GCSE Geography | Coastal Management: Hard Engineering (Coastal Landscapes 10)

Many coastlines are protected by hard engineering - this is when structures are built to either stop flooding, to reduce erosion, or to do both.

Hard engineering strategies are expensive so are only used in areas where the land is deemed economically valuable, such as tourist resorts. These methods are popular with home and business owners as they offer effective protection from the sea, but they are often seen as a bit of an eyesore as they don't look natural.

Hard engineering strategies include sea walls, groynes, rock armour and gabions.

Sea walls

Sea walls are barriers made of concrete that stop the waves from reaching the land behind. They are sometimes recurved in design which enables them to reflect the waves, rather than the waves 'overtopping' which can happen with straight sea walls. The curved face of the sea wall reflects the energy from the wave back to the sea, which hinders the next wave, reducing its energy and its ability to erode. However, the recurved design sometimes means that the waves come crashing back down onto the beach, which causes damage. Sea walls often have steps at their base to increase stability.

Advantages:

• they make home and business owners feel secure
• they are made of concrete so last for many decades
• they often have promenades on top so people can walk along them

Disadvantages:

• they restrict access to the beach, particularly for those with restricted mobility
• high waves can overtop them
• they are very expensive (between £5000 and £10,000 per metre),
• because they are made of concrete they do not blend into their natural surroundings
• they can destroy coastal habitats

Groynes

Groynes are fence-like structures that are built at right angles to the coastline and are usually spaced about 50 metres apart. They are usually made from wood, but can be made from concrete or piles of rocks, which lasts longer. The purpose of groynes is to trap the material transported by longshore drift to hold the beach in place. This is important for two reasons: firstly, the larger the beach, the more effective it is at absorbing the wave's energy, so less erosion will take place; and secondly, wide beaches are good for tourism so they are a valuable asset for the local economy.

Advantages:

• they are cheaper than many other defences (£5000-£10,000 each)
• if well-maintained they will last a long time
• they allow a large beach to build up, attracting more tourism, which has a positive multiplier effect for the local economy

Disadvantages:

• they restrict access along the beach (acting as a barrier)
• they become underwater obstructions when the tide is in, so can be dangerous to swimmers, and other water users (e.g. surfers)
• they are dangerous to climb on
• they restrict movement of sediment along the coastline (which is their primary purpose) however, this can starve beaches further along the coast, increasing their rates of erosion
• they are ineffective in storm conditions
• wooden groynes rot quickly without regular maintenance
• many consider them unattractive

Rock armour

Rock armour consists of huge boulders, usually made out of granite, that are placed at the base of a cliff. These boulders are heavy enough not to be moved by waves. They reduce the erosive power of the waves by forcing the water to enter all the little gaps between the boulders, which dissipates their energy, so by the time they reach the actual cliff face they are very weak, so cause little scouring of the base. They are sometimes also used at the base of a sea wall for reinforcement. Rock armour is also known as 'rip-rap'.

Advantages:

• cheaper than some other methods (between £1000-£3000 per metre)
• quicker and easier to build than other methods
• long-lasting as the boulders are made of granite, so won't erode
• can be used to reinforce other sea defences, to increase their longevity

Disadvantages:

• can cause access issues on the beach
• dangerous to climb on (can be slippery)
• rocks can move in storm conditions
• disturbs habitats when being installed
• considered ugly by many as the rocks don't blend in with the natural environment (and local geology)
• litter becomes trapped in the gaps between the rocks, which can attract rats

Gabions

Gabions are steel wire cages that are filled with stones and placed at the back of a beach. They work in a similar was to rock armour as the water enters the cage and starts to go between the pebbles, dissipating the wave's energy, so less erosion occurs. Gabions are often placed at the cliff base and planted with vegetation to make the cliff more stable, reducing the risk of a land slide.

Advantages:

• they are very cheap (less than £250 per metre) as they usually use local pebbles
• they are easy and quick to construct, and will last around 20 years
• because they use local materials they blend in to their surroundings better than many other strategies
• over time they can be colonised by vegetation, making them blend in even further

Disadvantages:

• they are used mainly on sandy beaches as they wouldn't withstand shingle being hurled at them
• they are weaker than other strategies so need regular maintenance - once they have established vegetation on them they can be expensive and complex to repair
• they are dangerous if damaged - sharp wire mesh (this is particularly hazardous to sea birds)
• damaged gabions are unattractive