Chapter i
What Do We Know About the Geomorphology and
Physical Oceanography of South American Estuaries?
Gerardo M.E. Perillo . M. Cintia Piccolo . Mario Pino-Quivira
1.1
Introduction
As long as freshwater is discharged into the sea, there is the potential for the develop,ment
of an estuary. Although this concept appears to be simple, the marked differences in
geomorphologic, oceanographic, atmospheric and biogeochemical conditions that occur
along the coasts of the world result in a wide variety of estuarine types. The variety is so
large that several ways have been used as mean to define and classify them (Perillo 1995a).
Although work in estuaries can be traced back to the beginning of the century, a
formal definition was not available up to the '50S when studies by Ketchum (1951) first,
and then by Pritchard (1952), shaped the basic concepts about their geomorphologic
and physical characteristics. Since them, the number of researchers and the knowledge about estuaries worldwide have bursted. Fifty years ago the estuarine oceanography was concentrated on Chesapeake Bay and few estuaries in Europe. Nowadays
estuarine research has spread so much that we have a very well defined knowledge of
their geomorphology and dynamics to the point that we are seriously developing classification schemes that are abstracting this vast knowledge.
Etymologically, estuary derives from the Latin word" aestus" which means "of tide".
That is to say that the term estuary has to be applied to any coastal feature in which
the tide has special significance. Although estuaries may be regarded only by their
physiographic parameters: that is, their geomorphology and hydrology, their biological
and chemical components should also be considered. Any comprehensive definition
must necessarily include all these aspects.
After analyzing over 40 different definitions introduced in encyclopaedia, dictionaries
but particularly from the specialized literature, Perillo (1995b) proposed a new definition of estuaries that incorporates features never discussed in previous definitions as:
"An estuary is a semi-enclosed coastal body of water that extends to the effective limit of tidal influence, within which sea water entering from one or more free connections with the open sea, or any
other saline coastal body of water, is significantly diluted with fresh water derived from land drainage, and can sustain euryhaline biological species from either part or the whole of their life cycle."
In considering the estuarine distribution, we are going to employ this definition as
the basic criteria in establishing the presence of an estuary along the coastline. The
coexistence of tidal action and intrusion of sea water is formally established. In fact,
the estuary extends inland up to the effective limit of tidal action, but it is within the
segment that stretches from that inland point to the mouth in which seawater dilution can occur. This model permits the differentiation within the estuary of the three
sectors proposed by Dionne (1963) (Fig. 1.1) and further described by Dalrymple et al.
(1992), and also allows for estuaries that have only one or two of these sectors.
What Do We Know About the Geomorphology and
Physical Oceanography of South American Estuaries?
Gerardo M.E. Perillo . M. Cintia Piccolo . Mario Pino-Quivira
1.1
Introduction
As long as freshwater is discharged into the sea, there is the potential for the develop,ment
of an estuary. Although this concept appears to be simple, the marked differences in
geomorphologic, oceanographic, atmospheric and biogeochemical conditions that occur
along the coasts of the world result in a wide variety of estuarine types. The variety is so
large that several ways have been used as mean to define and classify them (Perillo 1995a).
Although work in estuaries can be traced back to the beginning of the century, a
formal definition was not available up to the '50S when studies by Ketchum (1951) first,
and then by Pritchard (1952), shaped the basic concepts about their geomorphologic
and physical characteristics. Since them, the number of researchers and the knowledge about estuaries worldwide have bursted. Fifty years ago the estuarine oceanography was concentrated on Chesapeake Bay and few estuaries in Europe. Nowadays
estuarine research has spread so much that we have a very well defined knowledge of
their geomorphology and dynamics to the point that we are seriously developing classification schemes that are abstracting this vast knowledge.
Etymologically, estuary derives from the Latin word" aestus" which means "of tide".
That is to say that the term estuary has to be applied to any coastal feature in which
the tide has special significance. Although estuaries may be regarded only by their
physiographic parameters: that is, their geomorphology and hydrology, their biological
and chemical components should also be considered. Any comprehensive definition
must necessarily include all these aspects.
After analyzing over 40 different definitions introduced in encyclopaedia, dictionaries
but particularly from the specialized literature, Perillo (1995b) proposed a new definition of estuaries that incorporates features never discussed in previous definitions as:
"An estuary is a semi-enclosed coastal body of water that extends to the effective limit of tidal influence, within which sea water entering from one or more free connections with the open sea, or any
other saline coastal body of water, is significantly diluted with fresh water derived from land drainage, and can sustain euryhaline biological species from either part or the whole of their life cycle."
In considering the estuarine distribution, we are going to employ this definition as
the basic criteria in establishing the presence of an estuary along the coastline. The
coexistence of tidal action and intrusion of sea water is formally established. In fact,
the estuary extends inland up to the effective limit of tidal action, but it is within the
segment that stretches from that inland point to the mouth in which seawater dilution can occur. This model permits the differentiation within the estuary of the three
sectors proposed by Dionne (1963) (Fig. 1.1) and further described by Dalrymple et al.
(1992), and also allows for estuaries that have only one or two of these sectors.