The confluence of three major rivers- the Ganges, the Brahmaputra, the Meghna (03-05-2011 L: 3)

The runoff from their vast catchment (about 1.72 million km²)

passes through a small area, only 8% of this catchment lies within Bangladesh. During the monsoon season the amount of water entering BD from u\s is greater than the capacity of the rivers to discharge into the sea.

v Bangladesh is a land of rivers: There are about 310 major & minor rivers in the country. The total annual runoff of south west flowing through the rivers of BD is about 12000 billion m³.

v Man made environment: The construction of embankments in the u/s catchment reduces the capacity of rivers to store water. The unplanned & unregulated construction of roads & highway in the flood plain without adequate opening creates obstruction to flow.

v The influence of tides & cyclone: The frequent of low pressure areas & storm surges in the Bay of Bengal can implode drainage. The severity of flooding is greatest when the peak floods of the major rivers coincide with these effects.

v Long term environmental changes: Climate change could influence the frequency & magnitude of flooding. A higher sea level will inhalant the drainage from the rivers to the sea and increases the impact of tidal surges. Deforestation in hilly catchments causes more rapid and higher runoff, and hence more intense flooding.

# Snow-melt from the Himalayas in the late spring & summer further increases the flood risks as torrents of melt water enter the rivers at their sources.

The spring tide of the Bay of Bengal retards the drainage of flood water into the sea and locally increases monsoon flooding. A rise of mean sea level at times during the monsoon period due to effects of monsoon winds also adversely affect the drainage and raise the flood level along the coastal belt.

                             

The structural measures are aimed to migrate flood damage by regulating the movement of flood water and these include

# Construction of dykes/embankments/levels to stop the water from entering the areas to be protected & diverting through distributaries.

# Construction of water reservoirs to store the flood water temporarily.

# Channel improvement works to increase the carrying capacity of a river channel to pass the flood water quickly through the channel reach.

# Catchment treatment to induce holding of water in the catchment temporarily.

# Increasing stability of soil by afforestation to prevent soil erosion and siltation of river bed.

# Cutoff ( a new & shorter catchment cut by a river across a bend or dugout to straighter it) to enhance the drainage capacity of the river.