Protection of Livesfrom Sediment Disasters
About 1,000 sediment disasters occur
every year in Japan causing heavy
loss of human lives and damage topruperties.

Protection of Lives from Sediment Disasters
January 2016
NPO Sediment Disaster Prevention Publicity Center(SPC)
URL_http://www.sabopc.or.jp

不許複製・無断転載

A SABO Supplementary Reader

Protection of Livesfrom Sediment Disasters
A SABO Supplementary Reader

Contents2

1

Japan is prone to sediment disasters

4

2

Debris Flow Disasters

83

Landslide Disasters

10

4

Slope Failure Disasters

125Volcanic Disasters

14

6

Avalanche Disasters

15

7River Closure (Natural Dam)

16

Deep Seated Landslide

178Preventive measures against Sediment Disasters

18

9Disaster Information

22

10

Learn how to Evacuate

24

Check list to protect lives from sediment disasters

26

3

1 Japan is prone to sediment disasters

Let us learn more◊“Sediment disaster” is defined as the disaster where
houses, roads, agricultural lands etc. are buried andhuman lives are lost, by collapse of land mass ofJapan is blessed with abundant nature. On the other hand, however, various
natural disasters occur. One of them is the sediment disaster.

Various types ofsediment disastersediment (soil, sand, stone etc.) on slopes of mountains
and hillsides, or by the flow of the mixture of such
sediment with rain water and river water. Sedimentdisasters include debris flow, landslide, slope failure etc.

Volcanic
disasterpage 14

River closure
page 16
Debris flow

Mud flow of volcanic ash occurred after eruption(2014/Hiroshima sediment disaster, Hiroshima City,
Hiroshima Prefecture)

Avalanche
disaster(2000, Miyake Island, Tokyo)
映像/長野県建設部砂防課

page 15

Debris flow
disasterpage 8-9

Slope failure
disasterLandslide

Snow avalanche in Hakuba Village

page 12-13(2000, Hakuba Village, Nagano Prefecture. Photo by
Nagano Prefecture with supervision by Public Works
Research Institute of MLIT)(1995/Jitsukeyama landslide, Nagano City, Nagano
Prefecture)

Landslidedisasterpage 10-11

Slope failure of Shirasu terrace (a mass ofaccumulated volcanic ash)River closure(natural dam)
(2011/Typhoon No.12, Totsukawa Village, Nara Prefecture)(1986/Kagoshima heavy rainfall disaster, Hirano Town,
Kagoshima City, Kagoshima Prefecture)45

In recent years, very heavy rainfall concentrated over narrow areas in short period (localized heavy rainfall)has been increasing, and, as a result, sediment disasters are also increasing.
(events/year)
400

237

209

238

169

182

194

193

206
177

190

63
1
2

156

158

188

62

157

282

275
254

275
256

230

225
156

131
112

94

25
26

24

23

22

20
21

19

17
18

16

14
15

13

12

11

9

10

7
8

6

4
5

3

61

60

59

58

57

56

55

H

Mt.Osore

Rainfall distribution during Typhoon No.26 in October 2013(27 hours rainfall during 6:00 on15 October~9:00 on 16
October)

Mt.Hakkoda

Iriomotejima Northnortheast Submarine Volcano

Towada諸島沖縄

Hachimantai

Mt.Akita-Yakeyama

Mt.Iwate
The Iwate-Miyagi Nairiku Earthquake(2004)
Nishinoshima

Mt.Akita-Komagatake

Mt.Cyokai

Mt.Kurikoma
Mt.Naruko

Kaikata Seamount
Hijiori

Kaitoku Seamount

Mid Niigata Prefecture Earthquake(2004)

Iow-jima

Mt.Kusatsu-Shirane
Mt.Myoko
Niigata-Yakeyama

Mt.Agatsuma
Mt.Adatara
Mt.Hiuchigatake
Mt.Bandai

Itoigawa-Shizuoka Tectonic Line

Kita Fukutokutai

Mt.Nasudake
Mt.Takaharayama

Midagahara
Mt.Yakedake
Mt.Akandana

Fukutokuokanoba
Minami-Hiyoshi Seamount
Nikko Seamount

Abu Volcanoes

Mt.Nikko-Shirane
Mt.Akagi
Mt.Haruna
Mt.Asama
Yokodake

Mt.Hakusan
Mt.Norikuradake
Mt.Ontake

Mt.Sanbe

The Southern Hyogo prefectureearthquake(1995)

Izu Tobu Kazangun

kozushima

Li
onic
ect
nT
dia
Me

Yufudake
Mt.Kuju

Mt.Kaimondake
Satsuma-IoujimaneMiyakejima

Pacific plate

Hachijojima

Mt.Kirishima

Aogashima

Wakamiko
Sakurajima
Ikeda and Yamagawa

The rainfall in Oshima(Motomachi) of Izu Islands
recorded 122.5mm/one hourand 824.0mm/24 hours (about
2.5 times more than the average
rainfall of October), exceeding thepast maximum rainfall recorded
in 2012. Debris flows (mud flows)caused by the heavy rainfalls
claimed 39 persons, dead andmissing.

