5.
Discussion
5.1.
The Issue
Navigation
channels have so far been dredged in the East Coast of India only near the
shipping ports. This is the first time that an effort is being made to dredge a
channel that is not located near any shipping port. This probably is the first
effort by India to dredge a navigation channel that is to be located 30 to 40
km away from the coast. This, again, is the longest sea bed dredging project
planned so far in India.
Navigation
channels of ports of the East Coast of India have been facing two major
problems persistently. They are 1) problems due to sedimentation and 2)
problems due to the Tropical Cyclonic disturbances.
Sethusamudram
Shipping Canal Project will also be facing these two problems persistently,
during its operation. The examples of the silted pre-modern ports of Thondi,
Devipattinam, Alankulam, Adhirampattinam, the examples of the cyclone
devastated Pamban Bridge and Dhanushkodi and the cyclone battered boat building
yards of Mandapam and Morepanai that are located in the Palk Bay coast,
highlight the importance of studying these issues thoroughly during the design
phase of the SSCP itself.
The
Technical Feasibility Report (TFR) and the rapid Environmental Impact
Assessment (EIA) for the SSCP, both completed by the National Environmental
Engineering Research Institute (NEERI), are the two sources of study on the
basis of whom the SSCP authorities are claiming that the project would be safe
and stable.
Accepting
these two reports as thorough going studies on the SSCP, on the problems it
would face in the future from the environment around, its effect on the
environment, and the ways and means to overcome both these problems, the
Ministry of Environment & Forests (MoE&F) has given a No Objection
Certificate (NOC) for the project recently.
The
Tamil Nadu Pollution Control Board (TNPCB) is yet to give its clearance for the
project. It has arranged a series of Public Hearings from 19th to 30th
December 2004 and has invited the civil society to represent its opinion on the
issue.
The
present monograph is one such opinion. It is based on the published literatures
from various scientific journals, proceedings of various seminars conducted on
the environmental and geological problems faced by the Palk Bay.
This
monograph is of the opinion that the TFR and the EIA, as of present, are only
partial studies of the issue of sedimentation that the SSCP would be facing.
The monograph has also found that the TFR and EIA have not considered the issue
of the effect of cyclones on the project.
This
monograph feels that it would be premature to conclude, at the present juncture
(based on these incomplete study reports), that the SSCP would have the ability
to remain stable and operate safely in the environment of Palk Bay.
The
following portion of the monograph provides the necessary proofs for this
statement. It also presents important data unconsidered, at present, by the TFR
and the EIA.
5.2.
General conclusions:
1. Palk
Bay is one among the five major sediment sinks of India. (Chandramohan et.al., 2002) (TFR
& EIA have not stated this explicitly)
2. Tamil
Nadu coast bordering Palk Bay (between Nagapattinam and Mandapam) is classified
by the India Meteorological Department (based on the past storm surge values)
as a ‘High Risk Prone’ coast to cyclones.
(N. Jeyanthi,
2002) (TFR & EIA are, at present, blind to this finding).
3. Sea
Surface Temperature of Bay of Bengal is increasing; this is likely to induce
the formation of more intense cyclones (and thus more severe storm surges) in the
Bay in the future. (M.Lal,
2001) (TFR & EIA are, at present, blind to this finding).
4. Out
of the six major coastal regions of the Bay of Bengal, the coastal regions of
Bangladesh and Tamil Nadu are most vulnerable for Severe Tropical Cyclones as
the anticipation of occurrence of such weather calamities are difficult over
these two coasts. (Sutapa Chaudhuri et al., 2004). (TFR & EIA are, at present,
blind to this finding).
5. The
Sethusamudram Shipping Channel is to be located in an oceanographic environment
having the above said attributes.
5. 3.
The issue of Sedimentation
Palk Bay
receives its sediments from Gulf of Mannar, Bay of Bengal (Nagapattinam coast)
and from the Indian and Sri Lankan rivers draining into it.
Waves,
Tides and the longshore currents are responsible for transporting these
sediments to different locations.
5.3.1.
Net annual quantum of sediment transported into Palk Bay – Problems yet to be
solved
Chandramohan
et al (2002) have calculated the annual sediment load on the Palk Bay.
According to their study, this is about 0.30 X 1010 m3/51
years (1931 – 1982) for an area of 12,285 sq km. This is 0.00588 X 1010
m3/year (or 58.8 X 106 m3/year).
Sanil
Kumar et al (2002) have calculated the net annual quantum of sediment
transported by longshore currents from the Nagapattinam coast into the Palk Bay
for two cyclone free years (1995-1996 and1998-1999). This is 0.095 X 106 m3/year.
