Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Definition: River flooding, occurs when a river’s discharge exceeds the capacity of its channel to carry that discharge (exceeds
bankfull). The river overflows its banks – this may be caused by physical or in combination with human factors:
Generic Physical Factors:
Excessive levels of precipitation over a prolonged period leads to surfaces exceeding field capacity (saturation), when the water
table reaches the ground surface, runoff increases.
Intensive precipitation over a short period of time, particularly when the ground surface is baked hard after a long period without
rainfall. This means the infiltration capacity is reduced, meaning the ground cannot soak up the water quickly enough leading to
increased surface runoff.
The melting of snow, particularly when the soil underneath (subsoil) is still frozen, reducing infiltration capacity.
Climatic hazards such as cyclones in Bangladesh, which bring abnormally large amounts of precipitation.
The nature of the drainage basin: size, shape (rounded = steeper gradient, higher drainage density (network of tributaries) = shorter
lag time / elongated = opposite = longer lag time); type and amount of vegetation, soil type and geology (permeable / impermeable) also
play a part.
Generic Human Factors: Flooding is a natural event but human factors exacerbate the problem
Urbanisation increases the extent of impermeable surfaces such as tarmac and concrete; reducing the amount of vegetation which
would naturally intercept precipitation meaning a higher proportion of original rainfall reaches the river. Added to this are drains and
sewers which channel surface water to the river quickly, reducing the lag time between peak rainfall and peak discharge.
Bridges may slow down discharge and reduce carrying capacity of the river; made worse with debris deposited directly behind the
bridge supports e.g. Boscastle floods (Aug 2004) huge amounts of debris blocked culverts (drains) upstream.
Deforestation means there is less interception and infiltration; but increased direct impact and runoff (fastest transfer) into the
river. Added to this, increased soil erosion and sediment entering the river, obstructing and increasing the flood risk e.g. 50%
deforestation in Nepal has partly contributed to increased severity of flood events in low-lying Bangladesh.
River management: See below:
Embankments – Bangladesh (river Ganges, Brahmaputra & Meghna), designed to increase river capacity but prevents flood waters
returning to the river.
Dams – Farakka dam (river Ganges) in India (1988) allowed floodgates open to reduce the risk of the reservoir flooding; extra
discharge caused flooding in Bangladesh.
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Channelisation (lining river with concrete and straightening) allows discharge to flow more freely though will increase flood risk
downstream
Climate change leading to unpredictable weather patterns across the globe and increased incidence of hurricanes bringing heavy
precipitation.
Case study: Bangladesh Flood (Rivers Ganges, Brahmaputra & Meghna),
Where: Bangladesh (southeast Asia); rivers Ganges, Brahmaputra and Meghna
When: July to September 1998
Why:
Specific Physical Causes:
Topography:
 Most of the country is the huge floodplain and delta of the rivers Ganges &
Brahmaputra, with 70% of the land less than 1 metre above sea level and
therefore very flat.
 Rivers, lakes and swamps cover 10% of the land
Weather:
 Heavy monsoon rains (THE MOST IMPORTANT FACTOR), especially over
the Himalayas, the uplands of Assam and the Central Indian Plateau from
June to September
 Tropical cyclones are common in the region, bringing heavy rain; particularly
from May to November.
Snowmelt from glaciers in the Himalayas in late spring and summer increases
discharge.
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Specific Human Causes:
Deforestation: The headwaters of the Ganges are in Nepal where 50% of the forests have been cut down since the 1950s
for fuel, timber and grazing land; as the population is rapidly expanding. This reduces interception and increases soil
erosion; with an estimated loss of soil 400 times faster in deforested areas, raising the river bed of the Brahmaputra by
5cms per year.
Impact of hard engineering: Farraka dam built in India in 1971 is blamed for the raising of the river bed of the Hooghly
river, a tributary of the Ganges. During the dry season, the dam reduces the discharge of the river encouraging
sedimentation of the river bed. Also, in 1988, the flood gates of the dam were opened to avoid the reservoir flooding but
increased the flood risk in Bangladesh.
Global warming: Increased unpredictability and intensity of weather events e,g, the flood of 1998 was unusually prolonged
at 56 days.
Agricultural practices: The extraction of water for irrigation had lowered the water table and caused the land to subside in
places by up to 2.5 metres.
What were the consequences of river flooding in Bangladesh?
Specific Social Consequences:
 1040 people killed
 31 million people were affected
 14,000 schools flooded
 Respiratory infections (such as bronchitis) affected large numbers of people along with outbreaks of diarrhoea and
cholera.
