Plugging the breaches

Can the people of the Sundarbans find a viable solution to the problem of flooding?

Published: Sunday 31 October 1999

-- (Credit: amit shanker / cse) the Sundarbans -- home to the Royal Bengal tiger and comprising some of the most dense mangrove forests -- consists of 102 islands, most of which lie in Bangladesh. Fifty-four of the islands are devoid of any forest cover because of the century-long process of colonisation. These islands, with their encircling protective embankments, support a population of approximately 25 lakh. Of late, the incidence of storms has increased, resulting in breaches in these embankments that cause untold misery to the island-dwellers.

The Sundarbans is a natural delta situated at the confluence of the Ganga and the Brahmaputra, and the islands were formed by silt deposits from the rivers. However, the nature and timing of human settlements brought in a series of enduring problems for the region. Colonisation undertaken by land-hungry peasants and absentee landlords backed by colonial rulers did not take into account the fact that many of the islands were not entirely suitable for human settlement because of silt deposit levels.

The occurrence of tides at regular intervals of twelve and a half hours meant that a huge volume of water flowed into the rivers. Water levels go up by 4-5 metres; but for the embankments, which together stretch for around 2,500 km, the islands would be submerged by the high volume of saline water. The early embankments were pioneered by landlords who did not organise their efforts in a scientific manner but, nonetheless, managed to construct mud embankments that totalled 3,500 km. Breaches in the embankments were a common feature leading to loss of life and property.

Natural forces like storms and cyclonic conditions are the main reason for breaches. The impact of wave dash on the embankments results in erosion of the foundations and slopes. Subsequently, there are breaches and even collapses. The other more important reason is the steady wearing away of the foundations and slopes by the complex system of strong currents. Tidal flows in the Sundarbans occur at regular intervals and these affect the intensity and flow of currents under the river.

Water flows into the Sundarbans during rising tide, as long as the rivers and unprotected lands are lower than the sea level. Likewise, water flows to the sea as long as the water in the system of waterways and unprotected areas is higher than the sea level. When seawater flows in, strong currents are formed in the river to enable it to deal with the volume and intensity of the flow.

So, how do we address the problem of breaches? Theoretically, there are two approaches that can be used: the 'closed' and the 'open' systems. The 'closed' system consists of a series of interventions like closing river arms, building dykes (as in The Netherlands) and construction of large sluices in order to eliminate tidal movement in the area. This approach certainly merits attention, though it offers no absolute guarantee against Nature's fury and involves enormous capital investment in the initial stage.

The 'open' system, on the other hand involves alert monitoring of physical developments and taking adequate measures in anticipation of these developments and initiating natural defence mechanisms. The efficacy of this system is dependent on an improved data base relating to tidal regimes, impact of water flows on the waterways, and the accumulation and erosion of silt deposits. It is only when we can scientifically ascertain facts about tidal flows, about the quantity of water flowing from the sea into the rivers and the receding of the same into the sea that we can confront the problem effectively.

But the only solution that seems viable is to push back the existing embankments and encircle them with a ring embankment. Admittedly, the move is likely to dislocate some people who will have to be rehabilitated. Ultimately, the people of the Sundarbans will have to be involved in what should be a collective exercise, for the responsibility of maintaining the embankments is theirs.

However, the task can only be facilitated if government agencies, voluntary groups and panchayats functionaries come together to organise awareness camps to disseminate relevant information to the local residents. For the Sundarbans dwellers, embankments are crucial to their very existence and the need to maintain and strengthen them is a basic precondition to their survival.

The author is secretary of the Tagore Society for Rural Development, Calcutta.

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