THE IMPORTANCE OF WATER
FLOODPLAINS AND DELTAS
A floodplain is the flat land on each side of a river channel. It is
formed by the river flooding. A river floods when there is too
much water to stay in the river channel. When a river floods the
water spreads out across the land surrounding the channel. This
water slows down and deposits its load. The larger material is
deposited first alongside the river channel. This forms banks
called levees. The smaller material is called silt. This is deposited
to form the flat land of the floodplain.
A delta forms where a river metts the sea. The water slows down
and the river deposits its load. This is mainly silt. The main river
channel may split into smaller channels called distributaries.
The channels cut through the delta to sea.
Silt is very fertile. This means it is very good for growing crops,
as it happened in Ancient Egypt. Therefore floodplains and deltas
are very often used for agriculture.
Houses, factories and farms may all be built on floodplains.
Millions of people across the world live on floodplains. However,
floodplains always experience flooding, therefore people living
on them and using them are always at risk.
DELTA DWELLING
Bangladesh has the largest delta in the world. The country is at
the confluence of the Ganges, the Brahmaputra and the Meghna
rivers. The delta stretches for nearly 300km along the coast and
covers 105,000km2. The capital, Dhaka, lies on the delta and has
a population of over 12 million.
Most of Bangladesh lies less than 12m above sea level. Some
areas of the lower delta are at sea level. Bangladesh has a wet
tropical climate and experiences the monsoon and cyclones. In
addition melting snow in the Himalayas increases the discharge
flowing into Bangladesh.
The Ganges-Brahmaputra widens as it reaches the coast. The
river velocity slows down and the river load is deposited.
Distributaries cross the delta making a network of channels.
Monsoon rains, cyclones and high tides cause flooding of this
land. Dwellings, crops and livestock are soon inundated. The
Ganges-Brahmaputra delta is called the Green delta because of
the fertility of the soil. Over 140 million people live on the delta,
making their livelihood from agriculture, mostly on small
subsistence farms. The settle on land which is barely above the
water level. The regular flooding brings new nutrients to the soil,
and the paddy fields of the delta are very productive.
The many waterways provide fish for the population of the delta.
In a good year there can be three harvests of rice. When natural
disasters strike, however, the people of the Green Delta face
famine, homelessness, disease, destitution and death.
People living on the delta have learned to live in their
environment and to exploit the fertile soil, plentiful water
supplies and fish. However such benefits come at a cost. The
natural danger of monsoons, cyclones and storm surges are
enough to worry abiut but human activity has made things worse.
Subsidence caused by the extraction of groundwater has made
more land vulnerable to flooding. Upstream the diversion of river
water to irrigate crops has reduced the amount of silt carried
downstream. This has allowed land to disappear. The
contamination of the rivers by industry poisons fish and people.
The spreading urbanisation around Dhaka and deforestation in the
mountains shorten the lag times after down pours. Climate
change caused by global warming will make the situation worse.
Increased snow melt in the Himalayas and rising sea levels in the
Bay of Bengal could increase the flood damage. If the sea levels
were to rise by one metre it is estimated that 50% of Bangladesh
would be under water. In such an overpopulated region the
consequences would be disastrous.
Exercise – Decide who said it
 “When the waters rise I can do nothing but watch all my
hard work being destroyed”
EMERGENCY
WORKER
 “I can't go to school when the floods come. My mother
doesn't let me go out to fetch food because of the snakes”
SUBSISTENCE
FARMER
 “The waters stretch as far as I can see, and the bodies of
dead animals float past the aid station as we give food and
water to the hungry people”
INTERNATIONAL
ECOLOGIST
 “It is not the depth of the flood that is the greatest cause of
death but the contamination which spreads diseases such
as cholera”
MEMBER OF MEDICAL
TEAM
 “Global earming can no longer be ignored as natural
disasters are occurring more and more frequently”
SCHOOL CHILD
IN DHAKA
 “Our country needs and deserves international aid to help
us survive the effects of deforestation”
BANGLADESHI
POLITICIAN
AID