3.10 Managing coastal erosion and flooding

What is hard engineering?

Building structures along the coast, such as sea walls, groynes and revetments.

What is soft engineering?

An approach that is designed to work with natural processes in the coastal system, in order to manage (but not necessarily prevent) erosion.

What are groynes and how much do they cost?

These are timber or rock structures built at right angles to the coast. They trap sediment being moved along the coast by longshore drift— building up the beach. They cost £5000-£10000 each and are installed at 200 metre intervals.

What are the advantages of groynes?

• the built up beach protects the land behind it and increases tourism

• it works with natural processes to build up the beach

• not too expensive

What are the disadvantages of groynes?

• they starve beaches further along the coast of fresh sediment because of the interruption to longshore drift

• they are unnatural and rock groynes can be very unattractive

What are sea walls and how much do they cost?

They are walls made of stone or concrete at the foot of a cliff or the top of a beach. They usually have a curved face to reflect wave energy. They cost £6000 per metre

What are the advantages of sea walls?

• they are an effective prevention of erosion

• often form a promenade for people to walk along

What are the disadvantages of sea walls?

• they reflect wave energy instead of absorbing it

• they can be intrusive and unnatural looking

• they are very expensive to build and maintain

What is rip rap (rock armour) and how much does it cost?

Large rocks placed at the foot of a cliff, or at the top of a beach. They form a permeable barrier to the sea— breaking up the waves but allowing some water to pass through. It costs £100,000 to £300,000 for 100 metres.

What are the advantages of rip rap?

• it is relatively cheap and easy to construct and maintain

• it is often used for fishing from or sunbathing by tourists

What are the disadvantages of rip rap?

• the rocks are usually from somewhere else so they may not fit in with local geology

• it can be very intrusive

• they can be dangerous for people clambering over them

What are revetments and how much do they cost?

They are sloping wooden, concrete or rock structures, which are placed at the foot of a cliff or the top of a beach. They break up wave energy, and cost up to £4500 a metre.

What are the advantages of revetments?

The are relatively inexpensive to build

What are the disadvantages of revetments?

• they are intrusive and very unnatural looking

• they can need high levels of maintenance

What is an offshore breakwater and how much does it cost?

A partly submerged rock barrier, designed to break up the waves before they reach the coast. The cost is similar to rock armour, depending on the materials used

What are the advantages of an offshore breakwater?

It is an effective permeable barrier.

What are the disadvantages of an offshore breakwater?

• it is visually unappealing

• it’s a potential navigation hazard

What is a cost-benefit analysis?

An analysis where costs are forecast, and then compared with the expected benefits. Costs and benefits are of two types:

• tangible

• intangible

What are the defences at Hornsea and their impacts?

The defences at Hornsea include concrete sea walls, groynes and rock armour. The impact is positive in Hornsea, but has starved the beach in Mappleton of sediment, causing a rate of erosion of 4 metres per year in the 1990s

What are the defences in Withernsea and their impacts?

In the 1990s, a curved sea wall was built to replace a straight sea wall, at the cost of £6.3 million. However, the waves are now noisier when they break against the wall, and the promenade is smaller. The views from the sea-front hotels have been restricted, and some tourists find the rip rap at the base of the sea wall unattractive.

What are the defences at Mappleton and their impacts?

Two rock groynes were built in 1991 to prevent the removal of the beach by longshore drift. However, at Cowden, which is 3 km south of Mappleton, the resultant sediment starvation caused increased erosion of the cliffs.

What is beach nourishment and how much does it cost?

It is the addition of beach material to an existing beach to make it larger. The sediment is normally dredged from a nearby seabed. It costs around £300,000 for 100 metres.

What are the advantages of beach nourishment?

• it is relatively cheap and easy to maintain

• it looks natural and blends in with the existing beach

• it increases tourism potential by creating a bigger beach

What are the disadvantages of beach nourishment?

It needs constant maintenance because of erosion and longshore drift.

What is cliff regrading and drainage?

Regrading reduces the angle of the cliff, and drainage removes water to prevent landslides and slumping.

What are the advantages of cliff regrading and drainage?

• regrading can work on clay and loose rock, where other methods won’t work

• drainage is cost effective

What are the disadvantages of cliff regrading and drainage?

• regrading basically causes the cliff to retreat

• drained cliffs can dry out, which can lead to collapse

What is dune stabilisation and how much does it cost?

Plants such as marram grass can be planted to stabilise dunes, and areas can be fenced off to keep people away from newly planted dunes. It costs £200-£2000 for 100 metres.

What are the advantages of dune stabilisation?

• it maintains a natural coastal environment

• it provides important wildlife habitats

• it is relatively cheap and sustainable

What are the disadvantages of dune stabilisation?

• it is time consuming to plant marram grass

• people may respond negatively to being kept off certain areas

What is marsh creation and how much does it cost?

It is a form of managed retreat, by allowing low-lying coastal areas to be flooded by the sea. This land then becomes a salt marsh. The cost is variable, as it depends on the size of the area left ot the sea.

What are the advantages of marsh creation?

• it is relatively cheap because it often involves land reverting to its original state

• it creates natural defences and provides a buffer to powerful waves

• it creates an important wildlife habitat

What are the disadvantages of marsh creation?

• agricultural land is lost

• farmers or landowners need to be compensated.