by AUFA MARDHIAH / pic by TMR FILE

THE flash flood which had badly hit areas in Kuala Lumpur (KL) on March 7 was due to overflowing of rivers and capacity excess of localised drainage networks.

According to the Stormwater Management and Road Tunnel (Smart), the flash flood was also caused by insufficient carrying capacity at rivers particularly Sungai Kerayong, Sungai Bunus and Sungai Kuyoh, which are outside of the Smart Tunnel flood alleviation zone.

On March 7, the Smart Tunnel diverted more than one million cu m of floodwater using only one-third of the overall capacity of its four-mode system, without having to activate Mode 4 (full closure for flood water diversion).

“This is because the catchment area it serves experienced a relatively low rainfall intensity compared to other areas in KL that were hit by flash floods.

“This was unlike the December 2021 flash flood where the Smart Tunnel had to use 100% of its capacity to divert flood water because the pattern of rainfall intensity then affected different areas, in particular, the upstream catchments of the Klang River and the Ampang River,” Smart said in a statement yesterday, to explain Monday’s situation.

“During the intense rainfall around 2.30pm in KL on March 7, Mode 2 was activated at 3.45pm with the rising flow rates of Sungai Klang followed by Mode 3 at 4.40pm in anticipation of proceeding to Mode 4 which involves complete closure of the tunnel for flood water diversion.

“However, Mode 3 remained active only until 8pm as the rain intensity started to subside and Sungai Klang levels remained manageable and did not spill over throughout without needing to progress to Mode 4. The Smart Tunnel was reopened to the public at 10pm,” it said.

Smart added that Masjid Jamek, which is within its coverage zone, experienced some rising flood levels not from Sungai Klang but the backflow from the overwhelmed Sungai Gombak, Sungai Keroh and Sungai Batu.

“The severity of the flood at Masjid Jamek was indirectly alleviated to a certain extent via the diversion of the Sungai Klang floodwaters by the Smart tunnel.

“The tunnel had saved Masjid Jamek from extensive flood damages multiple times in the past. To date, Mode 4 was activated nine times including two occasions in 2021,” Smart said.

The dual-purpose tunnel was designed to directly mitigate flooding issues within catchments associated with the overflowing of Sungai Klang passing through the KL city centre to provide flood relief to areas such as Dataran Merdeka during heavy downpours.

It also functions as an alternative option for traffic dispersal to ease traffic congestion at the southern main gateway to KL when not diverting floodwaters.

“The flash floods that impacted multiple areas within the Klang Valley on Monday, including Kuchai Lama and Jalan Klang Lama, were not within the Smart Tunnel flood alleviation system coverage area,” it explained.

Initially, the Smart Tunnel was capable of storing three million cu m of flood water at any one time but in December last year, it diverted a total of five million cu m of flood water by extending its diversion period to a record 22 hours.

Earlier, the Environment and Water Minister Datuk Seri Tuan Ibrahim Tuan Man described the heavy rain as “an average of half a month’s rain in two hours” which exceeds a “one-in-100-year” event in some areas.

Such events are happening increasingly due to the effects of climate change, he had said.

Smart said given the advent of climate change, 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.

“This is so our local drainage networks can minimise the future impact of these extreme weather events in KL,” it added.