土砂管理研究グループ

雪氷チーム

雪崩・地すべり研究センター

Snow and Ice Research Team

Snow Avalanche and Landslide Research Center

短時間の多量降雪による雪崩危険度評価に関する研究
Hazard Assessment for Avalanches Caused by Intense Heavy Snowfall
平成 18 年豪雪以降、北海道や東北、北陸、中国地方と各地で豪雪が続いています。
特に、平成 26 年 2 月は雪の少ない関東甲信などの広い地域で、短時間の多量降雪により記録的な大雪となりました。短時間の多量降雪は、雪崩の多発につながり、豪雪地帯はもとより豪雪地帯以外の地域でも突発的に雪崩が発生する可能性が高くなります。
土木研究所では、短時間多量降雪による雪崩発生の危険度評価技術に関する研究に取り組んでいます。

短時間多量降雪による雪崩事例
An avalanche caused by intense snowfall

Since the Heavy Snowfall of 2006, there have been heavy snowfall events in many areas of Japan, including Hokkaido,Tohoku, Hokuriku, and Chugoku. In February 2014, a record intense heavy snowfall occurred in large parts of the Kanto
and Koshin areas, which ordinarily have little snow. Intense heavy snowfalls lead to many avalanches. In such cases,
unpredictable snow avalanches become highly likely in areas within and beyond the areas of heavy snowfall. The Civil
Engineering Research Institute for Cold Region has been pursuing research on ways to assess the risk of avalanche
occurrence from intense heavy snowfall.

雪崩発生の気象・積雪条件の検討

雪崩発生の地形・植生条件の検討

短時間に多量に雪が積もる場合、雪の強度が十分大きくなる前に斜面積雪が不安定となり、明確な弱層がない状況でも表層雪崩が発生します。現地調査結果に基づく理論的な解析によって、降雪強度や気温などを指標にした雪崩発生条件を検討しています。

短時間に多量に雪が積もる場合、一般には雪崩発生の可能性が低い積雪深が小さい場合や樹林内でも、雪崩が発生する傾向にあります。
この研究では、短時間多量降雪による雪崩発生場における植生や地形等の特徴を調査しています。

When thick snow cover develops in a short period of time, the snow cover on a slope becomes
unstable before the snow cover develops strength. A surface avalanche occurs even when there
is no clearly identifiable weak layer in the snow cover. Based on theoretical analyses using theresults of onsite surveys, the occurrence conditions for avalanches have been examined byusing snowfall intensity and temperature as indexes.

When snow cover develops in a short period of time, avalanches tend to occur even at locations
with a relatively shallow snow depth and in forest, where avalanches tend not to occur. In thisstudy, the vegetation and topographic characteristics of locations where avalanches haveoccurred from intense heavy snowfall have been investigated.

Examination of weather and snow cover conditions for avalanche occurrence

(-7℃)
3cm/h

(-10℃)
3cm/h

大StableHigh(-3℃)
3cm/h

安定

短時間多量降雪による雪崩発生

Snowfall intensity

Avalanche caused by intense heavy snowfall

降雪強度

3.0
2.0
1.0

Unstable

61218

243036

雪が降り始めてからの時間 (h)

42

小不安定

00

Low

積雪安定度 SI

Snowpack stability SI

4.0

Examination of topographic and vegetation conditions for avalanche occurrence48

低Hours since the start of snowfall

Low▲斜面積雪の安定性に関する検討例
Example of examination on the stability of thesnowpack on the slope

気温高Air temperature

High▲降雪強度と気温を指標にした雪崩発生条件（イメージ）
Avalanche occurrence conditions
when the snowfall intensity andtemperature are used as indexes(conceptual diagram)▲樹林内の雪崩発生箇所の例
An avalanche location in a forest▲雪崩発生箇所の植生調査例
A vegetation survey at an avalanche starting zone

雪崩の到達範囲と衝撃力の検討

雪崩危険度評価手法の検討

現地調査や雪崩発生条件の調査結果に基づいて、短時間多量降雪時の雪崩に対する既存シミュレーションのパラメータ等の適用性を調査し、雪崩の到達範囲や衝撃力の算出手法を検討しています。

雪崩発生条件の調査結果に基づいて、短時間多量降雪時の雪崩発生に関わる頻度分布などを作成します。
さらに、雪崩の発生条件と衝撃力の算出手法の検討結果をとりまとめ、短時間多量降雪による雪崩危険度評価手法を提案する予定です。

Based on the results of onsite theoretical analyses and surveys on avalanche occurrence
conditions, the applicability of existing avalanche simulation parameters has been investigatedwith regard to their application to avalanches that occur after intense heavy snowfalls. Based on
the results of this investigation, we have been conducting examinations towards the establishmentof a method for calculating the runout distance and impact force of such avalanches.

Based on the results of surveys on the conditions under which avalanches occur, a frequency
distribution map will be created that shows avalanche risk from intense heavy snowfall. The
examination on methods for calculating the conditions under which avalanches occur andimpact forces will be completed, and an evaluation method for the risk of avalanche from
intense heavy snowfall will be proposed.

Examination of runout distance and impact force of avalanches

Examination of hazard assessment for avalanches

短時間多量降雪に適したパラメータの検討

短時間多量降雪への適用性の検討

Examination of the applicability of the parameters of theexisting simulation program to intense snowfall(one-dimensional simulation)

Examination of the applicability of the parameters of
the existing simulation program to intense snowfall(three-dimensional simulation)

150

1050

120

縦断地形 Longitudinal profile of the area

1000950
900850▲短時間多量降雪による雪崩の流下経路の例
A track for an avalanche that
occurred from intense heavy
snowfall

010090

雪崩衝撃力 (hPa)60
Avalanche impact force
雪崩の速度 (m/s)
30
Avalanche velocity
被災箇所 Damage location
0200
300
400500水平距離 (m)Horizontal distance▲既存シミュレーションによる雪崩の解析例
An avalanche analyzed by the conventional
simulation program

安全・快適

北の道Safe, pleasant driving on Northern RoadsAvalanche impact force

1100 発生点 Start position

雪崩衝撃力 (hPa)180

Avalanche velocity

1150(3次元シミュレーション)

雪崩の速度 (m/s)

Elevation

標高 (m)(1次元シミュレーション)

雪崩危険エリアを把握
Understanding the areas at riskof avalanche occurrence

高 High
雪崩高さ
Avalanche height
543
2
10(m)

▲既存シミュレーションによる雪崩の解析例
An avalanche analyzed by the three-dimensional
simulation program

国立研究開発法人土木研究所 寒地土木研究所

低 Low▲短時間多量降雪による雪崩発生頻度分布（イメージ）
Distribution of avalanches caused byintense snowfall (conceptual diagram)

National Research and Development Agency Public Works Research Institute Civil Engineering Research Institute for Cold Region