Présentations Colloques

Oral Presentation
Session 6.02: Treated WasteWater REUSE for groundwater recharge: addressing the challenge
Jarraya Horriche Faten
Modeling of groundwater artificial recharge in a heavily exploited coastal aquifer- The case of Mornag (Tunisia)
In the framework of an integrated water resources management project, different options of artificial groundwater recharge are studied as means to mitigate the effects of over-exploitation of the Mornag coastal aquifer in Tunisia. While the aquifer is also utilised for drinking water supply, the over-exploitation is primarily due to an increasing irrigation water demand caused by a substantial expansion of irrigated agriculture during the last decades. In recent years, the number of wells has dramatically increased, leading to a drawdown of groundwater levels of more than 20 m in some locations.**Starting in the 90s, artificial groundwater recharge using fresh water is being practiced in two former quarry sites at outcrops of the deep sandstone aquifer. In the present study different artificial recharge options are compared, e.g. activation of further quarries, intensification of recharge in the non-perennial river beds (wadis), construction of injection wells and recharge ponds. Re-use of treated wastewater is also considered, given the quality complies with the national standards and does not adversely affect the aquifer chemistry. **The impact of the different alternatives is assessed using FEFLOW, a 2D 3D finite element saturated unsaturated subsurface flow and transport modeling software. The regional scale conceptual model is based on an existing study (with Processing Modflow) where the aquifer is represented by a shallow phreatic and an underlying confined part. Grace to a local refinement of the finite element mesh, the important recharge structures like wadis or recharge ponds are precisely modeled. At recharge sites where a significant distance to the groundwater table exists a vertical unsaturated approach is used to model the respective flow. **First results show that, because of unfavourable vertical hydraulic conductivities at the possible recharge pond sites, a combination of several recharge alternatives is necessary. As today’s quality of the treated wastewater is not appropriate for injection into the groundwater, temporal recharge scenarios are presented that bridge the deficit until treated wastewater of sufficient quality is available.