Contents

Preface ..................................................................................................................................................1
1.

Background ...............................................................................................................................22.

Definition of Flood Hazard Map...............................................................................................43.

Map Preparing Body .................................................................................................................5

4.

Scope.........................................................................................................................................65.

Purpose......................................................................................................................................7

6.

Effectiveness of Flood Hazard Map........................................................................................10

7.

Process of Production, Distribution and Usage of Flood Hazard Map ...................................128.

Production of Flood Hazard Map............................................................................................13
8.1

Collection and Classification of Information......................................................................13

8.2

Setting-up of Basic Conditions ...........................................................................................14

8.3

Drawing-up of Historical Flood Map .................................................................................15

8.4

Drawing-up of Flood-prone Area Map(Cases in which Flood Simulation Analysis is possible) ...................................................17

8.5

Establishment of Evacuation Plans.....................................................................................28

8.6

Establishment of Issuance Criteria for Evacuation Warnings.............................................29

8.7

Production of Flood Hazard Map .......................................................................................30

9.

Distribution and Usage of Flood Hazard Map ........................................................................31
9.1

Distribution among Local Residents...................................................................................31

9.2

Administrative Use .............................................................................................................32

9.3

Issues on Flood Evacuation ................................................................................................33

9.4

Issues on Residents’ Understanding of Flood Hazard Map ................................................34

9.5

Effective Use of Flood Hazard Map ...................................................................................35

Concluding Remark ............................................................................................................................36

Appendix- Flood Hazard Map examples of Educational-use for Disaster PreventionPreface
This manual describes in brief the background, purpose, production and distribution of Flood
Hazard Maps, as well as their verified effectiveness and current usage in Japan. Realistic questions on
the evacuation of local residents in the event of flood are clarified, and the practical and effective
usage thereafter of Flood Hazard Maps is reviewed in turn.
The features and characteristics of rivers, flooding mechanisms, social framework, viewpoints on
flood protection, collaboration of river management and residents, and the background andcircumstances of Flood Hazard Maps of Japan might be different from those of other countries.
The experience gained from the use of Flood Hazard Maps in Japan would be of significant use toother countries as well, provided the maps are used according to the specific circumstances of therespective countries.

11. Background
With economic growth, urbanization and the subsequent concentration of population and property,
people who have never experienced a flood are moving in increasing numbers to flood-prone areas inmany countries. Conversely, residents are less aware of the threat of floods where flood control
facilities have been improved and the frequency and magnitude of inundation are reduced. In suchcases, they are hardly prepared for floods and by no means assured of proper actions to take,consequently suffering more serious damage once a flood occurs.
It is time-consuming and costly to thoroughly construct flood control facilities to lower the risk offlood damage. It is advisable to enhance local residents' awareness of the importance of flood
protection efforts concurrently with the steady development of flood control facilities so that overall
flood damage shall be mitigated. Flood Hazard Maps are essential in achieving this goal and assist
local residents in becoming aware of the vulnerability of the area they live in, the important roles thatthey play in disaster prevention activities and proper evacuation in the event of floods.
In Japan, the rivers generally have steep-gradient beds, and even now several urbanized areas are hit
by flood damage every year. For example, Nagoya, the third largest city in Japan, and its outskirts,
experienced intensive rainfall of more than 500 mm around the middle of September 2000 andsuffered extremely serious damage.

Levee Break of the Shinkawa-river September, 2000 in Nishibiwajima

Downstream

Upstream2

Flood damage mitigation in Japan thus far has primarily been developed through structural measures
such as flood control dams and flood protection levees. As a result of these efforts, the frequency andmagnitude of floods have definitely been reduced. The structural measures have so far had aremarkable effect; however, floods and inundations still occur year after year, demonstrating thatimportant issues remain to be tackled:
1) Structural measures, such as dams and levees, are primarily time-consuming and costly. Until
these structures are fully completed, there is a need for other effective measures for flood
damage mitigation.
2) The structural measures for large rivers in Japan are based on the assumption of very heavy rain
occurring, in principle, once in 100 years. In a case where heavy rain exceeds this target rainlevel, the structures could not prevent the occurrence of flood damage, even if they werecompleted. There is a need for another measure for whenever heavy rains exceed the target
level.
3) Where the construction of levees has been developed, the frequency and magnitude of flooding
are reduced, and accordingly, factories and dwellings will certainly be set up. In such a case, theflood damage would be even more formidable if inundation occurs even once in these areas.
Although the structural measures reduce the frequency and magnitude of floods, they increase
the potential damage. This issue needs to be solved.
4) The residents who live in those areas where flooding has been reduced due to the improvementof levees, might be overconfident in the structural measures, and less conscious of the potential
danger. They are not able to take proper action in the event of flood occurrence, and so theextent of damage would even be greater.
To cope with these issues in Japan, non-structural mitigation measures are currently underdevelopment, hand in hand with the structural measures. Flood hazard mapping is a good example ofsuch non-structural measures.

32. Definition of Flood Hazard Map
The “Flood Hazard Map” herein referred to is a map that graphically provides information on
inundation (predicted inundation areas, inundation depth, etc.), as well as on evacuation (location ofevacuation refuges, evacuation routes, dangerous spots on evacuation routes, etc.) in aneasy-to-understand format. The goal is to quickly evacuate local residents in a safe and proper mannerin the event of floods. The map is produced and publicized through a joint effort by those in charge ofdisaster prevention and those in charge of rivers and hydrology in the respective local municipalities.

43. Map Preparing Body
Flood Hazard Maps shall be prepared principally by the local disaster prevention division of therespective municipalities, in close cooperation with the local residents, qualified experts, NGOs andother pertinent bodies.
In Japan, the head of the respective local municipality, such as the city mayor, town headman, or
village headman, is stipulated as the executive official in charge of the local disaster prevention
division, and is authorized to issue evacuation warnings and orders. The evacuation activities in theevent of flood are thereby implemented on the level of the respective cities, towns and villages. The
Ministry of Land, Infrastructure and Transport, together with the Prefectural government concerned,
provide the flood-related information (predicted inundation areas, inundation depth, etc.) to therespective local municipalities. They produce the Flood Hazard Maps on the basis of the presented
information on the inundation.

5

4. ScopeThis manual applies to areas that have rivers with steep stream-gradient and suffer flash floods
within several hours to several days from start to peak.

