Thailand's National Water Command Centre (NWCC) has issued a warning about the swelling Chao Phraya and Pasak rivers as the Pasak Jolasid Dam is doubling its discharge volume.
The Pasak Jolasid Dam fuels the Pasak River which, in turn, feeds the Chao Phraya. The dam is releasing 800 cubic metres of water per second, twice the amount discharged previously.
Riverside residents have been told to monitor water advisories.
Heavy rainfall has sounded flood alarm bells in many provinces as the monsoon trough is expected to cover the lower Central Plains Region, the East and the upper South until Sunday.
Downpours can be expected in such regions including Bangkok, according to an announcement issued by Chayan Muangsong, deputy secretary-general of the Office of the National Water Resources (ONWR).
During the next several days, a significant increase in water flowing through the Pasak Jolasid Dam in Lop Buri province is expected to cause widespread inundation. The Royal Irrigation Department has had to double the water it has been releasing from the dam to reduce pressure.
Areas stretching from the Pasak Jolasid Dam's spillway in Phatthana Nikhom district of Lop Buri to the Rama VI Dam, in Tha Rua district of Ayutthaya, are predicted to see higher water levels.
The water level of the Chao Phraya's tributaries in Ayutthaya will rise by a further 0.25-0.50 metres. Floods are also likely to be severe in parts of Bang Sai district in Ayutthaya where water in the Chao Phraya River is flowing at a rate of 3,300-3,500 cubic metres per second, causing the Noi River, its tributary, to burst its banks, according to the NWCC.
The centre also said that water from the upstream Yom and Ping rivers was raising the level of the Chao Phraya. Officials tried to divert water into the low-lying Bang Rakam field in Phitsanulok province, but the field was already full.
To reduce flooding in low-lying areas between the Chao Phraya barrage in Chai Nat province and Samut Prakan province, it is necessary to maintain the discharge rate at the barrage at 2,700-2,800 cubic metres per second, said the NWCC.
According to the Central Region Irrigation Hydrology Centre, water released by the Chao Phraya barrage was recorded at 2,668 cubic metres per second, as of 11am yesterday.
Meanwhile, the ONWR, the Royal Irrigation Department and the Disaster Prevention and Mitigation Department will consider diverting water from the Pasak River to Khlong Rapipat so it can drain quickly into the Gulf of Thailand.