1Flood Risk Management for Wide-area and Long-lasting Rainfall
- Multi-layered countermeasures for complex disasters -
Council Report
December 2018
River Council
for Social Infrastructure Development
Contents
1. Introduction
2. Trends of July 2018 Heavy Rain
(1) Background of the rainfall
(2) Outline of the damage and response
(3) Features of the floods
(4) Problems to be solved
3. Key concepts of countermeasures
4. Recommendations to be implemented promptly
(1) Life-saving measures against hazards exceeding infrastructure capacity
(2) Preventive measures to minimize socio-economic losses and launch
quick recovery
(3) Adaptive measures to more frequent and heavier rains over wider
areas, exacerbated by climate change
(4) Research and development
5. Message to societies21. Introduction
From the end of June toward the beginning of July 2018, a lingering rainy front
hovered over the Japan Islands, which combined with Typhoon Prapiroon coming from
the South, generated record-breaking rainfall over widespread areas of Western Japan.
River flooding and debris flow occurred extensively and simultaneously. Two hundred
people perished or went missing, 30,000 houses collapsed and huge socio-economic
losses resulted from the suspension of urban lifeline services, such as electricity and
water-sewer services and transportation interruptions.
After the Kinu River levee breaches stranded many people during the Kanto-Tohoku
Torrential Rain in September 2015, MLIT had notified that "river infrastructure have
limited capacities and large-scale floods can exceed them" and had initiated a policy
vision of "Rebuilding Flood-conscious Societies" to prepare for flood disasters in
coordination with all social sectors.
Following the tragedy of the Hokkaido-Tohoku Torrential Rain in August 2016, where
the most vulnerable victims succumbed in a nursing home due to overdue evacuation,
MLIT amended the Flood Risk Management Law and River Law to accelerate "Rebuilding
Flood-conscious Societies" in small and medium river basins managed by prefectures.
While MLIT promoted emergency recovery projects in small-scale river basins after
the July 2017 North Kyushu Heavy Rain, the July 2018 Western Japan Heavy Rain forced
MLIT to further boost "Rebuilding Flood-conscious Societies".
In this context, the Minister of Land, Infrastructure, Transport and Tourism
requested the chair of the Council for Social Infrastructure Development to consider
how to manage flood risks of wide-areas and long-lasting rainfall. The chair entrusted
the bill to the chair of the River Council and the "Sub-panel on Flood Risk Management
for Wide-area and Long-lasting Rainfall" started up in September 2018. After three
intensive discussions, the River Council finalized a report with key concepts and
recommendations to be implemented promptly.32. Trends of July 2018 Heavy Rain
(1) Background of the rainfall
<Hydrological phenomenon>
+ Rainfall on widespread areas of Western Japan reached 1,800mm in Shikoku and
1,200mm in the Tokai region, during June 28th to July 8th. The amount was four times
larger than July monthly averages at several stations.
+ The long-lasting rainfall broke the records of 24-hour rainfall at 77 stations, 48-hour
rainfall at 125 stations, 72-hour rainfall at 123 stations among 1,300 AMeDAS
Observatories. (AMeDAS: Automated Meteorological Data Acquisition System)
+ 125 stations with the 48-hour rainfall records were widely distributed in North Tokai,
Hokuriku, Kinki, Chugoku, Shikoku and Kyushu Regions. 30-year data analysis identified
over 100-year excess probability at 13 among 16 stations in Okayama, 18 among 19
stations in Hiroshima and 9 among 10 stations in Ehime Prefectures.
+ 1-hour rainfall also marked a new record at 14 AMeDAS Observatories in Gifu and
Hiroshima Prefectures.
+ The total rainfall of the first 10 days in July 2018 throughout Japan was above the
record for 10-day rainfall during January 1982 to June 2018. There was no such
precedent in the observation archives. The new records were 208,035.5mm in total
and 215.4mm on average for 966 AMeDAS Observatories.
<Meteorological factors>
+ Typhoon Prapiroon, born on June 29th, 2018, moved Northward on the East China Sea
and turned Northeast near Tsushima Island to be categorized a tropical cyclone on the
Japan Sea on July 4th. By July 8th, a rainy front lingering over Western Japan with
extremely warm and wet air was on course for heavy rain.
+ The warm and wet air was supplied by Okhotsk Sea High Pressure enlarged by 2
meandering jet streams: the Tibet High Pressure and Pacific Ocean High Pressure. The
Japan Meteorological Agency announced there was a "contribution of water vapor
increased by climate change". This was the first time the agency attributed a specific
impact to climate change.
+ The Agency determined that the amount of water vapor was the largest since 1958.
+ In addition, 15 linear rainbands were formed during July 4th to 8th over Gifu,
Hiroshima and Kochi Prefectures. Nine of them caused over 150mm during 3-hour
rainfall, and some of them contributed over 50% of total precipitation.