 Short- and long-term risks of serious food shortages due to millions of hectares of land under water.
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Specific Economic Consequences:
 2.5 million farmers affected
 Floods destroyed a total of 668,529 ha of crops = 2 million tonnes of rice destroyed
 500,000 cattle and poultry killed
 980,000 houses were destroyed or partially damaged
 Infrastructure including 6500 bridges and11000 kms of roads damaged and in need of repair
 Overall cost of the flood was almost $1 billion.
 Required international aid and donations e.g. UK providing steel bridge materials and 100,000 tonnes of wheat.
Specific Physical (Environmental) Consequences:
 75% of the country was affected with over 108,000 km2 of area flooded.
 Some areas under water for more than 2 months
Assessment:
The physical causes of river flooding in Bangladesh suggest that these were the most important. Significantly, the intense
monsoon period from July to September which left many areas submerged for up to 56 days; combined with spring /
summer snow melt and increased discharge from the headwaters in the Himalayas reaching the low-lying floodplain of
Bangladesh. Therefore, the human causes serve mainly to increase the scale of flooding; in this instance the inadequacy of
flood management strategies such as the 4528kms of embankments which were damaged; and increased sedimentation of
the Ganges due to deforestation in Nepal.
It could also be argued, however, that the social consequences of river flooding are more significant here compared to the
physical impacts, given the displacement of over 30 million people with 980,000 houses destroyed or partially damaged.
Acute shortages of food and safe drinking water meant that people were far more susceptible to water-borne diseases such
as diarrhoea, compounded by poor access to health care. However, the frequency of flooding in Bangladesh has meant that
people are more resilient and accustomed to dealing with this challenging situation.
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
What are the similarities and differences in river flooding between Carlisle, UK (HIC) and Bangladesh (LIC)?
Causes:
Physical Factors:
 Heavy precipitation
 Topography: Flooding occurred in low-lying areas
Similarities
Human Factors:
 Urbanisation
 Global warming and increasingly unpredictable weather patterns
Consequences:
Social:
 Deaths
 Displacement
Economic:
 Cost of repairing infrastructure, homes and flood defences
Physical (environmental):
 Roads and bridges damaged
 Homes & schools flooded
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Differences
Causes:
Physical Factors:
 Heavy monsoon = far more prolonged period of precipitation
 Considerable snow melt (in the Himalayas) increasing discharge levels
 Extent of floodplain covering nearly 145,000 km2.
Human Factors:
 Deforestation in Nepal resulting in reduced interception and increased sedimentation due to soil erosion.
 Management of the Farraka dam; increasing sedimentation by restricting flow; but also increasing risk of flooding by
opening the flood gates to relive pressure from the reservoir.
Consequences:
Social:
 Number of deaths
 People of Bangladesh more able to cope in longer term due to frequency of flood events
 Homes & schools flooded
 Scale of people affected
 Availability of food and clean drinking water
 Access to health care and incidence of water-borne diseases
 Intangible effects – far greater incidence of depression in UK compared to Bangladesh (accustomed to frequent
flooding and deprivation?).
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Economic:
 Insurance claims (UK)
 Afford emergency services to co-ordinate response (UK)
 Need for international aid to supply food, water and medicine (Bangladesh)
Physical (environmental):
 Scale of flooded area – over 108,000 km2 (Bangladesh)
Summary
The sheer scale, frequency, lack of preparation, paucity of preventive infrastructure and capital to address these problems
make the impacts on LICs far more severe and long lasting than those on HICs. Particular to Bangladesh, many of the human
causes links to the actions of other countries (especially India (Farakka Dam) and Nepal (Deforestation) making any longterm sustainable preventative flood strategies intractable.
The most significant consequence for LICs are social given the number of deaths, homelessness and exposure to waterborne diseases; whereas in HICs, the key impact is economic given the significantly higher land values; density of housing
and businesses requiring insurance claims.
PLEASE NOTE:
 MUST SUBSTANTIATE THESE COMPARISONS / CONTRASTS WITH PLACE-SPECIFIC FIGURES FROM BOTH
HIC & LIC FLOODING CASE STUDIES
 MUST USE CONNECTIVES WITHIN A PARAGRAPH TO MAKE CONVINCING COMPARISONS / CONTRASTS
(SEE MIND MAP ON FOLLOWING PAGE)
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Yr12 Rivers: River flooding in a LIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
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