March 2012
E d i t o r i a l
Water:
sharing knowledge
© NASA
By Michel Laurent
Executive President of the IRD
I
IRD has made the issue of water in
countries of the South one of the
core scientific priorities that
mobilise its network of researchers.
Together with their partners in the
North and the South, they are
helping to build communities that
are actively involved in knowledge
acquisition, relying for instance on
technological platforms such as
those used for environmental
monitoring from space.
Encompassing nearly half of the
planet’s arid and semi-arid areas,
sub-Saharan Africa and the region
south of the Mediterranean demand
particular attention. African,
Brazilian and French partners,
through IRD and its agency AIRD, on
the occasion of the 6th World Water
Forum are launching a call for
projects to combat desertification.
The aim is to meet the challenge of
sustainable management in these
regions that experience water
scarcity.
Sharing this body of knowledge will
lead to a better defining of public
policies and therefore governance
for this coveted natural element. In
the scope of the 6th World Water
Forum, this integrated approach,
ranging from knowledge of water as
an environment and resource to
proposals for action, should lead us
to solutions. And thereby, open the
way to sustainable management and
fairer access to water for the
countries and peoples of the South.
Understanding to predict…
W
hile all arid and semiarid regions are poor in
water supply, human
activities and climate change are inflicting even greater risks of shortage on
these areas. “Water management formulae must take into account uncontrolled urban, tourism and demographic development, as well as the
growing need for irrigation in these
regions that are particularly vulnerable
to climate change,” explains
Abdelghani Chehbouni, head of
research at IRD and IRD representative
to the Middle East. Giving decisionmakers the tools to plan their water
use more efficiently is another important objective of the research conduc-
ted by IRD teams in these regions.
A c c o rd i n g t o p a l e o c l i m a t o l o g i s t
Abdelfettah Sifeddine, “past climate
reconstructions help to control climatic models in order to improve future
forecasts”. By studying lake sediments
and speleothems (limestone formations found in caves) in the semi-arid
region in the northeast of Brazil, the
researcher has recorded natural climate changes on scales that vary from
a thousand to ten thousand years. The
aim is to supplement instrumental
data obtained in recent decades to
describe modes of climate fluctuation
with the help of information on natural variations on a longer scale. There
is no lack of work by researchers who
Groundwater
under threat
I
rrigation and groundwater are
not always a good mix, particularly in a Mediterranean setup.
“Whether groundwater tables provide water for agriculture or receive
its excess, their use is too often
unsustainable,” reckons hydrologist
Christian Leduc. To develop farming
production, particularly fruit and
vegetables, in this region with its
lack of surface water, groundwater
has been extracted abundantly in
recent decades. This resource holds
many advantages, such as being
accessible when surface water is
remote or absent, and when
droughts deplete the volumes stored
i n d a m s . B u t t h i s u n d e r g ro u n d
resource must be used discerningly:
its balance is fragile, and it is important not to take out more than can
be replenished naturally. “Examples
abound of agricultural overuse of
aquifers in the Mediterranean basin,
and they are likely to increase if you
take human pressure into account,”
the expert laments. “Critical cases
are seen everywhere, especially in
the south of Spain and in Tunisia.”
Extractions that are completely out
of control and that largely exceed
the natural renewal of groundwater
resources have lowered the levels by
dozens or even hundreds of metres
in fifty years. Elsewhere, for instance
in the south of Libya, the choice was
made of irrigating with fossil water.