Izu-Oshima
NiijimaMikurajima

Mt.AsoMt.Unzen-Fugendake

Yonemaru and Sumiyoshiike

Beyonnaise Rocks

Philippine sea plate

Sumisujima

Kuchinoerabujima
Izu-Torishima
Nakanoshima
Suwanosejima
Suwanose
Suwanosej
eejjjiieji

Source: A quick reporton heavy rainfall byfront during 15~16
August 2014 (JMA)

Mt.Fuji
Mt.HakoneToshimaTsurumidake and Garandake

Mt.ZaoNumazawa

SofuganIn the case of Hiroshima sediment disaster in August
2014, the rainfall ceased for some time and resumed
intensively, The sediment disaster occurred in only twohours thereafter. The disaster caused extensive damage
claiming 74 casualties.

90

Source: A quick report on 2013
Typhoon No.26 (Tokyo MeteorologicalObservatory)

I now know thatearthquakes occur along
boundary of plates.

◊“Active Volcano” means a volcano which erupted in recent
world. Japan’s land area is only 0.1% of the world, but theWater in the soil

◊It is thought that earthquakes occur by the movement

very
abundantof the plates. The plates are hard base rocks covering
opinions about the number of the plates). Four of them are

30
20

200

150

Rainfall at Takasestation
Maximum rainfall inteusity 87.0mm/h
accumulate rainfall 247.0mm

100

Source : Sabo Department,MLIT
50

10
0

8/19

8/20

extremelyabundant

number of the active volcano is as many as 7%.

the earth by about ten blocks (There are several different

250

Sediment Disaster Warning
information at
1:15 on 20 August

60

0Soil Water Index
10:30 on 10 Sept.

10,000 years. There are about 1,500 active volcanos in the

Hourly rainfall
Accumulated rainfall

70

40

Soil Water Index at the time of Kanto-Tohoku Heavy Rainfall
Disaster in September 2015
(The figure shows the rainfall amount infiltrated into the soil)

(mm)
300

3:00-3:30

80

50

Let us learn more

Debris flow

(mm/h)
100

Source : JMA

9:00

Eurasian plate

6:00

Funka Asane

The 2011 off the Pacificcoast of Tohoku
Earthquake(2004)

0:00

小笠原諸島

Rainfall distribution during Hiroshima sedimentdisaster in 2014
(One hour rainfall during 2:00~3:00 on 20 August)

18:00

Earthquakes occur frequently in Japan.
They trigger slope failures, landslides etc.
Further, there are as manyy as 110 active
volcanoes in Japan.

S

Mt.EsanMt.Iwaki

Fukue Volcanoes<Frequent earthquakes andmany volcanos>0

KuttaraMt.Hokkaido Komagatake

Oshima-Ohshima

12:00

Mountains in Japan are generally highand steep, therefore, rivers originating insuch mountains are “rapids”. The more rapid
the current is, the stronger is the erosion in
upstream mountain areas, resulting in muchsediment discharge to downstream areas.

100

Mt.Tarumae

Mt.UsuMt.TomariAround 70% of Japan is mountainous
areas. Further, most mountains are steep andfragile in geology, and collapse easily.

<Steep rivers>

Mt.Oakandake
Mt.Meakandake

103

Mt.Maru

Mt.Yotei

Events of heavy rainfall ( >= 50mm/h)par1000 observation stations
Source : Sabo Department,MLIT

NisekoMt.Rausu<Mountainous topography withfragile geology>

Masyu

110

Mt.Etorofu-Yakeyama
Mt.Berutarube
Mt.Chachadake

150

Atosanupuri

Mt.Tokachidake

54

Etorofu-Atosanuburi
Ruruidake

169

186
Mt.Eniwadake

140

Mt.Taisetsu

Iwo-Torishima
Mt.Sashiusu

145

Mt.Moyorodake

Mt.Odamoi

200

53

Mt.Chirippu

Mt.Shiretoko-Iow
Mt.Rausudake
Mt.Tencyo

52

北方領土

North American plate

Mt.Rishiri

222

Plate boundaries,active volcanos andrecent major Earthquakes in Japan.

251

250

51

One of main causes for sediment disasters
is heavy rains. Japan is a country where
rainfall amount is particularly great in theworld. Moreover, concentrated heavy rains
occur by typhoons, Baiu-front (stationary front
in the rainy season) etc.

295

175 events inaverage for1971-1988

300<Heavy rains>

331

350

356

202 events inaverage for
1989-2001

173

The area of green
color is surprisingly sonarrow on the map.

230 events inaverage for
2002-2016244

The causes are attributed mainly to the climate andthe geology/topography of Japanese archipelago.

237

Why so many sediment disasters in Japan?

<Hazardous heavy rainfall has been increasing.>

abundant

Earthquakes(M>6)and plate boundaries in the world
Sourse:Disaster Prevention White Paper,2013,Cabinet Officelocated in the vicinity of the Japan archipelago.

As a result of the combined effect of the wind towards the depression
originated in Typhoon No.18, and the wind from Typhoon No.17 in the
Pacific off Japan, the cumulonimbus clouds were generated one after
another in a long line, and brought about heavy rainfall. In the upstream
areas of Kinu River, sediment disasters occurred at many places, whilein the downstream areas, Joso City of Ibaraki Prefecture was affected
severely by floods due to breach of river embankment.

Source : weather map

67

2 Debris Flow Disaster
Debris flow is a phenomenon that
sediment produced by heavy rainfalls
in mountains and valleys becomes
muddy with water and runs down
rapidly towards downstream areas. It
grows on the way by eroding valleys
and taking in rocks and large woods,
and extends widely from the exit of thevalley to assault villages and towns.

