Khlong Rangsit Prayoonsak overflowed slightly near the mouth of Khlong 1 yesterday. It flooded the compound of the Pun Thao Kong shrine there.
Decha Klinkusum, deputy mayor of the Rangsit municipality, said the flood might have resulted from persistent rain and the increasing discharge of water into the khlong by the Irrigation Department.
He ordered municipality workers to tell people living by the canals to move their belongings to higher places.
Thongpleaw Kongjan, director of the Irrigation Department's Hydrology and Water Management Bureau, said his bureau directed water to Khlong Rangsit Prayoonsak yesterday to prepare for the government's drainage test in the eastern part of Bangkok today.
The test in the capital will take place in the Khlong Lat Phrao, a drainage tunnel and the Khlong Saen Saep.
Mr Thongpleaw said the government and the Bangkok Metropolitan Administration would test the capacities of propellers that push water into the drainage tunnel that adjoined Khlong Saen Saep as draining into the tunnel had failed last year.
Nineteen propellers have been installed in Khlong Lat Phrao and Khlong Bang Khen in Bangkok.
Mr Thongpleaw said the test should not pose a problem because the flow into Khlong Lat Phrao would run at only at 3-4 cubic metres per second and the water level of the canal was one metre lower than its banks.
However, he admitted that rain would be a factor that could prompt the government to reconsider the drainage test.
Prime Minister Yingluck Shinawatra said yesterday if it rained heavily, the drill could be called off. She said a test took place on the western side of Bangkok on Wednesday and the government used a limited amount of water to prevent negative impacts. She said the test was aimed at gauging downstream drainage capacities in particular.
Sanya Cheenimit, director of the Department of Drainage and Sewerage of the Bangkok Metropolitan Administration, said rain increased the level of Khlong Lat Phrao yesterday and if it continued today, it might affect the drainage exercise.
His department tried to minimise water in the eastern part of Bangkok yesterday to prevent problems.
Accelerated drainage took place throughout Wednesday night in the western part of the capital and water levels nearly fell to normal after the earlier drainage drill on Wednesday.
Somchai Baimuang, deputy director-general of the Meteorological Department, said rain would decrease in Bangkok today so it would not affect the drainage test in the eastern part of the capital.
Meanwhile, Chaiyaporn Thampakdi, irrigation chief of Ang Thong province, said water discharge was increased from the Chao Phraya dam to the Chao Phraya River in Chai Nat province to relieve floods in the upper North that resulted from persistent rains.