Salem Bouri

Sensitivity analysis in groundwater vulnerability assessment based on GIS in the Mahdia-Ksour Essaf aquifer, Tunisia: a validation study

Abstract The assessment of groundwater vulnerability to pollution has proved to be an effective tool for water resource management, especially in arid and semi-arid regions like Mahdia and Ksour Essaf. The main objective of this study is to assess the aquifer vulnerability by applying the DRASTIC method as well as using sensitivity analysis to evaluate the effect of each DRASTIC parameter on the final vulnerability map. An additional objective is to demonstrate the role of the GIS techniques in the vulnerability assessment. The DRASTIC method assigns a high vulnerability to the coast of the Mahdia-Ksour Essaf. The lowest values are observed in the southern part of the study area. A sensitivity analysis applied in this study suggests that net recharge, aquifer media and depth of groundwater are the key factors determining vulnerability. The model is validated with groundwater quality data and the results have shown strong relationships between modified DRASTIC Vulnerability Index and nitrate and chloride concentrations. Citation Saidi, S., Bouri, S. & Ben Dhia, H. (2011) Sensitivity analysis in groundwater vulnerability assessment based on GIS in the Mahdia-Ksour Essaf aquifer, Tunisia: a validation study. Hydrol. Sci. J. 56(2), 288–304.

Erratum to: Groundwater management based on GIS techniques, chemical indicators and vulnerability to seawater intrusion modelling: application to the Mahdia–Ksour Essaf aquifer, Tunisia

In arid and semi-arid countries worldwide, conflicts between human development activities and conservation of groundwater resources are widespread and attract many public debates. This research aims to propose groundwater management alternatives for a coastal aquifer by studying its vulnerability and in particularly the risk of seawater intrusion. An additional objective is to propose some agricultural policies aimed to conserve groundwater resources in Mahdia and Ksour Essaf. Intensive groundwater mining, for irrigation and for water drinking, has caused an overexploitation of the water resources. In addition, the degradation of water quality, caused by septic tanks and intensive agricultural activities, has given rise to notable crucial state of the groundwater resources. With the aim of tackling the groundwater degradation problem, integration into a common platform of vulnerability assessment, seawater intrusion modelling and hydrochemical analysis is proposed. This platform can considerably reflect the water resources state in order to propose some solutions reducing the contamination of the Mahdia–Ksour Essaf aquifer. The groundwater management alternatives, proposed in this study, were prepared within a geographical information system.

Application of chemical geothermometers to thermal springs of the Maghreb, North Africa

Abstract In order to assess the geothermal potential in the Maghrebian region, several studies have been undertaken in the three countries concerned, Morocco, Algeria and Tunisia, during the past decade. Research programmes have considered the surface evidence (thermal springs) and underground thermal information from deep and shallow wells. The main chemical characteristics of the sampled thermal springs and the results of the application of geothermometers as result from these studies are presented. Of the 238 inventoried thermal springs, 169 have been selected, on the basis of complete water analyses and acceptable ionic balances. Measured temperatures range from 22.5 to 98°C, thermal indexes from 0.5 to 78°C and salinities from 0.13 to 52.5 g/L. Most studied springs are sodium-chloride type waters. These basic data allow identification of the main thermal anomalies in the Maghrebian zone, which are located in regions of the Libyan-Tunisian, Algerian-Moroccan and Algerian-Tunisian frontiers, of northern Tunisia, the Eastern Rif and the northern part of the Saharan Atlas. Several chemical geothermometers have been applied to selected springs: NaK, NaKCa, NaKCaMg, Na/Li, Mg/Li, K 2 /Mg, quarts, chalcedony (Fournier) and chalcedony (Arnorsson). The NaK, NaKCa, NaKCaMg, Na/Li and Mg/Li geothermometers seem to give unreliable results, while K 2 /Mg and silica temperatures are apparently reasonable. However, dissolved silica seems to be governed by quartz solubility for some thermal springs and by chalcedony solubility for others. The results are tentatively compared with known geothermal gradients and geological features.

Hydrochemistry and geothermometry of thermal groundwater of southeastern Tunisia (Gabes region)

Given the vital importance of water and energy in desert regions, we undertook a study dealing with the deep reservoirs in Gabes area, which is located in the southeastern part of Tunisia. Geothermal resources are taken from the Intercalary Continental [or Continental Intercalaire (CI)], known as the largest deep aquifer in Tunisia and are used in a number of applications, mainly in agriculture. Previous investigations performed on the thermal waters of this area focused on the genesis of the deep waters with regard to the thermal features of geothermal reservoirs. A more detailed investigation has been carried out, considering both deep and shallow waters. In order to estimate the potential temperatures of deep reservoir in the Gabes area, we developed a synthetic study including chemical geothermometers, multiple mineral equilibrium approach, and other approaches. Chemical types of the thermal waters and effects of mixing between shallow cold waters with deep thermal waters were also discussed. In fact, the application of Na–K–Mg diagram relative to deep geothermal reservoir capitulate estimated temperatures (about 90°C). In addition, the multiple mineral equilibrium approach submits a similar estimated temperature ranging between 65 and 70°C, showing a disequilibrium status which indicates a possibly mixing with surface water. Indeed, wells exploiting the CI aquifer in the south part of the studied area showed the same characteristics, corroborating the reliability of the applied methods.

