Prime Minister Yingluck Shinawatra insisted yesterday the tests "must be done" in order to know whether the canals in western and eastern Bangkok can effectively drain run-off from the North, expected later this year.
Under the plan, the government will tomorrow release more water from the Chao Phraya in Chai Nat province into the capital. Water will flow into Khlong Mahasawat and Khlong Bangkok Noi in western Bangkok before emptying into the Nakhon Chai Si River.
On Friday, discharge will flow into floodways in eastern Bangkok and may reach Khlong Song and Khlong Lat Phrao.
Though Water and Flood Management Commission (WFMC) chairman Plodprasop Suraswadi has told the public the amount of released water will be small, many people are still worried about the tests, according to an Abac Poll which has interviewed more than 2,000 people in 17 provinces, including Bangkok.
Ms Yingluck assured people yesterday the tests would be stopped immediately if the water volume becomes difficult to control.
Asked whether Bangkok will be saved from flooding this year, the premier said the government "will wait for the test results" before making any prediction.
The WFMC will today conduct a final check on watergates and water-controlling devices at Khlong Thawi Watthana in preparation for tomorrow's test.
"We want to make sure that all sluice gates can be closed immediately if needed, such as if there is heavy rainfall," said Royol Chitradon, chairman of the WFMC's sub-committee on water situation analysis.
Under the test plan, sluice gates at Khlong Thawi Wattana will be opened to receive water flow from Nakhon Pathom province. The water will be then channelled to Khlong Bang Phai, Khlong Bang Wag and to a water pumping station at Khlong Phraya Ratchamontri, before heading out to sea.
Water measuring devices had already been installed at Khlong Thawi Watthana, while 14 water-pushing machines will be set up in other canals to speed up water flow, Mr Royol said.
The tests have City Hall on alert for a worst-case scenario in which the capital may simultaneously encounter additional water from heavy rain.
"Who can ensure rain will not fall in the morning [of the testing day]?" asked Bangkok Governor MR Sukhumbhand Paribatra. "No one can really control water levels in canals."
City officials have been ordered to monitor canals in areas prone to flooding during the tests. They include those near the bottleneck section of Khlong Thawi Watthana, near Phetkasem Road in western Bangkok and Khlong Lat Phrao in the east.
Areas under close watch include the Sena Nikhom and Chokechai Si areas in Chatuchak district, said Ukrit Klonsukhon, of the City Hall's Department of Drainage and Sewerage.
Mr Plodprasop said the encroachment of some houses on the city's canals presented difficulties to state water management and drainage there.
The cabinet wants the Social Development and Human Security Ministry to build new housing estates for these householders, but the relocation of residents would be on a voluntary basis, Mr Plodprasop added.