<About Typhoon Jebi in September>
+ Typhoon Jebi was born near Minamitorishima Island on August 28th and made
landfall in Tokushima and Hyogo Prefectures, with very strong force on September 4th.
The typhoon brought strong winds and rain over Western to Northern Japan, and
caused the highest recorded storm surge in Osaka Bay.4(2) Outline of the damage and response
In July 2018, Heavy Rain caused simultaneous river floods, waterlogging, debris flow,
among others, in a wide area of Western Japan. As a result, 224 people died, 8 people
went missing, 21,460 houses collapsed, and 30,439 houses were inundated. Local
governments issued evacuation orders for 2,007,489 people (915,849 families), and
evacuation advisories for 2,304,296 people (985,555 families). Lifeline infrastructures
were also damaged, such as 263,593 households affected with disrupted water supply.
<River floods>
+ The number of rivers, in which the water exceeded the hazardous water level, was the
largest ever, with 50 rivers in 26 basins under MLIT management and 234 rivers in 138
basins under prefectural management.
+ Levees were breached at 37 points in total. Of these, 2 breaches occurred on the Oda
River in Takahashi River basin under MLIT management, and 35 breaches were in rivers
under prefectural management; namely, 16 breaches in 10 rivers in Okayama and 16
in 12 rivers in Hiroshima.
+ Especially in Oda River and its 3 tributaries, levees were breached at 8 points due to
the "backwater phenomenon" in which branch river floods synchronized with the
major river flood.
+ Among 558 dams managed by MLIT, 213 dams conducted flood control operations. 22
dams used over 60% of their flood control capacity. 8 dams almost exhausted their
flood control capacity and shifted to emergency discharge operations, under which the
outflow was equal to the inflow. Some operations triggered floods in the downstream.
<Waterlogging>
+ Inundation, including waterlogging, occurred in 47 rivers in 22 MLIT-managed river
basins and in 242 rivers in 69 prefecture-managed river basins.
+ Record breaking and long-lasting rainfall and intensive short-period squalls in
widespread areas caused a mixture of river flooding and waterlogging at 88
municipalities in 19 prefectures in Western Japan. Municipalities reported that 18,853
houses were affected by waterlogging, and 90% of them were in areas undergoing
construction of sewage drainage systems.
<Sediment disasters>
+ Sediment disaster warnings were issued to 505 municipalities in 34 prefectures.
Sediment disasters occurred in 31 prefectures especially in Hiroshima and Ehime
Prefecture. The total number of 2,512 was 2.3 times higher than the annual sediment
disaster occurrence of the past 10 years.
+ Sediment-water synergistic floods, wherein preceding sedimentation in the
downstream dammed up subsequent sediment and water, hit Oya-ohkawa and Sozu
rivers in Hiroshima Prefecture.
+ Many masonry sabo dams in Hiroshima Prefecture, which had passed periodical
inspections, collapsed or were flushed away by debris flows.5<Human loss>
+ 232 people perished or went missing during the July 2018 Heavy Rain. This is the first
time a human toll exceeding 200 occurs since 1982.
+ Fatalities and reports of missing people occurred in 14 prefectures, concentrating in
Okayama, Hiroshima and Ehime Prefectures. 80% of the deaths (87 of 109 people) in
Hiroshima perished in sediment disasters. Almost all deaths (59 of 61 people) in
Okayama were from drowning in floodwaters.
+ A half of the victims in the Hiroshima sediment disasters and 90% of victims in the
Mabi Town inundation were people over 65 years old.
<TEC-FORCE >
+ MLIT dispatched the Technical Emergency Control Force (TEC-FORCE) to affected
municipalities. The number of MLIT members who worked on these disasters
amounted to 10,820 man-days (as of October 29th, 2018), and 607 per a day at a
maximum.
+ Pump vehicles conducted 24-hour drainage operations of 1,200 ha waterlogging over
3 days at Mabi Town in Kurashiuki, Okayama.
+ Road sprinklers and road sweepers supported dust-proofing and water supply to
recover primary services for living conditions.
+ Staff members removed sediment, driftwoods and garbage on rivers and roads in Kure
City, Hiroshima.
<Search and rescue>
+ The Ministry of Defense operated search and rescue operations with 33,100 self-
defense force soldiers, 28 vessels and 38 aircrafts, at its peak.
+ The Fire and Disaster Management Agency rescued 397 victims during searches
performed by 15,000 fighters and 271 helicopters in Okayama, Hiroshima, Ehime and
Kochi Prefectures.
<Road and rail interruption>
+ Expressways were interrupted by debris flows, bridge collapses and rainfall regulations
at 77 sections of 63 routes in many areas from Chubu to Kyushu.
+ Railways were stopped by debris flow, rail submersions and bridge collapses on 115
routes of 32 companies.
+ The JR Freight Company suspended 30% of its operations and provided substitute or
alternate transportation.