“The groundwater that is used to
grow alfalfa in the middle of the
desert, infiltrated in the last great
pluvial episode of the Quaternary
period, some 8,000 years ago. They
will therefore never be renewed and,
once they are depleted, the “Great
Man-Made River” – as this titanic
project is called – will dry up and that
will be the end of this costly feat of
technology. Irrigation also raises
other problems, related to water
q u a l i t y. F i r s t l y b e c a u s e n o t a l l
groundwater is suitable for irrigation. Secondly, because the development of irrigation often increases the
salinity of groundwater. The intensive use of fertilisers and pesticides
must be thought through carefully in
irrigated areas, in order to preserve
groundwater from contamination,
are interested in the impact of future
climate variations in the field, and
who find research topics worth exploring in this domain. “To predict the
future, you must know the past:
where do we come from, and where
are we going?” summarises
Abdelghani Chehbouni, who considers that the studying of factors that
contributed to rainfall patterns in the
past, can help to improve our interpretation of current observations, and
eventually, predict the future. Water
experts agree that the techniques of
measuring and assessing the resource
are mastered today, and that the challenge of foreseeing evolutions in
terms of climate change reside in
taking into account the use of the
resource. How does one quantify
unauthorised pumping? How do you
predict needs depending on land-use
scenarios? How must the evolution of
the plant cover be integrated in fore-
casts? These questions are addressed
in different scientific fields, from
sociology to pedology, of which the
stakeholders are not always accustomed to working together. “It is crucial
that such work be carried out by multidisciplinary teams if the results are to
be of use to decision-makers,”
explains Abdelghani Chehbouni, who
is also intensely aware of the political
dimension of these issues. Though the
models and tools are already operational and available, the challenge now
lies in getting society and decisionmakers to accept the use constraints
that scientists recommend.
●
Contact
abdel.sifeddine@ird.fr
UMR LOCEAN (CNRS, IRD,
MNHN, UPMC)
Ghani.chehbouni@ird.fr
UMR CESBIO (CNES, CNRS, IRD,
Université de Toulouse III)
Source : Sciences au Sud n° 56-2010
which is not always the case, far
from it. “Drip irrigation, which is
promoted by developers for its
sobriety, also has an impact on the
quality of aquifers,” the researcher
says. “Because it increases the salinity of the soil, leaching operations
are necessary from time to time,
which puts back large quantities of
minerals in the groundwater.” A
great environmental threat comes
from numerous drillings in the south
of Spain that are now linked to desalination plants to clean up the water
for citrus farming!
●
Contact
christian.leduc@ird.fr
UMR G-EAU (AgroParistech, Irstea,
CIRAD, IAMM, IRD, Montpellier
SupAgro)
© IRD / T. Ruf
ndispensable to life on Earth,
water is at the same time an
environment, a resource and a
shared asset. As an environment, it
is important to know more about its
functioning through physical,
geochemical and biological
mechanisms, and understand how it
interacts with the climate and the
earth, its soil and vegetation, and the
needs that it fulfils. As a resource, it
is necessary to grasp its
vulnerability as well as
sustainability, amidst global change.
Lastly, we more than ever need to
understand and define the services
that this shared asset provides.
Source : Sciences au Sud n° 59-2011
Irrigation in Morocco
Improving Sahelian
agricultural water management
© IRD / P. Cecchi
“Monitoring the water consumption
of crops with no need for intensive
field instrumentation, costly both in
terms of financial and human
resources, is now possible thanks to
Remote Sensing Space Systems,” says
Mehrez Zribi, researcher in space
hydrology. A great deal is at stake,
since water withdrawal in Tunisia
comes close to 88% of the available
surface water. The same is true for
Morocco, which is about to join Libya
or Jordan on the list of countries that
will know water scarcity by 2025.
Faced with the growing shortage of
this precious liquid, farmers have an
interest in using it parsimoniously. “To
steer irrigation by getting as close as
possible to the water needs of plants,
we rely on time series of satellite
images,” explains Michel Le Page,
Geographic Information Systems
engineer at IRD. The SUDMED1 programme team therefore designed
and developed SAMIR (Satellite
Monitoring of Irrigation), a computerassisted irrigation management tool
that receives data from Remote
Sensing Space Systems. Field trials in
the Tensift (Morocco, since 2002) and
Merguilil basins (Tunisia, since 2008)
have made it possible to link space
observation to different resolutions
and the water consumption of dominant crops in the region (oranges,
olives, wheat…). “First of all, water
that is ‘transpired’ by the plants, and
that corresponds to the water they
have used, is measured exactly on
certain sites, by means of micrometeorological instruments,” explains
Prof. Saïd Khabba, expert in the functioning of irrigated crops at the
University of Cadi Ayyad. “But the
process is cumbersome and costly,
and can therefore not be extended to
all farming areas.” However, different
satellite wavelengths supply largescale data that will be graded and
confirmed locally by field measurements: state of plant life, soil humidity, water stress level… By the use of
models, this information makes it
possible to estimate the water
consumption of crops. The Remote
Sensing Space System therefore procures an image of the state of crops
at a point “t” in time, and periodically repeats the exercise. SAMIR thus
provides answers to crucial questions
asked by farmers: where, when and
how much to irrigate? More in general, this irrigation management support tool was integrated in a decisionsupport system for groundwater
management in Haouz (Morocco).
