starting a Dialogue
on Future Flood
Management in
Thailand
Bas Jonkman04
It is an inconvenient trutli tliat societies appear to be willing to invest in adequate flood risk reduction only after devastating disasters. The Netherlands has constructed an extensive system o l dyl<es and barriers to protect flood-prone areas that cover 60% oi the country. This was in response to the latest major flood disaster in 1953 where a storm surge flooded large coastal areas and killed more than 1,800 people. In earlier centuries, many more river and coastal floods affected the country and shaped its landscape, Recently, as a response to near-river floods in 1995, the "Room for Rivers" program has been implemented to increase the discharge capacity of the main rivers and to reduce the risk of flooding.
The water system and flood threats
The 2011 floods in Thailand have led to societal disruption and enormous damage, which is currently estimated at around $45 billion. Large parts of central Thailand are to some extent comparable to the Netherlands as they consist of deltaic and flood-prone areas, however; the nature of the water system and land use in Thailand will necessitate a different response than in the Netherlands. Most flood-prone areas in the Netherlands are protected with flood detences (dykes and dams) designed to safely withstand extreme events with return penods of 1OO0 years or more. In Thailand, the protection level is much lower and the system is more "open" to allow seasonal floods to irrigate the fertile land. Thailand has a long history and experience in dealing with water and floods. Historically, Bangkok was a water city that w a s once called the Venice of the East. Nowadays, most of the old canals are filled in and the drainage system is hidden under the city with insufficient capacity. It is a great challenge to hydrau-lic engineers and architects to bring back the water system in Bangkok and other parts of Thailand in a more visible and attractive manner. \Ne expect that this will also offer opportunities to combine water management solutions, such as water storage, canals and floating houses, with high-quality spatial develop-ment on the waterlronts. In identifying an effective flood risk reduction approach
for Thailand, it is important to consider the existing land use and water management system, the various flood threats in the country, and the effectiveness of different measures that can be applied at various geographical scales within the Thai context.
fhe water system in the Chao Phraya River basin in the central part of Thailand has a lorm ol a typical river catchment or drainage basin (Fig. 1). It is characterized by relatively last and steep runoff in the hills and [iiountains in the North of the country (leading to potential flash floods) and more gradual flow through fivers and canals in the flat, deltaic part of the catchment, referred to as the Lower Chao Phraya tjasin. Dams have been built to store water for dry periods, control floods and to generate power. In addition to the flows through this system, heavy tropical fainfall may lead to local (street) flooding. Floods from typhoons and storm surges and tsunamis could threaten coastal areas, as demonstrated during the 2004 Boxing Day tsunami. One of the challenges for Thailand is that areas around Bangkok have transformed from agricultural to highly urbanized/industrial land use throughout the last decades. Moreover, large parts of the urban areas suffer from land subsidence due to groundwater pumping, turning the drainage more complex. The water system has not been modified to adapt to these changes and it seems that current system is more adapted to the use for irrigation, and less for flood management purposes (ENW, 2012).
Figure 1: InunrJalion m a p of lire Lower Paris o l Ihe Chao Phraya River basin during Ihe 2011 Hoods ( E N W , 2012).
Flood management strategies
Developing and realizing an ellective flood manage-ment strategy for Thailand is a comprehensive task that is likely to take several decades. W e outline a number of key elements below.
Storage
For the higher and steeper parts of the Chao Phraya basin it is important to improve storage capacity and flood warning. (Re-)Forestation could help delay runoff and reduce flood peaks. Also in urban environ-ments, the storage capacity to accommodate heavy rainfall should be improved by means of local storage basins and by increasing the amount of green areas, e.g. by means of parks or green roofs.
Increased discharge capacity
For the middle and lower parts of the basin, increase of the retention, storage and discharge capacities are crucial. Several ideas have been developed to create additional conveyance and to bypass some of the river waters around Bangkok by means of additional canals (e.g. Monkey Cheek project). The operation and water management in reservoirs and dams will have to be optimized with respect to water storage and energy generation, yet minimizing the flood risks associated with these dams during the flood season.
