FIGURE 5. Time series of mean daily depth to water table (2019 red line and 2020 blue line) observed at 9 locations during the period April 1st to July 1st in the Izas catchment. Red (2019) and blue (2020) dots show the mean snow depth measured with a UAV around (10 m2) each location.
During 2019 and 2020, electrical conductivity and temperature of the streamflow water showed a very similar temporal evolution. In both cases, a regular increase associated to the melting of snow cover was detected around the snow depletion date. Comparison between 2019 and 2020 years reveals that the shallower and shorter snowpack during 2020, triggered an earlier and faster increase in conductivity during the melting period.
In combination with streamflow data, the depth of the water table (and local snow depth) observed at 9 locations in the catchment (2019 and 2020) yield some additional information about the snowmelt influence on the dynamics of spring streamflow in the Izas catchment (Figure 5). The depth of the water table showed contrasted responses between piezometers. However, several common dynamics may be observed. Before the start of the main melting season (April and May), the water table was low (i.e. deeper than 0.6-0.9 m) at all location. However, when melt starts rapid water table fluctuations are observed in most locations, leading to several short periods close to saturation. Water table reaching the surface only was observed for short periods during the main melting events. Overall, the 2019 year showed shallower water table, associated to a deeper and longer-lasting snowpack than in 2020. In 2020, the water table dropped significantly in most of the piezometers, by the end of May, when snow cover was almost depleted in the catchment. At the contrary, in 2019, during the same period, water table was still close to the surface in several piezometers coinciding with a much larger snow-covered area in the catchment (Figure 2). Despite this general pattern, higher water levels were observed in some piezometers that had greater snow depth in their surroundings in- 2020 than in 2019.