In 2011, Thailand had one of its worst floods in the history. Starting in late July, the flood effected the North and Northeast of Thailand as the result of several tropical cyclones. Accompanied by the following heavy rain season, the dams that was nearly full due to drought in 2010 could not hold enough water. The flood hit Bangkok in October, and was prolonged until January 2012, covered the total of 90 billion square kilometers of land, and costed around 45.7 million dollars. 

The land that is covered by the flood in each month from January (light green) to October (purple) of 2011

One of the tropical cyclones that effected

                          July 29                                                     July 30                                                      July 31

The higher sea-level made draining the water out even more difficult.

The effect in an area of Ayuddhaya province as in July and October 2011

sources:

http://www.thaiwater.net/web/index.php/ourworks2554/379-2011flood-summary.html

http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=76234

http://www.thaiwater.net/current/flood54.html (in Thai)

- Warittha