Identification, explanation and quantification of the hydrologically important components of an Andean Watershed

Puna grasslands, found above the tree line and below the permanent snow line from southern Perú through central Chile and Argentina, regulate the flow of water to streams in unglaciated uplands. Water originating in these landscapes is already used by small to large Andean populations, and this water source will become increasingly important as communities reduce their dependence on glacial runoff, and as a warming climate demands greater irrigation inputs. Our project, funded by Geoscientists Without Borders, employed geologic, hydrologic, and geophysical field based techniques to identify the water holding and releasing portions of the Ramuschaka Watershed, a 6.2 km² basin draining puna grasslands that supplies irrigation water to the agrarian community of Zurite, Perú. Through two month-long field seasons (July 2018 and June 2019) we led groups of 10-19 American and Peruvian geologists, engineers and hydrologists in a geological, hydrological and shallow-geophysical investigation of the watershed. We found that lithology, and structure, as well as the geomorphology of recent glaciations, have first order controls on the presence or absence of water in the watershed. Specifically, the location of low permeability mudstone or quartzite underlying low gradient, glacially excavated basins allow for the growth of bofedales, or high elevation peat lands, which are saturated most of the year. Water supplied to these bofedales comes from fault-controlled springs, or the proximity of low-permeability unweathered bedrock to the surface. Furthermore, the presence of bofedales within the landscape appears to moderate discharge and sustain vitally important dry season flows in the Ramuschaka Watershed.