Sediment Cells And Sources

Sediment Cells and Sources

AS Geography

Learning Objectives

• Demonstrate an understanding of wave refraction

• Develop an awareness of littoral cells and different types of sediment

• Demonstrate a knowledge of coastal processes including erosion

• Evaluate the concepts behind mass movement

Wave Refraction

• As waves leave deep water they become affected by frictional drag as they come into contact with the seabed

Sediment Sources

• Erosion of the cliffs can provide direct sediment input

• currents bring in material from the sea bed• Rivers bring sediment downstream

• There are several methods by which sediment can reach the sea

What happens to sediment

• Sediment is either stored as a depositional landform

• As a nearshore feature such a bank or offshore bar.

• Alternatively it is transported as a throughput and become outputs from the system being deposited either in deeper water or away from the coastal area in question.

Types of Sediment

• Clastic and Biogenic sediment

• Clastic sediments are from rock weathering and erosion

• Biogenic sediments are the shells and skeletons of marine organisms

Sediment Transport and Deposition

• What do you think is the main agent of moving sediment and depositation?

• Waves, currents, tides and wind move sediment from source areas and deposit it in the form of coastal land forms

• These exist in a state of “Dynamic Equilibrium”

Sediment Cells/ Littoral Cells

• These depositional landforms (such as beaches, sand dunes, salt marshes and mudflats) act as a dynamic sediment store and sediments are transported onshore, offshore, and alongshore to create them.

• These stores in turn provide sediment for stores further down the coast.

• The next slide explains this

Sediment Cells of the UK

Definitions

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

• There are 11around England and Wales. Smaller ones are within these.

• The main cells are defined as a length of coastline and its associated nearshore area within which the movement of coarse sediment (sand and shingle) is largely self contained.

• Interruptions to movement of sand and shingle within one cell should not affect beaches in an adjacent sediment Cell

Transport

• As the particles are moved they become rounded by Attrition.

• Larger sediment is deposited during high energy and form beaches whilst some are also carried in suspension in areas of reduced energy

• Adjustments to these dynamic environments happen continuously to maintain the flux

Coastal Processes

• Now for the fun bit• Coastlines differ due to differing erosion• Coastal Erosion is the wearing away of the

land by the sea.• Different types of rocks wear away at

different speeds and in different ways.

Types of erosion

• Hydraulic Action. This is the force of water hitting the cliff and squeezing air into the cracks in the rock

• Abrasion. This is the force of the bits of rock carried in the water blasting into the cliff.

• Attrition. This is the process of rocks hitting each other and breaking into smaller rocks

• Corrosion. This is a chemical reaction between the sea water and the minerals in the rocks

The secret art of Coastal kung fu!

• Hydraulic Action: make punching movements with hand- demonstrates force of water hitting cliff.

• Abrasion: make a throwing gesture with hands like you are throwing dealing cards very rapidly

• Attrition: make 2 fists, and then bring them towards each other, hitting each other, then open hand to resemble a stone breaking.

• Corrosion: have arms out stretched in front of you, waving fingers, and moving arms downwards. Sound effect of something dissolving is needed.

• Solution: Put arms out in front of you waving fingers and moving down.

Please Don’t be embarrassed

• Oh OK be embarrassed then

• Here we go:

Mass Movement

• Exposed weathered rocks are often susceptible to mass movement

Soil Creep

• Slow less than 1cm a year• Caused by raindrop impacts• Wet periods add moisture to soil which

swells and expands then falls down slope• Freeze thaw

Solifluction

• Occurs mainly in colder areas, where freeze and then thaw creates movement due to lack of percolation

Earth flows and Mudflows, slides slumps and Rockfalls

• Faster movements • Occur on steep slopes• Found often on unconsolidated slopes• Can be large or small

Other Mass Movement Reasons

• Students are to write short paragraphs on the following separate into physical and human causes

• Runoff• Marine Erosion• Waves and Beaches• Geology• Human Activity• Sea walls and Coastal Defences• Land reclamation• Development

Learning Objectives

Demonstrate an understanding of wave refraction

Develop an awareness of littoral cells and different types of sediment

Demonstrate a knowledge of coastal processes including erosion

Evaluate the concepts behind mass movement