<Lifeline infrastructure suspension>
+ Lifeline infrastructure of electricity and water-sewage services was damaged in many
areas of Western Japan.
+ Many blackouts occurred in Okayama, Hiroshima and Ehime Prefectures, but
electricity was quickly restored in urban areas as of July 13th.6+ Water outages occurred due to debris flows into purification plants and pump stations
in Okayama, Hiroshima and Ehime Prefectures. Temporary water purifiers were
working for a long time in Kure and Uwajima Cities.
+ Sewage treatment plants were damaged in Okayama and Fukuoka Prefectures.
Residents were asked to perform voluntary bans.
<Stagnation of medical care>
+ Inundation and water outages hit 95 medical centers in Japan. Some of the damage
remained until September 13th.
+ Large-scale inundation hit the Mabi Memorial Hospital after 4:00 am on July 7th, and
isolated 300 patients and evacuees.
+ Roof leaks and inundations struck 268 nursing houses for the elderly. 657 occupants
from 30 houses had to move to other facilities or hospitals.
<Damage on industries>
+ Agricultural damage was estimated to amount to 167.5 billion yen in agriculture, 160.8
billion yen in forestry, 2 billion yen in aquaculture, and 330.3 billion yen in total.
+ Industrial factories were inundated due to a levee breach in Mihara City, Hiroshima
Prefecture and water logging around industrial parks in Okayama City, Okayama
Prefecture.
<Disaster garbage>
+ Floods generated a large quantity of disaster garbage. The amount in Okayama,
Hiroshima and Ehime Prefectures was 290 tons in total.
+ Waste treatment plants were damaged directly by floodwaters and also from road
interruptions and water outages.
<Damage of Typhoon Jebi>
+ Kansai International Airport and Rokko Island were submerged by the storm surge in
Osaka Bay. However, Osaka City was protected by tidal gates and pump stations, which
were constructed and put into operation following typhoon disasters in 1934 and 1961.7(3) Features of the floods
Based on the rainfall background (1) and the damage outline (2) mentioned above,
features of the water-related disaster caused by the July 2018 Heavy Rain were
summarized as follows:
< Meteorological factors of recent heavy rains>
+ Heavy rain, which caused water-related disasters in Japan can be sorted into typhoon-
type, rainy front-type, rainband-type, and others.
+ The August 2014 Sediment Disaster in Hiroshima and the July 2017 Heavy Rain in
Northern Kyushu were caused by linear rainbands settling in relatively narrow areas.
The September 2015 Kanto-Tohoku Heavy Rain on Kinu River was induced by linear
rainbands boosted by a typhoon and a tropical cyclone. The 2016 Hokkaido-Tohoku
Heavy Rain had moving rainbands along a typhoon’s path and intensive rainfall.
+ The July 2018 Heavy Rain was caused by a lingering rainy front enhanced by rich vapor
supply from two high-pressure systems that generated long-lasting rainfall over a
wide-area.
+ Each water-related disaster had different breakout mechanisms due to natural
phenomena, with differing impacts on residents. These factors often worked
synergistically.
< Unprecedented hydrological features in 2018>
+ Average precipitation exceeded the flood discharge simulation scenarios in 8 major
river basins of Western Japan, including in Takahashi and Hiji Rivers, however, the peak
discharges were less than the discharge estimates. This means the July 2018 Heavy
Rain had no intensive peaks as in the case of a typhoon, rather, the record-breaking
total precipitation occurred over a long-lasting period. Hence, rainy front-type rainfall
occurred in Setouchi region where typhoon-type events were heretofore dominant.
+ This explains why many river floods occurred, not only in small and medium scale river
basins but also in major river basins, which had relatively wide catchment areas, and
that backwater phenomena caused several levee breaches along the Oda River in
Takahashi River basin.
+ Large amounts of rainfall exceeding sewerage design capacities and long-lasting high-
water levels hindered drainage causing waterlogging.
+ Excessive inflows were stored in dam reservoirs, however 8 dams exhausted the flood
control capacity and shifted to emergency discharge operations.
+ Many sediment disasters occurred in the Southern area of Hiroshima Prefecture. With
a total 1,242 sediment disasters registered in the prefecture, this is more than their
annual occurrences in the whole of Japan.
+ Sediment supply from upstream disasters flowed through the river channel
continuously and settled around the slope turning point. The rise in the riverbed
downstream caused sediment-water synergistic disasters.
+ Local linear rainbands in long-lasting rainfall episodes created wavy precipitation in
each area and produced a couple of water level peak and discharge in each river.8Intensive squalls on fully-moistened soil triggered sediment disasters and quick
discharge to rivers and dams.
<Evacuation advisories and residents’ evacuation>
+ Municipalities in MLIT-managed river basins, including the severely affected Oda River,
issued evacuation advisories citing maximum probable inundation scenarios, a
timeline plans of emergency operations, and hotline to MLIT river offices. However,
some municipalities in prefecture-managed river basins hesitated to issue evacuation
advisories after acknowledging the dangerous water levels. Also sediment disaster
warnings did not help in evacuation advisories.
