The Royal Irrigation Department (RID) has pledged to spare Bangkok from severe flooding after the capital was hit with the heaviest rainfall in more than 30 years.
RID director-general Somkiat Prajamwong insisted on Saturday his agency would not allow a huge amount of water to hit the capital, vowing runoff would be diverted to other provinces.
His comments came as the capital was pounded overnight from Friday to yesterday with the heaviest recorded rainfall since 1986, causing flash floods in several parts of the city.
Heavy rains hit Bangkok from 11pm on Friday to 6am on Saturday, with additional downpours in the afternoon, causing floods in 55 spots in the capital.
The heaviest deluge was recorded in Phra Nakhon district, which received an average of 214.4mm of rain per hour, followed by Phasi Charoen district with 214mm of rain per hour and Bangkok Noi district with 208mm of rain per hour.
Bangkok governor Aswin Kwanmuang said the last time Bangkok faced more than 200mm of rain per hour was in 1986 when Maj Gen Chamlong Srimuang was governor. At that time, 270mm of rain per hour was recorded, he said.
On Saturday, the most critically flooded spots were reported on Vibhavadi Rangsit Road and Mit Maitri Road. Other major roads, including Sri Ayutthaya, Ratchaprarop, Rama I and Phaya Thai, were also submerged.
Some parts of the downtown area were also affected, including the high-rent Thong Lor region and the home of former prime minister Abhisit Vejjajiva.
Mr Abhisit, who lives in Sukhumvit Soi 31 in Watthana district, sent a message via the Line application that his house had been flooded for the first time and that his car had been damaged.
In Thong Lor, several condominiums reported flooding in basement-level car parks, with scores of vehicles damaged.
Pol Gen Aswin offered an apology to Bangkokians who bore the brunt of the deluge.
"I want to apologise to people for being troubled by flooding," the governor said. "With a substantial amount of rainwater and a high volume of water in the canals, the water drainage could not be fully made and it took more time to do so."
He insisted Bangkok Metropolitan Administration (BMA) officials worked at full force to deal with the problem but the severity of the downpour exceeded predictions.
RID head Mr Somkiat meanwhile promised Bangkok would not be hit by runoff from excessive river levels building upstream.
He said excess water in the Chao Phraya River will be diverted to Khlong Chai Nat-Pasak above the Chao Phraya barrage dam in Chai Nat province. This water would pass through Lop Buri, where it would be funnelled to the Rama VI Dam in Tha Rua district of Ayutthaya before flowing to Khlong Rapipat in Saraburi.
The water would then flow to Khlong Phra Ong Chao Chiayanuchit and the Bang Pakong River in Chachoengsao, where it would be pushed out towards the sea through small canals.
Various waterways in Pathum Thani, which receives water from upstream, would also be diverted to the Chao Phraya in the Rangsit area via Chulalongkorn sluice gate, where high-powered water pumps are deployed, Mr Somkiat said.
Excess Chao Phraya water would also be pushed out to sea via Chonlahan Pichit sluice gate at tambon Khlong Dan of Samut Prakan's Bang Bo district. The Khlong Lat Pho sluice gate in the same province will also be used as a shortcut for the river to the sea, the RID chief added.
Governor Aswin said the Chao Phraya Dam is discharging 2,300 cubic metres of water per second. He said the capital can cope with this as Bangkok's maximum capacity to handle the water is 3,500 cu m of water per second.
He however expressed concerns about 18 communities outside the Chao Phraya River embankment zone, saying they could risk facing overflow.
The governor denied social media reports that Khlong Saen Saep will be used to push out water to the sea, saying this is groundless. The drainage chiefly relies on the Chao Phraya River.
City Hall's Department of Drainage and Sewerage said four locations remained submerged on Saturday. They were Asok intersection, Phetkasem Soi 37, areas around Khlong Yai Pian in Phasi Charoen district, and Vibhavadi Rangsit Road, which remained under some 30cm of water for much of SaSaturday.
First Army region commander Kukiat Srinaka said his region has prepared tools and personnel to be deployed to help flood-stricken people and that military officers helped remove vehicles stranded in floodwater on Saturday.