Prof. (Dr.) Thrivikramji. K.P.
(Retd.)
Kariavattom Campus 695 581
Sea sand – a part of the mixture of clay and sand that gathered in
the sea bed during the last several 10’s of million years - finally graduated
as a promising substitute for vanishing river sand or the fine aggregate, along
with cement in the construction industry. The proposal for dredging of seabed
is wrought with several objections, viz., a). Loss of the fishing ground (hence
livelihood of thousands of fish workers and their families); b). “Death” of the
mud bank and consequent “demise” of Chakara; c). Deepening of the seabed to the
disadvantage of opportunities for fisheries; d). Aggravation of beach erosion
by waves, and e). Aggravation of water scarcity in the already water scarce
coastal belt due to water washing of salty sea sand to remove salt for sale.
Firstly, some unknown facts about sand. For the layman sand is the
granular, nearly clean accumulation of relatively hard natural material
covering the riverbed, the sandy beaches, small and large deserts and a chief
component enhancing soil quality and hence profitability of the farmer. If sand
is not available from any of these sources, then one will go blast the rock –the
ultimate source - crush and grind it to manufacture sand.
For the specialist sand is mineral quartz, SiO2, and has no doubt
about the existence of an extensive sheet of sandy-clayey sediment and
associated heavy minerals, hidden below the vast expanse of seawater of the Laccadive Sea
Most people do not worry about the ultimate source of sand and for
them, source is where it is found. It is untrue. Sand is an original
constituent (~1/3 of the bulk) of the common crystalline rocks, The latter is
now also marketed as sawed and polished slabs, as raw stone for foundation.
Lions share of the 2/3 of bulk is feldspar – an aluminum silicate of potassium
or sodium and calcium. The accessories (the ferromagnesian silicates) and
heavy minerals (ilmenite, sillimanite, zircon, garnet and monazite) together
contribute to 1 or 5 % of the total.
A process known as chemical weathering, Wc, unique to the monsoon
climate of clear wet dry spells, is responsible for transforming the hard
crystalline rock in to a state (soil formation) enabling running water to erode
and transport the constituent rock minerals (soil erosion) to new sites of
deposition. Wc also chemically converts feldspars and ferromagnesian minerals
to a group of minerals called clays. Quartz and heavy accessories are an
exception. This Wc, an extremely slow process, and a 1.0 m. thick slab of
crystalline rock takes at least a million years to weather to soil or laterite.
The water erosion did remove all the minerals including the clay. While the
quartz and heavy (black sand) traveled down the river by rolling and jumping on
the riverbed during flood, the micron sized clay physically floated down river
in times of flood at the very same velocity of floodwater to reach the final
resting place in the sea bed.
Land, Sea and Sand
In fact, a portion (6500 Km2. of the coastal land) of today’s land
area (38855.0 Km2) of Kerala, is only a later addition, in the last 12,000
years ago, i.e., by end of the last glaciation. Coastal land added by
deposition of SW monsoon wave driven seabed sand.
During the Pleistocene (1.8 ma ago), due to at least 4 different
phases of continental ice sheet and glacier ice advances, the sea level did
stand well below 100.0 m. exposing vast expanses of the continental shelf
around the continents. Kerala was no exception. As a result, a shelf area nearly
equivalent of present extent of Kerala stood above sea level, enjoying a
sub-aerial environment and forcing the Kerala Rivers to have a longer run up,
say 30 to 40 Km. more to the then shoreline. Thus, today a large alluvial
deposit of sandy-clayey nature sits in the sea bed.
But then, on set of monsoon climate in Kerala ~50-55 M.a. ago,
initiated Wc, Consequently during the same time span at least 50-55 m of
crystalline rocks would have been transformed to laterite/soil, and that too
along the length and breadth of the 30000 Km2 (pre-Pleistocene area) of the
state. And handsome portion of the detritus (heavy mineral laden sandy-clayey
sediment) must be now sitting in the Laccadive sea bed. A portion of the latter
is has already been deposited (since the Pleistocene) as the low coastal land.
This process of deposition continues even today, driven by the monsoon waves to
renew the blacksand deposit in the Chavara – Neendakara – Thirkunnapuzha
sector.
Myths of Sea Sand Mining Uncovered
The response of fisheries potential to sea sand mining is beyond
my specialty and hence not addressed in the following. Let us examine the
concerns one by one. The chakara, a relatively thick suspension of bottom mud
(like a submerged break water) triggered by the onslaught of the SW monsoon
waves on the seabed sediment appears between Thirkunnapuzha and Kozhikode . The nutrients stirred up from bottom, attracts
large schools of fish and fish-workers like a magnet. The fundamental
requirements for chakara are the wave climate and substrate of mud. The
dredging process automatically enhances the mud content in the sea bed and
hence only adds to strength and vigor of chakara.
The dredging removes large volumes of sand and hence will lower
sea bed. Look at the ship channels in the Kochi
The Chief Hydrographers maps do not show any depth changes either.
The sea bed has a very rich in sediment reservoir. The plume of murky water of
about 20 to 30 times the diameter of the barge is in fact very short lived,
especially in a region with the monsoon wave climate. Secondly, the dredger
will have to remain in-operational during the same period for safety reasons.
Secondly, the clayey sandy sediment with ilmenite and other placer
minerals is stirred up by the monsoon waves and is transported shoreward toward
the mining lease tracts of the IRE and KMML. But the finer clay particles do
not settle in the beach and is kept in suspension and is transported seaward,
southward or northward toward Thirkunnapuzha and beyond to nurture the source
sediment of Chakara. The proof of northerly transport is absence of chakara in
any place to the south of Thirkunnapuzha.
The acceleration of beach erosion is a natural concern of the
public. In Kerala, no single beach is known to have consistently undergone
erosion. It is always a mixed bag. When there is erosion it is featured in the
press and media, but not when there is accretion and gain. In fact about 6000
Km2 area in the coastal land was created by wave deposition only and that too
in the last 12,000 yr. Therefore, erosion and deposition are two sides of the
same coin and dredging as such does not influence both as long as seabed has an
optimal reserve of sediment.
Finally about the waste of water in washing the sand coming off
the dredger before it is sold. Take a look at the bridge constructed by the
L&T Ltd., connecting Kochi with Island or
the wharfs in the Kochi Bahrain Bridge
Therefore, we can always look at the sea not only for food but also
for the mineral wealth including sea sand waiting to be mined or exploited. The
choice of words is yours.
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thrivikramji@gmail.com
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