Annaba is famous as an agricultural region. The main crops are water melon and tomatoes. These crops grow in the summer, thus need intensive irrigation that requires an overexploitation of water, which leads to an imbalance of freshwater-saltwater interface. To explain the marine intrusion and its extension, we examined the information given by geomorphologic, hydrochemistric and hydrodynamic studies. The studied area is characterized by horst and graben structures. The effects well localized of those faults allow to explain the presence of preferential areas of flow. The calculated ratio values were compared to critical level values (Mg/Ca = 4.5, SO 4 /Cl = 0.1 and Cl -/conductivity < 0.30). The obtained results show that the ratio values are over the limits, presenting a possible marine intrusion. This intrusion could particularly be from the Salines, regions in the North to Besbes in the South, which explains the water's salinity in this region, despite its distance from the sea.

The Guelma sub-basin, an integral part of the Middle Seybouse basin, covers a surface area of 818 km 2 , subject to subhumid climate. The main surface water reservoir is the Bouhamdane dam with a regulated volume of 55 hm 3 . The main underground reservoirs are found in the aquifer systems of the Guelma plain, the Bouchegouf plain, the H'lia water table and the Heliopolis karst. To enable the rational use of water resources in the study region, integrated management of these resources remains essential. In this work we used WEAP 21 software (Water Evaluation and Planning), for the modeling of water resources, considering the year 2017 as the reference year for 2020-2050, with a base scenario «water demand". The results of the simulation show a significant water shortage of around 50.5 hm 3 , marking a scarcity of the resource, noticed from the reference year 2017, because of the unfavorable climatic conditions which significantly impacted the water reserve in the municipalities of the watershed. This shortage will decrease to a volume of 31 hm 3 in 2024, and 104.20 hm 3 in 2050.

The North-Western Sahara Aquifer System (NWSAS) is a complex multi-layered aquifer system with extraordinary continental groundwater reserves. This largest aquifer in the world straddles three countries: Algeria, Libya, and Tunisia. It contains more than 50,000 billion cubic meters of water; of which, 70% is in Algerian territory in the southeast of the country. This water is the result of accumulation over 1 million years. In the Wadi Mya basin (Algeria), this system is characterized by two overlaid aquifer systems: the complex terminal (CT), a shallow aquifer housed in the Senonian-Eocene and Mio-Pliocene formations, and the continental intercalary (CI), a deep aquifer hosted in the Albian, Aptian and Barremian formations. The main purpose of this study is to carry out a correlation between the geochemical composition of the water and the facies of the aquifer formation. The adopted approach will allow deciphering the hydro-chemical relationships between the different levels of the two aquifer systems in the Wadi Mya basin. To acquire the chemical composition of water, the study method goes through a targeted sampling and physicochemical analysis of water followed by a statistical analysis as well as correlation and geochemical modelling: the interpretation of specific diagrams (Piper), correlations between chemical elements in binary graphs, and principal component analysis (PCA). The performed geochemical modelling by examining the saturation index and chemical balance of water helps to better understand the origin of mineralization, elucidate the mixing of waters originating from different aquifers, as well as highlight the relationship between deep and shallow aquifers in the Wadi Mya Basin hydrodynamic conversion. The obtained results indicate that the overall mineralization occurring within the study area is dominated by sodium chloride and calcium chloride-sulfate facies. This can be explained by the dissolution of halite, gypsum, and anhydrite evaporitic rocks, intercalated in the aquifer matrix besides the effects of the extended stay of fossil waters with low recharging and cation exchange reactions resulting from water-rock interactions. The interference recorded between the geochemical signatures of the two aquifers favors the hypothesis of interconnection between aquifers through fractures. Through the implementation of such academic research, this invaluable source of life will stay sustainable for future generations.

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In order to characterize the physicochemical quality of groundwater, and to examine the behavior of factors influencing water chemism in the Tebessa Plain, which is part of a semi-arid region located in the northeast of Algeria, physicochemical analyses were carried out on 32 water samples from the Mio-Plio quaternary water table. In the east of the study region, in the Djebissa area, most of the Triassic formations form a depression made up of masses of gypsiferous clay, where some outcrops of Triassic dolomites appear together with several blocks of carbonate rocks, torn off during the Aptian- Albian age. In the center and to the west of the plain, carbonate formations are represented by a significant layer of limestone marl and marl from the Cretaceous to Tertiary periods. The results obtained showed that the quality of the water is influenced by the heterogeneity of the geological formations. The concentrations of chlorides, sulphates, and sodium are high in the eastern part of the study area, which can be explained by the impact of gypsum formations, confirmed by the Sr2+/Ca2+ ratio being greater than 3 ‰ for the majority of samples. In the wells of the Tebessa and Ain Chabro areas, the concentrations of calcium, magnesium, and bicarbonates increase due to the predominance of carbonate formations of borders. The use of the statistical tool confirmed the evaporitic origin of the anions, especially in the east of the study region.