Isle of Purbeck - Sea level change and coastal systems

Question 1

Where is Durdledoor?

Answer 1

Durdledoor is part of the jurrassic coast in southern england, Dorset.

Question 2

What processes affect chichester harbour?

Answer 2

erosion - abrasion, attrition, hydraulic action, corrosion (solution), wave pounding, wave quarrying, caultation.
Transportation

Question 3

Where is Chichester harbour?

Answer 3

It is an area a site of specific scientific interest (SSSI). It consists of an area that is 31km2 of mudflats, salt marshes, spits and deep mud banks.

Question 4

When was Chichester habour formed?

Answer 4

The natural harbour was formed when part of an ancient river system was indundated by the post-glacial rise in sea level.

Question 5

How is chichester harbour a system?

Question 6

What are the inputs for Chichester harbour?

Answer 6

Energy inputs include- winds, waves, tides and sunlight, offshore sediment, fluvial sediment, basin and edge and estuary sediment, beach recharge, sea grass and saltmarsh plants,

Question 7

Which winds is the coast protected from?

Answer 7

The coast is protected from south westerly prevailings winds and waves by the isle of wight but is exposed to southerly gales especially in winter, and these can create high waves.

Question 8

How does the shape of the harbours entrance protect it from sea waves?

Answer 8

The entrance to the harbour is narrow which protects from sea waves penetrating too far in to the basin, creating a low energy environment.

Question 9

What limits the power of the local waves?

Answer 9

The local waves are created by wind blowing across the water surface inside the harbour, also have limited power because of the restricted fetch.

Question 10

What are some inputs for sediment and nutrients?

Answer 10

Sediment and nutrients inputs are derived from several sources. Waves and currents erode material from the floor of the solent, which is carried into the harbour by the incoming flood tide.

Question 11

How do waves at chichester harbour contribute to the system?

Answer 11

Input - waves
Processes - erosion
Outputs - silt and clay
Stores - saltmarshes

Question 12

How do tides at chichester harbour contribute to the system?

Answer 12

Input - tides
Process - transport
Output - sand
Stores - mudflats

Question 13

How do currents at chichester harbour contribute to the system?

Answer 13

Input - currents
Process -deposition
Output - Organic matter
Stores - sand banks

Question 14

How does sunshine at chichester harbour contribute to the system?

Answer 14

Input - Sunshine
Process - sedimentation
Outputs - tides
Stores - sand and gravel beaches

Question 15

What is accretion?

Answer 15

Growth in height of the land owing to accumulation of sediment.

Question 16

What is coastal squeeze?

Answer 16

Loss in intertidal habitat which occurs when the high water mark

Question 17

What feature at Chichester harbour is an example of a feature that has changed due to natural and human influences?

Answer 17

East head spit.

Question 18

Why is understanding the function of the system important for successful management of the harbour?

Answer 18

It means that because the area is an SSSI for birds

Question 19

what are some limiting factors for sediment and nutrient input?

Answer 19

Yeilds of sediment are low despite the rock being relativley easy to erode (gravel, sands and clays) because the local waves have limited energy. The coastal bluffs are also low in height which limits the amount of sediment available for wave erosion like attrition and abrasion.

Question 20

What kind of coastal management strategies have been put in place at Chichester harbour?

Answer 20

90% of Chichester harbour is protected by hard engineeering strategies like sea walls, rock armour, gabions and earth embankments, which all reduce rates of erosion.

Question 21

What are some limiting factors of smaller sediment inputs such as sand and gravel?

Answer 21

This input is transported westwards by longshore currents and is in limited supply by the coastal defences.

Question 22

What is East head spit?

Answer 22

It is a single spit that flanks the entrance to chichester harbour, it is topped with sand dunes and its about 1km in length. its southern end is known as a hinge is only 25m wide and it broadens out to the north to about 400m.

Question 23

What is the name for the area of land that lies between the channel entrance?

Answer 23

Between the main channel entrance and and the spit is The winner which is an area of sand and gravel. Behind the spit is a saltmarsh and mudflats.

Question 23

How did the spit grow before 1870?

Answer 23

It grew westwards, supplied by shingle and sand eroded from cliffs and beaches near Selsey and carried west by longshore currents. The drift is westwards here (contrary to much of the south coast ). This is because the isle f wight acts as a waterbreaker, causing prevailing southwesterly waves to refract and diffract to more southeasterly approach.

Question 24

What happened with the spit after 1870?

Answer 24

The spit began to rotate clockwise, largely because sea defences built between Selsey and west wittering deprived it of longshore drift sediment, Occasional storms may also have contributed to the sift in spit orientation. Rotation and retreat have resulted in -
The creation of The winner. This feature plays an important role in dissipating wave energy, and supplies wind blown sand for dune reformation, both of which help to protect the spit. There is evidence that since 1926 its surface has been lowered by erosion, which in turn threatens the existence of the spit.

Question 24

How did the changing of the spit after 1870 contribute to the harbour entrance?

Answer 24

The harbour entrance became wider. Although this has reduced the speed of tidal currents and, in turn the circulation of sediments within the coastal fringes in the harbour to more wave erosion.

Question 25

How did the neck of the harbour change in 1963?

Answer 25

The narrow neck and hinge of the spit remain vulnerable to breaching. In 1963 for example, a combination of high tides and a winter storm surge caused a breach in the neck. Human trampling of the sand dune ridges may have reduced their effectiveness in preventing a breach.

Question 26

How did the national trust try to protect East head?

Answer 26

The national trust owns East head and tried to use gabions to protect the neck. It has also put up brushwood fences are orientated at an angle,