Geomorphological and sedimentological influences in groundwater hydrodinamics: an example from Peninsula Valdés, Patagonia, Argentina

ALVAREZ MARÍA DEL PILAR; HERNÁNDEZ MARIO ALBERTO; ARIZTEGUI DANIEL

Encuentro; SwissSed Meeting; 2014

Geomorphology, geology, and climate are first-order determinants of hydrogeological phenomena, not just hydrodynamic but also hydrochemical ones. A study case is presented to assess the relationship between geomorphology and hydrodynamics and its relevance in studies in arid regions, where there is a closer correspondence between hydrogeological units and the geoforms containing them (Alvarez et al 2010). The area has an average rainfall of 232mm/year and a soil moisture deficit of about 472mm/year. The main geomorphic units were identified by interpreting Landsat 7 satellite images and then surveyed in the field, as well as by sedimentological characterization. The forms analyzed were grouped into four major units according to Súnico (1996): Terrace-like plains (Tp), Endorheic depressions (Ed), Sand dunes and sandy layers (SdSl) and Coastal area (Ca). The local hydrogeological system was identified on the base of the hydrolithological and stratigraphic characteristics emerging from the geological map (Haller et al 2001) and the field observations. The system is formed by an unsaturated zone corresponding to the Quaternary deposits (mainly sand, gravel and silt) and partly to the Tertiary sediments (mainly marine deposits formed by sands, coquinas, silts and clays with abundant volcanic ash) of the Puerto Madryn and Gaiman Formations. A phreatic aquifer is contained within these same deposits or in the sands of the Puerto Madryn Formation, which is exploited mainly in the region. Below it there are one or more semiconfined or confined aquifers, limited by clayey or siltyclay strata in the same Puerto Madryn Formation or in the underlying Gaiman Formation. All the aquifers are unconsolidated and porous. The hydrodynamic analysis was based on a survey of 89 monitoring wells, the construction of equipotential maps, and the interpretation of pumping-test results by a nonequilibrium method. The combination of geomorphological, sedimentological and hydrodynamic elements allowed the definition of hydromorphological units. The SdSl unit corresponds to major recharge areas (highly permeable aeolian sands), where the phreatic surface has a radial morphology with a tendency towards a divergent cylindrical one, the Tp unit has the most extensive groundwater circulation areas, with the lowest hydraulic gradients in the region (