Hamed Ben Dhia

Minimization of environmental risk of landfill site using fuzzy logic, analytical hierarchy process, and weighted linear combination methodology in a geographic information system environment

This paper presents a GIS-based multi-criteria site selection for municipal solid waste landfilling in Ariana Region, Tunisia. Based on the regional characteristics, literature related to disposal sites and waste management, local expert, data availability and assessments via questionnaires, 15 constraints, and 5 factors were built in the hierarchical structure for landfill suitability by multi-criteria evaluation. The factors are divided into environmental and socio-economic groups. The methodology is used for preliminary assessment of the 20-year most useful lifetime suitable landfilling sites by combining fuzzy set theory, weighted linear combination (WLC) and analytic hierarchy process (AHP) in a GIS environment. The criteria standardization is undertaken by application of different fuzzy membership functions. The fuzzy membership functions shape and their control points are chosen through assessment of expert opinion. The weightings of each selection criterion are assigned depending on the relative importance using the AHP methodology. The WLC approach is applied for alternative landfill sites prioritization. The results of this study showed five potential candidate sites, which are generated when the environmental factors are valued higher than socio-economic factors. These sites are ranked in descending order using the ELECTRE III method. However, the final decision will require further detailed geotechnical and hydrogeological analyses toward the protection of groundwater as well as surface water.

The geothermal gradient map of central Tunisia: comparison with structural, gravimetric and petroleum data

Abstract Five hundred and fifty temperature values, initially measured as either bottom-hole temperatures (BHT) or drill-stem tests (DST), from 98 selected petroleum exploration wells form the basis of a geothermal gradient map of central Tunisia. A “global-statistical” method was employed to correct the BHT measurements, using the DST as references. The geothermal gradient ranges from 23° to 49°C/km. Comparison of the geothermal gradient with structural, gravimetric and petroleum data indicates that: 1. (1) the general trend of the geothermal gradient curves reflects the main structural directions of the region, 2. (2) zones of low and high geothermal gradient are correlated with zones of negative and positive Bouguer anomalies and 3. (3) the five most important oil fields of central Tunisia are located near the geothermal gradient curve of 40° C/km. Such associations could have practical importance in petroleum exploration, but their significance must first be established through further investigation and additional data.

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.

Geochemical and isotopic study of the multilayer aquifer system in the Moulares-Redayef basin, southern Tunisia / Etude géochimique et isotopique du système aquifère multicouche du bassin de Moulares-Redayef, sud tunisien

Abstract Major ion geochemistry, and water molecule isotopes (18O, 2H) and radiogenic carbon (14C) of dissolved inorganic carbon (DIC) were used to investigate the hydrodynamic functioning of the multilayer aquifer system in the Moulares-Redayef basin, southern Tunisia. The groundwater of different aquifer levels is characterized by sulphate to calcium sulphate water type. The major geochemical processes in the aquifer system are evaporite mineral dissolution and mixing. The isotopic study allows two groundwater types to be identified: an old palaeoclimatic groundwater, marked by low 14C activity and relatively depleted stable isotope (18O and 2H) content characterizes the shallowest aquifers of the Plio-Quaternary and Miocene formations; however, a recent groundwater, distinguished by relatively high 14C activity and slightly enriched 18O and 2H content, characterizes the deep Upper Cretaceous artesian aquifer. In addition to these two water groups, other groundwaters are identified, indicating a mixing effect.

Groundwater evolution of the Continental Intercalaire aquifer of Southern Tunisia and a part of Southern Algeria: use of geochemical and isotopic indicators

AbstractThe expansion of irrigated agriculture and the overexploitation of groundwater aquifers are leading to saltwater intrusion, severe deterioration of groundwater quality and soil subsidence at arid areas. The geochemical processes taking place along an 800 km flow line in the non-carbonate Continental Intercalaire aquifer (CI) in North Africa are described using chemical (major and trace element) and isotopic indicators. The aquifer is hydraulically continuous from the Atlas Mountains in Algeria to the Chotts of Tunisia and the geochemical evidence corroborates this. The CI aquifer of North Africa is one of the largest confined aquifers in the world. The aquifer is hydraulically continuous from the Atlas Mountains in Algeria (recharge area) to the Chotts of Tunisia (discharge area) and the geochemical evidence corroborates this. The isotopic study (Delta18O, Delta2H) permits classifying groundwater into three groups. The first group is characterized by low 3H concentrations, low 14C activities and d...

A methodology to design and predict operation of a solar collector for a solar-powered desalination unit using the SMCEC principle☆

A methodology is proposed to design and predict operation of a solar collector for the desalination unit using the SMCEC principle. The corresponding dynamic model developed from the thermal energy and mass balances is based in the double infinite temperature hypothesis for the fluid and the absorber. This model represents an extension of the one-temperature model presented in a previous paper [1]. Two numerical methods are used for solving the corresponding model. The first method uses the well-known finite difference method, while the second solves the equations by using the functional approximation method. Experimental validation is carried out on the solar collector and the whole desalination unit to determine which of the two methods is most suited for theses studies. The good results confirm that the new theoretical model resolved with the orthogonal collocation method represents better the real behavior of the system and can be used to investigate the effect of various parameters on the performance of the collector and the production of the desalination unit.

Tunisian geothermal data from oil wells

Since direct measurements of steady‐state temperatures are not readily available in Tunisia, a geothermal investigation has been made using 1319 values of bottom‐hole temperatures (BHTs) obtained from 217 petroleum exploration wells. An empirical relation based on the differences between BHT and DST (drill stem tests) was used to correct BHTs and estimate geothermal gradients. The estimated geothermal gradient of the country varies between 21 and 52 °C/km. A few regions with similar gradients have been identified, and similarities between gradient contours and the main structural directions are noted. Furthermore, for 25 points from 12 wells, it was possible to apply the Horner‐plot method to determine the equilibrium formation temperature (Tf). Comparison of Tf values with those calculated by the estimated gradients reveals a good correlation (r = 97 percent) between the two estimates. This agreement permits greater confidence in the statistical method used and consequently in the estimated gradients for...

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.

Multivariate statistical and geostatistical techniques for assessing groundwater salinization in Sfax, a coastal region of eastern Tunisia

AbstractIn this study, we investigate the ability to combine a multivariate statistical analysis with the cokriging method to point out the groundwater salinization in the coastal Sfax aquifer (eastern Tunisia). First, multivariate statistical analysis such as principal component analysis (PCA) and cluster analysis were performed on 75 water samples. PCA identifies three main processes influencing groundwater chemistry which are seawater intrusion, water–rock interaction, and contamination by nitrates, these three factors accounted for 76% of total variance of the groundwater. Furthermore, cokriging is applied to take into account spatial dependence between the studied variables. Five variables were processed: concentration of sulfates, chlorides, sodium and the sodium adsorption ratio, as primary variables, and the more numerous data for total dissolved solid, as auxiliary variables. The generated spatial variability maps highlighted the high-risk zone of groundwater contamination of the superficial aqui...

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.