This makes it possible to explore
water-resource evolution scenarios in
terms of public policies, land planning, and agricultural reconversion in
view of the sustainable management
of the water table. ●
Burkina Faso
«
Water productivity in subSaharan Africa must improve,”
a c c o r d i n g t o h y d r o l o g i s t
Jacques Lemoalle. “It is a crucial condition for attaining food safety and
fighting against rural poverty.” Water
productivity corresponds to the
amount of cereal, livestock meat and
rice produced with one cubic metre of
the precious liquid. In the Sahel
region, this is ten times less than in
Beauce, the breadbasket of France.
These issues are at the core of the
“Challenge Programme for Water and
Food” drawn up by the Consultative
Group on International Agricultural
Research (CGIAR), which aims to
improve water management on the
scale of large river basins and reinforce the availability of and access to
food. To define the main research
questions to be addressed and find
specific answers, Basin Focal Projects
(BFPs) were set up prior to the programme. The “Niger basin” and the
“Volta basin” BFPs, steered by IRD
hydrologists, have just handed in their
final reports. “A solution would be to
store water from rainfall, and to develop off-season crops,” explains
Jacques Lemoalle, coordinator of the
BFP for the Volta basin. Subsistence
farming, in this basin as well as in that
of the Niger which has roughly the
same climate conditions, is mainly
rain-fed: crops can only be grown in
the rain season. The rest of the year,
small farmers without work and
resources often have to migrate seasonally to other sub-regional activity
centres, leaving their land untended
for months on end. “To continue their
activity during the dry season, it is
necessary to preserve rainwater artificially in small dams, and develop local
irrigation systems,” they recommend.
The challenge is not only to keep farmers focused on their land, but in particular to increase agricultural production in this region that is still
confronted with periodical food shortages. “Optimising water resource
management is vital,” according to his
Niger-basin counterpart, Jean-Charles
Clanet. “Demographic forecasts
demand it.” The population of the
region through which the Niger River
runs, is in fact expected to triple over
the next four decades, increasing from
94 to 300 million inhabitants just in
H
ow can the Sahel be irrigated
to improve food supplies for
its inhabitants? A scientific
report on the Tillabéri region of Niger,
c o m m i s s i o n e d f ro m I R D b y t h e
German cooperation body GTZ1, provides some concrete answers on this
subject. “The question arises because
this apparently arid environment in
fact hides considerable water
resources,” according to hydrogeologist Guillaume Favreau who led the
investigation. “But they are used too
little to develop farming: only 1% of
farmland in Western Africa is irrigated
today, as opposed to 16% in the rest
of the world.” The Sahelian region
contains large regional aquifers (that
of the Lake Tchad basin in Senegal,
t h e Ta o u d e n n i i n M a l i , o r t h e
Iullemmeden in Niger), with a host of
natural ponds or surface water dams,
all along the temporary tributaries of
the main rivers, and abundant
groundwater reservoirs. Mobilising
these resources to develop irrigation
would make it possible to safeguard
food production in a region where
1. C
ESBIO, Cadi Ayyad University in
Marrakech, Tensift Basin Agency,
ORMVAH, Directorate of National
Meteorology, Morocco , INAT.
Contact
michel.le-page@ird.fr
mehrez.zribi@ird.fr
UMR CESBIO (CNES, CNRS, IRD,
Université de Toulouse III)
Source : Sciences au Sud n° 59-2011
Along a village in Niger, gardens of the valley floor, protected by hedges
of millet stalks and irrigated by village wells in shallow water (5-6 m);
here in the dry season.
Les dossiers de Sciences au Sud
the basin, and 300 to 900 million for
all of the ten countries concerned.
“The challenge is not insurmountable,” remarks Jean-Charles Clanet.
