A multi‐method field experiment to determine local groundwater flow in a glacier forefield

Abstract

Abstract:We implemented multiple independent field techniques to determine the direction and velocity of groundwater flow at a specific stream reach in a glacier forefield. Time-lapse experiments were conducted using two electrical resistivity tomography (ERT) lines installed in a cross pattern. A circular array of groundwater tubes was also installed to monitor groundwater flow via discrete salt injections. Both inter-borehole and ERT results confirmed this stream section as a losing reach and enabled quantification of the flow direction. Both techniques yielded advection velocities varying between 5.7 and 21.8 m/day. Estimates of groundwater flow direction and velocity indicated that groundwater infiltrates from the stream nearby and not from the adjacent lateral moraine. Groundwater age estimated from radon concentration measurements supported this hypothesis. Despite uncertainties inherent to each of the methods deployed, the combination of multiple field techniques allowed drawing consistent conclusions about local groundwater flow. We thus regard our multi-method approach as a reliable way to characterize the twodimensional groundwater flow at sites where more invasive groundwater investigation techniques are difficult to carry out and local heterogeneities can make single measurements unreliable.

Linking baseflow separation and groundwater storage dynamics in an alpine basin (Dammagletscher, Switzerland)

“…This results in strong advection in the direction of streamflow, as shown in Kobierska et al (2015). The mean gradient between S1 and S7 is 13.5 % over a distance of 840 m. Between S0 and S5, the steepest section of the forefield has gradients of over 20 % for approximately 150 m. Near-stream lateral groundwater gradients are primarily influenced by diurnal stream stage fluctuations rather than by topography-driven longitudinal gradients (Magnusson et al, 2014).…”

“…1). In 2008, annual precipitation and evapotranspiration for the whole catchment were estimated at 2300 and 70 mm, respectively (Kormann, 2009). With a yearly cumulative discharge of approximately 2700 mm, the water balance of the catchment is clearly posi- Figure 1.…”

“…The area in the vicinity of S3 is composed of a relatively impermeable silty surface layer, which leads to surface runoff during storms, as evidenced by scouring of the surface (see Fig. 2 in Kobierska et al, 2015). The area between S5 and S0, where the topography suddenly steepens, is rich in springs, which display seemingly constant flows (in the order of 10 L s −1 per spring) during the summer season.…”

Resolution capacity of geophysical monitoring regarding permafrost degradation induced by hydrological processes

“…infiltration of meltwater or degradation of ground ice) (Hilbich et al, 2009;Merz et al, 2015). Their non-invasive nature also allows repeated measurements of the same profile (Hilbich, 2010;Hilbich et al, 2011;Kneisel et al, 2014), which can considerably improve the identification of hydrological processes in alpine permafrost systems Wright et al, 2009), non-permafrost catchments (Kobierska et al, 2015) and in 1-D infiltration studies (Scherler et al, 2010). Rock glaciers, however, belong to the most challenging landforms for geophysical monitoring.…”

Authors response to reviewers

“…infiltration of meltwater or degradation of ground ice) (Hilbich et al, 2009;Merz et al, 2015). Their non-invasive nature also allows repeated measurements of the same profile (Hilbich, 2010;Hilbich et al, 2011;Kneisel et al, 2014), which can considerably improve the identification of hydrological processes in alpine permafrost systems Wright et al, 2009), non-permafrost catchments (Kobierska et al, 2015) and in 1-D infiltration studies (Scherler et al, 2010). Rock glaciers, however, belong to the most challenging landforms for geophysical monitoring.…”