+ In the case of Mabi Town of Kurashiuki City, inundation maps and hazard maps almost
corresponded to the actual flooding and evacuation advisories that were issued. Some
residents testified that they started evacuation just after hearing the advisories at
midnight but that roads were so crowded. However, because the rainfall was not so
heavy, a number of residents could not decide to evacuate. In the inundation area, due
to levee breaching, 44 among the 51 people who drowned were found in their houses.
The fact that most of them were on the ground floor suggests that even vertical
evacuation was difficult to perform, especially for elderly people.
+ 90% of human loss due to sediment disasters occurred within sediment disaster
warning zones, where early warnings were issued in advance. In the case of Hiroshima
City, many people might have decided not to evacuate because they had no experience
of past warnings. Long-lasting but weaker rainfall than the 2014 Sediment Disaster
might have enhanced their normalcy bias.
+ Huge inundations occurred downstream of the dams that had exhausted flood control
capacity. Dam operators delivered operational information to mayors through hotlines
and the media, however in many cases, the information without inundation areas did
not trigger evacuation of residents.
+ Some victims lost their way to the shelters or got into accidents during the evacuation
because evacuation routes were already endangered. In some communities,
evacuation routes ran through a sediment disaster-warning zone. In other cases, debris
flows hit a housing development from several valleys.
<Socio-economic losses over wide areas>
+ Damage to emergency operation centers and core medical services, to lifeline
infrastructure services of electricity and water-sewage, and to transport infrastructure
of rail and roads, disrupted emergency response work and quick recovery. The damage
even impacted companies that were not in the affected areas.
+ The impact spread widely to areas that were not themselves inundated, through
interrupted supply chain networks and employee absences. Automobile factories in
Hiroshima and other enterprises had to stop their manufacturing and service
operations.
+ Self-defense force soldiers and fire fighters supported search and rescue and the TEC-
FOECE members assisted in infrastructure recovery. But widespread damage and
interrupted road communications required extended support.910
(4) Problems to be solved
+ Limited capacity of existing infrastructure against large-scale flood
- Floods occurred at many sections where channel capacity was limited in both
prefecture-managed and MLIT-managed rivers.
- Dams exceeded the flood control capacity and caused flooding downstream. Some
dams, which had limited outflow possibilities due to narrow downstream channels,
reached their full capacities earlier.
- Much rain caused waterlogging and debris flows simultaneously in wide areas.
+ Complex factors of water-related disasters
- The backwater phenomenon, in which branch river floods synchronized with the major
river flood, caused tributary flooding and waterlogging.
- Much sediment flowed through rivers from upstream landslides and settled in the
downstream channel. The ensuing riverbed rise caused sediment-water synergistic
disasters.
+ Climate change impacts relative to water-related disasters
- This was a confirmed instance of climate change impact. "Increased water vapor due
to global warming" contributed to the July 2018 Heavy Rain. Further extreme climate
change impacts will make rainfall all the more frequent and violent.
- Rainy front-type rainfall occurred in the Setouchi region where typhoon-types were
heretofore dominant. Climate change might alter meteorological factors across
regions.
+ Human damage due to overdue evacuation
- Even though hazard maps, local risk information and evacuation advisories were
provided, many residents could not understand the risks nor perceive the immediate
threats. They did not decide to evacuate and perished from the water-related disaster,
especially so in the case of elderly people.
- In instances where evacuation routes were dangerous, victims lost their way to the
shelters or got into accidents during the evacuation.
+ Miscommunication on infrastructure operational information
- Dams, sewerage networks, pumping stations, floodgates keep localities safe against
heavy rain under a certain threshold. Local residents did not understand the possibility
of floods due to heavier rainfall in excess of infrastructure capacity. Lack of information
of area-specific risks and of real-time operations made residents unconcerned.
+ Local socio-economic damage
- Damage on local emergency operation centers, core medical centers, lifeline
infrastructure networks of electricity and water-sewage services, rail and road
transport infrastructure, disrupted the emergency response and quick recovery11processes. Long-term business suspensions and population outflows are an ongoing
concern.
+ Wide-spread damage
- TEC-FORCE members were dispatched from all over Japan but it was insufficient to
cope with the overwhelming number of requests due the wide-spread of areas
affected.
- MLIT Regional Bureaus mobilized staff members and materials. But insufficient
information hindered resource allocation.
- Emergency operations faced difficulties in determining the extent of the damage at the
initial stage and permits to access private properties for garbage disposal hindered the
process.123. Key concepts of countermeasures
+ Long-lasting rainfall of the July 2018 Heavy Rain caused huge human damage and
socio-economic losses in wide areas, not only from river floods exceeding channel
capacities but also from complex causes, such as backwater phenomenon and water-
debris synergistic disasters.
