Mounira Zammouri

GIS based DRASTIC model for groundwater vulnerability assessment: Case study of the shallow mio-plio-quaternary aquifer (Southeastern Tunisia)

Groundwater is the main source of water in arid regions. Thus, groundwater pollution becomes a major issue due to the increasing contamination, which poses serious and harmful risk to the environment. Groundwater vulnerability maps can be used as a tool to help decision makers to protect groundwater resources from contamination. The vulnerability of the Mio-Plio-Quaternary shallow aquifer (Southeast Tunisia) has been assessed using a DRASTIC model based on Geographic Information System (GIS). The different parameters of the model were collected from several sources and converted into thematic maps using ArcGis©. Each DRASTIC parameter was assigned a weight and rating based on a range of information within the parameter. Groundwater vulnerability map shows a large area (48%) with high risk of pollution. It indicates that the Southern part of the aquifer and the wadi beds are the most susceptible to contamination. The measured nitrate concentration is coherent with the DRASTIC model results.

Coupling WetSpass and MODFLOW for groundwater recharge assessment: case study of the Takelsa multilayer aquifer, northeastern Tunisia

The water scarcity and its socio-economic significance with respect to water demand for agriculture, industry and tourism, in the northeastern Tunisia (Cap-Bon), are at the origin for prospecting new groundwater resources and for developing groundwater models that can be used to their control and management. The Takelsa multilayer aquifer is one of the important aquifers of the northeast in Tunisia. It is among the aquifers which are still slightly known in spite of its exploitation since the 80s. This paper is aimed to quantify the groundwater recharge of the Takelsa multilayer aquifer. The groundwater recharge is assessed using WetSpass which is a physically based model integrated in GIS ArcView as a raster model. The simulated results are given seasonally and yearly at the grid level. These results are subsequently incorporated in the groundwater flow simulation model MODFLOW in order to simulate the hydraulic head distribution. The steady state groundwater flow calibration was obtained by comparing the observed and the simulated hydraulic heads. The mean annual evapotranspiration, surface runoff and groundwater recharge simulated by WetSpass, are 461, 92 and 22 mm, respectively. The groundwater recharge represented 4.3% of the precipitation while 17.8% and 89% are respectively lost by surface runoff and evapotranspiration.

Effect of the spatial variability of transmissivity on the groundwater flow and budget of the Takelsa multilayer aquifer, Tunisia

Groundwater models are vulnerable to uncertainties, especially those that are developed based on incomplete knowledge of the hydraulic parameters. Transmissivity is often the most uncertain parameter in groundwater modeling. This work evaluates the effect of the spatial variability of transmissivity on the outputs of the groundwater flow model of the Takelsa multilayer aquifer. The study was based on a combination of deterministic and stochastic modeling. Groundwater flow modeling and stochastic simulations were made using the PMWIN software (a version of MODFLOW). Initially, the groundwater flow model was developed in the steady state. The criteria used for the calibration process were based on the comparison between the observed and the simulated hydraulic level. Then, a stochastic approach was used and 100 simulations of transmissivity were performed. The simulated transmissivity values were used to recalculate the hydraulic head and the water budget of the Saouaf deep aquifer. Finally, the consequent 100 results obtained by running MODFLOW were analyzed. The results showed variations in the hydraulic head levels, but the flow direction remained the same. The impact of the spatial variability of transmissivity on the water budget shows a range of inflow and outflow rates of Saouaf aquifer, with special relevance to the sea intrusion which may cause a probable deterioration of the quality of the groundwater.

Groundwater recharge modelling in semi-arid regions; a case study of El Khairat alluvial plain (Tunisia)

A regional decline of groundwater level is observed in the El Khairat plain. The increase in extraction is probably the main cause. The evaluation of groundwater recharge is an important step for the sustainable management of groundwater resources. A conceptual ‘rainfall–runoff’ model is developed to assess the El Khairat aquifer recharge. The model calibration aimed to reproduce the measured surface runoff and the observed water table level. Only 17% of rainfall recharges the aquifer, and the rest is mostly lost to evaporation. Analysis of the groundwater-level hydrographs indicated different hydraulic responses of the aquifer following rainfall events. Upstream, the water table rise is fast with a large amplitude, whereas a dampened response is observed downstream.

