Spatial Variability of Snow-Pack Outflow at a Site in Sierra Nevada, U.S.A.

Water flow through natural snow-packs is generally accepted to be extremely variable even over short dista nces. Differences in snow properties, and discontinuities in the horizontal and vertical structures of snow-packs, are responsible for variations in the effective area of the snow surface associated with outflow from a part of the base of the snow-pack. At the Central Sierra Snow Laboratory snow-pack outflow has been monitored using four snow-melt Iysimeters of 6 m area each; two of these collectors were subdivided into three sections of equal area. Substantial variatIOns in daily and monthly outflow volumes were noted between the individual collectors and also to a greater degree between the 2 m2 sub-units of the divided containers. The relative collecting efficiency of the snow-melt Iysi meters also changed over time. In the deep warm snow-packs of the Sierra Nevada forest zone, snow-pack water routing appears to be highly variable, and this variability is on a much larger scale than was previously recognized. The large differences in snow-pack outflow measured in this study suggest that structural discontinuities and microtopography of snow strata can redirect percolating water over an area of several square meters.