] Floods in Bangladesh can be divided into three categories: (a) monsoon flood - seasonal, increases slowly and decreases slowly, inundates vast areas and causes huge losses to life and property; (b) flash flood - water increases and decreases suddenly, generally happens in the valleys of the hilly areas; and (c) tidal flood - short duration, height is generally 3m to 6m, blocks inland flood drainage.The combined annual flood wave from the Ganges, brahmaputra and Meghna rivers passes through a single outlet, the lower meghna tide levels in the bay of bengal, reducing the slope and discharge capacity of the Lower Meghna. The effects of these high river water levels extend over most of the country and are the main determinant of the drainage condition and capacity. The discharge from minor rivers is reduced and surface drainage by gravity is limited to land above the prevailing flood level. Flooding caused by this drainage congestion exists nearly everywhere except in the highland and hilly areas in the northern and eastern parts of the country. | | | | | | | |
The factors for causing floods in Bangladesh are: (a) general low topography of the country with major rivers draining through Bangladesh including a congested river network system, (b) rainfall in the upstream country or in the mainland, (c) snow-melt in the himalayas and glacial displacement (natural), (d) river siltation/lateral river contraction/landslides, (e) synchronisation of major river peaks and influences of one river on the other, (f) human intervention of the environment, (g) tidal and wind effects on slowing down the river outflow (backwater effect), (h) construction of barrages and protective works along the banks of the river - some are very close to both the banks - in the upper reaches thus making the passage of water flow downstream increasingly narrower and resulting in greater