Action Plan toward Effective Flood
Hazard Mapping in Thailand
JICA region-focused training course on
flood hazard mapping
JFY 2006

Prepared by Mr.Kunpote Buatone
Civil Engineering
Water Crisis Prevention Center,
Department of Water Resources
A. The role of flood hazard maps to mitigation flood
damages in Thailand
The causes of floods, in general, may come from two main
sources: nature and human intervention, as follows:
Natural causes
The main natural causes are overbank flow of the rivers,
heavy rainfalls and tides.

Overbank flow : Floods in Thailand are also generallycaused by overflow from the rivers, which results in widespreadflooding. During the peak flood in 1995, the flow in the Chao
Phraya River passing through Bangkok metropolis to the Gulf ofThailand was much higher than the capacity of the Chao Phraya
River and caused severe flooding in the Chao Phraya Delta andBangkok metropolis.

Heavy rainfall : Heavy local rainfall is usually the maincause of inland floods, as it often exceeds the drainage capacityof the local areas or streams. For example, several tropical
cyclones passed through Thailand and caused heavy rains in1995, including the depression storm.

Influence of tides : Tidal fluctuation at the river mouth hasoften affected the drainage of river floods into the Gulf ofThailand. This effect prolongs the period of flooding, especiallyin the coastal provinces of the Chao Phraya River basin, SamutPrakan, Bangkok metropolis and Samut Sakhon.
Man-made causes
The most common man-made causes in Thailand aredeforestation,
abstraction

ofuncoordinatedurbandevelopment,

over-groundwater,andflood

destructionofembankments.

Deforestation : This is the most significant man-madecause that increases flood peak fromrainfall and reduces the lagtime between rainfall and run-off. In a deforested area, surface
run-off and peak flood discharge tend to be higher, since there
are no trees to obstruct the flow. Moreover, the rapid run-off will

increase erosion of soil surface particles, resulting in higher
turbidity and more serious sedimentation. This results inreducing function of the river and water sources.

Uncoordinated development : In urban development, mostof the surface areas are covered with houses, roads or paved
surface having lower water absorption and rainfall tends toconvert almost immediately into run-off flowing into the drainage
system. This phenomenon is in contrast to that in rural areas,
where rainfall can be retained by vegetation cover and absorbed
by soil. Many kind of development in delta area have related tocreating higher flood risk for example protection of urban andhigh-value farm will reduce space of flood inundation accordingly
such as orchards, aquaculture, etc. Construction of roads andrailways will also obstruct flow especially for inland flow. Housingconstruction in public areas along river or canal banks is anotherexample of action that reduces the stream cross-section andthus its flow capacity. Uncontrolled dumping of sewage andgarbage may obstruct the flow and cause situation in thedrainage

streams.

Asa

consequence,

uncoordinateddevelopment in many parts of the country has resulted indecrease in drainage efficiency both inland and river courses.

Destruction of flood embankments : There have beencases in which inhabitants living in areas outside the protection

of flood embankments destroyed those embankments in thehope of reducing the flood-water level in their areas. Protectionof these embankments was difficult, although there aregovernment agencies responsible for the maintenance andmonitoring of the embankments. These events resulted in abrupt
flooding of the protected residential areas.

Over-abstraction of groundwater : Pumping of groundwater
is one of the main causes forland subsidence, which hasresulted in deeper flooding and longer waterlogging. The
Government agencies concerned are trying to limit the pumpingof groundwater and this effort has been emphasized in theBangkok metropolitan Area.
The outline of the present countermeasures for mitigating
flood damages in Thailand.
Flood control and management has become an importantcomponent of water resource infrastructure development. The
post-World War II up to the 1980s marked the massive water
infrastructure development in the kingdom aimed at flow regime
regulation and water conservation (ESCAP 1999).

Water

resources projects have been a major public investments since
1961 (ESCAP 1999). Several large and small-scale water
resources projects were constructed for power generation,

irrigation and flood mitigation nationwide. The Royal IrrigationDepartment has been mandated to protect agricultural areaswith dikes. For example, a 300 km dyke has been constructedby the Royal Irrigation Department along the Chao Phraya Riverto protect irrigated areas from Nakhom Sawan to Bangkok(ESCAP 1999). Flood mitigation is one rationale for medium tolarge scale water infrastructure projects in the Mae Nam Ping
Basin in Northern Thailand.
InThailand

economic

activities

andprosperity

isconcentrated in the Chao Phraya River basin, particularly theGreater Bangkok Metropolitan Area, and few other urban andindustrial enclaves. The government invested in flood control
infrastructures to control flooding in these urban centers. Since
the beginning of the Eighth National Economic and Social
Development Plan (1997-2001), the government has allocatednecessary budget to various agencies concerned to implement
various flood control measures, such as the construction of flood
control systems, multi-purpose reservoirs and other hydraulicworks, aiming at reducing the magnitude of flooding. For
example, as a response of the catastrophic flood in Hat Yai in
2000, the Hat Yai municipality with the support of the national
government has made considerable investment in flood
mitigation schemes, which include the construction of levees,