+ The September 2015 Kanto-Tohoku Heavy Rain reminded the nation that "large-scale
floods can inevitably exceed river infrastructure capacity", which triggered a new
policy vision of "Rebuilding Flood-conscious Societies" to prepare for the next flood in
coordination with all social sectors.
+ These efforts helped advance emergency information delivery from the public sector
and risk communication of water-related disasters. However, lingering problems were
clarified, such as the miscommunication in evacuation advisories and local risks, and
the misunderstanding of many residents who decided not to evacuate.
+ Lifeline infrastructure suspension of electricity and water-sewer services and transport
interruption of road and rail networks over a wide area affected local emergency
control operations and socio-economic activities.
+ In recent years, climate change impacts have increased the number of heavy rains.
Enormous damage has occurred every year. Many rivers have often risen up above
hazardous water levels. We should be aware that climate change has shifted water-
related disasters into a new phase, surpassing our flood control efforts. Moreover,
climate change will make heavy rain more frequent and violent, exacerbate river floods,
waterlogging and debris flow, and cause more severe damage.
+ Therefore, key concepts should stress the importance of structural measures from
critical authorities, and urgently strengthen multi-layered countermeasures against
complex disasters to prevent and minimize disaster damage through a whole-of
society approach. It can be achieved by all social sectors working together in the Mega-
flood Management Committees.
+ In practice, the following four key concepts are important to accelerate "Rebuilding
Flood-conscious Societies":13"Life-saving measures against hazards that exceed infrastructure capacity"
- Information sharing of local disaster risks, infrastructure functions and real-time
information through communications improvement, simplified indicators, easy access
and collaboration with the media.
- Self-decision making of residents for safe evacuation through proactive information
acquisition in local communities.
- Life-saving initiatives by constructing disaster preventive infrastructure, durable levees
to delay breaching and temporary shelters for stranded victims.
"Preventive measures to minimize socio-economic losses and launch quick recovery
and reconstruction"
- Proactive facilitation, such as water-proofing facilities of private companies,
reinforcement of lifeline infrastructure and core functions, and capacity building for
resilience/recovery through power duplication and material storage.
"Adaptive measures to more frequent and heavier rains over wider areas,
exacerbated by climate change"
- Prompt response to climate change impacts confirmed, step-by-step increases of
safety levels, advanced monitoring and maintenance, preparation for wide-area
disasters and rethinking of our way of living.
"Research and Development"
- Scientific research on disaster breakout mechanisms, focusing on meteorological and
social factors, and practical development of effective countermeasures for disaster
prevention and mitigation.144. Recommendations to be implemented promptly
(1) "Life-saving measures against hazards that exceed infrastructure capacity"
1) Seamless information from routine times to emergency
- Emergency warning with local risk information during routine operations
Disclose area-specific risks such as river water levels to guide evacuations and
probable inundated areas on hazard maps during routine time. Deliver real-time
river information with local risk information through the media and the internet in
times of emergency.
- Visualized information to assist emergency risk perception
Deliver water level information with visualized information to assist risk
perception through simple and low-cost cameras.
- Timeline plans of disaster operations for evacuation
Enrich timeline plan of disaster operations to clarify time-series disaster
operations before and after evacuation advisories to manage locally-specific flash
floods, storm surges and sediment disasters, involving dam operators in the Mega-
flood Management Committees if necessary.
Develop district-level and personal-level timeline plans of operations.
Involve the media and ICT companies to enhance emergency communication
capacity.
- Risk level indicators standardized and shared among various disasters
Develop a user-oriented website to integrate various types of disaster
information of river and slope conditions, weather forecasting and hazard maps.
Standardize, summarize and simplify disaster information to assist risk
understanding.
- Information delivery through active media channels
Improve river information delivery systems in active cooperation with media and
ICT companies, and strengthen interdependent partnerships with them.
- Capacity disclosure of disaster management infrastructure
Disclose the capacity of reservoirs, sabo weirs and levees, and damage due to
hazards exceeding their capacity, to assist in risk perception for evacuation.
Share dam operation rules with residents in the downstream areas, and deliver
operational information during flood control.
2) Risk information sharing without a blind spot
- Probable inundation zoning15Publish probable inundation zones caused by the worst-case rainfall in all legally
designated flood-forecasted rivers. Install 3L water level gauges (low-cost, long-life
and localized).
Boost probable inundation zoning around sewage networks and coastal areas.
- Probable inundation mapping for downstream dams
Simulate and publish probable inundation areas and depth caused by the worst-
case rainfall for downstream dams.
- Probable sediment disaster zoning
Prompt prefectures to complete basic surveys and publish probable sediment
disaster zones under the Sediment Disaster Management Act.
- Hazard map revision using maximum flood scenario
Enhance professional support to municipalities for revising hazard maps using
maximum inundation scenario with the worst-case rainfall.
Assist public-help for residents with technical and mental challenges for local
specific disaster risks.