6

5. Purpose
Flood hazard mapping in Japan commenced in 1994, when the Ministry of Construction (currently
the Ministry of Land, Infrastructure and Transport) circulated an official notice to all local
municipalities on the preparation of the maps.
The Government officially publicized “Past Inundated Area Maps” for about 500 rivers that
historically inflicted flood damages, as well as “Flood-prone Area Maps” through 1993 into 1994 forthe rivers under their ministerial jurisdiction. Since 1995, taking these opportunities, flood hazard
mapping has been positively implemented by local municipalities, and as of June 2002, 173 Flood
Hazard Maps had been produced.
Flood analysis results have been publicized since 1999 through such media as CD-ROMs andInternet homepages. Furthermore, the publicity of “Flood-prone Area Maps” became obligatory in2001 under the Amendment to the Flood Fighting Law, consecutively with the Amendment in 1996 to
the River Law and the Enactment in 2001 of the Sediment-related Disaster Prevention Law. Whereas
structural flood mitigation measures are aimed at preventing flooding and inundation, the Flood
Hazard Maps are based on the premise that flooding will inevitably occur, and are aimed atminimizing loss of life by intensively expediting the evacuation of local residents.
The purpose and advantageous effects of producing Flood Hazard Maps are summarized below:
1) For local residents (Publicizing effects of flood information)- Local residents receive various types of information on potential flood damage and become awareof the importance of voluntary disaster prevention efforts and proper evacuation.
- When flood warnings are issued and a flood occurs, local residents are able to evacuate promptly
and smoothly to avoid injury.
2) For local municipalities concerned (Administrative crisis-management effects for flood prevention
and preparedness planning)- Producing Flood Hazard Maps demands that the administrative staff in charge of disasterprevention simulate emergency drills, and thus urges local municipalities to develop disasterprevention and preparedness countermeasures.
- Local municipalities are able to promptly and smoothly accomplish the evacuation of local
residents, using information on the Flood Hazard Maps.
Table 1 shows several examples of the effective use of Flood Hazard Maps.

7

Table 1 Use of Flood Hazard Maps
Category
Everyday life

Local Residents- Consider proper land-use patterns andwater-resistant buildings suited to the flood
vulnerability of the area
- Prepare emergency kits, emergency food,etc.
- Prepare boats and other appropriate means ofevacuation

Local Municipalities- Review urban planning and land-use
patterns that are resistant to flood- Confirm proper refuges, evacuation routes,
emergency kits, etc.

- Identify flooded areas, inundation depth,
location of refuges, and evacuationroutes- Provide information on weather forecast
and flood forecast- Update disaster-prevention andflood-fighting plans of the area
- Review refuges and evacuation routes- Update specific assistance plan toevacuate or rescue the vulnerable(elderly, handicapped, sick, injured,etc.)- Identify proper communication channels and - Update communication channels andsystems for information on evacuation
systems for information on evacuation- Organize voluntary disaster prevention units - Develop voluntary disaster preventionunits- Learn about past inundation history and risks - Promote education on disasterprevention and conduct evacuationof inundation of the local area
- Organize educational sessions on potential
practice drills
flood damage, preparedness and evacuation - Publicize importance of disasterprevention and preparedness
Emergency
situations- Evacuate independently, following weather
forecast, flood-related information,
emergency warnings, etc.
- Assist in evacuation of those vulnerable to- Support and rescue those vulnerable tofloodsfloods- Evacuate to proper refuges through safe - Provide continuous flood-relatedroutes, following advisory
information on evacuationand imperative evacuation warnings- Set up refuges- Issue advisory and imperative
evacuation warnings- Direct evacuation

The information incorporated in Flood Hazard Maps shall be those items that are practical and usefulin the event of flooding, ensuring the safety and proper evacuation of local residents. Items such aspredicted inundation areas and location of refuges, are termed “Evacuation-use Information,” anditems that will be helpful in everyday life, by notifying the residents of potential flood damage andenhancing their awareness of the importance of flood disaster preparedness, are termed“Educational-use Information.”
To make efficient use of Flood Hazard Maps, local residents must be thoroughly convinced of thereal danger of flooding. The indispensable information on evacuation and, accordingly, theevacuation-use information, shall be incorporated in the hazard maps. Educational-use information
shall be appropriately incorporated or not, depending on the purpose of preparing the Flood Hazard
Maps in the respective municipalities.
8

The key items to be incorporated in the maps are listed below:
Table 2 Key Items to be Incorporated in Flood Hazard Maps
Evacuation-use Information
Educational-use Information- Predicted inundation area, inundation- Flooding mechanism
depth, flood concentration time
- Topographic features, flood types- Real danger of flood, predicted extent of- Historical inundation records- Areas to be evacuateddamage- Location of evacuation refuges- Meteorological information- Evacuation routes- Past flood records (rainfall, inundation and- Dangerous spots on evacuation routes
damage- Rules to follow in the event of evacuation- Rules to follow in the event of flood- Communication channels and systems- Explanation and directions tofor information on evacuation
use-up Flood Hazard Maps
- Issuance criteria for evacuation warnings- Preparedness against flood- Map preparing body, date of preparation

Note:- The more detailed items are stated later.

96. Effectiveness of Flood Hazard Map
In Japan, the effectiveness of Flood Hazard Maps has already been verified in several cases. The firstcase was the flooding of the Abukuma River in the Tohoku district in August 1998. The city of
Koriyama is located in the middle reach of the Abukuma River, and the Flood Hazard Maps had been
produced and distributed among the local residents well before the occurrence of the flood.
Flooding in Koroyama City, August 1998

According to the questionnaire survey conducted immediately after the flood, the effectiveness of the
Flood Hazard Maps was satisfactorily verified as stated below:
1) The majority of the local residents referred to the locations of the refuges on the Flood Hazard
Maps, and evacuated to the proper refuges.
2) The number of evacuees was 1.5 times more for those who referred to the maps than for those who
did not.
3) Residents who referred to the maps commenced evacuation one hour earlier
than those who did not.
< Number of evacuees six hours
after notice to evacuate >Number ofevacuees

Approximately one hour

1.5 timesThose who did not
see the Hazard Map

Those who saw
the Hazard Map

Notice toevacuate

Order toevacuate

Source : “Survey Report on Local Residents’ Reaction during the Rainstorm in Koriyama at the End of
August 1988”
Katada Laboratory, Faculty of Engineering, Gunma University

10

The Flood Hazard Maps of the city of Koriyama were highly effective for the risk management of thecity. In the process of producing the maps, the administrative staff in charge of river management forthe city were astonished that the flood-prone areas ranged so widely, and that so many residents were
scattered within the areas.
Crisis Management Effects

The necessity for establishing practical and detailed evacuation plans, such as the location of refuges
and the pertinent timing of issuing advisory evacuation warnings, was fully realized, and the relevant
actions were immediately put into practice and implemented. Such planning played an extremely
important role in the effective and efficient evacuation of the local residents during the 1998 flooding.
If the Flood Hazard Maps had not been prepared, the evacuation would not have been smooth.

