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.