Didier Pennequin
3. Sustainable or reasonable groundwater management
• Transparency and communication toward the general public (sustainable groundwater management is everybody’s business) … although care and screening is needed according to the context and the target
aimed at, to avoid either confusion or paral-ysis of the process.
3. Sustainable or reasonable groundwater management in Africa
Groundwater is plentiful in many areas of Africa. In fact, many of the very large aquifer systems lie in Africa (Fig. 2) : the Nubian sand-stone (No. 1), the SASS (North-Western Sahara Aquifer System – No. 2), the Murzuk aquifer system (No.3), the Taoudeni-Tanezrouft system (No.4), the Senegalo-Mauritanian Basin (No. 5), the Iullemeden-Irhazer (No. 6), the Lake Chad Basin (No. 7), the Sudd Basin (Um Ruwaba Aquifer – No. 8), the Ogaden-Juba Aquifer (No. 9), the Congo Basin aquifer system (No. 10), the Upper and Lower Kalahari Basin (No. 11 and No. 12) and the Karoo Basin (No. 13) extend over large portions of Africa.
Yet, many of them lie in arid or sub-arid areas, characterized by extreme dry conditions and water stressed situations (Fig. 3). Indeed, the average yearly natural recharge in many parts of Africa, mainly in northern, eastern and southern Africa, remains very low. In these areas, the large aquifer systems were formed millions of years ago when the African plate was under more favourable latitude and cli-matic conditions, and therefore are the result of past precipitation events. Today they have little renewable water and often the foreseen cli-matic trends tend to suggest further degrada-tion of this situadegrada-tion.
On the contrary, in other parts of the continent, as in equatorial Africa and in southern portions of western Africa, humid climates prevail, enhancing the replenishment of the aquifer sys-tems, and triggering periodic floods and high water events.
Nearly all large aquifer systems extend over two or more countries, and are transboundary or shared water resources (Fig. 4). In many areas, interactions with large river systems have been demonstrated or are strongly sus-pected to occur.
1
25 33
4
9 7
19
2
36 26
22
21
10 3 14
18
6
11 8 5
13 20
31 27
37 15
24 28
23 17
12 34
29 35
32 30 16
0 2 500 5 000
Kilometres
Figure 2. The very large aquifer systems in the world: many of them lie in Africa (see text above for more details) (Margat, 2008)
Figure 3. Global scale estimation of diffuse groundwater recharge (Döll et al., 2005)
Most African countries rely heavily on ground-water to satisfy human needs and socio-economic activities. The more intensive uses are for agriculture and drinking water, and to a lesser extent, for mining and industrial activity.
Some countries in Africa, in semi-arid and arid regions, are sometimes heavily dependent on groundwater as it is their only water resource:
this is the case for example of Libya and Algeria (Fig. 5).
After WWII economic development has led to large increases in groundwater abstraction in many regions of the world (Fig. 6). Africa has started to follow this trend too, and so in many places in Africa today, average annual
ground-1. Nubian Sandstone Aquifer System (Egypt, Libya, Sudan, Chad)
2. Murzuk Basin (Libya, Niger, Algeria) 3. Northwest Sahara Aquifer System (Algeria,
Libya, Tunisia)
4. Tindouf Aquifer (Algeria, Morocco)
5. Maastrichtian Aquifer (Mauritania, Senegal, Gambia, Guinea-Bissau)
6. Taoudeni Basin (Algeria, Mauritania, Mali) 7. Iullemeden Basin (Mali, Niger, Nigeria) 8. Chad Basin (Niger, Nigeria, Chad, Cameroon) 9. Ogaden-Juba Aquifer (Ethiopia , Somalia) 10. Merti Aquifer (Kenya, Somalia)
11. Congo Intra-cratonic Basin (Dem. Rep. of Congo, Angola)
12. Karoo Sandstone Aquifer (Mozambique, Tan-zania)
13. Coastal Sedimentary Basin (Mozambique, Tanzania)
14. Northern Kalahari/Karoo Basin (Angola, Botswana, Namibia)
15. Nata Karoo Sub-basin (Botswana, Namibia, Zambia, Zimbabwe)
16. Kalahari/Karoo Basin (Botswana, Namibia, South Africa)
17. Karoo Aquifer (South Africa, Lesotho ) Figure 4. Main transboundary aquifer systems in Africa (BRGM, 2008 and UNESCO, 2004)
0 2 500 5 000 Kilometres
Legend
0 - 25%
26 - 50%
51 - 75%
76 - 100%
No data
Figure 5. Part of groundwater abstraction in total freshwater abstraction (Margat, 2008)
United States India
China
Pakistan Iran
Mexico Saudi Arabia
Japan Russia
France India
Bangladesh
Pakistan
China
Mexico
0 50 100 150 200 250
India China Pakistan Iran Mexico Saudi Arabia Japan United States Russia France National sources :
continous line
Estimations from T. Shah, IWMI, 2004:
not continous line Abstraction (km3/ year)
1970 1980 1990 2000 2010
1960 1950
Figure 6. Evolution of groundwater abstraction in the second half of the 20th century (Margat, 2008)
water abstraction already exceeds or starts to exceed average natural recharge of the aquifer systems, leading to groundwater level drop and often to water quality degradation. When this situation develops and persists over a long time period – when discharge from the aquifer system exceeds recharge years after years – groundwater mining is said to occur. In fact, large scale groundwater mining is already widespread in Africa in water stressed areas, where renewable water is scarce (Fig. 7).
If no corrective steps are taken, this will even-tually end up depleting the groundwater resources and the associated surface water bodies which may exist in these areas. This sit-uation clearly threatens socio-economic devel-opment and social well-being in many parts of Africa, and this may even get worst in the future, with the negative impacts of present cli-mate evolution and global changes which pro-gressively take place, notably with increasing uncontrolled urbanization and irrigation.
Sustainable ways to manage groundwater resources must clearly be searched for to ensure water availability to oncoming gener -ations and to support socio-economic develop-ment within a framework of acceptable condi-tions. Striving toward sustainable development
in terms of water resources management, land development and economic acti vities must clearly be a target to aim for to guaranty a rea-sonable level of well-being and social welfare to local populations.
However, it is true that the WFD concepts will not be all directly applicable to the whole African context, without running the risk of threatening the present day economy in many places. Much of the ideas and concepts it con-veys can nevertheless be adopted and adapted to the different facets of the African continent, on a progressive basis. A reasonable water resources management concept must first be derived for a transitional phase, which would allow the continent to progressively adapt its economy according to the availability of the water resources, while preserving at the same time a relative well-being for the local popu lations. It is necessary to develop active management schemes for groundwater resources (and more generally for all water resources) at the catchment level, making use as best as possible of excess water naturally lost every years (i.e. through controlled arti-ficial recharge), as well as alternative water resources, including recycled wastewater, so as to reach sustainable conditions in the middle to long term.
0 2 500 5 000
Kilometers
Legend
7 km3/year
Figure 7. Areas with major groundwater mining in the world.
The total yearly groundwater mining in the world is estimated to reach about 32 km3, most of it taking place on a large scale
in North Africa and the Gulf countries (Margat, 2008)