Debris Flow Disasters Caused by Typhoon Wipha(T1326) on Izu-Oshima Island and Technical Supportof NILIM TEC-FORCENISHI Masato , Director of Research Center for Disaster Management
WATANABE Fumito , Research Coordinator for Sediment-related Disaster Prevention
KANBARA Jun’ichi , Head, SABO (Erosion and Sediment Control) Division
UCHIDA Taro (Ph.D.), Senior Researcher
HAYASHI Shin-ichiro , OKUYAMA Yuki , Researchers
EKAWA Masafumi , HATA Masayuki , NIWA Satoshi , Guest Research Engineers(Key words)

Izu-oshima Island、Debris flow、TEC-FORCE、Technical support

1. Introduction
On October 16, 2013, Typhoon Wipha brought
precipitation exceeding 800 mm over a 24-hour period toIzu-Oshima Island, Tokyo. As a result, simultaneousdebris flows occurred on hillsides of the volcano, Mt.
Mihara, resulting in 36 deaths and 3 missing (as of Jan.
15, 2014; Photo 1). The SABO (Erosion and SedimentControl) Division of the Research Center for Disaster
Management at the National Institute for Land andInfrastructure Management (NILIM) and the Erosion andSediment Control Research Group of the Public Works
Research Institute (PWRI) implemented technical supportfor the Tokyo Metropolitan Government and OshimaTown Office from the moments immediately after thedebris flow disasters to early in November to prevent
secondary disasters and to implement emergency
recovery.

landslides of volcanic ash layer deposited on the hillsides.
The ash was approximately 1 m deep and transformed
into downhill debris flows. In addition, a huge numberof trees, toppled by shallow landslides and debris flows,
were carried downhill by the debris flows. The
Motomachi-Kandachi district suffered serious loss of lifeand property damage from the direct impact of the debris
flows. Downhill from the Motomachi-Kandachi district,blockage caused by driftwoods at bridges caused floods,resulting in more loss of life and property damage (Photo2).

BridgePhoto 2 Blockage of driftwoods at Motomachi Bridge

Photo 1 Debris flows on hillsides of volcano Mt. Mihara
2. Characteristics of debris flow disasters on
Izu-Oshima Island
The disaster was characterized by multiple shallow

On the contrary, the Motomachi district has
sediment-related disaster prevention facilities (i.e. checkdam) and these facilities protected residents or reduced
damage by capturing debris flows and driftwoods (Photo3).Photo 3 Capture of debris flows and driftwoods by asediment-related disaster prevention facility
along Okanesawa River
3. Implementation of technical support
After the debris flows, weather forecasts predicted thatTyphoon Francisco (T1327) would arrive in 10 days,
creating the risk of secondary disasters in the stricken
area.
The SABO (Erosion and Sediment Control) Divisionof the Research Center for Disaster Management at theNILIM and the Erosion and Sediment Control ResearchGroup of the PWRI implemented technical support forthe Tokyo Metropolitan Government and Oshima Town
Office after the debris flow disasters, to prevent
secondary disasters and to implement emergency
recovery activities as the TEC-FORCE (TechnicalEmergency Control Force) over an 18-day period from
October 16 to November 2, by dispatching personnel
equal to 48 man-days in total.
The type of technical support NILIM provided was asfollows.
- Emergency ground surveys to identify damage andprevent secondary disasters (Photo 4)- Providing technical advice to the Tokyo Metropolitan
Government on preventing secondary disasters andimplementing emergency recovery activities- Providing technical advice on selecting target areas andprecipitation criteria for issuing evacuation advisories,orders and cancelation by the Mayor of Oshima-Providing technical instruction to ensure safety duringrescue activities
Moreover, NILIM provided advice on organizing
results of emergency inspections of locations at risk ofsediment disasters performed by the MLIT Regional
Office TEC-FORCE immediately after the disaster(Photo 5).

Photo 4 Emergency ground survey

Photo 5 Providing advices to the MLIT Regional OfficeTEC-FORCE
4. Continuing technical support for Izu-oshimaIsland’s recovery and future research plans
The Director of the Research Center for Disaster
Management participated as an administrative member in
the Izu-Oshima sediment-related disaster countermeasureplanning committee that was tasked by the Tokyo
Metropolitan Government with establishing a mastercountermeasure plan. The NILIM is continuing toprovide technical support for Izu-Oshima Island’srecovery.
NILIM has plans to implement research activities toanalyze the mechanisms of the shallow landslides anddebris flows of this disaster and to establish technologies
for structural and non-structural measures against
sediment-related disasters in volcanic regions.
[Sources]
Research Center for Disaster Management, NILIM &Erosion and Sediment Control Research Group, PWRI:Sediment-related Disasters Caused by Typhoon Wipha(T1326) on Izu-oshima Island, 2013, Civil EngineerJournal, Vol. 55, No. 12, p.4-7, 2013 (in Japanese).