Abstract
Abstract The Oued Souf free aquifer located in the South East of Algeria represents the main water resource used mostly for urban and agricultural activities. The intensive use of chemical fertilizers has led to serious environmental problems such as contamination of the free aquifer in the region. Thus, aquifer vulnerability has been assessed using several different methods (DRASTIC, GOD, and the Susceptibility Index ‘SI’) based on a geographic information system (GIS). For each method, two vulnerability maps have been developed in the years 2002 and 2012. These maps show that the study area is more exposed to urban, and especially agricultural, pollution. Two classes of vulnerability (moderate and high) have been identified by both DRASTIC and GOD methods. A combined analysis reveals that the moderate class showing 48% (for the GOD method), and the high class showing 57% (for the DRASTIC method) are the most dominant. However, the Susceptibility Index method (SI) revealed that the vulnerability varies from moderate to very high-level classes. In 2012, about of 53% of the study area was dominated by moderate vulnerability classes. The high vulnerability class also includes a considerable part of the land (41%) around urban or strongly agricultural areas, while only 6% is under very high vulnerability groundwater contamination. In addition, a marked decrease in the vulnerability level was noticed in 2012 compared to 2002. This decrease is mainly due to the lowering of the water table after the installation of a vertical drainage network to evacuate the surplus water to the depression and Chotts areas in the North of the region. These results provide a guide for decision-makers involved in the protection of groundwater pollution in such a vulnerable area.
Highlights
The region of Oued Souf has experienced a great agrarian revolution during the last two decades, and the agricultural area which covered 200 ha in 1993, currently exceeds 50 000 ha
The class of high vulnerability found in 2002 dominates the study area with a rate of 89%, and this would be due to the shallow depths of the water table, while the moderate vulnerability class represents only 11% of the zone and is due to depths exceeding 10m
Regarding the GOD vulnerability map, the high vulnerability class found in 2002 dominates the study area with a rate of 89%, and this would be due to the shallow depths of the water table, while the moderate vulnerability class represents only 11% of the zone, owing to the water table depths exceeding 10m
Summary
The region of Oued Souf has experienced a great agrarian revolution during the last two decades, and the agricultural area which covered 200 ha in 1993, currently exceeds 50 000 ha. This economic revolution requires highly important hydric potentialities and, thereby, generates negative effects on the environment and groundwater [8]. The safeguarding of this precious resource from contamination has become indispensable to preserve the economic, environmental, and social welfare in the region [9]. The DRASTIC and GOD methods were applied and compared with the Susceptibility Index (SI) method map to evaluate the potential risk of groundwater contamination
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