PUB launches study on underground water reservoir and drainage system

Monica Kotwani, Channel NewsAsia 26 Jun 15;

SINGAPORE: The national water agency, PUB, is exploring the feasibility of constructing an underground drainage and water reservoir system which could mitigate the impact of climate change, and act as a buffer against droughts.

The move was announced by Environment and Water Resources Minister Vivivan Balakrishnan at the Singapore International Water Week (SIWW) and Innovation Summit on Tuesday morning (Jun 16).

The two-year study will look into the design of such a system, which PUB said could include tunnels to transport excess stormwater to underground caverns for storage. A pumped storage hydropower system could also be developed to harness energy from when water flows from the surface to underground caverns.

The study will include geological surveys to obtain detailed information on soil and rock properties. PUB said knowledge of such geological conditions is critical, as there are challenges involved in the construction of underground facilities. The location and development of caverns and underground reservoirs will also require suitable rock material.

The study is expected to be completed by the end of 2017.

- CNA/es

PUB to explore underground space for drainage and water storage
AsiaOne 16 Jun 15;

SINGAPORE - National water agency PUB will be studying the technical and economic feasibility of developing an integrated underground drainage and reservoir system, according to a statement from the agency.

PUB will launch a 24-month study to look at the feasibility of the system to reduce the impact of climate change and enhance resilience against droughts.

This study will look into the design options for an Underground Drainage and Reservoir System (UDRS), which could integrate three key components - stormwater conveyance tunnels, underground reservoir caverns, and a pumped storage hydropower system.

One possible option is to have tunnels to convey excess stormwater to underground caverns for storage. The caverns can add to Singapore's reservoir water storage and enhance drought resilience. In addition, the study will explore the possibility of having a pumped storage hydropower system to recover energy from the flow of water from surface water bodies to the underground caverns.

"Besides allowing us to overcome land limitations for key drainage and water storage infrastructure, the UDRS study can potentially allow us to mitigate the impact of climate change and flood risks, and strengthen the overall drought resilience of Singapore's water supply," said Mr William Yeo, PUB's Director of Policy and Planning.

There are challenges involved in the construction of underground facilities and the knowledge of underground geological conditions is critical. The location and development of caverns and underground reservoir will require suitable rock material. The study will include geological surveys to obtain detailed information on soil and rock properties.

"In carrying out this study, we will work closely with key agencies and stakeholders to ensure that the geological surveys are conducted with care and sensitivity to the environment," added Mr Yeo.

The study is expected to be completed in end-2017, according to PUB.

Singapore to look into underground reservoirs
LAURA ELIZABETH PHILOMIN Today Online 17 Jun 15;

SINGAPORE — Flood water from intense storms here that would have otherwise gone to waste could eventually be turned into another water and even power source.

National water agency PUB is exploring using underground space to collect and store excess storm water. It will call for a tender for a 24-month study on the technical and economic feasibility of developing an underground drainage and reservoir system.

The study will explore design options for the system, such as stormwater conveyance tunnels to transport water to an underground reservoir cavern. There could also be a pumped storage hydropower station that could convert kinetic energy of the water flowing in the tunnels to electricity.

Expected to be completed by the end of 2017, the study will also include a geological survey to find a location with suitable soil and rock properties.

Announcing this at the Singapore International Water Week (SIWW) Technology and Innovation Summit yesterday, Minister for the Environment and Water Resources Vivian Balakrishnan said Singapore receives about 2.4m of rainfall a year. But because of a shortage of land to capture and store rainfall, much of it is discharged into the sea. At the same time, prolonged droughts dry out the current reservoirs, leading to water shortage.

“Climate change increases the probability of both intense rainfall and prolonged periods of drought,” said Dr Balakrishnan in a speech. “ ... Consequently, an underground drainage and storage network will mitigate the impact of climate change and enhance Singapore’s drought resilience, whilst overcoming our land limitations.

“We will be able to take the excess rainfall from the storms, convey it to underground storage, harvest its energy as it percolates through those tunnels and reuse that energy later when we need to pump the water out again.”

Civil and environmental engineering experts TODAY spoke to said the caverns could be as big as five million to 50 million cubic metres, and finding the most cost-effective way of building this underground system would be the biggest challenge.

