"Many areas of Bangkok were heavily flooded following heavy rain on Tuesday, as Bangkok Governor Sukhumbhand Paribatra said the giant tunnel does work and floating debris does not obstruct the draining process.
Traffic police said the flood levels in parts of Bangkok such as Sutthisarn, Din Daeng, Don Muang, Pracha Rat Bamphen and Phaya Thai were as high as 80 centimetres.
The flooding caused heavy traffic congestion in many areas of the capital city.
The Bangkok Metropolitan Administration posted a message on the social networking site Twitter apologising for the delay in its drainage effort.
"All workers are doing their best to alleviate the problem for the people of Bangkok," the BMA said."