Environmental Engineering Reference
In-Depth Information
reasons
for
the
programme
of
large
hydro-agricultural
and also to consider aspects related to forecasting the future
evolution of the lower Senegal River estuary.
installations of the OMVS.
1
Since the early years of operation of large dams on the
Senegal River, many research studies have been devoted to
the consequences of these structures on the hydrological
cycle, water quality and environmental changes on the local
to regional scale (Diakhate
1988
; Kane
1997
; Equesen
1993
). A near unanimity has emerged about their appro-
priateness and their effects, some of which are considered
highly beneficial.
In 2003, the issue of water in the Senegal River basin has
raised new developments with the opening of a new chan-
nel. The creation of water reservoirs behind the dams offers
now the opportunity to develop the agriculture through
irrigation during a longer dry period. The return to better
rainfall conditions in 2003, particularly in the upper basin,
resulted in threats to the viability of the hydraulic installa-
tions and especially the city of St. Louis, in the lower part of
the Senegal River. To avoid flooding, the Government of
Senegal decided to open a channel, 7 km south of St. Louis,
on the night of 3-4 October 2003.
Designed specifically to allow a release of hydraulic
energy and preserve the city from flooding, this breach now
functions as the real mouth of the Senegal River. From an
initial width of 4 m, the opening today is more than 2 km
wide and the changes continue, since the baseline scenario
was that the gap would close very quickly.
However, this breach, the new mouth of the Senegal
River, is now considered as a real option for flood control of
the city of St. Louis, despite all the criticisms raised by
environmentalists. This explains the decision to pay great
attention to increasing knowledge of the Langue de Barbarie
and the evolution of the Senegal River's mouth. Indeed, at
present, the river mouth is the centre of wide-reaching pro-
jects whose results are likely to be predictable and harmful.
The purpose of this study, in addition to understanding
the dynamics of the breach, is to determine its major effects
on the functioning of the estuary at the hydrodynamic and
morphological level. It is based on an analysis of the evo-
lution of factors such as tidal levels, salinization of land and
water, and a cartographic analysis of morphological chan-
ges in the estuary.
The opening of the breach, a decision of the Government
of Senegal, has met expectations well; however, the absence
of accompanying measures and monitoring plans has
resulted in an environmental and socioeconomic disaster
unprecedented throughout the Senegal River estuary, which
is now severely threatened. It is therefore necessary to
identify research directions in the short and medium term
The Study Area
The Langue de Barbarie sand spit and the mouth are central
focus in the management of the Senegal River estuary. The
social environmental system is highly vulnerable to change
due to decade of various threats impacting the Senegal
River estuary (Kane
2010
). Vulnerability is related to the
damage which an ecosystem is likely to suffer following
natural or anthropogenic catastrophes (D'Ercole
1994
).
Vulnerability is a concept related to resilience which
translates the capacity and the mechanisms of response of a
community to a shock that is comparable to natural disasters
related to water (Berkes
2007
). To understand the current
configuration of the estuary, it is necessary to review recent
trends and especially the mechanisms that led to the current
situation.
The Senegal River Estuary
The Senegal River estuary, the lower part of the basin
(Fig.
1
), with landscapes strongly marked by salinity,
includes the Langue de Barbarie and its hinterland, also
named Gandiolais. The notion of an estuary of the Senegal
River has been widely discussed by experts on coastal
geomorphology such as Tricart (
1961
) who defended the
thesis of a pseudo-delta. Kane (
1985
and
1997
) talk of an
estuary despite the discharge of river water through a single
channel, a phenomenon that can be explained by the
hydrological regime and coastal dynamics in the lower part
of the Senegal River Basin.
This estuary was formed between 6800 and 4200 B.C.
by the formation of a lagoon behind coastal sand, the
Langue de Barbarie (Kane
1997
). The late Holocene evo-
lution has been studied by Elouard et al. (
1977
), Monteillet
(
1977
and
1988
), Kane (
1985
) and Diouf (
1989
), mainly on
the basis of an analysis of the sea level variations.
The city of St. Louis was built in the estuary on flat land
and semi-fixed dunes with alternating mudflats, creeks and
tributaries of the Senegal River. It is a city only slightly
above sea level, almost everywhere it is less than 2.5 m
NGI (Durand et al.
2010
), which exposes it to frequent
flooding.
The Senegal River estuary is composed of:
• Two water bodies on the right bank, immediately down-
stream of the Diama dam (the Nthialakh and Gueyeloubé)
draining lagoons located in Mauritania;
• The Djeuss, crossed at Dakar-Bango by a bridge-dam
and whose upstream part constitutes the water reservoir
1
Organisation pour la Mise en Valeur du fleuve Sénégal (Organiza-
tion for the Development of the Senegal River).
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