Tan Kin Lian's Blog: Marina Barrage

Monday, July 19, 2010

Marina Barrage

Some people think that the Marina Barrage could be the cause of the flood. Read here.

4 comments:

rex said...: REX comments as follows,

Let us take stock of the situation.
First the minsitry said it was a once in 50 years freak event.
Then it was a block culvert.
Next they say it was Typhoon Cosoon.
TODAY 20July, at last in the straits times we see the only techncial answer from discussions at the Parliament proceedings. They now say STAMFORD CANAL was not able to handle to volume of water.
What they didnt say: STamford canal discharges into Marina Bay: and, Marina bay exit to the sea is narrowed by design, to the width of Marina Barrage (mere 0.3 km).

With all the gates open there is still a massive superstructure supporting the barrage. Therefore the barrage presents an obstruction to the discharge of Stamford Canal even with all its gates blown away.

I accept the reason by the Minister, Stamford Canal can be widened and we will solve all the problems forthwith. Good, honest Logic.

But then, this wouldn't have been necessary if not for the blockage at the dam. Stamford canal was sufficiently dimensioned for the last umpteen years.

Incidentally, do we have enough land or stucutres to support the widening of Stamford canal?

If no, then, my friends, you have to either live with 50 floods a year (not 1 flood 50 years) or else do something to the dam (on 17 July, China exploded one of its dams according to the news, to relieve floods).

rex; July 20, 2010 8:48 AM
Steve Wu said...: The PUB and the MEWR (being the overseer) have found themselves wanting in the areas of flood planning, flood prevention and management. They also appear to lack the skills to reassure the public who has yet to see transparency and accountability.

1. Orchard Road flooded 3 times on 16 June 2010, 25 June 2010 and 17 July 2010. Neither PUB nor MEWR bothered to acknowledge the second flood. It required a third flood to force the admission that there was a design limitation in the Stamford Canal, along with more excuses. It should have been obvious from the first flood that things did not add up, e.g. clogged culvert was upstream, not downstream. Was PUB less than candid?

2. PUB/MEWR have released very little details about the efficacy of the Marina Barrage. The minister still thinks that tides play a part in the flooded areas in the catchment areas of the Marina Reservoir. I remind the minister that the Barrage separates the sea and hence the tides from the catchment areas. Being a doctorate in engineering, was the minister been less than candid?

3. The Barrage pumps can collectively pump 280 cubic meters per second of water out of the Reservoir during high tides. Assuming a catchment area of 25 sq.km, the rainfall of 100mm will accumulate a volume of 2.5 million cubic meters of water per hour or 41.6 thousand cubic meters per second. It should be recognized that it far exceeds pumping capability at the Marina Barrage. This means any expulsion MUST be done well ahead (hours ahead) of the flood development to make room for the accumulation.

4. There are presently insufficient water level sensors. PUB should also install speed of flow sensors. Without such sensors in the upstream canals/rivers, how can the operators at the Marina Barrage know how much water need to be released into the sea? The more often it is repeated that the "Marina Barrage is operating at the normal levels", the more People are convinced that the PUB does not know what it is doing.

5. If PUB wants to warn the public about floods, that's well and good in preparation of even larger calamity. However, if it is intended to replace the requirement highlighted in 4, then it is unacceptable. The People expects PUB to prevent floods, not just warn about them.

6. In highly built-up areas, e.g. Orchard Road, the canals must be sealed, not just covered. This means that water may only flow into the canal but not out of it. This should be PUB's responsibility. The costs may be shared by building owners by an update in the building codes. The approach of setting up flood barrier piecemeal proposed by PUB is inefficient.

7. In a PUB statement on 16 June 2010 PUB Chief Executive confirmed that Singapore has spent $2 billion on drainage works alone. This amount was also declared in parliament by the MEWR minister as reported by AFP on 19 July 2010 and other media. The question is whether this large amount of money has been effectively spent. The recent floods and the aftermath confirm the contrary.; July 20, 2010 12:01 PM
Steve Wu said...: I would like to correct a typo error in the previous post. I intend to write 41.6 thousand cubic meters per minute but wrote per second instead.

Just as well, since PUB has confirmed that the catchment areas of the Marina Reservoir total 100 sq.km (10,000 hectares) not my original estimate of 25 sq.km, we may update the potential inflow rate as about 2780 cubic meters per second. This is about 10 times the peak discharge rate that the Barrage pump station is capable of.

Of course, this simple model does not take into account of factors like ground retention. However, due to the urban build-up, we should expect to receive a significant percentage (> 70%) at the Marina Reservoir.

Pre-flood release is still necessary for intense rainfall, particularly during high tides.; July 21, 2010 11:33 AM
rex said...: REX comments as follows,

On 20th July, finally we have a good update from PUB complete with computer simulation graphics to help us understand this damn dam.

After listening to the explanation, i came to the conclusion that marina barrage pushes the sea further outward, which is a good thing, provided that the space so created is able to carry the original discharge from the drains. However, this is not necessarily a given fact. In the past, by gravity, the water drains Stamford Canal etc all eventually drain out naturally straight to sea, no problem. Orchard road may be far upstream as Mr Tan Nguan Sen of Pub had said, but still all the water has to go out to marina bay. But for some reason, now, we need PUMPS to drain out the water. I suspect that the gradient calculations were incorrect, and the construction of the bay area did not take into account the loss of natural gradeint downstream; previously available for inland canals to drain out.

Therefore, as steveWu noted, pre-flood release has to be implemented, and this is really primitive. After spending millions of dollars, we have to rely on pumps to do what nature has done in the past 40 years to drain the stamford canal rain water to sea!!!!

Another point which puzzles me is the statement that ORchard road is 4 to 5 meter above sea level. How can 4 to 5 meter above sea level get flood and sea level don't get flood? Does this not prove conclusively, that the gradient discharge to sea is not optimal and should is say not even correct?

Most countries which build dams, do so in mountainous topography's because of the need for gradient in drainage system.

I also read with amusement shops trying to build barricades, and "follow PUB advice". Hey, flood is like, cancer lah. YOU stop the cancer in the neck it pop up in the lymph node. You block the entrance to Liat Towers and Wendy's, therefore somebody else get flooded. It is a very selfish if not stupid suggestion. Every man for himself! you have no money to build barricade, you die your business!! Why dont you follow Pub advice!

Next, U shaped canal instead of V shaped, some officer suggested it. Does this help> The increase in water pressure may force more water bursting at the weakest point!! Where is the space to make the structures, there are too many buildings in the concrete jungle.

My advice: The best solution is to examine the entire gradient map of the flow towards the sea. Also to find out if canal diversions have caused high resistance paths bends.

If you have to knock down a building to straighten the canal so be it. Somebody has to admit the mistakes.

rex; July 21, 2010 8:19 PM