Hard engineering reduces the energy of breaking waves by building big structures between the sea and the land, or by building breakwaters that force the waves to break before they reach the beach.

Sea walls are reinforced concrete structures that create a rigid barrier between the sea and the land. They are incredibly expensive to build - about £5000 per metre. Sea walls can be straight or have a curve at the top. This sends the energy of the waves back out to sea and is sometimes called a splashback.

Rock armour (which is also known as rip-rap) is another form of hard engineering. Large rocks are put at the foot of the cliff, or in front of a sea wall, to reduce erosion by absorbing the power of the incoming waves. They also help prevent materials from being scoured from the beach by the backwash as the water is slowed down when it runs through the gaps between the rocks, reducing its power. Rock armour costs about £3000 per metre.

Revetments are sloping structures of wood or rock. They are built parallel to the coastline and they absorb the power of the advancing waves before they reach the cliff face. Beach material that is flung against the revetment by the swash of the waves can go through the gaps in the structure. It then stays on the upper beach, above the revetment, acting as a further protection for the cliffs. Revetments cost approximately £2000 per metre to build. They need to be replaced regularly.

Gabions are steel cages filled with rocks. They are placed in front of cliffs, often stacked one on top of another, to reduce erosion and prevent cliff falls. They absorb the power of the incoming waves and prevent the cliff from slumping forwards.

Gabions cost about £100 per metre, so they are much cheaper than many of the other types of hard engineering.

Offshore breakwaters are usually made from large rocks. They are built up into offshore bars to make waves break before they reach the beach. As well as absorbing wave energy, they can change the direction of longshore drift. The rocks must be large so that they are not moved by storms. They cost about £2000 per metre to build.

How do groynes work?

Groynes trap the sand which is carried along the coast by

longshore drift.

The sand acts as a natural protection against the force of the

waves. The waves break onto the beach and not the cliffs.

© Boardworks Ltd 20059 of 24

What are the disadvantages of groynes?

In 1991 a rock revetment and

two rock groynes were built.

Sand accumulated and halted

erosion.

South of Mappleton, the rate of

erosion has increased

significantly.

Material that usually moves

south via longshore drift is

becoming trapped within the

groynes.

Now there is no beach to

protect the cliffs - the sea

reaches the base of the soft cliffs

and erosion occurs.

Mappleton is located

on the Holderness

Coastline.

Gabions that have failed

In general, hard engineering methods are very effective in protecting the coast.

However, they are expensive and are not always visually attractive.

They can also prevent people from accessing the beach, and destroy natural habitats and ecosystems. Many people think that they are not environmentally friendly.

Suggest why some coastlines are not protected from the sea.

Soft engineering is used in environmentally sensitive areas, where the area is less built up. This sustainable option attempts to work with the natural environment and is often cheaper.

Dubai – building islands

Re-profiling the beach

Recycling the beach

http://www.pevensey-bay.co.uk/feature.html

Why does Pevenseynot have a sea wall?

?

Challenge Qs:

-How does the use of GPS improve coastal management?

- How might the coastline look in 50 years if the scheme is only maintained and not changed?

Managed retreat

Salt marshes: 200 years ago, many coastal areas in the UK had salt marshes to absorb wave energy during storms and protect areas inland from flooding.

In tropical areas mangrove swamps provide protection against tropical storms and hurricanes. The root systems in swamps in Florida, USA protect the coast from erosion and flooding.

2004 tsunami: the effects were worse because the mangrove forests were removed for hotels to be developed for tourists.

Salt marshes and mangrove forest have been restored in some parts of the world to protect coastal areas from the threat of flooding.

Managed retreat This is often the policy where existing sea defences are allowed to fail. The sea floods the land behind the breached defences, but builds up its own natural defences such as mudflats, marshes and beaches. This can only really work where population density is low and there is little infrastructure to protect. It is seen as being a much more sustainable way of the managing the coastline than using hard engineering methods. It can also be much cheaper than hard engineering projects.

Managed retreat is well suited to low-lying, saltmarsh environments, for example the estuaries of Essex and Suffolk. Over time, the broad tidal marshes will help absorb and reduce wave energy, providing a low-cost coastal defence. They also enhance the ecosystem.

A problem with this form of management is that good quality agricultural land may be lost. Settlements and property along the coastal strip may also be destroyed. Coastal blight occurs where the price of properties in an area subject to managed retreat falls significantly, meaning that homeowners may find themselves in negative equity and unable to afford the cost of a move inland. There have been reports of properties in the village of Happisburgh, North Norfolk being valued at just £1 due to the policy of managed retreat being proposed for the area.

The Wallasea Wetlands Creation Scheme, Essex

Wallasea Island is on the Essex coastline. It is between two estuaries - the River Crouch and the River Roach. In the past, the area was protected by a sea wall, and the land behind the wall was used for farming. However, due to lack of repairs to the wall on the north shore over a long period of time, it was in very poor condition. By 2004. it had begun to collapse in several places. There was a high risk that the walls would fail resulting in flooding the island and causing damage to the estuary.

It was decided that rebuilding the existing sea wall was not worthwhile. It would be very costly, and rising sea levels would put other areas at risk of flooding as the water was funnelled elsewhere. The agricultural land behind the wall was poor quality and there were very few buildings in the area. As a result, managed retreat was proposed for the northern bank of the island. The project involved several elements:

(a) building a new sea wall inland of the existing coastline (the sea wall is 4 km long as was build over 4 km behind the existing line of defence))(b) building an earth bund to separate freshwater from saltwater(c) building seven artificial islands to provide nesting places for birds, using materials excavated during the building of the London Cross rail project(d) pumping 700,000 tonnes of mud onto the area to create a new salt marsh(e) flooding the new area naturally when the old sea wall was breached (this happened in July 2006) to take the pressure off other locations further inland

Realigned landscape at Wallasea