Omens(presage)for debris flows
Most debris flows are caused by heavy rainfalls. If such phenomena as shown below are perceived in rivers or
torrents, they may be omens of debris flows. Let us evacuate immediately.

collapse in mountains
Erosion of riverbeds and banks
Flow down wards containing
more stones and woody debris
Extend widely from theexit of the valley>>>Rumbling sounds like “Goro Goro” areheard and sparklings are seen in rivers
and torrents.

>>>Current of rivers and torrents becomesturbid and muddy, and trees drift with thecurrent.

This suggests that slope collapses have occurred in
upstream mountain areas and large stones are flowing
down thence. They collide with each other and spark.

This suggests that slope collapses have occurred in
upstream mountain areas, and sediment and trees are
flowing down thence.

“Doo”“Goro Goro”
assauit villages and towns“Doo”

A town affected by debris flows(2014/Nagiso Debris flow disaster, Nagiso Town,
Nagano Prefecture)>>>Mountain rumbling is heard andabnormal smell is perceived.

>>>River water decreases, while rains
continue.

This suggests that slope collapses have occurredin upstream mountain areas.

This suggests that sediment from slope collapses in
upstream mountain areas has blocked the current of
the river. The sediment which blocks the current may
collapse all at once, resulting in debris flows to affectdownstream areas.

>>>Ground rumbling is heard.
This suggests that debris flows are alreadycoming down.

“Goon”

A rock as large as thissize can be drifted.

“Doon”“Zuun”

Debris flows (mud flows) by heavy rainfalls
lls
of a typhoon( 2 0 1 4 / H i r o s h i m a D e b r i s f l o w d i s a s t e r,
Hiroshima City, Hiroshima Prefecture)(2013/Typhoon No.26, Oshima Town, Tokyo)

Debris flows run
down so fast. The
velocity may reachas fast as 40 km/
hour!

“Zawa Zawa”

A large rock drifted down by debris
flows

20-40kLet us learn more
◊Debris flows do not always have omens. However, once something unusual or strange is perceived, it is necessary to inform it

m/hou

r

to neighbors as well as to village/town office, and to evacuate to a safer place as soon as possible.
◊In order to perceive such abnormal phenomena, it is necessary to observe the nature around us carefully from time to time atordinary time and to know well the nature at ordinary time.

It is as fast as cars
running in the town.

◊“Abnormal smells” include burnt smell, smell of decay, smell of soil etc.
◊It is possible that, while there is no rainfall where we are, heavy rainfalls in upstream areas may cause debris flows to hit us
all of a sudden. When camping in river side, for example, it is necessary to move away from the river to a safer place as soon as
possible, once black clouds are seen over mountains and /or rumblings of thunder are heard in the distance.

89

3 Landslide Disaster
Landslide is a phenomenon that awide area of relatively gentle gradientslides down a slope. Some moveslowly over time but others movequickly as fast as several meters all
at once, causing serious damage tohouses, agricultural lands, roads etc.

Types of landslide
Landslides can be classified into three types as follows.

Tertiary strata landslide
Shear zone landslide

Tertiary strata landslide

Solfataric landslide

Tertiary strata were formed about 65~1.7 million
years ago through accumulation of volcanic ash, mudetc. They easily turn to clay.

Relatively gentle slope

Shear zone landslide

Landslide moues down together
with houses and farms on the slope

Sheer zone is a stratum where the rock is fragile
with a number of fissures and is easily turn into clay.
This type of landslide prevails in the vicinity of major
faults such as the median tectonic line.

Distribution of landslides in Japan(Areas susceptible to landslides)

Solfataric landslide
Tertiary strata landslides move slowly,
while shear zone landslides movequickly like steep slope failures.

This type of landslide occurs where the strata havebeen turned into clay by the effect of hot springs,
volcanic activities etc.
Landslides sometimes bury the river

Mechanism of landslide
Landslides caused by Chuetsu Earthquake
in Niigata Prefecture(2004, Nagaoka City, Niigata Prefecture‹Former
Higashi Takezawa area of Yamakoshi Village›)
Earthquake can cause landslides.

Landslides occur where there are strata which areimpermeable, such as clay layer. Rain water, snow
melted water, underground water etc. permeatesthe soil and accumulates above the impermeable
strata. Then the mass of soil is lifted by the buoyant
force and slides down the slope. Landslide may startmoving detonated by earthquake.

Omens(presage) for landslides
Following omens may be perceived before landslides occur. cracks in the ground may appear even several
months before the mass movement.

>>>Changes in the ponds:
water becomes turbulent,water level decreases etc.

Water accumulates.

“Zawa Zawa”“Meki Meki”
Impermeable strata such as the clay layer
A mass of surface soil is lifted
up by buoyant force of water.

Landslide buried a community and reachedthe highway.
(2010, Takigo Town, Kagoshima Prefecture)>>>Sounds of trees like “Zawa Zawa”,“Meki Meki”
Let us learn more>>>Sounds of trees being split◊The conditions to provoke landslides are the existence of strata>>>Sounds of roots of trees being cutof much different water permeability, similar inclination between>>>Sounds of rumbling mountain roaring

the surface slope and strata and so on, in addition to the existenceof clay or other impermeable layer.