drainage canals, water diversion channels and pumping stations.
The Eighth National Economic and Social Development Plan
calls for the establishment of institutions to solve flood problems
through the formulations of policies and action plan. These
institutions would coordinate the implementation of the action
plan so as to ensure effective flood management in conformity
with the law and complementary of the activities of all
departments concerned working toward the same goals andpreventing conflicts.
At the present, there are two types of countermeasures toreduce flood damages in Thailand:
Structural measures
Government organizations responsible for flood control andmitigation have proposed many flood control projects. Howevera few projects are completed due to lack of the budget. The
examples of structural-measure projects are dam constructions,weir constructions, embankment and levee constructions, etc.
The evidence of the effectiveness of structural measures
was on 1995 flood. Due to the severe damage caused byfloodingin

Bangkokin1980,

severalmeasures

wereimplemented for flood protection. Flood protection works for theBangkok Metropolis included the construction of embankments,improvement of drainage canals, and provision of drainage

pumps, dikes and zoning. The effect of the project was studied
and a diversion canal was built to discharge excess flow directly
to the sea, together with preventing tidal effects by building asea barrier. It is effectively protect the city core of Bangkok frommajor flooding in 1995.
Nonstructural measures
Many nonstructural measures, e.g. rainfall and flood
forecasting, flood warning, and historical flood maps areimplemented. However, the implementation are not well enoughdue 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 to countermeasures.

I thing Flood Hazard Maps will be useful in Thailand
because FHM consist of the necessary information on
inundation area and evacuation point in an easy to understandway in order to enable people to evacuate safely and smoothly
in emergency situations from the flood disasters are anticipatedto occur due to extreme rainfall events. In my country we haveflooding almost in the central area and north path of countryespecially in the north path flash flood all way occur on the upperpath. If we can make FHM in that path we can announce to thepeople the know disaster from flood will occur and the people
that know where is the evacuation center and which one issuitable or not far from their house.
B.The allocation of roles in making flood hazard maps inThailand.
In Thailand, after re-organization, we have 2 mainlyorganization responsible in case of flooding. One is Royal
Irrigation Department (RID) another is Department of water
resources(DWR).

Thoseorganizations

havedifferent

responsible target area. RID involve in the irrigation area ormidstream. DWR involve in the upstream and downstream. In
my opinion both of them should be hold the main responsibility
for making inundation area maps.
In Thailand, Central Government should be hold the main
responsibility because the government has made considerable
investment in flood mitigation schemes, which include theconstruction of levees, drainage canals, water diversion
channels and pumping stations by use stakeholder who haveauthority about the raw data and make flood hazard map for
distribute this map for the people who live in the flooding area.

The most important thing is the budget because this map should
be more detail an easy to understand should be use morebudget than normal map.
C The “Action Plan” of making flood hazard maps inThailand
Ping basin is my target river basin because Ping basin is
one of eight sub-basins in Chao Phraya

basin.

Ping basin

originated in Pee Pan Nam mountain range in Chiang Dao
district, Chiang Mai province. The river flows from north to southpassing Chiang Mai, Lamphun, Tak and joins Wang river in Tak
province then passes along Kamphang Phet, Nakhon Sawan
and then joins Nan river at Pak Nam Pho in Nakhon Sawan
province. The total length is 740 km. Main tributaries are Mae
Tang, Mae Ngad, Mae Kuang, Mae Khan, Mae Jaem and also
the main river Mae Wang.
Changmai province is flooding because heavy rains occur
in the upper ping basin area and the city sit on the lower area.
The drainage system in this city was disturbed by housing andthe roads block the flow of

the water flow by rain. This city is

the important city or can call main city in the north path ofThailand economic depend on the tourist or travel business if theflooding occur in the peak season its will be lose income.

In Changmai province, we have the data for flood forecast
and rain gauge station for rain forecast. We have many raw data
about this in daily data, incase of flood we have hourly data. Thisis the main important that I’m chosen Changmai province tomake hazard map. And its also have flood inundation if wecontinues make FHM project its will be as soon as complete.
Propose your own “Action Plan” within the next five years.

The following issues are the main problems found inmaking flood hazard maps in Thailand:
1. Lack of data
The topographic data of the area in Thailand is rarelyavailable. Only in some specific area that has this data, e.g. thearea that is planned to use as the construction site. Although it isavailable, in some area, it is not in the digital form. Thus, moreworks 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 andmitigation projects can not be implemented due to lack of thebudget. Many projects are still in waiting list to be implemented.
Hence, receiving the budget for making flood hazard maps isvery difficult.

D My own Flood hazard map on Ise city
What is the improvement from the FHM on Ise City
currently available.

conclusion
 Flood hazard map in Japan is more useful and easy tounderstand Flood hazard map is the tool for announce to people inflood area know how to when, where and how toevacuation.