融雪流出の研究 (I)

山地積雪と融雪季流出率について

抄録

The snow survey and the investigation of snowmelt runoff were carried out in the basin (of an area of 28.3 km²) of the Tsukari, a branch of the Hira-Kawa, Aomori prefecture, during the winter of 1955-1961.
The paper presents the full analysis of geographic distribution and time variation of the snow cover and the runoff ratio in the melting season.
The analysis are summarized as follows:
(1) During the melting season, the equivalent water of snow increases with increasing latitude, and the relation is approximated in the good accuracy by the expression of linear function, as shown in Fig.2. A similaf latitudinal variation is discernible to the snow depth.
(2) The mean decrease of the equivalent water of snow at several latitudes on the basin, during the melting season, can be expressed by the following equations:
d<16 days...E=22.0-0.50d+ (0.043+0.002d) h
16<d<60 days...E=44.7-1.92d+ (0.043+0.002d) h
where d is days from the beginning of spring thaw, E is equivalent water of snow and h is latitude.
(3) The frequncy distribution of the snow density measured at several points over the basin throughout the melting season are normal as shown in Fig.4, and 95 percent of the density falls within a range of ± 0.15 about the mean density of 0.38. After the beginning of melting, the average density over the basin increases approximately at the rate of 0.04 per 10 days.
(4)The average depth of equivalent water of snow over the basin is represented considerably by the equivalent water of snow observed in the central part of the basin near its median elevation.
(5) The runoff ratio to the whole melting season (from the beginning of the melting to the time when the snow cover disappeared over the basin) changes between 0.50-0.80 every year, and it average value is 0.60±0.14.
(6)The ratio of the short period runoff (about 20 days) ranges between 0.30-0.95 during the melting season. One of the factors determining the ratio of the short period runoff is the ratio (D) of the no snow-cover area to the whole area. The average short period runoff ratio takes following values depending upon the values of D:
D<50 percent...0.69+0.11
D>50 percent...0.47+0.15