Thursday, October 15, 2009, 4:30PM - 5:30PM
Full title: "Three-dimensional quantification of meltwater flow through a snowpack using a snow guillotine: Methods, fieldwork, and some preliminary results."
In areas containing seasonal snowpacks, snowmelt contributes significantly to the hydrological cycle. Thus, quantifying the spatial distribution of flow through a snowpack is essential to accurate hydrograph interpretation and representation in snowmelt runoff modeling. Movement of liquid water through snowpacks is generally recognized to occur in distinct flow paths rather than as uniform flow through a homogeneous porous medium. Although dye tracer experiments have provided valuable qualitative information on meltwater flowpaths, quantitative descriptions of their spacing and location are not commonly available because of the difficulty in precisely excavating and measuring pathways. This makes it difficult to study scale and time-dependent processes such as the evolution of preferential flowpaths. Here we provide proof-of-concept using a new instrument we term ‘snow guillotine’ that provides quantitative information from dye tracer experiments in melting snowpacks. The structure of the snow guillotine allows the ability to take cross-sectional slices at 1-cm intervals of a snowpit where dye tracer has been applied. Photographs are taken of each cross-section over a one meter distance. Application of image processing and geostatistical analysis allows collection of high resolution (1cm3), three-dimensional data on meltwater flow through a snowpack.
Results from 2003 illustrate preferential flowpaths, with the majority of vertical flow occurring in the upper 20-55cm of the snowpack, while fewer preferential flowpaths are apparent below 100cm. The number of vertical flowpaths in the upper half of the snowpack averaged almost 100 per m2, with the highest number of flowpaths reaching almost 300 per m2. Layer interfaces were found to significantly increase the volume of dye, indicating dominance by lateral flow at these boundaries. 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. Preliminary results for guillotine experiments carried out for the 2009 melt season indicate the evolution of preferential flow did not transition from distinct flowpaths to matric flow as obviously as in 2003. This difference may be partly attributed to the difference in weather patterns between the two seasons, with colder temperatures and frequent precipitation events dominating the 2009 melt season.