Embankments of Sunderban: A Legacy of Historical Blunder

By: Abhay Sankar Sahu
The construction of the embankments and the occurrence of floods in the Sunderban have raised the question of relevance and maintenance of the water front embankments to protect the region.
Planning n Mitigation

Sunderban, or the part that falls within the boundaries of India, is located on the lower part of the Ganga-Brahmaputra-Meghna delta along the Bay of Bengal, between Hugli estuary on the west and Ichamoti-Raimangal river on the east. Prone to varied natural disasters, from flooding to cyclones, Sunderban offers a fragile refuge to its teeming masses.

Natural hazards cannot be prevented, but their impacts might be diminished if proper scientific remedial measures are adopted in time. From the beginning of our civilisation, embankments have been constructed to redress the damage incurred by monsoonal floods, and tidal and wave incursions during severe tropical cyclones affecting the coastal areas.

From the last quarter of the 18th Century to the beginning of 19th Century, the British reclaimed the islands of Sunderban by placing a girder of water-front mud embankments along the coasts. However, as the insides of these loamy dynamic islands were lower than the surroundings, it resulted in depth differences in the post construction phase with serious and far-reaching environmental problems. In the British period, zamindars were the intermediaries between British rulers and their subjects, insofar as the socio-economic system was concerned. Following the technical advice of the British rulers, local zamindars constructed embankments by mobilising the poor peasantry without paying heed to proper and necessary engineering specifications. The purpose was clear – settle their subjects and increase the revenue.

Thus began the saga of floods. The depth of the rivers and creeks of the estuarine belt progressively decreased with increased sediment deposition along drainage channels. Embankment height along riverbeds increased continuously, whereas; land within remained as and where it had been earlier creating a negative gradient. Generally a gentle slope is found from the river channels to the interior of the islands. With the presence of huge water bodies around Sunderban it would have been advantageous if the interior were of lesser negative gradient. In that case the pressure of the water bodies could have been counteracted. But this is not the case — since the embankments were constructed during the formation of the islands, the natural dynamic process of gradual sediment transfer from the riversides to the interiors of the villages was artificially blocked leading to a difference in depth and a resultant manifold flood potential.

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Image 3: Covering an area of 9630 sq.kms, including 102 islands, with an average elevation of 3 to 4 metres above mean sea level, the region supports a total population of about 42 lakhs as per the 2001 census.
Image 3: Covering an area of 9630 sq.kms, including 102 islands, with an average elevation of 3 to 4 metres above mean sea level, the region supports a total population of about 42 lakhs as per the 2001 census.

When engineering embankments, technically sound methods and proper maintenance measures need to be put in place — according to soil conditions, height of the tides (base-width and top-width), slope of land, point heights etc. In the Sunderban the total length of the flood-embankments on rivers, tidal creeks, and sea is around 3,500 km. Tidal water level swings between 3.5 to 4.0 m. As per engineering prescriptions, when increasing the height of an embankment is necessitated the base of the same has to be widened accordingly. But this widening of base cannot be carried out since it usually envelops land already occupied for agriculture, fishing and other public uses. Under these circumstances, compromises are often sought and height increase or vertical dimension of the embankments is commissioned. Vertical propping up of embankments without horizontal expansion cannot endure the pressure of water bodies. Also locals use embankments for their various socio-economic pursuits. Cows are tethered to stakes along the banks and events and meetings are held on the high ground. Rampant activity creates cracks and fissures that make the embankments prone to breaches.

In the post Independence era Sunderban has found little respite in the form of scientifically engineered interventions. Today embankments are a necessity and a reality for the survival of the people inhabiting these lands despite the fact that they may have in many ways compounded the problem of flooding and salt water inundation. With a climate change crescendo in the wake Sunderban seems to be more vulnerable now than it ever was before. Faulty design compounded by anthropogenic pressure on the embankments make it vulnerable. They are unable to withstand the continual pressure the high and low tide exerts and are on many occasions breached successively. Since this vulnerability is visible to the local people, they demand continuous maintenance, an unending exercise and a serious drain on our resources. The demand becomes more acute and prolific during the rainy season, particularly during the highest astronomical tidal phases.

Wetlands occur where the water table is at or near the surface and land remains covered by water. Once treated as transitional habitats or seral stages in succession from open water to land, wetlands are now considered to be distinct ecosystems with specific ecological characteristics, functions and values.
Wetlands occur where the water table is at or near the surface and land remains covered by water. Once treated as transitional habitats or seral stages in succession from open water to land, wetlands are now considered to be distinct ecosystems with specific ecological characteristics, functions and values.

On a pessimistic note, with unmet environmental challenges serving as a propellant, perhaps it would be better to allow the islands here to meet their deadly fate. The treasure of the mangrove forest overlaying the entire region is not such a bad idea after all. Why construct these embankments at all? As for the communities that have made their homes here, they will need to be phased out, relocated, in just the same way as we have relocated millions during the construction of so many dams and projects. A special status of climate change refugees may be awarded to these vulnerable sections, and the demand for environing the islands with embankments to protect them from the devouring water will be eliminated once and for all. I am not suggesting that embankments are faulty in their principle – it has worked well in many countries world over, but perhaps in the context of Sunderban they were untimely in their origin, ill-designed during their maturity, and inadequate in their final hours.

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