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

冬期の降雨等に伴う雪崩災害の危険度評価技術に関する研究
Danger Rating Method for Snow Avalanches Caused by Rain and Other High-Moisture Weather Conditions during Winter
近年、冬期における気温の上昇や降雨の増加が報告されています。
このような気候変動に伴い、積雪寒湿雪雪崩の発生事例
Sites of wet-snow avalanches

冷地では雪の乾湿などの性質が変化し、湿雪雪崩による災害の多発が懸念されています。
しかし、湿雪雪崩の発生条件については不明な点が多いことから、雪崩・地すべり研究センター（新潟県妙高市）と連携して、冬期の降雨等に伴う雪崩災害の危険度評価技術に関する研究に取り組んでいます。
In recent years, there have been increasing numbers of reports on elevated air temperatures and rain in winter. Snowcharacteristics, including water content, have changed with recent climate changes, and concerns have arisen over theincreasing frequency of wet-snow avalanche disasters. The occurrence conditions of wet snow avalanches, however,
have not been clarified. The Snow and Ice Research Team of the CERI, in cooperation with the Snow Avalanche andLandslide Research Center (Myoko City, Niigata Prefecture), has been engaging in research on a danger rating method
for snow avalanche disasters caused by high-moisture weather conditions including rain in winter.

湿雪雪崩発生の気象条件に関する調査

積雪への水の供給量が少なく、表層雪崩がみられる
Water supply to the snowpack is small;surface avalanches are observed.

日射Insolation

気温上昇

Air temperature risesng

雪 eltim
融nowS
雪 overrc
yela積nowng
S層beari
水 帯 er

水の浸透

Water inﬁltration

Wm

tto

出 bo流t the面
底low aF

250

湿雪全層
Full layer is wet

200

湿雪表層
Surface layer is wet

150
100

2月

50

February

0

強度低下

at300

0

Decreasing strength↓

積雪深（発生時）(cm)

Rainfall

積雪への水の供給量が多く、全層雪崩が多い
Snow depth at the occurrence of avalanche

To clarify the weather conditions that lead towet-snow avalanches, analyses and fieldobservations on avalanches that have involved
warm temperatures, considerable insolation andrainfall have been conducted.
Analyses of the past cases have revealed that theoccurrence conditions for wet snow avalanches
in the severe cold period (February) differ fromthose in snow-melting period (March).

降雨

積雪深（発生時）(cm)

湿雪雪崩の発生に関わる気象条件を明らかにするために、気温上昇や日射、降雨等に着目した過去の雪崩事例の解析を行いました。
これまでの事例解析より、厳冬期（２月）と融雪期（３月）で湿雪雪崩の発生条件が異なることなどが明らかになりました。

Snow depth at the occurrence of avalanche

Survey on Weather Conditions That Lead to Wet-snow Avalanches

204060

雪崩発生

250

湿雪全層
Full layer is wet

200

湿雪表層
Surface layer is wet

150
100

３月

5080

March

0

20

406080融雪量と降雨量（当日＋前日）(mm)

Water from snowmelt and rainfall(amount on the day of occurrence + the previous day)

▲湿雪雪崩の発生過程の概念
Concept of the occurrence process of wet-snow avalanches

300

0

融雪量と降雨量（当日＋前日）(mm)

Avalanche occurrenceWater supply to the snowpack is large;full-depth avalanches are observed.

Water from snowmelt and rainfall(amount on the day of occurrence + the previous day)

▲湿雪雪崩発生時の積雪深及び融雪量と降雨量の合計値
Snow depth and the total water from snow melt and rainfall at the occurrence of wet snow avalanche

湿雪雪崩発生の積雪条件に関する調査

雪崩危険度評価技術の検討

湿雪雪崩の発生に関わる積雪条件を明らかにするために、積雪中の帯水層の形成過程や含水率を変化させた場合の積雪の破壊強度特性に関する現地調査と実験を行います。
これまでの調査から、平地と斜面における雪質と水の浸透状況の違いや、含水率と積雪硬度の変化状況などが分かりました。

気象条件や積雪条件の調査を基に、積雪推定モデルの改良を行いました。
積雪内の水の浸透における水みちを考慮した積雪モデルをベースに、透水係数、帯水層の含水率、水みち流出量などの設定値を観測データと比較して検討し、特に斜面における積雪構造の再現性を向上させました。
これにより、斜面積雪内の水の浸透状況を考慮した湿雪雪崩発生の危険度評価が可能であることを示せました。

Survey on Snow Cover Conditions of Wet-snow Avalanches

Examination of technology for a danger rating method for snow avalanches

To clarify the snow cover conditions that promote wet-snow avalanches, fieldsurveys and experiments were done on the formation of water bearing layers insnow cover and the failure strength characteristics of snow cover at different
moisture contents.
Surveys have clarified the difference in snow grain type and pattern of water
infiltration on the flat areas vs. on slopes, and the changes in water content andhardness of the snowpack.

均一な浸透帯水層

Homogeneous
seepage

Water-bearing layer

帯水層

Water-bearing layer

水みち

均一領域

Water flowpath

Homogeneouszone

水みち領域

Water flow zone

平地と斜面の積雪への水の浸透状況の例
Water infiltration into the snowpack on a flat area and that on a slope
斜面 Slope

平地 Flat area

A：実際の状況

B：従来の積雪モデル

Actual conditions

帯水層を突破して水が流下
Water seeps down through thewater-bearing layers

Conventional snowpack model

しまり雪

帯水層

ざらめ雪

Compacted snow

Water-bearing layer

積雪内の帯水層に沿って水が流下
Water ﬂows along the water-bearing
layer in the snowpack.

Water-bearing layer

帯水層

Water-bearing layer

Granular snow

安定度が低いときに、雪崩が起こる傾向あり
Avalanches tend to occur when the stability is low.
雪崩発生回数
Number of avalanches

帯水層

C：水みちを考慮したモデル

Model that takes the water ﬂow
path into consideration

1098765432
101/5

湿潤雪崩
Wet snow avalanche
安 定 度
Stability

The snowpack estimation model was
improved based on surveys of weather
and snowpack conditions.
The model was improved based on asnowpack model, that takes into
consideration the water flow path in theinfiltration of water in the snowpack. The
set values of the model, including thecoefficient of permeability, the moisture
content of the water bearing layer and theflow rate of the water flow path, werecompared with the observed data. The
reproducibility of the structure of asnowpack on the slope was particularlyimproved. It was demonstrated that it ispossible to rate the danger of wet snowavalanches by using the improved model,in which the infiltration
conditions of water within
5
安定
the snowpack on the slope
Stableare considered.
432

安定度
Stability1

1/10 1/15 1/20 1/25 1/30

2/4

2/9

2/14 2/19 2/24

3/1

3/6

不安定
0
3/11 Unstable▲積雪モデルを用いた積雪安定度の計算（2002-2003年、新潟県糸魚川市柵口）
Calculation for snowpack stability by using the snowpack model (2002 - 2003, Maseguchi, Itoigawa City, Niigata Prefecture)

安全・快適

北の道

Safe, pleasant driving on Northern Roads

国立研究開発法人土木研究所 寒地土木研究所

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