Flood Hazard Map - a tool for comprehensive flood management- Kenzo Hiroki National Institute for Land and Infrastructure Management Ministry of Land, Infrastructure and Transport
Flood Hazard (Awareness) Map is defined as : a map that provides with geographical information that is essential for local residents to conduct safe & smooth evacuation
When flood comes Residents : are not aware of possible flooding at their home are not willing to move even when danger is coming close do not know how to react to warnings do not know where to evacuate
When flood comes Flood response (civil defense) officials : are immersed with (mis-)information & cry for help have to triage various needs for actions may not know what are actually happening in the field Flood Hazard Map is a tool to mitigate recurrent tragedies by addressing lack and/or confusion of essential information for evacuation
Dilemma of Disaster Managers Disaster response is struggle against confused information Disaster managers have much less time to gather/analyze/transmit emergency information Information is necessarily confused during disasters Trade-off between accuracy & collection time of information
Example Abukuma River Flooding in 1998 9:00 August 26 to 9:00 September 1 (total precipitation in six days) Rainfall map Pacific Ocean Mafune Rainfall Ganging Station: maximum hourly precipitation of 90 mm total precipitation of 1,268 mm in a week
Precipitation and change in water level 14:00 Precipitation 15:00 Maximum hourly precipitation 時間最大 90mm of 90 mm Warning stage Specified stage Water level (m) Precipitation (at Mafune) Water level (Sukagawa River) Water level August 26 August 27 August 28 August 29 August 30 August 31 September 1 6 days of flooding above specified alert level
Overflow of the river Sukagawa City Main stream Shakado River
Overflow of the river Koriyama City Ose River Main stream
Disaster Response Manager has to in this case give appropriate response directives to critical areas communicate with local mayors on residents evacuation discuss with supervising organizations manage media relations to ensure accurate disaster news coverage Priority of tasks have to be changed according to the disaster status
Measures taken when the bank collapsed in the Arakawa District (Top priority given to the communication with the head of the municipal government) 8:30 The patrol staff reported that the bank had started to break off and was highly likely to collapse. 8:40 The office judged that the bank would collapse, and asked the mayor to issue the evacuation order. Setting up of hotline between the Mayor and the Flood office 9:00 About 500 households received the evacuation order. 9:02 The bank collapsed. 11:20 The office requested the dispatch of the Defense Force. 13:00 The office started to repair the broken section of the bank after the water level dropped below the specified level. 2:00 on the next day The broken section was sealed.
Start of bank breaching at 8:29 a.m.
8:30 a.m.
8:35 a.m.
8:37 a.m.
Collapsed at 9:02 a.m.
Flood Hazard Map is a tool to help disaster response officials ; to train themselves for flood response actions ; to take appropriate actions in emergency
People are not willing to move even when actual danger is drawing near Number of people who have (not) evacuated and their reason in Section a : Voluntarily evacuated Section b : Evacuated when directives issued Section c : Not evacuated because they judged evacuation was not necessary Section d : Not evacuated because they did not know how to do Section e : Not evacuated because necessary information was not available Section f : Not evacuated because the area was already flooded
It is often too late when people decide to evacuate (case of Ise-Wan Typhoon in 1959) Water depth in which evacuation is possible Water depth (assumption) 70cm 50 30 Adults 30cm 20 Children Male Number of persons 2 11 42 2 8 70cm 50 30 30cm 20 Female 0 7 35 1 15 Water depth when adults lost the accompanying children 45cm 25 Water depth when children lost the accompanying adults 60cm 45 3 5 2 5 3
Status of belongings when evacuating Evacuated without belongings 12% Evacuated with belongings 88% Have thrown away their belongings 46% Have not thrown away their belongings 42%
Flood Hazard Map is a tool to help residents to be preliminarily prepared for flooding ; to be alert when flood occurs ; to safely evacuate in emergency
How effective are Flood Hazard Maps? Result of research in Koriyama City in 1998 flooding Survey by Prof. Katada, Gunma Univ. 1 Quicker evacuation 2 Higher evacuation ratio 3 Correct direction to evacuate
Effectiveness of flood hazard maps In case of Koriyama City in 1998 flooding Peak of evacuation after order to evacuate Approximately One hour Those who saw the Hazard Map Those who did not see the Hazard Map Advice to Order to evacuate evacuate Source: Survey Report on Local Residents Reactions in the Rainstorm in Koriyama at the End of August 1998 Katada Laboratory, Faculty of Engineering, Gunma Univ.
Effectiveness of flood hazard maps In case of Koriyama City in 1998 flooding Rate of evacuation 30% 20% 10% Rate of evacuation six hours after advice to evacuate 1.5 times 0% Those who did not see the Hazard Map Those who saw the Hazard Map Source: Survey Report on Local Residents Reactions in the Rainstorm in Koriyama at the End of August 1998 Katada Laboratory, Faculty of Engineering, Gunma Univ.
