Roadmap toward Effective Flood Hazard MapinLampang Thailand

JICA region-focused training course on flood hazard mapping
JFY 2005

Prepared by MR. SOMCHIT AMNATSAN
Chief of Water Planning and Solution Branch
Regional Irrigation Office 2, Royal Irrigation Department

ThailandNameMr.Somchit Amnatsan

Organization

Regional Irrigation Office 2;
Royal Irrigation Department

Address

Regional Irrigation Office 2, 271 Boonyawat Road,
Suandok, Muang, Lampang, 52100

E-mailsomnatsan@yahoo.com, somnatsan@hotmail.com

A) The role of flood hazard maps to mitigate flood damages in Thailand
1) The flood status in Thailand
General background
Thailand is a Southeast Asian country comprising 76 provinces with 60
million inhabitants, lying in the tropical zone within latitude 5°37' N and 20° 27 Nand longitude 97° 22'E. The country covers an area of 514,000 km2, is some
1,650 km from north to south, and is 770 km from west to east. The narrowest
portion is only 15 km across. Thailand is situated in the Indo-Chinese Peninsula,sharing borders with Myanmar to the west and north, Laos to the east and north,Cambodia to the east and Malaysia to the south.
Topographically, Thailand is characterized by mountains in the north which
continue to the south-east; flat alluvial plains intersected by winding rivers andirrigation canals which flood during the rainy season; a certain amount of
undulating country; and maritime features such as sandy beaches, mangroveswamps, irregular coastlines and numerous islands.
Major causes of floods in Thailand
Floods in Thailand are normally caused by tropical storms and depressions,rarely by typhoons. The tropical storm season is from about May to December.
During the first two mouths and the last month of the season, the probability ofstorms occurring in the country is minimal. It rises during August to November,especially in September and October where the probability is maximum.
Statistics of a 46-year period (1951–1996) show that on average 3.5 storms
occur annually, while 0.9 storms occur during the months September andOctober.
The most common storm track is westward from the north-east of Thailand.
It causes heavy rain in its passage over land. The low-lying areas of the Central
Plains usually have the flood condition according to the intensity of heavy rain
during the storm season.
From early September to mid-November 1980, severe flooding wasexperienced over vast areas of northern, north-eastern and central Thailand,
including the Bangkok Metropolis and adjacent areas. It was apparently caused1

by excessive rainfall brought about by two depressions which occurred on 6 and
7 September and 17 September. The maximum 24-hour rainfall was 156 mm in
Uttaradit Province in the north in September and 147 mm in Kalasin Province inthe north-east on 15 September.
Including the active monsoon pass trough the upper Thailand during
September and early October with those depressions, flooding in 47 provinces ofupper Thailand and in one province in Southern Thailand affected 203,386
families, or 831,368 persons, whereas 2,394 houses were destroyed. A total of
61 persons were reported dead, with others injured during the flood events. It
was estimated that about 928,000 hectares of farmland were damaged, fromwhich about 12,000 families or 70,000 persons were evacuated to safe places.
The total damage caused by the 1980 flood in upper Thailand, excluding theBangkok Metropolitan area, was estimated at around 1,546 million baht. Floodingin the lower Chao Phraya River Delta areas, particularly in the Bangkok
Metropolis, was prolonged from early October to mid-November. Damage
incurred by the 1980 flood in the Bangkok Metropolis itself has been roughly
estimated at many millions of baht. Thousands of urban residents wereinundated. The 1980 flood is regarded as one of the most disastrous natural
events ever recorded in Thailand.
In 1995, Thailand experienced very severe floods caused by thecombination of tropical storm Lois, the south-west monsoon and low pressuresystems. They caused major floods in upper Thailand including Bangkok
Metropolis and adjacent areas during the period from mid-July to the end ofSeptember. A total of 64 provinces (15 provinces in the North, 19 in theNortheast, 17 in the Central plains, eight in the East and five in the South) wereflooded. It was estimated that about 1.7 million hectares of farmland weredamaged, which affected 1.4 million families or 5 million persons were affected.
More than 12,000 houses were destroyed. There were 413 deaths and about
18,000 families or 60,000 persons were evacuated to safe places. The total
damage in upper Thailand, excluding the Bangkok Metropolitan area, wasestimated at around 10,545 million baht (US$ 421.8 million).
Besides the major cause of floods described above, the other causes that
aggravate flood problems in flood plain areas include insufficient capacity ofrivers and canals, poor drainage and sewerage systems in populated areas,
destruction of forest, poor management of land, and the inadequacy of reservoirs.
Especially for the Bangkok Metropolitan area, flooding in urban areas is due toheavy rain downpour in the area, over-bank flow on the flood plain of the Chao
Phraya River, tidal effect superimposed on the flood wave of the Chao Phraya
River, land subsidence which is due to groundwater abstraction, obstruction ofwater ways by extension of the urban area and metropolitan irregularity, anddestruction of public utilities.

