Is Singapore's Deep Tunnel Sewerage System viable given rising groundwater?

 by Ganesh Sahathevan 

Singapore's Public Utility Board  says it is building a used water superhighway for the future, the Deep Tunnel Sewerage System (DTSS). The DTSS is a cost-efficient and sustainable solution conceived by PUB to meet Singapore’s long-term needs for used water collection, treatment, reclamation and disposal. DTSS is a key part of our long-term used water system which comprises a network of link sewers leading to two major tunnels (Phase 1 & 2) criss-crossing Singapore with three large WRPs at the northern (Kranji), eastern (Changi) and western (Tuas) ends of Singapore, as well as outfall pipes. Both deep tunnels have diameters of up to 6 m and stretch across Singapore at depths of up to 55 m underground.

In Singapore, the groundwater level is about 1–3 m below the ground surface due to the considerable precipitation and the low elevation.The figure below shows the  distribution of main geological formations in Singapore

In December 2021 MIT's Technology Review alerted readers to the probability that higher sea levels will push the water table up with them, causing flooding, contamination, and all manner of unseen chaos (see story below).

The Singapore Government has made climate change and rising sea level policy priorities. However, the issue of rising groundwater seems to have been ignored, even in projects like the DTSS which go 55m underground.

TO BE READ WITH 

Saturday, July 16, 2022

A seawall may not save Singapore from rising sea levels-The real problem may be rising groundwater that will make Singapore uninhabitable

 by Ganesh Sahathevan 

                                                                                    NDR 2019: Singapore may build polders, dykes to                                                                            protect eastern coastline from rising sea levels

In December 2021 MIT's Technology Review published an article under the headline
How rising groundwater caused by climate change could devastate coastal communities : Higher sea levels will push the water table up with them, causing flooding, contamination, and all manner of unseen chaos.

The gist of the story is this:


For something you’ve probably never heard about, rising groundwater presents a real, and potentially catastrophic, threat to our infrastructure. Roadways will be eroded from below; septic systems won’t drain; seawalls will keep the ocean out but trap the water seeping up, leading to more flooding. Home foundations will crack; sewers will backflow and potentially leak toxic gases into people’s homes.

Any coastal area where “the land is really flat, and the geology is [the kind of] loose material that water moves through really easily,” says (Kristina Hill, an associate professor at the University of California, Berkeley), is “where this is really going to be a problem.” This includes places like Miami, but also Oakland, California, and Brooklyn, New York. Silicon Valley communities like Mountain View are susceptible to groundwater rise, as is Washington, DC. Worldwide, the area at risk includes portions of northwestern Europe and coastal areas of the United Kingdom, Africa, South America, and Southeast Asia.

Hydrologists are aware of the problem and it’s all over the scholarly research, but it has yet to surface in a significant way outside of those bubbles.

The Government Of Singapore has made climate change mitigation a priority and has estimated that a 100 Billion Singapore dollars will be required for mitigation initiatives which are to include Dutch style polders, sea walls, and raising coastal ground levels.

Nothing has been said about protecting the country and its vast underground network of commercial property , infrastructure including an extensive transport system from rising groundwater. Then again, contemplation of the problem may cause a revaluation of commercial and residential property values.

Ultimately Singapore residents will have to ask if their island can remain habitable.   
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