Management of a Tropical River: Impacts on the Resilience of the Senegal River Estuary - The Land/Ocean Interactions in the Coastal Zone of West and Central Africa - page 41

during the 1970s, but also exploited the higher levels of
rainfall, particularly prevalent during those years.
The Senegal River estuary is an extremely fragile envi-
ronment; it is threatened by natural hazards such as the
recurrent floods. This situation stems from the physical
environmental conditions. The risk is thus permanent, which
can be exacerbated by human presence and its multiple
actions on the environment. By interventions was generally
failed to seriously predict the effects induced, and they fre-
quently destabilized environments characterized by precar-
ious equilibriums. The new mouth of the Senegal River is
causing significant damage to the estuary. This arrangement
does not fail to change the hydrological regime of the estuary
and especially led to changes in estuarine ecosystems and
increased the vulnerability of the estuary. Anthropogenic
actions lead, most often, uncertainty of the occurrence of
catastrophic events. In this context, the domino effect can be
triggered, resulting in, as a result, increasing vulnerability.
The impacts associated with climate change will be much
more catastrophic in Africa because of the weakness of the
economy and the rapid growth of the coastal population
(Nicholls and Cazenave 2010 ). Climate change and rising of
sea levels will increase the risks to which the estuary of the
Senegal River is already exposed, whereas the system has
low capacity to absorb disturbance.
Enhancing disaster risk reduction before a disaster
occurs, and also during the reconstruction process, requires
enhanced knowledge regarding the most vulnerable groups,
the areas at risk, and the driving forces that influence and
generate vulnerability and risk (Birkmann 2007 ; Bogardi
and Birkmann 2004 ). Better take into account of the
physical environment in policy development is essential.
Environmental assessment aims to contribute to environ-
mental awareness among proponents and competent
authorities and to environmental protection by requiring the
ex ante evaluation of the environmental impacts of a wide
range of public and private initiatives such as spatial plans
(Runhaar et al. 2013 ). The vulnerability of the Senegal
River estuary area was accentuated by the water manage-
ment of the Senegal River with the opening of the new
mouth that was made without prior impact assessment. To a
certain extent, the resilience of the system is strongly found
to disturb. For this reason, it is essential to carry out detailed
studies of the impacts of development on the hydrological
regime of the river and the consequences in the upstream
and downstream portions. All positive and negative impacts
should be considered before making a layout and fairly
weigh the consequences of choices.
In this chapter, the consequences of the watershed
management of Senegal River in the estuarine area are
analyzed. This last appears as a space where a variety of
risk factors which may cause significant damage. Its occu-
pation makes these areas vulnerable for local riparian. The

latter has a low capacity of resilience from watershed
management issues.

Human Pressures and Functioning
of the Senegal River Estuary

The presence of a risk linked to existence water resources in
an area determines the way the population exploit it; that
situation influences strongly the type of structure and
management settled consequently (Beucher and Rode
2009 ). The situation of the Senegal River obeys to this
concept. Somehow, it could be promoted some existing
geo-engineering technologies when used properly have low
or no significant negative impacts (Olson 2012 ).
Climatic variability is determining factors in risk man-
agement. In the 1970s, the Sahel region experienced a
period of exceptional water deficit in terms of duration and
intensity. This period of rainfall decreasing is still on going
(Dai et al. 2004 ; L'Hôte et al. 2002 , 2003 ) although less
strong since the mid 1990s than during the 1980s. The
average rainfall over the last 37 years has remained below
the 1900-1970 average in this region with large-scale
consequences (Hulme et al. 2005 ). For almost all rivers of
West Africa has decreased (Mahé and Paturel 2009 ). More
than 125,000 people died in the African French-speaking
countries during this period, in addition to the successive
food shortages of the 1972-1974 period (Dauphine 2003 ). A
loss of 600,000 tonnes of the grain crops was also recorded,
equivalent to about a 15 % reduction in average annual
income. In livestock farming and during the same period of
1970s, there was an 80 % cattle loss (Guillaumie et al.
2005 ). As a consequence, the survival of the socio-eco-
logical system was endangered, in addition to being subject
to severe risks that resulted in destructive disasters. Water
control appeared to be essential for reducing the system's
vulnerability. Thus, the ''taming'' of nature became a sig-
nificant challenge for riparian states and the construction of
the Diama and Manantali dams on the Senegal River
(Fig. 1 ) was the solution adopted to ensure sustainable
development and food security.
The Diama Dam resulted in considerable modification of
the hydrological regime of the Senegal River downstream
of the structure. Freshwaters are stored in the upstream of
the dam. They arrived in the estuary during the rainy season
(Saint-Louis station), when dam gates are opened and when
they are some releases from Diama Dam. In addition, the
principle of functioning of the Diama dam is to close it in
periods of low water to prevent the intrusion of saltwater
and to open in period of floods to allow floodwaters to flow
downstream (OMVS 2003 ). The role of the Diama Dam in
controlling the Senegal River is strengthened by the Man-
antali Dam.