Indo-Lanka land bridge-a study

By Pushpakumara Dissanayake,  Prasanna Egodawatte, Dilumie Abeysirigunawardena & Ranjit Galappatti - Lanka Hydraulic Institute
There is technical capacity in the two countries to design and build such a bridge. Indian construction firms already have experience of buildings such structures. Because of this, there is a feeling among politicians and officials that construction can begin in a few years if the two governments could agree on building the link.

Such thinking does not take into account environmental factors, the need for massive investment in high-speed transport infrastructure to connect this bridge to Colombo and several cities in South India and the conditions likely to be imposed by the agencies financing such a project. Judging by the time it has taken for similar projects to take off in Europe and elsewhere, it is not likely that we could be in a position to get through the preparatory planning and environmental study phases in less than ten years. It will be impossible to obtain any consensus among the interested parties in two countries in a climate where the environmental and economic impacts of the project are based almost entirely on speculation and pre-conceived notions.

This paper argues that if the basic preparatory studies are not set in motion immediately, we will be caught unprepared when the two countries finally agree to go ahead, as they are likely to do. One of the conclusions of this paper is that the proposed Sethusamudram navigation channel could be easily integrated into the bridge design with massive savings in cost.

Large environmentally sensitive projects have not fared well in recent years in South Asia. This is largely because environmental issues were taken up after the project has been conceptualised and designed. Heightened controversies emanating from interested pressure groups have disrupted project timetables at tremendous cost to national economies.

The need to reverse this order of project formulation and arrive at an "environmental design", possibly with near-zero impact, would pay for itself many times over in making it possible to stabilise project costs and deliver results on schedule. An environmental design cannot be arrived at without extensive studies and public discussion of issues and concepts. Doing this in the two countries would require an unprecedented effort at mutual co-operation, trust and transparency.

Adam's Bridge
The distance between Dhanushkodi at the eastern tip of Pamban Island in India and Talaimannar at the western tip of Mannar Island in Sri Lanka is about 27km. A curved chain of islands known as Adam's Bridge straddles this shallow gap. Along Adam's Bridge there is a total of 21 km of water and 9 km of islands to cross. The average depth of the straits is about 0.5 m interspersed with several deeper channels. While some of the islands are stable, others are less stable with shifting sands. The deeper channels are not stable and consequently there are no recognised navigation routes crossing Adam's Bridge.

Swan(1983) describes Adam's Bridge as a shallow ridge of recent conglomerate and sandstone mantled with islands and shoals of shifting sands. The shape of the chain of islands is expected to indicate that there is a net movement of sand and water from the Palk Bay towards the Gulf of Mannar. The adjacent coastline along the Gulf on both sides of the straits are fringed by coral reefs growing on cemented beach rock at about -3m MSL. The movement of water and sand does not allow coral to grow on Adam's Bridge. There appears to be a deeper layer of sand stone at the levels of around -10m MSL.

The shallow sea in this area is said to contain highly productive and rich fishing grounds, which could be temporarily disrupted by construction activity and affected in the long term by any changes in circulation patterns and water exchange across the strait. Swan also reports that the 1964 cyclone which crossed the island of Ceylon and reached the Gulf of Mannar caused a water level rise of more than 2 metres at Vankalai near Mannar, underlining the need to take into account storm and barometric surges in designing any bridge.

Bridging the Straits
Bridging the straits does not pose any great technical challenge. The straits are so shallow that it is even possible to fill in a long embankment to connect the two land-masses. However, this is not a realistic option because of the fisheries potential and environmental value of the Palk Strait and the Gulf of Mannar. Any construction in Adam's Bridge would have an impact on water exchange across the gap and circulation in the adjacent areas. Furthermore, there is insufficient data and understanding of the phenomena to enable us to predict accurately the consequence of constructing such a bridge.

The initial concept for the bridge (BOI, 2002) takes the most cautious approach, which is to make the minimum interference with the waterway by bridging the entire 21 km with a shallow bridge. The preliminary design, however, does not account for storm surges that can occur in the event a severe cyclone crosses over from the Bay of Bengal.

