22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Combining unsaturated zone modelling with indirect and direct measurements to quantify solute transport during snowmelt

23 Sep 2019, 15:15
Auditorium 2 ()

Auditorium 2

Oral Topic 5.3 - Advanced modelling tools for subsurface hydrology: from the vadose zone to deep environments Parallel


Prof. Helen Kristine French (Norwegian University of Life Sciences)


To improve risk assessment, monitoring, and treatment strategies of contaminated sites in cold climates, we require improved methods for monitoring solute transport and infiltration in the unsaturated zone. Previous studies have documented a highly heterogeneous infiltration during snowmelt this may have a large influence on the risk of contaminating the groundwater in areas where the use of de-icing chemicals is required for winter maintenance of roads and runways. In the last decades the use of geophysical techniques has become more widespread in order to monitor hydrogeological processes. The bulk electrical resistivity of an unsaturated soil profile is a function of soil water content, electrical conductivity of the fluid phase and soil temperature. Time-lapse electrical resistivity tomography (ERT) of a thawing partly frozen unsaturated zone during snowmelt infiltration gives a qualitative impression of how meltwater and salts moves through the unsaturated zone. Here we explore whether the ground truthing methods such as soil water samples from suction cups providing electrical conductivity of the water, tensiometer readings providing information about soil water content and soil temperature can quantify the different contributors to the change in electrical resistivity. The work is based on a combination of a field experiment during the snowmelt of 2010 and unsaturated zone modelling with Sutra_2D3D. The field experiment was conducted at Moreppen experimental lysimeter trench. Which is located next to Oslo airport, Gardermoen, Norway, where large amounts of de-icing chemicals are used to remove snow and ice every winter. During snowmelt these chemicals (Propylene glycol is used for the air planes and Potassium Formate used for the runways) infiltrate into the soil. Bromide, as an inactive tracer, and de-icing chemicals potassium formate and propylene glycol were applied to the snow cover prior to the onset of snowmelt and their percolation through the unsaturated zone was monitored with water sampling from 30 suction cups. At the same time cross-borehole electrical time-lapse measurements (with Syscal Pro, Iris instruments) and automatic measurements of soil tension and temperature were collected. Individual inversions were temperature corrected, to compensate for the change in soil temperature throughout the melting period. To estimate water contents from the ERT values, petro-physical relationships and fitting parameters from soil at Moreppen were used, this gave water contents similar to those estimated from tensiometers. Since petro-phyiscal relationships are required to convert from changes in electrical resistivity to changes in water contents and electrical conductivity of the fluid phase, experimental data was compared with a numerical model. We used the unsaturated zone model SUTRA-2D3D to explore the sensitivity of the parameters in the van Genuchten soil retention curve, and porosity, to the quantitative interpretation of the water and solute behaviour based on the time-lapse electrical resistivity measurements.

Primary authors

Prof. Helen Kristine French (Norwegian University of Life Sciences) Dr Esther Bloem (Norwegian Institute of Bioeconomy Research (NIBIO) ) Ms Astrid Søiland (Multiconsult, Norway) Prof. Andrew Binley (Lancaster University)

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