PUB to study underground drainage and reservoir system in Singapore

NATIONAL water agency PUB will be studying the technical and economic feasibility of developing an integrated underground drainage and storage system to boost its water and energy sustainability.

The city-state has a limited land area of 718 square kilometres to capture rainfall, and most of the excess rain is discharged into the sea.

The 24-month 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, PUB announced at the Singapore International Water Week on Tuesday.

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, PUB said in a statement.

William Yeo, PUB's director of policy and planning, said: "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."

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

"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," Mr Yeo added.

The study is expected to be completed in end-2017, and findings from the study will help PUB decide whether the UDRS can be pursued further.

PUB will be working with the Ministry of National Development for the study and will be rolling out tenders to the industry in the next few weeks.

An underground drainage and reservoir network was also one of the seven "realistic ways" to achieve water and energy independence by 2061, as highlighted by Minister for Environment and Water Resources, Dr Vivian Balakrishnan, at SIWW's opening address on Tuesday.

Singapore receives 2.4 meters of rainfall each year, which in theory, is sufficient for the country. But what is limited to Singapore is the land to capture the rainfall. "There is not enough to store all the water that falls during a storm or a rain," Dr Balakrishnan said.

In addition, there is hope to harvest some energy from the falling rain through low intensity turbines.

It presently costs about 3.5 kilowatt hour to produce one cubic meter of water through reverse osmosis, and Singapore satisfies over 95 per cent of its energy use through natural gas imports.

By the next decade, Singapore aims to halve its energy imports by improving its energy efficiency and though renewable energy.