Coasts (unknown only) Flashcards
What kind of coastline is the Dorset Coast?
A discordant coastline
Name four hard engineering strategies for coastal management.
Sea wall, gabions, rock armour, groynes
Name two soft engineering strategies for coastal management.
Beach nourishment and reprofiling, dune regeneration
What is a sea wall?
A wall made of hard material like concrete that reflects waves back to sea.
+ It prevents erosion of the coast and acts as a barrier to prevent flooding
- It creates a strong backwash, eroding under the wall. It is also expensive to build and maintain.
£5,000 to £10,000/m
What are gabions?
Wire cages filled with rocks, as a wall, usually built at the foot of cliffs.
+ Gabions absorb wave energy, so reduce erosion. They’re cheap and easy to build.
- They’re ugly to look at and the wire cages can corrode over time.
£100/m
What is rock armour?
Boulders piled up along the coast.
+ They absorb wave energy and reduce erosion and flooding. They are fairly cheap.
- Boulders can be moved around by strong waves, so need to be replaced.
£3000/m
What are groynes?
Wooden or stone fences that are built at right angles to the coast. They trap material transported by longshore drift.
+ They create wider beaches, which slow the waves. This gives greater protection against flooding and erosion. They are fairly cheap.
- They starve beaches further down the coast of sand, making them narrower and more vulnerable to erosion.
£1000 to £4000/m
What is beach nourishment and reprofiling?
Sand and shingle from elsewhere is added to the upper part of beaches.
+ It creates wider beaches, which slow the waves, giving greater protection against erosion and flooding.
- Taking material from the seabed can kill organisms like sponges and corals. It’s a very expensive defence, and has to be repeated.
£3,000/km, repeated
What is dune regeneration?
Creating or restoring sand dunes by nourishment, or by planting vegetation to stabilise the sand.
+ Dunes create a barrier between land and sea and absorb wave energy, preventing flooding and erosion. Stabilisation is cheap.
- The protection is limited to a small area. Nourishment is very expensive.
£200 to £2,000/100m
Where is Lyme Regis?
In Dorset, on the south coast of England
What are the reasons to protect Lyme Regis from erosion?
- Lyme Regis has a population of over 3,600 people.
- Around 500,000 tourists visit each year.
- Around 900m of the A3052 road, linking Lyme Regis to other towns along the coast, would have been lost within 50 years.
- The local economy depends on tourism (about £42 million was spent on tourists in 2015), but erosion of the coast could threaten the historic town centre and the tourism industry.
How did Lyme Regis protect itself from erosion?
I) 1995: rock armour on the eastern end of the sea front
II) 2007: the front of the main town, beaches replenished and stabilised, rock armour extended, drainage systems implemented to reduce landslides. Cost: £26 million.
III) was going to prevent landslides to the west of Lyme Regis, never carried out due to cost versus benefit.
IV) 2015: 390m of sea walls and rock armour, protect rounds into the town. Cost: £19.5 million.
What were the benefits of Lyme Regis’ coastal management?
- It’s thought the improved beaches increased trade by up to 20% in some parts of town.
- The rock armour absorbs the energy of the powerful waves, protecting the harbour and the boats inside.
- People feel more secure buying houses there — the new defences made it easier to insure property against erosion.
Describe the three different types of mass movement.
Slides: material shifts in a straight line along a slide plane
Slumps: material rotates along a curved slip plane
Rockfalls: material breaks up, often along bedding planes, and falls down a slope
Describe the stages of sand dune formation.
- Created when sand is moved up the beach by onshore wind.
- An obstacle decreases wind speed so sand is deposited, forming small embryo dunes.
- Embryo dunes are colonised by plants, such as marram grass. The roots of the vegetation stabilise the sad, encouraging more sand to accumulate there, forming foredunes.
- Foredunes eventually become mature dunes, and more embryo dunes form in front of the stabilised dunes.
- A dune slack is a small pool that can form in hollows between dunes.
