THE Institution of Engineers, Malaysia (IEM) is concerned and deeply saddened by the massive floods that hit Penang and Kedah on November 4 and 5, with more than 1,900 flood victims evacuated with some casualties, as reported by the media.

The flooding in Penang and Kedah is an unprecedented event. From the recorded rainfall data by the Irrigation and Drainage Department and Meteorological Department, many locations in these two states exceeded the 100-year Average Recurrence Interval (ARI). This prolonged flooding was also further aggravated by the high tide and strong winds that generated a storm surge. This storm surge resulted in high tailwater levels at affected river and drain outlets to the sea. The high tailwater at sea not only prevented floodwater run-off to be drained effectively but also caused tidal flooding due to the backflow of sea water into the catchment.

The rainfall started on Saturday afternoon, with the storm centre of the event focused on Penang and Kedah, and kept raining until today.  The heavy rainfall persisted for more than 24 hours and the Irrigation and Drainage Department reported that in many locations, rainfall depth exceeded the 100-year ARI.  At critical locations in affected areas, recorded rainfall depths in the 24-hour period were more than 300mm, with a few even exceeding 350mm. The capacity of most of the river and drainage systems in these two states is less than a 100-year ARI. This resulted in water spilling over banks and flooding surrounding areas.  Concurrently, the tide level was also close to the Highest Astronomical Tide (HAT) level, which prevented floodwaters from discharging effectively into the ocean. Furthermore, with the strong winds, a storm surge can be generated at river and drainage outlets.  With these combination of factors, the flood run-off could not be discharged effectively to the sea, resulting in a compounding effect on the flood situation.

IEM proposes that comprehensive flood mitigation measures be implemented to avoid similar flood incident from recurring.  The Irrigation and Drainage Department has implemented some flood mitigation measures in both states to alleviate the problem, and further efforts are ongoing to improve the situation.  More allocations are needed in view of the current 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 systems for all major river basins, relocation of people from flood-prone areas and land use control.

Developers also have a major role to play.  All developments should comply with the Manual Mesra Alam Malaysia (MSMA), where source control is emphasised. The increase of flood run-off from urban developments should be attenuated by having flood detention ponds or equivalent systems to ensure there is no increase in flood run-off peak discharge before and after the development. Furthermore, the MSMA also emphasises soil embankment erosion and sediment control during construction periods.  If the control measure is not effective, large amounts of soil can be eroded and washed from the sites into the river systems.  This can lower floodwaters-carrying capacity due to the obstruction of river flow by sedimentation.

Various parties should also start to focus on climate change, as many locations across the country are experiencing extraordinarily heavy rainfall, with many areas exceeding the 100-year ARI. Prominent examples of these include severe flooding in Johor at the end of 2006 and beginning of 2007 as well as the end of 2014 floods in Kelantan and Pahang. The country should seriously look into climate change as a factor, which is becoming a more obvious factor in flood problems.  Climate change should be considered in all developments and flood mitigation measures. The National Hydraulic Research Institute Malaysia (Nahrim) Technical Guide on Estimation of Future Design Rainstorm under the Climate Change Scenario in Peninsular Malaysia is a good reference for adoption.

IEM would like to propose that the government implement a comprehensive and integrated flood mitigation master plan to cater for development planning in the affected states. The master plan should include flood mitigation and prevention action plans for current and future developments, land use changes as well as include climate change as a factor.

IEM, through its Water Resources Technical Division, is most willing to assist the authorities in providing the necessary technical advice on flood mitigation and prevention measures, including creating public awareness on flood-related issues. As a learned society with more than 40,000 members and affiliations with several international engineering organisations, IEM is recognised locally and internationally as a learned society and professional body representing a wide cross section of the engineering practice. Many of its members are learned and experienced practitioners in their own fields of expertise, and can offer technical assistance and advice. – November 6, 2017.

* Dr Tan Yean Chin is Institution of Engineers, Malaysia president.