EXECUTIVE SUMMARY
The hydrologic and environmental impacts that the proposed Hidrovia
navigation pro
ject would have on the Pantanal of Mato Grosso are evaluated in this
report. The Pan
tanal is a seasonally inundated depression, characteristically a wetland
(or closely related
wetlands), wholly contained within the Upper Paraguay river basin. It
encompasses an
area of 136 700 km2 in the states of Mato Grosso and Mato Grosso do Sul,
in Central
Western Brazil. The Hidrovia project entails navigational improvements
along the exist
ing Paraná-Paraguay Waterway, which links five countries of South
America: Argentina,
Bolivia, Brazil, Paraguay, and Uruguay. The project considers extensive
river engineering
works, including channel straightening, dredging, blasting of rocky
sills, and other struc
tural interventions to render 3442 km of the river navigable for oceangoing vessels.
The affected region would be from the downstream point at Nueva Palmira,
Uruguay, to
the upstream point at Cáceres, Brazil, near the headwaters of the Upper
Paraguay river.
At issue is the impact that extensive channel modifications will have on
the Pantanal, the
largest remaining wetland in the world.
The proposed navigational improvements are likely to have a
substantial impact on
the flood regime of the Upper Paraguay river. The degree of the impact
will vary de
pending on the type and extent of intervention and location along the
river. In particu
lar, channel straightening upstream of Corumbá will accelerate the
concentration of flood
runoff and increase the flood wave peak at Ladario, a key reference point
in the Pan
tanal, during high mean (2-yr), extraordinary (4-yr), and exceptional
(10-yr) floods. The
Upper Paraguay river upstream of Porto São Francisco (located 146 km
upstream of Co
rumbá) is incapable, without extensive artificial channel deepening, of
accomodating
ocean-going vessels (requiring a 3-m draft) throughout the year.
Currently, autodredging,
the river's natural self-cleaning/deepening process, provides a minimum
depth of 1.2 m,
except where rock outcrops do not permit autodredging to take place.
The longitudinal profile of the Upper Paraguay river is convex when
observed from
above, revealing the presence of substantial geologic controls. These
controls operate in
the form of rock outcrops on the banks or rocky sills in the middle of
the channel. The
Pantanal exists largely because of these geologic controls, which
influence the regional
flow patterns in at least three places: Amolar, Porto da Manga and Fecho
dos Morros.
The rocky sills act as natural dams; if they are removed, extensive areas
of Pantanal will
no longer be subject to seasonal flooding. Blasting rocky sills as a
means of deepening
the navigation channel will have an irreversible impact on the hydrology
of the Upper
Paraguay river. Furthermore, the removal of one rocky sill may lead to
the appearance
of another rocky sill which was previously submerged. This is a distinct
possibility in the
Upper Paraguay river, where rock outcrops have been documented to occur
every 40
km on the average, and where the prevailing channel slopes are so mild
(around 1-2
cm/km) that the backwater effect of a 0.5-m flow obstruction can be felt
for about 400
km upstream.
The acceleration of runoff concentration caused by navigational
improvements will in
tensify most annual floods, may reduce the recurrence interval of
multiannual droughts,
and may eventually lead to regional climatic changes in the direction of
greater aridity.
The Pantanal exists because its climatic/geologic/geomorphologic setting
conditions it to
retain water, sediment, and nutrients. Increases in flood magnitude will
result in increased
losses of sediment and nutrients.
The annual flooding of extensive areas of Pantanal serves the dual
purpose of effec
tively controlling overgrazing while replenishing the soil with
nutrients. In addition, the
seasonal flood pulse is instrumental in maintaining the extensive
grasslands, since com
peting vegetation types, particularly the woody species, are not well
adapted to extreme
alternations of saturation and desiccation.
Changes in hydrologic regime resulting in increased intensity of
floods and droughts
will impair nutrient replenishment in the Pantanal and lead to decreases
in biotic produc
tivity. These changes will produce a succession from herbaceous to woody
species, which
will eventually change the dominant character of the Pantanal, from
savanna woodlands
to more mesic forests. The open grasslands will shrink, and the cattle
raising industry
will be negatively impacted.
_ _ _