Snow melting water infiltration mechanism of farmland freezing-thawing soil and determination of meltwater infiltration parameter in seasonal frozen soil areas

In seasonal frozen soil areas, much meltwater is formed during the thawing period, which easily causes snowmelt floods and waterlogging disasters. The meltwater simultaneously replenishes groundwater and produces surface runoff to provide water for crop roots. However, there are insufficient researches on the infiltration process of meltwater under day thaw and night freezing conditions. Meltwater infiltration process and estimation could provide an important reference for spring irrigation, meltwater disaster early warning systems and soil pollution research. In this study, the law of mass conservation was adopted for meltwater infiltration estimation under 15 and 30 cm snow covers. According to the hypothetical curve trend characteristics of meltwater infiltration rate, it is proposed to adopt Boltzmann distribution function and determine the curve parameters through experimental results, and the average daily maximum infiltration rate of frozen soil is 0.0622 cm/hour. During the thawing period, the soil moisture content changes periodically, and the period lasts approximately 10 h. We also put forward the concept of the maximum meltwater storage volume (Ϝ) of farmland meltwater, which provides a new analysis structure for meltwater runoff research. During the thawing periods, when the snow cover thickness in the early stage of thawing period exceeds Z, the amount of meltwater infiltration does not greatly change, and the maximum infiltration volume is between 3.15 and 5.25 cm. The average daily meltwater infiltration amounts to 0.15 cm.