11

7. Process of Production, Distribution and Usage of Flood Hazard Map
The chart below shows the key steps for production, distribution and usage of Flood Hazard Maps.
8. Production of Flood Hazard Map
1. Collect and Classify Information- Past and estimated inundation, evacuation activities, facilities concerned and otherrelevant information on flood damage
2. Set-up Basic Conditions-Magnitude of target flood, extent of areas to be mapped, and scale and sizeof base maps
3. Draw up Historical Flood Map- Flood marks- Extent and depth of inundation
4. Draw up Flood-prone Area Map(Cases in which Flood Simulation Analysis is possible)- Simulated inundation depth (through flood analysis)- Inundation depth contour lines- Inundation isobars by rating levels of danger
5. Draw up Evacuation Scenarios-Refuges, evacuation means, evacuation distance and time required, evacuation routes
and dangerous spots-Accommodation plan for refugees-Communication channels for flood information and evacuation warnings
6. Establish Evacuation Criteria-Evacuation criteria and timing of issue
7. Produce Flood Hazard Map-Evacuation-use type information-Educational-use type information on disasters, as well as disaster prevention

9. Distribution and Usage of Flood Hazard Map
1. Publicize and Distribute among Local Residents- Distribution of maps among local residents, municipalities concerned, public facilities,
schools, etc., publication on Internet homepages, organizing briefing sessions andevacuation trainings, cooperation with NGOs, and distribution among voluntarydisaster prevention units
2. Use in Local Municipalities (Disaster Prevention Plans)- Review and updating of refuges, evacuation routes and evacuation warning systems- Updating and developing of emergency actions and relevant countermeasures, andsystems for collecting and providing information- Review of urban planning and land-use patterns

128. Production of Flood Hazard Map
8.1 Collection and Classification of Information
It is desirable to collect the following information for producing Flood Hazard Maps.
Table 3 Information to be Collected
Category
Base maps

Information on
inundation

Past inundation

Estimated inundation

Areas to be evacuatedNumber of residents tobe evacuatedEvacuation refuges

Communication
channels
Underground spaces
Evacuation criteria

Facilities for thosevulnerable in the eventof emergency
Bodies andagencies
concerned
Other information to be collected

Information on evacuation

Dangerous spots on
evacuation routes

Disasterprevention
facilities andequipment
Medicalfacilities
Lifelines
Social welfare
facilities

Description-Base maps (topographic maps in scales of 1:2,500, 1:10,000 and 1:25,000)-General-purpose maps
-Spill overtopping and levee-break spots, inundated areas, inundated depth-Damage suffered-Hourly water level and hourly rainfall on major spots of the river-Results of flood simulation analysis, such as flooded areas, inundation level, inundation
depth, etc.
-Flood diffusion process-Change of inundation depth with time elapsed-Flood flow velocity-Boundaries of jurisdictional districts and blocks, school districts and neighboring
associations' territories-Population by district-Households by district-Refuges-Public facilities (kindergartens, elementary schools, junior and senior high schools,
colleges and universities, civic centers, assembly halls, gymnasiums, etc.)-Spots with potential steep-slope collapse, mud flows and debris torrents-Roads blocked by past inundation-Past landslide spots-Underpasses-Bridges-Communication channels and appliances for use in emergency-Locations of underground spaces, and emergency communication system to users-Evacuation criteria-Past evacuation activities (issuance and communication channels of advisory andimperative evacuation warnings, refuges set up, number of refugees accommodated)-Number of residents to be assisted-Facilities for the vulnerable (hospitals, homes for the elderly and handicapped, andother facilities concerned)-Local municipal facilities-Prefectural facilities-National facilities-Firefighting facilities-Police stations and call boxes-Administrative wireless radio stations for disaster prevention, loudspeakers, sirens-Disaster prevention centers-First-aid stations, information-display facilities on flood damage-Water level stations and rain gauge stations-Emergency hospitals-Public health centers-Hospitals, doctors' offices and clinics-Water supply and sewerage plants, gas works, power plants and substations-Telecommunication facilities (telephone exchange offices)-Homes for the elderly and handicapped

138.2 Setting-up of Basic Conditions
The following basic conditions shall be set up beforehand, taking into consideration pastinundation records and evacuation activities, as well as the existing circumstances of possible
inundation areas and topographic features:- Magnitude of target flood- Extent of areas to be mapped- Scale and size of base maps
(1) Magnitude of Target Flood
The target flood shall, in principle, be specified among the following floods:
1) Design flood2) Largest flood previously recorded
3) Largest flood occurring once in several years
However, in the many areas where flood analysis has not been sufficiently conducted, it isadmissible to select from the largest flood recorded, historically severe flood, or the largest flood
occurring once in two years.
(2) Extent of Areas to be Mapped
The extent of areas to be mapped shall, in principle, be the entire areas of the local municipalities.
If the potential flood areas are only a part of the municipalities, these areas and their outskirts shallbe properly mapped.
The neighboring territories shall be integrally incorporated and produced in the map when thepotential flood areas extend to neighboring municipalities. Evacuation to other municipalities shallbe planned and incorporated accordingly.
(3) Scale and Size of Base Maps
The standard scale of base maps shall be 1/10,000 to 1/15,000 in order to enable identification of
not only individual houses, but also evacuation routes and extent of inundation. Topographic mapsof 1/25,000 to 1/50,000 are generally undesirable because they do not allow identification ofindividual houses.
The standard size of base maps shall be A0 to A1. If these sizes are not appropriate, specify
alternate appropriate sizes, taking into consideration relevant factors such as proper scale, numberof subdivided maps, necessary cost, ease of use, etc.

14

8.3 Drawing-up of Historical Flood Map
Historical Flood Maps are to be drawn up immediately following flooding.

START
Preliminary Survey- Classify flooded areas by topographical features- Refer to past newspapers and other literature on floods- Conduct interviews with elderly residents in the pertinent areas

Identification of Flood Marks

Estimation of the Extent and Depth of Inundation

Integration of all Information and Survey Results

Drawing-up of Historical Flood Maps

- Example of Historical Flood Map
The Kurobe River floods of 1952 and 196915

(1) Preliminary Survey
For cases in which so much time has passed after inundation that no flood marks remain:
1) On the map, identify the place names recorded in past newspapers and literature, and estimate theapproximate extent of inundation on the basis of topographic features.
2) Interview elderly residents in the pertinent areas, to collect information on the extent and depth ofinundation.
(2) Identification of Flood Marks
When identifying flood-level marks:
1) Identify the mark levels as soon as possible after the flood reaches its peak.
2) Specify the flood marks, preferably based on mud marks.
Mud marks fade out in the meantime, or disappear within a short time, particularly after rain. Even
if they do not disappear, they might be worked into a lower level by rain.
3) In cases of specifying the marks based on trash, look carefully and extensively around the spots
beforehand, and exclude those trash levels unusually lower than the surrounding ones.
Trash often slides down by its own weight, or might otherwise be moved unnaturally, such as bywind. Mud marks seem to offer more accurate marks than trash. Draw up a proper level-line,
connecting the reasonable marks, and define its level by surveying.
4) Compare the mark levels with the peak flood levels recorded at the nearby water-level stations, ifany, in order to verify them.
5) Sampling of flood marks in the flow direction shall be done at intervals of 50-100 m in a straightriver channel, preferably ensuring the collection of at least one set of reliable data from both sidesof the channel.
(3) Drawing-up of Historical Inundation Map
Draw up a map of past inundation, integrating all relevant data collected, that is, the surveyed flood
marks, topographically classified feature maps, and estimated inundated area maps through interviews
with elderly residents, etc.