“There are no special challenges compared to typical tunnelling and underground excavation work,” said Associate Professor Tan Soon Keat, director of Nanyang Technological University’s Maritime Research Centre. “The challenge is more on the balance sheet.”

Some experts felt the reservoir should be designed as one big central cavern, while others said smaller, multiple caverns spread across an area was more cost-effective. They also differed on how deep the reservoirs should be.

Professor Lui Pao Chuen, who is adviser to the National Research Foundation and who first floated the idea in 2012, said there could be multiple caverns, starting with a first “module” of five million cubic metres and having its capacity increased over the years.

Prof Tan said keeping it relatively near the surface at 30m to 40m underground would be a good depth to move the stored water freely.

“The longer it (takes water) to pump up, the more friction you have to overcome,” he added. “Whereas in a shallower surface, there is still friction but it is manageable.”

On the other hand, Assistant Professor Chew Soon Hoe from the department of Civil and Environmental Engineering at the National University of Singapore said it may be more cost-effective to build a big central cavern. Conveyance tunnels to transport water from different areas can be built cheaper at shallower depths, he said.

A permanently half-filled underground reservoir, if located at the fringes of the more densely-populated central areas of the island, would also be useful for collecting excess storm water and alleviating floods where economic costs would be the highest. But that would require a sizeable cavern and greater depths of 100m to 150m underground, Asst Prof Chew added.

While more power is needed to bring up water from greater depths, the hydropower that could be generated from the system could come in handy. “If you need to supply power, it’s very costly,” he said. But if the water going in can generate power supply, then “the newly-generated power to pump the water up to the reservoir … would be ideal”.

Given that the caverns would require rock that is not porous, experts suggested potential sites in central and north-eastern Singapore. Prof Lui said the rock mass west of Bukit Timah Expressway may offer a few potential sites.

As for concerns about the extent of underground digging done on the island, Asst Prof Chew gave the assurance that engineers would be able to mitigate any impact on the surroundings with proper design.

“The underground still promises a great opportunity for bigger exploration ... We can afford to build a lot more at a greater depth,” he added.


PUB delves into underground reservoirs
Audrey Tan My Paper AsiaOne 17 Jun 15;

Singapore could soon be digging deep for an answer to its water challenges.

National water agency PUB is looking into creating underground reservoirs to get around the space crunch above ground, said Minister for the Environment and Water Resources Vivian Balakrishnan yesterday.

Tapping on such structures will also help the city better deal with the effects of climate change, such as more intense rain and prolonged dry spells, as excess water can be stored and used when needed.

"In Singapore, we receive an average of about 2.4m of rainfall a year... In theory, we should not be short of water... The real limiting factor is not rainfall, but land," said Dr Balakrishnan at the opening of the inaugural Singapore International Water Week Technology and Innovation Summit yesterday.

The two-day water conference, which focuses on research and development, is a prelude to the Singapore International Water Week next year.

The underground drainage and reservoir system is likely to have three key components: Tunnels to channel stormwater below ground, caverns for water storage and a pumped storage hydropower system, which can convert energy from water flowing into underground caverns to electrical energy. This can then be used to pump the water back to the surface.

Such systems have long been championed by experts here as solutions to weather fluctuations and land scarcity.

One of them, Lui Pao Chuen, a National Research Foundation adviser who spearheaded research into Singapore's underground ammunition facility, noted: "One third of Singapore is made up of granite rocks, which are very strong, and rock caverns for underground reservoirs can be constructed there."

Chua Soon Guan, PUB's deputy chief executive, said that a tender for a two-year feasibility study on building such a system will be called in the next few months. Expected to be completed at the end of 2017, it will include geological surveys on soil and rock properties, and look into the design options.

William Yeo, PUB's director of Policy and Planning, stressed that it will work with relevant agencies and stakeholders to ensure that the surveys are "conducted with care and sensitivity to the environment".

Geological studies are essential since the underground storage reservoir must be built on rock mass instead of softer soil, which may not be able to support it, said Chong Kee Sen, president of The Institution of Engineers, Singapore.

Tan Soon Keat, director of the Nanyang Technological University's Nanyang Environment and Water Research Institute, added that building in a rocky area would also ensure that there is less water loss and would prevent the water from being contaminated by soil minerals.

PUB would not comment on possible locations or other details, but the three experts believe it could be located in the central or north-eastern part of Singapore.