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 27

Fig. 3 Spatial and temporal mobility of the Langue de Barbarie and the Senegal River mouth from 1970 to 2002 and turbid plume dispersion
(Niang 2002 )

Context of Opening

rainfall, the hydrological functioning of the system was
found to be highly dependent on the management options of
the dams.
The chronic instability of the Senegal River mouth (Gac
et al. 1981 ; Kane 1985 ; Nakamura et al. 2002 ) grew blurred,
giving way to a regular progression of the Langue de Bar-
barie towards the south. This southward progression of the
spit constitutes indeed a characteristic of the Langue de
Barbarie.
In the case of extreme events, the flood risks are also
multiplied. The vulnerability of the city of St. Louis to
floods has increased significantly due to the double influ-
ence of maritime and fluvial waters on the estuary.
The context of the emergency that led to the opening of
the breach makes it possible to understand, partly, the
impacts that it caused on the environment of the estuary.
Monitoring the dynamics of the breach gives us hope for the
definition, in the long term, of a model of evolution of the
Senegal River estuary.

The establishment of dams on the Senegal River, especially
the Diama dam, initiated a new operating pattern in the
lower part of the basin. Sediment retention at Diama is one
of the first elements that influenced the evolution of the
lower estuary. Indeed, under the predominant effect of
marine dynamics, the sandy spit is subjected to intense
degradations. The immediate consequence is a significant
reduction in the depth and the width of the estuarine area
which thus prevents a normal discharge of floodwaters to
the sea, causing flooding in St. Louis and its environs (Dia
2000 ).
A city that is hardly 7 m above sea level, St. Louis,
because of its configuration and its urban dynamic space, is
highly vulnerable to flooding from rain and rivers. Storm
floods are primarily related to the coverage of wetlands,
about 900 ha, which were previously able to absorb these
waters. Low parts of the city are flooded when daily rainfall