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Monitoring changes in Sunderban Mangrove Forest using RS/GIS
Atanu Kumar Raha
Introduction :
The famous "Sunderbans" region cover the southern parts of Gangetic delta bordering the Bay of Bengal. Upto 14th August 1947, the entire forest area of Sunderbans was under one single forest division, namely Sunderbans Division with Headquarters at Khulna, now in Bangladesh. After the partition of the country, the western part of Sunderbans, confined within the then 24-Parganas district of West Bengal, came to be known as "24-Parganas Division" with Headquarters at Alipore, Calcutta. Spatially, nearly one-third of the total Sunderbans forests lie within the Indian jurisdiction and the rest is under the control of Bangladesh. The Reserved Forests of Indian Sunderbans is bounded on the north and west by cultivated lands/settlements, on the east by the rivers Kalindi, Raimangal and Harinbhanga, and on the south by the Bay of Bengal. The islands in the rivers of Muriganga, Saptamukhi and Thakuran are also included in the Sunderbans forests. The Sunderbans forests are situated between the latitudes 22º15' and 21º30' North and 88º10' and 89º51' East. The total area of Sunderbans forests in Indian part is 4262 sq km, out of which 2585 sq km has again been reconstituted as Sunderbans Tiger Project from the year 1973. (Land area = 1680 sq.km and water area = 905 sq km). The river Matla separates the Tiger Project from the 24-Parganas(S) Forest
Division.
- Chief Conservator of Forests and Director, Sunderbans Biosphere
- Reserve, Forest Dept., W.Bengal, India
General Information of the area :-
A close network of rivers, channels and creeks intersect the entire Sunderbans forest area comprising hundreds of islands which get either partially or fully inundated during the diurnal high tides. The existing large rivers running from north to south are the remnants of the old courses of the Ganges. The main current of Ganga had gradually shifted eastwards over the last few centuries. A major tectonic movement in the sixteenth century might have caused lifting of the upper crust towards the west, thus forcing the Ganga to drain mostly through its eastern channel Padma, flowing through Bangladesh (Cartis, 1928). The rivers Matla, Saptamukhi and Thakuran have practically no connection with their original mother streams and are now inlets of the sea. The sources of all the rivers in the western part of Sunderbans have been progressively silted up, thus disconnecting the inflow of fresh/sweet water into the mangrove delta. This has resulted into increased salinity of the river waters and making them shallower over the years. On the other hand, during the ebb tides, the receding water level causes scouring and creates innumerable number of small creeks, which normally originate from the centres of the islands. The receding water, while draining into the Bay of Bengal, carries large volumes of silt load. These silt, on the other hand, get deposited along the bank of the rivers and creeks during high tide, resulting into increase in height of the banks as compared to interior of the islands. As a result, high tide cannot normally reach the interior of home of the islands.
Topography: -
Sunderbans delta is one of the most dynamic ecosystems of the world. Erosion of banks and formation of new islands is continuously going on and the mangrove vegetation is subjected to ever changing salinity of water, soil texture, tidal actions as well as ecological factors arising out of increasing biotic pressure in the western and northern fringes of the Reserved Forests. Lands in the sea faces are continuously denuded by tidal waves. Towards the west, new land formation is taking place due to heavy silt load deposition from Hooghly River and its affluent Muriganga at their confluence with Bay of Bengal.
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