The Bangkok Metropolitan Administration (BMA) has defended its giant drainage tunnels, saying they at least "speed up" the drainage of flood water in the capital.
The BMA was forced to respond after many people including firebrand activist Srisuwan Janya and politician Khunying Sudarat Keyuraphan raised doubts over the effectiveness of City Hall's tunnel project, worth more than 8 billion baht, after several key roads in the capital were repeatedly flooded following recent downpours.
"True, to say the giant tunnels are able to completely ward off all flooding is incorrect," said deputy Bangkok governor Chakkaphan Phewngam, in charge of water drainage. "But people need to understand our flood prevention system. I can confirm the tunnels help accelerate water drainage."
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The Rama IX tunnel was unveiled in early 2011 amid high expectations that it would be a major solution to Bangkok's flooding.
But people in the capital were not satisfied after the city continued to experience flooding after being inundated by heavy rains, especially in areas near the tunnel such as Lat Phrao Road and Vibhavadi Road.
Mr Chakkaphan admitted a mass deluge is "inevitable" if rainfall exceeds a rate of 60mm daily, but he insisted the tunnels help speed up drainage by more than half an hour.
He said rainfall from last Friday night to Saturday morning reached 214.5mm, much more than the tunnels can cope with. However, the water was pushed out quickly, helped by the tunnels.
There are eight water drainage tunnels connected to the project that are in operation. Three are giant drainage tunnels as large as 5m in diameter. These tunnels are located in Rama IX, Bueng Makkasan and Khlong Bang Sue. The Bueng Makkasan tunnel was launched in September, 2007 and the one in Khlong Bang Sue started operations in September this year.
The Khlong Bang Sue tunnel was constructed with the aim of speeding up water drainage in Huai Khwang, Din Daeng, Phaya Thai, Chatuchak, Lat Phrao, Wang Thonglang, Bang Sue and Dusit districts.
The five smaller tunnels are between one and three metres in diametre.
Mr Chakkaphan said effective tunnels have to divert water from flooded areas to the Chao Phraya River directly. However, only the one at Khlong Bang Sue meets this criteria.
It links Khlong Bang Sue to the Chao Phraya River in the Kiakkai area.
The other seven tunnels are only used to siphon water to canals or major pumping stations before being diverted to the Chao Phraya River, he said.
Referring to the BMA's flood warning system, Mr Chakkaphan said City Hall relies on three radar stations monitoring rainfall. They are in Nong Bon, Nong Chok and Nong Khaem areas.
The radars helps City Hall predict when and in which areas rain will hit the capital two hours in advance, he said, though they are unable to pinpoint how long the rain might last.
"We send staff to the areas forecast to experience rainfall so they can prepare water pumps to drain water," said Mr Chakkaphan, adding other officials are sometimes deployed later to assist people in heavily-flooded areas.
Referring to why the BMA does not focus on only building giant tunnels, the deputy governor said the capital has various other tunnels and poles underground which impede the construction of substantial facilities.
Work is, however, underway to replace drainage tunnels that are 20-30 cm in diametre with tunnels that have diametres of 1-2 metres in flood-prone areas, such as the Southern Bus Terminal in Taling Chan district and Suthiporn Soi 2 on Pracha Songkhro Road.
According to the deputy governor, the BMA is in the process of constructing a giant tunnel linking Bueng Nong Bon to the Chao Phraya River.
The 4.9-billion-baht structure, which aims to speed up the drainage in Prawet, Suan Luang and Bang Na areas, is slated to be launched in December 2019.
Three other giant tunnels are also in the pipeline. They are in Khlong Saen Saep, Klong Taweewattana and Khlong Phraya Ratchamontri.
"In the future, the BMA will try to come up with a flood defence system that can handle more than 60 mm of rainfall per day," Mr Chakkaphan said.
