Bangladesh is a riverine country. According to Bangladesh Water development board (BWDB) about 230 rivers currently flow in Bangladesh (during summer and winter), although the number stated are ambiguous in some sources. As stated by a publication called বাংলাদেশের নদ-নদী by BWDB (Bangladesh Water development board), 310 rivers flow in the summer although they republished another study in 6 volumes where stated 405 rivers. The number differs widely due to lack of research on the counts and the fact that these rivers changes flow in time and season.Old sources and history states about 700 to 800 rivers but most of them dried out or extincted due to lack of attention and pollution. The numbers differ also because same river changes name in different regions and in history. About 17 rivers are on the verge of extinction and the 54 rivers flow directly from India and 3 from Myanmar. Total of 57 international rivers flow through Bangladesh. The international number of rivers can be 58 as Brahmaputra is called "Nod" while the general term for river is "Nodi". The gender division of rivers is interesting from history and mainly depending on the source of the river but not the size or flow briskness.Sangu and Halda are the only two internal rivers originated and finished within Bangladesh. Surma is the longest river and Karnafuli is the swiftest.Jamuna is the widest river. According to banglapedia 700 rivers flow in Bangladesh, but the information is old and obsolete.There is an including tributaries flow through the country constituting a waterway of total length around 24,140 kilometres (15,000 mi). But the number differs ambiguously due to the lack of updated information.Most of the country's land is formed through silt brought by the rivers. Bangladesh geography and culture is influenced by the riverine delta system. Bangladesh lies in the biggest river delta of the world - the Ganges Delta system.
River long water course that flows down a slope along a bed between banks. It originates from a 'source' and culminates to a sea or lake at its 'mouth'. Along its length it may be joined by smaller rivers called 'tributaries'. A river and its tributaries form a 'river system'. Land surfaces are never perfectly flat, and as a result the runoff water after precipitation tends to flow downward by the shortest and steepest course in depressions formed by the intersection of slopes. Runoff water of sufficient volume and velocity join to form a stream that, by the erosion of underlying earth and rock, becomes deep enough to be fed ground water or when it has as its source an ultimate water reservoir, for example, the ganges flowing from the Gangotri Glacier and the brahmaputra from the Manas Sarovar.
A river tends to eliminate irregularities and forms a smooth gradient from its source to its base level. As it approaches base level, downward cutting is replaced by lateral cutting, and the river widens its bed and valley and develops a sinuous course that forms exaggerated loops and bends called meander. A river can open up a new channel across the arc of a meander, thereby cutting off the arc and creating an oxbow lake. River velocity determines quantity and size of rock fragments and sediment carried by the river. Whenever velocity is checked by changes of flow of gradient, by meeting the water mass of lakes or ocean, or by the spreading of water when a stream overflows its banks, part of the load carried by the stream is deposited in the river bed or beyond the channel. Landforms produced by deposition include the delta, the floodplain, the channel bar, and the alluvial fan and cone.
Traditionally, river systems have been classified according to their stage of development as 'young', 'mature', or 'old'. The young river is marked by steepsided valley, steep gradients, and irregularities in the bed; the mature river by a valley with a wide floor and flaring sides, by advanced headward erosion by tributaries, and by a more smoothly gradient bed; and the old river by a course graded to base level and running through a peneplain, or broad flat area. Most of the rivers of Bangladesh are at their old stage and enter into the bay of bengal.
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