10>>>Cracks, deformationin the ground>>>Augmentation of spring water11

4 Slope Failure Disaster
Collapse of steep slope (cliff) is termed “Slope
failure”. It is caused mainly by infiltration of muchwater from rainfall, snow melting etc. into slopes. A
large mass of sediment collapses so suddenly thatmany people fail to escape and die.

Omens(presage) for slope failures
Houses above
the cliff are also
at risk.

Various omens (presage) as mentioned below may be perceived before the occurrence of slope failures. Slope
failures occur in a short time after the omens are perceived, Once any omen is perceived, let us communicate
each other in the community and evacuate to a safer place as soon as possible.

>>>Cobbles roll down theslope clatteringly.

>>>Cracks appear on the slope.

>>>Muddy water springs out on the slope.

>>>Trees tremble and tilt.

The slope collapses suddenly.

Houses at the foot of the cliff are buried by sediment.

Houses collapsed by a slope failure

Slope failure may affect area
within a distance twice theheight of collapsed slope(1999/Baiu front heavy rains, Kure City, Hiroshima
Prefecture)

Let us learn more
◊Slope having a gradient of 30 degrees or more is one of criteria
as target area for countermeasures according to Sediment Disaster
Prevention Act.
◊It is said that the possibility of slope failure is generally high in theslopes where the height is more than 5 meters, big boulders are on

Slope failure in a housing area developedon a hillside slope(1999/Baiu front heavy rains, Kure City, Hiroshima
Prefecture)12

Let us learn more

the surface, much water springs out even at ordinary times, and so◊In addition to these omens, following omens may also be perceived: change in the spring water (sudden increase or decrease,on. Precautions are particularly necessary when it is raining.

spurt out or stop), swelling of the slope surface, ground rumbling etc. However, slope failures may occur all of a sudden◊Slope failures may be provoked by earthquake, strong winds andwithout omens, therefore residents living near the foot of steep slopes are recommended to evacuate without delay earlier thanso on.

rosidents of other areas.

◊Slope failures may occur even after the rain is over. Precautions◊If going out of the house for evacuation place is considered no more possible, it is recommended to evacuate to a room of theshould continue even after the rainfall has ceased.

house of the second or higher floor and away from the hazardous slope.

◊Slope failures occur rather frequently in populated areas such as◊Deference between landslide and slope failure: Landslide has “sliding surface” and the mass above the sliding surface moves

housing areas developed in hillsides.

slowly. In many cases landslides occur on the slope of gradient gentler than those of slope failures.

13

5 Volcanic Disaster6 Avalanche Disastervolcanic gas/pumice/volcanic bomb

Vo l c a n i c d i s a s t e r s a r e c a u s e d b y
volcanic eruption and the damage extends
over wide areas. Heavy rainfall overvolcanic ash accumulated on the flank ofmountain may trigger debris flow/mud flow,
and the damage may be further extended.

A cold day in midwintervolcanic ash

A warm day in early spring

Avalanche is a phenomenon thatthe snow accumulated on the flank ofmountains runs down the slope. There
are two types: a surface avalanche
and a full depth avalanche.

Full depth avalanche

pyroclastic flow
debris flow, mud flow
Surface avalanchelava flow

Surface avalanche and Full depth avalanche

Pyroclastic flow

If caught up in the
pyroclastic flow, any creature
will die instantly by the hightemperature and gas.

(June1991, Unzen-Fugendake, Nagasaki Prefecture)
Pyroclastic flow is a flow of the mixture of volcanicash, lava, hot gas and air erupted from the crater. The
maximum speed may exceed 100km/hour and thetemperature at the center is nearly 1,000℃

Rescue operation for persons buried in anavalanche(1986/Maseguchi avalanche disaster, Itoigawa City
(former Nou Town), Niigata Prefecture)
13 persons died by the surface avalanche.

Debris flow by volcanic eruption ofUnzen-Fugendake(1991, Shimabara City, Nagasaki Prefecture)

Avalanches slide down so
rapid: 100~200 km/hour forthe surface avalanche and40~80 km/hour for the full
depth avalanche

Surface avalanche: When much snow accumulates
anew on the old snow, the new snow may slide down.
This phenomenon is called surface avalanche. Surface
avalanche occurs when temperature is low and snow
is continuously falling.
Full depth avalanche: Full depth avalanche occurs
when weather is fine and temperature is rising, or inrainy days. Both the old snow and new snow melt andslide down together.
Surface avalanche

Full deprth avalanche

New snow

Let us learn more

Snow

◊Debris flows are triggered by much rainfall over areas where
volcanic ash is deposited. The volcanic mudflow triggered by snow

Ontake-san blowing off volcanic smoke(September 2014, on the boundary between Gifu
Prefecture and Nagano Prefecture)

Avalanche is so strong tocollapse even reinforced
concrete buildings

melting due to heat of erupted materials when eruption occursd
during snow season is called “Snow melting type volcanic mud flow”.

groundold snow

groundThis type of volcanic mudflow resembles debris flow, but is faster inmovement and greater in magnitude.
◊Debris flows around volcanos last long as long as volcanic deposits

Omens(presage) for avalanches
Photo taken and provided by National Research Institute for Earth Science and Disaster Prevention and Niigata Prefacture

remain and volcanic mud flow continue to occur as long as erupted
materials remain on the mountain even after the volcanic activities
end.