In Nigeria, shallow groundwater is
being put to good use, and in Côted’Ivoire and Burkina Faso, people are
beginning to organise rainwater
retention by building small dams. “On
the other hand,” he adds regretfully,
“current works on the central part of
the Niger delta, situated in Mali,
remain highly insufficient. Only a part
of the formidable potential of this
wetland, which is one of the largest in
the world, is being exploited.” Apart
from promoting technical and hydrological solutions, BFPs also recommend the development of water
governance on a local, regional, national and transnational scale, and
encouraging the emergence of proactive policies. “Establishing coherent
management arrangements is determining in getting the most out of the
resource,” says Jean-Charles Clanet.
“Without concerted steering, water
releases and withdrawals will disrupt
the farming activities of the Niger
river’s users, for example. The tempta-
tion to give unilateral preference to
hydroelectricity and irrigation will
necessarily be detrimental to the interests of peasant farmers.” As for
managing the resource on a regional
level, Jacques Lemoalle is confident in
the reach of work conducted by the
two programmes. “Research can
contribute to the dialogue between
countries that do not have the same
climate constraints, to coordinate the
allocation of water resources in the
catchment area,” he explains, referring to the contrast between countries
in the Volta basin: Burkina Faso, with
its low rainfall, and Ghana, which is
more humid and home to the world’s
largest artificial dam. ●
Contact
jacques.lemoalle@ird.fr
jean-charles.clanet@ird.fr
andrew.ogilvie@ird.fr
UMR G-EAU (AgroParistech, Irstea,
CIRAD, IAMM, IRD, Montpellier
SupAgro)
Source : Sciences au Sud n° 55-2010
Irrigating the Nigerian Sahel
© IRD / M. Oï
Water: sharing knowledge
2
Estimation
by satellite
rain-fed agriculture remains largely
dominant. Ultimately, the objective of
Nigerian and European developers
who carried out the work is to reduce
rural households’ vulnerability to climate. Despite the natural assets of
their environment, they are too often
exposed to uncertainties related to
the spatiotemporal irregularity of
rainfalls. “In the first phase, we drew
up an updated, detailed list of every
single water source, and community
b y c o m m u n i t y, o f a l l t h e w a t e r
resources in the region,” the researcher explains. By using GIS technology2 to compare these data with those
of land that is in fact suitable for farming – since a percentage of the soil
is deteriorated – we made a precise
assessment of the potentials that are
usable for irrigation. Based on this
comprehensive analysis, the experts
recommended a few adjustments and
practical measures to make efficient
use of the water that is available in
the agricultural landscape. Thus, in
the valley surrounding the river and its
tributaries, where surface water
resources are abundant but vary
greatly according to the season, they
recommend that preference be given
to irrigation from storage facilities
and regulation on streams. In these
same valleys, which operate on a basis
where groundwater is not very abundant, they nevertheless suggest the
use of alluvial water tables for smallscale, private irrigation, as they are
s h a l l o w a n d re g u l a r l y re n e w e d .
Around permanent or semi-permanent ponds, which are numerous but
can quickly dry up through evaporation, they recommend flood-plain tilling on the banks, and drilling wells
nearby to maximise the use of the
resource over time. In the fossil valleys
to the east of the Niger River, they
advocate the use of the abundant
alluvial and artesian groundwater for
growing off-season crops. Regarding
catchment, for the pumping of subterranean water resources, they make
specific recommendations for adapting techniques and equipment to the
local economy and to the characteristics of the aquifers. A sound approach,
suited to the geological context, and
one that could be emulated throughout Sahelian Africa.
●
1. D eutsche Gesellschaft für Technische
Zusammenarbeit
2. Geographic Information System
Contact
guillaume.favreau@ird.fr
nazoumou@gmail.com
UMR HSM (CNRS, IRD, Universités
Montpellier 1 et 2)
Source : Sciences au Sud n° 58-2011
Y
ears of drought have depleted the old water networks
around the Mediterranean.
