Saving Bangladesh from sinking due to sea level rise
Courtesy New Age 17/2/09
If we can trap ten per cent of the sediments coming to Bangladesh through its rivers, we can save ourselves from the curse of sea level rise. This should not be difficult. Some sediment is deposited any way and this is how Bangladesh delta has been built. We have to take some extra measures to accelerate this sediment building process,
writes Dr AM Choudhury
| 
|
THOMAS Malthus published in 1798 the ‘Essay on the principle of population as it affects the future improvement of society.’ He theorised that population tended to increase in a geometrical progression (1, 2, 4, 8, 16, 32…) while subsistence increased only in arithmetical progression (1, 2, 3, 4, 5, 6…). If Malthus’s theory was correct, mankind would have suffered extinction by now. The fact is that economists including the great ones like Adam Smith, Karl Marx, and Maynard Keynes propound their theories based on existing situation and they fail to perceive the future development of society due to increased application of science and technology and other factors. For example, the present global economic depression could not be predicted by any living economists including many Nobel laureates. Nevertheless, the warnings of the economists serve one purpose, i.e. we have to change if we want to avert the impending disaster as predicted in their theories.
Malthus’s predictions did not come true firstly because of the development of contraceptive devices helped to arrest the increase of population so much so that in advanced countries the population has stabilised; it is not increasing rather in some countries there is a negative population growth. Resources on the other hand increased tremendously because of the revolution in application of science and technology typified by the industrial revolution and green revolution in agriculture. As a result, in advanced countries people instead of living an impoverished life are more prosperous than ever before. However, this is not so in the case of least developed countries. Here Malthus’s theory still has relevance. In Bangladesh, for example, the population has doubled during the last 40 years and the agricultural production though trebled during this period and there has developed quite an affluent society, but a sizeable portion of population lives in abject poverty. Moreover, arable land is decreasing and there is a limit to growth of agricultural production, industry has not advanced as much as needed.
Bangladesh is the most densely populated country in the world. There live 150 million people in an area of nearly 148,000 square kilometres of area including forests, rivers and wetlands giving a population density of 1,000 people per square kilometre, which is the highest in the world. If we include only the habitable area, this density will be much more. But the situation is disastrous because of the prediction that, as the coastal area of Bangladesh is too low a significant section of its land area will sink as a result of rise in the sea level due to global warming arising mainly out of the use of fossil fuels at a high rate. The WMO/UNEP Intergovernmental Panel on Climate Change has predicted that the globally averaged surface temperature is to increase by 1.4-5.8 degrees Celsius between 1990 and 2100. The global mean sea level is expected to rise by about one metre during this period. The sea level rise occurs due to melting of ice in the Antarctic and in Greenland which are the major sources of land ice. Now as Bangladesh is a very low elevation delta some 20 per cent of its land area stands to be devoured by sea. The shaded area in the attached figure shows the land to be submerged by sea as a result of one metre rise of sea level. It is estimated that our GDP will incur a loss of 7 per cent due to this. This will have far-reaching consequences for Bangladesh. The rise of ocean water will force population to be congested into smaller areas, destroy agricultural lands, force migration and with a population density of 1,000 people per sq. mile will simply be unbearable for Bangladesh and it will face the greatest natural catastrophe in its history.
We know that the great river system of Bangladesh namely the Ganges, the Brahmaputra and the Meghna carry a sediment load of two billion tonnes annually. If we can develop technology of trapping ten per cent of the nature’s gift of sediments the calamity of sinking of Bangladesh coast will be averted. This is shown in the very simple calculations which are as follows. We assume that Bangladesh coast from Khulna to Chittagong has a straight coast of 300 kilometres in length. One metre rise of sea level will penetrate to a distance of 100 kilometres from the coastal boundary as is shown in the figure though this is not straight. But we have to make some simplifying assumptions for the ease of calculation. This gives us a volume of 15km cube of water that will enter into Bangladesh as a result of one metre rise of sea level in say 100 years. Now let us see the volume of two billion tonnes of sediments that comes annually through the river systems of Bangladesh. Taking the sediment density slightly heavier than water say 1.3 gram per cm cube this volume comes out to be 1.5km cube per year. Over hundred years this comes out to be 150 km cube which is ten times the volume of water that will enter Bangladesh coastal territory due to sea level rise during this period.
Thus, we see that if we can trap ten per cent of the sediments coming to Bangladesh through its rivers, we can save ourselves from the curse of sea level rise. This should not be difficult. Some sediment is deposited any way and this is how Bangladesh delta has been built. We have to take some extra measures to accelerate this sediment building process. Massive afforestation has to take place along all the river banks, along the embankments and all vacant places. Every citizen, every government institutions and every citizen will have to take part in afforestation to trap sediments. This will generate a lot of employment. Next, cross dams at appropriate places have to be constructed to reclaim land. The government has to form a land reclamation authority for this purpose. Top experts in the world can be recruited for this purpose. The world community has pledged to help Bangladesh in its effort to fight climate change. Here is a chance to save Bangladesh from a calamity. The calculations here have been kept simple, but detailed calculations involving computer and digital elevation model will not give a much different result.