Following phenomena suggest possible occurrence of avalanche. Please keep away from the slope.

◊Big earthquakes may trigger volcanic eruption. Besides the Great
East Japan Earthquake of 2011, there were five huge earthquakes
with the magnitude exceeding M9 since the middle of the 20th century

Snow melting type volcanic mud flow byeruption of Tokachidake(1952 Kamchaka M9, 1957 Andreanof (Aleutian Is.) M9.1, 1960 Chile(1926, Tokachidake, Hokkaido)
The heat of volcanic ash melted the snow on themountain, resulting in the large scale mud flow.
Villages at the foot of the mountain were buried and anumber of persons were dead or missing.

followed by eruptions of nearby volcanos. In fact, as many as 20

14

M9.5, 1964 Alaska M9.2, 2004 Sumatra M9.2), each of which was
volcanos across Japan from Hokkaido to Kyushu became active after

CorniceSnow ball

Crack

Snow wrinkle

the Great East Japan Earthquake.

Snow overhangs from theridge.

Lumps of snow like balls roll downover the slope.

Cracks appear on the snow
as if the slope is scratched.

Snow surface becomes
wrinkled, like a sodden finger.

15

7 River Closure (Natural Dam)
Huge amount of sediment due to earthquakes, landslides, heavy rains, volcanic eruption etc. isdischarged to river and close the river channel, creating a water pool like a pond on the upstreamside. This situation is called “river closure (natural dam). In the upstream areas, houses, roads etc.
are submerged, while, in the downstream areas, floods containing much sediment, debris flows
etc. may cause damage, once the sediment which is closing the river collapses abruptly (breach).
The process from the river closure to the occurrence of debris flow

Deep Seated Landslide
The phenomenon that mountain slopes collapse from the deep bed rock is called “Deep SeatedLandslide”. The deep seated landslide is greater than surface land slide in terms of the amount of thecollapsed sediment, and accordingly the magnitude of debris flow and river closure, and the extent of
the damage.
The mechanism of occurrence of the deep seated landslide is thought as follows: A large amountof rainwater or snow melt
water infiltrates deeply
Deep seated landslide
Surface landslide
Bed rock below surface soil also
Surface of the slope (surface layer)
into the crack of bed rockcollapses.
collapses and slides down
and lifts the surface soil
together with bed rock by
Surface
urfa
fa
ace
e so
soil
oiil
Surface soil
the force of water (buoyant
force). Deep seatedlandslide may also be
triggered by earthquakes.

BedrockckkSediment discharged from mountains
closes river channel (like a dam),
resulting in the creation of a waterpool (like a reservoir) on the upstreamside.

The water level rises gradually andoverflows the sediment mass which isclosing the river. The sediment mass
starts to collapse (breach).

Bedrock

The collapsed sediment mass ismixed with water and develops into
debris flow and floods.
映像/国土交通省湯沢砂防事務所

I came to know that so many riverclosures occurred by earthquakes
in the case of Niigata Chuetsu
Earthquake and Iwate/Miyagi Inland
Earthquake

Debris flow by deep seated landslide

Deep seated landslides by heavy rainfall(1997 Izumi City, Kagoshima Prefecture)
21 persons were killed by the debris flows(2011 Typhoon No.12, Totsuukawa Village, Wakayama
Prefecture)
River was closed by sediment produced by a landslide.

Let us learn more
◊Mechanism of deep seated landslide has not been fully cleared yet. However, through analysis of deep seatedlandslides in the past, progress is being made to identify geological and topographical conditions in which such

River Closure occurred by Iwate/Miyagi Inland
Earthquake(2008 Ichinoseki City, Iwate Prefecture)
A natural dam has been created by river closure as a resultof sediment discharge into the river.

Let us learn more

A village inundated by the river closure

landslides occur. Based on the results of such analysis, MLIT published in 2010 “Estimated frequency map of deep

(2004, Niigata Chuetsu Earthquake, Nagaoka City, Niigata
Prefecture (Former Yamakoshi Village)
The river was closed by sediment discharged due toearthquake, and an upstream village Kogomo wasinundated.

seated landslide”, and in 2012 “Deep seated landslides evaluation map at torrent level” which evaluates risk at torrent
level for areas identified as the high frequency area in the 2010 publication.
http://www.mlit.go.jp/mizukokudo/sabo/deep_landslide.html
Countermeasures against deep seated landslide is difficult. Therefore it is recommended to keep attention to heavy
rainfall and long-lasting rainfall, and to evacuate without delay, in areas which have been identified as high risk areas in“River Closure (Natural Dam)” issometimes called “Sediment Dam”

these maps.
◊Deep seated landslides sometimes occur fairly long time after rains ceased. The deep seated landslide which
triggered large debris flows in 1997 in Izumi City, Kagoshima Prefecture occurred four hours after the rains ceased. This

◊When a serious damage due to a river closure is presumed to riverine villages, countermeasures areis because it takes time for the rain water to infiltrate deeply to the base rock. When it rained heavily or continued forundertaken such as: To cut off the sediment and lower the height of the natural dam before the waterdays in areas where the risk of deep seated landslide is high, it is necessary to keep alert for days even after rains havelevel reaches the top of the natural dam, so that the water may over flow safely without causing damage

ceased.

to the natural dam; To construct drainage channels and/or drainage tunnels to drain the water.

