CHAPTER 9·' Geomorphological and Physical Characteristics of the Bahia Blanca Estuary
199
However, the analysis of an up to date chart made in 1990 indicates that marked
differences exist between two portions located to the north and south, respectively, of
a imaginary line running approximately parallel to the northern shore of Bahia Falsa.
The northern portion has a funnel shape and, although dominated by the Principal
Channel, has a large number of tidal channels and creeks that drain the flats. Numerous small, irregularly shaped islands top the flats. Very few of them have areas in excess of 1.5 km 2 . Even the large islands such as Bermejo and Trinidad, are actually a
combination of relatively small areas of dry land surrounded by high tidal flats.
On the other hand, the southern portion is dominated by the large channels named
Bahia Falsa and Bahia Verde. The head of both channels have the largest lower flat
area in the estuary and high flats are only found very close to the islands and in a
narrow stretch along the inner shore (Fig. 9.1).
Montesarchio and Lizasoain (1981) estimated the areas of the different environment
within the system. The total surface is approximately 2300 km2, corresponding only
410 km 2 to the islands, the intertidal sector covers 1150 km2 whereas the subtidal one
is 740 km 2 . Following the division proposed here, the largest intertidal and island areas are found on the northern sector meanwhile the converse is true for the southern
sector. There are no significant differences in areal coverage between neap and spring
conditions. The shores of the islands and inner coast are formed, in most cases, by a
1-2 m cliff. Normally the neap tides reach only to the bottom of the cliff, whereas the
spring tides rise to the middle or upper level of the cliff.
9.3.1
Geomorphology of the Tidal Channels
Most of the studies made in the Bahia Blanca Estuary have been concentrated on the
Principal Channel, the mouth of the major secondary channels flowing into it and on
the Bermejo Channel. There is no present bathymetry from the Falsa, Verde and
Brightman Bays except for very old surveys of their mouths and middle portions by
the Servicio de Hidrografia Naval (Hydrographic Chart H-212).
The first reconnaissance survey of the mouth of the estuary was made by Captain
Fitz Roy in 1833 on the HMS Beagle (coincidentally while Darwin was excavating the first
Megatherium fauna near Monte Hermoso Light, Fig. 9.1). Although maps of the area span
from 1854 to the present, last century charts concentrated on the external portion only.
The channel was actually surveyed after 1902 when Ingeniero White was established
as the main commercial port and Puerto Belgrano became the largest naval base in the
country. Several other harbours were constructed within short time, allover the northern
margin of the Principal Channel (Puerto Rosales, Puerto Galvan and Puerto Cuatreros).
All surveys made of the Principal Channel concentrated on the navigation channel and the entrances to the harbours. In 1983 a program to provide a morphologic
characterization of this channel was started. Detailed surveys were made from the
mouth and external reaches headward. General descriptions of different sectors were
presented by Aliotta and Perillo (1987), Gomez and Perillo (1992), Perillo and Cuadrado
(1991), Cuadrado and Perillo (1996), Perillo and Sequeira (1989) and Gomez et al. (1997).
All these studies were made with precision echosounder, electronic positioning system and side scan sonar. An integrated analysis of these separate studies will be provided heretofore from the inner portion seaward.
199
However, the analysis of an up to date chart made in 1990 indicates that marked
differences exist between two portions located to the north and south, respectively, of
a imaginary line running approximately parallel to the northern shore of Bahia Falsa.
The northern portion has a funnel shape and, although dominated by the Principal
Channel, has a large number of tidal channels and creeks that drain the flats. Numerous small, irregularly shaped islands top the flats. Very few of them have areas in excess of 1.5 km 2 . Even the large islands such as Bermejo and Trinidad, are actually a
combination of relatively small areas of dry land surrounded by high tidal flats.
On the other hand, the southern portion is dominated by the large channels named
Bahia Falsa and Bahia Verde. The head of both channels have the largest lower flat
area in the estuary and high flats are only found very close to the islands and in a
narrow stretch along the inner shore (Fig. 9.1).
Montesarchio and Lizasoain (1981) estimated the areas of the different environment
within the system. The total surface is approximately 2300 km2, corresponding only
410 km 2 to the islands, the intertidal sector covers 1150 km2 whereas the subtidal one
is 740 km 2 . Following the division proposed here, the largest intertidal and island areas are found on the northern sector meanwhile the converse is true for the southern
sector. There are no significant differences in areal coverage between neap and spring
conditions. The shores of the islands and inner coast are formed, in most cases, by a
1-2 m cliff. Normally the neap tides reach only to the bottom of the cliff, whereas the
spring tides rise to the middle or upper level of the cliff.
9.3.1
Geomorphology of the Tidal Channels
Most of the studies made in the Bahia Blanca Estuary have been concentrated on the
Principal Channel, the mouth of the major secondary channels flowing into it and on
the Bermejo Channel. There is no present bathymetry from the Falsa, Verde and
Brightman Bays except for very old surveys of their mouths and middle portions by
the Servicio de Hidrografia Naval (Hydrographic Chart H-212).
The first reconnaissance survey of the mouth of the estuary was made by Captain
Fitz Roy in 1833 on the HMS Beagle (coincidentally while Darwin was excavating the first
Megatherium fauna near Monte Hermoso Light, Fig. 9.1). Although maps of the area span
from 1854 to the present, last century charts concentrated on the external portion only.
The channel was actually surveyed after 1902 when Ingeniero White was established
as the main commercial port and Puerto Belgrano became the largest naval base in the
country. Several other harbours were constructed within short time, allover the northern
margin of the Principal Channel (Puerto Rosales, Puerto Galvan and Puerto Cuatreros).
All surveys made of the Principal Channel concentrated on the navigation channel and the entrances to the harbours. In 1983 a program to provide a morphologic
characterization of this channel was started. Detailed surveys were made from the
mouth and external reaches headward. General descriptions of different sectors were
presented by Aliotta and Perillo (1987), Gomez and Perillo (1992), Perillo and Cuadrado
(1991), Cuadrado and Perillo (1996), Perillo and Sequeira (1989) and Gomez et al. (1997).
All these studies were made with precision echosounder, electronic positioning system and side scan sonar. An integrated analysis of these separate studies will be provided heretofore from the inner portion seaward.