Natural and artificial recharge investigation in the Zéroud Basin,Central Tunisia: impact of Sidi Saad Dam storage

Hydrochemical and isotopic data of waters from the Zéroud aquifer have been used to potentially provide a means for locating occurrences and to trace movements of a variety of natural and anthropogenic recharge waters in the Zéroud Basin, Central Tunisia. Geochemical data have been measured during the dam water release, from May to September 2005, with a sampling time step of 15 days. An implication of dam water has been demonstrated that is noticeable up along the main flow path to a distance of 10 km far from the injection site. Environmental isotopes ²H, ¹⁸O and ³H of water molecule were studied to investigate the effect of dam water on the hydrological system, and an isotope balance was established to compute the contribution of water storage component in groundwater. Based on isotopic mass balance, we assess that an average of 13% of total groundwater in the upper aquifer came from dam water storage. Three distinctive recharge waters in the aquifer can be determined. Water from local rainfall (pre-dam Zéroud River) that infiltrated into the boundaries of the Draa Affane Mountain was easily distinguished from the water influenced by anthropogenic recharge located in the Zéroud right rivulet. Distinguishable isotopic signatures of native wadi Zéroud recharge due to “recent lineal recharge” through the riverbed were also identified.     

Enhanced pumping test using physicochemical tracers to determine surface-water/groundwater interactions in an alluvial island aquifer,river Rhône,France

Groundwater extracted from the Barthelasse Island aquifer, surrounded by the river Rhône (southeastern France), contributes to the drinking water supplies of 180,000 inhabitants. Owing to its location close to the river and the presence of two backwaters (oxbow lakes), the pumped groundwater is highly vulnerable to river pollution. A pumping test was conducted over 24 h to analyse and quantify the water exchange processes between the river, backwaters and groundwater. During the pumping test, isotopic (δ¹⁸O, δ²H and ²²²Rn), hydrochemical and hydrophysical monitoring of the groundwater was undertaken. Hydraulic heads were measured in pumping wells and at a piezometer located between the wells. Discrete water samples were collected at several observation points in the field, including the backwater and river. The results show mixing between three end-members, as defined by the deuterium excess and silica concentration, led by river Rhône water which had been affected by water–rock interactions over time and mixing with surface evaporated waters. The pumped water resulted from mixing between three end-members, all of which depended on the river Rhône but differed in terms of residence time in the system. Although the groundwater pumping wells are close to each other (<70 m) and have similar depths, the changes in the contributions from end-member waters at each well were different during the pumping test. Comparing isotopic tracers and geochemistry made it possible to quantify the different hydrological compartments that contribute to the groundwater pumped from the boreholes, which is critical in constructing a conceptual flow model.