16

17

8 Preventive measures against sediment disasters
Channel Works

Preventive measures against debris flows

In steep rivers, riverbed and river side are eroded by the force ofthe high velocity flow heavily and progressively. In order to weaken
the force of the flow, and thus to mitigate erosion and to reduce thevolume of the sediment transported to downstream areas, step works
and low dams are constructed in the river in a series. Revetment isconstructed to protect river side from erosion.

SABO Dam
SABO dam captures debris flow, drift
woods etc. and prevents damage in thedownstream areas,

Hillside works

SABO works are plannedand designed so that people
can enjoy playing with waterin the river and river side.

SABO dam (permeable type)

SABO dam (non-permeable type)

Channel works(Nomugi-Pass channel works, Matsumoto
city, Nagano Prefecture)
Parks constructed along the river.

Hillside works
Trees and grasses are plantedl t d ini nakedk d mountains
t i to prevent erosion and collapse of mountain slopes.

Channel works

SABO dam which captured debris
flow (non-permeable type)
The SABO dam captured sediment of debris
flow triggered by “2007 Baiu front heavy
rains” and protected towns in the downstream
areas.

Kobe City and Rokko Mountains
in early Meiji Era

Mitatabi-yama, Rokko Mountains
when hillside works began

The naked mountains seemed to becovered with snow from a distance.

Hillside was cultivated in steps along
contour line and seedlings were planted

Rokko Mountains at present“Green” has revived after 100 years of thehillside works.

Various types of SABO dam
Let us learn more
◊SABO means a variety of works to

Sediment and drifting
trees captured by dams
are taken out later.

protect our lives and livelihood fromsediment disasters. SABO works
include construction of SABO facities(SABO dams etc.)/reconstruction
works after disaster, routine works forinspection/monitoring/observation,

Cell type SABO dam (Kamisawagawa
SABO dam, Nagaoka City, Niigata
Prefecture)
The large steel cells are filled with the
mixture of the soil produced in the course of
construction works and cement.

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Steel Slit Dam (Maetanigawa SABO
dam, Echizen City, Fukui Prefecture)
One of permeable type SABO dam. It allows
sediment to pass through during ordinary
floods, and captures only large stones anddrifting trees flown down by debris flows.

SABO dam with a fish way(Sakauchi SABO dam, Ibikawa
Town, Gifu Prefecture)“Fish way” is a passage for the fish to
go upstream for spawning.

SABO dam registered as national
tangible cultural property (Dodo River
No.6 sunadome work, Fukuyama
City, Hiroshima Prefecture)
A stone masonry SABO dam called“Osunadome” which was constructed in 1835
in Edo era according to an old document.
Sunadome means sand capturing.

awareness activities about knowledge
on sediment disasters as well as
evacuation and other actions at thetime of emergency. SABO works arecarried out by central government(MLIT) and local governments.

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Preventive measures against landslide

Preventive measures against volcanic disaster

Measures include to drain underground water
which is a main cause of landslide, to drive instrong piles such as steel piles and RC piles torestrain movement of landslide.

Soil removal work
To remove soil mass in theupper part of the landslide.

Vibration Sensor, Wire sensor

Measures include to construct training
dikes to divert volcanic debris flows/mud flows
towards area where there are no houses andagricultural lands; to construct SABO dams tocheck such volcanic flows.

When debris flows/mud flows occur,
they are monitored and warning isissued.

Consolidation works
Consolidation works prevent riverbed
erosion and thus prevent intensificationof debris flows/mud flows.

Channel work
To prevent infiltration of rainwater into underground

Water collecting well

Training dikes

Drainage well, Drainage tunnel
To collect ground water bywells and to drain throughtunnels

Counterweight fill work
To heap up soil at the bottom of the landslideas the counter weight against sliding

Volcanic eruption can
not be prevented but
damage can be reduced.

Training dikes guidethe direction of debris
flows/mud flows forthem to safely flow
into the sand pocket.

SABO dams
SABO dams check debris
flows/mud flows.

Sliding surface

Sand pocket

Soil mass over the sliding
surface slides down

Sand pockets temporarily store
debris flows/mud flows so thatthey do not flow down all at once.
Sediment in the sand pocket istaken outsides later.

Pile work
To drive piles into beneaththe sliding surface to resist
against sliding force

Preventive measures against slope failures

Facilities to prevent avalanche disaster

Concrete frames are placed over slopes at risk of slope failure to press and stabilize such slopes, and walls
and fences are built to check collapsed soil from the cliff and protect houses.

There are two types: Facilities to prevent avalanche to occur, and those to prevent avalanche to run down to
the foot of mountains.
Prevention fence

Frame work (Grating crib work)

Concrete frame is used to press andstabilize the slope. Trees can beplanted within the frame to protect theslope surface from weathering anderosion.

Frame work

Protection wall

Prevention fence
prevents slide downof snow on the slope.

Protection wall checks
avalanche.

Protection fence

Prevention fence

Protection fence
checks avalanche.

Prevention fences are set up in the upper part ofmountain slope in rows to prevent occurrence ofavalanche.

Trees planted in the frame are growing well.

Retaining wall work
Concrete frame is placed
to press and stabilize theslope. Trees can be planted
within the frame to protect
the slope surface fromweathering and erosion.

