Groundwater / meltwater interaction in proglacial aquifers

Abstract

Abstract. Groundwater plays a significant role in glacial hydrology and can buffer changes to the timing and magnitude of meltwater flows. However, proglacial aquifer characteristics or groundwater dynamics in glacial catchments are rarely studied directly. We provide direct evidence of proglacial groundwater storage, and quantify multi-year groundwater-meltwater dynamics, through intensive and high resolution monitoring of the proglacial system of a rapidly retreating glacier, Virkisjökull, in SE Iceland. Proglacial unconsolidated glaciofluvial sediments comprise a highly permeable aquifer in which groundwater flow in the shallowest 20–40 m of the aquifer is equivalent to 4.5 % (2.6–5.8 %) of mean annual meltwater river flow, and 9.7 % (5.8–12.3 %) of winter flow. Groundwater flow through the entire aquifer thickness represents 9.8 % (3.6–21 %) of annual meltwater flow. Groundwater in the aquifer is actively recharged by local precipitation, both rainfall and snowmelt, and strongly influenced by individual precipitation events. Significant glacial meltwater influence on groundwater within the aquifer occurs in a 50–500 m river zone within which there are complex groundwater / meltwater exchanges. Stable isotopes, groundwater dynamics and temperature data demonstrate active recharge from river losses, especially in the summer melt season, with more than 25 % of groundwater in this part of the aquifer sourced from meltwater. Such proglacial aquifers are common globally, and future changes in glacier coverage and precipitation are likely to increase the significance of groundwater storage within them. The scale of proglacial groundwater flow and storage has important implications for measuring meltwater flux, for predicting future river flows, and for providing strategic water supplies in de-glaciating catchments.

Proglacial groundwater storage dynamics under climate change and glacier retreat

“…This is made up of loosely consolidated, moderately to poorly sorted, dominantly medium-to F I G U R E 1 Study site including topographical map of Virkisá river basin and proglacial sandur groundwater catchment with instrumentation (a); conceptual model of water flow along cross section from glacier to groundwater adapted from Ó Dochartaigh et al (2019) (b); and photograph of sandur floodplain, meltwater channels and Virkisjökull taken from the southern boundary of the groundwater catchment (c) coarse-grained glaciofluvial sand, gravel and cobbles which have been deposited from actively shifting meltwater streams and frequent (c. 5 per century) jökulhlaups (Robinson, Fairchild, & Russell, 2008). Geophysical evidence from Tromino® passive seismic surveys indicate the deposits are up to 150 m thick within several kilometres of the lake outlet (Ó Dochartaigh et al, 2019). The Virkisá groundwater catchment forms part of the world's largest sandur, Skeiðarársandur.…”

“…Shallow borehole investigations have shown that the groundwater flows downstream, approximately parallel to the river (Ó Dochartaigh, MacDonald, Wilson, & Bonsor, 2012). However, stable isotope data have shown that there is a zone of meltwater-groundwater mixing within 500 m of river channel where more than 25% of groundwater is derived from mountain meltwater runoff (Ó Dochartaigh et al, 2019). River-aquifer water exchanges in both directions are promoted by the shallow water table which is typically between 0 and 4.4 m below ground level.…”

“…Given that the sandur is unconfined, the specific storage was also fixed to a representative value for unconsolidated coarse sand aquifers (Domenico & Schwartz, 1990). The river bed hydraulic conductivity and drain conductance were both set using the mean of the surface permeability measurements undertaken by Ó Dochartaigh et al (2019). Finally, the Manning's roughness coefficient was set to 0.05 based on the "normal" value for mountain streams with beds made up of cobbles and large boulders (Chow, 1959).…”

Improving understanding of shallow urban groundwater: the Quaternary groundwater system in Glasgow, UK

“…In the 19th and early 20th Centuries, groundwater, abstracted largely from Carboniferous bedrock aquifers in and around Glasgow, was widely used in industries that included distilling, brewing and other food and drink manufacture, dye works, iron works, sawmills, chemical manufacture, printing, shipbuilding and laundries (Ó Dochartaigh et al . 2011). Extensive groundwater abstraction also occurred from coal-bearing Carboniferous rocks during mine dewatering operations, with an estimated total abstraction at peak dewatering activity of approximately 215,000m 3 day –1 (Ó Dochartaigh et al .…”

“…Extensive groundwater abstraction also occurred from coal-bearing Carboniferous rocks during mine dewatering operations, with an estimated total abstraction at peak dewatering activity of approximately 215,000m 3 day –1 (Ó Dochartaigh et al . 2007). As industrial activity declined during the 20th Century, so did groundwater abstraction, and by the early 21st Century there were only a handful of groundwater abstraction boreholes within the city boundary, all from bedrock.…”