Concept and idea

The applied methodology is shown in Figure 7.1. Initially, we studied water infiltration at the plot scale by measuring the different discharge components of surface runoff, subsurface flow and deep percolation for two winters (2000/01, 2001/02) at two locations in the southern Swiss Alps (Hannigalp, Gd St Bernard) Figure 7.2. The main purpose was to quantify the local effect of soil frost on the snowmelt infiltration. In addition to the water balance measurements, we ran dye tracer

Figure 7.1 Methodology of the project
Figure 7.2 Location of the two experimental sites (Basic map provided by BFS GEOSTAT/Bundesamt für Landestopographie). Courtesy BFS GEOSTAT

experiments in situ, as well as in the laboratory to obtain visual and quantitative information on the snowmelt infiltration pathways. By conducting these studies at two locations, which differed in their altitude, exposure and climate, we gained a better insight into the geographical and topographical induced variation of the snow and frost distribution.

Second, a one-dimensional SVAT-model was run to reproduce the detailed water and heat dynamics in the snow and the uppermost 3 m of the soil for the two experimental winters. For that purpose, we selected the model package COUP (Jansson and Karlberg 2001), which is one of the few SVAT-models that describe in detail freezing and thawing ofthe soil with all its influence on the water transport. The model was extensively calibrated to fit measured snow depth, frost depth and soil water content. By comparing the simulated fluxes with the runoff measurements, we aimed to indicate how well the model described the partitioning between surface runoff, lateral subsurface flow and deep percolation.

Third, long-term simulations were run with the calibrated model to extend our period of observations to earlier winters with known meteorological conditions. We simulated snow depth, snow water equivalent, frost depth and groundwater discharge for the recharge area beneath Hannigalp at a 250m-resolution, adjusting the meteorological inputs to the altitude. Finally, we compared these results with water-table elevation measurements, so as to evaluate a possible effect of soil frost on the aquifer recharge.

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