Hydrology revision WJEC UNIT 1

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  • Created on: 30-04-13 10:09
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Hydrology topic case studies revision
Boscastle, South West England August 2004:
Causes of flooding:
89mm rain fell in an hour
Confluence of rivers Valency and Jordan
Topography-land acted as a funnel
Already saturated ground
Steep hills and intercepting valleys
Narrow river channel
No preparation or warning
Impacts of flooding:
150 people rescued by 7 helicopters
75 cars and 6 buildings washed away
No loss of life
90% of Boscastle's economy is tourism and 2/3's is generated during school holidays so it
had a negative impact on the economy
Flood management:
Spent £4.5 million on flood defences
Built stronger bridge
Raised the car park
Improved sewerage systems and storm drainage basins
Deepened and widened the river channel
Bangladesh 2012 flooding:
Monsoon rainfall
Snow melt from the Himalayas
10% of the land is made up of swamps, rivers and lakes
Flat land- less than 10 metres above sea level
Ganges and Brahmaputra rivers
139 killed
5 million affected
300,000 homes and 230,000 fields of crops damaged
50,000 had to be evacuated
Combination of hard and soft strategies

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Planting of trees in Nepal
12-15 storm basins developed
7 metre high embankments built
Pumping of water to create storage for monsoon
Mississippi Flood management:
Shortened course of river by 300km
Built 6 dams to create 1600km chain of 105 reservoirs
Planted trees
Strengthened levees
Built overflow channels for surplus water
Santa Cruz, Trinidad:
Natural forest used to cover 50% of the land
High annual rainfall of 170cm
265 hectares of forest removed
250 Hectares of land developed
Surface run off is now 300x greater…read more

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Water can be used to generate electricity
SOFT Strategies:
Schemes that do not involve engineering e.g. replanting trees cheaper and involves local people,
good for the environment
HARD Strategies
Use of hard engineering e.g.…read more

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Soil moisture levels depend on soil texture:
1. Free draining (gravel)
2. Absorbs water easily (Crumb structure)
3. Fine clay soils easily become saturated
Ground water accounts for nearly 25% of all freshwater on earth and is the major
supplier of river flow
Below the water table, water is trapped in joints and pores called AQUIFERS
o Physical factors:
o Moorlands-increase surface runoff
o Impermeable surfaces e.…read more

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Drainage basin characteristics (A drainage basin is an area drained by a river and its
BBC Online article AND extreme UK floods booklet focused on :
the causes, impacts and comparison of UK floods to the world e.g. The UK floods are
insignificant compared to the fact that 1/3 of the land in Bangladesh is flooded every
Also people's perceptions of our increased flood risk ­ we are now in a flood rich period
AND the Government's response to flooding e.g.…read more


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