“But with the return of rainfalls in the
last 5 years, water resources are reviving,” says Thierry Ruf, agricultural
economist at IRD. The water now
“sings” like the names of the systems
in which it is flowing anew: khettaras
in Morocco, foggaras in Algeria, or
qanats in Iran. “Underground drainage tunnels are one of the most typical as well as original examples of this
recovery by local populations.” 1 As
their name indicates, these tunnels
drain water from the water table to
the foot of a mountainous area (see
diagram). In the Tafilalet province in
Morocco – region of the Meknes –
where the researcher and his partners
are in fact conducting their studies2,
450 khettaras have been recorded in
total. Dug from the end of the 18th or
beginning of the 19th centuries until
the 1950s, these “water mines” in the
middle of the desert have led to the
development of an oasis with nearly
600,000 inhabitants in the vast region
at the foot of the Atlas, tucked
between the mountain and the
Sahara. And yet, five years ago, only
about a dozen tunnels were still continuously in active use. “From the
middle of the last century, modern
hydraulic networks started overlapping the traditional structures,” the
water-management expert relates.
The great droughts that afflicted the
region in the 1970s and again in 1995
and 2005 gave the deathblow to the
khettaras system. “A great number of
tunnels were abandoned.” But May
2006 brought a turnabout: rainfalls
are once again replenishing the
groundwater tables above the catchment areas of certain tunnels. The
inhabitants have therefore started to
repair them. “In five years’ time, at
UMR LISAH (INRA, IRD, Montpellier
SupAgro)
Recent analyses have shown that the
chrome used by tanneries in the Medina of
Fes (Morocco) is found in the water of the
wadi that runs through the city. In the
absence of water treatment plants, the
use of water from the Sebou and its tributary, the wadi Fes, for the irrigation of
vegetable crops forms a serious public
health hazard due to the presence of pollutants in the water. Wadis are intermittent
rivers that are characterised by periods of
flow, alternating with long months in
which the riverbed is partially or completely dry. Pollutants can then accumulate in
the sediment of the dry bed, forming veritable reservoirs that are likely to be washed
along by the next flood. This feature
makes such environments particularly
vulnerable to pollution. The “Intermittent
Rivers” project brings together the Faculty
of Science and Technology of the Sidi Ben
Abdellah University (Fez), the Sebou
Hydraulic Basin Agency, and the IRD. “The
aim is to measure the impact of human
activities on the wadi Fes in order to evaluate the consequences on the quality of
surface water, both as a source of water
and as a vector of pollutants towards
downstream aquatic systems,” explains
Nanée Chahinian (IRD). The wadi Sebou is
considered as a national priority area by
the Moroccan government, since it alone
represents more than 30% of Morocco’s
water resources, and its tributary receives
waste from Fes, the country’s third largest
city. The “medina” (old town) of Fes is
home to most of the city’s traditional arts
and crafts (tanneries, brassware workshops, iron work, etc.). Waste produced in
this area, as in the rest of the Fes agglomeration (200,000m3/year, 47% comes from
household refuse alone), is dumped directly in the nearby streams, in particular the
wadi Fes. Since 2008, the FrenchMoroccan team has been studying the
rainfall-runoff relationship on a multi-year
scale. The collected data have been integrated in a hydro-meteorological database, in order for them to be distributed to
all the project partners. At the same time,
information is collected regarding the quality of water in the wadi Fes. Two spatial
studies were made to identify the chemical
and physical characteristics of its main tributaries. To establish its impact on the
wadi Sebou, measurements were taken
upstream and downstream of the
confluence of the two rivers. Regular
monitoring of the water’s chemical composition, in particular nutrients and heavy
metals, confirms that there is a substantial
amount of chrome pollution from the
Medina tanneries. However there is still
little known about the mechanisms underlying the origin and transfer of this pollution and its evolution over the medium
and long term, which is why further studies will be necessary. Researchers thus
hope to find answers regarding the temporal and spatial dynamics of pollutants,
their behaviour in water and in river sediments, their possible interaction with
other composites present in the environment, etc. This requires regular monitoring
over long periods of time and at different
places in the streams, as well as in-situ
experiments in the riverbed itself. ●
Source : Sciences au Sud n° 59-2011
Contact
stay? Scientists find it hard to confirm.
But a gamble that rural societies are
willing to take in order to breathe new
life into collective action, having had
enough of individual groundwater
exploitation through uncontrollable
pumping. Their goal is to establish a
new justice of fair access to water…
precisely with a view to facing possible
shortages in the years to come.
●
1. An application for registration of khettaras
in tangible and intangible heritage of
humanity has been suggested to UNESCO
in late 2010.
