If you have ever been lucky enough to be out in the rainforest during a tropical downpour, you will have noticed one amazing thing: very little of the rain actually hits the forest floor.  
 
The reason is that the forest canopy and the layers of vegetation beneath it trap the rain, and much of the water is absorbed through the leaves. 
 
The rest trickles slowly down the branches and trunk and down root channels into the subsoil. 
 
The water that does hit the forest floor is rapidly absorbed by leaf litter and slowly released into the soil.  There is very little surface runoff. 
 
It’s only after the water table has been recharged that water is released into streams, slowly and cleanly. 
 
If you can think back to the period after the recent Selangor water shortage, you will remember that many people were asking why the levels in the dams had not increased even though it had been raining. 
 
The reason is that the water table, drawn down during the dry period, had to be recharged before there was any excess to replenish the streams.  
 
Rivers’ role in removing excess water
 
Now, let’s look at the rivers. Rivers have evolved to remove excess water from the landscape as slowly as possible. 
 
A young river is composed of rapids and riffle zones followed by compensation basins to dissipate the energy of the water. 
 
As the rivers mature, they begin to meander, which further slows down the rate of flow and deposit any silt on land instead of out at sea. 
 
River banks will be choked with vegetation and levee banks will form naturally on flatter land to contain the excess water during major storm events. 
 
But rivers have not evolved to handle the massive amounts of water released from cleared land.
 
Now, let’s look at present day land use. Many people claim that logging is the cause of flooding. That is not the case because the area is small and in a forest being logged, at most 10 percent of the forested area will be disrupted. 
 
Sure, it looks bad, and there is much unnecessary damage caused, but the overall affect is minimal and the land will soon recover
 
Oil palm and water runoffs
 
In contrast, land that is clear felled and planted with oil palm and rubber trees is the biggest culprit. Of the two, palm oil is the worse offender. 
 
The oil palm is a shallow-rooted tree that uses very little of the subsoil water in the landscape. 
 
The structure of the fronds and their thick waxy surfaces limit the amount of water absorbed and directs the excess water away from the tree trunk directly onto the ground. Ground where there is virtually no leaf litter and little understorey to use and store the excess water. 
 
In addition, the soil is often compacted by vehicles. So this is where the surface runoff comes from, and as can be seen by the colour of the flood waters, with the runoff comes the topsoil, the fertiliser, and the available nutrients necessary for plant growth, but fatal for offshore coral reefs.
 
In addition, plantations are often developed on land that should never have been cleared because it is too steep.
 
To plant these steep slopes requires major soil disruption, hence further increasing erosion.
 
Measures turning rivers into drains
 
Then along comes an engineer with his lap top and little understanding of the cause of the floods. He'll recommend river straightening and deepening, dredging the river mouth, levee banks, compensation basins, etc, etc. 
 
Most of these measures will speed up the flow of water in the river and turn it into a lifeless, characterless drain, but they will not address the cause of the problem.
 
To do that, it’s necessary to retain the water in the plantation for as long as possible and to slow down the rate at which it’s released into the river.
 
There are plenty of effective strategies to produce this effect, but they cost money or reduce profitability, and they also reduce nutrient loss from the plantation.. 
 
Examples would be: maintaining ground cover, mulching, planting on the contour, wider strips between rows of trees, planting oil palms with alternating strips of high absorbancy plantation timber, compensation basins, grassed and graded waterways, on-farm compensation basins, retaining native vegetation along drainage lines, etc.
 
Forecasts are that as a result of global warming, the Malaysian rainfall will increase by between 10 to 30 percent by 2050. Worse still is that the rainfall is more likely to come in major storm events. 
 
Both events will increase the likelihood of flooding, so there is a serious need for Malaysia to address the problem at all levels. 
 
All these water control strategies are known by Agriculture Ministry officers, but in all my travels around the country, I have rarely seen them applied, except in very limited areas and to a very limited extent