KUALA LUMPUR, March 10 — The management of Stormwater Management and Road Tunnel (SMART) Tunnel today said that it had only utilised a third of its overall capacity, amid recent heavy rain that saw the capital city flooded in some areas.

It said that the tunnel had diverted over one million cubic metres of floodwaters on March 7 when the most recent flash floods occurred, but the areas affected on that day were not under its alleviation zone.

“Flash floods typically occur via two mechanisms from intensive rainfall — via overflowing of rivers and exceeding the capacity of localised drainage networks,” it said in a statement.

“The badly hit areas in Kuala Lumpur on March 7 suffered from these two contributing factors — insufficient carrying capacity at rivers particularly Sungai Kerayong, Sungai Bunus and Sungai Kuyoh, which are outside of the SMART Tunnel flood alleviation zone, and intense rain overwhelming the local drainage networks in these areas.”

This had, in turn, caused flash floods in surrounding areas such as Kuchai Lama and Jalan Klang Lama, it said.

In comparison, it said catchment areas which the SMART project serves experienced relatively less rainfall intensity compared to the other areas that were hit by the flash floods on that day.

It also called for a holistic flood mitigation project to quickly be undertaken, especially for north-western Kuala Lumpur, in order to cope with climate change.

“Given the advent of climate change which is now upon us, increased frequency of extreme weather events is forthcoming,” it said.

“Given this, a holistic flood mitigation solution particularly targeting the north-western side of Kuala Lumpur within the catchments of Sungai Gombak and Sungai Bunus will need to be expedited on top of a robust maintenance regime for our local drainage networks to minimise the future impact of these extreme weather events in Kuala Lumpur.”

It compared the situation earlier this week with another flash flooding event in December last year, when the tunnel had to utilise 100 per cent of its capacity to divert floodwaters, with the heavy rain then affecting Sungai Klang and Sungai Ampang upstream catchments.

The tunnel is capable of storing three million cubic metres of floodwater at any time and had diverted a total of five million cubic metres of floodwater in the December 2021 floods by extending its diversion period for a record 22 hours, SMART said.

SMART said that the Masjid Jamek area, which is within its coverage zone, experienced rising water not from Sungai Klang but rather the backflow from the overwhelmed Sungai Gombak, in addition to aggregated flows from Sungai Keroh and Sungai Batu upstream.

The March 7 flash floods which hit the city centre, crippled traffic and caused massive property loss.

In December last year, Klang Valley experienced one of its worst flash floods in recent history, severely affecting areas such as Shah Alam, Klang and Kuala Lumpur — displacing thousands, killing 25 people and causing losses worth RM3.1 billion in Selangor.