Fieldwork: Interrupted Line Transect

We did an interrupted line transect across the sand dunes every 10m.

Appropriate?

Yes

• We were looking for changes between the sea and trees, so it was appropriate for our hypothesis.
• If we had done random sampling all 20 sites might have been in the same place and we wouldn't have observed change with distance

Fieldwork: Systematic Sampling

We sampled slope angle, vegetation, wind speed and temperature every 10 metres.

Advantages:

• It meant every area of the dune was sampled - we could see that trend changes with distance

Disadvantages:

• Most of the sand dunes are missed out because we only sampled every 10m
• We may have picked out a trend in nature - eg underlying limestone might cause chalky soils which only allow some plants to grow - This could give us a false impression

Appropriate Method?

Could have used random sampling and put numbers 1 - 200 in a hat to decide where to do our measurements.

BUT in order for it to be truly random we would have to put the numbers back, and all the places we picked out might be the same place 20 times which wouldn't give us an appropriate picture

Fieldwork: Quadrat

To assess vegetation changes we used a Quadrat. It had 25 squares (each square was 4%), and we placed it on the ground every 10 metres (systematic sampling). We estimated the total vegetation cover as well as the number of species, which was vital to our hypothesis.

Advantages:

• Gives consistent/closed area to analyse
• Helps estimate percentages

Problems:

• Can crush/squash larger vegetation like marram grass
• Percentages were a crude guess
• Some species might have been misidentified or obscured
• Might have missed out some vegetation that grows in clumps
• Mights have missed out some species eg trees

Formation of Wave Cut Platforms

High and steep waves crash into the foot of the cliff, focusing their erosive capabilities into a small area.

A wave cut notch is created by undercutting the cliff:

Continual undercutting causes increased stress and tension in the cliff which eventually collapses.

Rock debris collects at the foot of the cliff and forms a terrace which is eventually moved into deeper water by backswash or along the beach by longshore drift.

The cliffs continue to retreat leaving behind a gently sloping (less than 5 degrees) wave cut platform.

This means that the waves break further out to sea and have to travel across more platform before reaching the cliff line.

This leads to a greater dissipation of wave energy which reduces the rate of erosion of the headland which slows the growth of the wave cut platform.

Managing Coastal Environments: Shoreline Management Plans

have been developed by local councils and the environment agency, adopting a more holistic approach.

Coastal defence authorities can't carry out works without the aid of a shoreline management plan.

Tend to include:

1. Hold the Line - maintain/upgrade the level of protection provided by the existing coastal defences
2. Advance the line - Build new defences seaward of the existing defence line
3. Managed Realignment - allow retreat of the shoreline inland with management to control or limit that movement
4. No active Intervention - a decision not to invest in providing or maintaining defences

Sustainable Future?

• Sea levels are predicted to continue to rise approx 6m a year because of global warming
• Areas of the UK continue to sink because of isostatic uplift, changing at the rate of 2mm a year
• The use of public money to defend the undefendable is unsustainable
• A 'do nothing' approach is often the only affordable way in the long term

Sediment Cells

The movement of sand and shingle in the nearshore zone by longshore drift has been found to occur in discrete, functionally separate sediment cells.

There are 11 such cells around England and Wales with smaller sub cells within them eg from The Wash to The Thames.

The main cells are defined as a length of coast and its associated nearshore area within which the movement of coarser sediment is largely self contained.

Interruptions to sediment within one cell should not affect beaches in adjacent cells.

Rock Types at Lulworth

Rock Type	Sediment	Picture
Chalk - limestone	Marine Organisms
Greensand - sandstone	Sand grains
Wealden Beds – Sandstone, clays	Sand grains, clays and organic matter
Purbeck Beds – limestone, clays, shales	Shells, clay, silt
Portland Limestone	shells

Coastal Management: Sea Wall

• Hard Engineering
• Deflect wave energy - storm waves are deflected

Pros	Cons
Highly Effective Provides walkway for tourists	Aesthetically unattractive Very Expensive Where cliffs are prone to slumping landslides can cover the wall Stronger backwash which can worsen longshore drift

Cove Formation

Lulworth Cove is one of the world's best examples of a cove:

Formation:

1. In the glacial period 10,000 years ago the ground was frozen, including the underlying chalk (which is normally permeable) so a river could flow over the concordant coastline.
2. The river erodes a valley on the frozen rocks
3. During the inter glacial period the climate warms and sea levels rise. The sea uses the river valley to enter the coast line.
4. The sea erodes the rocks, particularly the less resistant ones like Wealden Beds and Green Sands
5. The erosion continues and the cove grows
6. Finally there is a fully mature cove, wide in the middle (because of the less resistant rock there), narrow at the neck (the purbeck and portland limestone is more resistant to erosion) and elliptical (the chalk is also quite resistant to erosion)

