GEO Brasil - UNEP

) The gradual expansion of the city along estuaries and
lagoons towards mangrove swamps causes serious
problems during the rainy season Lack of urban
planning, inadequate infrastructure for industrial plants
and uncontrolled human occupation of these lowlands
increase potential risks factors in the event of a rise in
the sea level
c) Recife has a long history of coastal erosion, particularly
around the city of Olinda Seawalls and buttress dams
were built in order to protect the city The interruption
in the coastal transportation of sediments led to the
erosion of the beaches immediately to the north of
each buttress dam, which led to the construction of
other dams The cumulative effects of erosion
extending from the dams towards the sea extend 30
km towards the north of Olinda
d) When comparing 1975 and 1984 ortophotomaps of the
whole coastal area, it is possible to observe up to 25-m
retrogradation of certain coastline segments
and the southern borders of the state were found to be
suffering erosion The causes of such erosion were
associated to diverging zones leading towards the actual
leeway These were generated by the dispersion of wave
rays or the occurrence of shade-zones for waves from
southeast to south-southeast (the most energetic), making
the northeastern waves more effective The sediment deficit
in these diverging zones seems to be the cause of erosion
in the southern part of the coastal plain, associated to the
Jequitinhonha river mouth, as well as the active cliffs
between Ponta do Corumbau and Prado, and in the Itaquera
region
In other coastal tracts, erosion is associated to regions where
there is accentuated intensification of the potential for drift
Other areas suffering from erosion are:
Coastal strip between Coroa Vermelha and Ponta
Grande;
Southern part of Ponta da Baleia; and
Caçumba Island
the state of environment in Brazil
e) The beaches lost their sedimentary balance due to the
dams built along the rivers, repeated dragging of the
Recife Harbour (located on the Capibaribe river estuary),
and sand extraction from the mouths of the Jaboatão
and Doce rivers In addition, the presence of beach
sandstone prevents sand from moving from the
internal continental platform to the beach, especially
after a storm, when part of the sand moves towards
deeper areas
f) It has been proved through measurement that the
relative sea level is rising HARARI and CAMARGO
(1994) observed a rise of 5-6 mm/year in Recife between
1948 and 1986, which could be related to neotectonic
settling, for example (MAGNO, 1989)
Recife seems to be sinking, and a 1-metre rise in the relative
sea level in that city would actually correspond to a smaller
rise in the global level of the oceans The physical effects of
floods and erosion are assessed quantitatively, whereas their
social and economic consequences are considered from
the qualitative point of view
Along the southern coast of the State of Bahia, several
coastal strips between the mouth of the Jequitinhonha River
Coastal erosion is associated to an essentially natural
phenomenon: the relative rise of average sea level However,
the result of human intervention on the coast (insufficient
sediments, dismantling of dunes, asymmetric sediment
distribution caused by buttress dams) accelerate this
process, contributing towards a high percentage of coastal
erosion
The silting process in a given water basin is closely
connected to erosion processes, since the latter supply the
matter which, once transported and settled, will generate
siltation Therefore, siltation is a direct consequence of
erosion
The retraction of the coastline constitutes a serious threat
to most coastal cities nowadays An estimated 70 percent
of all coastlines in the world are suffering from erosion
The main environmental impacts on the Brazil’s Coastal
Zone are associated to: introduction of nutrients; habitat
alteration or destruction; sedimentation changes;
overexploitation of fishing resources; industrial pollution,
mainly caused by persistent pollutants; and the introduction
of exotic species On a global scale, the eutrophication
deriving from the introduction of excessive anthropic
nitrogen, the contamination produced by domestic sewage
121