SHAH ALAM – Recurring flash floods in Kampung Melayu Subang suggest that the area's existing drainage infrastructure may no longer be able to cope with increasing surface runoff and changing conditions.
This has prompted calls for a comprehensive engineering study to assess the drainage system's limitations and identify sustainable flood mitigation measures.
Water engineer and former Department of Irrigation and Drainage (DID) director-general Datuk Ir Nor Hisham Mohd Ghazali said the repeated flooding was likely caused by several factors, including intense rainfall following consecutive days of rain, saturated soil, low-lying terrain and drainage systems being overwhelmed by surface runoff.
“Prolonged rainfall could leave the soil with limited capacity to absorb additional water, while parts of the village relied on detention ponds and pumping systems to remove excess water.
“During this particular incident, the volume of surface runoff unfortunately exceeded the drainage system's design capacity,” he told Sinar Daily.
Hisham said inadequate drainage capacity and surrounding urban development could also contribute to the recurring incidents, as the expansion of paved surfaces increased surface runoff and the volume of water entering drainage systems.
He explained that although the Department of Irrigation and Drainage (JPS) required new developments to provide detention ponds to prevent downstream drainage networks from becoming overloaded, coordinating drainage connections between developments built in different phases remained challenging.
“When newer developments upstream discharge into older drainage systems downstream, the existing capacity must be reassessed, potential bottlenecks addressed and downstream infrastructure, including bridges, upgraded where necessary to ensure sustainable drainage.
“Recurring flash floods despite adequate maintenance could indicate that the existing drainage network no longer has sufficient capacity to cope with current conditions.
“I would therefore recommend conducting a comprehensive drainage master plan study covering the entire area to identify the system's limitations and determine the necessary improvements.
“Ultimately, the underlying causes of flooding and appropriate long-term mitigation measures in Kampung Melayu Subang can only be established through a proper engineering study,” he emphasised.
On immediate interventions, Hisham said authorities should pay closer attention to on-site drainage management, particularly when infrastructure projects were being carried out.
He cited serious and unprecedented flash floods during the construction of the Light Rail Transit (LRT) lines near IOI Mall in Puchong and in Section 23, Shah Alam, as examples of how construction activities could coincide with significant flooding.
“Contractors should therefore be required to submit flood response plans to the authorities before the rainy season, ensure pumps are on standby and anticipate potential flooding arising from their construction activities,” he said.
He also called for greater consideration of flood risks during the planning stage, alongside stronger engagement between engineers and town planners to ensure drainage requirements were adequately addressed before development and construction began.
His recommendations come as Kampung Melayu Subang continues to experience recurring flash floods, with more than 500 houses affected by four incidents within 30 days.
Following heavy rainfall on Nov 2, a total of 789 people from 325 families were affected.
Prime Minister Datuk Seri Anwar Ibrahim said the government would provide additional assistance to flood victims and prioritise mitigation measures, including river widening, the construction of additional retention ponds and river dredging, to reduce the risk of further flooding.