Marina Barrage not the cause of floods: PUB

Hoe Yeen Nie Today Online 21 Jul 10;

SINGAPORE - Recent flash floods have prompted MPs and some Singaporeans to ask if the Marina Barrage was doing its job.

And the PUB's reply is yes.

At a media briefing yesterday, the national water agency said data showed that during the two-hour storm on Saturday morning, the water level at the Barrage was within its capacity limits.

The range is determined by several factors, including sea levels during low and high tides.

PUB's director of Catchment and Waterways Tan Nguan Sen said if the water level in the reservoir exceeded its upper limit, water will be drained out, either by opening the flood gates, or by pumping the water out.

Data shows that at 5.30am that Saturday, the flood gates were activated. By then, it had been raining for an hour.

On the other side of the Barrage, the tide was also falling, and by 6am, the tide had fallen to below the water level in the reservoir. This allowed all eight gates to be opened fully so that the excess storm water could flow out.

Mr Tan added that the Barrage helped prevent severe flooding in the immediate downtown areas, though not in places that are further upstream, such as Orchard Road. Hoe Yeen Nie

July rainfall volume within Marina Barrage capacity: PUB
Hoe Yeen Nie Channel NewsAsia 20 Jul 10;

SINGAPORE: Recent flash floods have prompted Singaporeans to question if the Marina Barrage is doing its job.

At a briefing Tuesday, national water agency PUB explained it has done so - citing Saturday's downpour as an example.

The intensity of Saturday's early morning rain caught everyone off-guard.

When the two-hour storm ended, more rain had fallen than what the whole of July normally sees.

It was the third time in a month that severe rainfall had caused flash floods in parts of the island.

PUB data shows that despite the rising water level, the volume was well within the reservoir's capacity.

At 5.30am, the flood gates were activated.

By then, rain had been pouring for an hour.

On the other side of the Barrage, the tide was also falling, and by 6am it was below the water level in the reservoir.

All eight gates were then fully opened to let excess water out.

The decision to drain water out of the reservoir, and how much to drain away, depends on several factors. These include how fast water level in the reservoir is rising, and if the level remains within an acceptable range. PUB says it also has to ensure that there is enough water in the reservoir to meet Singapore's drinking needs.

Tan Nguan Sen, director of Catchment & Waterways, PUB, said: "The Marina reservoir was built for two main functions. One is to act as storage for fresh water, and the other one is for flood control purposes. For flood control purposes we want to keep the reservoir as low as possible, whereas as a storage for fresh water we want to keep it as high as possible."

PUB says if the level in the reservoir exceeded its upper limit, water will be drained out, either by operating the floodgates or the pumps.

But the Barrage may not release water every time it rains.

Mr Tan said: "Unless it is very sudden heavy rain, and we see that the water level is rising very much faster, we will as an added precaution release the water. We'll only release the water up till the lowest operating level that we have."

He also said the Barrage helped prevent severe flooding in the immediate areas downtown, though not in places further upstream, like Orchard Road.

- CNA/jm

Barrage 'won't affect Orchard Rd'
Straits Times 21 Jul 10;

THE Marina Barrage can prevent flooding only in low-lying areas, and not in places such as Orchard Road, which lies above sea level.

So suggestions that it was somehow responsible for the flooding along Singapore's premier shopping street recently are off-base, national water agency PUB said yesterday.

Mr Tan Nguan Sen, PUB's director for catchment and waterways, said: 'Orchard Road is very far upstream and 4m or 5m above sea level, and it cannot be affected by the barrage, which prevents the Marina area from being flooded by keeping out the high tide.'

In response to media queries, he explained that the barrage did not affect the way rain drained into the canals, which are built to slope down towards the Marina Reservoir.

Before the barrier was built, low-lying areas such as Little India were more flood-prone when a high tide coincided with heavy rain.

Mr Tan said the barrage did what it was supposed to do very well last Saturday, when Singapore was lashed by a storm and widespread flash flooding occurred over the central and eastern parts of the island. Without the barrage, things would have been much worse, he said, as the storm occurred just as a high tide was receding.

Explaining how the barrage works, Mr Tan said the level of the Marina Reservoir is kept between that of the high and low tides.

The barrage's nine gates and its seven pumps are used only when the level of the reservoir rises to the higher end of this range.

The gates are used when the sea level is lower than that of the reservoir, and the pumps, when the sea level is higher than the reservoir's.

Last Saturday morning, the reservoir was at its usual level, PUB said yesterday, but the sea level was much higher as the tide was high.

The storm began at 4.30am that day, and about 20 minutes later, the National Environment Agency issued a heavy rain warning. These warnings are issued if rainfall is expected to exceed 50mm over at least 20 per cent of Singapore, up to a duration of two hours.

About 10 minutes after the warning was received, PUB staff began to partially open eight of the barrage's nine flood gates - the last one was undergoing maintenance at the time - as the reservoir level was rising. The process took about 15 minutes.

Thirty minutes later, the gates were opened fully as the tide had receded, and the seawater level fell to below that in the reservoir.

Mr Tan said that although the volume of water coming into the reservoir from the various canals is not measured, the fact that the water drained quickly from the reservoir meant it was not overwhelmed by the deluge.

VICTORIA VAUGHAN