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).
Movement of snowmelt freshet for different conditions (a) water table percolating meltwater into stream (Dingman, 2002)
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)
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.
Prairie Ecozone boundary (Source: Esri Canada)
During the ice breakup period in the Upper Qu’Appelle River (QAR), higher flows from the freshet can lead to ice jamming, overtopping of channel dykes and bridge decks and flooding of surrounding agricultural areas along the river The Qu’Appelle River dam regulates the flow from the Lake Diefenbaker to the downstream upper Qu’Appelle River (Figure-1). At the end of the winter season, ice thicknesses begin to reduce due to increased air temperatures and river water temperatures. Despite of drastic reductions in discharge prior to freshet runoff, mechanical ice breakup and jamming may still occur, depending on the amount of snow remaining in the basin, the strength competency of the ice cover and the rate at which air temperatures increase. Previous studies provide an indication of the severity of ice jamming and flooding that could occur at the most vulnerable section of the Upper Qu’Appelle River, between the PFRA Bridge and Tugaske Bridge bridges (Figure-3), where dyke crests and bridge decks are lowest in elevation relative to the channel.
Figure 1: The Qu’Appelle River
Erosion is an action of fluid force which transport soil and rock from one location to another location. The driving forces for erosion are water, wind, ice and gravity. Soil loses its productivity as it loses the nutrient content, water storage capacity and organic content. Erosion due to hydraulic action is the most complex form of erosion. It occurs in land surface as well as riverbed and riverbanks. In the land surface, erosion initiates after fall of energized raindrop, which disrupts the soil integrity and cause loose soil. Both rain water and ice mass carry a lot of sediment and drains into the river. Runoff volume increases the amount of suspended sediment in the river. Based on river flow velocity, longitudinal slope, flow depth and bed roughness, riverbed also erodes and increases the amount of suspended sediment in the water.