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Anchor work
Iron bars driven into hardground and the frame areconnected so as to makeslopes more stable.

Protection fence
Protection fences are set up at the foot of mountains so thatavalanche does not directly hit houses.

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9 Disaster Information/// Let us obtain disaster information through internet
The latest information on dangerous spots is available through internet.

Disaster Information Dissemination Center, MLIT

In order to protect ourselves from sediment disasters, each of us should have correctknowledge on sediment disasters, and should be ready to evacuate quickly once faced withemergency.

http://www.mlit.go.jp/saigai/bosaijoho/

Sediment Disaster Alert, JMA
http://www.jma.go.jp/jp/dosha//// Let us make best use of hazard maps
There are as many as 530,000 places at risk of sediment disasters (debris flows, landslides, slope failures) inJapan. There are 47 active volcanos which are under constant observation by JMA (as of 2015). “Hazard Maps”
are available which show the hazardous places of sediment disasters and the areas possibly affected when
volcanos erupt. Hazard maps are distributed to each family and are available at municipal offices. Please be sureto get and see them carefully.
Maps showing the location of dangerous spots and hazard areas in each prefecture are available also at thehome page of MLIT.

Home page of SABO Department, MLITXRAIN: Rainfall Information Dissemination Site, MLIT
http://www.river.go.jp/xbandradar/
An example of HP of prefecture forsediment disaster information“Sediment Disaster Portal Hiroshima”, Hiroshima
Prefecture

In addition to these information sources, detailed weather
information and disaster information are available at HP of Sabo
Division of each prefecture.

Disaster Prevention Application is available which automatically provides information to the smart phone whendisaster risk becomes high so that such information is made available to any person whereas be is. In addition
applications are also made available by local governments.
Yahoo Disaster quick information>>>http://emg.yahoo.co.jp/
Goo Disaster Application>>>https://play.google.com/store/apps/details?id=jp.ne.goo.bousai.bousaiapp

http://www.mlit.go.jp/mizukokudo/sabo/index.html/// Let us know the meaning of “Alert” and “Warning”
JMA issues alert and warning when disaster is anticipated judging from information on heavy rainfall and other
weather conditions. These information is communicated to residents through local governments and information
media. Alert and Warning are as follows:
Alert/Warning and meaning

What we should do
Keep watch on weather information, andconfirm evacuation sites and articles/goods
to carry

Heavy Rainfall Alert
Sediment disaster may occur by heavy rains.

Heavy Rainfall Warning (sediment disaster)
Serious disaster may occur.

Special Heavy Rainfall Warning (sediment disaster)
Extremely serious disaster of the probability of once inseveral decades is most likely to occur.

An example of Hazard Map

Take action immediately to protect life
(Evacuate to evacuation place, or moveto safe place in the house if evacuation
outsides is not possible).

If danger of sediment disaster becomes further high while the heavy rainfall alert continues,
Sediment Disaster Warning Information is issued.

(Sediment Disaster Hazard Area Map) (Nagano City, Nagano Prefecture)

An example of Volcanic Hazard Map(Sakurajuima, Kagoshima Ptrefecture)

Let us learn more

As for active volcanos, “Eruption Warning Level” is announced by JMA.
Forecast/Warning Eruption warning level
Eruption
Forecast◊In 2000, “Sediment Disaster Prevention Law” was enacted with the aim of protecting human lives from sediment disasters
through soft approaches such as promotion of warning and evacuation system. According to the Law, prefecture governors
are responsible to designate areas prone to sediment disasters (Sediment Disaster Hazard Area: Yellow Zone), and, within theyellow zone, to designate areas where particularly heavy damage will occur once a sediment disaster occurs (Special Sediment

Warning forareas near
craterDisaster Hazard Area: Red Zone). The governors should inform the residents of the designation and restrict development
activities in the red zone.
◊After the heavy rain alert is issued, if the risk of sediment disaster becomes further high, “Sediment Disaster Alert Information”
is issued jointly by prefecture and JMA. In the HP of JMA and prefectures are given supplementary information on risks in detailfor each small area. It is recommended to take early action for evacuation even before such information is provided.

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Evacuate voluntarily in hazardous areas. In
other areas, prepare for evacuation.

Eruption
Warning

Volcanic activities

Actions of residents

Level 1
Volcanic activities are calm. Eruption of ashes are
sometimes seen in the crater (Entering into such
Keep in mind that the
volcano is an active volcano area may be fatal)
Level 2
Areas in the vicinity of the crater will be affected
Restriction in areas (Entering into such area may be fatal). Eruption will
occur or will be anticipated to occur.
near crater

Normal life

Residential areas will be seriously affected. (Entering Normal life. According to theLevel 3
into such area may be fatal). Eruption will occur or situation, evacuation preparations
Restriction of entry will be anticipated to occur.
for persons in need of help

Level 4
Preparation forevacuation
Level 5
Evacuation

Preparation for evacuation in
Eruption to seriously affect residential areas is
areas order warning Evacuation of
anticipated(Such possibility is increasing)
persons in need of help.
Eruption to seriously affect residential areas has Evacuation frombeen occurring or is imminent.
endangered areas23

10 Learn how to evacuate/// Protect lives by early evacuation/// What should be kept in mind for disaster in daily life

Evacuate in cooperation among community people

Evacuation place should be decided in advance in the family
All family members are not always together.
In order to avoid confusion in the face of
emergency, evacuation place should be
decided in advance in the family, and walkalong the evacuation route together
er forconfirmation.

