chapter - Atmospheric and Oceanic Science

The sub-basin of the Paraná River can be divided in two parts according to its
characteristics of height: upper and lower. The upper basin extends from the
sources of Paranaiba and Grande rivers up to the tributaries of the oriental region
of the Paraguay and Northwest of Misiones; it occupies a higher plane and its slope
is more significant that facilitates the water runoff. The lower basin, except for the
hilly region of the left riverbank, between the Corrientes and Gualeguay rivers, is a
continuation (due to its topography and geology) of the right part of the basin of the
Paraguay that is an immense plain of very scarce and uniform slope.
The sub-basin of the Paraguay River is an immense alluvial plain of very
scarce and uniform slope, except for the southern part of the left riverbank between
the Apa and Confluencia Rivers that presents a hilly landscape with valleys of regular
slope, and excluding as well the regions where are located the sources of
Pilcomayo and Bermejo rivers.
The sub-basin of the Uruguay River presents very different characteristic. The
terrain's landscape is complex, with numerous valleys and a branched fluvial system,
formed by water courses of short range and marked slope. Actually, this subbasin
lacks of expansion area, therefore can be considered as both, reception and
discharge basin.
As a resume, La Plata basin presents two well differentiated large regions. The
human relation with these two regions is also different. In the oriental part with
larger slopes, there is an important source of hydropower while in the occidental
part, large and long floods are the major concern.
4.6. Environmental problems
Physiography and Hydrology
The major concerns in the region are the floods, due to the damage they cause
in almost the whole basin (losses of human lives and considerable damages to infrastructures
and economy), mainly in the urban areas. This is the result of a complex
human interaction with the environment, where it is not absent the lack of planning
and the poverty problem, since most of those damaged by this phenomenon are the
poorest sectors of the society that, at a large extent, occupy precarious settlements
in easily floodable areas. Provinces of the Northeaster Argentine periodically have
floods as a result of the overflow of the three main rivers of the La Plata basin
(Paraná, Uruguay and Paraguay).
The extensive deforested areas, the acceleration of flood frequency and the
disordered riverside population's growth that occupy the flood plains, increase the
problem. The existent scientific literature indicates that the biggest events in floods
of disastrous characteristics are associated to the El Niño phenomenon, but they
would also be influenced by regional forcings of the climate.
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