Groundwater : meltwater interaction in a proglacial aquifer

• Main Authors: O Dochartaigh, B.E., MacDonald, A.M., Black, A., Everest, J., Wilson, P., Darling, W.G., Raines, M., Jones, L.
• Format: Text
• Language: English
• Published: British Geological Survey 2016
• Subjects: Earth Sciences; Glaciology; Hydrology; glacier; Iceland
• Online Access: http://nora.nerc.ac.uk/id/eprint/514786/; https://nora.nerc.ac.uk/id/eprint/514786/1/ODochartaighetalGroundwaterMeltwater.pdf

Groundwater plays a significant role in the hydrology of active glacial catchments, with evidence that it may buffer changes in meltwater river flow and partially compensate for glacial loss. However, to date there has been little direct research into the hydrogeology and groundwater dynamics of proglacial aquifers. Here we directly investigate the three dimensional nature of a proglacial sandur (floodplain) aquifer in SE Iceland, using hydrogeological, geophysical, hydrological and stable isotopic techniques, and provide evidence of groundwater-melt water dynamics over three years. We show that the proglacial sandur forms a thick (at least 50-100 m), high permeability (transmissivity up to 2500 m2/day) aquifer, extending over an area of approximately 6 km2. At least 35 million m3 of groundwater is stored in the aquifer, equivalent to ~23-28% of total annual river flow through the catchment. The volume of mean annual groundwater flow through the aquifer is at least 0.1-1 m3/sec, equivalent to ~10-20% of mean annual river flow. Groundwater across the aquifer is actively recharged from local precipitation and strongly influenced by individual rainfall events and seasonal precipitation. Glacial meltwater influence on groundwater also occurs in a zone extending from 20-500 m away from the meltwater river, for at least 3km down-sandur, and to at least 15 m deep. Within this zone summer recharge from the river to groundwater occurs when meltwater river flows are high, maintaining high summer groundwater levels compared to winter levels; and groundwater temperature and chemistry are strongly influenced by meltwater. Beyond this zone there is no substantial meltwater influence on groundwater. From ~2 km down-sandur there is extensive groundwater discharge via springs, supporting semi-perennial streams that form distinct local ecosystems, and providing baseflow to the main meltwater river. This research indicates that predicted continued climate change-related reductions in glacier coverage and increases in precipitation ...