GROUNDWATER CONTRIBUTIONS TO STREAMFLOW IN A GLACIERIZED CATCHMENT OF THE CORDILLERA BLANCA, PERU
We present the results of a study of groundwater-surface water interactions in the Quilcay watershed, which is typical of the western-facing valleys of the central Cordillera Blanca in that the stream flows through a series of low-gradient wet meadows, punctuated by steeper moraine and landslide units. We performed a series of artificial tracer dilution experiments along the stream in both meadow and moraine reaches, including a 4-km-long constant-rate tracer injection, which covered two moraine-to-meadow sequences. We were able to estimate both gross and net inputs of groundwater to the stream along this length and characterize the geochemistry of inputs. We found that groundwater contributions were significant as the stream flowed through both meadow and moraine units; however, we observed concentrated zones of groundwater discharge to the stream where it transitioned from steep moraines into shallower meadow reaches. In these locations, we measured net increases in stream discharge of 10-to-20 percent over relatively short reaches. We discuss the implications of these findings for our conceptual model of valley hydrogeology, as well as for downstream water quantity and quality.