Number of Flood Hazard Maps in Japan 400 by march 2003 300 298 200 217 Number in the year Total number 100 0 148 101 82 69 40 49 47 24 33 19 12 12 16 9 12 1996 1997 1998 1999 2000 2001 2002 2003 81 estimate till summer of 2003
Legal framework of Flood Hazard Mapping in Japan River authorities (Central / Prefectural governments) Information on possible inundation areas (Technical advice when map planning) Flood Hazard Map planners (Local governments) Planning Committee Draft Maps Inquiry to community information Local governments Advisers (researchers, experts, etc.) Residents Residents Feedbacks to draft maps Community information
Flood Hazard Map (example of Koriyama City) Akutsu bridge Ause River Koriyama Central Gymnasium Umeda punping station Yokotsuka punping station Enjuji Temple Yasuhara bridge Yamazaki community hall River Abukuma Yata River Otakine River
Process of Production and Distribution of the Flood Hazard Map 1 Collect and classify information 2 Set-up Basic Conditions 3 Draw-up Historical Flood Map 4 Draw-up Predicted Flood Area Map 5 Draw-up Evacuation Scenarios 6 Establish Evacuation Criteria 7 Produce Flood Hazard Map 8 Distribute and Dissemination among residents 7 Use in Municipalities
Inundation area by the Ise-Wan Typhoon in 1959
Flood Simulation Hydrological data Hydrograph of the target flood Data on Dike-collapse Meshed data of Floodplain (mesh size about 250m for calculation) Ground level Ground roughness (according to land use) Other data of Floodplain Drainage channels Banks Pumps etc. 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. Hazard mapping Info. on evacuation, etc.
Flood Simulation Cases Levee break point Draw the flooding boundary from the calculation at all levee break points
Additional information in the Flood Hazard Map Guidance to the Flood Hazard Map Information source to residents Emergency take-out kit checklist Flooding mechanism Guidance to warning
Guidance to Flood Hazard Map Flooding mechanism Topographic features and flooding types Real danger of flood, Predicted extent of damage Meteorological information Past flood records (rainfall, inundation, and damage) Rules to follow in cases of flood Explanation and directions to use Flood Hazard Maps Preparedness against flood
Information source for residents
Emergency take-out kit checklist
Flooding mechanism
The evaluation items in Hazard-Map by citizens Location of shelters Past flood records 123 135 Information flow of flooding / warning 150 Family 125 100 75 55 50 52 25 35 42 38 28 0 19 40 15 25 82 In the flood of torrential rain (26,Aug.~1,Sep.in1998) Dangerous places when evacuating Check list when evacuating Expected water depth 76 87 86 Actions to be taken when evacuation directive is issued Evacuation kit check list useful not useful
Be careful! - Inadvertent effect of Flood Hazard Map 1. Fixation problem (a) Residents tend to think the flood size described in Flood Hazard Map will be the same as that of the coming flood It should be more or less, but not the same maximum depth (by Prof. Katada)
(b) Flood Hazard Map can be interpreted as Flood-Free Area Map Dangerous Never be inundated! (by Prof. Katada)
2. Interpretation problem People may not understand how difficult it is to evacuate in flooded roads even though they are shallow Water depth (assumption) 70cm 50 30 Adults Male Number of persons 70cm 2 11 42 50 30 Female 0 7 35 Water depth in which evacuation is possible 30cm 20 Children 2 8 30cm 20 1 15
Thank you for your attention!
Set-up Basic Condition (1) Magnitude of Target Flood Design flood The largest flood recorded in the past Flood that may occur once in several years (2) Areas to be mapped Inundation areas and their surrounding areas should be mapped The neighboring areas should be included in a map when the potential flood areas include neighboring municipalities.
Set-up Basic Condition (3) Scale and Size of Base Maps Standard scale of base maps should be 1/10,000 to 1/15,000 because identification of not only individual houses but evacuation routes and the extent of inundation are necessary Standard size of base maps : A0 to A1 as they are easy to handle
Drawing-up of Historical Flood Map old residents in the area
Drawing-up Predicted Flood Area Map Identify current status of levees Identify existing crosssection al areas of river channel Identify current status of river m anagem ent facilities such as flood control facilities, their annexed dikes, etc. Identify w ater levels on various spots along the river channel that allow discharge w ithout flooding W ater levels in river channel through the w ater level ca lcu lation m eth od used in cases of channel im provem ent. Identify flood discharge, on the basis of target rainfall Identify discharge at the start of flooding Id en tify p ossible hydrograph on various spots along the river channel Identify possible flooding spots D efine the target flood plain Identify topographical features of the target flood plain D efin e p rem ises for Flood Sim ulation Analysis b y lev ee b rea k a n d sp ill overtop p in g F lood S im u la tion A n a ly sis D efin e flood -p ron e area Represent inundation depth D raw -up Flood-prone Area M ap
Guide to warning
Collapse of the bank in Arakawa District