cyclogenesis resulting in strong winds over 30 m S-1 from the southeast in
extreme events, and storms affecting the area for several days. This phenomenon is
called "sudestada" and is responsible for disastrous flooding in the littoral of the Rio
de la Plata. Statistics of the wind field (Servicio Meteorologico Nacional (SMN) 1982),
based on 10 years of data from the weather station Ponton Pnicticos Recalada, located
in the outer estuary (Fig. 8.1), show that the winds generally range from southwest-