M.B. Framifian . M.P. Etala . E.M. Acha . R. A. Guerrero· C.A. Lasta . O.B. Brown
model (Fig. 8.5). The location of the maximum surge currents is coincident with those
of the fine mesh model and their values are similar. Another maximum is observed
entering the estuary from the south. This alongshore current is generated as a response
to the higher surge levels towards the coast of Punta Rasa (Fig. 8.5) and is a typical
feature in these situations. The water level at Buenos Aires at the time of the peak was
accurately reproduced by the model, although its decrease was delayed probably due
to the poor temporal and spatial resolution of the available wind fields (Etala 1996a).
The analysis of a similar, but less intense, event can be found in Etala (1996b), where
an improved version of the model is tested in a pre-operational stage.
8.4
Salinity and Water Stratification
8.4.1
Background
Studies in the Rio de la Plata are technically and financially difficult because of its
great geographic extent. A large number of observations are needed to obtain a synoptic description of the estuary and to resolve the spatial and temporal variability.
Many investigations of its physics, chemistry, geology and/or biological properties have
been conducted in the area. Most of them include salinity measurements, which were
used by several authors to describe the salinity fields of the upper and lower estuary.
The upper part of the Rio de la Plata has salinity less than 0.4, and the outer region
presents high spatial variability, with salinity values from 0-33 (CARP 1989). Descriptions of the salinity field in the upper estuary can be found in CARP (1989), Bazan
and Janiot (1991), Bazan and Arraga (1993); here, the focus will be on the salinity fields
of the outer estuary. On the southern coast, based on in situ observations, studies
(Urien 1967; CARP 1989) have located approximately the landward limit of salt intrusion in the area of"El Codillo". On the northern coast, Nagy et al. (1987) located this
limit between Punta Tigre and Punta Brava. Remote sensing studies give a more complete description of its spatial and temporal distribution, based on the distribution of
the associated turbidity maximum at the surface (Framifian and Brown 1996), as reviewed earlier. Previous studies of the vertical structure suggest a highly variable regime. Ottman and Urien (1965) analysed the relation between the evolution of the
salinity profile and the tides and wind. They compared hourly surface and bottom
salinity data measured at a fixed station in the outer region (at Ponton Practicos
Recalada), during periods of 15 days for each season in three consecutive years, with
tidal height and wind speed and direction. Their conclusion was that, at times of eastward winds, a fresh-water layer was found at the surface, and that in light wind or calm
conditions, the variation in salinity follows the tide. The sampling was limited to two
levels which restricts analysis of the vertical structure. CARP (1989) presented the
analysis of vertical profiles obtained from bottle-samples at several stations in the outer
estuary taken between 1981 and 1985. High spatial variability of the vertical structure
was found, as well as strong stratification, during events of high river flow.
Based on the distribution of salinity, the parameter controlling the density in the
estuary, several attempts have been made to understand the river circulation. Ottman
and Urien (1965) suggested that the shallow banks in the outer estuary split the river
model (Fig. 8.5). The location of the maximum surge currents is coincident with those
of the fine mesh model and their values are similar. Another maximum is observed
entering the estuary from the south. This alongshore current is generated as a response
to the higher surge levels towards the coast of Punta Rasa (Fig. 8.5) and is a typical
feature in these situations. The water level at Buenos Aires at the time of the peak was
accurately reproduced by the model, although its decrease was delayed probably due
to the poor temporal and spatial resolution of the available wind fields (Etala 1996a).
The analysis of a similar, but less intense, event can be found in Etala (1996b), where
an improved version of the model is tested in a pre-operational stage.
8.4
Salinity and Water Stratification
8.4.1
Background
Studies in the Rio de la Plata are technically and financially difficult because of its
great geographic extent. A large number of observations are needed to obtain a synoptic description of the estuary and to resolve the spatial and temporal variability.
Many investigations of its physics, chemistry, geology and/or biological properties have
been conducted in the area. Most of them include salinity measurements, which were
used by several authors to describe the salinity fields of the upper and lower estuary.
The upper part of the Rio de la Plata has salinity less than 0.4, and the outer region
presents high spatial variability, with salinity values from 0-33 (CARP 1989). Descriptions of the salinity field in the upper estuary can be found in CARP (1989), Bazan
and Janiot (1991), Bazan and Arraga (1993); here, the focus will be on the salinity fields
of the outer estuary. On the southern coast, based on in situ observations, studies
(Urien 1967; CARP 1989) have located approximately the landward limit of salt intrusion in the area of"El Codillo". On the northern coast, Nagy et al. (1987) located this
limit between Punta Tigre and Punta Brava. Remote sensing studies give a more complete description of its spatial and temporal distribution, based on the distribution of
the associated turbidity maximum at the surface (Framifian and Brown 1996), as reviewed earlier. Previous studies of the vertical structure suggest a highly variable regime. Ottman and Urien (1965) analysed the relation between the evolution of the
salinity profile and the tides and wind. They compared hourly surface and bottom
salinity data measured at a fixed station in the outer region (at Ponton Practicos
Recalada), during periods of 15 days for each season in three consecutive years, with
tidal height and wind speed and direction. Their conclusion was that, at times of eastward winds, a fresh-water layer was found at the surface, and that in light wind or calm
conditions, the variation in salinity follows the tide. The sampling was limited to two
levels which restricts analysis of the vertical structure. CARP (1989) presented the
analysis of vertical profiles obtained from bottle-samples at several stations in the outer
estuary taken between 1981 and 1985. High spatial variability of the vertical structure
was found, as well as strong stratification, during events of high river flow.
Based on the distribution of salinity, the parameter controlling the density in the
estuary, several attempts have been made to understand the river circulation. Ottman
and Urien (1965) suggested that the shallow banks in the outer estuary split the river