The Sunderbans Biosphere: a Study on Uncertainties and Impacts in Active Delta Region

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THE SUNDERBANS BIOSPHERE: A STUDY ON UNCERTAINTIES AND IMPACTS IN ACTIVE DELTA REGION

Shivashish Bose

Architect, Conservationist, Researcher

Centre for Built Environment

2/5, Sarat Bose Road, Kolkata – 700020, India

Sunderbans in India on the coast of Bay of Bengal is part of the world’s largest Active Delta having a network of tidal rivers, channels, creeks, islands, mudflats, coastal dunes with hydrodynamic uncertainties, changing geomorphology and climatic hazards, a vast area of mangrove forest with rich variety of flora and diverse fauna in a unique ecosystem. Unscientific and excessive human interferences and exploitation of natural resources have caused physical disaster to the natural environment and ecosystem. Conservation and environmental management plan for safeguarding this declared ‘Biosphere Reserve’ including coastal area is urgently required.

INTRODUCTION

The Sunderbans Delta in West Bengal state in India is the western part of the largest Active Delta of the world, the (Himalayan) Ganges-Brahmaputra river Delta at the mouth of Bay of Bengal, falling south of Tropic of Cancer between latitude 21°31’-22°40’ North and longitude 88°05’-89°06’ East [1] with its network of tidal rivers, channels, mudflats, creeks, dunes, archipelago of around 54 islands and numerous distributaries, geologically being still under formation, providing a great diversity in the eco-system [see Figure 1]. This low flat country would be completely submerged if the sea level rises by only a few metres [1]. The Sunderbans tidal estuary comprises an area of 4266.6 sq. km, of which the tidal and inter-tidal mangrove forest area is estimated of 2300 sq. km, water area is 1750 sq. km and the rest are river banks, beach areas or naked forest floors [2,3]. There are eight blocks having rural settlements at the tidal mangrove forest area with wildlife, prone to environmental and natural disaster.

NATURAL ENVIRONMENT, GEOLOGY, TECTONICITY, CLIMATE – ITS CHARACTER AND UNCERTAINTIES

Eco-geography

The eco-geography of this area is totally dependent on the tidal effect. There are two flow tides (inflow) and two ebb tides (outflow) within 24 hours and tidal range varies from 3m to 5m rising up to 8m in normal spring tide [1, 2]. The tidal action of the sea inundates the whole of Sunderbans in varying depths. Due to the tidal action, the silts carried down to the sea are pushed back to the channels and get deposited there. The bed of the channel thus gets steadily raised ultimately blocking the flow of water and gradually evolving a small island. This is the basic geographical history about the origin of innumerable islands of the region [6].

There is a great natural depression called “Swatch of No Ground” in the Bay of Bengal, south of the Raimangal Estuary between 21º to 21º22’ latitude. The surrounding waters, which are around 20m, change almost suddenly to 500m in depth. Fergusson’s theory (1863) [2, 9] is that the sediments are carried away from the spot and deposition is prevented by strong currents produced by a meeting of tides from the East and West coasts of Bay of Bengal. The silts thus carried away are diverted to the south of Sunderbans or are being pushed forward further eastward and new islands are formed. Geo-technologists opine that the unsettled condition of Sunderbans with periodic subsidence, natural hazards, etc, is solely due to this sub-marine hollow called “Swatch of No Ground”, the origin of which is still shrouded in mystery [6].

Figure 1. Map of Sunderbans Active Delta in India

Mudflats

The Sunderbans Mudflats [1] [see Figure 2] are found at the estuaries and on the deltaic islands where low velocity of river and tidal current occurs. The flats are exposed in low tides and submerged in high tides, and thus the unstable mudflat changes morphologically even in one tidal cycle. The interior parts of the mudflats are the magnificent home of luxuriant mangroves. The morphology of the swamps is characterized by the occurrence of saltpans, ditches and banks with a thick mud substratum of decomposed organic matters [1, 7]. The spring tides submerge the swamp floor and the ebb tides affect the slope of the floor with lateral erosion and gradually form a new creek, which is further lengthened by the quick flow of the splitting tides. The Sunderbans mudflats control the food chain in the estuarine ecosystem.

