Letter from Young Joo Chye Director, Policy and Planning, PUB
Today Online 18 May 12;
THE national water agency, PUB, thanks Mr Paul Chan for his letter "Deepen reservoirs to increase capacity" (May 14). PUB concurs with his suggestion to harness water in the remaining streams and rivulets near the shoreline.
Since 2007, PUB has been researching the use of variable salinity technology to obtain potable water from rivulets and brackish water at the shoreline.
This new technology integrates processes that are well established in both sea water desalination and NEWater recycling.
PUB currently operates a pilot variable salinity plant with a capacity of 4,500 cubic metres per day at Sungei Tampines. The results have been promising, and PUB envisages using more of this technology to increase our yield from local water sources.
Mr Chan is also correct in emphasising the importance of maximising storage capacity. Dams in our reservoirs have been built as high as the topography of the areas allowed.
PUB monitors the depth of our reservoirs through regular hydrographic surveys and dredges sediments in the reservoirs when necessary. PUB has also optimised the catchment and storage capacity of our water network by active linkage of complementary reservoirs.
PUB will explore ways to further increase the yield of our local water sources, including deepening existing reservoirs and the construction of new reservoirs or even underground caverns.
However, we must be careful to choose the most cost-effective method, using the best available technology at that point. This requires long-term planning, innovative research and prudent investment in infrastructure.
PUB welcomes suggestions, and members of the public can call our 24-hour call centre at 1800-2846600 or email PUBone@singnet.com.sg.
Deepen reservoirs to increase capacity
Letter from Paul Chan Poh Hoi
Today Online 14 May 12;
I WAS impressed with the recent thought-provoking idea from former chief defence scientist Lui Pao Chuen that building underground reservoirs in rock caverns could increase our rainwater storage capacity by 10 million cubic metres.
This may increase rainwater harvest by 1.67 per cent of our annual consumption of about 600 million cu m.
Based on his estimate, though, of S$1 billion to build 20 rock cavern reservoirs 100 metres below ground, the return on investment seems expensive in terms of water storage cost.
Even if we were to amortise infrastructure costs over 50 years, the price for one cubic metre of free rainwater would still be more than S$2 per cu m, considering the energy costs to pump the water up and the annual maintenance of the facilities.
Perhaps better alternatives could achieve incremental storage capacity with less capital outlay.
To boost our catchment area and rainwater collection, we could harness water from the remaining streams and rivulets near the shoreline, using available technology to treat water of varying salinity.
To increase storage capacity, we could deepen shallow reservoirs instead of going underground, since enlarging their surface areas are not an option.
Increasing reservoir depth by 20 per cent through dredging would give us another 28 million cu m of fresh water, based on the storage capacity (140 million cu m) of our 14 older reservoirs.
This would boost our first national tap without an increase in surface evaporation. Between dredging on the surface and digging underground to store more rainwater, the former is cheaper and would not involve any recurring and maintenance costs.
