General information: the Great Flood of 2011
The large floods occurred in 1942 and 1995. The causes are monsoon rain and high water level spill over the river bank. Moderate flood in Thailand normally occurs every 4 to 5 years with period of 1 month. Local people used their own knowledge to adapt their living style with floods. The damage causes were not high. The flood prone area is paddy field. The exchange of flooded water from river and floodplain is natural process that occurs to scale down the flood peak propagated to downstream area. In 2011, rice productivity is very important to farmers. They protect their paddy field by constructing temporary dikes along the river so that the flooded water is confined in river only. Therefore dike failed at the weak location and causes flooded water flow irregularly and it is uncontrolled.
The Chao Phraya is the largest river basin in Thailand having area approximately 160,000 km2 which is one-third of the total area of the country. The total length of river is 1,000 km. The upper watershed has 4 sub-basins which are Ping, Wang Yom and Nan. There are 2 big dams, namely Bhumibol dam in Ping and Wang river, Sirikit dam in Nan river. There is no dam in Yom river basin. Rivers are joined at Nakon Sawan. The lower watershed area is mostly paddy field. The downstream of Chao Pharaya river has gentle slope with gradient around 1/10,000 and 1/15,000. With this condition, flood in downstream is expanded to floodplain and it take long time to drain out to the sea.
The 2011 flood in Thailand caused tremendous damage to country. World Bank (2012) estimates the damage cost with US $81,000 million and it has rank number 4 of the world. It is mainly contributed from industrial sectors with losses from 7 industrial estates, 900 factories and 400,000 employees are directly affected. The factories related to electronics equipment, appliances, semi-conductors, hard disk and car manufacturers. The shortage from these supply chains occur in the world. Ayutthaya historical park, a world heritage was flooded for 2 months with 1 to 2 meter flood depth. This is the consequence effect of the greatest flood in Thai history. The causes of flooding are heavy rainfall in the north of Thailand from strong monsoon troughs and five tropical storms. The high rainfall occurs successively from March to August. The annual rainfall broke down the highest records in 60 years. Devastating broad scale flood occurs. Finally flood approaches to Bangkok, the capital of Thailand.
- Strategic Flood management in a large river basin scale;
- Long term planning and implementation infrastructural development for flood;
- Regional flood forecasting scale and dissemination/communication to local people.