The delta, the seaward prolongation of sediment deposits from the Ganges and Brahmaputra river valleys, is about 220 miles (355 km) along the coast and covers an area of about 23,000 square miles (60,000 square km). It is composed of repeated alternations of clays, sands, and marls, with recurring layers of peat, ignite, and beds which were once forests. The new deposits of the delta, known as the khaddar, naturally occur in the presence of channels. Tidal processes dominate the delta’s growth.
The southern surface of the Ganges delta has been formed by the rapid and comparatively recent deposition of enormous loads of sediment. To the east of the seaward side of the delta is changing at a rapid rate by the formation of new lands, known as chars, and new islands. The western coastline of the delta, however, has remained practically unchanged since the 18th century.
The rivers in the West Bengal area are sluggish; little water passes down them to the sea. In the Bangladeshi delta region, the rivers are broad and have active water flow, carrying plentiful water and are connected by innumerable creeks. During the rains (June to October) the greater part of the region is flooded to a depth of 3 or more feet (at least 1 metre), leaving the villages and homes, which are built on artificially raised land, isolated above the floodwaters. Communication between settlements during this season can be only made possible by boat.
To the seaward side of the delta as a whole, there is a vast stretch of tidal mangrove forests and swampland.
In certain parts of the delta, layers of peat occurs, composed remains of forest vegetation and rice plants. In many natural depressions, known as bils, local farmers as fertilisers have used peat, still in the process of formation,, and it also has been dried and used as a domestic and industrial fuel.
The main streams of Ganges which are Alaknanda and Bhagirathi originates from a subglacial meltwater cave at the base of the Himalayan glacier known as Gangotri.