Abstracts

Freeze and Cherry, 1979) hypothesized that diurnal watertable fluctuations commonly
observed in shallow monitoring wells could be used to estimate actual evapotranspiration
rates. In recent years, application of the White method has gained renewed interest in the
literature, although the theoretical basis of the technique has not yet been explored to our
knowledge. In order to test the applicability of White’s method, we applied HydroGeo-
Sphere (HGS), a 3D fully-integrated surface and variably-saturated subsurface flow and
transport model that can account for vegetation-dependent evapotranspiration processes,
coupled to an Atmospheric Boundary Layer Model (ABL). ABL is a 0D time-dependent
energy and water balance model. A number of test cases are examined involving different
vegetation types and hydrologic conditions. Our simulations replicate the diurnal watertable
oscillations commonly observed in field data, and, when the model output data are
analyzed using White’s method, it is found that the results generally agree with the actual
evapotranspiration computed internally within the coupled HGS-ABL model, but significant
discrepancies can occur.
218 – Impact of Snow Cover and Frozen Soil on Water and Gas
Fluxes through Unsaturated Sands
Sophie Guillon, Florent Barbecot, Marie Larocque, & Daniele L. Pinti
GEOTOP, UQAM, Montréal, Québec, Canada
Eric Pili
CEA, DAM, DIF, Arpajon, France
Seasonal freezing of part of the vadose zone and presence of seasonal snow cover is of
concern for all regions in Canada. The occurrence and thickness of frozen soil and snow
cover are directly responsible for water, energy and gas fluxes from the surface to aquifers
and vice-versa. In these cold environments, groundwater recharge mainly occurs during
the spring snowmelt and as a result of fall rain. Smaller recharge events also occur during
the winter due to melting at the snow-soil interface and infiltration into frozen or partly-thawed
soil. But soil water dynamics and water infiltration before the onset of spring
snowmelt are neither well studied nor constrained, and they are not considered by the
models currently used to calculate groundwater recharge. The intensity and duration of
these winter recharge events appear to be controlled by the thickness and permeability of
frozen soil and its frozen water content. Fluxes of CO 2
and other trace gases such as CH 4
and N 2
O have been shown to occur during winter and to contribute to the annual gas
budget, but they are often not measured or considered. Microbial processes, temperature
and soil permeability are involved in controlling these gas fluxes, which need to be better
understood and quantified. The objective of this work is to better understand the influence
of soil freeze/thaw events on water infiltration and gas fluxes during winter. This presentation
will describe a case study based on the monitoring of water and gas fluxes in the
frozen vadose zone and in the snowpack during the winter season at an instrumented site
located on a sand deposit (esker), west of Montreal (Canada). Water content, temperature,
air pressure, CO 2
and radon concentrations are measured in the first meters of soil and in
the snowpack during winter season. Water stable isotopes depth profiles are used to identify
spatial and temporal variability of water infiltration. These data are used to develop,
184 IAH-CNC 2015 WATERLOO CONFERENCE