The Chao Phraya River barrage, which controls the water flow from the North to the Central Plains Region and Bangkok, is releasing more water as heavy downpours are expected this week.
A large volume of water has been accumulating from the North which has been hit by heavy rainfall. The water has flowed downstream, forcing the Chao Phraya barrage in Chai Nat to discharge more water on Wednesday.
The barrage is now discharging 1,692 cubic metres of water per second, pushing up the water level in the Chao Phraya River by 29 centimetres.
Bearing the brunt are downstream provinces from Chai Nat to Ayutthaya where low-lying areas are being inundated.
Waterways have burst their banks in Klong Phon Pheng in Ang Thong and Klong Bang Ban in Ayutthaya -- where vast tracts of farmland are being flooded in tambon Hua Wiang of Sena district, tambon Talad Chid and Tha Din Daeng in Phak Hai district.
Flood warnings and advisories have been issued for residents along the Chao Phraya in flood-prone provinces.
Chavalit Chalom, director for water management at the Royal Irrigation Office 12, said the Chao Phraya has swollen to risky levels in Muang district of Nakhon Sawan.
Plans were in place to gradually slow the water flow to minimise the impact on farmland, he said.
"What we are watching out for is the heavy rainfall over the Chao Phraya River basin forecast for Sept 5-7," he said.
"We could see the Chao Phraya barrage accelerate the rate of water it releases to at least 1,800 m3/s," Mr Chavalit said, urging riverside residents to keep a close eye on flood warnings.
Thongplew Kongchun, the agriculture permanent secretary, said this year's water-related risks pale in comparison to the lead-up to the great floods of 2011.
He was responding to remarks by Seri Supharathit, director of the Climate Change and Disaster Center at Rangsit University, that the accumulated precipitation in the current rainy season is similar to that seen 11 years ago.