Causes
The main cause of the floods was unusually severe monsoon rains and an unusually high volume of runoff from melting snow from the snow caps of the Himalayas. These all increased the amount of surface water and the volume of water in Bangladesh's two main rivers, which are very large and connect. The Ganges and the Brahmaputra both had more than the normal amount of water that they could carry and so were overflowing and flooding.
A number of human factors also contributed to the devastating flooding of Bangladesh, including large amounts of deforestation and overfarming. Deforestation for logging or farming removes trees that would otherwise absorb and delay the flow of rainwater. Overfarming ruins the soil and so water just goes straight through it and doesn't soak into the ground for groundwater. This means that the maximum amount of surface water can travel down the hills and tributaries.
Bangladesh itself is a very poor and highly populated country and cannot afford necessary defense against flooding such as flood banks/walls or rescue services to help survivors and refugees.
Consequences
Following the 1998 floods a number of short term flood relief measures were put in place to try and minimize loss of life - these included: international food aid programmers the distribution of free seed to farmers by the Bangladesh government to try and reduce the impact of food shortages - the government also gave 350,000 tons of cereal to feed people; volunteers / aid workers worked to try and repair flood damage. In the long term a number of flood prevention measure are possible: the creation of embankments (artificial levees) along the river to increase channel capacity and restrict flood waters - however since 1957, 7,500km of flood embankments have been constructed and yet many were breached in the 1998 floods; constructing flood protection shelters (large buildings raised above the ground) to shelter both people and