If any danger or fear is perceived, it is important to evacuate as early as possible even without evacuation
alert and warning. Judgement when disaster is already imminent may not be correct due to evacuate confusion.
Evacuation at night time in the dark is dangerous. Let us take actions while it is still light.

Please call neighbors and evacuate together. Agedpersons and others who may take time for evacuation
should be assisted by community people for early
evacuation.

Let us decide on contact
points, supposing family
members are separated
each otherYou should be the first to evacuate
There are persons who are reluctant to evacuateeven danger is imminent. In such a case, pleaseevacuate by yourself. Then they will follow.
It’s a good idea towalk on a rainy day
and at night.

“Protect life” is the first priority in any occasion
In case that the road is already under water or it is dark outside,
movement to evacuation place is no more possible. In such cases it
is recommended to evacuate to RC building if available in the vicinity.
If that is also impossible, the last option will be to evacuate to a roomin the house which is located in the 2nd floor or above and away asmuch as possible from the dangerous slope. Do not get closer towidow glasses.

Pay attention to weather information
Let us keep watch on weather informationof TV and radio. Once sediment disaster
information and/or weather related warning
are issued, it is advised to be ready forevacuation any time. Let us pay attention to
information of local disaster radio.

Evacuation to a room on
the 2nd floor or above,andaway from the slope

Preparation of articles to be carried at the time of emergency
Articles to be carried should be decided by the family, as necessities
are different from family to family. It is also necessary to decide who will
carry what.

Let us measure the rainfall
Most sediment disasters are triggered by rains. Generally, small scale slope failures will
start to occur when the rainfall exceeds 20mm /hour. However please keep in mind thatrainfall of less intensity may cause disaster if it lasts for days.

What is the difference between Evacuation
Recommendation and Evacuation Order«Simple method of rainfall measurement»

Let us know the meaning of words on evacuation issued by municipal offices
Degree ofdangerWords on evacuation
Voluntary Evacuation

What we should do
Evacuate voluntarily, If judged dangerous byourselves

Never say “I am safe here
without evacuation”!

To place a small vessel (an empty tin can etc.) which has
the same diameter at the top and the bottom at a flat placeoutside the house. To measure the depth of the rainwaterin the vessel by a ruler after one hour. The mm figure is therainfall amount per hour.

Splashing of rains into thevessel can be prevented
by putting a piece of clothunder the vessel.

Those who take time for evacuation should evacuate.

1_Evacuation Preparation Information Others prepare for evacuation.

2_Evacuation Recommendation Start evacuation, because damage is likely to occur
3_Evacuation Order

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Please put the vessel at a place
where there is no obstacles
against rainfall.

Evacuate immediately, because damage is highly
likely or already taking place25

Check List to protect lives from sediment disasterA check list has been prepared which lists up what should be done
to prepare for emergencies in ordinary time in the family and theneighborhood.
How about your family? Please check how you are prepared using thecheck list with family members and neighbors.

Check the dangerous places around the house!
1.

The hazard map (Sediment Disaster Hazard Area Map) is at an easily accessible place.

2.

Whether there are “Sediment Disaster Hazard Area (Yellow Zone)” / ”Special Sediment Disaster Hazard Area
(Red Zone)”, and sediment disaster hazardous places (places which are prone to debris flow, slope failure,
landslide etc.) or not near the house has been checked on the hazard map.

3.
4.

Hazardous places identified on the hazard map have been visited and confirmed.
Whether major sediment disasters occurred or not in old times was inquired to aged persons, or wasinvestigated at a library, the municipal office etc.

Check the evacuation place and contact points!
5.
6.

Location of a near-by evacuation place has been confirmed on the hazard map.
Whether there are dangerous places (such as cliffs, ditches without cover, and channels without fence) or noton the way to the evacuation place at the time of raining was checked by walking to the evacuation place byfamily members.

7.

Decision has been made on the building in which to evacuate when movement to the evacuation place is no
more possible (such as a nearby RC building).

8.

Decision has been made on the room in the house in which to evacuate when going out of the house is no
more possible (such a room as is located on the 2nd floor or above, and away from the dangerous slope).

9.

Decision has been made on the contact points in case when family members are separated each other(preferably two places: friend or relative in a nearby area, and those in an area a bit away)

10. Evacuation place and contact points are well known by all the family members. Each member has a memo on
telephone numbers. Telephone numbers have been registered in each mobile phone.

Check the articles to be carried with at the time of emergency!
11.

Decision has been made, through discussion in the family, on emergency articles which should be carried withwhen moving to the evacuation place.

12. The emergency articles have been collected and put at an easily accessible place.
13. Decision has been made on the distribution of responsibility: who will carry what.

Check the disaster information properly!
14. Addresses of internet sites which provide rainfall information and disaster information have been registered in
PCs and mobile phones in the house.
15. The meaning of Heavy Rainfall Alert Heavy Rainfall Warning Special Heavy Rainfall Warning, and Sediment
Disaster Warning Information are well known in the family.
16. The difference between Evacuation Preparation Information, Evacuation Recommendation and Evacuation
Order are well known in the family.
17. Various omens for each sediment disaster are known in the family.

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