PowerPoint 9: Coastal management strategies

Hard engineering strategies Hard engineering strategies act as a barrier between the sea and the land. Artificial structures are used to change or disrupt natural processes. Examples of hard engineering strategies include sea walls, groynes, revetments, rock armour (rip rap), gabions and offshore breakwaters.

Sea walls Sea walls are often built at the foot of cliffs to prevent cliff erosion and subsequent collapse. They are often curved, to deflect the energy of the waves back onto themselves. Advantages very strong coastal defence, particularly where wave energy is high long life span – at least 25 years reassuring to the public may provide a walkway along the top Disadvantages very expensive – up to £4000 per metre can impede access to the beach for tourists can cause beach erosion at the base of the wall Photo © Tony Atkin.

Groynes Groynes are barriers of wood or concrete, at right angles to the beach. They trap sediment transported by longshore drift, and help to create wider beaches, which absorb wave energy, reducing cliff erosion. Advantages comparatively cheap – approximately £7000 each do not affect access to the beach retain a wide, sandy beach for tourists Disadvantages beaches further along the coast are starved of the sediment trapped by the groynes will not last as long as other hard engineering strategies Photo © Chris Parfitt.

Revetments Revetments are wooden slatted barriers, usually built at the back of beaches to protect the base of the cliff. They dissipate the energy of waves breaking on the revetments. Concrete revetments called accropodes may also be used. Advantages erodes less beach material than a sea wall cheaper than a sea wall – approximately £2000 per metre Disadvantages Short life span, particularly those made of wood not suitable for areas of high wave energy Photo © BazDaRambler.

Rock armour Rock armour, or rip rap, is placed at the bottom of cliffs or the back of beaches. The large boulders of hard resistant rock absorb wave energy. Rock armour may be used in combination with revetments or a sea wall. Advantages cheap compared to sea walls, approximately £3000 per metre lasts a long time and is efficient at absorbing wave energy Disadvantages unattractive and makes access to the beach difficult and dangerous costs increase dramatically if the rocks have to brought a long distance or imported Photo © John Lyon.

Gabions Gabions are cages of wire mesh filled with rocks and stones, which are placed at the back of beaches or at the base of cliffs. They absorb wave energy, reducing erosion. Advantages relatively cheap, approximately £100 per metre efficient at absorbing wave energy Disadvantages unattractive short life span compared to sea walls not very effective in areas of high wave energy Photo © Colin Babb.

Offshore breakwater Offshore breakwaters are built of rocks or boulders. They protect the shoreline by absorbing wave energy, which reduces erosion, and by changing wave direction, which reduces longshore drift. Advantages as this form of coastal management is located offshore, the beach retains its natural appearance Disadvantages unattractive expensive to build and maintain (£2000-£20,000 per metre) do not directly protect the cliffs beach material continues to be eroded Photo © Marathon.

Soft engineering strategies Soft engineering is enhancing natural features, such as beaches and sand dunes, to protect the coast from erosion. Examples of soft engineering strategies include beach nourishment, managed retreat and dune stabilisation.

Beach nourishment Beach nourishment is where sand and shingle (dredged from offshore or inland) are used to make the beach higher and wider. A wide beach is an effective way of reducing cliff erosion. Advantages beach nourishment is relatively cheap, approximately £20 per cubic metre the natural appearance of the beach is preserved Disadvantages has to be carried out regularly, usually twice a year, and sometimes more frequently, for example after a storm offshore dredging can increase erosion in other parts of the coastal system Photo © Pevensey Coastal Defence.

Dune stabilisation Sand dunes are effective barriers to wave erosion, but without vegetation they disappear. To prevent this, dunes are planted with marram grass whose roots keep the sand in place. Newly planted areas are often fenced off to allow the marram grass to become established. Advantages it is relatively cheap, about £2000 per 100 metres it maintains the natural environment and is popular with wildlife and people Disadvantages planting marram grass is time consuming people do not always keep away from newly planted areas Photo © Scottish Natural Heritage.

Managed retreat Managed retreat lets the coastline erode naturally, often by removing coastal protection. Areas of the coast, usually land of low value such as grazing land, are allowed to flood in order to protect areas further inland. Advantages maintains the natural balance of the coastal system beaches and salt marshes can be created to protect against erosion Disadvantages previously protected land is flooded farmers and other coastal dwellers can lose incomes and even their homes Photo © Southwest Coastal Group.

Coastal management in Lyme Regis Phase III: Monmouth Beach and Ware Cliffs Phase V: The Cobb Phase III: Cobb Gate to the Harbour (completed) Phase I: Cobb Gate to Church Cliff (completed) Phase IV: East Cliff (completed) © Crown copyright & database rights 2016.