2. Professors and researchers, Cadi Ayyad
University in Marrakech and Faculty of
Arts and Social Sciences of Agadir.
Contact
thierry.ruf@ird.fr
UMR GRED (IRD, Université
Montpellier 3)
Source : Sciences au Sud n° 59-2011
Khettara - Illustrative Diagram
Palm Grove
Channels
Receiving pond
Vertical shafts
for aeration
and maintenance
Cut cones
Surface of
the aquifer
Outlet for khettara
Underlying galleries of water
The impact of
hydro-agricultural structures
T
erraces, ditches, dams or
bench terraces form an integral part of Mediterranean
landscapes. These traditional hydroagricultural structures retain water and
sediments and facilitate farming production. “Understanding the influence
of this type of structure on water
resources is one of our long-term
goals,” says Olivier Grünberger, assistant director of LISAH1. In Tunisia, after
the commissioning of the last great
barriers at the start of the 1980s,
hydro-agricultural layouts have been
multiplying in the form of anti-erosion
bench terraces and small hillside reten-
tion reservoirs. The latter are designed
to limit the inflow of sediments to
large dams and increase the number of
waterholes in the landscape. Studies
carried out by this laboratory and its
partners over the past two decades
show that farmers use water from
these small dams less frequently than
one might hope. The dams sometimes
also fill up with sediment in a matter of
a few years if there is no anti-erosion
bank terracing, in other words sloping
banks built along the side of a hill, following the contour lines, above the
dam. “The effects of the different
types of facilities are sometimes
contradictory,” Olivier Grünberger
underlines. For instance, bank terracing reduces the amount of sediment
that flows down, but also prevents the
water flow to storage reservoirs. On
another scale, increasing the number
of hillside storage reservoirs reduces
the water supply to large dams. The
impact that hydro-agricultural structures, in particular dams, have on
groundwater is difficult to assess and
requires the use of simulation models2
and geochemical tracing their flow
patterns3. The latter also contribute to
the flow of wadis to an extent that
depends on the scale. For example, in
the scope of the Kamech Observatory4,
the preliminary results of LISAH show
that for a surface are 175ha, groundwater movements can contribute as
much 20% to the annual flow of the
wadi that runs into a hillside storage
reservoir, whereas this contribution is
only 4% for a surface area of 15ha. To
assess the overall efficiency of such
structures in Mediterranean landscapes, it is necessary to combine the
effects observed for different spatial
scales, while taking groundwater flows
into account. Researchers have taken
up this challenge by starting a monitoring programme of interlocked hydrological systems in the Cap Bon region,
which includes the OMERE observatory
in Kamech and its watershed boundary
of about 100km², the Lebna.
●
1. In partnership with INRGREF, INAT, General
Direction of Management and Agricultural
lands Conservation – Tunisian Minister of
Agriculture and Environment.
2. In partnership with ENIT (Tunisie).
3. In partnership with ENIS (Tunisie).
4. E nvironmental Research Observatory
(OMERE).
Contact
olivier.grunberger@ird.fr
© IRD / L. Corsini / M. Janvois
© IRD / T. Ruf
Interviews with those involved in the khettara management.
Jorf, in the western
part of Tafilalet,
nearly 50 khettaras
were restored
through these collective initiatives,” the
scientist explains.
Local and regional
authorities are now
also working in this
direction and are
offering a programme to restore
the systems. This
new upsurge in
water resources
enable populations
to reinvest in oasis farming – 75% of
the inhabitants live mainly on an agricultural income –, in particular young
people who are coming back to rural
areas due to the unemployment they
are faced with in the cities. In fact,
many have recently started returning to
the oasis to help with the restoration
and maintenance of these khettaras. A
risky gamble considering climate uncertainty: has the water come back to
Wadis
and pollution
© IRD / J. Touma
nanee.chahinian@ird.fr
perrin@msem.univ-montp2.fr
UMR HSM (CNRS, IRD,
Universités Montpellier 1 et 2)
Half-moon traditional
hydro-agricultural structure
Source : Sciences au Sud n° 52–2009
Les dossiers de Sciences au Sud
Water: sharing knowledge
The return of water
resuscitates former networks
3
© IRD / J. Champion
Small islands of the Pacific are particularly vulnerable to the impacts of global
warming: the rise of sea levels,
droughts, growing scarcity of freshwater that is indispensible for the development of the flora and fauna, and for
the human populations’ food supplies.
