Fethi Lachaal

Implementation of a 3-D groundwater flow model in a semi-arid region using MODFLOW and GIS tools: The Zéramdine-Béni Hassen Miocene aquifer system (east-central Tunisia)

In this work, an integrated methodology was developed to investigate hydrological processes in Zeramdine-Beni Hassen Miocene aquifer and to validate the groundwater proprieties deduced from the geological, geophysical, hydrodynamic and hydrochemical studies done in the region, using the coupling of groundwater flow model MODFLOW 2000 code with Geographic Information System tools. A 3-D groundwater flow model was developed for this aquifer using a large amount of available geological and hydrological data. The groundwater flow model was calibrated and validated with datasets during the 1980-2007 period. The results show that the ZBH aquifer exhibits the highest sensibility to changes of water infiltration and hydraulic conductivity. The model simulation shows a good degree of understand to the aquifer hydrogeology. The model can be regarded as a useful tool for analyzing the hydrological processes for complex groundwater that have similar geological and hydrogeological conditions and will help to propose a management rescue plan for the studied aquifer, especially for aquifer characterization in arid and semi arid regions.

Comprehension and hydrogeological conceptualization of aquifer in arid and semi-arid regions using integrated hydrogeological information system: case of the deep aquifer of Zéramdine-Béni Hassen (east-central Tunisia)

In arid and semi-arid regions, the groundwater overexploitation caused drawdown in piezometric levels and a degradation of chemical water quality. That is why the groundwater monitoring needs a good comprehension of the hydrogeological aquifer properties. This is specially the case of Zéramdine–Béni Hassen deep aquifer (east-central Tunisia). Seismic profiles interpretation highlights the existence of the Zéramdine fault corridor, the Boumerdès anticline, the Moknine and Mahdia grabens that represent lateral boundaries for the study aquifer. The outcrop of the aquifer is located in the Zéramdine, Béni Hassen and Ain Ben Jannet regions, where two lithostratigraphic sections were realized. The piezometric study shows that the principal groundwater flow is from west to east. A secondary flow is from NW to SE. The hydrochemical study of 22 sample shows that the aquifer is characterized by freshwater, dominated by Na–Ca–Cl–SO4 facies. The salinity increase is from the west to the east, which coincides with the principal water flow direction. The integration of all results deduced from the hydrogeophysic, hydrodynamic and hydrochemical studies is developed to investigate hydrological processes of Zéramdine–Béni Hassen aquifer and consequently to propose a conceptual model, which will help to propose a rescue plan for the studied aquifer and to implement a spatial hydrogeological database using the global information system and then to characterize the complex aquifer system.

Impact of water resources management on groundwater hydrochemical changes: case of Grombalia shallow aquifer, NE of Tunisia

Grombalia region (NE Tunisia) exploits multiple sources of water: groundwater from shallow and deep aquifers, local surface water, and external surface water transferred from the North-west of Tunisia (Medjerda River and Ichkeul basin). The coordinated control of the water sources is very week while no evaluation of the impact of anthropogenic activities on groundwater resources was carried out so far. The present study use water-level time series, rainfall, and groundwater extraction data to identify the piezometric changes. Geochemical data were used to characterize and classify water samples and to study water–rock interaction based on ion plots and diagrams, mineralization, and nitrate contamination processes, as well as their fate and origins. The lack of regulation of the water use is potentially responsible of the increase of both level and salinity of groundwater in the central and downstream parts of the basin and of a large groundwater drawdown in the upstream region.

Quantification of Groundwater-Saline Surface Water Interaction in a Small Coastal Plain in North-East Tunisia using Multivariate Statistical Analysis and Geophysical Method

  Amultivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge varies from 1.4% in the upstream region of Wadi Al Ayn to 77% near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn varies from 1% to 13%; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region varies from 2% to 21%.