City Hall is warning Bangkok residents to brace for possible flooding when the Chao Phraya Dam in Chai Nat increases its discharge rate next month in response to increasing water run-off from upstream provinces during the rainy season.
Bangkok Governor Chadchart Sittipunt said riverside communities where flood walls have yet to be constructed due to opposition from landowners will be particularly vulnerable to floods, especially during high tides.
To date, City Hall has built 88 kilometres of flood walls across the city, which are 3.5 metres high. These walls, it said, will protect riverside communities as long as the discharge rate from upstream does not exceed 2,000 cubic metres (m³) per second.
When Bangkok was flooded during the catastrophic floods in 2011, water from the North flowed at a rate of 2,200-2,500m³ per second, the governor said.
At present, the discharge rate is capped at 1,000 m³ per second as the situation upstream is not considered critical, though the Royal Irrigation Department is closely monitoring the dam's water level, Mr Chadchart said, adding once the discharge rate is adjusted, it will take about seven days before the added flow reaches Bangkok.
The governor said there are more than 20 gaps in the city's flood walls, which renders some communities particularly vulnerable to flooding when water level rises during high tides.
City Hall, he said, is working on plugging 10 of the gaps, though work on these sections may not be finished this year.
Some of these gaps cannot be sealed for the time being due to opposition from private landowners, he said. In one such property off Songwat Road, the gap stretches for 18 metres.
To minimise the risk of flood in these areas, sandbags will be temporarily placed.
Separately, the Department of Disaster Prevention and Mitigation is urging residents in Uthai Thani, Chai Nat, Sing Buri, Ang Thong, Suphan Buri, Ayutthaya, Lop Buri, Pathum Thani, Nonthaburi and Bangkok to watch out for sudden increases in water levels along the Chao Phraya River on Wednesday.
The RID is discharging more water through the Chao Phraya Dam following recent heavy rainfall in the North, bringing the rate up to 1,050-1,150m³ per second, it said, adding water levels downstream may rise by 60-80 centimetres.