NEERI
EIA (2004) has presented a calculation of the net annual quantum of sediment
transported by tides and longshore currents into the Palk Bay from Gulf of
Mannar through the Pamban Pass and the Adam’s Bridge. The net annual
contribution by the longshore current (from Dhanushkodi west to Ariyaman) is
2,46,200 m3 (or 0.2462 X 106 m3). The net
annual contribution by the Tides is 19,500 m3 (or 0.0195 X 103
m3). Thus, the total net annual quantum of sediment transported into
the Palk Bay from Gulf of Mannar through Pamban Pass and Adam’s Bridge is
2,65,700 m3 (or 0.2657 X 106 m3). (NEERI EIA,
p- 2.22 to 2.33).
|
The
annual sediment load = 58.8000 X 106 m3 The net annual
quantum of sediment
transported by longshore currents from the Nagapttinam coast into the Palk Bay = 00.0950 X 106 m3 The total net annual
quantum of sediment transported by tides
and longshore currents into the Palk Bay fro Gulf of Mannar through
Pamban Pass and Adam’s Bridge =
00.2657 X 106 m3 |
|
The net annual
quantum of sediment for which the source is not yet
pinpointed (58.8000 X 106 m3
–(00.0950 X 106 m3 + 00.2657 X 106 m3 ) = 58.4393 X
106 m3 |
So,
we are yet to have studies that pinpoint the source for 99.386% of the net
annual quantum of sediment entering into the Palk Bay. Studies on the quantum
of sediment transported in the Palk Bay during cyclonic disturbances are non
existent.
Here,
let us briefly analyze the sedimentation data presented in the NEERI EIA.
1.
The
EIA has made a selective attempt to present the data on the net annual
quantum of sediment transported by tides and longshore currents into the Palk
Bay from Gulf of Mannar only. It has not tried to calculate the quantum
of sediments deposited into the Bay by the rivers, and also it has not
attempted to present the data on the quantum of sediment entering into Palk Bay
from the Bay of Bengal.
2.
The
EIA has not referred the most recent studies conducted by various
research groups on the sedimentation problem of Palk Bay. For instance, it has
included P.Chandramohan’s paper titled ‘Distribution of longshore sediment
transport along the Indian coast based on empirical model’ in its bibliography.
This paper was presented in a conference held in December, 1989. Since then, he
and his colleagues at the National Institute of Oceanography (NIO) Goa and the
National Institute of Ocean Technology (NIOT) Channai, have published their
further studies in sedimentation in various journals like ‘Journal of Coastal
Research, Indian Journal of Marine Science and Current Science’. Data presented
on the net annual quantum of sediment transported by the longshore currents in
the Nagapattinam coast in the studies published as late as 2001 have been
rejected summarily by the studies published in 2002 (Sanil Kumar, 2002). Hence,
in this fast improving field of research, quoting a study that is almost 15
years old and neglecting the more recent important ones does not seem a right
scientific practice.
3.
The
EIA, instead of analyzing the total sedimentation issue of Palk Bay, has
tried to underplay the issue by presenting statements like: ‘The east coast
between Chennai and Paradeep experiences a gross transport rate of more than
1X106 m3/year. On the other hand, along the study region,
it remained always less than 0.1X106m3/year (?), which
shows only 10% of the rest of the Indian east coast.’ (EIA, 2.19). This comparison is made between the gross
sediment transport rate of the coastal stretch of Chennai – Paradeep and the net
transport rate calculated for the the Dhanushkodi-Ariyaman coastal stretch
(shouldn’t the gross sedimentation rate for this stretch be 0.476 X 106
m3/year?); first of all, this comparison is an incorrect one, as it
should have been a comparison between the net sediment transport values
of the two coastal stretches; while comparisons made among the various coasts
will help us to form a picture of our study area in relation to the other
stretches, they will not help us much in devising our planning strategies, as each
coastal stretch has its own unique characteristics.
5.3.2.
Calculations on the extent of sediment deposition in various sections of the
PalkBay – The yet to be answered questions:
I)
S.M.Ramasmy et al (1998) have calculated the accretion of sediments and the
extent of land building activity in the Vedaranyam offshore area. They have
concluded that in the Vedaranyam – Jaffna peninsular stretch of Palk Bay, the
sediment building activity due to littoral currents seems to be happening at
the rate of 29 meters/year and hence they have opined that there is a
possibility for such land building activity to connect Vedaranyam to the Jaffna
peninsula in another 400 years.
