coasts case studies

• BENIN, GULF OF GUINEA rate of coastal recession


  Cotonou, Benin's largest city is threatened by rapid coastal recession 6m p.a.
• BENIN, GULF OF GUINEA natural causes for coastal recession


  Unconsolidated layer of alluvial sands
• BENIN, GULF OF GUINEA human causes for coastal recession


  Dredging of sands offshore has increased water depth which allows higher energy destructive waves to reach the beach, increasing erosion rates (banned in 2007 but still continues)

  Companies extracted sand for raw materials for expansion of Cotonou
• IMPERIAL BEACH, CALIFORNIA coastal recession

  Large town 10km south of San Diego retreating 4m p.a.

  6km drift-aligned beach acts as transport zone in Silver Strand sediment cell
• IMPERIAL BEACH, CALIFORNIA coastal management

  sea wall and revetments built along source region which has cut supply of sediment to beach due to decreased erosion rate
• IMPERIAL BEACH, CALIFORNIA human causes

  Construction of Rodrequis Flood Control DAM on Tijuana River reducing sediment supply
• NILE DELTA, EGYPT site and situation

  Delta of river nile on mediterranean sea forms 240km stretch of coastline

  95% of Egypt's population live in fertile agricultural land of delta region
• NILE DELTA, EGYPT human causes for recession

  Construction of Aswan High DAM in 1964 reduced sediment supply to delta
• NILE DELTA, EGYPT coastal recession

  Erosion rates at Rosetta Promontory reached 200m p.a. 1965-1970
• Location


  Yorkshire coast
• Rate of erosion at holderness

  1.8m a year due to the combined effects of sub-aerial and marine erosion.
• How long is the holderness coastline

  61km
• What does it lie between

  Flamboruogh head and spurn spit
• Where has erosion been 10m per year

  Great Cowden - due to sediment starvation
• Naturally narrow beaches


  They give less protection
• People worsen the situation

  Rock groynes have been built at Mappleton, leaving places further down the beach with a sand shortage. South of the groynes, the cliffs have been suffering from basal scour and are eroding. At Cowden, erosion has increased since the groynes to 10m a year - sediment starvation.
• Social impacts


  Homes at Skipsea are at risk of collapsing. 200 homes and and several roads will fall into the sea between Flamborough head and Spurn point by 2100. Very little compensation is paid out by loss of private property or land caused by coastal erosion in England.
• Economic impacts


  Property prices have fallen sharply along the coast. Businesses are at risk from erosion so people will lose thier jobs. Eg a caravan park at Ulrome is losing an average of 10 pitches a year.The gas terminal at Easington is 25m from the cliff edge. 80 000 meters of farmland are lost a year. Between 2010 and 2012 the east riding Yorkshire council used £1.2 million from Defra to help people adapt to living on an eroding coastline
• Environmental impacts


  SSSIs are threatened. Eg the lagoons at Easington.
• Why does the geology mean that the Holderness coastline is vulnerable to erosion?

  The coast is made of boulder clay which is relatively soft and easily eroded - created when the glacier pushed up soil to create unconsolidated rock. The eroded clay particles are easily transported out to sea and don't accumulate as finer sediment . The narrow beaches means that the sea can easily reach the cliffs at high tide. Longshore drift transports sediment southwards, especially at Hornsea where backwash is far stronger
• Why does the fetch mean that the Holderness coastline is vulnerable to erosion

  Exposed to winds and waves from the north east - despite the small fetch currents circulate around the UK from the Atlantic. The North sea also has low pressure weather systems - very high tides. Sea is relatively deep - little friction to slow down waves.
• Why does longshore drift mean that the Holderness coastline is vulnerable to erosion

  There is a strong prevailing wind from the north east which pushes sediments down the coast. Estimated that 1/2 a million tonnes of sediment is moved south each year in suspension.
• Why does rip currents mean that Holderness is vulnerable to erosion?


  They can excavate ords
• Cost effectiveness of the rock groynes and a revetment at Mappleton

  They were built in 1991 and cost £2 million. They protect 12 homes and one business and the cost effectiveness is 0.76
• Cost effectiveness of the sea wall, rock armor and 15 wooden groynes at Hornsea

  Has a score of 1.25, so the cost benefit score is poor. There are 50 homes and 1 caravan park but they only add up to £9.1 million and the defences cost £11.46 million
• My future plan for the area

  Managed retreat, due to the costs of defences being so high and the weakness of the rock itself.
• What coastal features are at Flamborough head

  Arch, stack, wave-cut platform. Horizontal bedding planes
• Why does increasing leisure facilities and homes mean that the coast is more vulnerable to erosion

  There is a higher population in those areas so more people will be vulnerable. Clifftop housing and hotels increases the chances of slumping along natural slip planes
• What types of weathering are the most present at Holderness?

  Mechanical and biological. Freeze - thaw and wetting/drying is making the boulder clay crumbly.
• What is the main type of mass movement at Holderness?

  Slumping. Wetting and drying of the clay causes expansion and shrinkage, creating cracks. Heavy rain then lubricates the rock making it much heavier. The weakened cliff then collapses under gravity. The slumped material collects at the cliff base.
• Name all the key players at holderness

  Central government agencies, local government, local economy stakeholders, environmental stakeholders
• Central government agencies


  The environment agency is responsible for coastal management. They have had budget cuts since 2010
• The local government


  The local authorities are jointly responsible for coastal management with the environment agency. However, in 2010, local government funding was cut and the councils could only increase tax minimally
• Stakeholders in the local economy

  The tourist industry wants greater spending on coastal protection. Farmers want money to protect their farmland, yet it is lower value than urban spaces. Residents at Hornsea want guaranteed protection for their homes and businesses. Insurance companies are refusing to cover vulnerable properties
• Environmental Stakeholders


  English nature and RSPB want to protect spurn head, so a continuous flow of sand southwards by Longshore drift is essential. Protects the mudflats of the Humber estuary, which is one of the most important bird life reserves
• What is the main impact of coastal management

  Higher rates of erosion tend to occur below the groynes due to sediment starvation. Terminal groyne syndrome
• When was the first sea wall built and how long did it last for

  The first sea wall was built in 1870 in Hornsea and lasted for 6 years. In 1906 a stronger sea wall was built and it has been extended 5 times
• What happened in Mappleton after the groynes were built


  By the 1990s 4m of cliff was being eroded each year
• East Riding coastal change fund


  Relocation package and advice: Funding demolition cost, relocation costs up to £1000, moving home expenses up to £200. Adaptation package: Rollback covers planning applications for businesses like caravan parks. Assistance grants adapt properties that may be at risk from coastal erosion in the future. E.g. relocating septic tanks and changing acres routes.
• How much of holderness is being protected by hard defences


  9.2km and 2.15 private defences