Friday, 9 January 2015

Letter to the Editor: Stormwater Management Can Reduce Risk of Urban Flash Floods


Professor Chan Ngai Weng raised many salient points in his letter, 'The human factor in floods' (The Star, Jan 6). While the recent floods in the East Coast of Peninsular Malaysia and many coastal towns and villages received a lot of media attention and concern due to the unprecedented scale of destruction it left in its wake, we must not forget that Kuala Lumpur and many other Malaysian cities are also susceptible to flash floods. As someone who volunteers with the homeless communities, I have heard many accounts of how homeless individuals were swept away by the rapidly rising waters of the Gombak and Klang rivers during the monsoon season. Further, we are all familiar with the frequent traffic congestion and damage to property caused by flash floods. 

It is wonderful to witness the generosity, compassion and solidarity of Malaysians in contributing and delivering aid to the East Coast flood victims. However, unless urgent measures are taken to find and implement permanent solutions to the problem of flash floods, the floods will keep recurring, and Kuala Lumpur and other cities may soon find themselves having to deal with floods as devastating as those in the East Coast. 

The first step towards preventing and mitigating floods is without doubt, to halt deforestation. Biologically-diverse forests with their complex systems of canopies, roots, soil and leaf litter act as giant sponges which soak up rainwater and release the water slowly and evenly. Monoculture plantations could never be able to replicate this effect. The second step obviously lies in reducing sedimentation in rivers and waterways and blockages caused by littering. 

There are many things governments, local authorities, developers and property owners can do to reduce the risk of urban flash floods. Urban development has a profound impact on hydrologic cycles and water quality. The penchant of property owners for tiling up their compounds with impermeable materials contributes directly to flash floods and downstream flooding. Rainwater cannot infiltrate naturally into the soil, but is instead channelled directly into storm drains and streams. This rapid disposal of stormwater causes downstream flooding because water channels are often too small for the sudden high flow. 

Water management agencies and the local authorities need to encourage responsible stormwater management and educate houseowners and commercial property owners that if stormwater is captured at its source and gradually released downstream, the impact on rivers would be mitigated and, consequently, the likelihood of soil erosion, water pollution and flash floods would be greatly reduced. The Drainage and Irrigation Department has advocated this ‘control at source’ method in the past but there has been no active enforcement of these guidelines by those with the authority to do so. 

To discourage littering and to allow water to be absorbed into the soil, it is recommended that open drains be replaced with gravel trenches, permeable pavements and buried waterways. Gravel trenches will not only slow down the water runoff and allow water to seep into the soil, it will also trap solid waste (e.g. fallen leaves and litter) and prevent these from being washed downstream and causing blockages. In addition, litterbugs are far less likely to throw rubbish into a gravel trench than into an open drain. 

Guidelines must be drawn up by the state governments and local authorities to ensure that pavements and driveways in new development projects may be tiled only with water permeable tiles such as interlocking bricks. Housing developers and property owners who wish to renovate their homes should be subjected to these same guidelines for drainage and tiling. Urban renewal and upgrading projects should include measures to replace impervious surfaces (concrete slabs, tiles) with permeable surfaces (porous bricks, interlocking bricks), planting trees, groundcover and shrubs in open areas and creating 'buffer strips' with indigenous water-loving native plants alongside waterways and in flood-susceptible parts of town to filter and slow down water runoff and soak up pollutants. Currently the upgrading of the Medan Pasar area into a 'historical walk' has exacerbated the risk of flash flooding, as it has replaced tar-bound macadam roads and shrubbery with impermeable tiled surfaces. It is hoped that it is not too late to incorporate some buffer strips in the area with gravel trenches and native plants with roots directly in the soil and not in concrete or plastic planters. 

Property owners and apartment management bodies should also take steps to implement similar measures in their renovation and beautification projects. Beautification should not only mean creating surfaces that are easy to maintain and clean, but also finding ways to mitigate damage to the environment, discourage littering and reduce inconvenience to residents in the form of traffic congestions, water damage and slippery surfaces. The implementation of these stormwater management measures can help us find a means of controlling the volume of water run-off and, in the long run, may also improve water quality if action is taken to store and filter stormwater captured at its source before gradual release into rivers. 


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