(Unattributed) IGCSE Geography Rivers

1. Flooding In Bangladesh: A case study
When? July/August 2004
Causes of the Annual Monsoon Seasonal Flooding:
Natural / Physical Human
Climatic Human Activity
Terrestrial Processes

2. What is a Monsoon?
A seasonal reversal of winds,
caused by the different heating of
land and sea, resulting in
seasonal heavy rain.

3. In summer the land is
warmer than the sea
making LOW PRESSURE
so the summer Monsoon
winds bring moist air off
the sea = really wet
In winter the land is cold
making HIGH PRESSURE.
The dry winds blow out from
the land to the sea.

4. Climatic Causes: Random variations in the intensity of
monsoon rains cause the flooding.
Bangladesh has a
tropical monsoon-
type climate, with a
hot and rainy summer
and a dry winter. The
climate is one of the
wettest in the world.
Most places receive
more than 1,525 mm
of rain a year, and
areas near the hills
receive 5,080 mm ).
Most rains occur
during the monsoon
(June-September).

5. Historical records to 1781, show that a major flood
could be expected every seven years and a
catastrophic one every 33-50 years.
More detailed records since 1954 show the worst
flooding since then occurred in 1974, 1987, 1988 and
1998, when 70 percent of the country was submerged
in the most serious flood Bangladesh had ever seen.

6. Then 2004: The mighty Brahmaputra river, swollen by rain
and a Himalayan burst dam, has flooded huge swathes of
north India and Bangladesh, killing dozens and forcing
millions to seek refuge on higher ground.

7. In late-June 2004, heavy monsoon rains swelled the waters
of the Meghna River, which reached its peak level in early-
July. The other rivers burst their banks in early-July, due to
heavy rains in the north of the country, causing flash floods
in the north and the west-central districts. The floods
spread, eventually impacting Dhaka and 36 million people
(about 25 percent of the population) with 38% of
Bangladesh inundated by the time the waters began to
recede in late-August.
" … we are only at the
beginning of the monsoon
season and still have another
two months to go," The rainy
season lasts from June to the
end of September, and
slightly later in some areas.

8. September 2004: Monsoon rains have hit Bangladesh
once more. For the past four days most of the country
has been under water after what is ostensibly the
country’s worst bout with bad weather in the last 50
years.
This week, according to official sources, the “average
rainfall was 300 mm per day, the highest rate since
1952”.
Four days of constant rain
have caused floods in parts
of Bangladesh, as in this
village 100km north of
Dhaka.

9. Himalayan
Snow Melt
…
Every
summer
Gangotri glacier, in the
Indian Himalayas,
feeds the Ganges river.
The glacier is
retreating an average
25 metres yearly.

10. Terrestrial Processes:
Relief Rainfall in the Himalayan Mountains
feeds the rivers

11. Most of
Bangladesh
sits astride the
deltas of a
series of large
rivers flowing
from the
Himalayas, and
about a third of
the country
floods every
year during the
monsoon.
Daniel Landi
Standard Bank

12. Roughly 80 percent of the landmass is made
up of fertile alluvial lowland called the
Bangladesh Plain. This means that it is prone to severe
and heavy flooding.
Flooding irrigates crops and adds fresh silt to padi
fields maintaining the fertility.

13. Most of Bangladesh is below 10 metres above sea level

14. Human Activity : Global Warming leading to sea level
rise. The flow of water coming from the Himalayas -
which is huge - depends on the differential of height.
"When the sea level is higher, the flow of that water
will be restricted.
So when you
hear now of
Bangladesh
being a
flood-prone
country - it
will be a
much more
flood-prone
country in
future."

15. The extraction of groundwater for irrigation had lowered
the water table and caused the land to subside by
about 2.5m.
The groundwater contains
naturally high levels of
arsenic!

16. The use of water upstream for irrigation and storing water in
reservoirs has reduced the amount of silt deposited so
the level of the land has not been built up.
People live on river
sandbanks called Chars.

17. Increased amounts of urbanisation has led to higher peak
flow on the rivers with much shorter lag times and a greater
frequency of floods.

18. Population Growth in
Himalayan headwater
countries like Nepal puts
pressure to produce more
food by increasing the area
of land farmed…..

19. …. So Deforestation in the Himalayas has increased
leading to increased run off….
No leaves to intercept , no
roots to bind soil in place.
It has also destabilised
slopes leading to
landslides and soil erosion.
The soil is carried by rivers
and deposited in channels
on the low ground.
This reduces channel
capacity and increases the
likelihood of flooding.

20. A dam at Tsatitsu Lake in the Himalayan kingdom of
Bhutan had burst, spilling water into tributaries of the
Brahmaputra.
A furious G.L.O.F.
hit the dam and
HEP plant at
Kurichu and
breached it.
The Glacial Lake
Outburst Floods
may be linked to
increased melting
because of Global
Warming.