Main northern water flow takes 2–3 days to reach Bangkok

Heavy rainfall from tropical storms has filled Thailand’s major northern rivers and reservoirs close to capacity, forcing increased water releases downstream. The Royal Irrigation Department reported that four major dams — Bhumibol, Sirikit, Pa Sak Jolasid, and Khwae Noi — are nearly full, prompting high-volume discharge from the Chao Phraya Dam at up to 2,800 cubic metres per second while reducing outflow from the Pa Sak Jolasid Dam to minimise impacts on Ayutthaya and Bangkok.

Northern runoff and dam conditions

Recent weeks of heavy rain have caused severe flooding in northern provinces including Phrae, Nan, Chiang Rai, Sukhothai and Lampang. Water from the Ping, Wang, Yom and Nan rivers continues to flow into the central plains, converging at Nakhon Sawan’s C.2 hydrological station, where the water level remains stable.

As of 6 am on November 10, the main Chao Phraya Basin dams recorded:

Bhumibol Dam: 13.32 billion m³ (99% full), inflow 98.6 million m³/day, discharge 44.9 million m³/day.

Sirikit Dam: 9.28 billion m³ (98%), inflow 13.5 million m³/day, discharge 10 million m³/day.

Khwae Noi Dam: 0.95 billion m³ (101%), inflow 7.8 million m³/day, discharge 5.2 million m³/day.

Pa Sak Jolasid Dam: 0.93 billion m³ (97%), inflow 12.6 million m³/day, discharge 25.9 million m³/day.

At the C.2 station in Nakhon Sawan, flow was 2,965 m³/s, 0.91 m below the riverbank, while the Chao Phraya Dam in Chai Nat discharged 2,800 m³/s, with upstream and downstream levels at +17.70 m and +16.49 m MSL respectively.

Flow timeline from Chao Phraya Dam to Bangkok

Chai Nat → Sing Buri: ~10 hours

Sing Buri → Ang Thong: ~8 hours

Ang Thong → Ayutthaya: ~6 hours

Ayutthaya → Pathum Thani: ~8 hours

Pathum Thani → Nonthaburi–Bangkok: ~24 hours

In total, runoff from the Chao Phraya Dam takes around 2.5 days (139 km) to reach Pathum Thani and another day to arrive in Bangkok.

Management and impact outlook

Irrigation officials are diverting as much water as possible into eastern and western irrigation canals, currently at a combined intake of 590 m³/s, to ease pressure downstream. The department confirmed that the current release rate represents the seasonal peak and is being closely monitored.

Although northern inflows remain high, authorities stressed that the combined flow of the Chao Phraya and Pa Sak rivers at Bang Sai — about 2,700 m³/s, or 68% of river capacity — is unlikely to flood Bangkok or its vicinity.

Communities outside flood barriers along the Chao Phraya River in Chai Nat, Sing Buri, Ang Thong, Ayutthaya, Pathum Thani, and Nonthaburi remain under close watch as the water crest moves southward.

Sources: Royal Irrigation Department; Office of the National Water Resources