16

8.4 Drawing-up of Flood-prone Area Map(Cases in which Flood Simulation Analysis is possible)
For cases in which Flood Simulation Analysis is possible, Flood-prone Area Maps are to be drawn up
and used as basic information for producing Flood Hazard Maps.

Identify current status of levees Identify existing cross-sectional
areas of the river channel

Identify water levels at various
spots along the river channel that
accommodate discharge without
flooding

Identify water levels in the river
channel through the water-levelcalculation method used incases of channel improvement

Identify current status of rivermanagement facilities, such as
flood control facilities, theirannexed dikes, etc.

Identify flood discharge on
the basis of target rainfall

Identify possible hydrographon various spots along the river
channelIdentify discharge at the startof flooding

Identify possible flooding spots

Define the target flood plain
Identify topographical features of
the target flood plain
Define premises for
Flood Simulation Analysis
on levee-break and spill overtopping
Flood Simulation Analysis

Define flood-prone area

Designate inundation depth

Draw up Flood-prone Area Map

17

Example of Flood-prone Area Map

Source: The Kurobe River Flood-prone Area Map(1) Defining the Target Flood Plain
A pertinent flood simulation model is to be set up, based on the conditions of the current flood plain.
1) Target flood plain
Define the target flood plain on the basis of estimated flooded area maps from past inundation
records, so as to include possible inundation areas by the target flooding, particularly the maximum
extent of inundation areas corresponding to the respective assumed levee-break spots.
In lowland areas near the river mouth, the inundation area may be delimited by artificial structures
such as levees of a neighboring river, and so forth.
2) Defining the flood plain for the simulation model
In order to accurately estimate the inundation depth of a flood, it is necessary to identify factors suchas topographic features, existing continuous banking structures, e.g. roads or railways, and dikes ofsmall- or medium-sized rivers, which affect the overflowing water.
(2) Identification of Ground Level and Land-use Pattern in the Target Flood Plain
To ensure the accuracy of topographic conditions, identify the ground levels in the target flood plain,and define them by 50-m meshes (commonly used in Japan). It is desirable to coordinate these mesheswith 250-m flood-simulation meshes (commonly used in Japan), as described later.

181) Identification of averaged ground level
Identification of ground levels is done by specifying the averaged ground level at the centerand the four corners of the respective 50-m meshes by using a large-scale urban planning map of
1/2,500 (commonly used in Japan) or the “National Land Base Map,” published by the National
Geographical Survey Institute.
Supplementary field surveys shall be conducted, as needed, in order to represent all
topographic features as accurately as possible. “Numerical Elevation Map of 50-m Meshes,”
published by the Japan Map Center, may be used in Japan for base maps.
2) Identification of current land-use patterns and tenement rate for roughness coefficient
It is necessary to define the roughness of the flood plain for simulation analysis. Survey anddefine the current land-use patterns and tenement rate thereof.
(3) Defining the Premises for Flood Simulation Analysis by Levee-break and Spill
Overtopping
1) Identification of premises for flooding due to levee-break, discharge capacity of river channel
and flooding-start discharge
Identify the possible flooding spots on the levees, and successively possible flooding-startwater levels for the respective spots, taking into consideration the current status of protection
and maintenance for the existing river channel.
Here, it shall be assumed that levees break when the channel discharge exceeds water levelsof those that could possibly start flooding for the respective dangerous spots.
The water levels shall be specified taking into consideration the levee height and current
status of protection works against leakage, filtration, and erosion for the respective spots. In
principle, those levels shall be estimated by means of the same analysis method as that for river
channel planning.

Flood Simulation
Meshed data of Floodplain(mesh size about 250m for calculation)-Ground level-Ground roughness (according to landuse)

Hydrological data

Hydrograph of the target flood
Other data of Floodplain-Drainage channels-Dikes-Pumps etc.

Data on Levee-break

FLOOD SIMULATION MODEL
1D or 2D model based on the equation of continuity and the equation of motion

Time variation of inundation depth, velocity, etc.

19

Refer to the following notes for defining the flooding-start discharge due to levee-break:a) River channel
The river channel for estimating the flooding-start discharge shall be the existing channel.
b) Assumption in estimating flooding-start discharge
The flooding-start discharge due to levee-break shall be estimated by the same hydraulicanalysis method as that for river channel planning. Currently, in cases of planning large river
channels, the non-uniform flow analysis (quasi-two-dimensional non-uniform flow
analysis) is widely used, taking into consideration the existing trees and shrubs.
c) Establishment of H-Q correlation formula
Using the above-mentioned analysis method, estimate the respective water levels “H”
corresponding to the respective discharge “Q” in the current river channel, and establish the
H-Q correlation formula in such a form as:
Q = a(H + b)2d) Estimation of flooding-start discharge
For the respective cross sections of the river channel, define “Hj” as the design high-waterlevel (HWL) for the reach where the levee is completed. Similarly, define the marginal
water level, at which the river water could barely be accommodated in the channel without
spill, for the reach where the levees are not yet completed. Estimate the respective discharge“Qj”, which corresponds to respective “Hj” through the H-Q formula to obtain theflooding-start discharge. It shall be assumed that flooding due to levee-break would start at a
specific water level, just exceeding the “Hj” for the embanked reach. Similarly, the flooding
due to spill would start at another specific water level, just exceeding the land-level in theflood plain for the non-embanked reach.
The level “Hj” for the non-embanked reach shall be appropriately specified, taking into
consideration the current cross sections of the levees, and their protection against infiltration,
leakage and erosion.
2) Defining possible flooding spots
It is necessary to estimate the maximum inundation depth of the flood plain, due to flooding
at overall dangerous spots. Define the minimum number of flooding spots where levee-breaks
bring about the maximum equal extent of inundation, wherever the target flood discharge
respectively attains the flooding-start discharge for all possible levee-break spots.

20

(4) Flood Simulation
1) Basic concept of simulation analysisa) Flood wave
The flood wave to be used in the flood simulation shall be specified on the basis of the target
rainfall through the same runoff analysis method as that for river channel planning.
b) Flood simulation cases
The flood simulation shall be repeated the same number of times as that of possible flooding
spots, as described above. Use only one flooding spot for each case, so that the respective
maximum damage (maximum inundation depth) in the flood plain shall be estimated incorrespondence to each possible flooding spot.

Levee break point
Draw the outskirt from the calculation
at all levee break pointsc) Precautions in flood simulationi) Spill overtopping and flooding in upstream areas
The discharge hydrograph to be given at a possible flooding spot shall be the one thatgenerates the maximum peak discharge for the respective possible flooding spots in the river
channel.
For cases in which spill overtopping or flooding occurs upstream of the possible flooding
spots, and the flooded water does not return to the channel (namely, diffusion-type flood), a
modified discharge hydrograph is to be given for the respective possible flooding spots,
taking into account the reduction of river discharge due to the aforesaid overflow.
ii) Dams and flood control channels
Runoff calculation shall be conducted, taking into account the effect of the existing flood
control dams and channels, when designating the target possible flood plain. The inflow
from drainage pump-stations, located upstream of the possible flooding spots, is likely to beincorporated as well.

