Investigating proglacial groundwater systems in the Quilcayhuanca and Yanamarey Pampas, Cordillera Blanca, Peru.

摘要

High-elevation Andean water storage is extremely important for water resources for the arid western coast of South America. Pampas (a subset of paramos) are a freshwater reservoir in the Cordillera Blanca, Peru. These organic-rich clay systems buffer stream and river runoff to the Rio Santa and provide water to surrounding communities. More than 50% of dry season discharge from pampas is groundwater derived, however little is known about their geomorphology and subsurface sedimentology. Watertable measurements, streambed temperature sensors, and ground penetrating radar (GPR) were used to characterize the subsurface and develop a formational model for the Yanamarey and Quilcayhuanca pampas, Cordillera Blanca, Peru.;The water table in July 2009 was found on average to be 0.35 m and 0.57 m below the land surface at Quilcayhuanca and Yanamarey respectively. In the Yanamarey Pampa, streambed temperature sensors showed that upstream, water flows from the stream into the ground and further downstream, water flows upwards recharging the stream. From watertable measurements, a watertable map was produced that showed steeper watertable gradients further up valley. GPR was an effective tool for imaging the subsurface to a depth of 8 meters in the high permittivity material and delineated four stratigraphic units at both sites. In sequence the units are; dry sandy peat soils with pebbles at the surface, water saturated soil with sand and pebbles, linear stratified clay and glacial outwash intermixed with colluviums deposits. The identification of the subsurface sedimentary units allowed for the creation of formation models of both sites. The valley walls of Quilcayhuanca are steeper than Yanamarey, which caused more landslides and consequently more extensive colluvial deposits throughout the Quilcayhuanca valley subsurface. These connected colluvial deposits are likely the primary zone for groundwater flow and storage.