Présentations Colloques

Oral Presentation
2.01
Session 2.01: Groundwater in semiarid regions – a long-term view on changes in aquifer balances. Hydrogeology in developing countries.
Hassen Imen
Estimating groundwater recharge in an arid region in Central Tunisia using Chloride Mass Balance and Unsaturated modeling
Central Tunisia is characterized by a semi arid to arid climate where groundwater is the primary source of water supply. Oum Ali-Thelepte aquifer, located in Kasserine (Central Tunisia) with an arid climate, is among the most available water resources in the region. Natural recharge quantification is thus a crucial issue for a better evaluation of this resource.**The present work aims to estimate and study groundwater recharge processes at the long term in an arid context. Chloride Mass Balance (CMB) and variably saturated numerical modeling are the retained methods to fulfill these objectives.**Potential recharge areas of the aquifer were already identified using hydrogeological, geochemical and isotopic methods. Selected sites (in the recharge areas) were then retained to perform soil sampling. In the present study we are presenting investigations carried out in one representative site located near the North West of the Algerian border. 18 interstitial water samples have been obtained from the unsaturated zone using a dry drilled soil profile of 8m depth (reaching groundwater level). Soil texture, bulk density, gypsum content, water content and physico-chemical analyses (pH, Temperature, Electrical Condictivity, Na, Ca, Mg, K, HCO3, Cl, SO4, F and NO3) were performed. **CMB was applied for both groundwater and the unsaturated zone (chloride profile method). Hydrus-1D was calibrated using field and climate data at a daily scale and for a long time period to reach a nearly steady state regime.**The mean annual recharge calculated was 7.13 mm year (2.34% of the mean annual rain) using the chloride profile method and 3.81 mm year (1.26% of the annual rain) using the CMB for groundwater. Model calculations showed that the average annual recharge was about 11.28 mm year (3.7% of the mean annual rain). The recharge rate obtained from these different methods is relatively of similar range values. Calculations are to be continued for the remaining selected sites in order to attribute recharge rates for each recharge area. **
Tunisia