Life’s a beach!

‘The coast’Why do we love

it?

What is ‘the coast’?

Defining the ‘coast’. Task - Write a definition of the coast and draw a basic diagram of the coastal zones‘Example 1A coast is the link between the sea and the land, and there is a strong spatial interaction between these two zones. What happens on land affects the sea and what happens in the sea affects the land’.

(Taken from Place and Change by Pask. R et al, 2002) Example 2Technically, the term refers to the region that stretches from the shallow water of the continental shelf to the furthest extent of wave and tide influence on the land.

Coasts are not just.... Beaches!

Task - Write down as many different types of coast as you can think of.

What will we study?Over the next few weeks, we will look at:

• How coasts are formed• Coastal features• Coastal protection• Uses for the coast• Issues (i.e. surfers against sewage, dredging the bay)• Create a ‘CAMPAIGN’

Open Jacaranda essentials Geography 2, page 82 and 83

Task Write down a definition for each of the following terms and also draw a simple diagram to illustrate the term.

Swash BackwashDestructive wave Constructive waveFetch Longshore drift

Task Once you have finished your definition of ‘longshore drift’, attempt Activities 6 and 7 on Page 83 of Jacaranda Geography 2.

How coasts are formed

Erosion = the wearing away of material/land

Transportation = the movement of

material

Deposition = the setting down of material

What is erosion, transportation and deposition?

Coastal features caused by erosionNow we will be looking at types of coastal features that are formed bycoastal erosion.

Open Jacaranda essentials Geography 2, page 84 and 85.

Coastal features/landforms caused by erosion

• Headlands and bays

• The influence of wave refraction and wave reflection

• Wave-cut notch and wave-cut platform

• Caves, arches, stacks and stumps.

Headlands and bays form on coasts where bands of rock of alternating resistance run perpendicular (at right angles) to the coast.

Bays form where weak/less resistant rocks (such as sandstone or clay) are eroded, leaving bands of stronger/more resistant rocks (such as chalk, limestone or granite) forming a headland.

Headlands and bays

Swanage Bay

An example of headlands and bays on the Dorset coastline.

Wave refraction: is the bending of waves as they reach shallow water. This causes the curving of wave crests around the headland.

Wave energy is concentrated around the headland , causing eroded landforms such as wave-cut notches, stacks, and arches.

Wave reflection: The reflecting of wave energy back towards the sea, usually occurring where a wave strikes a solid surface such as a cliff or sea wall.

This causes the erosion and transportation of sediment back into the sea.

Wave cut notchA wave-cut notch forms after destructive waves hit against the cliff face, causing undercutting between the high and low water marks.

Wave cut platformOver time, a wave-cut notch enlarges into a cave. The waves undercut this portion until the roof of the cave cannot hold due to the pressure, and it collapses, resulting in the cliff retreating landward. The base of the cave forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces and transported by waves as sand sediment.

How are cliffs and wave-cut platforms formed?

The waves attack the base of the cliff through the processes of abrasion, corrosion, hydraulic action and attrition.

Over time the cliff will be undercut and a wave-cut notch is formed.

Eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave-cut platform.

Wave-cut platform

CaveCaves form when the sea attacks small cracks in a headland and opens them. The cracks then gradually get larger and turn into a small cave.

ArchAn arch is formed when a sea cave is eroded away

on both sides of the headland.

Sea stackContinued erosion of an arch causes the arch to collapse, leaving the pillar of hard rock standing away from the coast called a stack.

Sea stumpEventually, erosion will cause the stack to

collapse, leaving a stump. This stump is usually a small rock island; small enough to be submerged by high tide.

How are caves, arches, stacks and stumps formed?

Caves, arches, stacks and stumps

The formation of caves, arches, stacks and stumps

Task – photo annotation

Each photograph provided includes examples of a variety of coastal processes and coastal features formed by erosion.

• Cut out each photo and stick it in your folder.

• Annotate each photograph, using arrows, terms and explanations . Explain each coastal feature or process you can identify.

• Include: headland, bay, wave-cut notch, wave-cut platform, arch, cave, stack, stump, wave refraction, and wave reflection.

Lesson 5 - Coastal features caused by deposition

Now we will be looking at types of coastal features or landforms that are formed by coastal deposition.

Constructive waves are responsible for building up coastlines by transporting sediments to the shore and depositing them.

Coastal deposition features/landforms

• Beach

• Sand dune

• Sand spit

• Tombolo

BeachA beach usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle or pebbles. Beaches can sometimes have biological origins, such as shell fragments.Beaches are formed when sand or other loose sediments are transported by wave action. Beach materials come from erosion of rocks offshore, as well as from headland erosion and slumping (collapsing).

Sand dunesDunes occur in different forms and sizes, formed by interaction with the wind, when dry sand is blown to the black of the beach(transportation). Most dunes are longer on the windward side where the sand is pushed up the dune and have a shorter slip face in the lee of the wind.

TaskStudy the information and diagram on sand dunes on page 89 of Jacaranda Geography 2.

