Geological factors can influence flooding, says expert

The criteria include unsustainable and uncontrolled development that upset the ecological balance and put additional pressure on the soil surface and hydrological cycle of the areas concerned.

Dr Nor Shahidah Mohd Nazer, an expert in geological engineering and soil mechanics, said gone are the days when logging and exploitation of forests were solely responsible for flooding.

"The situation has become more worrying now because other physical factors are also influencing the occurrence of floods," said Nor Shahidah, who is a senior lecturer at the Department of Earth Sciences and Environment, Universiti Kebangsaan Malaysia.

She said natural disasters can occur as a result of exogenous processes on the earth's surface. However, these processes can worsen due to unsustainable and unregulated development which adds more stress to the soil surface and hydrological cycle.

"This can lead to flooding and landslides which, essentially, are normal reactions of the exogenous processes but turn into catastrophic events when uncontrollable exploitation of land (in highlands and lowlands) occurs," she said.

(Exogenous processes refer to the soil erosion, sedimentation and weathering that take place on the surface of the earth.)

Pointing to Taman Sri Muda in Selangor, which was one of the worst-hit areas during the recent floods, Nor Shahidah said being located in low-lying terrain, its rather shallow groundwater level makes the area vulnerable to flooding due to the low water storage capacity of its soil.

"Another point that must be noted is the existence of soil with high peat and marine clay deposits in Shah Alam. Both are components that cause the ground to be soft and unstable and such areas have a high potential for sedimentation and water retention to occur.

"So, floods occur easily in such areas. Not only that, the water remains stagnant over a long period of time," she told Bernama.

She said there is nothing new about the impact of development on soil surfaces and the hydrological cycle as it has been evident since the nation began to develop rapidly after attaining independence.

The series of floods recorded in this country over the years, including the severe flooding in 1971, signified the impact of human influence on the environment, she added.

"It must be understood that each river system consists of a network of water channels and is interconnected with other river systems. Hence, the rising water level of a river in a certain area can impact the river systems located tens of kilometres away," she explained.

She said when an area located near a river's upstream portion is inundated, water flowing downstream will overflow onto the floodplains which mostly comprise highly developed areas.

The situation is worsened when water overflows onto urban areas that have poor drainage systems and low permeability zones, as well as lack sufficient mitigation measures to deal with the effects of climate change.

Nor Shahidah also urged the authorities to limit development in areas deemed as high-risk to prevent adding more stress to their soil and hydrological systems.

She said in any urban area undergoing rapid development, only a limited number of megaprojects should be allowed and all small-scale projects should be regulated as well.

Calling for the implementation of flood management plans, she said a structured contingency plan must be put in place by constructing flood mitigation zones that take into account extreme rainfall and soil saturation rates after rainfall.

"Pakistan, for example, experienced the worst floods in its history in 2010 and 2011. It continued flooding for two more years simply because the soil's saturation rate had remained high following the 2010 flooding.

"The same thing can happen in Malaysia if no measures are taken to ensure the soil and river systems in areas previously affected by floods are ready to face heavy rainfall in the future," she said.

Pointing to the flood mitigation measures that are in place now, Nor Shahidah said they were created during the 1980s and 1990s without taking into account current development and population projections.

She also said now that 15 years have passed since SMART came into operation, it is time to review the Stormwater Management and Road Tunnel's capacity to alleviate floods in the capital city.

She said even in Japan, the experts are worried whether or not Tokyo's mega underground tunnel system can withstand the effects of extreme weather events.

Universiti Teknologi Mara Faculty of Civil Engineering senior lecturer Azinoor Azida Abu Bakar, meanwhile, called for the development of flood mitigation infrastructure that provides more comprehensive protection.

She said the Department of Irrigation and Drainage has been managing floods effectively and efficiently throughout the nation through the application of hard and soft engineering methodologies aimed at reducing risks as well as the negative effects of flooding.

The hard engineering methodology focuses on the building of dams, retention ponds and river embankments, and diverting, deepening, widening and realigning rivers and providing pumping systems.

"... although more attention has been given to building infrastructure, previous (disaster) experience has shown that it must be supported by (environmentally-friendly) soft engineering measures in order to resolve flooding issues effectively and comprehensively," she said.

She said water-permeable landscapes have also been created in new development areas through the use of the environmentally-friendly drainage manual.

"This environmentally-friendly drainage approach involves collecting rainwater in man-made lakes or ponds. To avoid flooding, the water is only released into the existing drainage system after the rain stops," she said.

Azinoor Azida said urbanisation has led to an increase in areas with soil deemed as impervious (where the soil does not allow water to pass through) which, in turn, causes a sharp spike in surface run-offs during heavy rainfall.

To address this, the existing drainage systems will have to be upgraded to cope with the increasing rainfall rates, she added.