Mechanics: How it flooded in Orchard Road

Causes of flooding in Orchard Road

1) Heavy storms and high rainfall

 About 100mm of rain fell in the central parts of Singapore between 8am and 11am on Wednesday. This was more than 60 per cent of the average monthly rainfall for June.This time, flooding occurred because of the pattern of rainfall: An intense amount of rain in short bursts at about 9.30am and at 10.30am.

2) A blocked culvert

A culvert is a drain that diverts water. The culvert, which is 2.7m in width and depth, diverts water from drains in Nassim Road and Cuscaden Road into two sections of Stamford Canal, which runs along Orchard Road. However, there was a blockage which caused the flood that submerged Orchard Road in knee-high water.

This was because there was a heavy storm on Wednesday, thus a lot of debris - such as leaves, branches and litter – was being swept into the culvert, causing part of it to be clogged. As a result, water could not flow into Stamford Canal's smaller section, which stretches from Delfi Orchard to Lucky Plaza and it flowed into the canal's other section stretching from Orchard Parade Hotel to Liat Towers and Wisma Atria. It was unable to handle the full load despite being larger.

The first burst of rain washed the debris into the culvert, but there was insufficient rain in the ensuing hour. Flooding occurred because of the pattern of rainfall: An intense    
amount of rain in short bursts at about 9.30am and at 10.30am.

The next burst of rain then washed more debris into the culvert, aggravating the initial blockage and clogged a third of the culvert.