Publish revised hazard maps, probable inundation zones and probable sediment
disaster zones promptly through the hazard map portal site.
- Hazard map portal site of water-related disasters
Enrich and open data on the hazard map portal site for local residents and
companies. For instance, publish probable inundation maps, even in small and
medium-scale river basins, and maps for storm surges and waterlogging. Disclose
topographic classification maps to understand disaster risks without inundation
maps.
3) Real-time information to encourage evacuation
- Time-series flood risk-line system
Develop and install a system to assess varying flood risks continuously up-down,
right-to-left and hour-by-hour.
Improve forecasting accuracy of the peak water level and arrival times to assist
risk-based evacuation and advisories.
- Water level monitoring and flood forecasting
Carry out flood forecasting at more rivers, sewage plants and on the coast. Install
3L water level gauges on small and medium-scale rivers and enrich real-time water
level data delivery.
- Flood commentary by river authorities
Explain actual flood management using flood forecasting, water level data and
live images from river authorities (MLIT or prefectures) through the local media.16- Dam information delivery for evacuation
Review dam information management, such as releasing discharge and schedule,
for local governor’s evacuation orders and evacuee’s actions. Discuss how to use
dam and river information with municipalities, and share it among local communities.
- Supplementary sediment disaster warning
Improve sediment disaster warning to support varying risk perception using time-
series risk indicators. Assist in the issuance of evacuation orders by automatic
indicators of risk level over criteria.
- Warning system ensured during for mega-scale flood
Secure the water-resilience of water level gauges and dam communication
systems, even for mega-scale floods, to provide essential data for operation and
evacuation.
4) Individual disaster response initiatives
- Multi-help enhancement
Promote neighborhood-level evacuation planning and foster leaders for local
disaster management. Enhance local communications among neighboring voluntary
groups, social welfare councils and flood fighting teams to ensure evacuation of all
residents including the elderly at home and the socially-vulnerable. Promote
evacuation planning of nursing homes and keep close ties with the community.
- Personal evacuation planning and risk mapping
Support each community to promote "My Timeline Plans" so individuals can
make disaster operation decisions in advance, and "My Evacuation Maps" to
reconfirm safe evacuation routes and danger points, keeping adequate relations
with the district-level disaster management plan.
- Support tools for evacuation planning
To support individual proactive evacuation planning, develop area-specific and
time-series inundation simulations, which indicate inundation areas and arrival times
along MLIT-managed rivers and in small and medium-scale river basins, and
distribute it through the internet.
- Human resources development for local resilience
Nominate and dispatch experts in water and sediment disaster management to
municipalities to support hazard mapping, disaster operation planning, and
participatory evacuation drills.
- Disaster education17Promote disaster education using the numerous lessons learned in recent water-
related disasters and through locally-specific disaster histories, using the Mega-flood
Management Committees. In particular, transfer basic knowledge to students
through natural and social science classes at elementary and junior high schools.
- Evacuation drills with public participation
Conduct evacuation drills with public participation using practical evacuation
orders and river/dam information. Share various trials in the Mega-flood
Management Committees.
5) Structures for flood risk reduction
- Resistant levees to delay breaching
Develop and build durable levees as a crisis management infrastructure in flood-
prone areas to gain a little longer time for vulnerable residents’ evacuation.
- Sabo works to Protect evacuation routes and shelters
Prevent sediment disasters using sabo structures, like weirs, around the one and
only route or shelters, to enable smooth evacuation.
Negotiate to use private buildings as an emergency shelter in high inundation risk
areas.
6) Life-saving shelters for stranded victims
- Life-saving shelters as an emergency operation
In areas with no permanent evacuation shelters, reserve life-saving mounds
made of disposed soil or private buildings as temporary shelters, under local initiative.
7) Risk management against complex disasters
- Confluence improvement
Strengthen and heighten levees around confluences where backwater
phenomenon might breach levees and cause deep inundation.
Reinforce levees of tributaries considering backwater phenomenon.
- Sediment flow management
Build sabo weirs and sediment pools through sound coordinated planning with
river improvement to prevent sediment-water synergistic disasters.
- Channel maintenance
Cut trees and dredge riverbeds to secure channel capacity of narrow sections
around probable inundation areas of dense housing and critical institutions.
- Cooperative action against complex disasters18Enhance cooperation among various agencies to implement integrated projects
to reduce risks of large-scale water-related disasters, which are caused by
simultaneous river flood, debris flow, waterlogging, storm surge and others.
8) Countermeasures against unexpected floods
- Dam upgrading for flood control
To enhance flood control capacity, upgrade existing dams through operational
improvement, capacity alteration, discharge capacity enlargement and crest
heightening. Adjust spillways and remove sediment of retarding basins. Negotiate
with dam users to divert reservoir capacity more for flood control purposes.
- Flood control capacity development
Improve downstream channels to enable increased discharge during flood
control operations. Prevent sediment inflow to the reservoir and remove sediments
hindering full flood control capacity.
