Erosion threat- rapid coastal retreat

Question 1

What physical features do rapidly eroding coastlines have in common?

Answer 1

• long wave fetch, large destructive waves
• soft geology
• cliffs with structural weaknesses, like seaward rock dip or faults
• cliffs vulnerable to sub aerial processes and erosion
• Strong longshore drift so that eroded debris is removed quickly exposing cliff base to further erosion

Question 2

How do humans effect coastal retreat?

Answer 2

They can make the situation worse, which usually involves interfering with the sediment cell model.

Question 3

How can humans interfere with the sediment cell model and cause further coastal retreat?

Answer 3

• Construct major dams on rivers that can trap river sediment behind the dam wall. Starves the coast of a sediment source, which has consequences.
• Dredging, taking sand and gravel for construction, removes sediment source.

Question 4

Examples of human interference of the sediment cell

Answer 4

• Aswan High Dam, River Nile. Reduced sediment vol from 130 million tonnes to 15 million tonnes a year. Erosion rates jumped from 20-25m a year to over 200m a year as delta starved of sediment.
• Akosombo Dam in Ghana, reduced flow of sediment from 70 million m3 per year to 7 million m3 per year, impacts on longshore drift and coastal erosion.

Question 5

Dredging

Answer 5

Involves scooping or sucking sediment up from the sea bed or the river bed.

Question 6

What influences the rate of erosion?

Answer 6

• wind direction
• fetch
• seasonal changes to weather
• occurrence of storms

Question 7

How does erosion vary?

Answer 7

• in time, with peaks of erosion in some seasons, and some years having more erosion than others
• spatially, with some locations having much less erosion than others

Question 8

How and why does erosion rate vary on the Holderness coast?

Answer 8

• variations of rate from 0m to 6m per year
• coastal defences Hornsea and Mappleton and withernsea, stopped erosion
• these defences starved places further South of sediment, groynes interrupted longshore drift
• erosion rate increases from north to south
• some areas boulder clay more vulnerable than others
• some cliffs more susceptible to mass movement

Question 9

How does erosion of Holderness vary over time?

Answer 9

• Winter, up to 6m of erosion, with storms and spring tides
• Summer erosion is lower due to constructive waves
• Storms cause mose erosion, long wave fetch from north Norwegian coast

Question 10

What are ords?

Answer 10

Deep beach hollows parallel to the cliff.

Question 11

How do ords promote erosion of the beach?

Answer 11

Concentrate erosion on particular locations by allowing waves to directly attack the cliff with little energy dissipation. Ord locations erode 4x faster than locations without ords

Question 12

Dissipation

Answer 12

Describes how the energy of waves is decreased by friction with beach material during the wave swash up the beach. Wide beach slows waves down and saps energy, so most of their energy is gone when they break