“On these coral-reef islands,” explains
Jean-Lambert Join, hydrologist of the
University of Reunion, “freshwater
occurs as underground reservoirs, in the
form of lenses in equilibrium with the
underlying seawater.” Rain-induced
groundwater recharge ensures their
natural renewal. Understanding the
functioning of these freshwater lenses,
their development, capacity and vulnerability is the only way to work towards
sustainable management of this
resource – an objective that several IRD
teams and their partners have fixed for
themselves 1-2. To this end, “we have
combined geological, hydrogeological
and geophysical investigations to establish a baseline of the morphology and
dynamics of the freshwater lens on
M’ba Island in New Caledonia,” says
IRD paleologist Guy Cabioch. It hence
appears that the balance between freshwater and saltwater in coastal and
island aquifers is unstable and that the
processes involved are difficult to characterize. Observation drilling is not
enough to confirm the hydrogeological
models. However, the use of electrical
resistivity tomography as investigation
tool has proved to be conclusive for
studying, in 23/34 high resolution, the
configuration and functioning of the
freshwater lens on this coral-reef island.
Combining models based on electrical
resistivity parameters, and comparing
them with salinity data collected in the
field, have yielded important information on the structure and shape of the
reservoir, flow velocities, etc. In particular, it was found that on a coral-reef
island, salinity is more concentrated in
the middle and that it depends to a
large extent on the plant cover. ●
Irrigation in Tunisia
Farmers as scapegoats
A
re Mediterranean farmers
really the thoughtless
water squanderers, responsible for dramatic hydrological
situations that they are often made
out to be? “This preconceived idea is
usually both untrue and unfair,”
according
to
hydrogeographer
François Molle, who is an expert on
the matter. “One cannot hold farming to be the only culprit when it
comes to shortages and the associated health and environmental deterioration that affect the entire
region.” The Middle-East/NorthAfrican sphere is indeed experiencing
a disquieting overuse of its water
resources. According to data from
the Blue Plan1, 5 countries draw more
than 80% of their renewable water
and 8 others between 20 and 60%.
There are even extreme cases for
some basins or aquifers, like Jordan
where it is as high as 103%! These
1. Les équipes CoRéUs, Camélia, Paléotropique
de l’IRD, de l’UMR CEREGE et des
Universités de la Réunion et d’Avignon.
Dans le cadre du projet INTERFACE subventionné par l’ANR (programme Vulnérabilité,
Milieux, Climats)
2. Jean-Christophe Comte, Queen’s University
Belfast et Olivier Banton, Université
d’Avignon, Guy Cabioch et Jean-Lambert
Join, Université de la Réunion
Contact
join@univ-reunion.fr
olivier.banton@univ-avignon.fr
Source : Sciences au Sud n° 57-2010
Le journal de l'IRD
sas@ird.fr / www.ird.fr
Publishing director
Michel Laurent
Managing editor
Marie-Noëlle Favier
Editor-in-chief
Manuel Carrard
Graphic designer
Laurent Corsini
Coordinated with
Amélie Travers
Les dossiers de Sciences au Sud
figures would be even more alarming
if the calculation excluded unusable
resources, such as non-storable
floods, saltwater or polluted water…
“It is true that Mediterranean farming activities account for 85% of
the water withdrawal, which is higher
than the worldwide average of
70%,” he admits, “but this is due to
bioclimatic conditions as well as the
fact that other uses, for instance
industrial and domestic, remain fairly
limited.” The outrageous extension
of large-scale irrigation programmes,
often motivated by the financial or
political interests of governments,
also contributes to this state of
affairs. Even more so considering that
private irrigation systems, based on
the use of groundwater, often get
added to planned irrigation areas.
These initiatives come from urban
investors, in Morocco and Egypt in
particular, as well as farmers who try
to intensify or secure a highly precarious rain-fed agriculture, or those
farming in or near dysfunctional irrigation areas. “To waste water, farmers must receive it in abundant
quantities or at will,” he explains,
“and that is almost never the case.”