This is
an empirical finding backed up by 14C dating. Usha Natesan’s study
(published in April,2004) explains, using satellite imagery, how such an
accretion and land building in the Vadaranyam offshore area is possible. It
describes how the SW monsoon disturbs the sediments of the tidal flats in the
northern portion of Palk Bay and how these sediments are obstructed in their
northerly movement by the Vedaranyam land projection; it also describes how the
sediments transported from north during the NE monsoon are unable to take a
bend around the Vedaranyam tip; it also describes that a portion of these
sediments start traveling eastwards and the rest move down south along with the
longshore currents.
An
earlier study done on the extent of shoreline oscillation of the Tamil Nadu
coast (Usha Natesan, 1993) presents some interesting findings:
a) Annual mean berm
crest fluctuation decreases as we go from north to south from Nagapattinam to
Rameshwaram from 20 meters to 2 meters.
b) Accretion is high
always in the period between June and August. It is low (or say erosion is
high) in the period between November and January (Here Mandapam is an exception
as there is accretion in January). There is a deviation from this trend in
April in Point Calimere, where there is a sudden decrease in accretion (or an
increase in erosion) in the month of April.
This data indicates
to us that the southern portion of Palk Bay is accretionary though out the year
where as the northern portion experiences both erosion and accretion.
Accretionary tendency is greater during the South West Monsoon period (June to
August) and it is low (or erosion is high) during the North East Monsoon
(October to January).
V.J.Loveson et al
(1990) have stated that since
drainage network is absent in the coastline between Kodiakkarai to Rajamadam
area, the seaward migration of this shoreline can be attributed to the
accumulation of marine sediments only.
Sanil
Kumar et al (2002) have given the value of the annual net quantum of sediments
transported by the longshore currents (during cyclone free years) from the
Nagapattinam coast into the Palk Bay as is 0.095 X 106 m3/year.
Chandramohan
et al (2002) have stated that the depth of Palk bay is getting decreased by
0.010 meters (1 cm) every year.
The
foregoing findings throw up the following questions:
1.
How
can the finding of the sea depth reduction of 1 cm/year explain the empirical
observation that the coast of Vedaranyam is migrating seawards at the rate of
29 meters / year?
2.
Can
0.095 X 106 m3 of sediments transported by the longshore
currents from the Nagapattinam coast annually explain the 29 meters per year
seaward migration of the Vedaranyam coast?
3.
V.J.Loveson
et al state that the seaward migration of this coastal stretch is due to the
accumulation of marine sediments only. Usha Natesan (1993) states that
accretion of sediments in this coast is happening during the SW monsoon and
erosion during the NE monsoon. She also notes that there is erosion in this
coast during the pre-monsoonal month of April. Prakash Chauhan et al (1996)
have noted that ‘during the non-monsoon season sediment boils were observed near
Vedaranyam and Mandapam.’ This they say ‘may be attributed to the difference of
the density of the different water masses and the prevailing current
direction.’ How do all these findings help us explain the 29 meters / year
seaward migration of the Vedaranyam coast?
4.
64 cyclones have crossed the Tamil Nadu coast in the
period between 1891 – 2000 A.D. 55% (36) out of these cyclones happened to be
Severe Cyclonic Storms (wind speed more than 89 kmph). Out of the 61 cyclones
that have crossed the Tamil Nadu coast in the period between 1891–1995 A.D., 6
have directly crossed the Palk Bay; 14 have crossed the Nagapattinam coast; 3
have crossed the Gulf of Mannar. What would have been the pattern of
sedimentation during these? What would have been the role of these cyclones in
causing the 29 meters / year seaward migration of the Vedaranyam coast? No
studies have been conducted so far on this topic of cyclones and sedimentation
for this area. (However, some observations do exist on this issue. For instance,
the NEERI EIA states: ‘The studies carried out by NSRDC signify that the region
around Adam’s Bridge forms a significant sink for littoral drift. The prolonged
accumulation in this area may lead to emergence of new island. In case of
occurrence of cyclone in Gulf of Mannar, such prolonged deposition of sediments
move north and enter Palk Bay through Pamban Pass and Adam’s Bridge. Once the
sediments enter Palk Bay, the environmental condition favors immediate
deposition. Hence the occurrence of cyclone in Gulf of Mannar and the
associated northerly waves might, exchange more sediment from southern part of
Peninsular India to Northern part of east coast. Thus the quantity of
maintenance dredged spoil will increase in the channel across Adam’s Bridge in
the event of cyclone.’ (p-6.4) Sanil Kumar (2002) notes: ‘It has been observed
that for the occurrence of every cyclone, there was a permanent loss of beach
due to erosion (Jena, B. K., Chandramohan, P. and Sanil Kumar, V., J.
