HYDROGEOLOGY IN GLACIATED HIGH-ELEVATION ANDEAN WATERSHEDS – RESULTS FROM THE CORDILLERA BLANCA, PERU
Our research focuses on low-relief ‘pampa’ valleys which have a total area of ~65 km2 and are comprised of unconsolidated glacial, talus, lacustrine and wetland (bofedales) deposits. The valleys commonly have buried talus aquifers (hydraulic conductivity of 10-5 m/s) that are overlain by low permeability, glaciolacustrine deposits (hydraulic conductivity of ≤ 10-7 m/s). Glaciofluvial outwash deposits also act as aquifers (hydraulic conductivity of 10-4 m/s), and are enhanced when cross-cut by streams. A ubiquitous feature of the pampa valleys are springs located at the base of talus deposits, which comprise a large component of the hydrologic systems, based on hydrochemical mixing analysis. Groundwater discharge and recharge to streams is spatially heterogeneous. For example, for a headwater basin of the Llanganuco Valley, almost all of the stream water exiting the catchment spent some time in the subsurface, with approximately half of the surface water originating as groundwater. The residence time of water stored in these systems is generally less than 3-4 years and the maximum observed dry season groundwater velocity is 60 cm/day (based on average linear velocity calculations). The results are synthesized with conceptual models of pampa formation and hydrogeology.