Messages from Departments and Centers of NILIM

For the Prevention of Sediment Disasters
NISHI Masato, Director
Research Center for Disaster Management
Keywords: sediment disaster, deep-seated landslide, crisis management, technical support

1. Introduction
The Sediment Disaster Prevention Department will belaunched on April 1, 2014. This new department has beenorganized by the former Erosion and Sediment Control
Division of the Research Center for Disaster
Management, the newly established Research
Coordinator for Deep-seated Landslide Prevention, andthe former Sediment Disaster Prevention Division.
The Erosion and Sediment Control Division had been
studying causes of sediment disasters and planning andformulating countermeasures therefor and standards forwarning and evacuation. It was, nevertheless, decided tostrengthen the study of erosion and sediment control bylaunching a new organization in order to establish
effective measures for major sediment disasters,including the deep-seated landslide that occurred on theKii Peninsula.

The Erosion and Sediment Control Division was
mainly in charge of structural measures including
erosion and sediment control planning andinfrastructure design methods, while the Sediment
Disaster Prevention Division mainly engaged in
non-structural measures including warning andevacuation systems and remote sensing technology,
and the Research Coordinator for Deep-seatedLandslide Prevention directed the focus of their studies
on deep-seated landslide in coordination with bothdivisions.
2. Issues on recent sediment disasters
Sediment disasters occur repeatedly every year andcause loss of human lives and property damage, totaling
about 1,000 cases on average and killing dozens ofpeople every year. In recent years, Typhoon No. 12 in2011 caused serious damage to the Kii Peninsula, heavyrains in July 2012 including the Kyushu Heavy Raincaused disasters, and the Great East Japan Earthquake in2011 caused large-scale sediment disasters in manyplaces including Shirakawa in Fukushima Prefecture.
As a volcanic disaster, Mt. Shinmoe in Kirishima erupted
in January 2011 and many residents around the mountainwere forced to evacuate. Furthermore, still fresh in ourmemory is Typhoon No. 26 that hit Izu-Oshima in

October 2013 and caused large-scale mudflows andserious damage including 39 people dead or missing.
Looking back on these disasters, many of them werecaused by record-high rainfalls. The continuous rainfall
caused by Typhoon No. 12 in 2011 reached about 1,800mm, the largest rainfall ever observed in Japan, and the24-hour rainfall of 824 mm observed in Izu-Oshima in2013 was also the highest as an observation point value
since 1938. There is concern that climate change maylead to frequent occurrences of abnormal weather.
Accordingly, we have to think that the trend of large-scale
sediment disasters will continue under intense weather
conditions.
Furthermore, in hilly and mountainous areas, which areprone to sediment disasters, resistance against natural
disasters is declining due mainly to a progressive lowbirthrate and aging, while the development of erosion andsediment control infrastructure is limited due to financial
constraints. Thus, disaster prevention projects are facedwith a difficult situation because of social factors.
Under such circumstances, in order to prevent
sediment disasters and ensure the safety of people,
multiple measures should be promoted in both structuraland non-structural aspects, including efficientdevelopment of erosion and sediment control
infrastructure and the advancement of warning andevacuation systems. Also, to enhance the effectivenessof such measures, it would be necessary to conduct
technical reviews. This paper introduces the direction ofresearch and studies into the aforementioned issues bySediment Disaster Prevention Department.
3. Erosion and sediment control plan fordeep-seated landslides, etc.
The slope failure that occurred on the Kii Peninsula
was very large in scale and resulted in the formation of ahuge natural dam, so it was necessary to take differentactions from that of the past. For this reason, in order toformulate a method for drafting an erosion and sedimentcontrol plan in consideration of the debris flow resulting
from this deep-seated landslide, the study is proceedingby identifying locations vulnerable to deep-seatedlandslides, external force settings for infrastructure, etc.

