SENEGAL: Senegal's Shoreline is Already Receding and
Salinity Threatens Wetlands
All effects of sea level rise would impact the coast of Senegal
- the estuaries, the delta, the long, sandy ocean stretches -
but erosion of residential, industrial and tourist areas would
be the most serious. More than half the population and most of
the economic activity is concentrated in the coastal zone, and
the high birth rate and expansion of the tourist industry are
likely to exacerbate problems. Many thousands of international
tourists, particularly from France, supply important foreign exchange
to the country. The most feasible response is likely to be nourishment
of beaches to protect the string of single row tourist houses
and villas built close to the shore.
Two million people and 90 percent of the industry are in the capital
city of Dakar and surrounding metropolitan area where the shoreline
is already retreating. The city itself is built on cliffs which
are, in places, slowly eroding. The Dakar Harbor, crucial to the
economy, needs upgrading.
South of Dakar are large and important areas of marshes and mangroves
where lower rainfall in the last few years has increased salinity,
sometimes killing these wetlands which , while not highly populated,
support fisheries and are valuable to the agriculture sector.
Not enough space is available for them to migrate, and with no
feasible, cost-effective protection measures, a one-meter sea
rise would inundate 2150 km2 of land, killing all existing mangroves.
(There is little evidence of subsidence along the Senegal coast;
global sea level rise and relative sea level rise are synonymous.)
The delta at the mouth of the Senegal River is used extensively
for agriculture, particularly rice and sugar cane. The river flow
is very seasonal; at its lowest stages, tide flows as far as 230
km upstream, carrying salt water with it. A dam has been built
to prevent the salt intrusion, and another dam has been built
upstream for hydroelectricity and irrigation. However, both dams
prevent sediment from enriching the delta.
Erosion on the open coast, not inundation, accounts for most
of the value at risk, It threatens the loss of structures and
degradation of beaches. Buildings alone valued at $500 - $700
million (12 - 17 percent of the 1990 GNP). Because they are so
close to the shore, tourist structures represent 20 - 30 percent
of the value at risk. The major cost of protection of medium to
high development would amount to $255 -$845 million. This would
consist mainly of beach nourishment for the tourist resorts, accounting
for 75 - 85 percent of total expenditure. From 110,000 t o 180,000
people would be displaced as the ocean rises. The authors suggest
that the Government, therefore, should increase tourist planning
adaptation measures:
-
Make future developments more concentrated, avoiding single
rows of houses and villas
-
Establish a setback line for new buildings
-
Minimize coastline development to restrict protection costs
-
Allow only easily moved tourist structures near the beach
-
Encourage development away from the coastal zone
Saltwater intrusion into the aquifers and surface water, unless
it is offset by increased rainfall, poses a further risk of sea
level rise, though these risks have not been quantified. The salt
could damage agricultural production. Intrusion is already occurring
in the aquifer supplying Greater Dakar, as demand exceeds recharge.
With the rapidly expanding population, demand is likely to increase
even more.
Follow-up studies, for instance of historical shoreline evolution
or improved topographic analysis, would provide better data for
estimating the physical impact of sea level rise and a basis for
developing plans to manage it. They might help answer the question:
with accelerated sea level rise, what are realistic responses
to the mangroves? An evaluation of the long-term viability of
Dakar's drinking-water aquifer should consider population growth
and climate change, including sea level rise and change in precipitation.
Examination should be made of other coastal impacts of climate
change:
a) the changing size and direction of waves
b) storm frequency and intensity
c) upwelling of deep ocean waters
d) precipitation and run-off
e) sediment supply
(Karen C. Dennis, University of Maryland, USA, Isabelle Niang-Diop,
Universite Cheikh Anta Diop, Senegal, and R.J. Nicholls, University
of Middlesex, UK)
