As part of the government's efforts to bolster the capital's flood defences, the Bangkok Metropolitan Administration (BMA) is seeking help from the army and Royal Irrigation Department to dredge the Lat Phrao and Saen Saeb canals.
Bangkok governor Chadchart Sittipunt joined volunteers at a clean-up event along Phai Sing To canal on Sunday when he gave details of the plan.
He said Prime Minister Prayut Chan-o-cha has told the army's commander-in-chief, Narongphan Jitkaewthae, 1st Army Area Commander Lt Gen Suksan Nongbualang and the Directorate of Civil Affairs to arrange help to dredge the canals.
Many canals across the city are on the verge of overflowing after the torrential rain over Bangkok on Wednesday deposited massive amounts of precipitation into their courses.
City Hall will start dredging Lat Phrao canal on Monday to help optimise its capacity before more rain falls.
"We must do whatever we can now. Afterwards, we will focus on drainage tunnels as part of our long-term plan," the governor said.
Mr Chadchart said optimising the canals' capacity is important because all water on the street level ultimately drains into the city's canal network.
Drainage tunnels, he said, will only improve flood defences by about 10%.
The BMA will also set up more water pumps to help divert water into larger waterways, including the Chao Phraya River, the governor added.
The Regional Irrigation Office 11 is also draining excess water from Bangkok to Bang Pakong River in Chachoengsao through Prawet Buri Rom and Nong Chok stations, according to the office.
Excess water is also being pumped into the Gulf of Thailand through a network of canals by the coast to avoid overwhelming waterways connected to the river.
Separately, RID director-general, Prapit Chanma, said the department will closely monitor the weather forecast and water levels across Bangkok over the next couple of days.
According to the Thai Meteorological Department on Sunday, showers are forecast across 60% of Bangkok and its adjacent provinces on Monday.
Waves of up to two metres are expected across the upper Andaman Sea, while conditions are slightly less severe in the lower Andaman and the upper Gulf of Thailand, with waves of up to a metre.
The TMD also warned people to brace for flash floods as heavy rainfalls was reported in some areas in the North, Northeast, Central Plains, East and western parts of the South.
Meanwhile, the Office of the National Water Resources (ONWR) is closely monitoring the flood situation in Phitsanulok, Phichit, Lampang and Uttaradit, which were hit by torrential rain, its secretary-general Surasri Kidtimonton said.