Coast Res., 2001, 17, 322–327). As the Palk Bay is well protected
for southerly waves, no mechanism is set to transport these deposited materials
towards the north.’)
5.
What are the factors that are responsible for the 29
meters / year seaward migration of the Vedaranyam coast?
Pertinent answers to these questions are necessary for
designing ‘the course and the structure’ of the proposed 54.2 kilometer length
of the channel that is to be dredged in the northern portion of Palk Bay.
Moving forward with the project with out these answers might turn out to be
costly for our Nation in terms of money and honor.
II) G.Victor Rajamanickem’s paper (2004) states: ‘The spit growth in Manamelkudi is
of the order of 0.75 meters per year…
(It is interesting to see that the maritime surveys conducted between
1960 and 1986 reveal the change of contour to the tune of 6 meters shallowness
in the Palk Strait. That shows that around 24 cm per year is being silted off
in the Strait.) Similarly, one can visualize the growth of spit from the
Talaimannar side. If both the spits grow in the existing rate of growth, one
can visualize the merger of this two within the next 50 years. Once these spits
join, the Palk Strait will become into two lagoons of north and south.’
The
findings of this paper are different from that of Chandramohan et al (2002).
This paper notes that the spit in Manamelkudi is growing at the rate of 75 cm/
year; Palk Strait has become shallower by 6 meters in 26 years i.e. it is
becoming 24 cm shallower every year. On the contrary Chandramohan et al (2002)
state that it is only 1 cm/year for the whole Palk Bay. What should we conclude
from these findings?
We
may safely conclude that a few portions of Palk Bay are more prone for
excessive sedimentation than other areas. The finding of Chandramohan et al (2002) is an
average value for the whole Bay and so to have a real picture of the
sedimentation regime in the Palk Bay, we require micro level studies in
the various portions of the Bay having different sedimentation patterns. In
this context, we shall note here that Agarwal (1988) has studied the
Manamelkudi area; Chandramohan et al (2000) have studied Puduvalasai
coast.
The
proposed alignment of the Sethusamudram Shipping Canal Project passes through
three different sections of Palk Bay having three different sedimentation
regimes. The northern leg of the channel is 54.2 km long and it passes through
Palk Strait. The southern leg of the channel is 20 km and it passes through
Adam’s Bridge. Both these regions are noted for their high sedimentation
profile. The central leg of the channel is 78 km long and has a comparatively
lower sedimentation profile. Dredging is proposed only for northern and
southern legs and the central leg would not require any dredging.
Knowledge
on the sedimentation regimes existing in these three sections is sketchy at the
present time. A series of studies on the sedimentation patterns and dynamics
existing in these sections both during cyclone free years and during the
cyclonic years is a basic necessity for designing ‘the structure and the
alignment’ of the canal.
It
is important to note here that both the NEERI EIA and the TFR have not
consulted any of the studies (even though they are only preliminary) that have
been conducted by various research groups to understand the sedimentation
pattern and dynamics of these three sections of Palk Bay.
Thus
accepting these reports as scientifically complete ones would definitely prove
hazardous for the future of the canal.
5.4.
Handling the Dredged Spoils
The total quantity of spoils that would come from capital
dredging is supposed to be 81.5 to 88.5 X 106 m3. The
quantum of dredged spoil that would come from maintenance dredging is supposed
to be 0.1 X 106 m3 / year.
The top clayey layer that will be dredged from the Adam’s
Bridge leg of the canal is supposed to be 7-8 million m3 (7 to 8 X
106 m3 ) in volume. The lower dredged stratum is supposed
to be sandy and it will be 24.5 to 25.5 million m3 (24.5 to 25.5 X
106 m3)in volume. About 50 to 55 X 106 m3
of dredged spoil is supposed to come from the northern leg of the canal.
The nature of the dredged spoil is presumed
to be clayey and sandy for both the legs but there is an uncertainty here. For
the northern leg of the channel passing through Palk Strait, no borehole investigation
has been done so far. Unlike the Adam’s Bridge section, hard substrata
are expected by NHO. In such a
scenario, blasting might be required for the canal excavation and strategies to
dump these rock spoils be devised freshly.
The net annual sediment load to Palk Bay (Chandramohan et
al, 2002) is 58.8 X 106 m3 (for an area of 12,275 sq km).