212) Setting-up of conditions for simulation analysisa) Analysis method of flooding dischargei) Flooding discharge
The flooding discharge shall be estimated on the basis of the relationship between the riverwater level at the possible flooding spots, the water level within the protected land behindthe levees and the threshold level of the levee-break spots.
ii) River water level
For consistency with river channel planning, the river water level shall be estimated on thebasis of the discharge obtained by the unsteady flow analysis for the channel, following the
H-Q formula through the same water-level analysis method as that for river channel
planning.
iii) Determination of flooding discharge
The flooding discharge due to levee-break shall be dealt with as the transverse outflow
across the possible flooding spots.
It is necessary to concurrently conduct both the unsteady flow analysis for the channel andthe flood simulation analysis for the plain, with the exception of cases in which the flooding
discharge is inevitably determined only by the river water level.
- Floodplain[Equation of Continuity]∂h ∂M ∂N
=0
+
+
∂t
∂x
∂y

[Equations of Motion]∂M∂∂H gn 2u u 2 + v 2∂(vM)=-gh
+
(uM)+
∂t
∂x
∂x
h1 / 3∂y∂N∂∂H gn 2v u 2 + v 2∂(vN)=-gh
+
(uN)+
∂t
∂x
∂x
h1 / 3∂ywhere,u, v : velocity in the x and y directions
M, N : flow flux per unit width in the x and y directions(M=uh, N=vh)h: water depthH: water leveln: equivalent roughness coefficient(considering drag force by buildings)- River channel[Equation of Continuity]

∂A ∂Q
+
=q
∂t ∂x

[Equations of Motion]n2 Q Q
1 ∂Q
1 ∂ Q2)+ 2 4 / 3 =0+(
A R
gA ∂t gA ∂x A

where,
Q : discharge
A : cross sectional area
R : hydraulics radius

H : water levelq : lateral flow

These partial differential equations are discretized by an explicit finite difference scheme,
and solved numerically.

22b) Defining of conditions for analysisi) Spill overtopping extent
The spill overtopping range across the levee at the possible flooding spots shall be either thelevee-break extent stated below, or the integrated extent up to the successive levee-break
spot immediately downstream, whichever is smaller.
ii) Levee-break extent
The pattern of levee-break shall be defined by referring to past break records, if available. If
not, estimate the levee break extent “y(m)”, based on the river width “ x(m)”, through theformula as shown below, whether the levee-break spot is in the vicinity of the confluence ornot. Here, “the vicinity of the confluence” means that the effects of the confluence shall not
be ignored, the width of the tributary is greater than 30% of the width of the main river, andthe extent thus affected would be around twice the width of the main river, upstream as wellas downstream of the confluence.
-In the vicinity of the confluence: y = 2.0 x (log10x)3.8 + 77

-Not in the vicinity of the confluence: y = 1.6 x (log10x)3.8 + 62iii) Threshold level of levee-break spots
The levee is assumed to break down to its threshold level of the spot, which shall be either
the ground level of the protected land or the level of the high-water channel, whichever ishigher.
iv) Levee-break progress in time
The levee is assumed to immediately break to half of the final break extent “y/2”,
simultaneously collapse to the aforesaid threshold level, and break to the full extent within
one hour. The break is assumed to proceed at a fixed rate.
v) Facilities to affect flooding discharge
The structural facilities that are likely to affect flooding discharge shall be incorporated into
the flood simulation model, to the degree that is possible.
-Embankments: If the relative height from the averaged ground level is 50 cm or greater,incorporate the embankments into the model. These are continuous dikes, railroads,
highways or other bankings.
-Waterways: If the flooding is such that it surmounts the dike height of small- or
medium-size rivers in the flood plain, the waterways are assumed to be full of water
as if there are continuous embankments.

23vi)Spill overtopping discharge
To estimate the spill overtopping discharge, an appropriate formula shall be selected, taking
into consideration the relation between the river channel alignment and the shifting of thewater route during a flood, for the respective flooding spots.
-In the case of frontal overflowing
Use Honma's formulae:- Complete overflow(h2/h1 < 2/3)

Q = 0.35 × h 1 2gh 1 × B- Submerged overflow(h2/h1 > 2/3)

Q = 0.91 × h 2 2g(h 1 − h 2 ) × B

where
h1 = Inundation depth to the levee-break threshold, whichever is largerh2 = Do, whichever is smaller-In the case of transversal overflowing
Use the formulae below:
where
Q0 = Flooding discharge, obtained through Honma’s formula
I = Riverbed slope
and the unit in parentheses of cosine is degree:- Flooding discharge (Q) due to levee breakI > 1/1,580

Q/Q0 = (0.14+0.19 x log10(1/I)* cos(48-15 x log10(1/I))

1/1,580 > I > 1/33,600

Q/Q0 = (0.14+0.19 x log10(1/I))

1/33,600 >Q/Q0 = 1I- Overflowing discharge due to spill overtopping:
1/12,000 >I > 1/12,000

Q/Q0 = cos(155-38 x log10 (1/I))

I

Q/Q0 = 1vii)Roughness
Roughness shall be identified taking into consideration all factors, such as simulation model
type, land-use patterns of the flood plain, past inundation records, etc.
The effects of existing buildings and others are approximately incorporated into the model
constant. The effects of buildings and others are related in the form of roughness
coefficients for the simplified one-dimensional unsteady flow model among
one-dimensional models, as well as for two-dimensional models.
- Overflow pond modelWith the progress of urbanization, the coefficient of discharge “c”, which includes theroughness coefficient “n”, increases due to the vena contracta effect of existing buildings.
In the majority of simulation cases, the roughness coefficient is more or less defined as:
c = 0.05 to 0.1- Open-channel pond model, flood pond model, and simplified one-dimensional unsteadyflow model.
The roughness coefficient is defined in accordance with the land-use pattern, which iscommonly classified into two types: “rice field and farmland” and “urbanized area.” In
majority of simulation cases, the roughness coefficients are more or less defined as:24

- Rice field and farmlandn = 0.1 to 0.25

- Urbanized arean = 0.1 to 0.3

In the flood pond model, however, the roughness coefficient often varies in accordance with
the inundation depth.
- Two-dimensional unsteady flow model
The formula shown below is proposed to define the roughness coefficient of the flood plain“n”, integrating the roughness coefficients, through the weighted average formula, on thosefacilities other than buildings, the tenement rate “ θ ” and the inundation depth “h”. The
areas of respective land-use patterns are to be identified for each divided mesh.
- Agricultural land:
A1 = Area of rice field, farmland, forest, orchard, bamboo thicket, etc.
n1 = Roughness coefficient for agricultural land
- Roads:
A2 = Area of national highways and major local roads, including sidewalks
n2 = Roughness coefficient for roads- Other types of land-use:
A3 = Area of wasteland, grass lawn, marshland, salt field, etc.
n3 = Roughness coefficient for other types of land use
n2 = n02+ 0.020*

n02 =

θ
*h4/3
100 - θn12 A1 + n2 2 A2 + n3 2 A3
A1 + A2 + A3

where
n1 = 0.060, n2 = 0.047, and n3 = 0.050
3) Performance of Flood Simulation Analysis
The two-dimensional unsteady flow analysis is commonly applied, although other analysis
methods may be used if appropriate in view of the topographic features of the flood plain. When
dividing the flood plain into meshes, they should be consistent with the meshes for the averaged
ground level data, coinciding with the “Numerical Map Information” or “National Land
Numerical Information” data.