Maintain spillways and remove sediment from retarding basins.
- Masonry sabo weirs reinforcement
Reinforce and rehabilitate masonry sabo weirs to secure functions against
possible debris flows.19(2) "Preventive measures to minimize socio-economic losses and launch quick recovery
and reconstruction"
1) Measures to minimize socio-economic losses
- Resilience of critical infrastructure
Protect lifeline infrastructure of electricity, water-sewer services and transport
infrastructure, through sediment control, in cooperation with facility managers.
Promote waterproofing of emergency control centers, core medical centers,
water supply and sewage networks in cooperation with facility managers who
conduct business continuity planning, evacuation drills and facilitation of storage
tanks and barrier walls.
- Protection of the urban center and core functions
In urban and rural flood-prone areas, promote basin-wide flood control
integrating river improvement, sewage drainage and existing infrastructure
maintenance. In coastal areas, build sea levees and storm surge walls through
comprehensive planning.
In areas below sea level, maintain river and sea levees, and strengthen drainage
capacity. In dense asset areas of Tokyo or Osaka, develop life-saving levees in
collaboration with private developers.
Hasten waterlogging drainage using reserved pumps and pump vehicles from
rivers where the water level is not forecasted to rise.
2) Measures to launch quick recovery and reconstruction
- Drainage operation and maintenance
Foster an effective scheme to build and operate drainage facilities against long-
lasting waterlogging around river confluences or in areas below sea level.
- Waterproof drainage facilities
Hold the waterproof function of drainage facilities throughout the inundation,
and stock materials for quick recovery from interruption.
- Persistent emergency control centers
Hold functions and reliability of the emergency control center through power
duplication and other measures.
- Preparation for quick recovery and reconstruction
Share damage simulation scenarios from large-scale water-related disasters with
the Mega-flood Management Committees and prepare for quick recovery and
permanent reconstruction with all sectors involved.20(3) "Adaptive measures to more frequent and heavier rain over wider areas,
exacerbated by climate change"
1) Adaptation to climate change
- Systematic upgrade of safety level
Promote urgently necessary countermeasures against frequent and violent
heavy rain due to climate change, and upgrade safety levels systematically in
accordance with aggravating climate change impacts.
- Strategic observation and advanced maintenance
Observe river channel capacity periodically, forecast sedimentation and
forestation quantitatively using cross-section surveys and 3-D laser imaging. Refine
river management and facility operation with more intensive water level monitoring.
2) Preparation for wide-area and long-lasting heavy rain
- TEC-FORCE legalization and activation
Establish the legal basis for TEC-FORCE to prepare for wide-area and long-lasting
heavy rain and activate it by involving human resources from the private sector and
by installing real-time disaster information management.
- Real-time disaster information collection
Install remote measuring instruments, such as unmanned aerial vehicles and
laser imaging sensors, to gather information during simultaneous disasters or
successive typhoons. Share the information with local governments.
- Timeline plans of emergency operations involving various agencies
To take integrated actions against wide-area water-related disasters, establish
timeline plans of emergency operations to identify time-series countermeasures for
each agency involved in the Mega-flood Management Committees. Involve public
transportation sectors especially in areas below sea level. Keep mutual
communication and information sharing under the timeline plans during disasters.
3) Rethinking the way of living
- On-street disaster risk indicator
Promote on-street hazard signage, such as indication of probable inundation
depth, to raise awareness for area-specific risks. Set local risk signboards in sediment
disaster risk zones.
- Disaster risk internalization in the societies
Strengthen partnerships between disaster management sections and urban
planning sections to reflect disaster risks to consolidated urbanization and house
relocation. Cooperate with the real estate industry and the insurance companies to
encourage house owners to avoid disaster risks; house renovations can be a good
opportunity for this .21In sediment disaster risk zones, encourage owners of existing buildings to
implement necessary countermeasures such as safety check, reinforcement and
relocation.22(4) Research and Development"
1) Advanced disaster risk assessment
- Changing risk assessment due to climate change
Advance a technical study to reflect on future climate change impacts for
infrastructure planning and design, based on past heavy rains and storm surges. For
the study, pay close attention on the interactions between flood control, sabo,
sewage and coastal management to respond to complex disasters.
In particular, estimate rainfall volume quantitatively and accurately in a trend of
frequent and violent heavy rain due to climate change, and analyze rainfall patterns
in each region according to meteorological factors.
- Breakout mechanism analysis of various water-related disasters
Develop methods of hazard prediction and risk assessment through analyzing
breakout mechanisms of sediment and flood disasters.
Evaluate relative risks in sediment disaster risk zones to save lives.
- Standardized risk assessment method for various disasters
Develop standardized assessment methods of various local disasters in the
region for municipalities to promote risk-based town planning, relocation guidance
and voluntary disaster preparedness of private companies.
