Imagine trying to hoist a giant door and installing it so that it rests precisely on the hinges of the door post. A centimeter off and the door probably would not open and close properly.

That was the experience 40 men had when they installed the crest gate for the Marina Barrage. Except they could only afford to be two millimeters off, which is barely the thickness of two credit cards stacked together.

The size of the "door"? It was 29.75 metres wide and five metres high. A heavyweight, it weighed 70 tonnes which is roughly the weight of 1000 men.

This was the crest gate for the Marina Barrage, which boasts a series of nine crest gates. Marina Barrage is a unique 3-in-1 project that will bring about three important benefits: a source of water supply, flood control and a new lifestyle attraction in the heart of the city.

The crest gates fulfill an important function as they act as a tidal barrier to keep seawater out, preventing flooding in the low-lying city areas. In a series of nine, these gates will usually be closed, and lowered during heavy downpour and low tide to release excess water into the sea. If the heavy downpour coincides with high tide, the gates will be kept closed and drainage pumps will channel the excess water out to the sea.

The first four crest gates were successfully installed in September 2006. Each gate took an average of eight hours to install and involved 40 men.

Mr Yap Kheng Guan, the Director of Marina Barrage, said, "It is quite an operation as you have to use a 400-tonne crane barge to lift the 70-tonne crest gate from a barge outside the working area and put it on concrete bedding where there are nine pivots waiting for this gate to be lowered onto. The whole operation has to be done with little room for mistakes. In fact, the tolerance for mistakes is like two millimeters - almost precision engineering."

The successful installation of the fourth crest gate marks an important milestone in the first phase of this project. In the next phase, another marine cofferdam will be built on the Marina South side to enable the installation of the remaining five crest gates.

The Marina Barrage will create Singapore's 15th reservoir and the first in the city. Over an estimated period of one to two years, it will be converted into a freshwater reservoir that will be part of the local catchment water supply. It has the most urbanised and largest catchment at 10,000 hectares or one-sixth the size of Singapore.

By SU PEI LIN