Snowmelt Water Infiltration into Frozen Soil in Red River of the North Basin
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Infiltration into frozen soils is an important process in the hydrological cycle. Though infiltration occurs at the soil surface, it is affected by many factors, e.g. soil water content, temperature, and hydraulic conductivity. Understanding the snowmelt water infiltration processes into frozen soil helps to address issues about runoff generation and spring flooding in seasonally frozen area like Red River of the North basin (RRB). In this study, the methods of soil water release curve (SWRC) development, the effect of soil water content on frozen soil infiltration, and the variation of hydraulic conductivity for different RRB soils in frozen and unfrozen conditions were examined and evaluated. The objectives of this study were: (1) to construct SWRC using combined HYPROP and WP4 method, (2) to evaluate the soil water and temperature effects on the infiltration into frozen soil, and (3) to compare predicted hydraulic conductivity of three frozen soils of RRB with measured values using minidisk infiltrometer. It was found that HYPROP+WP4 combined method produced acceptable SWRC of RRB soils compared to other available traditional methods. However, shrinking and swelling of clay content of the soils might cause difference with in-situ measurement. Infiltration into frozen soil depended on initial soil water contents. The drier the frozen soil, the higher the infiltration rate. Soil water content changed gradually with rising temperature in a dry soil but in a frozen wet soil, it was very rapid due to the phase changing of water. The Horton infiltration model was fitted with measured frozen soil infiltration data with good agreement. Hydraulic conductivity of frozen soils decreased with an increase in soil water contents, but it was also subjected to sand and clay contents of the soil. Simple nonlinear regression model fitted with measured data and resulted reasonable agreement compared to Motivilov model. Freeze-thaw cycles altered the soil pore distribution, decreased the infiltration rate and hydraulic conductivity of frozen soils.