Coasts 1 (Elesson)v2

8/7/2019 Coasts 1 (Elesson)v2

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What is a Coast?

A coast is the zone where the land meets with

the sea.



Coasts

Tides

CurrentsWaves

Wave Energy-Wind energy

-Duration of Wind-Fetch

Wave Movement

Types of Wave:-Constructive (S>BW)

- Deposit>Erode

- Tombolo & Spit- Beaches

-Destructive (S<BW)

- Cliff & Wave-cut

Platform

-Headland & Bay

Coastal Processes

Erosion Transportation Deposition

Hydraulic ActionAbrasion

Attrition

Solution

Factors affecting

rate of erosion

Longshore Drift Depends on :-Is sediment

available?

-Slope steep

or gentle?

- Coast

sheltered or

protected?

Erosion:

- Cliff & Wave-cut Platform

-Headland & BayDeposition:

- Tombolo & Spit

- Beaches

Landforms/features

Hard

Engineering

SeawallsBreakwaters

Groynes

Gabions

Coastal

Management

Strategies

Soft Engineering

Beach nourishment

Planting mangroves

Growth of Corals

1. How they are built

2. Uses

3. Egs

4. Ltms



1.1 Agents shaping Coasts

1. Waves: A rising and falling movement of the

water surface produced by winds blowing

across the ocean or sea.

2. Tides: The alternate rising and falling of sea

level caused by the gravitational pull of the

Moon and the Sun.

3. Currents: Large-scale and persistent

movements of water in the ocean, driven

largely by prevalent winds.




� Waves

Wind

Surface of ocean/ sea



1.1 Agents Shaping Coasts

� Tides refers to the rise and fall in sea level

due to the gravitational pull of the Moon and

the Sun.

� The coast experience a high tide or a low tide

every 12 hours.

Source:http://app2.nea.gov.sg/12hnowcast.aspx



1.1 Agents Shaping Coasts

�Currents are flows of water that move

horizontally or vertically in a certain direction.

http://www.hickerphoto.com/data/media/171/ocean_current_mg5851.jpg http://www.kidsgeo.com/geography-for-kids/0053-climatic-controls.php




1. Waves: A rising and falling movement of the

water surface produced by winds blowing

across the ocean or sea.

2. Tides: The alternate rising and falling of sea

level caused by the gravitational pull of the

Moon and the Sun.

3. Currents: Large-scale and persistent

movements of water in the ocean, driven

largely by prevalent winds.



1.2 Wave Movement

� How are waves formed?

Waves are formed by wind blowing across the

surface of oceans or seas.



1.2 Wave Movement

� How do waves move?

Waves approach coast friction is created as the seabed

gets increasingly shallower wave loses energy & slowsdown

But,

waves behind keeps pushing it forward forced to Rise

When waves become too steep collapse & breaks onto

the beach



Waves approach coast friction is created as the seabed gets

increasingly shallower wave loses energy & slows down

But, waves behind keeps pushing it forward forced to Rise

when waves become too steep collapse & breaks onto the

beach

Forward movement of waves onto the beach is called Swash.

Backward movement of waves back into sea called Backwash.



1.2 Wave MovementSwash and Backwash

When waves breaks against the beach,

Forward movement of waves onto the beach is called Swash.

Backward movement of waves back into sea called Backwash.

12



� S s bri gs at rials t t beac a

eposit t em.

� Back as bri gs materials on t e beaca ay as it moves back into t e sea.

1.2 Wave MovementS as and Back as

SWASH

Forward movement of waves onto the beach.

BACKWASHBackward movement of waves back into the sea.



1.3 Wave Energy

� Factors affecting WAVE ENERGY

i. Wind Speed

� Higher wind speeds will generate higher wind energy

Larger waves are formed Higher Wave Energy

ii. Duration of Wind

� Longer the duration of wind blowing across the

ocean Larger waves are formed Higher Wave

Energy

iii. Fetch refers to the distance of ocean over which

the wind blows

� Longer the fetch Larger the waves Higher Wave

Energy



1.4 Types of Wave

� Two types: ± Constructive Waves: Low-energy waves where swash is

stronger than backwash.

± Destructive Waves: High-energy waves where backwash

is stronger than swash.



1.4 Types of Wave

Constructive vs. Destructive Waves



1.4 Types of Wave

When do you experience different waves?

Constructive Waves Destructive Waves

1. Calm weather Stormy weather2. Gentle-sloping coasts Steep-sloping coasts

3. Sheltered coast Open coast

4. Low energy waves High-energy waves

5. Strong Swash, Weak

Backwash Deposition

occurs

Strong Backwash, Weak

Swash

Erosion occurs



1.4 Types of Wave

Landforms formed from

Constructive VS. Destructive waves



1.5 Coastal Processes

Erosion Transportation Deposition

Four ways:

1 Hydraulic Action

2 Attrition

3 Corrasion/

Abrasion

4 Solution

3 Agents:

Waves

Tides

Currents

Factors affecting

coastaldisposition:

1.Supply of

sediments

2.Position of coast3.Gradient of slope



1.5.1. Coastal Erosion

� Hydraulic Action: Direct impact of wavesagainst the coast. Air in cracks may be

compressed by water entering the cracks.

Pressure exerted can widen and enlarge thecracks, causing it to breakdown over time.




� Attrition: Rocks carried by the waves

rub or hit against each other, they break down

into smaller pieces. Over time, the rocks

become more rounded.




� Corrasion/ Abrasion: Impact of

materials carried by waves scraping against the

coast. Powerful impact of rocks thrown against

coast erodes it over time.




� Solution: Waves react chemically with

soluble minerals contained in rocks and

dissolves them. E.g. A coast made up of

limestone.



1.5.2 Coastal Transportation

� Materials can be transported along the coast

through a process called

Longshore Drift




How does longshore drift happen?

1. Waves approach the coast at an oblique

angle according to the wind direction2. Swash carries materials up the coast in an

oblique angle

3.

Backwash carries them back to the sea atright angles due to the pull of gravity

4. Gives rise to a zig-zag movement parallel to

the coast




1. What happens if the wind blows from a

northeast direction?

2. What is the direction of the longshore drift?

Beach

Sea

N



1.5.3 Coastal Deposition

� Coastal Deposition happens when waves lay

down sediments along the coast.

� When waves do not have enough energy tocarry their load, deposition occurs.

� So, what causes low wave energy?

*R

ecall:1.Wind Speed 2.Duration of Wind 3.Fetch



� What then, causes waves to lose energy/ nothave enough energy?


1. Supply of

Sediments

3. Gradient

of slope

Steep

Gentle

Sheltered

Coast

Open

Coast

Sediments

transported to

coast by rivers &

Sediments from

coastal erosion

are too heavy to be

carried by waves

Deposition occurs

2. Position of

coastline

Sheltered

vs.

Open Coast

Gentle-sloping

vs.

Steep-sloping

coast




3. Gradient

of slope

Steep

Gentle

Sheltered CoastOpen

Coast

2. Position of

coastline

Sheltered coast: short fetch

low-energy (constructive) waves

Deposition

Open coast: long fetch high

energy (destructive) waves

Erosion

Steep-sloping coast: forms

destructive waves erosion

Gentle-sloping coast: Forms

constructive waves deposition

Coasts 1 (Elesson)v2

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