Thus the actual cost would then be much higher than anticipated. Even a shallow bridge, with short spans in shallow water will cost about three times as much per kilometre than a sand-fill embankment adequately armoured on both sides. Therefore it is necessary to investigate whether a combined bridge-embankment could be engineered at a lower cost with adequate compensation dredging to nullify the blockage of water exchange caused by the embankment.
The idea of "zero impact" design is not new. In particular, this concept was implemented successfully in Denmark in the Great Belt and Oresund fixed link crossings.

However, a very important characteristic of this approach was the long gestation period, which was necessary for carrying out the environmental studies and to evolve the final concept and design. While the long gestation period is considered by some to be a disadvantage, it is also ensures that a true consensus is reached about the project concept to the satisfaction of all parties.

Once this stage is reached, such projects are usually completed within schedule and without major cost over-runs. The "environmental design approach" is foreign to South Asia where projects are driven by powerful government agencies with very little concern for transparency or, apparently, for environmental and social impact. This approach, which has made them easy prey to interest groups, has resulted in even greater delays, massive cost over-runs and on occasion outright cancellation of projects, is now discredited. A new approach is needed.
A numerical model study was carried out at Lanka Hydraulic Institute to explore and demonstrate the possibilities of using a combined embankment and bridge is place of a long bridge.

There was sufficient data available in the public domain to make a valid preliminary exercise using MIKE 21 hydrodynamic modelling software. From an examination of the tidal constituents and phases as published, it is apparent that the shallow Adam's Bridge prevents the transmission of the tide across it and the tidal wave travels all the way around Sri Lanka to create a phase difference of about 10 hours across the straits.

Although the two sides appear not to be too far out of phase, the semidiurnal daily inequality can cause significant water level differences to drive a strong current both ways. The bathymetry was obtained from Admiralty Charts. The scenarios tested first examined the exchange of water across Adam's Bridge in the natural state at a spring tide, with and without a strong southwesterly wind.

A third scenario simulates the flow when an embankment is built to block all but 2km of the gap. The model also looked at what would happen if a 2 km wide channel is dredged down to -10m MSL. The fifth scenario simulates the dredged channel with the strong southwesterly wind.

It was possible to demonstrate that the effects of blocking much of Adam's Bridge with an embankment can be countered by "compensation dredging" a deeper channel to allow the same volume of water to be exchanged.

Project cost
Some project costs are given in BOI(2002). These can be considered to be preliminary, as they do not take into account the full cost of investigations and the need to take storm surges into account. A more realistic estimate is needed as well as a comparison of the cost of the two alternatives.

The first option is the original proposal strengthened to allow for a higher bridge deck and double rail track. The second is the option to build only a short high bridge of total span 2 km and an embankment of 28 kilometre length with material from the 78 million cubic meters of material generated by the dredging for the channel.

The cost figures are to be taken as very preliminary given that no site specific subsurface data are available. Nevertheless it has been demonstrated that up to 30 percent savings in costs are achievable with the combined bridge/embankment.

The objective of this very rough analysis is to show how much cost can be saved while obtaining the additional benefit of a 10 m deep navigation channel. The policy document "Regaining Sri Lanka" outlines a vision of the future where Sri Lanka becomes the gateway to South Asia in general and to India in particular.

It is not the purpose of this paper to make the economic case for building this bridge between Sri Lanka and India. However, it is the stated policy of both governments to improve trade to a point where the two markets work as one.

There are comparisons that can be made to the essential role played by Hong Kong in the commercial and economic emancipation of China. Sri Lanka too has the geographical position and the fast developing service industry that can complement the emerging industrial power of India.

The future prosperity of the region would be built on a growing interdependence of the two economies. There are those, in both countries, who are politically opposed to such a symbiotic relationship - a relationship that might turn out to be very difficult to dismantle once entered into.

The advantages to both countries are manifest - even though it is not yet possible to quantify these advantages.The building of this bridge is inevitable. The danger is that our leaders do not realise the planning stages can take up to three years before the financing plan and detailed design could even begin.

Thus it is necessary to begin planning now so that the concepts refined and the environmental concerns are dealt with before the political decision is finally made. This bridge is not merely a transport link for people and goods.

There are possibilities for oil and natural gas pipelines and electrical power grid linkages that could revolutionise the availability of low cost electricity to Sri Lankan industry. It is well nigh possible that the best plan would be to develop the bridge together with a navigation channel passing under it in place of the present proposal for the Sethusamudram navigation channel. synergies are compelling.

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