Need for a flood master plan

THE Institution of Engineers Malaysia (IEM) is concerned and deeply saddened by the unprecedented floods in Penang and Kedah on Nov 4-5.

According to the Department of Irrigation and Drainage (DID) and Malaysian Meteorological Department, many locations in both two states received rainfall that exceeded the 100-year Average Recurrence Interval (ARI).

The prolonged flooding was aggravated by the high tide and strong winds which generated a storm surge.

This storm surge resulted in high tail water levels at all the affected river and drain outlets to the sea.

The high tail water at the sea not only prevented the effective drainage of floodwater run-off but also caused tidal flooding due to backflow of sea water into the catchment.

At the critical locations, the recorded rainfall depths in the 24-hour period was more than 300mm with a few sites exceeding 350mm.

IEM proposes that comprehensive flood mitigation measures need to be implemented to avoid similar floods. DID has implemented some of the measures and further efforts are on-going to further improve the situation.

More allocations are needed in view of the dire situation so that the problems can be solved in an integrated and comprehensive manner.

Non-structural measures are also important to improve the situation such as flood forecasting and warning system for all major river basins, relocation of people from flood-prone areas and land use control.

Developers have a major role to play.

All their developments should comply with the Manual Mesra Alam Malaysia (MSMA) where it emphasises source control.

The increase of flood run-off from urban developments should be attenuated by having flood detention ponds or equivalent systems to ensure that there is no increase of flood run-off peak discharge before and after the development.

The MSMA also stress on soil embankment erosion and sediment control during the construction period.

If the control measure is not effective, large amounts of soil can be eroded from the sites into the river systems.

This can lower the flood carrying capacity due to reduction of the river flow section by sedimentation.

Various parties should also focus on the climate change situation where many locations in the country are experiencing extraordinary heavy rainfall and many have also exceeded the 100-year ARI.

The climate change factor should be considered in all the development and flood-mitigation measures by assessing its impact and how resilient we are in facing the changes.

The National Hydraulic Research Institute Malaysia Technical Guide on Estimation of Future Design Rainstorm under the Climate Change Scenario in Peninsular Malaysia is a good reference for adoption.

IEM proposes that the government implement a comprehensive and integrated flood-mitigation master plan to cater to the development planning.

IEM through its Water Resources Technical Division is willing to assist the authorities to provide the necessary technical advice.

Ir Dr Tan Yean Chin
The Institution of Engineers Malaysia