Hard and Soft Engineering - Coastal Defences

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Sea wall environmental costs
Ugly, Destroys habitat
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Sea Wall environmental benefits
Don’t impede movement of sediment downdrift – don’t disadvantage other areas
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Sea wall economic benefits
• Last for many years
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Sea wall social benefits
• Sense of security • Promenade doubles as cycle route outside peak walking periods and aids tourism • Steps act as seating
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Sea wall social costs
• Restrict access to the beach • Coastal flooding may occur if waves break over the sea wall
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Sea wall economic costs
• Expensive to build ($5,000-10,000 per metre) • Expensive to maintain/repair – reflected waves scour the beach in front of a sea wall and this undermines its foundations
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Groynes social costs
• Barriers – impede waling along a beach • Dangerous – deep water on one side & shallow on the other – children climb on them • Wind surfers collide with them
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Groynes social benefits
• Rock groynes at Sandbanks, Poole, have concrete crests for people to walk along to reach a viewing/fishing point. • Act as windbreaks
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Groynes
Wooden or concrete barriers built at right angles to the beach – typically wooden or stone Prevents LSD and trap sediment – builds beach on updrift side – absorbs wave energy and reduces impact on sea wall
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Sea wall
A wall built on the edge of the coastline Protects base of cliffs, land and buidings
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Groynes economic benefits
• $5,000 each – relatively cheap • Last up to 40 years A larger beach attracts tourism and boosts local economy
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Groynes economic costs
• Restrict supply of sediment down-drift (traps sediment) • Ineffective in stormy conditions • Wooden type has short life span
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Groynes environmental costs
Unattractive
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Rock armour
Downward slope arrangement – deflects wave’s energy Water enters gaps – releases pressure – reduces waves energy – little scouring of the base
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Rock armour economic costs
• Highly resistant rockrom Norway or Sweden are often used in preference to rocks from local quarry – resentment – inflates cost • Heavy storm waves move rocks – needs maintenance
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Rock armour social costs
• Makes access to beach difficult – long detours • Accidents occur from climbing – slippy seaweed
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Rock armour environmental costs
Ugly • Driftwood and litter become trapped Imported rocks don’t blend with local geology.
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Rock armour economic benefits
• Relatively cheap ($1,000-3,000 a metre) • Quick to build (weeks) and easy to maintain • Can last a long time if maintained Versatile – can be placed in front of a sea wall (lengthen its lifespan) or to stabilise slopes on sand dunes
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Gabions
Water enters cages – absorbs & dissipates some of the wave’s energy – reduces rate of erosion May be back of sandy beach or in front of a cliff (stability-reduce landslide risk) May be covered in vegetation
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Gabions economic benefits
• Relatively cheap ($110 a metre) • Easy to construct • Constructed on site using local pebbles – cheaper • Quick-fix solution • Last 20-25 years
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Gabions environmental benefits
Blend in better than other hard engineering, especially when sand is blown over them or vegetation covers them
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Gabions environmental costs
• Damaged ones are unsightly Sea birds may damage feet
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Gabions economic costs
• Restricted to sandy beaches as shingle would quickly degrade them • Easily destroyed – maintenance needed – can be expensive when covered in vegetation and embedded
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Gabions social costs
• Dangerous when damaged – sharp broken steel
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Beach nourishment
Wave energy is absorbed and dissipated by beach – decreases erosion Beach recharge – sediment taken from bay – placed on beach that’s losing sand – dredger collects shingle from seabed Beach recycling – removal of sand from downdrift area which is
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Beach nourishment social costs
• Access to beach is restricted during process for several weeks • Beach recycling may cause resentment from residents in donor area
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Beach nourishment economic costs
High overheads – costs $300,000 to hire dredger
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Beach nourishment social benefits
• Wider beach – more room for users • People living along seafront are more protected from coastal flooding
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Beach nourishment economic benefits
• At Sandbanks, the wider, nourished beach protects very expensive properties • Reduces sea wall maintenance costs • Attracts tourism
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Beach nourishment environmental benefits
• Nourished beach is natural Blends in with environment
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Beach reprofiling
Reshaping of beach using existing beach material Winter – beach lowered by destructive waves – after winter storms, bulldozers move Effective buffer between land and sea
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Beach reprofiling social benefits
• Residents feel safe
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Beach reprofiling social costs
• Major reprofiling can be expensive
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Beach reprofiling economic costs
• Major reprofiling can be expensive
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Beach reprofiling environmental costs
Steep, high crested beach may look unnatural and uninviting to tourists
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Beach reprofiling environmental benefits
• Beach looks natural Beach is protected
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Sand dune regeneration
Artificial creation of sand dunes or restoration of existing dunes Physical barrier between sea and land Absorb wave energy and water
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Sand dune regeneration social costs
• While being established, signs tell people to keep out and areas are fenced off – may deter tourists
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Sand dune regeneration social benefits
• Protects land uses behind dunes • Popular for picnics and walking
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Sand dune regeneration economic costs
• Must be checked twice a year and have fertilisers applied • Expensive systems have to be put in place to protect planted areas from trampling – boardwalk, fire warnings, fire beaters, soltary car park.
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Sand dune regeneration economic benefits
• Costs are minimal – local grass and volunteer labour
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Sand dune regeneration environmental costs
Dynamic environment – no guarantee they’ll be stable – may be damaged by storms
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Sand dune regeneration environmental benefits
• May help maintain habitats for certain species
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Managed retreat
People moved out, buildings demolished Breach is made in sea defences – sea inundates land – creates new intertidal habitats Sustainable long term solution
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Managed retreat costs
May need to compensate people for lost land and buildings, and only suitable for low value sites
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Managed retreat benefits
It encourages the development of beaches and salt marshes which are natural and is a low cost option
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Other cards in this set

Card 2

Front

Sea Wall environmental benefits

Back

Don’t impede movement of sediment downdrift – don’t disadvantage other areas

Card 3

Front

Sea wall economic benefits

Back

Preview of the front of card 3

Card 4

Front

Sea wall social benefits

Back

Preview of the front of card 4

Card 5

Front

Sea wall social costs

Back

Preview of the front of card 5
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