- Socio-economic loss assessment due to heavy rain
Develop quantitative assessment methods of socio-economic losses within and
around affected areas to understand total actual damage and prepare for next
disasters in coordination with all social sectors.
2) Risk-based disaster prevention and mitigation
- Step-by-step approach to climate change impact
Implement risk management measures one-by-one to respond to confirmed
climate change impacts and adapt to uncertainty in the future.
- Flood forecasting accuracy improvement
Improve flood forecasting accuracy by enriching water level observation and
applying radar rainfall forecasting to ensure smooth evacuation and adequate dam
operation. Enhance flood forecasting even in small and medium-scale rivers using 3L
water level gauges and image analysis technology.
For forecasting accuracy improvement, consider required accuracy at the site
with a long-term strategy.
- Advanced dam operation using rainfall/inflow forecasting
For further flood control ability, improve accuracy of rainfall/inflow forecasting,
and develop forecast-based dam operation methods.233) Risk information management to support evacuation
- Advanced sediment disaster warning
For accuracy improvement of sediment disaster warnings, develop a higher-
resolution soil-rainfall index, and improve website displays and information delivery
methods to assist warning and evacuation.
For mayors to issue timely and appropriate evacuation advisories, develop
longer-period sediment disaster forecasting and supplementary information such as
rainband prediction from radar monitoring data.
- Risk information delivery for evacuation
Develop real-time river information delivery systems to support residents’
voluntary risk perception and mayors’ timely evacuation advisories, using latest
CCTV cameras and artificial intelligence technology.245. Message to societies
During the July 2018 Heavy Rain, long-lasting rainfall caused substantial human
damage and socio-economic losses. Following the September 2015 Kanto-Tohoku Heavy
Rain Japan was reminded, "inevitable large-scale flood can exceed river infrastructure
capacity" and started a new policy vision of "Rebuilding Flood-conscious Societies" to
prepare for the next flood in coordination with all social sectors. However, we should
remind ourselves again that structural and non-structural measures have limits. We
have to use both in collaboration and exert synergistic effects of disaster prevention and
mitigation.
The Sub-panel on Flood Risk Management for Wide-area and Long-lasting Rainfall
closely cooperated with other independent panels on each issue, discussed
comprehensive solutions from different angles, and in the end generated measures for
prompt implementation.
River flooding, waterlogging, debris flow and complex disasters in July 2018
triggered the promotion of conventional treatment and of further cooperative
approaches among concerned authorities.
Many people were stranded in water although hazard maps and evacuation
advisories were delivered in advance. This fact reveals that governmental services were
insufficient. We should promote personal evacuation planning in each district and local
communications among neighboring groups to help each other. For this target, we
should standardize and deliver disaster information through various channels in
cooperation with the media and ICT companies.
Climate change impact undoubtedly contributed to the July 2018 Heavy Rain.
Climate change adaptation is not a future problem but an actual challenge today. We
should research increasing trends of heavy rain and further study how to assess it
quantitatively.
Typhoon, rainy front or local squall have specific mechanisms that lead to water-
related disasters. We should understand characteristics of local water-related damage
and research climate change impact scientifically to discuss comprehensive solutions for
the whole of society.
Basic river data, such as water level and rainfall, are essential to construct
infrastructure efficiently and to effectively maintain them. We should advance data
collection schemes and develop data management institutions.25All sectors in society should take initiatives. Residents should make decision to
evacuate to save own life. These are essential in disaster management. Government
should support all sectors and each entity should take self-motivated actions.
It is impossible to build such a society in a couple of days with all sectors involved.
We should initiate practical policies and implement them at the local level step-by-step.
We should continuously review policies, for policy progress and in response to social
changes. We should promote research and development to catch up with the changing
climate.
Japan has been improving proactively resilient and reliable land management to cope
with frequent heavy rain disasters, however recently, vulnerability to water-related
disasters are increasing with regards to hazards magnified by climate change, social
transformation of aging population, and other factors. Japan is expected to mobilize all
social resources and cutting-edge science and technology to develop a policy system for
disaster prevention and mitigation of the world.
Sub-panel on Flood Risk Management for Wide-area and Long-lasting Rainfall
under River Council for Social Infrastructure Development
Chaired by Professor Toshio KOIKE:
Director, International Centre for Water Hazard and Risk ManagementwithEiichi NAKAKITA: Professor, Kyoto University (Meteorology and Hydrology)
Shiro MAENO: Professor, Okayama University (River engineering)
Masaharu FUJITA: Professor, Kyoto University (Sabo engineering)
Atsushi TANAKA: Professor, Tokyo University (Disaster information)
Mayumi SAKAMOTO: Associate Professor, University of Hyogo (Disaster policy)
Tetsuya SUMI: Professor, Kyoto University (Dam engineering)
Hiroaki FURUMAI: Professor, Tokyo University (Environmental Engineering)
Keisuke HARADA: Mayor, Hita City, Oita Prefecture