25

(5) Defining the Flood-prone Area
Identify the highest inundation level, through the flood simulation, of each divided mesh foroverall cases of possible flooding spots and, in turn, define the maximum one for the respective
divided meshes.
Estimate the inundation depth of each mesh by subtracting the averaged ground level (commonly,
50-m mesh in Japan) from the maximum inundation level as defined above, and finally, define theboundary of the flood-prone area, taking into consideration the relevant factors such as existing
continuous structures and micro-topographic features.

26

(6) Designation of Inundation Depth

Designation, by using colors, the inundation depth so that the local residents are able to easily
understand accurate inundation information.
Inundation depth is normally classified into five ranks, as shown below. Whenever necessary,other ranks such as 2.0 to less than 3.0 m, 3.0 to less than 4.0 m and 4.0 to less than 5.0 m areacceptable.
Category ofReference description

inundation depth
0.0 m

no inundation

0.5 m

around the level of the knee of an adult1.0 m

around the level of the waist of an adult2.0 m

around the level of the eaves of the first floor

5.0 m

around the level of the eaves of the second floor

Inundation depth (m)Walking inwater isdangerous
Walking inwater ispossible

Velocity (m/s)
Limits where evacuation on footin water is possible

Evacuation on foot in flowing water would be substantially difficult and dangerous. Accordingly,
evacuation well in advance of the start of flooding, is strongly recommended.

27

8.5

Establishment of Evacuation Plans

1) Identification of Evacuation Refuges
Identify existing buildings and facilities suitable for use as refuges. It may be possible to set up
the temporary refuges in the flood-prone area, which flood-resistance and number of stories havebeen affirmed in relation to the potential inundation depth.
2) Determination of Evacuation Means
It is not advisable to use cars to escape from flooding, except under special circumstances. Traffic
jams and unexpected accidents may result from many residents evacuating by car at the same time.
Evacuation on foot is a primary rule.
3) Identification of Evacuation Distance and Timing
It is desirable that the distance of evacuation on foot shall be less than 2 km in all cases. Identify
proper refuges for the respective areas to be evacuated, taking into consideration the distance andthe accommodating capacity of the respective refuges.
4) Identification of Evacuation Routes
Identify the evacuation routes that are safe from flooding and other disasters, such as mudflows
and debris torrents. If recommended routes exist, clearly specify them on the map.
5) Identification of Dangerous Spots on Evacuation Routes
Identify flood-prone roads, bridges and other potential dangerous spots, and clearly show themon the map.
6) Zoning of Areas to be Evacuated and Appropriate Evacuation Refuges
Establish zonings for proper refuges, in correspondence with the location and population of therelevant areas to be evacuated, and the location and accommodating capacity of the respective
refuges.
7) Establishment of Positive Assistance Plans to Vulnerable Residents
Establish evacuation means for those who are vulnerable, such as the elderly and handicapped(preparation for evacuation, issuance of advisory evacuation warning, specifically-prepared refuges,etc.).
8) Establishment of Communication Channels
Establish reliable communication channels for urgent, essential information, ensuring safe
evacuation (TVs, radios, walkie-talkies, cable broadcast telephones, CATV, ordinary telephones,
Internet homepages, messengers, loudspeaker vans, sirens, electric-light notice boards, etc.).

28

8.6

Establishment of Issuance Criteria for Evacuation Warnings
Evacuation warnings are issued in the following order and steps:-Preparation warning for
Warning to residents to make preparations for possible
evacuation
evacuation (earlier preparation warning is particularly
effective).
-Advisory evacuation
warning

Warning to residents advising start of evacuation.

-Imperative evacuation
warning

Warning to residents ordering immediate evacuation.

(1) Issuance Criteria for Imperative Evacuation Warning
1) Define flooding-start levels
Define possible water levels (such as HWL) for levee-break or spillover water levels for thereaches without levees.
2) Define necessary time for evacuation
It is desirable, in principle, that evacuation would be completed by the time the floodwaterreaches the above-mentioned reference levels. The necessary time for complete evacuation after
the issuance of the imperative evacuation warning is to be specified.
3) Define reference water levels for issuance of respective warnings
Assuming that the necessary time for evacuation is n hours, find the water level from which theriver water reaches the specified flooding-start level n hours later. Define this level as thereference water level for issuance of the imperative evacuation warning. To predict specificwater levels, it is conceivable to use the predicted flood-forecast results in cases ofjurisdictionally-designated rivers. However, such flood-forecasts are not yet sufficiently
accurate, and, in some areas, more accurately predicted water levels may simply be derived bycorrelating the observed water levels at nearby stations with the predicted water levels.
(2) Issuance Criteria for Advisory Evacuation Warning
The issuance of the advisory evacuation warning shall be done well in advance of the imperative
evacuation warning, and the timing of issuance of the advisory evacuation warning shall be one or
two hours earlier, depending on the specific conditions of the respective areas.
(3) Issuance Criteria for Preparation Warning for Evacuation
When urging evacuation prior to inner-basin inundation, the advisory evacuation warning shallbe issued before the occurrence of inner-basin flooding and accordingly, the timing of the issuanceof the advisory evacuation warning shall be one or two hours ahead, estimating the starting time of
the inner-basin flooding.

