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In sand, the grain of life

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We need to develop a substitute for this material and let it remain where it belongs

The spectacular growth of the construction industry has had unintended consequences for every river in India today. The mining of sand — which is an essential part of construction — has often been in the news, largely due to the control of local mafias over this minor mineral. Most people also intuitively recognise that sand-mining has damaged, and continues to damage, the delicate ecosystem of India’s rivers, on which millions of people depend for their drinking and household needs, livelihoods and irrigation. Yet, what is little understood is this: why is sand necessary for the river, and what role does it play?

Sand, simply, is the soil of the river, providing and sustaining virtually all life that exists in the river itself. Along with another very important mineral, gravel, it forms part of the hyporheic zone, an intermediate zone between the surface water of the river and the groundwater beneath.

The hyporheic zone has been studied extensively all over the world for the last seventy years and it is now well accepted that this zone performs critical functions, each necessary for the long-term survival of a river.

Recharging the ground water table far beyond the river basin itself by slowing down the flow of water in the river and allowing for percolation, not just downwards but laterally across large areas on either side of the river as well — exactly how large an area is recharged by the river depends on various factors, including nature of the soil, the topography and so on. Indeed, a study in the United States showed that where the hyporheic zone was minimal, water recharge was limited and wells often went dry in summer.

It is a refuge for fish and an incubator for eggs. While lakhs of fishermen are critically dependant on fishing, fish itself is a vital source of rural protein and, as is now being studied, the humungous scale of sand and gravel extraction (along with the number of hydel projects coming up) is impacting fish availability all across. Ironically, many fishermen, in an effort to keep their incomes from falling, are part of the extensive sand mining network, working the river-beds for a fraction of the amount the sand is sold to end-users.

Sand served the function of buffering agricultural lands and towns from rising water levels during floods as by its very nature it is porous. To understand this better, one only needs to fill a glass with sand and pour water into it! This value of sand — that of being a vast storage tank of clean water — has an additional property: during the dry months, sand releases some of this water to keep the river flowing, ensuring (sand-filtered) water for our needs.

Harbouring unique invertebrate fauna and micro-organisms such as fungi and microbes that filter the water, due to its physical, chemical and biological conditions. The sediment particles, for instance, impede the flow of silt and particulate matter as water enters and moves through sand. A second, biological filtering mechanism works in a manner similar to the trickle filters of sewage treatment plants, where nutrients dissolved in river water are taken up or transformed by microbial bio-films coating the sediments, into food for the many species of invertebrates that live in the hyporheic zone. The chemical conditions prevalent within the hyporheic zone allow the precipitation of dissolved minerals and metals, which is then trapped by the physical filter, where it may be degraded biologically. These are complex processes, evolved over thousands of years, and the removal of the sand-and-gravel layer of the river ecosystem is inhibiting the self-cleaning mechanism of the river, even as India’s rivers receive increasing loads of toxic and sewage wastes from urban and agricultural areas. The removal of sand and the increasing pollution are irreversibly damaging the ecology of all rivers in India.

What is needed is a national effort to develop an ecologically safe, cost-effective, technically comparable substitute for sand and to critically evaluate the impact on the hyporheic zone prior to the clearance of a hydroelectric project. To ensure water security for India’s future, we need to keep sand where it belongs — in the river.

>gopakumar.rootcause@gmail.com

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Printable version | Jan 19, 2020 11:38:03 PM | https://www.thehindu.com/opinion/open-page/in-sand-the-grain-of-life/article6229347.ece

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