Locating and characterising groundwater storage areas within an alpine watershed using time-lapse gravity, GPR and seismic refraction methods

Unconsolidated sediments in alpine watersheds can store glacier melt and snowmelt as groundwater, which helps sustain flow in mountain rivers during dry periods. However, the amount and distribution of groundwater storage in rugged alpine terrain is not well understood, hindering our ability to predict the rate and timing of groundwater discharge into alpine streams. We show how non-invasive time-lapse microgravity surveys can be used to gauge the spatial distribution of groundwater storage changes within a large (ca 1500 x 1000?m) morainetalus field of the Lake O'Hara alpine watershed of the Canadian Rockies. Additional ground-penetrating radar (GPR) and seismic refraction surveys provide complementary information on subsurface bedrock topography and reveal the location of a major northwestsoutheast trending depression that likely controls groundwater flow to an alpine lake contiguous with the morainetalus field. Repeat relative gravity measurements made on a network of 80 gravity stations over and around the morainetalus field during the summers of 2009 and 2010 reveal gravity changes of up to 25 mu gal. Although the small gravity changes associated with groundwater flowing out of storage areas are noisy, significant changes are evident on the eastern side of the morainetalus field. (C) Her Majesty the Queen in Right of Canada 2012.