Hydrochemical analysis and evaluation of groundwater quality of a Mio-Plio-Quaternary aquifer system in an arid regions: case of El Hancha, Djebeniana and El Amra regions, Tunisia

A hydrogeochemical approach has been carried out in the Mio-Plio-Quaternary aquifer system of northern Sfax to investigate the geochemical evolution, the origin of groundwaters and their circulation patterns. The groundwater samples collected from different wells seem to be dominated by sodium chloride type to sulphate chloride type. Detail analysis of chemical data including the thermodynamic calculations was used to assess that the chemical evolution of groundwater is primarily controlled by water–rock interactions. The values of sodium absorption ratio and electrical conductivity of the groundwater were plotted in the US Salinity Laboratory diagram for irrigation water. Most of the water samples in northern Sfax fall in the fields of C4S1, C4S2 and C4S3 indicating very high salinity and medium to high sodium alkalinity hazard. Thus, groundwater quality is ranging between doubtful to unsuitable for irrigation uses under normal condition, and further action for salinity control is required in remediating such problem. Principal component analysis of geochemical data used in conjunction with bivariate diagrams of major elements indicates that groundwater mineralization is mainly controlled by (1) water–rock interaction processes, (2) anthropogenic process in relation with return flow of NO3-rich irrigation waters and (3) domestic discharges.

Shallow geothermal studies in Tunisia: Comparison with deep subsurface information

Abstract Shallow geothermal prospecting has been undertaken in three zones in Tunisia for which few deep thermal data are available. Five areas have been included in this work, and temperature data from depths between 35 and 335 m from 46 wells in these areas have been analyzed. In addition, thermal measurements have been made on 112 limestones, dolomites, and sandstones to add to the data base. Temperature profiles from the different areas vary substantially from well to well, and these variations depend on both the local and regional geological and hydrological conditions. The shallow thermal gradients vary from 11 mkm -1 to 132 mkm -1 , compared with the maximum deep gradient so far observed in Tunisia of 52 mkm -1 (Ben Dhia, 1988). The discrepancies between shallow and deep gradients in the various regions appear to strongly depend on the geological continuity between the shallow and deeper layers, especially in zones where substantial tectonism has occurred. It is concluded that although near surface geothermal data are useful in areas where few deep data are available, great care must be taken in their interpretation, and both regional and local conditions must be considered. Furthermore, predicting the temperature conditions at depth from these observations can be uncertain, and so combining results from such studies with those from deeper data must be done with care. The Zazghouan area appears as an interesting geothermal prospect, while the others need more investigation to be conclusive.

Mapping recharge potential zones and natural recharge calculation: study case in Sfax region

The groundwater constitutes the major water resource in the study area of the current paper that is Sfax region. The latter is located in the south of Tunisia where the climate is arid. In fact, the natural groundwater recharge of the region is deeply affected by the lack of precipitations which affects its natural groundwater recharge. The aim of the current paper is to define recharge potential zones and to estimate the rainfall recharge of the shallow groundwater. Henceforth, the potential recharge map was established, based on the basin characteristics using lithology, topography, slope, and stream network parameters. Recharge estimations were based on the numerical methods: the Estimation of Recharge in Overexploited Aquifers (Estimación de la Recarga en Acuíferos Sobreexplotados) (ERAS) numerical model, the Schoeller equation, the Fersi equations, and the Direction Générale des Ressources en Eaux (General Administration of Water resources) (DGRE) coefficients. As a matter of fact, applying the Fersi equations and the DGRE coefficients on the potential zones allowed the deduction of a new spatial repartition of both favorable and unfavorable recharge zones.

Impacts of climate change on water resources in arid and semi-arid regions: Chaffar Sector, Eastern Tunisia

AbstractGlobal warming is a worldwide phenomenon causing a temperature increase, which affects water resources. In Tunisia, high temperatures were recorded in the last decades with a warming tendency of about 1.1°C for 2020 and 2.1°C for 2050. The Chaffar region is characterized by an important agricultural activity and a semi-arid climate in which the irregular precipitations reach low values. Its shallow groundwater is overexploited with a disturbed hydraulic balance. A drawdown of its piezometric head has been noticed in the last decade because of high exploitation and rainfall deficit as a consequence of global warming. To highlight the impacts of the climatic changes on water resources in the Chaffar region, a mathematical model was prepared using MODFLOW program. It is of great importance to predict and simulate the effects of global warming on hydraulic head of Chaffar shallow aquifer, which is considered as a forbidden area for creating new wells. Considering a constant consumption, the piezometri...

Assessment and mapping groundwater quality using hybrid PCA-WQI model: case of the Middle Miocene aquifer of Hajeb Layoun-Jelma basin (Central Tunisia)

Dramatic increase of population in the Hajeb Layoun City and its surrounding areas (Sbeitla, Jelma) has led to a higher consumption of water for both domestic and irrigation demands. The various uses of these resources lead to the degradation of their quality and quantity. Therefore, water quality issues and its management options need to be given greater attention in this semi-arid region. The present study is the first attempt to determine the groundwater suitability for drinking and irrigation. The Middle Miocene aquifer of Hajeb Layoun-Jelma basin), Central Tunisia, was studied using hydrochemical and statistical approaches. According to the principal component analysis approach, the source of the groundwater mineralization is manifested by both natural (lithology, quality of recharge waters, and mixing with other types of water) and the anthropogenic processes (agriculture, urban development, and increasing exploitation of water resources). Thus, the suitability for drinking purpose was tested by “water quality index.” However, irrigation quality was evaluated by the sodium absorption ratio, the electrical conductivity, the Wilcox diagrams, the “water quality index,” the soluble sodium percentage, the magnesium hazard, and the Kelly’s ratio. Results indicate that only one third of the study area groundwater quality is suitable for drinking and irrigation uses. Thus, obtained results can be used as a basic document for realistic management of groundwater quality.

Guideline for Groundwater Resource Management Using the GIS Tools in Arid to Semi Arid Climate Regions

Food security emerged as an issue in the first decade of the 21st Century, questioning the sustainability of the human race, which is inevitably related directly to the agricultural water management that has multifaceted dimensions and requires interdisciplinary expertise in order to be dealt with.