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Dredging India's Sethusamundram ship channel poses environmental risks, and could even magnify future tsunami damage, says C.P. Rajendran.

The Sethusamundram ship channel project is deepening a 75 kilometre section of the 152 kilometre passage in the shallow sea between India and Sri Lanka. On the face of it, the idea is excellent as it cuts out the need for ships to circumnavigate Sri Lanka, shortening the journey by about 335 nautical miles between India's east and the west coasts. The Rs 2,428 crores (US$609 million) project is already forging ahead.

Because of their enthusiasm for the scheme, the Ministry of Shipping appears to be soft-pedalling possible environmental impacts and show little interest in initiating scientific discussion on the venture.

Insufficient assessment

An environmental impact assessment (EIA) by the National Environmental Engineering Research Institute in 2004 certified the project as feasible, and did not envision serious side-effects. Only 75 kilometres need dredging because the rest has sufficient clearance for shipping.

But I and many others, including representatives of several nongovernmental organisations, have a number of objections. I believe the EIA did not fully address the enormous variation in the amount of sediment at different times carried by rivers in the area. In particular, the lack of data meant that studies were ambivalent about the overall amount of sediment carried into Palk Bay.

The Tamil Nadu coast in general, and the project area in particular, are highly vulnerable to tropical cyclones. The storm surge from a cyclone in December 1964 washed away the Pamban Bridge between Rameswaram and the bustling township on Dhanushkodi Island. Cyclones can affect how sediment and dredged material moves.

The EIA did not properly address cyclonic disturbances, so the amount of material to be dredged could be much greater than predicted, which in turn could have serious implications for the cost of the dredging work, as well as on the cost of maintenance dredging.

The EIA also failed to take account of tsunami hazards. It was carried out before the Asian tsunami of December 2004, when the issue was not a serious concern. But some models of the 2004 tsunami show waves entering the Palk Bay from the north as well as from the south, coinciding with the canal's alignment. Tsunami experts like Tad Murty, from the department of civil engineering at the University of Ottawa in Canada, are concerned that the canal project could provide a deep water channel for a future tsunami, magnifying the impact of the surge on the west coast.

Oil spills

There is little information on the seafloor here, yet understanding the substratum is crucial in deciding whether to dredge or blast, and in planning safe disposal of dredged material. The EIA appears to be ambivalent about adequate environmental controls with respect to identifying areas where dredged material can be dumped. Engineers need precise information if they are to identify which parts of the canal are prone to landslips.

The shallow Sethusamundram sea is constantly bridged by natural sedimentation processes. They contribute to its role as a special ecological niche for various marine organisms, including corals, in an area already degraded by human activities. New dredging and blasting will have serious, lasting effects on the local biodiversity as well as on traditional fishing.

How pollutants from ships will be dispersed in such a narrow channel is another concern. Potential threats to the area's ecology include ships that run aground or stray off course, environmental disturbances from rescue operations, and oil spills.

And if ships need to be guided by tugs, there will certainly be a huge financial cost, potentially making the journey more expensive and time-consuming than sailing around Sri Lanka.

In other words, the Government has not made a realistic cost-benefit analysis of this project.

In highlighting the major outstanding scientific issues arising from the project, I want to act as an honest broker rather than an overt advocate. I call on the Government to make a sincere effort to address these questions by referring them to an independent group of experts.

C.P. Rajendran is a scientist at the Centre for Earth Science Studies, Trivandrum, India

The opinion expressed here does not necessarily represent the views of the Centre for Earth Science Studies.