Dykes
For densely populated and high-value areas flood protection will be an important component in reducing flood risks. This would imply the use of flood defences, such as gates and dykes, for industrial and highly urbanized areas in and around Bangkok. During the 2011 floods, water flowed into Bangkok near the Don Muang Airport through weaker and lower sections of the ring dyke around the city (see Fig. 3). It would be a no regret measure to close and upgrade the ring dyke around Bangkok, so that large parts of this megacity is protected at a reasonable level. In addition, other valuable industrial and heritage areas could be protected by means of flood defences. After the floods, dykes and lloodwalls around high-value industrial estates have already been built or strengthened. Since full flood protection for the entire delta at the same level of protection is not likely to be feasible, there will be a need to develop a plan for differentiated flood protec-tion levels, in agreement with the economic value of the protected land.
Emergency measures and flood forecasting
Emergency measures, such as sandbags, should be available and prepared, but cannot replace the need for system wide implementation of permanent measures. Also during emergencies, movable flood gates and barriers can be installed to protect buildings or other important sites. Adequate and timely flood prediction and forecasting are of great importance to be able to reduce damage and take effective emergency and management measures. By combining meteorological and hydrological information sources and flood routing models, floods in the basin can be predicted hours or even days before the arrival of the flood peaks.
Hgure 3; Flooding of Don Muang Airport in Ihe north of Bangkok during the 2011 Hoods,
Local flood proofing
Local measures, such as flood praoling of buildinns p . design of floating houses, can mainly reduce thp ,i due to rainfall at a local building scale. These measi, are often most appropriate to reduce flood risks at a I
local level, mostly for new buildings. ^ The time scales at which these measures can I,
implemented differs. Local flood proofing and fion protections can be constructed within a couple r, months. However, adapting the water system throun increased storage and discharge capacity is likely take years or even decades as measures have to h taken throughout the whole river basin. It is therefor important that an integrated national plan is prepared i which longer and shorter-term measures are combined to come to an optimal solution.One important lesson ol centunes of flood management in the Netheriands is thai after the construction of these systems, it is necessary to take care of the management and maintenance on a continuous basis. In the Netheriands, the first water boards were established hundreds of years ago for this crucial task. The performance and serviceability of the system has to be guaranteed over time and clear roles and responsibilities are needed in combination with financial arrangements. Only then will it be possible to considerably reduce flood risk.
I I .
Figure 3 : Overview of a characlerislic river basin a n d measures lhal could be applied in various parts o l the
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Tf)e need for integrated solutions
We have discussed how an effective flood management strategy can be developed by combining different measures that affect flood risk at various spatial scales in different parts of the river catchment. In order to be success-ful, it is necessary that bottom-up (local) measures such as flood-proof houses and flood protection are combined with top-down and system-wide strategies that focus on improved storage and discharge capacity, land use planning and reforestation. In addition, the different flood sources, local rainfall and high river discharges from upstream, need to be taken into account in the overall design and planning of the measures.
Therefore, the challenge for the future is to consider and elaborate alternative strategies for different parts of Thailand in an integrated and interconnected way. In final decision-making, the effectiveness of these strategies in terms of flood risk reduction, costs, benefits and ecological and societal effects will play a key role. Criteria in these various categories can be formulated to support decision-making.
To develop and maintain such integrated solutions, an extensive knowledge "inlrastructure" is needed, consisting of research centers, experimental facilities and academic institutes to train (future) experts. These institutes should cover various disciplines, including hydrology, hydraulic engineering, urbanism, governance and land use planning. In the Netheriands such research institutes and the related partnerships with government and industry have been successfully developed as part of the large flood management projects that were realized in the 20th century to protect the country against flooding. The Thai and Dutch have both faced the threats of floods for many generations. Sharing experiences can contribute to the further development of a much needed research and development network for flood and water management in Thailand which suits the local tradition, culture and landscape.
R e f e r e n c e s :
E N W (Expertise Network on Flood Proleclion) Jonkman S,N., Barames Vardhanab-huli, Blommaart P., de Bruin B., Hardeman B „ Kaensap l<„ v a n d e r Meer M., Schweckendiek T., Vrijiing J.K. {20\Z)Posl-llood Held investigalion in Ihe Lower Chao Phraya River Basin, 23 27 January 2012 Preliminary findings o l the Thai -Dutch Reconnaissance T e a m
