Geoscience Reference
In-Depth Information
to sink much faster than any predicted rise in sea level, increasing their vulnerability to
storms and floods.
In the case of Bangladesh, over three-quarters of the country is within the deltaic region
formed by the confluence of the Ganges, Brahmaputra, and Meghna rivers. Over half the
country lies less than 5 m above sea level; thus flooding is a common occurrence. During
the summer monsoon a quarter of the country is flooded. Yet these floods, like those of
the Nile, bring with them life as well as destruction. The water irrigates and the silt fertil-
izes the land. The fertile Bengal delta supports one of the world's most dense populations,
over 110 million people in 140,000 square kilometres (km
2
). Every year, the Bengal delta
should receive over one billion tonnes of sediment and a 1,000 cubic kilometres (km
3
) of
fresh water. This sediment load balances the erosion of the delta both by natural processes
and human activity. However, the Ganges, Brahmaputra, and Meghna have been dammed
for irrigation and power generation preventing the movement of silt down river. The re-
duced sediment input is causing the delta to subside. Exacerbating this is the rapid extrac-
tion of fresh water.
22. Areas most at risk from sea-level rise
In the 1980s, 100,000 tube wells and 20,000 deep wells were sunk, increasing the fresh-
water extraction six-fold. Both these projects are essential to improving the quality of life
for people in this region, but have produced a subsidence rate of up to 2.5 cm per year,
