Even as the sun blazes and Madurai faces severe water shortage, there is one man hopeful of recharging the city’s water table. If the plan he has drawn up is accepted by non-government organisations and the district administration, says B.Thomas, river Vaigai can be rejuvenated within three years. Anybody listening?
He is not an eco-warrior. But this consultant in community development and Hony.Secretary of INTACH, Madurai chapter, is one who “feels for his city”.
Ask him that one thing he would like to change — “Theppakulam should have water round-the-year and the young boys should go hunting for an alternate place to play cricket!” he smiles.
And how can that happen? “By building at least three to four sub-surface dams at strategic points across river Vaigai,” he says without a blink.
Sub-surface dams are sand dams which are constructed under the riverbed.
Roughly a three metre wide trench is dug right across the river and the sand layer is removed to a depth till the hard soil is reached. Then the trench is filled with hard clayey soil from any riverbed or field in place of the sand excavated. It is beaten up and compacted very well. The top is then covered with sand so that the mud partition underneath remains hidden.
During the rainy season, the run-off water is trapped on one side of the sub-surface dam and gradually forms a sub-surface water reservoir. Unlike a conventional dam that stores water above the surface, this earthy dam traps and stores water between the pores of the riverbed’s sand.
Thomas exudes confidence that the water table and the quality of water will improve substantially by the percolation effect from the sub-surface reservoirs within three years. His knowledge in sub-surface dams stems from his experience of designing drought-proofing projects in arid and semi-arid areas of Africa and India.
What got him studying more about sub-surface dams recently is the dip in water supply to his home which is less than a kilometre from the river. “The Corporation tap water supply got reduced to only an hour every alternate day,” he says, adding the calcium deposit on utensils and other items after a wash was another factor that rankled him.
Thomas started wondering how the situation could be reversed without spending much money. His main concern was why Vaigai should be allowed to go dry even if there is scant rainfall? More so when the city topography reveals that the perennial river of years still has reserves of water. The fact that Vaigai has turned into a seasonal river today gave him the push to take up the matter seriously. “Sub-surface dams”, he says, “are useful in seasonal rivers because they flow during the rainy season and in other times though they appear to be dry, the riverbed’s sand contains water.”
The benefits of sub-surface dams, according to Thomas, are multiple. They can not be damaged by erosion or floodwater as they are situated below the surface of the sand in riverbeds.
The water does not evaporate from storage as it is in the case of conventional dams. Further, the sand acts as a natural filtration system and does not run the risk of contamination. “The sub-surface water does not require any treatment and is safe to drink,” he emphasises. Also, the sub-surface dams are cost effective as they do not require any technical skills for construction. For someone who has also designed training capsules for grass root community and aid workers for activities during natural calamity management, Thomas says, “the locals can just be given an orientation on the concept and then see how well the city replenishes itself.”
According to him, once the quality of water is enhanced and the water table is improved, the foundations of all the old structures and ancient monuments in the vicinity of the river will also be safe.
“If the water table goes down more and the sub-surface soil becomes dry, then there is a greater risk. It may cause the foundations to sink and the structures to collapse,” he warns.
The time has come to move beyond lip service. Amidst loss, Thomas sees hope and plans to submit his proposal shortly to the Collector through INTACH.
“The responsibility of conserving our resources and preserving our heritage,” says Thomas, “has to be shared."
(Making a difference is a fortnightly column about ordinary people and events that leave an extraordinary impact on us. E-mail to soma.basu@thehindu.co.in to tell about someone you know who is making a difference)
