Impact Des Changements Climatiques Sur Le Renouvellement Des Ressources En Eau Souterraine : Cas Du Bassin Hydrographique Cheliff-Zahrez, Algerie/IMPACT OF CLIMATE CHANGE ON THE RENEWAL OF UNDERGROUND WATER RESOURCES (CASE HYDROGRAPHIC BASIN CHÉLIFF-ZAHRE

Mohamed MEDDI, A. BOUCEFIANE

Résumé


Résumé:
L?eau souterraine, constitue une ressource très utilisée, dans le bassin hydrographique
Chéliff-Zahrez, autant pour l?alimentation en potable que pour l?irrigation, malgré l?existence
d?un important périmètre d?irrigation qui couvre la majorité de la vallée du Chéliff. Toutefois,
suite à la sécheresse qui a touché toute l'Algérie du Nord, les agriculteurs de la région ont eu
recours à la mobilisation intense des ressources en eau souterraine par le biais de forage
souvent subventionnés par l'administration. Le travail a permis tout d'abord d'identifier les
tendances générales des variations climatiques dans le bassin hydrographiques Cheliff-Zahrez
et d'étudier la relation entre ces tendances et la fluctuation du niveau des nappes d'eau
souterraines les plus exploitées dans la région (aquifères du Cheliff et de la Mina). Cette
démarche nous mène vers la mise en évidence des impacts des changements climatiques sur la
recharge des ces nappes, en vue d'identifier les indicateurs climatiques et surtout les introduire
dans les plans de gestion et de planification à court terme des ressources en eau de la région.

Abstract :
The aims of our work is the study of the impact of climate changes on the renewal of the
groundwater in the Chéliff-Zahrez watershed. It is based on analysis of the relationship between the
evolution of rainfall and and the piezometric head. The relationship between rainfall patterns and
fluctuations piezometric level of the water will be analyzed. The aquifer of Uper Chellif, Middle
Chellif, Lower Cheliff and Mina is the most important one in the studied area.Groundwater is the most
important resource used in the watershed Cheliff-Zahrez. The renewal of the resource depends on the
groundwater recharge which is a function of rainfall and following evapotranspiration. An increase in
evaporation and evapotranspiration, the increase in temperature would lead to a decrease in recharge
and would have a direct impact on the level and quality of groundwater. Several recent studies have
shown that the climatic trends are well correlated with changes in the groundwater level.
The studied area encompasses two watersheds : the basin of Cheliff in the North and the basin of
Zahrez-Sersou in the south.The climate of the region is semi-arid to temper.The rainfall pattern has
undergone a change from the seventies. Thus, the emergence of a rainfall deficit from 1970 and the
continuation of this diminution in precipitation over the last decade of the last century. The rain
diminishes with distance from the Mediterranean sea, with a little degradation of rainfall from east to
west, the wettest region is the north east of the basin. Wich is characterized by an important elevations
and its exposure to the wet wind of the North. The annual average rainfall varies from 600 to 700mm.
On the plains, the rains are less than 500mm, in the south of the Cheliff-Zahrez basin, High-plateaux
and Zahrez, the annual averages rainfall varies from 100 to 300mm.A filter of moving averages over 3
years has been applied to highlight the main trends. The resultants found show that the periods 1980-
1994 and 1998-2001 are characterized by a significant deficit in rainfall recorded on the various
stations. Thus, the annual average rainfall recorded was below the average reported for the period
1968-2001. Generaly, the piezometric analysis have shows that the variations of the piezometric levels
of Chelif valley reflect, faithfully, the pluviometric evolution recorded in the rainfall stations of Ghrib,
El Khemis, Chlef and Relizane. With certain time lag. The response of the water level to the climatic
variations requires a period, depending on the hydraulic conductivity, the storage of the aquifer, and
also on the distance between the recharge zone and the point of observation. We have seen a marked
decrease in the level of the water since 1997, with a decline of 0.5 to 1m.

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