Non-structural measures against landslides and debris flows in Japan

Keigo NAKAMURA, Ph.D

8 Sep. 2009Sabo (Erosion and Sediment Control) Department,

Ministry of Land, Infrastructure, Transport and Tourism (MLIT)

Earthquake country~20% of the world’s earthquakes

Distribution of epicenters of earthquakes with M=3.0 or

more in 1998-2000

Volcanic country~10% of the world’s active volcanoes (108 active volcanoes)

Japan: the hot spot of landslides and debris flows

Depth of hypocenter (km)

Magnitude of earthquake (M)

Vulnerable and steep geologyWith many faults and complex geology, the Japanese islands are vulnerable to collapses.

Japan: the hot spot of landslides and debris flows

Rainy countryHeavy rains caused by the rainy season and typhoons.

台

16台

6

台

4

台

18

台

15

台

11

台

10

台

21 台

22

台

23

Landfalls of typhoons in 2004

0

200

400

600

800

1000

1200

1400

1600

平成13年 平成14年 平成15年 平成16年 平成17年 平成18年 平成19年

539

897

2,537

814

2500

509

1,441

1400

10

20

4 4

23

30

25 30

Num

ber of the dead and missing: person

Number of the dead and missing

Number of disasters

60

50

40

62

0

Num

ber o

f sed

imen

t-rel

ated

dis

aste

rs: c

ase

Landslides and debris flows in recent years

966

2001 2005 2006 20072002 2003 2004

Three major categories against landslides and debris flows mitigation

Hard

Warning &

Evacuation

Restriction&

regulation

Non structural measures

Structural measures

Essences of Public Warning

Timingand

Area

AREA

Hazard area Special hazard area100m

Presumed maximum force

Height of debris flow

Warning area designated by the Landslides and Debris flows Prevention Law

• An area prone to landslides and debris flows shall be designated as a landslides and debris flows hazard area (Yellow Zone).

• In the Yellow Zone, – Early warning systems must be established,– Hazard map against landslides and debris flows

should be produced.– But NO RESTRICTION ON LANDUSE

Landslides and debris flows Hazard Area

• An area in serious hazards shall be designated as a special landslides and debris flows hazard area (Red Zone).

Special landslides and debris flows Hazard Area

Landslides and debris flows hazard map

TIMING

Warning information on landslides and debris flows(Sediment Disaster Alert)

•Warning information on landslides and debris flows (WILD) based on rainfall intensity and duration was launched in 2008 all through Japan in collaboration with JMA.

40

20

0

Rai

n in

tens

ity (m

m h

-1)

Index on soil moisture

Critical line (CL): Threshold for landslides or debris flows

How WILD works?

Disaster baseAnnouncement base

~12% of WILD announcement predicted landslides or debris flows.

138

991 # of landslidesand debris flow

Total 1129announcements

295

121

# of WILDannouncements

~70% of landslides and debris flows was picked up by WILD.

Total 416disasters

Notify weather advisory, warnings and WILD through diverse media

Push based mobile services

土砂災害危険度情報（５ｋｍメッシュ）

7月19日 15時00分現在

・ 前の画面へ戻る・ 市町別発表状況へ・ TOPへ

1時間前を表示

■ レベル３（現在土砂災害警戒避難基準に達している区域）■ レベル２（１時間以内に警戒避難基準に達すると想定される区域）■ レベル１（２時間以内に警戒避難基準に達すると想定される区域）

【危険度情報】

loudspeaker broadcasting

Individual receiver

Urgency of time Rumbling of mountain, rumbling of ground

Abnormal turbidity of flowing water

Driftwood, sound of rolling rocks in the stream

Debris flow

Slope failure Increase in spring water

Turbidity of spring water

Cracks

Constant fall of small stones

Debris flow

Slope failure

Landslide

Landslide

Frequent fall of small stones

Cracks Turbidity of well water

Rumbling of mountain, rumbling of ground

Increase in spring water

Abrupt decrease in water level

Education on symptoms of landslides and debris flows