22) The outline of the present countermeasures for mitigating flood
damages in Thailand
At the present, there are two types of countermeasures for mitigating
flood damages in Thailand:
1. Structural measures
Government organizations responsible for flood control andmitigation have proposed many flood control projects. However a few projects
are completed due to lack of the budget. The examples of structural-measureprojects are dam constructions, weir constructions, embankment and leveeconstructions, etc.
The evidence of the effectiveness of structural measures was on
1995 flood. Due to the severe damage caused by flooding in Bangkok in 1980,
several measures were implemented for flood protection. Flood protection works
for the Bangkok Metropolis included the construction of embankments,
improvement of drainage canals, and provision of drainage pumps, dikes andzoning. The effect of the project was studied and a diversion canal was built todischarge excess flow directly to the sea, together with preventing tidal effects bybuilding a sea barrier. It is effectively protect the city core of Bangkok from major
flooding in 1995.
Nonstructural measures
Many nonstructural measures, e.g. rainfall and flood forecasting,flood warning, and historical flood maps are implemented. However, theimplementation are not well enough due to lack of modern instruments such as
the real time rainfall and runoff recorder, the coordination between concernedorganizations is not good enough, and the attitude of the people in flood plain tocountermeasures.
Practically, Thai central government assigns the flood control andmitigation system into three stages. The stages and tasks in each stage are as
follows:
1. Before flood stage;
1.1

Preparation of historical flood map.

1.2

Setting up the special center for flood protection andmitigation.

1.3

Flood defense planning and workshop.

1.4

Preparation of manpower, machines, equipments, and rapid
flood alert team.

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1.5

Installation of rainfall and runoff recorders, alarming
equipments, and assign recording persons at each recording
stations.

1.6

Dissemination of rainfall, water level, runoff, and flood riskarea.

1.7

Construction of reservoirs, ponds, and excavation of channels.

2. During flood stage;
2.1

Evacution of people and properties to the safe area.

2.2

Distribution of emergency food.

2.3

Damage investigation and offering of the first aids.

2.4

Set up the security system.

2.5

Report the situation until it is recovered

3. After flood stage;
3.1

Setting up the mitigation unit.

3.2

Provision of the temporary residences, food, clothes cleanwater, and treatment of injurers.

3.3

Investigation of the damages and losses in detail.

3.4

Disposal of rubbish, removing mud, restoration of household
and public goods.

3.5

Distribution of relief funds.

3.6

Restoration of affected facilities.

3.7

Provision of jobs for jobless people who are affected fromflood.

Many organizations are assigned to act on flood control and mitigation,e.g. Land Development Department, Water Resources Department, Disaster
Prevention and mitigation Department, Meteorological Department, RoyalIrrigation Department, Provincial Office, army forces in flood area, and the privateorganizations.
As mention above, historical flood maps are used as nonstructural
measures on flood control and mitigation in Thailand. The role of these maps isto provide the warning to the people who live in the past flood area. However, theusefulness of these maps is limited because no relation between flood area andamount of rainfall or flow in the river is shown in these maps. Hence, it will bebetter if we have flood hazard maps which show such relation. These maps canbe used effectively for flood warning and evacuation purposes.

