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, very simply, is the soil of
the river, providing and sustaining virtually all life that exists in the river
itself. Alongwith 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. These
include
-
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.
-
Being a refuge for fish and an incubator for
eggs and for spawning. While lakhs of
fishermen in India 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
across the country. 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 that the sand is sold to the end
user for.
-
Buffering agricultural lands and towns from
rising water levels during floods. This
function is performed by sand by its very nature of being porous and is a
process known as bank storage. 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 priceless property:
during the dry months of the year, 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 every river in India
today.
Dams, while they do not remove sand, have decimated
this cleansing property of a river as well.
Indeed, a report by the National Environmental Engineering Research Institute
(NEERI) attributed the self-purifying ability of Ganga’jal’ to river sediments,
notably sand, and data indicated that the blocking of sediments behind the
Tehri Dam had diminished this property.
What is needed therefore is an
urgent 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.
