Vertical transport of rain through a snowpack: Experimentation and numerical modeling

Rainfall on top of an existing snowpack can result in significant flooding. Recent advances in climate science indicate that rain on snow events are likely to become more frequent in the future. Resultant flooding, however, can be difficult to predict without accurate estimates of snowpack characteristics and an understanding of the processes that translate the rainfall and snowmelt to runoff. A laboratory experiment was conducted to observe rainfall traveling through snow and the flow released from the snowpack. The snow was made in a laboratory cold room and sifted into an insulated box to a two foot depth. The snow was instrumented with temperature and soil moisture probes at 2 inch intervals. Two leaf wetness sensors were placed in the snow to test their ability to detect liquid water moving downward. In addition, an upward-looking radar was placed at the bottom of the snow to observe the wave front as it moved down. Rainfall was simulated by a box above the snow which dripped at a known flow rate onto the surface of the snow. The instruments were able to detect the wave front as it moved through the snowpack. The experimental results were used to validate a one-dimensional model of vertical flow through the snow. The experimental and numerical model results are presented with suggested improvements for future tests.