Geographical Distribution

The Bangladesh Sundarbans lies between the latitudes 21o 31′ and 22o 30′ N and between the longitudes 89o and 90o E in the district of the Khulna, Bagherhat and Satkhira. It occupies a land area of 401,600 ha, of which 395,500 ha are covered by forests (Chaffey et al. 1985) and comprises 44% of the total productive forest of Bangladesh (Anon 1989). Of the total area, approximately 70% lands and 30% are waters. The distance between the northern and the southern boundaries averages about 80 km, although the distance between the extremities is about 100 km. The east to west distance within Bangladesh is about 80 km. The Bangladesh Sundarbans is a Reserved Forest and has been divided into four administrative Ranges with 55 compartments. The forest is flat with a slope of 0.47cm/km and the maximum ground elevation is 3m above the mean sea level (Siddiqui 2001).

River systems: 

A complex network of streams and rivers varying considerably in width and depth intersects the entire area. Some of the big rivers are several kilometers in width. The Sundarbans receives large volumes of fresh water from inland rivers flowing from the north and of saline water from the tidal incursions from the sea. The fresh water is charged with alluvium containing plants nutrients. This together with the salinity of the tidal water is the major factor determining the productivity of the forest ecosystem (Siddiqui 2001). At a comparatively recent period, all of the rivers were connected with Ganges. Now, only the Baleswar has direct connection and is responsible for fresh water supply to the eastern part of the Sundarbans. A number of rivers namely the Passer, the Sipsa, the Arpangasia, the Malancha and to slight extent the Jumuna and the Raimangal have indirect connections and receive the overflow of the Ganges during the rainy season. They also receive a considerable amount of local drainage throughout their long and meandering courses during the monsoon (Siddiqui 2001).

Raimangal estuary: 

 The rivers that contribute their water to this estuary are Harinbanga, Raimangal and Jamuna (Mamdut). The Kalindi river from the international boundary between India and Bangladesh, and takes the name Raimangal towards the south as it flows through the Sundarbans. The Jamuna, originating from Kishenganj in India, bifurcates at Bangsipur where it is called Madder gang and flows through the north of Sundarbans. Further south, it empties into the Bay of Bengal taking the name Jamuna again. This river is connected with the Malancha Faringi gang and with the Rimangal through Atarabankhi and some other connecting channels (Siddiqui 2001). The rivers that drain this estuary are the Malancha and the Barapanga. The latter is formed by the Bal river and the Arpangasia. These two rivers in turn receive that originate out side the Sundarbans. Arpangasia receives water through the Khulpetua and the Kobadak while the Bal river is connected with the Sipsa system through Jafa and to the Kobadak system through the Andarmanik khal and Chalki gang.The estuarine rivers are maintained by runoff from internal rivers such as Kobadak- and Betna. Major estuaries important for navigation e.g., the Passur and the Sipsa, receive fresh water principally from the Goari-Madhumati system. The Baleswar Haringhata estuary is dominated by tidal exchange with Meghna and to a lesser degree with the Padma through Arialkhan. In general, the estuaries of the west are classified as part of the moribund delta while estuaries of the eastern region are part of the active delta. The rivers in the west are strongly influenced by tides. In the east they are tide dominated during the dry season and less so during the wet season (Siddiqui 2001).

Soil characteristics: 

Mangrove soil differ from other inland soils in that they are subjected to the twin effects of salinity and water logging, both of which are detrimental to the normal functioning of plant life. Tidal inundation and low water table, combine with poor drainage, generally lead to characteristically saturated water condition, low oxygen content and sometimes free hydrogen sulphide in mangrove soils. These soils are often semi-fluid and poorly consolidated (Hossain and Acharya1994). In general the Sundarbans soil is finely textured and the sub-soil is stratified and at greater depth is compacted (Choudhury 1968). Hasan and Mazumder (1990) mentioned that soils were slightly calcareous, uncured are partly cured clayey deposits which were homogenous both vertically and horizontally. In the eastern part of the forest, where the rivers supply fresh silt every year, the top layer is soft and fertile. In the western Sundarbans where there is little fresh supply of silt, even the surface soil settled down to a hard mass, and the ground is much less suitable for fast tree growth (Siddiqui 2001).