chapter - Atmospheric and Oceanic Science

Physiography and Hydrology
The Pantanal itself is the downstream part of this sub basin, an area of 138000
km 2 . 50-60% of the water volume and sediments from the tributaries are retained in
the flood plain, which reduces hugely the volume downstream. Since precipitation
is smaller than evaporation, in the Pantanal there is a mixture of swamp vegetation
proper of the rainy station and of savannah at the dry season.
From the Pantanal exit up to the outlet of the Paraguay, the river flows along
a plain with low coasts, which facilitates the floods in both the Paraguayan and
Argentine territories. In the Low Paraguay the river receives an important tributary,
the Bermejo River. From the outlet of the Bermejo River, the riverbed of the
Paraguay River is characterized by its lack of stability, due to the solid discharge of
this tributary. The decrease of the capacity of discharge of the Paraguay River is
associated to the hydrodynamic linger produced by the Paraná River, causing a
reduction of speed from the confluence area up to more than 340 km upstream.
The Paraguay River presents the major discharges in Autumn-Winter and low
waters in Spring-Summer, with regular regime and slow variations. In this behavior
it is important the influence of the Pantanal, diminishing the propagation of the
large discharges and the length of the low water. But it is also a consequence that
in the Low Paraguay basin the evaporation balances the rainfall in Summer, while
it is very inferior to it in Autumn (Barros et al. 2004).
Figure 4.3 illustrates the annual hydrological cycle of the Paraguay River in
some sections. It can be observed the retard effect in the freshet wave with regard
to the one at the North of the Pantanal. The Cáceres section in the Pantanal plateau
registers the largest flows in March, while in Porto Murtinho and Puerto Bermejo
they take place in June.
Fig. 4.3. Mean flows of the Paraguay River at different sections.
[ANA WWWeb, Mining of the Argentine Republic, WWWeb]
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