Hard engineering coastal management involves building artificial structures which try to control natural processes.
Hard engineering approaches to coastal management tend to be expensive, last only a short amount of time, are visually unattractive and unsustainable. They often increase erosion in other places further down the coast.
The image below shows a range of hard engineering strategies at Hornsea, Holderness Coast.
Sea defences at Hornsea
Groynes are wooden barriers constructed at right angles to the beach to retain the material. The beach material, including sand and pebbles, are trapped between groynes and cannot be transported away by longshore drift. Groynes encourage a wide beach which helps absorb energy from waves, reducing the rate of cliff erosion. The photograph below illustrates the difference in how far waves travel inland when sediment is trapped by a groyne raising the height of the beach.
A groyne at Hornsea on the Holderness Coast
Advantages of groynes
Groynes act as wind-breaks for people on the beach
Groynes do not affect access to the beach.
At around £5000 each, they are relatively cheap, and if well maintained they can last 40 years.
They are much cheaper to repair than other hard engineering solutions.
A wide, sandy beach attracts tourists which brings benefits to the local economy.
Disadvantages of groynes
Groynes do not look attractive.
Groynes act as a barrier which impedes people walking along a beach
The beach on the downdrift side of the groyne can be much lower than the up-drift side. This can make them very dangerous, particularly for young children. At Hornsea on the Holderness Coast, there is a height difference of almost 2m between the beach either side of one groyne.
Beaches downdrift of the defences are starved of beach material due to their impact on longshore drift. This leads to increased erosion which has an economic impact further along the coast.
Groynes need regular maintenance.
Groynes are ineffective during storm conditions.
Typically around £5000 each
Seawalls are usually built along the front of cliffs to protect settlements or another land of high economic importance. They are often recurved which means waves are reflected back on themselves. This can cause the erosion of material at the base of the seawall.
Recurved sea wall and rock armour at Scarborough
The video below shows the sea wall at Scarborough.
Advantages of sea walls
A sea wall gives people a sense of safety and security.
Sea walls often have a promenade on top of them which are popular with tourists.
Sea walls tend to have a long life-span and provide excellent defence where wave energy is large.
Sea walls do not impede the movement of sediment along the coast by longshore drift
Disadvantages of sea walls
Sea walls can affect access to the beach.
Coastal flooding can occur when waves overtop (break over) the sea wall.
Sea walls are very expensive to construct and maintain. The UK Government is investing £30m on a new sea wall in Dawlish, Devon to protect the mainline railway after the line collapsed during storms on 4 February 2014.
Reflected waves scour the beach and can cause foundations to be undermined.
Recurved sea walls can increase the erosion of beach material.
Sea walls do not look attractive.
Sea walls destroy habitats.
Sea walls affect the coastal system and reduce the input of sediment.
Traditionally these have been wooden slatted barriers constructed towards the rear of beaches to protect the base of cliffs. Energy from waves is dissipated by them breaking against the revetments.
A wood revetment at Sheringham on the Norfolk coast.
In recent times concrete revetments have been used in places such as Hornsea.
Advantages of revetments
Revetments do not impede people walking along a beach
Cheaper and less intrusive than a sea wall.
Less beach material is eroded compared to a sea wall.
Disadvantages of revetments
Revetments can impede access to the beach.
A short lifespan (particularly when constructed from wood) and unsuitable where wave energy is high.
Revetments do not look attractive.
Revetments destroy habitats.
Revetments affect the coastal system and reduce the input of sediment.
Rock armour is a barrier of large boulders placed in front of a cliff or sea wall to absorb wave energy and reduce backwash by encouraging percolation.
Advantages of rock armour
It does not impede access along the beach (unless it is used as a gabion).
At £1000 to £3000, it is cheaper than constructing a sea wall.
The structure is quick and easy to construct. It can be built in weeks rather than months, reducing the economic impact of its installation.
If it is well maintained, it will last for years.
It is versatile because it can be placed in front of a sea wall, extending its life span. It can also be used to stabilise slopes on dunes.
Rock armour does not impede sediment movement along the coast by longshore drift.
Disadvantages of rock armour
Access to the beach is difficult as beach access is limited.
Costs increase when the rock is imported.
Rock armour looks unattractive.
Rock has to be quarried, which can cause environmental damage.
£1000 to £3000/m
Gabions are wire-mesh cages filled with pebbles or rocks. They are placed at the back of sandy beaches. As water enters the cages, wave energy is absorbed and dissipated.
The image below shows a gabion.
Coastal erosion defences in the form of interlocking concrete blocks in the foreground and stone-filled wired gabion baskets behind
Advantages of gabions
It does not impede access along the beach
At around £110 a metre, they are cheap and easy to construct
The structure is quick to build and cheap to maintain
For the cost, they are a good value for money as they can last between 20-25 years
Gabions do not impede sediment movement along the coast by longshore drift.
They blend in better than most other hard engineering solutions. This is especially the case when sand is blown over them or when they are covered by vegetation.
Disadvantages of gabions
Access to the beach is difficult as people may have to climb over the rock armour or make detours.
In a damaged state, gabions are very dangerous.
Gabions are restricted to sandy beaches as material thrown at them on shingle beaches would quickly degrade them.
Damaged gabions are unsightly and dangerous to sea birds.
These are large concrete blocks and boulders located offshore to change the direction of waves and reduce longshore drift. They also help absorb wave energy.
Beaches retain a natural appearance.
Difficult to maintain, unattractive, does not protect the cliffs directly and does not stop beach material from being eroded.
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