Geography - Coastal Landscapes and proceses (4 types of coastal erosion…
Geography - Coastal Landscapes and proceses
Saltation – particles bounced along the sea bed
Suspension – particles held up between the sea bed and the surface of the water
Traction – Particles rolled along the sea bed
Solution – Particles are dissolved.
Types of weathering
Freeze Thaw weathering
Burrowing animals, tree root growth and bird feaces
4 types of coastal erosion
Erosion - Breakdown of rock and transport away from the location.
Weathering - Breakdown of rock in situ. E.g. Freeze thaw
Hydraulic Action - waves crashing against the cliff. Overtime parts of the cliff will break down and fall.
Abrasion - This happens when fragments of rocks come together and get thrown at the bottom of the cliff
Solution - Weak and in the sea chemicals attack the rock. E.g. Acid rain
Attrition - Rocks crash into each other.
Slumping – Cliff is made of two types of rock. Top layer is permeable and water soaks through. Water reaches under layer which is impermeable. Top layer slides over the top due to water acting as a lubricant and weight of the cliff.
Sliding – Only one type of rock, and material slides down the cliff.
Rock Falls – Happens on steep cliffs made of hard rock. Can happen when freeze thaw weathering occurs or waves undercut the cliff.
Longshore Drift and Decomposition
Longshore Drift – Waves approach the beach at an angle, material is carried along the shore. If this occurs on a beach, this is said to be drift aligned.
Waves drop their load when they lose energy – largest particles are dropped first. Happens in bays when waves lose energy (beaches) and at a change in shape of the headland (spits).
Wave Strength, Constructive and Destructive Waves
Wave Strength depends on
Fetch – Distance of open water over which the wind blows
Wind duration – Longer duration, bigger waves will develop
Wind speed – larger speed and bigger waves will form
Large swash, small backwash. Adds material to the beach. 6-9 waves per minute.
Small swash, large backwash. Material removed from the beach. Steep beach produced. 11-15 waves per minute.
Headlands and Bays
Waves erode the soft rock faster than hard rock.
Hard rock – headlands produced – erosion concentrated here.
Soft rock – deposition – beaches produced.
Wave Cut Platforms
Eventually, cliff can’t support its own weight and collapses.
Leaves a gently sloping platform.
Waves attack the base of the cliff and undercut them. Wave cut notch.
Caves, Arches, Stacks and Stumps
Cave either breaks through or 2 caves go back to back into each other to form an arch.
Arch will be made wider at the base due to erosion. Top will also be weakened by weathering processes.
Turns into a cave.
Arch will collapse as it can’t support its own weight and a stack is produced.
Starts with a crack in the headland, this is made larger by erosion.
Stack will break down into a stump.
Depositional Landforms – Beaches, Spits and Bars
Spits – Finger of land sticking out to sea. Longshore drift brings material to a change in shape of headland. Material is deposited. Over time, more material builds up and new land is created. Spit has a curved end as 2nd most common wind direction pushes material around. Salt marsh develops behind the spit.
Bar – If a spit grows across between 2 headlands and joins them together.
Beaches are found in bays. If longshore drift happens – drift aligned beach. If waves arrive at 90 degrees to the beach – swash aligned beach.
Coastal Erosion – Causes and Effects
Will be more storm surges due to storms.
Groynes trap sediment on beaches and so areas further down the coast may be starved of sediment and so suffer more erosion.
Rising sea levels – due to climate change – mean that coastal erosion is likely to increase.
Loss of jobs – hotels lost to the sea
Loss of farmland – can impact on food supply
Loss of houses to the sea – people move away
Protecting the Coast – Shoreline Management Plan (SMP)
No intervention – Do nothing. People move away.
Hold the line – Build defences
Cost benefit analysis – section of coast must be more valuable than the defences used to protect it.
Managed Realignment – Allow the shoreline to change – but direct it using some defences in places.
A section of coast will have a SMP.
Advance the line – create new land by building defences on the seaward side.
Hard Engineering – Sea Walls, Groynes, Rip Rap
Groynes – Trap sediment and slow longshore drift. Need maintenance as they rot. Can be ugly. Makes beach bigger which may be good for tourism.
Rip rap – large boulders resistant to erosion, cheap and easy to maintain. Can stop access to the beach, don’t look attractive.
Sea Wall – Very expensive, very effective. Includes a promenade – good for tourism. Can block access to the beach and can be ugly.
Soft engineering – Beach nourishment, sand dune regeneration
Beach nourishment – material added to the beach, absorbs the power of the waves. Looks natural. May need to be re-done regularly as it could be removed in a storm event.
Dune regeneration – planting vegetation to hold the dune together, absorbs the power of the waves. Can easily be damaged by trampling. Looks natural. Takes a long time to be effective.
Dawlish Warren Case Study PAGES 32 33 ETC
Physical factors changing the spit
Erosion of the beach and dunes has caused the spit to retreat. As a result of the 2013-14 storms, for example, about 5 metres of sand was lost from the southern face of the sand dunes. At the same time, sands transported from the south and south-west have helped to rebuild some areas and extend the spit to the east.
The spit has continued to change due to erosion and deposition. High spring tides accompanied by strong winds have driven waves across the ridge that forms the spit's southern and eastern extents
When it was formed 7000 years ago it was two sand spits - the outer warren and the inner warren - separated by Greenland lake. By the 1930s, erosion had caused the two warrens to join, enclosing the lake and creating a single spit.
Human Factors changing the spit
Granite boulders (rip rap) were first used to protect the railway
Housing development, construction of flood defences and transport links have all played their part in shaping the coastline.
Where is it - it is on the south coast of Devon
What is it - it is a spit