Brazil Harbors and Mangrove Forests Face New Strains
Long-term sea level measurements and topographic and cartographic
records for Brazil do not exist, but despite the belief of many
Brazilians that the level is dropping, tide gauge records from
1946 to 1988 show the relative sea level rose 5.6 mm per year,
although some of this may be related to neotectonic subsidence.
While Brazilians also believe that their 30 million population
is concentrated along the coast, actually only 20 percent live
in coastal counties, indicating Brazil is less threatened by sea
level rise than expected. But many regions and localities are
at risk.
A strip of land 33 meters wide, bordering the ocean or estuaries,
belongs to the federated government, with private use allowed
under specific regulations and payment of taxes. The funds for
protecting coastal areas, therefore, usually come from public
- municipal, state or federal - sources.
Coastal mangrove forests are under a strain now as they are being
developed for resorts, cut for fuel, used as building material
or used for landfill. Rapidly rising seas will bring a new threat
as they inundate the mangroves. The seas will also threaten the
breakwaters and sea walls protecting ports and terminals - important
to domestic and international trade - and these facilities will
be flooded more frequently.
Recife, a city of two million people and the largest metropolitan
region in Northeastern Brazil, was selected as a case study on
the possible consequences of sea level rise of one meter. The
area has a high population density, 40,000 per square kilometer,
and suffers from coastal erosion problems, flooding, and inappropriate
drainage. The city is at the mouth of two rivers and is cut by
several canals. The entire business area would be directly affected
by rising seas; parts of downtown are already flooded by exceptionally
high tides or river runoff. Large areas with poor drainage and
prone to temporary flooding would suffer worse problems, complicating
sanitation, traffic and urban development. Fifty square kilometers
of low-lying coastal plains - more than half of it occupied by
mangroves - would be totally inundated.Gradual expansion along
the margins of estuaries and lagoons toward the mangroves has
caused serious problems during the rainy season; favelas have
invaded some of the mangroves. There is no control of occupation
in low areas, little urban planning, and utilities have been built
on unsuitable sites.
Throughout a long history of shoreline erosion- the shoreline
has receded up to 25 meters in some places - breakwaters, bulkheads
and groins have been built, but these interrupt transport of sediment
and lead to further beach erosion. The damming of rivers, dredging
of the port and mining of sand has further decreased the sediment
budget of beaches. Near shore reefs have provided some protection
to beaches, but the reefs might be submerged if sea level rose,
allowing larger waves to break on the vulnerable beaches. The
most valued beachfront in the city would recede 20 meters under
sea level rise. The authors recommend socioeconomic studies to
determine the size of the Recife population and its distribution,
the growth of the favelas, and the economic values in the risk
areas. A crucial question to be answered is which form of protection
is the most economical - sea walls or beach nourishment.
(Dr. Dieter Muehe and Dr. Claudio F. Neves, Universidade Federal
do Rio de Janeiro, Brazil)
