Construction
sand and Gravel: Let us be Scientific.
Times
Of India second page carried a story today (July 25, 12) offering a solutions
for the scarcity of construction sand as well as problems caused by continued
borrowing of river channel sand. The proposed solutions center around dredging
of sediment so far accumulated in the reservoirs (both Hydel and Irrigation) of
Kerala. There is a suggestion in the article that the LDF Government had
suggested this recourse and in fact launched sand collection from the
reservoirs. True, there was attempts in Malampuzha and Aruvillara reservoirs as
well as from the Veli Kayal.
The
suggested positive aspects of the reservoir- derived sands are, a. it will to a
large extent remedy the sand scarcity and hence a fall in market price, b. relieve
the rivers of Kerala from their over exploitation for channel sand, leading to
ecological death and c. it will raise the water storage of the reservoirs. All
the suggested outcomes are superficially attractive to a lay mind.
However,
the science of sand is mostly alien to the public as well as the journalists
and naturally to the minister-politicians. Indeed it is such real sand
situation. The current state of the rivers of Kerala are primarily the outcome
of a ruling by the High court of Kerala, while disposing of a PIL filed by some
of the concerned citizens.
The
court while passing the judgement ordered that the volume of sand available for
removal from the kadavus will be
assessed by the CWRDM (for the rivers of north Kerala) and CESS (for the rivers
of south Kerala). This happened in nearly a quarter century ago. The
panchayaths those days collected huge revenue from the auctioning of right to
collect sand from the various kadavus and the CWRDM and CESS also had a substantial piece of the pie.
As a
consequence of continued and unabated removal of sand on the guise of the
permits issued by CWRDM and CESS, we landed in a situation where all the rivers
of Kerala are practically ecologically dead.
The only natural recourse to save the rivers and
run the construction industry, is to use sand manufactured by crushing of solid
rock rubble coming off the quarries in the state or outside of the state. Our
technology parks, high rise commercial and residential buildings, four lane
roads, bridges, dams, the Vizhinjam harbor, seawalls etc need huge input of
rock rubble in phenomenal quantities. In fact in all these constructions
concrete is a principal ingredient, and the metal and sand going into these
modern construction can no way be outsourced from Tamil Nadu or Karnataka, or
from the already sediment (primarily sand) starved rivers.
We
go to source such construction material from within the state and for that we
will have to open up a large number of mega-rock-quarries.
Why
rock crushed sand? We need a tutoring on Sand-101, i.e., how in the first place
sand is formed. Well what we generically
designate as sand is primarily the fine aggregation of mineral quartz, which
only forms 28% of the rocks exposed in the midland and highland of Kerala or
for that matter in parts of Tamil Nadu or Karnataka. Mineral feldspar makes up
71% of the same rock, where as the remainder 1.0% is by accessories like
ferromagnesian minerals and heavy minerals. The latter is what finally and
annually accumulates in the beaches north of Chavara to Ambalappuzha as the
famed black-sand deposits of Kerala. Otherwise the black sand resides in the
inner-continental shelf of Kerala.
The
second point is regarding the process that leads to the release of these
various minerals from the parent rock. To the surprise of non-geologists, it is
very close to a million years, or else, for one-meter cube of rock to transform
to constituent minerals so that physical processes of surface erosion and
transport can transfer the “transformed” rock to the river system.
The
process of transformation is a dead slow process as the only reagent involved
is water, humic acid (derived by the decay of fallen leaves) and carbonic acid
(atmospheric carbon dioxide dissolving in to rain drops or otherwise available
moisture).
Now
what is the fate of the minerals like, quartz (28.0%), feldspar (71.0%) and
accessories (1.0%). The rock decay, or chemical weathering in the parlance of
geochemist, destroys all the feldspar to clay with an average particle size of
2.0 microns or less. The ferromagnesian minerals also transform to clay. What are the survivors of the chemical
weathering? They are the heavy minerals (part of 1.0%) and quartz (28.0%). This
quartz sand is what we see as sand bars in the rivers (only in the historic
past) and in the sea beaches.
Therefore,
if Kerala is serious about modernizing infrastructure of sorts and if we do not
come up with a substitute for concrete, we will have to make use of coarse and
fine aggregates (i.e., metal and sand). It is better that we manufacture it
from rock rubble of the stone quarries, existing or new ones.
In
this context one may also keep in mind that concrete used in Idukki arch dam,
consumed only manufactured coarse and fine aggregates. So is the case with the
dam in Pamba which fuels the Sabarigiri Power house.
So
the lesson to learn is if we need to save our river ecology, switch to “new
generation” construction inputs. The longer the hesitation, the longer is the
road to revive the river ecosystems.
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