Background: Managing Hydrogeological Risk in the Iullemeden Aquifer System

INTRODUCTION

The Iullemeden Aquifer System (IAS) is a sub-regional aquifer system representative for arid and semi-arid zones in Sahara and Sahel in West Africa. The Iullemeden Aquifer System (IAS) extends between latitudes 10°30 et 19°40 North and longitudes 0°50 et 9°20 East.

According the cretaceous Intercalary Continental aquifer and quaternary and tertiary Terminal Continental aquifers, the Iullemeden Aquifer System is shared by Mali, Niger and Nigeria. The area is 500 000 km². Considering the whole aquifers, IAS includes Algeria and Benin and the area is about 1 million km². between latitudes 10°30 et 22° North and longitudes 0°50 et 9°20 East. The Iullemeden Aquifer System is a part of Niger River basin.

In Iullemeden area, the range of the annual mean values of the precipitations changes from less than 100 mm in the North to 800 mm. According to the isohyets, several climatic zones are defined:

§         the Saharan zone (less than 150 mm);

§         the sahelian and nomadic zone (between 150mm to 300mm);

§         the sedentary sahelian zone (between 300mm to 600mm);

§         the sahelian and Sudanese zone (between 600 to 800mm).

ISSUES

The Iullemeden Aquifer System represents a strategic water resource to sustain Mali, Niger and Nigeria development, but:

·         IAS is in a very vulnerable position due to :

-         20% to 30% reduction of rainfall since 1968 ;

-         20% to 50% reduction of runoff ;

-         silting and sand dunes establishment ;

·         IAS is in front of several key issues :

-         technical and technological issues for water resources accessibility ;

-         High cost of water exploitation due to deep water lever;

-         water quality degradation ;

-         lack of legal land institutional strategy for groundwater resources management

·         IAS is submitted to :

-         Growing population pressure (15 millions en 2000, le double en 2025) ;

-         Annual water pressure: 50 millions m³ in 1970, 180 millions m³ en 2004.

SUCCESS

·         Transboundary Diagnostic Analysis done: Major Transboundary risks identified;

·         Common data base elaborated: more than 17000 boreholes recorded;

·         Geographic Information System developed;

·         Groundwater model developed : water budget, close relation between Niger river and aquifers (aquifers supply Niger river),

·         Iullemeden website elaborated;

·         Legal and institutional framework adopted by countries,

LESSONS LEARNED

·         Application of a Risk and Uncertainty based approach to Transboundary Water Resources, and in particular Transboundary groundwater management,

·         Joint Management of transboundary water resources;

·         Implementation of a common Information System;

·         Elaboration of consultative mechanism;

·         Possibilities of duplication in other sahelian aquifer systems.

CHALLENGES

·         Quantification of Major Transboundary risks in the IAS ;

·         Improving data/information : A need for country capacity building ;

·         Rational assessment and management of surface water and groundwater ;

·         Implementation of regional consultative mechanism for cooperation and coordination.

KEY MESSAGES:

The efforts of only one country could not identify and reduce transboundary risks. Therefore the efficient water resources management of aquifers shared by several countries for a sustainable development of the region must do it in a consultative mechanism between the concerned countries. First of all, this management must start by a better knowledge of surface water and groundwater resources, an identification and quantification of the common risks in order to delimit the affected zones and to control these risks.

By this process, it is more believable to convince the political decision-makers to take in account the results of these studies in their national documents of policies and strategies to promote the consultative and sustainable water resources management.