Field experimentation and modelling of salt transfer in Korba coastal plain: impact of seawater intrusion and irrigation practices

Seawater intrusion and agricultural pollution are the major sources of groundwater contamination and salinization in coastal irrigated areas. The Korba coastal aquifer, located in the Cap Bon peninsula, North-East of Tunisia, has been intensively exploited since the seventies. Several studies reported the sharp piezometric drop and groundwater salinization. Seawater intrusion was presented as the major source of salinity and irrigation return flow was rarely considered. <br> In this study, we are proposing to identify soil and groundwater salinization sources and processes. Besides, an endeavour to quantify solute irrigation return fluxes is presented. To fulfil these objectives experimental and numerical studies were performed. <br> Two transects perpendicular to the shoreline and following two flow paths (the first landward and the second seaward) were selected. Soil and groundwater investigations were periodically performed along theses transects. They involved soil and groundwater sampling, piezometric measurements and Electrical Resistivity Tomography Imaging. Various geochemical methods were applied to analyse the collected data. Besides, multivariate statistical analysis techniques were performed to assess salinity sources and processes. Modelling of the seawater/freshwater mixing problem was also carried out using PHREEQC code. HYDRUS1D was used to simulate long term salt transfer towards groundwater. <br> The results show that seawater intrusion and agricultural pollution are the major sources of salinity. Seawater intrusion was controlled by cation exchange, carbonate weathering and redox processes. Agricultural pollution is enriching the groundwater with NO3, Ca, SO4, and K elements. Geochemical and multivariate statistics techniques estimated the seawater penetration length of about 4000 m. <br> The soil survey confirms the latter result. It shows that the soil solution gets concentrated in the dry season with possible calcite and gypsum precipitation. Rainfall, afterwards, leaches the soil and reduces its salinity. <br> The unsaturated modelling revealed that the solute flux considerably depended on the irrigation amounts and the vadose zone thickness. It also demonstrated the important role of stormy episode in the leaching process.

Thèse de doctorat : Université de Neuchâtel, 2010 ; 2197