Mar 22, 2015

Movement of Snowmelt Water

Movement of snowmelt freshet occurs in two forms, vertical flow (infiltration, percolation) and horizontal flow (baseflow, overland flow). Liquid water percolate into lower layers in the snowpack when the total volumetric capacity of snowpack exceeds the water retention capacity. During the time of rapid snowmelt, overland runoff occurs when the infiltration rate becomes lower than snowmelt rate. Figure-4 shows the snowmelt freshet movement for different soil condition. Water follows horizontal unsaturated zone into stream (Hirashima et al., 2010). Canadian prairie is characterized as cold semi-arid climate with clay-rich soils and underlying glacial till. Snowmelt cause significant amount of runoff in upland. Prairie topography allow to hold a significant amount of water storage in the snowmelt period, but high evaporation and low precipitation dry up the soil by late fall. Upland snow accumulation, evaporation, antecedent soil moisture condition are important features for prairie snowmelt freshet movement (Shook et al., 2013; Winter & Rosenberry, 1995; Woo & Rowsell, 1993).

Energy Balance of Prairie Snowmelt

Snowmelt refers to the phase change of ice into water, which is involved with energy absorption. If net incoming radiation is negative then it refers as condensation and if net incoming radiation is positive it refers to melting. The net energy is the amount of energy used for phase change and transfer of radiation, convection, conduction, and advection flux into snowpack and the rate of change of internal energy. The amount of energy is estimated using simple empirical equation, which uses readily available measured meteorological variables.
Figure- Energy balance control volume (Pomeroy et al., 2007)

Snow-melting in Canadian Prairies

Figure- Prairie Ecozone boundary (Source: Esri Canada)
Snowmelt is one of the most significant hydrologic process in the Prairies. In hydrology, snowmelt refers to the melting and subsequent processes regarding snow. It is generally occurs at the end of winter, but mid-winter thaws and melt are not rare phenomena. Snowmelt freshet recharges soil moisture and groundwater and replenishes lakes, reservoir and river in Prairie region (Norum et al., 1976). Solar radiation energy flux plays a vital role for Prairie snowmelt (Male & Gray, 1981). Shortwave radiation is the dominant part of solar radiation energy and snow surface albedo controls the incoming radiation flux. Granger & Gray (1990) observed that albedo decrease of 0.0061 per day during pre-melt period and 0.071 per day during melt period in the prairies. The major features of snow melting in Prairies are-