29

8.7 Production of Flood Hazard Map
Flood hazard maps shall be produced in easy-to-understand format, integrating various types of
information on inundation and evacuation, as well as evacuation intent.
Table 4 Principal Items and Information to be Incorporated in Flood Hazard Maps
Category
Past inundation
Information
on inundation

Predicted inundation
Areas to be evacuatedEvacuation-use Information

Evacuation refuges

Information
on evacuation

Dangerous spots on
evacuation routes
Rules to follow in the event ofevacuation
Communication channels forflood forecasts
Communication channels for
information on evacuation
Underground spaces
Evacuation criteria
Facilities for the vulnerable

Base maps
Other information

Past inundation

Educational-use Information

RainfallCommunication channels for information on
disaster prevention efforts
Mechanism of flooding
Rules to follow in everyday life and in the eventof flood
Staying in refuges
Directions for familiarizing oneself with Flood
Hazard Maps

Description
Historical records of inundation (maximum or latest)
Inundation-prone areas, other possible inundation areas
Inundation depths, inner-basin water, time of flood concentration,
flood flow velocity
Degree of hazard when inundated
Endangered areas
Names, locations and phones number of refuges
Family's notes on disaster prevention activities
Dangerous spots on evacuation routes with potential mudflows, debris
torrents, steep-slope collapse and underpasses
Hints for evacuation
Communication channels for flood forecasts (usually the same as
those for information on evacuation)
Channels for information on evacuation (Evacuation Preparation
Warning, Advisory Evacuation Warning and Imperative Evacuation
Warning)
Information on evacuation for underground spaces (recognition ofdanger in underground spaces, locations of spaces, communication
system to users)
Criteria on evacuation warnings and guidelines for successive action
Names, locations and phone numbers of facilities, such as specifichospitals, welfare facilities and schools, ready to accommodate thevulnerable
Base maps to identify location and extent of inundation areas to be
evacuated
Title, explanation, scale, azimuth, local municipalities, authors, phone
numbers, date of production, and local organizations concerned fordisaster prevention activities
Data on hydrological and meteorological conditions (rainfall, waterlevel, flood discharge), inundation records (extent, depth and durationof inundation), damage suffered and evacuation records at inundations
Correlation of hourly rainfall, flood status and successive evacuation,
to be represented in easy-to-understand format with illustrations
Information in easy-to-understand format on meteorologicalwarnings, flood forecasts, evacuation warnings, etc.
Flooding mechanism with local characteristics
Hints in brief to follow in everyday life and in the event of flood
Rules to follow when staying in refuges
How to familiarize oneself with Flood Hazard Maps

Directions for using the Flood Hazard Map

How to determine the route between one’s house anda proper refuge on the Flood Hazard Map, andhow to specify family’s actions in the event of emergency

Other information

Other valuable information to encourage effective use of the Flood
Hazard Map in everyday life, such as:
Emergency evacuation from a flooded house
Rope knotting
Rescue procedures when one falls in a riverFirst-aid to the injured30

9. Distribution and Usage of Flood Hazard Map
9.1

Distribution among Local Residents(1) Public Relations
Once Flood Hazard Maps have been produced and distributed, the local municipalities shallmake efforts to enhance the local residents’ awareness of the purpose and advantageous effects ofthe maps through educational activities and flood evacuation practices. Consideration shall begiven to the following activities:
1) Providing information to local media (hometown newspapers and magazines)
2) Organizing briefing sessions at voluntary disaster prevention units, schools, private companies,etc.
3) Sending questionnaires to households, voluntary disaster prevention units, schools, privatecompanies, etc., with the goal of stimulating interest in the maps, active use of the maps byresidents, and collection of their opinions on the information contained in the maps, as well as
increasing their involvement in disaster prevention activities
4) Distribution at various events (voluntary and administrative disaster prevention fairs, emergency
evacuation practices, etc.)
5) Using CATV (local channels, teletext broadcasting)6) Using notice boards at public or district facilities
7) Cooperating with mass media (TV and radio stations, newspapers, etc.)
8) Insertion in telephone directories (Yellow Pages)
9) Using Internet homepages(2) Target Users
It is desirable to distribute Flood Hazard Maps to all local residents for the most effective use ofthem. However, it may be conceivable to restrictively distribute them to residents in the areas to be
evacuated.
- Distribute to local residents in the entire administrative areas concerned- Distribute only to specified districts and their town-block associations, covering the possible
inundation areas- Distribute only to households that will inevitably be evacuated- Distribute through Internet homepages
Possible distribution to pertinent institutions, bodies and agencies other than local residents,
such as:- Community centers and other public services (pin-up notices)- Schools (pin-up notices and teaching materials)- Private companies (pin-up notices to employees and visitors)

31

9.2

Administrative Use

It is important to identify various levels of risks and specific issues to be developed in the respective
areas, referring to the Flood Hazard Maps, and to successively update the emergency evacuation plan
as well as disaster prevention plans.
The table below shows several issues to be fully reflected in the prevention disaster plans.
Table 5 Examples of Issues to be Reviewed in Disaster Prevention Plans
Category
Description
Evacuation routes and refuges- Review evacuation routes and refuges currently used, taking
into consideration specific risks involved in the areas
Emergency activity system- Review and update mobilization plan, taking into
consideration widely scattered dangerous areas- Review and update arrangement and assignment plans forflood-fighting materials, equipment and staff members
Communication channels for- Establish more reliable channels for emergency evacuation
activities
emergency information- Provide more accurate and effective information on
evacuation
Evacuation encouragement- Review and update organization and assignment of staff forsafe evacuation- Review and update assistance plans for evacuation of thevulnerable (infants, elderly, sick, andhandicapped)- Review and update voluntary activities
Furthermore, Flood Hazard Maps shall be referred to in the design of flood-resistant buildings andurban planning, as well as land-use patterns.

329.3 Issues on Flood Evacuation
Much effort has recently been made on the prevention of flood disaster in Japan through the
production of hazard maps and their distribution to local residents, and the establishment ofcommunication systems for disaster information, providing timely and accurate evacuation
information in the event of a flood occurrence. It can not be said, however, that the smooth evacuationof local residents in the event of a flood occurrence is ever practiced based on these systems. There arestill many issues to be addressed in order to improve the current situation. Those issues are mainly
related to a lack of awareness of disaster, as well as a lack of understanding of disaster information
among the residents.
When the water level of a river rises and evacuation is deemed necessary, the mayor issues anadvisory evacuation warning and/or an imperative evacuation warning (the residents are, however, notcharged a penalty if they do not follow the warnings). Generally, the evacuation rate of residents isfairly low. In Japan, the following particulars are pointed out as reasons why the residents do notevacuate in the event of a flood occurrence.
1) The number of residents who have experienced the fierceness of flooding is becoming fewer due tothe development of structural flood countermeasures.
2) From the standpoint of disaster psychology, the view called “normalcy bias” predominates in theresidents’ minds, and accordingly, they feel disengaged from those who are suffering from a flood
disaster, even though the adjacent river has flooded.
3) The opportunities for playing in a river and learning about rivers have decreased due to riverpollution and the dangerous image of rivers. More and more residents do not recognize the strong
power of stream flow, and believe that they can evacuate even after the onset of flooding.
4) Those who have had property damaged by a flood, but not to a serious extent, often mistakenly
believe that the flood was not serious, and that the next flood will not be serious either. They do notcare about evacuation at all.
5) Even when it is certain that their houses will be inundated due to flooding, residents prefer to shift
their household effects to safe places rather than evacuate themselves. They hardly realize that they
are in serious danger.

Never beinundated!