4However, flood hazard maps in Thailand are different from ones inJapan on some characteristics as follows:
1) Difference in inundation area
Almost all of the inundation areas in Japan are protected by leveeand the inundation occur because of levee break and inland rainfall. But inThailand almost all of inundation areas have no levee and the inundation occur
due to the large amount of water flow from the upper part of basin and has thewide cross section of flow.
2) Difference in the characteristic of evacuation
Although the objective of the evacuation in Japan and in Thailand isto save the lives of the people and their properties, it has some difference in thecharacteristic of evacuation. In Thailand, people have high awareness in theirproperties. It seems impossible to evacuate on foot only as in Japan. Hence, it
should be considered on the evacuation by car. The evacuation route andevacuation order must be planed for smooth evacuation. Moreover, theevacuation during flood should be considered to evacuate the people who arestuck in their home.
3) Difference in the attitude of people in inundation area
In Thailand, the big floods rarely occur in the same area as in Japan.
Although floods occur in some area almost every year, it is only the small flood.
This phenomenon makes the people have less awareness in flood disaster. The
response of the people to flood hazard maps may not the same as in Japan due
to this reason. However, flood hazard may give the positive effect to the attitudeof people as in some cases in Japan. Seeing the expected inundation area map
together with their experience in the past flood may raise their awareness in flooddisaster.
B) The allocation of roles in making flood hazard maps in Thailand
There are many government organizations in Thailand that have theresponsibility in water management, e.g. the Water Resources Department andthe Royal Irrigation Department. These organizations can take responsibility formaking an anticipated inundation area map. In my opinion the Royal Irrigation
Department should take this responsibility because it has human resources andexperiences in this area.
Lampang municipality which is located in Wang river basin is the area Ichoose for making the flood hazard map. Hence, the organization which should
hold the main responsibility for making and disseminating flood hazard maps isLampang municipal office.

5C) The action plan of making flood hazard maps in Thailand
As I mentioned before, Lampang municipality is the area I choose formaking the flood hazard map. This area is in my responsibility and I am familiar
with its topography. it is easy for me to search for the necessary data for making
the flood hazard map. This hazard map, at the first stage, will be used for thegovernment official as a guideline to give the warning and to plan evacuation
when flood occur. Rainfall data, water level data, and flow data of this area areavailable. The topography or elevation data of this area is not available. However,in the first stage of making the flood hazard map, I will try to search for this datafrom internet website that I have known from this training course. Regardless ofthe accuracy, making the flood hazard map using elevation data from this sourceis possible. But if we need the more accurate flood hazard map, the survey ofelevation data is necessary. However, the lack of budget is the big problem toovercome.
The action plan within the next five years is shown in the table 1.
Table 1. The action plan of making flood hazard maps in Thailand
Action Plan

1

2

Year
3

4

5

1. Learning of how to make the FHM
2. Collection of necessary data
3. Compositon of anticipated inundation map
4. proposition and evaluation of anticipated inundation map
5. Proposition of budget required for ground survey
and publication of FHM
6. Ground survey
7. Composition of the FHMProblem in Making flood hazard maps in Thailand
The following issues are the main problems found in making flood hazard
maps in Thailand:
1. Lack of data
The topographic data of the area in Thailand is rarely available. Only insome specific area that has this data, e.g. the area that is planned to use as theconstruction site. Although it is available, in some area, it is not in the digital form.
Thus, more works have to be done to convert the logical data into digital data
and require more time to do so.
2. Lack of the budget
As mentioned before, many of flood protection and mitigation projects
can not be implemented due to lack of the budget. Many projects are still in
waiting list to be implemented. Hence, receiving the budget for making flood
hazard maps is very difficult.

63. Attitude of the administrators to flood hazard maps
This problem is the effect of lack of the budget together with thecharacteristic of flood in Thailand such that the big flood rarely occurs in thesame area. Although some areas have been flooded almost every year, it is asmall flood. Both of these reasons may result that, in the opinion of theadministrators of the organizations involved in flood control project, flood hazard
maps has less important compare to the other flood control projects. However,
the attitude of administrators may vary in each person depending on theirknowledge and understanding on flood hazard map.
D) My advice/suggestions for making this training course more meaningful
I very impress in flood management in Japan. It is well organized in both
structural and nonstructural measures. This training course is also well organized.
The only one thing I would like to suggest is the time distribution. We spend a lotof time in listening to the lecturers about their knowledge and experiences inflood hazard maps but we have a little time to do the important exercise such as
exercise on runoff analysis and GIS. Many lecturers provide us the same content
on flood hazard maps. In my opinion the time for the outline, the meaning, andthe status of flood hazard map should be reduced and give more time in exercise.

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