The flood preparedness trial must be carried out in September, insisted Science and Technology Minister Plodprasop Suraswadi yesterday.
The Water and Flood Resources Management Committee (WFRMC) has consulted with agencies _ including the Bangkok Metropolitan Administration (BMA) _ about the drainage tests to take place on Wednesday and Friday, said Mr Plodprasop, who serves as committee chairman.
The maximum volume of water that will be discharged into the canals for the drainage test is 20 cubic metres per second. Khlong Mahasawat has the highest rated capacity of 60 cubic metres per second, he said.
Therefore, water will definitely not overflow the banks of the canals and rivers, Mr Plodprasop said.
The water to be used in the test has already been set aside and stored somewhere outside the Chai Nat Dam. It is not the water in the dam now, he said.
To determine the drainage capacity of the canals, two methods will be employed, the minster said, allowing the water to flow freely and accelerating the water flow by pushing it using boat propellers.
Most canals along the drainage route from the North into the sea have been dredged and rubbish and water hyacinth have been removed, Mr Plodprasop said.
Broken sluice gates and water pumps have also been repaired as part of the flood prevention plan, he said.
The water drainage test in western Bangkok is scheduled for Wednesday. The water will be released from a reservoir near the Chai Nat Dam into the Chao Phraya River, before being diverted into Khlong Mahasawat in Bangkok.
From this main canal, the water will eventually empty into Nakhon Chaisi River in Nakhon Pathom and the Chao Phraya River in Bangkok Yai district of the capital via different routes.
The test in the eastern part of the capital will take place on Friday. Water from Chai Nat Dam will be diverted into Khlong Rapeepat in Pathum Thani before eventually being drained into the Gulf of Thailand through Makkasan swamp and through tambon Khlong Dan in Bang Bo district of Samut Prakan.
If there are signs of any problems, the exercise will be called off immediately, Mr Plodprasop said.
Prime Minister Yingluck Shinawatra defended the drainage testing plan, saying the government could assure Bangkok residents that they would not be affected.
Bangkok Governor Sukhumbhand Paribatra said he was not convinced by the government's assurances.
He called on the WFRMC to take responsibility for any possible accidents that might occur if the water drainage test does not go according to plan.
Weather forecasters say that a storm could form in the Philippines between Wednesday and Friday and this might affect Thailand, MR Sukhumbhand said.
He said the BMA now had in place its own measures to deal with possible impacts from the test.
If the test resulted in flooding problems, the BMA would reserve the right to make decisions on its own without consulting the WFRMC.
The governor said that Khlong Song and Khlong Lat Phrao run through densely populated neighbourhoods. The city administration has not yet completed repairs on seven water gates which were damaged during last year's flooding, he said.
Smith Dharmasaroja, former director general of the Meteorological Department and current member of the Strategic Committee for Water Resources Management (SCWRM), also voiced concerns over possible negative impacts of the drainage test.
To drain water from a major dam that was only 40% full now could lead to a more serious water shortage in the coming months, he said.
By December and January there will insufficient fresh water reserves to mitigate the seawater intrusion that usually is common at that time of the year, Mr Smith said.
The Stop Global Warming Association, an environment advocacy group, also called on the government to consider cancelling the drainage test for fear it could affect people living along the canal banks.