Morphological and Hydrodynamic Changes in the Lower Estuary of the Senegal River: Effects on the Environment of the Breach of the ‘Langue De Barbarie’ Sand Spit in 2003 - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 36

Table 2 Variations of the gap width and the length of the northern portion of the Langue de Barbarie

Date Breach Langue de Barbarie

Width (m) Expansion/decline (m) Length (m) Extension/drop (m)

Oct.-04-2003 04 - &7,000 -

Oct.-14-2003 273 269 6,497 -503

Oct.-06-2006 1,920 1,467 6,471 -26

Oct.-06-2009 2,374 454 6,408 -63

Oct.-06-2012 2,168 -206 7,612 1,204

Oct. 2003-Oct 2012 - 2,164 612

(Source images www.usgs.gov )

From 2011, there has been a relative stability of the size
of the breach which fluctuates between 2,500 and 2,700 m.
The width of 3.1 km measured by the US Army (Barry and
Kraus 2009 ) has not been found in our series of images. The
channel consequently seems to reach a critical size which
can cause weakening of the sandy spit. This threat is now
proven with the appearance of two new openings south of
the breach of 2003. Monitoring of these two openings is
essential because of the challenges to the evolution of the
lower estuary. What is now the probable evolution for the
lower estuary of Senegal River and the Gandiolais area?
Prospective studies should allow a better vision of the
possible patterns of evolution of the area at the morpho-
logical level and especially the socioeconomic and socio
environmental changes (Fig. 9 ).

access to drinking water for basically underprivileged
populations, land loss due to erosion, hydrodynamic mod-
ifications, and the reduction of freshwater supplies. Any
problems already present in the estuary were exacerbated by
the opening of the breach. The socioeconomic conse-
quences, such as income loss related to the impossibility of
practicing market-gardening, exodus towards urban areas
and extreme cases of clandestine immigration on board
fishing boats, also constitute many obstacles to the sus-
tainable development of the whole region.
The opening of the Langue of Barbarie sand spit, in an
emergency situation, fulfilled its primary objective, which
was to preserve St. Louis from flooding. However, no
accompanying measures were taken to mitigate its pre-
dictable effects on the environment of the estuary. The
negative impacts on hydrodynamics, salinization of water
and land, and the morphology of the lower estuary are such
as to naturally lead to questions on the appropriateness and
relevance of this government action.
The vulnerability of the Gandiolais region has both natural
and anthropogenic origins. The climate acts through reduction
in precipitation, rise of temperatures and physical (gravita-
tional water and groundwater) and physiological (plant spe-
cies and animal) evaporation; while the estuarine location (at
below sea level) supports the penetration of sea water into the
depressions and backwater tributaries of the river.
The Diama dam, as a result of the way it is managed,
especially in periods of low water (closing of the floodgates
for approximately 7 months), upsets the balance of river-
marine dynamics by storing water upstream, resulting in an
exclusively marine dynamics downstream.
The breach, through the replacement and the closing of
the previous river mouth, has accentuated the effects of
marine dynamics such as erosion and the salinization of
land and water. Today, all of these factors operate together
in the lower estuary, causing an upheaval of the local
environmental and socioeconomic situation.

Conclusion

The lower estuary of the Senegal River is a structurally
fragile, unstable area, changing very rapidly depending on
climatic, hydrodynamic and socioeconomic conditions. Its
evolution, since geological times, shows its strong depen-
dence on climatic and hydrodynamic factors. The change of
configuration of the Senegal River basin resulting from the
implementation of structural installations like the Diama
and Manantali dams was not without environmental impacts
on the estuary, whose cycles of evolution were conse-
quently broken.
The opening of the breach on the Langue de Barbarie, in
fact, corresponds to the displacement of the Senegal River
mouth by 30-7 km downstream from St. Louis. Originally
designed as a temporary structure intended to prevent
flooding of the city of St. Louis, the breach became estab-
lished and was accompanied by multiple environmental and
socioeconomic problems. Thus, we observe salinization of
surface water and groundwater, and of land, difficulties of