Forecast of thawing inundation is important for an effective operation of a hydroelectric power plant. A method of forecasting the date of inundation has been developed. In this method, the date of inundation is predicted on the basis of the correlation between the integrated atmospheric temperature during a certain period of time and the date of thaw. The integrated atmospheric temperature is checked by the critical point (0. 40 g/cm³) of the density over the whole layer of snow drifts that provides a necessary condition for inundation. The data of weather forecast are also adopted as reference.

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This paper presents the analysis of snow depth, snow melt and runoff using aerial photographs.
In the first place, the natural topographic features were divided into several waves of different wave length, using a digital terrain model. Then, the relations of the local topographic and climate components to the snow depth and the amount of snow melting were examined.
In the next place, the runoff analysis was made by the following method : The direction and the period of flow of snow melt were expressed by vectors using a vector model of the whole basin, from which the course and the total time of flow between a given point and the outlet of river were deduced.

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In the midwinter of 1968, the mountain lodging house “Raichoso” halfway up Mt. Tateyama in the Japanese North Alps was destroyed by a snow avalanche, and nobody knows when it occurred.
About 30 holes were made near the ruins of the house by melting snow with hot water which was led through a long tube from the “Jigokudani” hot spring. The debris layer containing the broken pieces of the house was easily distinguished from the naturally accumulated snow layers. In Fig. 2, the vertical length of each rectangle represents the depth of snow and the hatched part represents the location of the debris in snow. The heap of debris, as shown by Fig. 3, spread in the extension of the Raicho valley. The volume of debris was estimated at about 4. 3×10⁴m³ and the mass about 2. 3×10⁴ tons.
The lodging house had been almost completely crushed by the avalanche, leaving only a part of the partially destroyed first floor. Fragments of the broken house were scattered about in the area of 100 m by 150 m.
One of the requisite conditions for causing a large fresh snow avalanche is a continuous heavy snowfall. The depths of fresh snow observd at the weather stations in the vicinity of the Raicho valley are shown in Fig. 6, which reveals that at the Raicho valley it must have snowed heavily simultaneously with the neighboring area. The date of the avalanche was inferred from the location of the debris in snow as shown in Fig. 2 and from the integrated amount of precipitation at the Makawa Weather Station near the Raicho valley. Consequently, it is presumed that the heavy snowfall on January 15 caused the snow avalanche at the Raicho valley.

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Although it is necessary to examine the dynamics of snow deposit in order to establish the avalanche prevention forest or the method of planting and tending general forest in the heavy-snow area, the most fundamental subject is the knowledge of the effect of the snow pressure upon trees. For this reason, it will be important to clarify and study the adaptability or life-form of the trees in the snow-covered environment. From such a viewpoint the investigation was carried out in northern Hokkaido.
The results are summarized as follows.
1) In the heavy-snow environment, most of trees take a form of trunk-bending near the ground (Fig. 3).
2) From the bending portion, where the trunk touches soil, new adventitious roots sprout out and support the upper portion of trunk upright.
3) With the development of the adventitious roots, the trunk recovers from the bent form to the previous upright form externally. Todomatsu (Abies sachalinensis MAST.) (conifer) is superior to Itayakaede (Acer mono MAXIM.) (leaf tree) in ability of recovering from the bent form (Fig. 2 and 3).
4) A natural tree growing on the slope in a heavy-snow area adapts itself to its environment with a suitable method. This method and life-form of trees show their ability to grow against the snow pressure.

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The analytical investigation of the relation between the depth of snow on the young stand of Sugi (Cryptomeria japonica) in the experimental forest of Yamagata University and the microtopographic factors was repeated with the aid of partial and multiple correlation coefficients. The depth of snow was measured annually for five years from December of 1965 to April of 1970. Summary of the findings is as follows :
1) The progress of depth of snow varies with the duration of measurement, but the relation between the depth of snow and the microtopographic factors shows similar trends throughout the five winter seasons.
2) On the steep slope, on the convex surface and in the place which an ample supply of light, the depth of snow decreases rapidly during the spring thaw. On the other hand, the depth of snow decreases slowly in the place which has many trees over 6 m in height, but it seems likely that there is no effect of the trees under 5 m in height.
3) In the latter half of the duration of snowfall the multiple correlation coefficient increases remarkably as the day goes on, and the value of its square exceeds 0. 6 in every April.

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