A Barrage just dont hold water.

"To alleviate the risk of flooding in low lying areas of the city, the Marina Barrage has been in operation since 2008. It has served to remove tidal influence at the Stamford Canal outlet. During heavy rain, up to 9 gates and 6 pumps at the barrage will be operated to discharge excess storm-water to the sea. .."

~~ Response by Minister for the Environment and Water Resources Dr Yaacob Ibrahim in Parliament on Flash Floods. 19 Jul 2010.

I checked in Wiki, the common primary functions of a barrage are:
a) Increase the depth of a river (similar to a weir),
b) Maintain a separation between fresh and salt water,
c) Reduce the risk of tidal flooding up the river.

Secondary functions may include:

e) Tidal power generation,
f) Artificial whitewater leisure centres.

Curiously, I wondered: What is the difference between having the barrage at the mouth of Marina Channel as compared when without it in terms of flood control capability among low lying areas in the city?

Below are the stats for rainfall in Singapore recent years. We have seen heavier rainy days in 2003 and 2006.

Reference:
1. SingStat - Yearbook of Statistics Singapore 2009, Monthly Digest of Statistics Singapore Jul 2010.
2. Diary of a Singaporean Mind.