Dangerous…

33

9.4 Issues on Residents’ Understanding of Flood Hazard Map
The issues on Flood Hazard Maps presented here are related to the local residents’ understanding of
the information. These issues are of great importance in developing practical, effective Flood Hazard
Maps.
1) Even though Flood Hazard Maps have been distributed among the residents, many of them arethrown away or lost. The number of residents who lose their Flood Hazard Maps increases as timegoes by. The main reasons for losing the maps are that the residents are unconscious of the real
dangers of a flood, they have little interest in the information shown on the maps, and they do notrecognize the importance of the information. Once a flood evacuation is imminent, the Flood
Hazard Maps serve as evacuation manuals. It is of great significance to remind the residents of theirimportance and to encourage them to keep the maps.
2) Sometimes, the information that is shown on the Flood Hazard Maps leads to the residents’mistaken assumption that the information is correct and unchanged. Once the residents read thepredicted inundation depth for their houses on the Flood Hazard Maps, they misjudge the depth on
the map as being the maximum. If the depth is shallower than they expected, they feel a sense ofrelief, and either completely stop evacuation or wait until the water level reaches the level inquestion. This is, however, a serious misunderstanding. The Flood Hazard Maps present merely one
possible result obtained through a simulation based on the assumed rainfall patterns (once in ahundred years probability is commonly used in Japan), and levee-break spots in accordance with thedesignated scenarios. For cases in which the actual rainfall is heavier than that of the designatedscenario, the inundation depth will be deeper than that shown on the Flood Hazard Map.
3) There is another issue: how to represent information on Flood Hazard Maps. The predicted
inundation depths are usually shown in different colors on Flood Hazard Maps, while it is difficult
to show the flow velocities in the same way.
In the case of flash floods, the flow velocity, which is inundating city areas, is normally high, andthe inundation depth will be shallower as a result. When the flow velocity is high, it is extremely
dangerous to evacuate on foot in the water, even if the water depth is shallow. Safe evacuation is notguaranteed. Even though flow velocities can be shown on Flood Hazard Maps, it is difficult forresidents to understand the actual danger of high-flow velocity. The flow velocity is primarily
important information for the evacuation procedures.
4) In some cases, a Flood Hazard Map can mistakenly be interpreted as a “safety area map in the eventof a flood occurrence.” Non-colored areas on the hazard maps (non-inundation areas) are merely
results from the flood simulation, based on the designated scenarios.
The residents in those areas, however, believe that the areas will never be inundated during a flood
occurrence.

349.5 Effective Use of Flood Hazard Map
In Japan, the reason why local residents do not evacuate in the event of a flood occurrence is, asmentioned above, that they hardly recognize the necessity for evacuation. Flood Hazard Maps are
expected to play a major role in settling these issues.
In view of the relationship between flood evacuation and Flood Hazard Maps, there are several
steps of roles of the Flood Hazard Maps:
1) The first role of the Flood Hazard Map is to function effectively as an evacuation manual during aflood occurrence. The residents can confirm the safe refuge and safe evacuation route through themaps and attached explanation. In the cases of the floods at Koriyama City in 1998 and Tajimi Cityin 2000, it was reported that the Flood Hazard Maps were of great use as an evacuation manual.
2) The second role of the Flood Hazard Map is to provide the respective households with informationon the flood danger level of their own houses. The flood danger level is usually shown as inundation
depth, which is expected to increase the residents’ awareness of the necessity of evacuation.
On the other hand, the information shown on the Flood Hazard Map explicitly suggests several
issues to be settled concerning the residents’ understanding. These issues include the risk that
residents might think of the flood danger level as unchanged information and not understand themeaning of the information, which may result in an extremely dangerous situation.
3) The third role of the Flood Hazard Map is to offer the residents an incentive to realize the fiercenessof a flood, and how to properly protect themselves from the flood disaster. The residents are
expected to fully understand that the information shown on hazard maps presents merely one resultout of many possible scenarios that might occur around them. They are requested to decidethemselves what actions should be taken to protect their families’ lives during a flood occurrence, in
correspondence with the designated scenario as well as unexpected situations beyond the scenario.
The Flood Hazard Maps therefore work as preliminary instructive materials.
If Flood Hazard Maps are simply distributed among the local residents, without any educational
activities, they can not fulfill their role. The residents will not be aware of the importance of Flood
Hazard Maps, and will consequently throw them away. To fulfill their role, educational activities using
hazard maps as teaching materials, are essential. The local residents should be encouraged to actively
participate in the development of Flood Hazard Maps through discussions with the relevant local
municipality staff on what actions should be taken during a flood occurrence.

maximum

35

Concluding Remarks
In Japan, the importance of Flood Hazard Maps has undoubtedly been recognized
in recent years, and now the preparation of the maps is progressing in a positive direction. It has notbeen long since their preparation began, and yet various efforts are devoted to producing moreadvantageous and more effective maps.
The experience of producing Flood Hazard Maps in Japan is hereupon briefly introduced. The
respective staffs of the local municipalities involved are highly expected to make their utmost efforts,
with marked enthusiasm, in preparing reliable and effective Flood Hazard Maps.

36

Appendix

Examples of Flood Hazard Map for Educational-use- Predicted Inundation Depth...............................................................................................2- Refuge ...............................................................................................................................3- Evacuation Route ..............................................................................................................4- Emergency Kits .................................................................................................................5- Issuance Criteria for Evacuation .......................................................................................6- Communication Channels and Systems for Evacuation Information................................7- Flooding Mechanism .........................................................................................................8- Flood Fighting Practice .....................................................................................................9

Example of Integrated Flood Hazard Map- Neyagawa city Flood Hazard Map ....................................................................................101

- Predicted Inundation Depth(The city of Koriyama)

2

- Refugee(The city of Koriyama)3

- Evacuation Route(The city of Koriyama)Mark down evacuation route on the Map!

4

- Emergency Kits
(The city of Koriyama)5

- Issuance Criteria for Evacuation(The city of Koriyama)

6

- Communication Channels and Systems
for Evacuation Information(The city of Koriyama)

7

- Flooding Mechanism(The city ot Koriyama)

Source: Foundation of River & Basin Integrated Communications, Japan

8

- Flood Fighting Practice(Upper reaches of the Kitakami River)

Five Featuresof the Upper Kitakami River
Flood - Fighting Practice
1. The largest flood - fighting practice in the Tohoku
destricts ever performed with the combined effortsof pertinent flood - fighting units.
More than thousand flood - fighters participatingfrom 23 municipalities on the River.
2. Practical and integrated practice in close touchwith actual circumstances, to protect our area inunited efforts against floods.
3. Collection and provision of information, usingstate - of - the - art information technology, moreaccurately and more quickly.
4. Support those vulnerable to flood, to ensure allresidents’ evacuation without trouble.
5. Efficient use of the Kitakami River Learning andExchange Center, to know about and effectively
use the new facilities.

You can watch the
Flood-fighting
Practice also on
the Web site.
http://www.iwate.thr.
mlit.go.jp

9- Example of Integrated Flood Hazard Map(Neyagawa city Flood Hazard Map)

10