The Transboundary Aquifers reports of the Sahel
region: IAEA RAF7011 Project
Integrated and Sustainable Management of Shared
Aquifer Systems and Basins of the Sahel Region.
Hydrogeological, hydrochemical and isotopic
assessment of the common groundwater management
challenge of the Senegalo-Mauritanian transboundary
Basin
Credit:: M. Diaw
OBJECTIVES OF THE PROJECT
Geographical and
Practical Common
Interest
Thematic Common
Interest
Salinization
Problems
The Senegal
River
Recharge and
Palaeorecharge on the
2 sides
- Upward salinization from
connate water (Maastrichtian)
-Present or ancient sea water
intrusion
-- Evaporation
Available Data (RAF/7011)
Saline limit in the Maastrichtian aquifer
MAJOR FINDING
Palaeorecharge, Late Pleistocene, significant influence of more
recent water from the Senegal River, probably of Holocene age
(humid period and high sea level)
Recent Recharge in the area of “ the Lac de Guiers”
Salinization limit clearly defined by
Cl & Br tracing
Boron and Fluoride not directly
linked to the saline water
Role of connate water evident but
not still clearly defined
MAASTRICHTIAN
Senegal
Quaternary aquifer and a part of the CT
aquifer are recharged by present day rain
fall or River water.
The deeper aquifer systems (CT and
Eocene) are recharged by more ancient
waters, 14C dating giving transit time
between 0 (actual age) and 2800 years in
the Eocene
MAURITANIAN SIDE OF THE SENEGAL RIVER
The data clearly show two ways of
mineralization. The important effect of
evaporation on surface waters before
and during their infiltration has also
strongly marked geochemical
signature.
Major Gaps
Maastrichtian Aquifer = main challenge for Senegal water supply in the
future
More and more boreholes. A lot of studies but very scattered giving aquifer
capacities in localized zones. At the present time projects of transferring
groundwater from the eastern zone toward the western zone, but the knowledge
of the global available resources is few.
In the future, modeling the aquifer as a whole taking account of
palaeohydrological aspects is urgently needed.
THE PROBLEMS
Quantifying as finely as possible the available resources of the Trarza
and Brakna aquifer is fundamental for future water supply in Mauritania
This includes modeling after improving the knowledge of the recharge and
the role of saline water
- Reliable information on the present aquifer recharge in the
Northern limit around the “Lac de Guiers”, and in the Southern limit
in Guinea Bissau
- Exact nature and evolution of the Saline zone
Recharge quantification in the Tarza and Brakna aquifers
A better localization and definition of the source of salinity
- Palaeohydrological information in the central part of the basin
SENEGAL
MAURITANIA
RECOMMENDED ACTIONS
SENEGAL: Among the major works, 11
thesis which used isotope investigations
MAURITANIA: 2 thesis which used isotope
investigationsChemical and
hydrodynamic evolution,
since 60 years, especially
in the central zone
New sampling needed or not
needed? Eventually some
specific isotope for
palaeohydrological
information.
- SENEGAL: SEN 9 (1972); R C 9862/RB
(81-83); SEN/002 (1984), SEN/003 (1987);
SEN/005 & SEN/006 (2002-2005); RAF
8/012 (1987- 1992), RAF 8/022 ( 95-98)
- MAURITANIA : MAU 8/002 (2007)
For these purposes a better
knowledge of the Senegal River
signature is needed
Participation of Senegal and
Mauritania to the GNIR
The 2 sides of Senegal River
Piezometric framework
around the Lac de
Guiers
-National piezometric framework as
resources evaluation is difficult to be
carried out, at the present time, from
isotope and geochemical
interpretations alone as far as the
input signature is badly known
-- Some supplementary analyses for
dating (tritium and 14C)
The last unknown limit of
the
Maastrichtian aquifer
system is
in Guinea Bissau.
Necessity of collaboration
for sampling (Stable
isotopes and 14C profiles)
