Sri Lanka’s King Parakramabahu the Great, is famous for what he said, “Let not a drop of water flow to the sea without serving the people”. He is also famous for constructing the world’s largest man-made lake – the Parakrama Samudraya.
Sri Lanka had a system of ‘Wewas’ or man-made lakes that filled up during the rainy season and provided water during the dry season to Sri Lanka’s traditional rice-growing areas, the plains below the central mountains, extending from the North to the South, in what is now called the “Dry Zones”. That is why Sri Lanka came to be known as a centre of “Hydraulic Civilization”.
Probably no other country in the world developed such a smart and broad-based rain-water harvesting technology, though some countries do have man-made lakes for agriculture.
According to soil scientists, there are no major waterways or canals that brought water to these tanks – most of the water just seeps through the soil or through springs (ulpath). To make this possible, the rain that fell must have been absorbed completely into the soil. The water then slowly percolated through the soil absorbing minerals and other nutrients and then seeped into the lakes filling them with mineral-rich water. So what were the factors that made this such a novel way to harvest rain water?
Can we copy this system as a smart way of overcoming climate change problems we now face – massive floods and prolonged droughts. During the time of the kings, it is obvious that the rain that fell must have been completely absorbed by the soil – nothing just flowed away especially down the hills. This must have happened because the countryside was covered with leaves and twigs that naturally form to cover the soil when they fall from the trees. This mulch is then converted to top soil (compost) by worms and other creatures in the soil – something that can now be seen only in our forests, because wherever people live today, the ground is swept “neat and clean” – to look perhaps like the cemented courtyards of the rich.
What happens in the forest is that the eaves and twigs and the black top soil act like a sponges that absorb the rain water. The excess water then gradually seeps into the soil. Therefore on forested hillsides there are no eroding or rushing water flows that could loosen rocks. Therefore there are few or no landslides.
Further, during droughts the mulch acts as an insulating blanket minimizing water evaporation so that only the top layer dries out. At night the mulch absorbs moisture from the night air.
Thus it can be assumed that the whole land was protected by this “skin” of top soil and mulch, so that the rain that fell would have eventually seeped into the tanks - the Foundational Principle of the Hydraulic Civilization of the Wewa’s.
People who did chena or forest cultivation in those days must have cleared a few trees to have more sunlight and any unwanted plants and weeds would have been easily pulled out, because they are not deep-rooted when they grow in mulch.
Unfortunately when the British came they had little or no clue about tropical agriculture. They cleared the land for coffee and then tea and the top soil was washed away to the rivers and to the sea.
With no top soil they were forced to use chemical agriculture inputs and fertilizers and to have measures to prevent weeds competing for the added fertilizer. It is obvious that chemical agriculture has failed and that it is now poisoning us.
Today’s people too have forgotten nature- - they want a “clean and neat” garden or “midula” - so the fallen leaves are swept together and burnt. This deprives the worms and other creatures of their food, eventually killing them. The soil becomes barren and dead and without life, becomes rock-hard. Most of the rain water that falls just flows away to drains and to the sea.
So it is only in forests and grasslands that there exists this protective “skin” of top soil and mulch. Wherever there are people, there is no real top soil -- just barren earth. Today we can see this where humans live.