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Coastal defence (management) against flooding and erosion.

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What are the main types of soft and hard engineering used on the coastline of the UK? P57

(Coastal defences)Advantages and disadvantages of these techniques

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Definitions

• Soft engineering: method of coastal management which works with natural processes at work on the coastline and to be unobstructive (unnoticeable) visually. It does not involve major construction.

• Hard engineering: method of coastal management which involves major construction work.

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Hard engineering

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Rip-rap

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Recurved sea wall

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Groynes

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Gabions

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Offshore reef

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Revetments

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Soft engineering

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Beach replenishment

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Cliff regrading

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Questions on coastal management

• Page 5 • Page 11• Page 15

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Case Study

Swanage

In Dorset on the south coast of England

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RATES OF EROSION ESTIMATED ABOUT 40-50 CM PER YEAR

Chalk

Limestone

Clay

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Swanage Bay

Peveril Point

Durlston Bay

Location of study areas

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In Durlston Bay, erosion mainly occurs at one particular point, where there was a major weakness in the resistant limestone rock. There were three methods used to protect the cliffs from erosion (recession):

Cliff regrading – extending it forward, making slope longer and less steep. Reduces the risk of mass movement.

Rip rap placement – Large boulders at the base of the cliff to resist wave attack and dissipate wave energy.

Drainage – removing excess water, so slope wasn’t as heavy or lubricated after rain. Reduces the risk of mass movement and freeze-thaw weathering.

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Swanage BayThis is a popular recreational area for beach users, diving, fishing and sailing. Erosion occurred along a considerable length of cliff. The town has been developed on soft eroding cliffs and annual falls & slips have left some properties, such as The Pines Hotel, very close to the cliff top.Swanage landslide caught on cameraCoastal management issues:The potential impact of any coastal defence works on Swanage's tourism and the aesthetic and landscape quality of the coastline.Photo Gallery

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SEA WALL

• Built in the 1920s and provided a promenade as well as a barrier to wave attack.

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Groynes

A series of mainly timber groynes were installed in the 1930s, and eighteen of them have been replaced in 2005 with new ones. These reduced longshore drift and help make sure that a beach remained in place to absorb the energy of breaking waves.

The most cost effective method was found to be the replacement of the 1930s groynes and replenishment of the beach sediment.

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Beach replenishment

In November of 2005, 90,000 m3 of sand was deposited on the beach. The beach will need to be recharged with around 40,000m3 of sand every 20 years.This works with the groynes to ensure a good size beach.The works were finally completed in June 2006 at an estimated cost of £2.2 million.

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Cliff regrading

• A series of steps were made in the cliff to reduce slope angles

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However: January 1st, 2013 Dorset Coastguard have restricted access to Swanage beach and the South West Coastal Paths, after heavy rains over the holiday period caused further mudslides and cliff subsidence in Swanage.

What are the effects of coastal recession on people and the environment?

Coastal recession (when the coast is eroded and retreats)

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Coastal recession at Happisburg

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The effects of coastal recession on people and the environment

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Amount of effect is determined by the land use. Use for settlement>farmland

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P18 Explain the effects of coastal recession on people and the environment. Use examples in your answer. (6)

North Norfolk coast

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Managed retreat/Hold the line policies?

Managed retreat is an alternative to constructing or maintaining coastal structures. Managed retreat allows an area to become flooded.Hold the (existing defence) line – to build or maintain artificial defences so that the position of the shoreline remains. Use of hard and soft engineering

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Cliff recession along the North Norfolk coast

Why has The North Norfolk coast’s new Shoreline management Plan adapted a managed retreat rather than ‘hold the line’ policy?Erosion has always been a problem on the Norfolk coast because of its soft rock geology and its long fetch (Destructive/high energy waves)High rate of erosion.Erosion rates are between one and three metres per year, so it has become increasingly difficult and expensive to continue protecting certain locations - and trying to do so makes erosion worse in other areas along the coast. This will get worse as the effects of climate change increase. 37

Predicted impacts on people What will be lost to the sea over the next 100 years?- Nearly 1000 homes- 1400 caravan and chalet parks- Six hotels and guest houses- Seven historic buildings - 3.5 km of road- Seven golf course holes- Three community halls

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HappisburgVillage of Happisburg (population= 850)Photo gallery on coastal erosion Factors which explain high rates of erosion in this area:Geology: Cliff made of soft rock (clay, gravel and sand deposited by glaciers)No sea defences: 1958: use of revetments to reduce coastal erosion. From 1995 no repairing of coastal defences high rates of erosion.Government has refused to protect the village because it is not cost effective: the village is less valuable than the cost of the defences to protect it.

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Coastal recession along Beach Road

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Impacts on people

Loss of homesSince 1995: 25 properties and the village’s lifeboat launching station washed away.Loss of valueHouses worth £80,000 when the coast was defended, are now valued at 1£. No insurance of property against coastal erosionErosion-related stress and depression

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Impact on the environment

• Loss of land:At Durlston Bay near Swanage the cliff receded 12 metres between 1968 and 1988. In 200/01 severe storms and high energy waves led to a further retreat of another 12 metres.• Loss of natural habitatsDurlston County Park also lies on the top and is home to over 250 species of birds that nest on the cliff. These habitats are threatened by cliff recession, which can affect the breeding of rare species such as puffins and falcons.

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Causes of coastal flooding

How are the effects of coastal flooding reduced by prediction

and prevention?

Coastal flooding occurs when normally dry, low-lying land is flooded by sea water

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Causes of coastal flooding• Severe weather: Strong winds and storms which can

increase the height of waves and tides. • Storm surge: A storm surge is an offshore rise of water

associated with a low pressure weather system*, typically tropical cyclones. Storm surges are caused by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea level.*A low-pressure area, low or depression, is a region where the atmospheric pressure is lower than that of surrounding locations

• Sea level riseCoastal flooding associated with sea level rise will become a significant issue into the next 100 years.

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Storm Surge

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How are the effects of coastal flooding reduced by prediction and prevention?

This should be studied through forecasting, building design, planning and education

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The Bangladesh Meteorological Department has three radar stations that transmit minute-by-minute weather updates. The Bangladesh Disaster Management Bureau also issues cyclone alerts through the national media as soon as a cyclone is detected by environmental satellites.

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The Thames Flood Barrier

The Thames Barrier is one of the worlds largest flood barriers and serves to protect London from flooding during exceptionally high tides and storm surges.The Barrier can be lifted at high tide to prevent sea waters flooding London

51Flood shelters

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