The Runoff on the Snowfall Source Basins

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The phenomena of snowfall and snow melt are seemed very excellent storage functions of rain. The discharge during snow melting period occupies from 40 to 60 percent of a year discharge. Because the snowmelting period from April to June, there are very important problems at agricultural hydrotechnics as regards dam management.1. Because the construction of the Kanayam Dam at the upper basins of the Sorachi river, there is a change of runoff characteristics which are increase of low-flow and decrease of flood flow.2. The runoff of the source basins at the Ishikari river is regional differences. At the foot of the Tokachi Mountain, the discharge for a year is very small. On the other hand, at the foot of Syokanbetsu Mountain and the upper basins of the Aoyama dam, it is a great deal of discharge, about 3000mm.3. About low flow in dam basins, because rain fall stored as snow for snowfall period, the least discharge for snowfall period are smaller than for rainfall-runoff. It is ablo to regard it as the same phenomenon that non-rainfall circumstances continue for a long time.4. There is a correlation between the average discharge of the least five days for a year and the rain fall for n days before this value is occurred. At the basins of Horobetsu basins, there is the highest correlation value in n = 25. On the other hand, at Oyubari basins, the correlation coefficient is 0.71 as biggest value, in n = 70.5. At the basins of dam in cold regions, it is necessary to consider the coefficient of rain fall. This is the coefficient for place (plane, point) and for height. The value of the coefficient are very large and equal to the rainfall from 1.5 to 2.0 times as much as observed rainfall for basins.