Yr12 Rivers: River flooding in a HIC
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.
1
Yr12 Rivers: River flooding in a HIC
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: Carlisle Flood (River Eden), Cumbria, UK (1 in 170 year event)
Where: City ofCarlisle and River Eden, Cumbria, northwest England; 16 kms south of the Scottish border. Population 71,773
(2001 census)
When: Saturday 8th January 2005 from 2am
Why:
Specific Physical Causes:
Weather:
 Precipitation: River Eden catchment is 2400 km3 with average annual
precipitation of 2800mm in upper Eden and 760mm in Carlisle. Late
December 2004 had 2 weeks of heavy, continuous rain followed by extreme
rainfall between Thursday 6th and Saturday 8th January were 15% average
annual rainfall fell in 36 hours.
 Winds: Storm force winds of 90mph felled trees blocking rivers and drains.
Geology and soils: Catchment includes impermeable Skiddaw slate and thin soils in
upland reaches increased runoff
Drainage density: Carlisle is located at the confluence of the rivers Eden, Petteril
and Caldew.
Discharge in the Eden in Carlisle reached 1500 cumecs (tonnes) per second at its
max.
Gradient: Steep slopes in the upper Eden; flat floodplain in Carlisle
2
Yr12 Rivers: River flooding in a HIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Specific Human Causes:
Inadequate hard management techniques: Defences (flood walls) not able to withstand 1 in 170 year event. Flood levels in
some areas ended up 1 metre higher than the defences constructed after the last floods in 1968 (when discharge reached
1048 cumecs compared to 1500 cumecs in 2005)
Urbanisation: Impermeable surfaces and lack of interception increased run off into drains. The sewers and drains became
blocked with debris increasing the scale of the flood risk.
Problems with soft management techniques: Carlisle has always had a policy of leaving the majority of the floodplain
undeveloped through the city (flood plain zoning); but rising ground water (exceeding field capacity) accounted for the
flooding of many properties in the lower lying areas of the city.
What were the consequences of river flooding in Carlisle?
Specific Social Consequences:
Short-term:
 3 people died
 6000 people had to be re-housed because of displacement
 70,000 people without power for 3 days; 3,000 for 5 days
 All city schools closed for 3 days
 ‘Dunkirk spirit’ of the people to be cheerful in extreme adversity.
Medium term:
 Shortage of rental properties to house those displaced for prolonged period
 Worst affected school shut for 2 weeks
 Intangible social effects: increase in cases of depression and 1 suicide by uninsured householder
Long term:
 A year on, some flood victims still in temporary accommodation
3
Yr12 Rivers: River flooding in a HIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Specific Economic Consequences:
Short-term:
 1,600 homes flooded at an estimated cost of £100 million
 McVities biscuits, employing 1100, flooded
 Willowholme, Caldewgate and Rosehill industrial estates flooded; damaging 325 business properties with an estimated
cost of £100 million
 2 seriously damaged schools – estimated cost £4 million.
 70 buses lost worth £3 million.
 All shops closed = loss of trade
Medium term:
 Flooded residents paid to live upstairs in their flooded houses due to lack of temporary accommodation
 Shortage of second hand cars
 Builders and flood restoration firms drafted into city = boost to B & B in surrounding area.
 Concerns mount as to insurance premiums and mortgage availability
Long term:
 Reappraisal of flood defence needs for city; works expected to last 3 years and cost £20 million
 Many small family firms go out of business
Specific Physical (Environmental) Consequences:
Short-term:
 1,600 homes and over 325 businesses flooded; including magistrates court, police and fire stations
 Roads and bridges closed for 2 days
 1,150 trees felled in gales gusting up to 120mph.
4
Yr12 Rivers: River flooding in a HIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
Assessment:
The physical causes of river flooding at Carlisle suggest that these were the most important. Significantly, the intense 36
hour period between Thursday 6th and Saturday 8th January 2005 were 15% annual rainfall fell in the Eden catchment; as
well as gales gusting up to 120mph, felling trees and blocking river channels and drains, reduced the river Eden’s carrying
capacity. Likewise, the confluence of three rivers (Eden, Petteril and Caldew) just outside the city on a generally low-lying
floodplain led to discharge levels of 1500 cumecs, making this a 1 in 170 year event. Therefore, the human causes serve
mainly to increase the scale of flooding; in this instance the inadequacy of flood management strategies; both hard, with
flood defences equipped for 1048 cumecs rather than 1500 cumecs; and soft with the zoning of recreational spaces
through the city which still didn’t account for rising groundwater levels exceeding field capacity and increasing runoff.
It could also be argued, however, that the economic consequences of river flooding are more significant here compared to
the physical impacts, given the displacement of 6000 people with the cost of restoring the area at over £224 million. This
was exacerbated given the fact that the cost of new flood defences was re-appraised at £20 million, taking 3 years to
build. In the meantime, people were concerned about rising insurance premiums and mortgage availability.
P.T.O.
5
Yr12 Rivers: River flooding in a HIC
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
6
Yr12 Rivers: River flooding in a HIC
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?).
7
Yr12 Rivers: River flooding in a HIC
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)
8
Yr12 Rivers: River flooding in a HIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
9
Yr12 Rivers: River flooding in a HIC
Physical & Human Causes & Environmental (Physical), Socio-Economic Consequences (Case Study)
10