Figure 2. Location of Mudflats and Sand flats in the Sunderbans Delta

(Source : Paul and Bandyopadhyay, [1])

Coastaldune systems

Coastal dune systems, product of sea deposition on the coast, in the Sunderbans comprise a system of low ridges parallel to the coast, separated by large dry and wet sand flats [1]. A variety of dune landscape types provide protection of hinterland, water storage, biotic resources and recreation. However, coastal dunes of the western islands are now being engulfed by the encroaching sea waves with the activities of cyclones. The rate of coastal erosion is high on the coast of Fraserganj, Bakkhali and Sagar. The Fraserganj coast is almost destroyed by the long-shore current attack from the west.

Rivers, watercourses and islands

The main rivers of this region, including the estuarine and all having a southward course towards the sea are the Hugli, Piyali – Bidyadhari, Muri Ganga, Saptamukhi, Thakuran, Matla, Gosaba and Harinbhanga [see Figure 1]. They are separated from one another by numerous islands and the important ones from west to east are Sagar, Fraserganj, Lothian, Bulcherry and Halliday island. Between the large estuaries and rivers, there are innumerable watercourses called “Khals” (canals) forming a perfect network of channels, drawing water from every block of land [1]. Each block is like a saucer with high ground and one or more depressions and is drained off by the hierarchy of surrounding creeks and khals into the rivers.

Soil types

The Active Delta bears the soil types of silty clay loams, sandy clays and loams, soil with organic and peaty deposits, swampy and marshy soil also called as ‘mangrove soil’ [1, 2]. The salinity of the surface soil and the adjoining water-bodies change to a great extent through out the year and is governed mainly by the quantity of the fresh water flow and the monsoon rainfall.

Climate

The region has a typical tropical monsoon climate with excess of humidity. Annual average rainfall is around 1800 mm, maximum and minimum average temperatures in summer and winter are 29°C and 20°C [1, 2]. During pre-monsoon March to May, violent thunderstorms and accompanying hailstorms occasionally occur. From post-monsoon October to November, the cyclonic storm occasionally touches the area accompanied with high waves and tides near the sea and cause great disasters.

Flora and fauna

The flora is confined only to the forested tracts of the Active Delta, popularly known as Mangrove Tidal Forests. The mangrove [4] community of trees and shrubs has characteristic stilt root with numerous lenticels and pnumatophores and adapt with high salinity, submergence, fine clayey soils, tidal currents and fresh water flow. It should be mentioned that out of the fifty mangrove species of the world, around thirty five are found in Sunderbans in addition to 117 other halophytic mangrove associates [3]. Some important mangrove trees are Kala Bean, Tora, Krippa, Garjan, Jelegaran, Keora, Sundari, Genwa, Kankra, Golepata, etc. They are used as building materials for rural houses, for furniture, for making boats and as fuel wood. The mangrove habitat checks the tidal thrust of surges from the funnel shaped bay and trapping sediments protect the coastal region from erosion [10]. Mangrove functions as natural sewage treatment plant, as well as wind-breaking barrier. It also provides shelter for large number of euryhaline / brackish water algae, shell-fish and fin-fish species, prawns, crustaceans, estuarine crabs, ghost shrimps, mollusks, nematodes, annelids, animals like various types of jungle cat, the deer, rhesus monkey, wild pig, otter, water monitor, various snakes including python, estuarine crocodiles, sharks, dolphins, large variety of local birds and migratory pelican and the world-famous Royal Bengal Tiger [1, 2]. Fishes abound in the rivers and nutrient enriched creeks. Some mangrove trees give shelter to migratory rock bees from the Himalayas to build many beehives. On an average, 500 quintals of honey and 30 quintals of wax are being collected every year by people. The food chain of Sunderbans reveals that the Royal Bengal Tiger, adapted to swimming and even drinking honey from the beehives, is at the apex of the hierarchy of terrestrial as well as aquatic animals [1].

