Subsidence, low level of Bangkok hinder drainage
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Bangkok not only has problems with its drainage system, it also has ground subsidence, which causes land to be bowl-shaped in many areas of the capital. This caused flooding problems when it rained heavily and made drainage more difficult, a city official
Sansern Ruangrit, an engineer at the Department of Drainage and Sewerage at Bangkok Metropolitan Administration (BMA), said the capital was lower than sea level and had bowl-shaped land.
A road survey by the BMA’s Public Works Department found that on average roads in Bangkok were only about one metre higher than sea level. So, when it rained heavily – more than 60 millimetres in an hour – or when the level of the Chao Phraya River was higher than two metres, Bangkokians could not avoid flooding.
Sansern said Bangkok and its neighbouring provinces were located in the Chao Phraya delta with land between 0 metres and +2 metres above mean sea level (AMSL), which was shown on four zones of a map.
The first zone was on Bangkok’s Thon Buri side from Borommarat-chonnani to Rama 2 roads parallel to Kanchanaphisek road, the second was parallel to Phaholyothin Road, the third was parallel to Klong Song Canal and in Hathairat, Min Buri and Nong Chok areas, and the fourth was Bangkok areas.
“Bangkok has bowl-shaped land. Its estuary areas subside one to two centimetres per year,” he said.
Phetkasem road is 1.30 AMSL, Sri Ayutthaya road is 0.06 AMSL while Suan Pakkad Palace was 0.13 AMSL, according to a record in 2009.
“We have to use pumps to pump out water from low level areas. A system to release water through a lot of canals in the capital could also help,” said Sansern.
He said each residence should have “monkey cheek” areas to hold floodwater in its compound and release floodwater after it stops raining instead of get rid of flood-water from residences while public areas were still flooded.
Apart from releasing floodwater along the canals in areas west and east of Bangkok, the BMA planned to increase water release channels around Bangkok. Water pushing machines were also used to accelerate the release of floodwater into canals, he said.
