USING MULTIPLE, INTEGRATED HYDROGEOPHYSICAL METHODS TO UNDERSTAND GROUNDWATER/SURFACE WATER INTERACTIONS IN GLACIATED, TROPICAL CATCHMENTS OF THE CORDILLERA BLANCA, PERU

Tropical glaciers, which are particularly susceptible to global warming, are found in the lower latitudes of Asia and Africa, although 99% of the world’s tropical glaciers are located in the Andes of South America. The lack of seasonality in tropical temperatures, distinct wet and dry seasons, and year-round ablation of these glaciers give rise to concern over the availability of water resources in glacially-fed tropical catchments, especially in arid and semi-arid regions. Although the presence of mid-latitude glaciers tends to amplify intra-annual variability in runoff of glaciated catchments, in the tropics glaciers have a buffering effect on stream runoff, resulting in a lower variability in streamflow throughout the year. The Cordillera Blanca, Peru, contains the largest concentration of tropical glaciers, many of them draining westward through arid landscapes toward the Pacific via the Rio Santa. As temperatures increase and glacial volume reduction accelerates, the proportion of flow provided to the Rio Santa via glacial melt during the region’s dry season will decrease by up to 40%. Recent work has shown, however, that alpine catchments throughout the Cordillera Blanca also have the potential to store and transmit groundwater at a rate significant enough to supply the valley streams with up to half their flow during the dry season. With this context in mind, we are using innovative hydrogeophysical field and modeling techniques to quantify water fluxes between surface water and groundwater in the glaciated catchments of the Cordillera Blanca. Preliminary investigations of the relative contribution of glacial melt and groundwater in the Quilcayhuanca valley, a valley typical of the Cordillera Blanca, have used geochemical mixing models and dye tracing experiments. According to these studies, the talus and moraine deposits are significant groundwater reservoirs for these systems. The subsurface extent of these features, along with bedrock topography and the hydraulic conductivity of valley sediments, is currently being quantified using seismic and electrical geophysical methods. The information derived from these geophysical surveys will be used to conceptualize a groundwater flow model of the area in order to quantify groundwater inputs to the stream by subsurface connections and surface springs.