Human Settlements

The active delta has semi-nucleated, moderately dispersed and highly dispersed rural settlements. Population density figures of 1991reveal the lowest 393 persons per sq. km in the Western Sunderbans [1]. Agriculture, fishing, forestry, honey collection, gathering, animal husbandry, small scale commercial activities supporting tourism and pastoral activities are the most important economic activity of the region. Transportation is through ferry services (launch, motor boat and ‘dinghy’). There is successful use of solar reactors at SagarIsland.

MAN’S INTERFERENCES & IMPACT ON THE BIOSPHERE

Land reclamation by people for agriculture and human settlement destructing forest area, construction of series of irrigation and drainage canals over centuries interfering the natural gradients, setting up of fisheries in the rivers, canals, creeks and estuaries, raising embankments along the major river systems against insurgence of saline water, excessive exploitation of mangrove forest wealth like timbers and fire woods, poaching of animals of commercial importance, indiscriminate collection of prawn seedlings and excessive fishing round the year in Sunderbans water, pose a serious threat on the natural environmental balance, flora and fauna of the region, disturb the complex food chain and unbalance the animal population and enhance coastal erosion [1, 3, 12]. Moreover, the greater part of the inner estuarine zone has become more saline due to lack of required quantity of fresh water and the Sundari, already over exploited for its valuable timber, preferring less saline soil, do not proliferate in adequacy these days [1, 3]. The gradual extinction of forest has given rise to less resistance of the land from the ravages of cyclonic storm and soil erosion. Several important fish and prawn species have been declining in the region due to deterioration of the mangrove vegetations and disturbances in the natural ecosystem. During the last two centuries, more than 5000 sq. km of the mangrove forests in the Indian part of Sunderbans were reclaimed [3]. Actually, only the eastern part of river Matla now exhibits the true core area of the mangrove forest.

ACTIONS TAKEN TO SAFEGUARD ECOLOGY AND ENVIRONMENT

For the ecological, environmental and economic potentialities, it has become extremely necessary to conserve the natural ecosystem of the mangrove forests of the Sunderbans.

The Govt. of India declared on 29.03.1989 the mangrove forest area as the “Protected Biosphere Reserve” [8]. The Sunderbans, a National Forest, has a Tiger Reserve, where Project Tiger was launched in 1973 with the help of World Wild Life Fund to save the tiger from extinction as well as to conserve its natural habitat in the particular ecosystem. Killing of tiger and exporting its skin were banned during 1970-72. The Sunderbans Tiger Reserve covers 2585 sq. km. The Crocodile Project has been taken up to increase the number of estuarine crocodiles by raising and breeding inside the farms. Three Sanctuaries have been set up at Sajnekhali, Lothian and HallidayIslands.

In the Active Delta, the Sunderban Development Board, a joint enterprise of the state and central government, was formed in the 1980’s. It aims at improvement of drainage and irrigation facilities, encouraging agriculture, agro-processing, animal husbandry, fisheries, village industry, transportation, development of social forestry, strengthening of embankments and providing technical help [1]. However, its objectives and actions sometimes infringe into the issues of biosphere protection.

PROPOSALS

1. The management programme of conservation, environment and development (CED) of Sunderbans area should be planned primarily to retain the natural ecosystem of the mangrove forest, saving the diverse flora and fauna and providing for combating pollution, cyclonic hazards and coastal erosion following the “Conservation Function” prescribed by the UNESCO in its ‘Man and Biosphere Programme’ [11].
2. The Sunderbans should be divided into three territorial components – a) the core area, which should be restored, strictly conserved and protected, b) the buffer zone surrounding the core area, where within the framework of sustainable development, some activities benefiting local people may be permitted and c) the outer transition zone, where economic, tourism and recreation activities should be permitted (Batisse, 1997) [12].
3. The conservation and management planning of the coastal areas [6,11] should be based on proper understanding, analysis and assessment of the various complex geomorphologic, fluvial, oceanic and natural climatic characteristics of the whole area plus the unnatural influence by human interventions.
4. The overall planning policy should be implemented by all sectors of the government bodies with legislative and administrative control, strict vigilance and above all with greater cooperation among themselves to eliminate conflict [3].
5. People should be informed, educated and trained for accepting and integrating by actively participating into the policy-enforcing actions.
6. Monitoring over the situations and making necessary modifications in the implementation programme are to be done constantly along with periodic review and further assessment.
7. Social forestry [5] can be useful for eco-restoration of mangrove vegetation through creation of employment opportunities.
8. The beauty of the Sunderbans can be explored for attracting and managing (within tolerable limit of) tourism and associated economy. Tourism should be encouraged in the transit zone with such a control so that the natural environment, ecology and life style of the coastal people are not adversely affected.
9. To install cyclone warning system in the coastal and further areas and cyclone shelters should be constructed for people as part of disaster preparedness planning.
10. Energy requirements for local people, environmental and research programmes are to be met with the help of solar and wind energies (example – utilization of solar energy at SagarIsland by Govt. of West Bengal).

