Présentations Colloques

    Oral Presentation
    Session 2.01: Groundwater in semiarid regions – a long-term view on changes in aquifer balances. Hydrogeology in developing countries.
    Jourde Herve, Viguier Benoit
    Assessments of groundwater recharge in the hyperarid Tarapaca alluvial fan (Northern Chile) at various scales of time and space.
    In drylands, the scarcity of streams and their temporal variability have led to a particular interest for groundwater. The alluvial fans describe complex sedimentary patterns. In order to understand the current and future behavior of groundwater resources, especially under climate change, the recharge processes need to be properly characterized. The study focus on Northern Chile, where high seasonal precipitation events occur between December and March in the Precordillera (4500 m a.s.l) associated with ENSO variations. These events lead to local flooding above the alluvial fans in the downstream hyperarid Central Depression (1000 m a.s.l)+ where the regional size Pampa del Tamarugal Aquifer is located. This strategic resource is one of the main issues in Northern Chile. Groundwater recharge through the Tarapaca Alluvial Fan (TAF) - around 150 kmC - is assessed by combining environmental tracers, piezometric records, geomorphic surveys and flow modelling at different scales of space and time. **Vertical flows in the vadose zone were assessed by sensitivity analysis, computed with Hydrus-1D software, at the flood events scale. The saturated flows, at the TAF scale, were assessed by 2D flow modeling (Feflow software). These results are in line with the piezometric records analysis and highlight contrasted recharge areas, correlated with geomorphic patterns, implying various recharge rates between few mm.d-1 and mm.yr-1. In some areas, at distance from the TAF, the recharge can be considered as nil. Groundwater age inferred from 14C (between 14 and 107 pMC) and dating tools (3H He, SF6, CFCs) sampled at the water table depth, are compared with groundwater ages estimated from flows modeling.**The assessment of groundwater recharge in dryland alluvial fans, need to be quantified by multidisciplinary approaches (environmental tracers, piezometric records, geomorphic surveys, flow modelling) at different scales of space and time.**


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