More often than not, priority is given
to non-farming uses whereas irrigated areas have to deal with restrictions and quotas. In these parts,
where crop growers rarely know
ahead of time when and how they
will be supplied, forced investments
tend to develop in the form of wells,
pumps, pipes and reservoirs. Such
innovations, which help to maintain
production, hardly lead to wastage of
the resource, particularly when pumping costs are high. “If there are
losses in irrigated systems, the cause
is more likely to be found in their
overall management than with the
users,” the researcher feels. And
according to him, there is often
confusion between “withdrawal”
and “consumption”, due to a misunderstanding of hydrological mechanisms. In overused basins, water that
returns to the hydrological cycle after
withdrawal (50% for irrigation and
80% for towns) is seen as a loss,
whereas in fact it will be reused
downstream or in wells. “Therefore,
while you’re tracking down ‘wastage’, all that is happening is that
water is being reallocated from one
use to the next,” he concludes. ●
1. www.planbleu.org
Contact
francois.molle@ird.fr
UMR GRED (IRD, Université
Montpellier 3)
Source : Sciences au Sud n° 59-2011
Small dams are a valuable resource;
here in Kagamzensé, about thirty
kilometers in the south of
Ouagadougou.
© IRD / P. Cecchi
Water: sharing knowledge
4
Pacific islets’
freshwater
under scrutiny
The strengths and
weaknesses of small dams
A
s indispensible tools in the
gear of developers over
the last decades, have
small sub-Saharan dams fulfilled their
promise? The answer that hydrobiologist Philippe Cecchi suggests in a
recent publication on the subject, is
somewhat contrasted. These systems
do not meet all the goals that were
assigned to them when they were
built, but they have come to play an
irreplaceable part in the daily life of
rural African societies, in particular
due to the multiple uses that they
provide. It is true that the phenomenon has escalated. With the proliferation of these water reservoirs, Burkina
Faso today has at least 4,000 kilometres of artificial banks, which is
considerably more than the shorelines
of coastal countries in the region...
“These banks have become a continuously sought-after item for local
populations, who are even contributing to their financing. They benefit
from the support of both local and
national decision-makers as well as
financial backing,” the researchers
says, thus explaining the impressive
increase in the number of constructions of which there are now thousands in the West-African region. Yet,
analyses of the use of these facilities
carried out several years after their
impoundment show mixed results:
they do not always fulfil the expectations of their promoters, in any case
not to the extent that they had hoped
for. For instance, small dams intended
to support cattle farming did not lead
to as much development in the sector
as was foreseen, and those designed
for small-scale irrigation did not
engender the expected gains in agricultural productivity. The identified
obstacles have more to do with local
governance issues than with technical
problems. Despite these lukewarm
results, small dams continue to get
the wind in their sails. Several dozens
were built in Burkina Faso in the past
ten
years,
and
the
African
Development Bank is planning to restore fifty more in the north of Ghana
before the end of the decade.
According to Philippe Cecchi, this
persistent trend is due to other assets
that these facilities have, so-called
“side benefits” that the technocrats
did not foresee and that are not explicitly evaluated in their reports. “As
veritable country-planning items,
these infrastructures have caused a
positive upheaval in countryside life,”
he says. “They provide a continuous
source of water and fish, thanks to
fishing in regions where little of this
existed in the past, as well as real
opportunities for crops, even though
they haven’t attained the volumes
expected by those who designed the
projects.” And beyond these quantifiable performances, they have an
uncontestable intangible value. Small
dams for instance contribute effectively to counteracting the exodus of
farmer populations towards the cities,
and breathe new life into the rural
economy. “They have become a definite political stake, on a local level, in
allowing populations to regain a hold
on rural areas, as well as on the broader scale of countrywide agricultural
policies,” he confirms. This begs the
questions of preserving ecosystem
resources and associated services, and
first of all that of deteriorating health
conditions in these ecosystems (overfill, pollution…). To measure these
aspects, the hydrobiologist suggests
an analysis grid of the actual impact
that these structures have on a
watershed scale.
●
Contact
philippe.cecchi@ird.fr
IRD, UMR G-EAU (AgroParistech,
Irstea, CIRAD, IAMM, IRD, Montpellier
SupAgro)
Source : Sciences au Sud n° 61-2011