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UBC Theses and Dissertations

Scale dependence of factors controlling the release of water from snow and ice storage Braun, Ludwig Niklaus


A study of the scale dependence of the factors controlling the release of water from snow and ice storage was conducted during the ablation season 1978 in the watershed of Miller Creek, located in the Pacific Ranges of the Coast Mountains, B. C. The results of this investigation support distinct predictive relationships at an open site, a small-scale watershed (area 3.3 km²) consisting of a flat valley bottom and a forested south-facing slope, and a partly glacierized meso-scale watershed (area 23 km²) of complex topography. The role of snow storage in the small-scale watershed is complicated by the nature of the horizontal stratification. Slope was found to have a greater influence than vegetation density in determining the amount of snow storage. The vertical zonation of seasonal snow-cover is also complex in that there is a decrease with height up to 200 m from the valley bottom, and an increase of about 200 mm W.E. per 100 m above. Approximately 60% of the melt energy available at the Meadow site came from net radiation; of the remainder most is assumed to be advected sensible heat. Streamflow generation in the small-scale watershed was greatly influenced by the gradual release of water from poorly drained, swampy areas. At the Meadow site, the snow stratigraphy, the mean daily air temperature (as a surrogate variable for energy availability) and the vertical flow pathways through the snowpack were the dominant controls of water release at the base of the snowpack. Typical response times of the meltwater release were time lags of 1 to 4 hours between the peaks of net radiation and melt flux, and recession constants between two and ten hours. At the small watershed scale, vegetation cover, slope and elevation, topoclimatic unit distribution and horizontal as well as vertical flow pathways were the dominant controls of water release, as measured in a stream channel at the mouth of the watershed. Time lags between peak net radiation and peak streamflow changed through the melt season from 8 hours at the beginning to 3 hours at the end, while recession constants remained consistently high at 150-200 hours. At the meso-scale, the distribution of glacier ice, perennial and seasonal snowcover, and lake and channel storage complexities make the analysis of water release mechanisms via conventional hydrograph analysis impractical. Time lags varied greatly from 6 to 13 hours at the beginning of the melt season and became more steady during the summer, falling from about 10 hours to about 5 hours between late June and early September. Recession constants remained highly variable between 50 and about 200 hours through the whole melt season.

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