積雪内への融雪水の滲透

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Melting of snow begins at the surface of snow cover, and the melt water permeates downwards into the cover. However, permeation does not always occur uniformly in a downward direction. In order to study the permeation of melt water, the free water content was measured in each of the snow layers composing the snow cover at constant intervals by the use of the “Combination Calorimeter” designed by Z. Yosida. The figure (a) at the top of Fig. 2 is a diagram showing the change in the distribution of free water in the upper half of a snow cover on flat ground. Another example on the permeation of melt water into a snow cover is illustrated in Fig. 3. In the two diagrams of Figs. 8 and 9 are shown the results of the simultaneous observations made on both sides of a long hill. The free water content in the uppermost layer at the surface of the snow not only increases very rapidly as compared with that in the lower layers but also maintains a large value for the entire day as shown in Figs. 2 (a), 3 (a), 8 (a), 9 (a) and 9 (b). The thickness of this layer of large water content remains constant at 3 cm throughout the day, in spite of the descent of the surface of snow cover due to melting. The reasons of these phonomena were discussed in detail. There are two modes of permeation of the melt water : (1) water channel flow, Fig. 11 (a), in which the melt water fills the voids between the ice grains of snow and flows down rapidly through it as uninterrupted columns of water and (2) water film flow, Fig. 11 (b), in which the melt water covers the ice grains of snow and flows down slowly in the form of thin films which are from several to several tens microns thick. The speeds at which the melt water of these two modes permeates into the snow were observed and compared with those theoretically derived. In the case of water channel flow, the observed values ν, 1.21.5 cm/sec, agree with the calculated values ν* rather well in the case of fine grained snow but not so well in the case of coarse grained snow. In the case of water film flow, the observed and calculated values are in good agreement in the case of coarse grained granular snow, while they disagree in the case of fine grained snow, which is the opposite of the case of water channel flow.
社団法人日本雪氷学会の論文

著者

若浜五郎
北海道大学低温科学研究所

積雪内への融雪水の滲透

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