Visualizing meltwater flow through snow at the centimetre-to-metre scale using a snow guillotine

Movement of liquid water through snowpacks remains one of the least understood aspects of snow hydrology. Liquid water movement through snowpacks is generally recognized to occur in distinct flow paths rather than as uniform flow through a homogeneous porous medium. Dye tracer experiments have been used in studies of meltwater flow through snow since the 1930s. Although dye tracer experiments have provided valuable qualitative information about meltwater pathways, quantitative descriptions of their spacing and location are not commonly available because of the difficulty in precisely excavating and measuring pathways. Here we provide a new proof-of-concept instrument we term a 'snow guillotine' that provides more quantitative information from dye tracer experiments conducted on melting snowpacks. Photographs are taken of each cross-section over a 1-m distance. Application of image processing and geostatistical analysis allows collection of high-resolution (1 cm(3)), three-dimensional data on meltwater flow through a snowpack. The results show preferential flowpaths, with the majority of vertical flow occurring in the upper 20-55 cm of the snowpack, while fewer preferential flowpaths are apparent below 100 cm. The number of vertical flowpaths in the upper half of the snowpack averaged almost 100 per m(2), with the highest number of flowpaths reaching almost 300 per m(2). Layer interfaces were found to significantly increase the volume of dye, indicating dominance by lateral flow at these boundaries. At each stratigraphic interface, the number of individual clusters decreased and it was more likely for a dyed pixel to be part of a large cluster. Geostatistical analyses showed that there were large increases in correlation lengths and the connectivity function at stratigraphic layers in contrast to low values between layers. For example, the buried ice layer in Experiment A at 169-170 cm showed separation distances of 20 cm. In contrast, two rows above this layer the separation distance was only 2 cm. Implementation of the snow guillotine provides the ability to conduct geostatistical analyses on field measurements of meltwater flow while providing three-dimensional, quantitative data of unprecedented spatial resolution. Copyright (C) 2010 John Wiley & Sons, Ltd.