Dealing with developments near retention basins

Lead: The Batu retention pond in Kuala Lumpur is one of the biggest ponds used for flood mitigation in the city. - IZZRAFIQ ALIAS/The Star

MALAYSIA’S urban planning must prioritise effective stormwater management to prevent flash floods, say experts.

Wong Chee Fui, who is a specialist at Universiti Tunku Abdul Rahman (UTAR), said a key consideration in development projects was to ensure the amount of stormwater discharged was always less than pre-development levels, especially during heavy rainfall.

“In Malaysia, the drainage design concept is based on the Urban Stormwater Management Manual (MSMA).

“The manual emphasises the ‘control at source’ strategy where the rainfall peak runoff in any developed area should be contained within that development compound.

“Once the flood recedes, the extra runoff accumulated can be released towards the downstream section without affecting the livelihood of the downstream community.”

Wong said MSMA provides guidelines to develop sustainable stormwater systems that control potential flash floods and limit any adverse impact to the community.

“While all new developments should incorporate MSMA, there is a need to ensure stormwater detention facilities within the development are well maintained.

“Many previous development areas prior to 2001 (before the introduction of MSMA) were not designed with the ‘control at source’ concept.

“In such cases, there is a need to ensure more stormwater detention facilities are constructed to ensure that the stormwater is contained onsite during peak rainfall.”

Wong said retention ponds were only one method to contain stormwater within a development area during the peak rainfall period.

He said MSMA recommendations could be implemented with various stormwater facilities such as flood plain areas, grass swales, wetland, detention ponds, subsoil drainage and infiltration landscaping.

Wong, who is also former executive director at the Institution of Engineers Malaysia (IEM), said while there was a requirement that new developments have stormwater detention facilities, it did not specify the maintenance.

“This also raises the question of who should be responsible to develop stormwater detention facilities at areas built prior to 2001, after the developer has completed the development and sold the properties.

“Does the local government have an allocation to ensure stormwater is controlled at source for older development areas?”

Town planner Ihsan Zainal Mokhtar said while developing areas near retention ponds was possible with stringent conditions, it should not be encouraged.

“If the area (near the retention pond) is very big and the pond is small, it can be done.

“But there must be alternatives for how the extra surface runoff will be retained and dispersed.

“For example, smaller retention ponds can be built within the development area or by deepening the existing pond.”

To safeguard against potential flooding in potentially vulnerable areas, Ihsan emphasised the importance of a buffer or reserve, which would act as a protective measure if water levels exceeded pond capacity.

“Instead of seeking new land to develop, we should encourage redevelopment efforts.

“There are many areas in major cities which are due for redevelopment, and have the basic infrastructure in place.

Ihsan, who is Malaysian Institute of Planners (MIP) immediate past president, said detailed plans on stormwater management should be done before the commencement of any development project.

“Climate change is a serious concern and needs to be taken into consideration when planning.

“When current development already faces all sorts of challenges, why go to places where the risk of flooding is potentially higher?”

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