Studies on the Delay Mechanism of Runoff to Snowmelt
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概要
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In order to investigate the mechanism of the meltwater infiltration through a snowpack as a snowmelt runoff process, field observations were made at a watershed, 1.3km^2 in area, in northern Hokkaido, Japan. The time of peak runoff became earlier with decreasing snow depth and it differed yearly. The yearly difference was about 2 hours when the snow depth was 100 cm. The discharge at the bottom of the snowpack was observed with a large snow lysimeter. The result showed the yearly difference in the apparent infiltration speed which was consistent with that in runoff. The speed for the snowpack with several ice layers was about 30 cm h^-1 and 15 cm h^-1 for the snowpack with a few ice layers when the daily snowmelt was 20 mm. The author considered that meltwater concentrated at the ice layers and the concentrated meltwater flowed at a larger speed. The concentrated flow was observed with a lysimeter consisting of 100 compartments of 200 cm^2. At a certain compartment, the daily discharged exceed over 30 times of an average snowmelt. We classified meltwater flow to three groups : 1) small number of high concentrated flows; 2) relatively large number of low concentrated flows; 3) many non-concentrated flows. The simulation of the infiltration through the snowpack considering these meltwater flows reproduced the observed discharge at the bottom of snowpack and yearly difference in the infiltration speed better than that without concentration. The travel time of the infiltration in the snowpack on a slope was close to that on a flat site because the meltwater moved downslope on the ice layer much faster than vertical and the distance was small. The infiltration on a slope can be treated in a similar manner to that on a flat site. The simulation of the infiltration in the snowpack is extended to the whole watershed with a kinematic wave method for slope and stream flows. The simulation reproduced the observed discharge and the yearly difference in the runoff response very well.
- 北海道大学の論文
- 1995-03-31