1. Describe the conditions with which dune vegetation needs to cope.

2. List some adaptations that help plants to survive in dune environments.

3. What might be the consequences of removing vegetation from sand dunes?

Sand SpitA sand spit is one of the most common coastal landforms. A sand spit is a linear accumulation of sediment (a build up of sand in a line) that is attached to land at one end.

How it is formedSand is carried parallel to the shore by longshore drift. The transportation of sand may eventually extend across a bay or between headlands especially where water is relatively calm. Spits are typically elongated, narrow features built to several dozen feet by wind and waves.

Spits often form when wave energy decreases as a result of wave refraction (see notes to remind yourself what this means) in a bay. When a coastline turns abruptly, wave energy is reduced by a divergence of wave trajectories. This reduction in wave energy causes the deposition of sediment (mainly sand). In other words, sand accumulates as the water loses its ability to transport material.

Spits grow in size as sand is continually deposited in the direction determined by prevailing winds (longshore drift). As spits grow, the sheltered area behind them often develops into a marshland, where plant and animal species can thrive.

In a case where a sand spit forms near the mouth of a river (such as in the two diagrams below), the fast currents from the river mouth (estuary) erode the sand accumulating in the river channel, preventing it from depositing sand all the way across the river to the next headland.

In cases where a river estuary is not present, wave energy levels will determine the length of the sand spit. Sand will only accumulate where deposition occurs; not erosion.

Revel Island, Virginia, USA Dawlish Warren, Dorset, England

ExamplesTwo sand spits formed by longshore drift occurring in opposite directions.

A - right to left B - left to right

TomboloA tombolo is a deposition landform such as a spit or bar which forms a narrow piece of land between an island or offshore rock and a mainland shore, or between two islands or offshore rocks. They usually form because the island causes wave refraction, depositing sand and shingle moved by longshore drift in each direction around the island where the waves meet.

Task Describe the difference between a spit and a tombolo.

Lesson 6 – Coastal managementIn future lessons, we will explore human impacts in the coastal environment; positive and negative. Firstly, let’s use our knowledge of coastal erosion, transportation and deposition to explore the techniques used to protect this vulnerable and dynamic environment.

Today we will be looking at ways to protect the coastline through human intervention.

Coastal protection techniques

Hard construction Soft construction

• Groynes

• Revetments

• Riprap

• Gabions

• Breakwaters

• Beach nourishment

• Sand dune stabilisation

GroynesGroynes are wooden, concrete or rock barriers (walls) perpendicular to the sea. Beach material builds up on the up drift side, where littoral drift (longshore drift) is predominantly in one direction, creating a wider and a more plentiful beach. The groyne structure enhances the protection of the coast because the retained sand material filters and absorbs the wave energy.

There is a loss of beach material on the down drift side, requiring that another groyne to be built there. This is why groynes are often laid in groups, not on their own.Positives• Groynes are extremely common, cost-effective coastal defence measures, requiring little maintenance.

Negatives• Groynes do not protect the beach against storm waves and if placed too close together will create currents, which will carry sand material offshore.

• Groynes are increasingly viewed as detrimental to the aesthetics of the coastline, and face strong opposition in many coastal communities.

RevetmentsRevetments consist of wooden slanted or upright blockades, built parallel to the sea on the coast, usually towards the back of the beach to protect the cliff or settlement beyond. The most basic revetments consist of timber slants with a possible rock infill

RiprapRiprap is made from a variety of rock types, commonly granite, limestone or occasionally concrete rubble from building and paving demolition.

Riprap works by absorbing and deflecting the impact of a wave before the wave reaches the defended structure.

The size and mass of the riprap material absorbs the impact energy of waves, while the gaps between the riprap traps and slows the flow of water, lessening its ability to erode soil or structures.

GabionsGabions consist of boulders and rocks contained in a wired mesh cages and usually placed in front of areas vulnerable to heavy to moderate erosion: sometimes at cliffs edges . They may also be placed to jag out at a right angle to the beach like a large groyne. When the seawater breaks on the gabion, the water drains through leaving sediments, also the rocks and boulders absorb a moderate amount of the wave energy

Offshore breakwaterAn offshore breakwater is constructed using large concrete blocks and natural boulders. These materials are sunk offshore to alter wave direction and to filter the energy of waves and tides. The waves break further offshore and therefore reduce their erosive power. This often leads to wider beaches, which absorb the reduced wave energy, protecting cliff and settlements behind.Breakwaters can also be attached to the land. This is very common adjacent to a marina. In the case below left, two breakwaters protect the coast and provide shelter for the local marina.

Plymouth Breakwater, UK.Port Taranaki, NZ.

Aerial photo

Beach nourishmentBeach nourishment or replenishment is one of the most popular soft engineering techniques of coastal defence management schemes. This involves importing alien sand off the beach and piling it on top of the existing sand. The imported sand must be of a similar quality to the existing beach material so it can integrate with the natural processes occurring there, without causing any adverse effects. Beach nourishment can be used alongside the groyne schemes. Sand dune stabilisationVegetation can be used to encourage dune growth by trapping and stabilising blown sand. A common form of planting in the foredunes is Ammophila.

These grasses include Marram Grass, Bent Grass, and Beach Grass. Their extensive systems of creeping underground stems allow them to thrive under conditions of shifting sands and high winds.