Impacts of Snow Cover and Frozen Soil on Groundwater Recharge

English Abstract:

In many Northern Hemisphere locations, groundwater recharge mainly occurs during the spring snowmelt and as a result of fall rain. In these cold environments, smaller recharge events also occur during the winter due to melting at the snow-soil interface and infiltration into frozen or thawed soil. But soil water dynamics and water infiltration before the onset of spring snowmelt are neither well studied nor constrained. 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. We present a case study based on the monitoring of water fluxes during the winter season at an instrumented site located on a sand deposit (esker), southwest of Montreal (Canada). Water content and temperature are measured in the first meters of soil and in the snowpack during winter season. Tracing experiments using D₂O-enriched water are performed to identify water infiltration, fluid velocity and transport mechanisms. Heat and hydraulic parameters are determined for the frozen soil and the snow cover. These data are used to validate and calibrate a numerical scheme to quantify water and heat budgets as well as water recharge fluxes. This work focuses on the availability of liquid water at the soil surface and on the influence of soil freeze/thaw events on the possibility and extent of winter infiltration as opposed to surface runoff.