Waterways of the Sundarbans Mangrove Forest

Sundarban is the world's largest contiguous mangrove forest encompassing almost 600,000 ha. About 30% of the area is composed of a complex network of tidal waterways. The world's third largest river system, the Ganges-Brahmaputra-Meghna (Padma-Jamuna-Meghna) river system, passes an enormous sediment load to the delta, supplying the physical elements for the world's largest contiguous mangrove forest and the world's largest undersea sediment fan. The Ganges-Brahmaputra-Meghna (Padma-Jamuna-Meghna) supplies loads of nutrients to the Bay of Bengal - more than 1.5% of the total riverine input to the world's oceans.

Salinity levels in Sundarban are determined primarily by freshwater flows and tides. After construction of the Farakka Barrage (Ganges, India) significant increases in salinity levels were documented in Sundarban. Increased sediment deposition due to reduced river discharges has led to the gradual drying up of distributaries that previously drove back salinity encroachment.

Coastal Waters of the Bay of Bengal

The Bay of Bengal is a tropical ocean basin, bordered by Sri Lanka, India, Bangladesh and Myanmar. It is largely influenced by seasonally reversing currents and the discharge from the Ganges-Brahmaputra-Meghna (Padma-Jamuna-Meghna) river system. These big rivers bring enormous amounts of freshwater, nutrients and sediment, which help create highly productive coastal waters and supply the world's largest undersea fan.

The Bangladesh coast is dominated in the west by the Sundarban mangrove forest and in the east by the massive freshwater input from the Ganges-Brahmaputra-Meghna mouth. The coastal waters are generally shallow with the 50m contour ranging from 35 to 165 km offshore along the south facing coast. The coastline is characterized by sandy shoals with large and small emergent islands.

The Swatch-of-No-Ground

In the north-western part of the Bay of Bengal, a deep submarine canyon, known as the Swatch-of-No-Ground comes up close to the Bangladesh coast, south of the Sundarban Forest. The very deep canyon (900+ meters) has relatively steep walls (12-15) and is cone shaped, ranging from about 40 km wide at its mouth in Indian waters to about 6 km wide at its head in Bangladeshi waters. The Swatch-of-No-Ground plays a crucial role in transporting sediments from the continental shelf to the deep-sea fan and fish productivity. Due to the nutrient rich waters at the edge of the canyon, the cetacean fauna is diverse and relatively abundant.