More than 11.5 million people live within the Chao Phraya sub-basin in and around Bangkok. This sub-basin is located in a low-lying plain that has an elevation range from 0 to 20 metres above sea level. Several factors contribute to widespread flooding in this area, typically during the rainy reason.
Topography of the basin – the gradient of the Chao Phraya from its upper reaches to the lower areas of the Chao Phraya sub-basin causes water upstream to flow rapidly and slow down at lower elevations.
Flood protection systems upstream – due to urbanisation and industrialisation, and for protection of agricultural land to minimise crop damage
Land subsidence, caused by pumping groundwater in areas of soft clay, lowers the height of river walls and causes drainage problems
Global warming – as global warming continues, sea levels will rise further and rainfall will tend to fluctuate to a greater extent
Change in land use in the Chao Phraya has led to an increase in flooding. (Source: http://article.wn.com)
Changes in land use, urbanisation and more complex irrigation systems mean that heavy rains during the monsoon season can no longer be controlled naturally. Soil retention or lake and reservoir storage which were once sufficient are now no longer, and water levels frequently rise above embankment protection during the rainy season leading to widespread flooding. Hence a need to manage these conditions is paramount.