1. The Project:
This is an offshore project*.
It envisages dredging of the shallow sea bed of the Palk
Bay (PB) and Adam's Bridge (AB) to a depth of 12 meters in order to make
navigation possible for ships drawing a draught of 9.15 or 10.7.
The total length of the channel will be 152.2 km
(excluding the navigation route in the GOM). The canal will have two legs of
dredging totaling 74.2 km: one, the Adam’s Bridge leg (length 20 km) part;
second, the Bay of Bengal (BOB) leg (length 54.2 km). Apart from these two legs
it also will have one more leg in the PB (of length 78 km) where dredging is
not required (as this area has a depth of 12 m). (‘Executive Summary, Technical
Feasibility and Economic Analysis of Proposed Sethusamudram Channel’, NEERI,
July, 2004, p-X). The navigable route from Tutucorin to Adam’s Bridge is more
than 12 meters deep and hence it does not require dredging.
The canal will have 1:3 side slopes.
The calculated quantity of (capital) dredged material for
the total length is 81.5 to 88.5 million m3. Adam’s Bridge leg is
supposed to generate 31.5 -33.5 million m3. The Bay of Bengal leg is
supposed to generate around 50-55 million m3.
The annual volume of dredged material for the maintenance
of the canal is calculated to be 0.1 million m3 for the Adam’s
Bridge leg (20 km) of the channel (NEERI EIA, p-6.4). The same has not been
calculated for the Bay of Bengal leg (54.2 km length) of the channel yet.
The nature of dredged material is presumed to be clayey
and sandy for both the legs. Borehole soil investigations have been done for
the Adam’s Bridge part but the data for the Bay of Bengal leg is from subsoil
analysis only. However, presence of hard strata below the soft sediment is
envisaged in data collected by National Hydrographic Office (NHO),
Dehradun.
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 in volume.
The lower dredged stratum is supposed to be sandy and it will be 24.5 to 25.5
million m3 in volume.
The top clayey layer is expected to be dumped in an area
identified (using satellite imageries) as a wasteland in the Rameshwaram
(Pamban) island. This covers an area of 753 hectares and is located between
Rameshwaram in the west and Dhanushkodi in the east (NEERI EIA, p6.6). The
lower sandy layer from the Adam’s Bridge leg is supposed to be dumped in an
area in the Gulf of Mannar (GOM) 25-30 km away from the Adam’s Bridge where a
depth of 30-50 meters is available. (NEERI EIA, p-6.6)
* Project coming up in an area located beyond the low tide
line
If the dredged material from the Bay of Bengal leg of the
canal (50-55 million m3) 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 would be a preferred option. (NEERI
EIA, p-6.9)