Tohkamachi Experimental Station in Niigata prefecture, Japan, which is located along the Sea of Japan, usually has heavy snowfall in the winter. At this site, melting snow and rain are frequently observed in the middle of winter, because it has a higher temperature than other cold regions. As a consequence, water frequently infiltrates through the snowpack, creating vertical water channels. In this study, a new parameterization of the water channel process was implemented in a multiple snow layer model, which already had the infiltration process represented using the Darcy's law.
The conceptual procedure used to model the water channel was based on the impermeable processes through which water infiltrates into dry snow and a new snowpack. The model does not consider the impermeable processes associated with a capillary barrier at the boundary between the fine textured upper layer and the coarse textured lower layer or at the boundary between the snow upper layer and the ice lower layer. The new parameterization controlled the vertical water flux at the wetting front layer just above the dry snow layer by a limiter which was expressed as the threshold value of the liquid water content. The water which should go through the water channel was removed at the uniformly infiltrated part of the snowpack.
We found that the new water channel process implemented in this study worked well when it was applied to a rainfall event in the middle of winter, based on the vertical structure in the snowpack with a comparison between the pit observations and the simulated results. This comparison showed that the simulation with the water channel was more accurate than that with uniform infiltration. The seasonal mean of the agreement scores with the parameterization of the channel flow (0.91) became larger than the score under the uniform flow condition (0.79). (C) 2009 Elsevier B.V. All rights reserved.