NSL train disruption: Malfunctioning water pump system to blame for flooded tunnel

SINGAPORE — A water pumping system that broke down was to blame for the MRT underground tunnel flooding that completely shut down train services along six stations on the North-South Line (NSL) from Saturday evening to Sunday (Oct 8) afternoon, affecting thousands of commuters in one of the worst outages since 2011.

The Land Transport Authority (LTA) revealed this in an update Sunday evening, although it said it was still looking into how this had happened. Details on when the water pumping system, which should have siphoned off rainwater buildup in an adjacent sump pit, was last maintained were not given.

The malfunction allowed water to overflow from the storm water sump pit during a torrential downpour on Saturday afternoon, and enter the tunnel through the rail tracks where trains from Bishan MRT station go underground towards Braddell MRT station.

SMRT, which operates the NSL, was forced to deactivate the trackside power supply as a safety precaution, halting services from Ang Mo Kio to Newton, both ways, from 5.33pm. The clearup of the flooding in the tunnel involved officers from the Singapore Civil Defence Force (SCDF) and PUB working overnight alongside LTA and SMRT officers, and took nearly five hours longer than initially hoped. Normal service resumed at 1.50pm Sunday, after the water pumping system was repaired, and trackside equipment were inspected, cleaned, replaced and tested.

The LTA said checks have also been conducted on other tunnel portal pump systems located throughout the North-South and East-West Lines (NSEWL), the Republic’s two oldest and busiest MRT lines.

SCDF gave the public the first glimpse of the incident when it released a set of pictures on Facebook showing its personnel wading in almost knee deep water in pitch dark conditions as they worked to clear the water through the night on Saturday.

Their operation concluded after the water in the tunnels were completely cleared at approximately 11am on Sunday.

Before the cause of the incident was released by the authorities, commuters wondered why the flood protection works, such as barriers at entrances to keep out floods below 1.5m, carried out at 35 existing stations — including Braddell and Bishan — had failed. They also expressed concern that another downpour would result in another outage, especially during the work week, and given that heavy thunderstorms are forecast on Monday morning and the coming days.

The weekend’s unprecedented incident of a train disruption caused by flooded tunnels is possibly the worst disruption since December 2011, when over 200,000 commuters were affected by a major service disruption along the NSL over two days.

On Dec 15 that year, an estimated 127,000 commuters were affected by a major service disruption along the NSL from Marina Bay station to Braddell station.

At that time four trains stalled because of a misalignment between the train’s current collector shoes and the power rail, also known as the third rail. The trains draw locomotive power from the third rail through the train current collector shoes. As there was a misalignment, the trains were unable to draw power and thus stalled.

Two days later, another service disruption took place on the same line during the morning and affected about 94,000 commuters. During this disruption, five trains stalled after encountering similar mechanical problems. SMRT was only able to resume service around noon a day later.