Mechanism of Snowmelt Runoff Through Snowpack Pathways in Snowy Mountains

Abstract

We conducted an investigation assuming that the behavior of meltwater within the snowpack significantly influences the runoff mechanism during the snowmelt period in the heavily snow-covered mountainous region. In the watershed based on the Hida metamorphic rocks, which were the target substrate, the electrical conductivity of stream water during baseflow was high, and its value decreased with an increase in water discharge. In the watersheds of snowy mountainous regions, during the severe winter period, the daily average temperature was generally below 0℃. The water supply to the watershed occurred solely from the snowmelt water at the base of the snowpack. Subsequently, as the daily average temperature rose above 0℃, surface melting occurred, and the snowmelt water began to flow into the streams. During the initial stages of snowmelt, even a slight increase in water discharge led to a significant decrease in the electrical conductivity of stream water. However, as the snowmelt progresses and the outflow increased, the similar decrease in electrical conductivity shifted to occur with more substantial increases in water discharge. The observed changes in the relationship between snowmelt runoff and electrical conductivity (EC) were estimated to be due to some of the surface-melted water not infiltrating vertically to the ground surface. Instead, it was believed to flow laterally within the snowpack and reach the streams through subsurface pathways, contributing to the altered EC levels during the snowmelt period. Therefore, it was considered that snow accumulation plays a significant role in the runoff mechanism during the snowmelt period in snowy mountainous areas.