Floods an eye-opener


  • Letters
  • Thursday, 29 Mar 2007

I NOTE that the Government has invited six consultants to come up with a long-term plan to deal with flood problems. Much has been said about the effect of global warming on the incidence of flooding and the inadequate drainage provided by the existing drainage system.  

I would suggest that the predominant cause of the flooding lies in the picture on page one of Star Metro Central for March 27. 

Allow me take you for a walk around Malaysia.  

First, we visit some intact rainforests. The tree canopy is almost complete, the trees are mostly deep-rooted and branch from a central trunk. There are layers of sub storeys beneath the canopy, the soil is covered with a dense layer of leaf litter and the soil is rich in organic matter and porous  

In light to moderate rainfall the raindrops rarely hit the soil, and if they do, the velocity of the raindrops is greatly reduced. Instead, massive amounts of water are trapped in the leaf canopy where it either evaporates, is absorbed directly or trickles slowly down the branches and trunks into channels alongside the roots to finally replenish the ground water storage. 

In heavy rainfall the amount of water exceeds the ability of the canopy to trap it, so it falls gently to the forest floor where it is trapped by the dense leaf litter and the porous surface soil to be slowly released into the ground water.  

The overall effect is that there is virtually no surface run-off. Instead, the only water that is released from the ecosystem is the excess water from the ground water storage, and that water is clean, clear and unpolluted.  

During dry periods, the trees of the forest survive on the water stored as ground water, thus lowering the water table and providing for more storage during the next wet period. The whole process is slow and gentle and the natural drainage system has evolved to cope with the excess water. 

In contrast, let us look at a palm oil plantation. Even in a mature plantation the leaf canopy is far from complete because the density of planting is more related to yields per hectare than to protecting the environment. The trees themselves are shallow rooted so they do not draw down the water table to any extent during dry periods. 

Because of the structure of the tree, much of the falling rain is directed away from the trunk and onto the ground. There is rarely any under storey to protect the soil because this has been removed in an effort to maximise production. 

There is no leaf litter to protect the soil, and after a few years the organic matter level of the soil disappears and along with it goes soil porosity. The soil is further compacted by heavy machinery and the pounding effect of raindrops.  

Even under moderate falls, the rain is directed mainly onto the soil where it has nowhere to go but to run off, taking with it soil particles, nutrients and chemical pollutants.  

You can imagine what the run-off would be from an ecosystem like that pictured in your newspaper. I would think almost 100%.  

The whole process is rapid and violent, and it is no wonder that the natural drainage system cannot cope. 

It is not surprising that Malaysia’s rivers are polluted and the marine environment is threatened by excess fresh water and nutrients and that its coral reefs are dying?  

I would also point out that building dams and flood catchment ponds is not the answer to flood control. All they will ever do is become silt traps.  

I would be interested to hear what an economist has to say about the cost of the Johore floods versus the proportion of income from palm oil plantations in Malaysia. 

 

D. MADDEN, 

Petaling Jaya  

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