4.1(Spec2) - Portballintrae + Lyme Regis Flashcards
What are the types of hard engineering?
- Groynes
- Sea walls
- Rip Rap
- Revetements
- offshore breakwaters/reefs
- Gabions
What are offshore breakwaters?
- rock boulders aligned in short lengths in shallow water parallel to shore
- absorb/dissipate wave energy before back shore and foreshore are damaged
- allows LSD to occur behind them as breakwater is offshore
Advantages of offshore breakwaters?
- can create sheltered water areas for recreational use (beach + windsurfing)
- effective at protecting vulnerable sections of coast
- can create calm water conditions, ideal for harbour entrances
Disadvantages of offshore breakwaters?
- can be unsightly as they do not match geology of area they are placed in usually
- cost £1-2 million
- needs other coastal engineering to complement eg. Sea walls to fill gaps between breakwaters
- creates increased deposition on landward side, reducing effect of LSD
What is Rip Rap?
- tetrahedron boulders made of erosion resistant materials
- dissipate wave energy
Can hold back mass movement on unstable cliffs
Advantages of rip rap?
- are long lasting and flexible in use
- can be placed at susceptible points on back shore, to protect sea wall, or as a breakwater, or as groynes
Disadvantage of rip rap?
- cost £50 per cubic metre
- can create accessibility issues, can’t be easily climbed over
- water still passes through, so erosion still occurs on back shore
What are revetements?
- sloped wooden walls, parallel to backshore, placed slightly ahead of backshore
- take force of breaking waves, reducing erosive strength of waves, protecting backshore
Advantages of revetements?
- absorb wave energy
- traps beach sediment, reduces removal by backwash or LSD
- allows movement along beach
- cheaper than sea walls
- -
Disadvantages of revetements?
- costs about £1500 per metre
- reduces access down width of beach
- may need constant maintenance as waves can damage wood
What hard engineering was done in Lyme Regis?
- Granite breakwaters/rock armour brought in from Norway
- 1,000 deep bored pins in cliffs to prevent instability
- bore holes in cliffs
- sea walls
- groynes
What soft engineering was done in Lyme Regis?
- beach nourishment with material from France
What is the hazard at Lyme Regis?
- coast is subject to large landslips
- 400m section collapsed in 2008
- increased urbanisation and tourism has increased stress on coastline
- sea level rise and increased storm frequency has resulted in increased marine erosion
What coastal management option is in practice at Lyme Regis?
- Hold the line
- aim is to protect cliff from further mass movement as well as protecting beach from erosion by sea
How many people live in Lyme Regis?
- 5000
- majority live within 1km of coastline
How many tourists visit Lyme Regis every year?
- 15000
How much did the coastal management cost in Lyme Regis?
- Preliminary investigation: £1.5 million
- Proposed cost of entire project: £30 million
- beachfront closed for 2 years
- car park access restricted temporarily
- beach huts temporarily closed
What did the coastal management at Lyme Regis achieve?
- 2000 more visitors in year after coastal management was implemented
- ramp access improved
- beach kept in place
What is the geology at Portballintrae?
- rocky headlands
- reworked glacial sands
How much sediment has been lost from Portballintrae since the 1800s?
- 1000m2/yr
- beach is now dominated by large sediment (eg. Boulders)
How much has been spent on hard engineering over the past century at Portballintrae?
- > £1.5 million
What role has Leslie’s Pier played in Portballintrae?
- causes wave refraction
- waves focus on centre of bay
- LSD moves sediment to east of bay, away from centre
- combined rip currents move sediment offshore to deeper water
- beach is deprived of sand
What hard engineering has been done in Portballintrae?
- Groynes (1904, 1970s, 1997)
- Sand Nourishment, failed as sediment is carried away by LSD and rip currents
- Sea walls (1997, 2003 with groynes)
What is the scientific advice on Portballintrae?
- removal of Leslie’s Pier
- done 2022
- remove hard engineering
- sea walls are placed incorrectly
- resulting in scouring of beach sediment against wall
What is the average price of houses in Portballintrae?
- £350k-£400k
