Theme 1: The Boscastle flood 2004 (1)
Flash flood: an immediate response to short periods of intense rainfall. River levels rise without warning, reaching a peak within minutes/hours. It is very destructive.
- Boscastle flood in Cornwall 2004 was a flash flood which is rare in the UK.
- By lunchtime torrential rain fell and withing minutes river levels rose and 3 rivers had burst their banks; flooding the whole village.
- Over 500mm or rain fell in 4hours, creating a tide of water destroying everything in it's path.
- Natural characteristics make it vulnerable to flooding.
- Impermeable upland area of Bodmin Moor.
- Steep-sided valleys fun towards the sea, funneling water towards Boscastle.
- After heavy rainfall surface run-off quickly reaches rivers, increasing the likelihood of flash-flooding.
Theme 1: The Boscastle flood 2004 (2)
- During Summer 2004, there had been lots of rainfall so ground was saturated.
- Remnants of Hurricane Alex moved across Atlantic Ocean, remaining stationary over Cornwall due to converging winds.
- Flood risk was increased because of amount of buildings alongside the river and construction of small bridges across it which trapped material downstream creating a "dam-like" effect.
- Heavy rain falls.
- Power cuts caused by lightning.
- Fire brigade mobilised.
- Roads closed.
- Floods peak; cars swept away, buildings destroyed.
- Major incident declared and RAF search and rescue alerted.
Theme 1: Responding to the 2004 Boscastle flood (1
- Flood destroyed homes and businesses, sweeping away 100 vehicles.
- Bridges and roads damaged.
- Tons of med and debris left in lower part of village.
- 90% of income relied on tourism which was destroyed, damaging economically.
Human factors adding to damamge
- Building of low bridges, trapping boulders and trees.
- Trees growing along river washed into river, blocking channels.
- Artificially narrowing river reducing it's carrying capacity.
- Building alongside, not allowing expansion.
- Removing vegetation from sides increasing surface run-off.
Theme 1: Responding to the 2004 Boscastle flood (2
- Wider span bridge and remove lower bridge.
- RIver wider and deeper so can carry a larger capacity.
- Relocate defence walls and put in new ones.
- Remove trees near the river.
- Raise car park so cars are above a design flood level.
- Ensure dead trees and vegetation are removed from the river.
- Trash screen to stop boulders/trees blocking drainage channels.
Theme 1: Flooding in Bangladesh (1)
- It is affected by river floods (every year part of cycle of snow-melt and monsoon rainfall. If it is prolonged it can be cause of extreme flood events). It's also affected by coastal floods (created by cyclones building up in Indian Ocean so water is funnelled to Bangladesh creating a storm surge.
- Trees cleared for grazing=increased surface runoff.
- Ganges diverted for irrigation increasing deposition, reducing channel capacity.
- Melting of snow from Himalayas increases surface runoff.
- Deforestation of Himalayas increases surface runoff.
- Increased surface runoff leads to soil erosion and more silt, raising river beds.
- Meeting of 3 huge rivers increases flood risk.
- Silt blocks river channels creating islands and decreasing carrying capacity.
- Rapid unplanned urban growth adds to problem of flooding, largely made up of poor migrants living in vulnerable areas.
Theme 1: Flooding in Bangladesh (2)
- Flooding is an annual occurrence linked to the monsoon rainfall pattern.
- Yearly flooding brings lots of silt, adding to soil's fertility.
- Floodwater used to irrigate farmland so is important for yearly cycle of agriculture.
- In normal years it can be controlled by storm drains and embankments, few people are badly affected.
- Some years volume and pattern is extreme and water rises dangerously high.
- The rains were exceptionally heavy and water levels reached record heights.
- Resulting floods covered almost 60% of the country and main river channels flooded.
- Capital of Dhaka and regional cities were badly affected and cities underwater for weeks.
- Hundreds of people killed and millions homeless.
- Agricultural land/crops lots/contaminated by polluted water.
- 900 bridges and 15,000km of roads destroyed.
Theme 1: Responding to the flood hazard in Banglad
- Frequency and scale of flooding in Bangladesh increased in the last 50 years so more preparation and planning needed.
- Cluster villages- villages which have been raised 2m above water level.
- Raised homestead- individual homes raised 2m above sea level.
- Food shelter- 2 hectares of raised land to bring livestock to with space for 100 families.
- Rescue boats- located around areas most at risk from flooding near to flood shelters.
- Radios- given to "preparedness committee" so flood warnings issues and action.
Dhaka Integrated Flood Protection Project
- Embankments- earth embankments built to hold back rising water.
- Slope protection- to reduce erosion of embankments.
- Drains- Storm drains linked back to rivers.
- Sluice gates- able to close channels when water rises.
Theme 1: Blakeney Point, Norfolk (1)
Why constructive coastal areas are a valuable environment?
- Create salt marshes as inside of spits/bars are protected from winds etc.
- Salt marshes create important breeding grounds for birds and plant species.
- To protect them they've been labelled as "nature reserves", "areas of outstanding natural beauty (AONB)", "Sites of Special Scientific Interest (SSIS)"
- Many protected coastlines are used by the public for recreational and educational activities.
- An example is Blakeney Point National Nature Reserve in North Norfolk.
Theme 1: Blakeney Point, Norfolk (2)
- Blakeney Point is a sand and shingle ridge extending westwards from Norfolk coast for 5km.
- It is separated from the coast by sheltered tidal waters where fine sediment is deposited by rivers creating a rare salt marsh environment.
Why is it a rare environment?
- It is one of the largest unspoilt coastlines in Europe and has lots of environmental features including...
- Areas of rare habitats including salt marshes, sand dunes and vegetated shingle.
- International breeding area for sea bird colonies e.g. arctic terns, oyster catchers and Brent geese.
- Breeding area for grey and common seals.
- Rare plant species including sea lavender and sea campion.
- Uninterrupted coastal views and long stretches of sandy beaches.
Theme 1: The Pevensey Bay Sea Defence Scheme (1)
Soft engineering methods
- Beach replenishment- replacing sand/shingle removed by long shore drift
- Beach re profiling- shaping beach so it absorbs more energy during storms.
- Fencing/hedging- building fences/salt-resistant bushes at back of beach to reduce sand being blown inland by strong winds.
- Planting vegetation- planting grasses etc. in low-lying sandy areas to stabilise material.
Why does it need protection?
- Long shore drift removing increasing amounts of beach material.
- 50km of land would be flooded if defences failed.
- The Pevensey Levels, an environmentally sensitive area would be flooded by salt water.
- Over 10,000 properties in the area.
- Touristy with caravan parks.
- Main coast road and rail links run along the coast.
Theme 1: The Pevensey Bay Sea Defence Scheme (2)
Schemes at Pevensey Bay
- Beach replenishment.
- Beach re profiling.
- Beach recycling- three times a year large trucks are used to move beach material from east bank to western end so there is an even profile.
Why is it sustainable?
- Works with the natural environment.
- Doesn't involve massive building costs.
- Doesn't damage the environment.
- Resulting beach has an amenity value for the local people and is an important tourist attraction.
- However requires ongoing expensive maintenance.