Rock Stratas:

Beach Management: Groynes

• Hard Engineering
• Prevent longshore drift, holdng the beach in place
• Beach provides a buffer zone which reduces cliff erosion

Case Study: Swanage Bay Beach

• In Swanage, the groynes are only built up to the end of the town so it is protected while allowing  natural processes to continue beyond the town
• New timber groynes were built to replace old ones in 2005-6
• The old groynes had been in place for 75 years

Pros	Cons
Keeps beach in place for tourists Doesn’t look as unnatural as some other hard management schemes Relatively easy to maintain Cheaper than a sea wall	Inhibits people’s movement on the beach, making it less usable for elderly people and dogwalkers especially as they make the beach uneven Needs maintenance May have knock on effects where the groynes end, exposing area beyond the groynes to greater erosion

Case Study: Old Harry

Old Harry is located on the Jurassic Coast, Dorset, South West England.

Coastal Spits and Bars!

Longshore Drift occurs when prevailing winds transport sediment along a beach.

This results in a Spit, which is a long narrow piece of sand/shingle which sticks out into the sea/an estuary.

A Bar (or a barrier island) may form where there are changes to coastal direction but no estuary to break the sequence of sedimentation.

The 2 ends of a spit are...

1. The Proximal End - end nearest to the shore/land
2. The Distal End - end furthest away from the shore/land

Features:

Curved...	Doesn’t Grow...
-Secondary winds also shape the spit -Wave refraction	-A river’s current may stop deposition across the entire estuary -The river channel may be too deep, or the water may flow too fast

Formation:

1. Sediment is carried by Longshore drift
2. Shingle (larger sediment) is deposited behind the headland
3. Storm waves move sediment above the high water mark making the feature more prominent
4. Finer material is carried to the end of the spit
5. Sand dunes may form as the sand dries and is blown around at low tide which stabilizes the spit
6. Waves and rivers deposit sand and mud which makes salt marsh

Example:

Spurn Head in Humberside is 6km long, 15m hig, and 150m wide

Case Study: Coastal Management in Dawlish Warren

Dawlish Warren in South Devon is one of Britain’s best loved spits and beaches but is under threat as it is being eroded at an alarming rate. However the beach on the other side of the River Exe Estuary, Exmouth, is growing.

Its problems include:

• Less erosion of the cliffs at Langstone rock headland means less sediment for the beach
• Longshore drift restricted by the construction of a large breakwater designed to protect part of the headland
• Less constructive wave action than in the past

Protection: The spits at Dawlish Warren are protected by revetments, gabions and groynes, with its natural dunes and saltmarshes act as a soft defence structure both behind the Warren and on the seaward side.

Reasons for Protecting Dawlish Warren:

1.       It is a valuable habitat for birds and plants eg a wide array of wading birds like the avocet

2.       Highly popular with tourists - 20,00 people on the spit at peak times (the Environment Agency concluded that between 18^th August and the 12th December 2004, 487,624 visitors visited Dawlish Warren equating to a spend of £3,787,463)

1.       Tourism brings revenue to the area such as the car park charges of £1.75 an hour

2.       There are over 40 local businesses on the spit that provide goods for tourists and jobs for local people (122 full time jobs)

3.       The Spit protects other low lying areas of the Exe Estuary from waves and flooding

4.       This could result in damage to valuable infrastructure, such as the railway line, and increased flooding for the whole the Exe Estuary

5.       It’s a traditional bucket and spade resort serviced by approximately 11,260 bed spaces, 10,560 of which are holiday park units and touring pitches compared to Exmouth’s 8300

Hard Engineering in Dawlish Warren:

In 1992 the National Rivers Authority (part of the Environment Agency) began work to reconstruct the rock armoured revetment; landward of the timber piles, a 300m line of steel sheet piles were sunk to offer further stability; 35,000 tonnes of Norwegian granite boulder were imported to face the new sea wall. The cost was around £1.5 million.

Sustainable Development:

The existing Exmouth seawall frontage, owned and maintained by East Devon District Council, has arrested beach movement that would otherwise have taken place on that shoreline. Recent storms and associated damage to defences have highlighted the need for a long-term, sustainable coastal management.

SMP Suggests… Due to the dynamic nature of the distal end of the spit it would be preferable to allow it to evolve as naturally as possible. The protection that the spit affords must be continued. The short term policy is to Hold the Line along the seaward face of Dawlish Warren. The estuary-facing side of the spit would be left undefended and allowed to continue to evolve naturally during this period with No Active Intervention during this period. Beach management techniques such as recycling and/or recharging could also be considered in the short term. It is anticipated that the policy determined by more detailed study in the short term will result in either Hold the Line or Managed Realignment being adopted for Dawlish Warren.