CONCLUSION

Sunderbans is mystic. Its natural beauty with unique flora and diverse fauna, hydrodynamic uncertainties, geomorphology still under formation and devastating climate, has got its spellbound charm providing beauty in the ruggedness of danger in this region. Such a unique natural biosphere, which is indeed a World Natural Heritage Site, is under threat of physical disaster. Hence, an appropriate policy of sustainable intervention guided by a thorough research and followed by proper implementation, control and critical monitoring for necessary modification in action, is required to safeguard the biosphere drawing proper and sincere concerns of local people, regional and national governments and the world organizations.

REFERENCES

[1]Banerjee Anuradhha, “Environment, Population And Human Settlements of Sunderban Delta”, 1st edition, Concept Publishing Company, New Delhi, (1998).

[2]Mandal A.K., Ghosh R.K., “Sunderban–A Socio Bio-Ecological Study”, 1st edition, Bookland Pvt. Ltd., Calcutta, (1989).

[3]Naskar K.R., Ghosh A., “MangroveForest of the Sunderbans : Its Impact on Estuarine Fisheries”, Proc. Coast Zone Management of West Bengal, Sea Explorers’ Institute, Calcutta, Proc. (1989), pp A47-59.

[4]Chakrabarti Kalyan, “Development Perspective of Coastal Ecosystem of Sunderban Forests”, Proc. Coast Zone Management of West Bengal, Sea Explorers’ Institute, Calcutta, Proc. (1989), pp C4-11.

[5]Banerjee U, “Social Forestry in Sunderban : A Tool for Rural Development”, Proc. Coast Zone Management of West Bengal, Sea Explorers’ Institute, Calcutta, Proc. (1989), ppC12-17.

[6]Bhattacharya A.K., “Coastal geomorphology, Processes and Hazards : A Note on Management Measures”, Proc. Coast Zone Management of West Bengal, Sea Explorers’ Institute, Calcutta, Proc. (1989), pp D49-61.

[7]Naskar K.R., Guha Bakshi D.N., “Mangrove Swamps of The Sunderbans – An Ecological Perspective”, 1st edition, Naya Prakash, Calcutta, (1987).

[8]Ministry of Environment & Forests “Sunderban Biosphere Reserves”, Project Document – 10, Govt. of India, New Delhi, (1989).

[9]Fergusson J., “Delta of the Ganges”, Quarterly Journal of the Geological Society of India, Vol. XIII. Part-1, (1963).

[10]Mastaller M., “Destruction of Mangrove Wetlands – Causes and Consequences”, A Biannual Collection titled “Natural Resources and Development – Focus : Mangrove Forests”, Institute for Scientific Cooperation, Tubingen, Vol. 43/44, (1996).

[11]UNCHS (Habitat), “Issues in the Integrated Planning and Management of River/lake Basins and Coastal Areas” – A human settlement perspective, Nairobi, (1996).

[12]Ghosh Santosh, “Environmental Parameters in Agri-Aquaculture Development in Tidal Swamps and Estuaries – Case Study: Sunderbans Deltaic Region, India”, Paper Presented at EMECS Conference, Kobe, Japan, (2001).