There is a good reason for nuclear plants to be established close to the sea – the ready availability of massive amounts of water needed to cool down the reactors. But the advantage of loation can quickly turn into a liability in the event of a tsunami. The Kalpakkam nuclear facility situated along the coast, south of Chennai city, was reportedly inundated by the December 2004 tsunami but besides reassurances, little information was provided on the nature of damages. In Japan, the Fukushima nuclear complex was flooded by the tsunami of March 2011 leading to fears of a nuclear meltdown. Alarmed by these events, local people are protesting the construction of nuclear plants in Kudankulam, Tamil Nadu and Jaitapur, Maharashtra.
In late March 2011, the eminent agricultural scientist, Dr M S Swaminathan wrote a letter to Jairam Ramesh, the then Minister for Environment and Forests, suggesting that bio-shields of mangroves and other species around nuclear installations could act as tsunami retardants. Although the idea of vegetation protecting human lives and settlements from nature’s fury is not new, is it supported by scientific data?
In the wake of the 2004 tsunami, a glut of scientific papers touted the life-saving propensity of so-called bio-shields. By comparing before and after satellite images, scientists pointed out that areas sheltered by mangroves and other vegetation suffered less damage than other areas. One study suggested that a forest of at least 100 metre width could significantly reduce the force of a tsunami. But it hastened to add that much depended on tree density, stem and root diameter, gradient of the shore, and other factors. A paper in the prestigious journal, Science, specified further: 30 trees per 100 square metres would reduce the destructive speed of the tsunami by 90%.
Subsequently, other scientists reinterpreted the same data to draw completely different conclusions. Many other physical features such as seabed topography, elevation of the village above sea level, and the continental shelf, played a more effective role in reducing the force of the tsunami than vegetation. For instance, a shallow coast such as Nagapattinam is much more vulnerable, than a coast with a deep shelf such as Pondicherry.
Sea grass beds seem to have had a protective influence on the mainland coast. But in the Andaman and Nicobar Islands, which were closer to the point of origin of the 2004 tsunami, the beds were completely decimated. Coral reefs appear to aggravate the destructive effects of a tsunami.
Mangroves generally grow in sheltered areas where tidal currents and waves aren’t strong. In other words, the physical features of the place that protect these coastal forests may also be shielding the area behind it. Some have suggested that scientists promoting bio-shields may be mistakenly seeing the tidal vegetation as the bulwark against tsunami damage, when it’s actually the nature of the area itself to suffer less damage.
After assessing 52 sites around the Indian Ocean, one study came to the conclusion that vegetation did not reduce the impact of inundation. Another suggests that vegetation has the potential to diminish the impact of waves, but not prevent storm surges or post-tsunami inundation, and it is the latter that causes most of the damage.
A tsunami is not a single wave, but a series of them. The first wave typically knocks down vegetation allowing the subsequent waves greater penetration. This is what happened in the Nicobar Islands. Although it had large tracts of intact mangroves at the time of the tsunami, the devastation of the coast was complete. The vegetation could do nothing to lessen the brunt of the impact.
Saw Agu, a Karen tribal who survived the tsunami, recalled giant trees toppling like matchsticks when the first 15 metre high phalanx of water slammed against the Galathea coast on Great Nicobar Island. Indeed, the main author of the Science paper who linked vegetation to reduction in tsunami damage, acknowledged coastal vegetation can only reduce the severity of destruction in areas that were not badly hit. It cannot prevent catastrophic destruction in areas directly pummeled by tidal waves.
If anything can protect the coast from a tsunami, it is sand dunes. They act as windbreaks, dissipate storm surges and protect inland areas from inundation. A resort in southern Sri Lanka flattened a sand dune to afford its guests easy access to the beach. When the 2004 tsunami hit, the hotel was destroyed and many tourists lost their lives. Ironically, in India, instead of protecting these natural coastal barricades, they are being flattened in some places to plant trees as bio-shields.
Coastal erosion caused by infrastructure projects such as seaports, has increased the vulnerability of coastal communities to natural catastrophic events. Large chunks of villages in north Pondicherry and north Chennai are being washed away because of the construction of “coastal defenses” such as groynes and sea walls. Dr R S Bhalla of Foundation for Ecological Research Advocacy and Learning, Pondicherry, says, “Events such as the tsunami, catastrophic as they are, don't pose the same level of risk that others like cyclones and even a heavy monsoon with high winds do. We need to move towards a shoreline which has the natural buffering capacity provided by sandy beaches and dunes. Coastal bio-shields may actually prove deleterious to natural beach nutrition.”
Authorities plant casuarina, a tree from the Asia-Pacific, in neat rows as bio-shield at the expense of local flora, such as spinifex and beach morning glory. Since fishermen want easy access to the beach for parking their catamarans and boats, and drying their long seine nets, the trees are rarely planted in the front of a village but on the sides, defeating the very purpose of a bio-shield. Additionally, since these plantations go right up to the high tide line, they destroy sea turtle nesting habitats.
There is a strong argument to protect mangroves for biodiversity conservation, prevention of coastal erosion and to safeguard human livelihoods. However, playing up their ability to minimize destruction caused by tsunamis and storm surges would instill a false sense of confidence and hope in local communities and authorities.