Capital dredging, thus, would generate a sediment load
that is 138.61 % of the net annual sediment load to the whole Palk Bay; or in
other words, a sediment load that will be deposited in a time span of roughly
16 months in Palk Bay would be excavated from the channel from an area of 22.26
sq km.
The site chosen for dumping the upper layer dredged spoil
of the Adam’s Bridge section lies between Rameshwaram and Dhanushkodi and its
area is 7.53 sq km (753 hectares). The lower sandy stratum of dredged spoil
from the Adam’s Bridge is supposed to be dumped in an area in the Gulf of
Mannar 25-30 km away from the Adam’s Bridge where a depth of 30-50 meters is
available. The exact site is yet to be fixed. If the dredged material from the
Bay of Bengal leg of the canal turns out to have a high silt content, then land
disposal in proximity to dredging area (which shall avoid the ecologically
sensitive locations like Point Calimere Bird Sanctuary) is being thought of.
Also, as this area is close to Bay of Bengal where depth more than 40 meters is
available, disposal in sea is being thought of. Here also, the exact site of
disposal is yet to be decided.
Thus, specific dump site has been identified only for 8.5
to 9.5 % of the total dredged spoil. Idea about the nature of the dredged spoil
is available presently, only for about 38.5 to 40.5 % of the total dredged
spoil. No idea exists at the present time on the nature of the dredged spoil
that would be generated for 59.5 to 61.5 % of the total dredged material. We do
not know the exact dump sites for about 90.5 to 91.5 % of the dredged material.
Palk Bay is an oceanographic environment where we see
areas of higher and lower sedimentation rates. Dredging and dumping these
dredged spoil in the area around, will not only change the physiography of the
area but also is bound to change the sedimentation dynamics existing in the
area so far.
Knowledge about the nature of the dredged material, its
exact dumping location, the area of the dump sites and how it would behave
during the many changing environmental conditions is a must for giving a
clearance for the project, as all the above factors will have a great bearing
on the future of the canal, physiography of the area and the life forms present
in the environment around.
The dredged spoil from the upper layer of the southern leg
of the canal is equivalent to about 12% of the annual net sedimentation load of
the Palk Bay. This is to be dumped just in an area which is just 0.06% of the
total area of the bay. Similar will be the case for the dredged material from
the other components of the canal.
How will these dumps behave during the SW, NE monsoons and
the fair-weather periods? How will they behave during the times of cyclonic
disturbances?
Can the embankments planned (proposed by NEERI) for the
Dhanushkodi dump site protect the dump from leaching and erosion due to the
storm surges created by cyclones? (1964 and 1978 cyclones had produced storm
surges with 6 and 5 meter heights respectively). What would happen to the
environment around if this dumping yard is washed into the Bay as the 1964
storm surge had engulfed the Pamban Bridge and Dhanushkodi? Don’t we need
specific answers to these questions before giving a clearance for this project?
All the studies we have cited so far tell us that in the
event of cyclones (in Gulf of Mannar, Nagapattinam coast) sediments move into
Palk Bay. What would happen to the dredged spoil (equivalent to 126% of the
annual net sedimentation load of the Bay) that would be placed south (?) of
Adam’s Bridge and (possibly) north or north east of the Palk Strait, in the
event of cyclonic disturbances? How will these dumping sites behave during
cyclone free years? What would happen to them, the Dhanushkodi dump, the
Channel proper and the auxillary buildings and structures (remember the fate of
Mandapam & Morepanai boat building yards in the 17-24 November,1978
cyclone) during the cyclones that would cross the Palk Bay in the future?
Experts have been warning over the past few years that the
recent increase in the Sea Surface Temperature (SST) of the Bay of Bengal Sea
is bound to produce more intense cyclonic storms, which in turn will produce
higher storm surges. Sutapa Chaudhuri et al (2004) have concluded in their
study that prior prediction of cyclones that are to cross the Tamil Nadu and
Bangladesh coasts will have a higher uncertainty component than the predictions
done for the Andhra, Orissa, Bengal, Arakan (Burma) and the SriLankan (east)
coasts. Thus, the time required for prior preparedness to safeguard from the
storm will be less when compared to the other coasts. This fact has made them
to classify Tamil Nadu and Bangladesh coasts as the most vulnerable ones among
the many coastal regions of the Bay of Bengal, for Severe Tropical Cyclones.
Shouldn’t we consider these findings
while designing the channel, the dump sites and the auxiliary buildings and
structures?
The NEERI EIA and the TFR have not consulted
them.
Nevertheless, the Ministry of
Enviroment & Forests has given a clearance for the project.
This, we feel, is rather unfortunate.