EQ 3- coastal risks

Question 1

Three reasons for why sea level can change?

Answer 1

• high tides and low tides at coasts can alter local sea level
• low air pressure = slight rise in sea level
• winds can ‘push’ water towards a coast varying the wave height day to day

Question 2

isostatic change

Answer 2

a local rise or fall in land level

Question 3

eustatic change

Answer 3

involves a rise or fall in water level by a change in the vol. of water. this is a global change affecting all the world’s connected seas and oceans.

Question 4

post glacial isostatic adjustment

Answer 4

refers to the uplift experienced by land following the removal of the weight of ice sheets.

Question 5

barrier islands

Answer 5

offshore sediment bars, usually sand dune covered but, unlike spits, they are not attached to the coast- how they are created is debated often.

Question 6

storm surge

Answer 6

a sudden short term change in sea level caused by intense low level pressure systems from depressions and tropical storms.

Question 7

formation of a storm surge

Answer 7

1- depression moves into an area of the sea/ocean
2- air pressure on the sea drops, bringing sea surface up = rising sea level
3- during severe depression- it will move the risen water in a certain direction - reaching shore

Question 8

Pro’s and con’s of groynes ?

Answer 8

• encouraging deposition by preventing longshore drift - building a wider and higher beach via beach accretion = tourism industry gains
  con ; prevention of LSD = sediment starvation and increased erosion downshore

Question 9

pro’s and con’s of sea walls?

Answer 9

• designed to dissipate and not reflect wave energy , allowing for beach volume to remain
• can act as a physical flood barrier and an erosion barrier
• if reflective - can reduce beach volume
• destruction of a natural cliff face and foreshore .
• very expensive

Question 10

pro’s and con’s of rip rap (rock armour) ?

Answer 10

• breaks up and dissipates wave energy
• often used at base of sea walls to protect from undercutting
• sediment deposition between rocks and vegetated over time

Question 11

pro’s and con’s of breakwater?

Answer 11

• can force waves to break offshore rather than at the coast , reducing wave energy and erosive force
• deposition is encouraged between breakwater and beach
• interferes with longshore drift

Question 12

Pro’s and cons of beach nourishment ?

Answer 12

+ increase amenity value of a beach by adding fresh sand and also works with natural processes so it enlarges beach so it naturally dissipates wave energy = reduced erosion

• high maintenance costs of up to £2 mln/km
• un-sustainable source of sediment - sediment is dredged from offshore and pumped on to the beach = impact on coasts sediment cell

Question 13

pro’s and con’s of dune stabilisation ?

Answer 13

+ effective coastal defence - absorbs wave energy - prevent erosion
+ protects low lying areas from coastal flooding
+ environmental enhancement - providing a dune ecosystem
- vulnerable to major storm surges
- vulnerable to tourism+recreation = human trampling exposing surface to erosion
+ low cost maintenance and repair = cost effective to use as defence in long term