Groundwater Recharge Assessment Using WetSpass: Case Study of the Sidi Marzoug-Sbiba Aquifer (Tunisia)

The rainfall infiltration process depends on several factors related to climatic and hydrological conditions, land use and hydrogeological characteristics. These factors vary at spatial and temporal scales. The objectives of this work is to assess the groundwater recharge of the Sidi Marzoug-Sbiba aquifer using WetSpass, locate the favorable zones of natural recharge, and help water managers for selecting areas of possible artificial recharge following the global changes that can undergo the region. WetSpass calculates evapotranspiration, runoff and recharge. The Sidi Marzoug-Sbiba aquifer is located in the Center of Tunisia. It is formed by three juxtaposed reservoirs contained respectively in limestone, sandstone and coarse and fine sand. The study is carried out for an average state over the period 1980–1985 including wet and dry seasons. The results showed that the maximum recharge is 165 mm during the wet season, whereas it is reduced to 90 mm for the dry season. The mean annual recharge flux is calculated to 14.8 MCM/year, representing 28% of the average annual rainfall inflow. The most favorable areas to recharge are located upstream, at the level of the limestone outcrops and downstream at the level of the sandy formations. The assessment of the recharge and the identification of the favorable areas to natural recharge represent a fundamental guideline for water managers in order to consider a possible artificial recharge project. Other criteria such as global changes should also be considered before the final decision.

Assessment of Artificial Recharge Efficiency Against Groundwater Stress in the El Khairat Aquifer

The El Khairat aquifer located at the eastern center of Tunisia is mainly recharged by infiltration of flood water through beds of ephemeral streams. Since late 70s, the aquifer showed a continuous water table decline due to an excessive increase of groundwater extraction. The situation worsened by the damming of the El Khairat wadi which is the most important wadi of the region. Artificial recharge campaigns were carried out by Tunisian water agency to re-establish the natural groundwater recharge of the aquifer. They consisted of releasing water from the dam reservoir to the natural downstream bed of the wadi channel. This paper aims to assess the efficiency of the artificial groundwater recharge operations by developing a conceptual rainfall-runoff model. The model input consists of the daily water volume released from the dam. The wadi bed is divided into several serial reaches. For each reach, the production function is represented by a soil store and four transfer reservoirs. The model calibration consists of reproducing the daily surface runoff volume measured at the runoff gauging stations and the water table level measured at the piezometers located in close proximity of the wadi course. The modelling results indicate an infiltration coefficient ranging from 40 to 80%. Despite this high infiltration rate, the mean annual recharge in artificialized regime remains below the natural recharge. The construction of El Khairat dam could be a good resource management alternative under certain constraints as increasing the recharge campaigns frequency and avoiding releases with high discharge rate.

Groundwater quality assessment of the Takelsa phreatic aquifer (Northeastern Tunisia) using geochemical and statistical methods: implications for aquifer management and end-users

The Takelsa phreatic aquifer (Northeastern Tunisia) is an important source of fresh water for different economic sectors in the region that are strongly dependent on groundwater resources but, the aquifer is showing increasing signs of groundwater quality degradation like many other regions in the Mediterranean Basin. By integrating geochemical and multivariate statistical investigation methods, this research aims to identify the main geochemical processes and anthropogenic activities that are responsible for regional groundwater quality evolution, identifying the origins of salinity and nutrients, and their implications for groundwater use forcropirrigation and drinking water supply in order to improve aquifer management practices. The results show that groundwater facies vary from Ca–Mg–SO4 to Na–Cl water type and that mineralization is strongly controlled by mineral dissolution and cation exchange. The isotopic analyses indicate that groundwater is recharged by rainwater infiltration at higher altitudes and that a cumulative evaporative effect may contribute to local increase of salt content in groundwater. The Water Quality Index (WQI) used to determine the suitability of the Takelsa groundwater for drinking purposes reveals that just half of the groundwater points sampled show good to excellent quality for human consumption. The groundwater quality is also limited for irrigation purposes due to anthropogenic activities existing throughout the region. As groundwater in the studied region is crucial for irrigation and human supply, the identified groundwater quality problems and the identification of the main processes responsible for them should contribute to improve the infrastructure and managementpractices to allow the region to sustainable exploit the available groundwater resources.

Effect of planned marina on Enfidha groundwater (Tunisia) A local-scale groundwater modeling

The coastal Enfidha plain is located in the centre-east of Tunisia. A marina is planned downstream the plain and is likely to induce a risk on groundwater. A large scale modeling has been developed and used to evaluate the effect of the marina on the totality of the aquifer. Flow and solute transport models were built. In order to have results with higher precision, a local-scale modeling is developed by refining the mesh nearby the marina region. The submodel is calibrated over the period 1972-2005. Simulations are carried out for a 50-years period, to assess the impact details of the planned marina on groundwater quality. Results show an additional salinity increase reaching 10 g/l by the year 2055 around the planned marina. Affected areas are located mostly in the marshes regions.