We will also continue to study methods of long-term
assessment of sediment discharge to the downstream afterlarge-scale collapses.
Not only deep-seated landslides but also simultaneous
frequent occurrence of shallow landslides could cause amajor disaster as occurred in Izu-Oshima. In responseto this Izu-Oshima disaster, the Erosion and SedimentControl Department of the MLIT held its first meeting ofthe "Workshop for Strengthening Sediment-related
Disaster Prevention Measures" in December 2013, inorder to reinforce structural measures for phenomena notcontemplated in existing plans and for large amounts ofdebris, as well as non-structural measures including
warning and evacuation measures. The workshop
identified some new issues, including measures for areas
without clear valley topography, such as volcano areas,
and measures for debris, which increases the damage ofsediment disasters, and is urgently discussing thesemeasures.
It is also a major issue to establish strategic
maintenance approach for existing erosion and sedimentcontrol infrastructure. Conventionally, maintenance ofexisting infrastructure has not been of a satisfactory level
mainly because sites are separately located in
mountainous regions, so we plan to study ways tostrengthen management in order to utilize existing
facilities effectively.
4. Crisis management in major disasters
There is concern that an earthquake in the Nankai
Trough or directly under Metropolitan Tokyo would
cause catastrophic disaster across a wide area. To
minimize damage in such cases, it is necessary to act
appropriately. Since sediment disasters often occur inremote isolated locations, it is important to grasp thewhole picture of a disaster including the location andscale at an early stage.
Individual disasters were conventionally grasped byreporting or patrols, but the conditions of area-wide
disaster are understood using helicopters deployed toeach Regional Development Bureau. Moreover, inverifying the damage in the Great East Japan Earthquake,
Typhoon No. 12 of 2011 and other disasters, attempts
were made to obtain pictures and information collectedby synthetic aperture radar from an airplane or satellite
and use them for addressing disasters. This approachachieved a certain level of success.
In addition, the development and utilization oftechnologies that contribute to crisis management areproceeding, including efforts to develop a seismographfor instant pinpointing of the location of large-scalecollapses, efforts to estimate collapse-prone areas fromseismic intensity distribution, efforts to estimate upstream
channel blockage from water gauge data, and systems tocollect information from residents using SNS. Thus,
study is underway to grasp of large sediment migration
phenomena in real-time.
In the future, we are going to improve the accuracy ofsuch information and study the development of
information transfer systems to support resident warningand evacuation systems.
The findings from theaforementioned studies are used not only for crisis
management in disasters but also for long-term landmonitoring through constant monitoring of mountainous
areas and the logging of that data.
5. Technical support in sediment disasters
Sediment disasters frequently occur in Japan, but local
governments have few technical experts with thoroughknowledge of sediment disasters. In the event of asediment disaster, personnel of NILIM and PWRI often
provide technical advice, as experts, at the site since it isurgently required to prevent secondary disasters in search
activities, etc., ensure the safety of residents, and takeemergency measures. In fiscal 2012, a total of 12
persons were dispatched from NILIM to 10 disaster
stricken areas, and 8 persons were dispatched as
Tec-Force in fiscal 2013 to Izu-Oshima to support theactivities of Tokyo and Izu-Oshima.
Regional Development Bureaus also need personnel
familiar with disaster response in order to provide active
support to local governments in the event of a disaster.
In order to support the development of such personnel,
the Erosion and Sediment Control Division has been
receiving personnel from the Regional Development
Bureaus since fiscal 2013, who concurrently serve bothorganizations.
We provide such personnel withopportunities to study and discuss issues on disaster
response and support them in acquiring the requiredcapabilities, including how to grasp the flow of on-site
response and technical viewpoints, by introducing ourknow-how when they accompany us on visits to provide
technical guidance on disaster response.
We would like to continue efforts to reflect the findingsof our division in the policies on sediment disasterprevention measures, to contribute to the improvement indisaster response capability of MLIT in general, and toeliminate disasters.