A coast is the zone where the sea and ocean meets the land.

Coastal erosion, transportation and deposition are processes performed by waves, tides, currents and winds which produces the different costal features.

Waves

They are generated by wind.

As wind blows, wind energy is transferred to the water.

This cause the surface water to rise and fall, resulting in waves.

Wave Energy

It is the energy produced by the movement of waves.

Factors that determine the size and energy of waves include:

Wind Energy: The faster wind speed, the greater wave energy.

Duration of wind: The longer wind blows, the larger the waves.

Fetch: Distance of sea over which winds blow to generate waves. The greater, the more energy the waves have.

Wave Movement

Waves move in a series of circular loop-like motions. As the waves approach the shore, the water becomes shallower; the friction of the waves against the sea floor slows down wave movement. The frictional force cause the waves to rise and bend forward, and eventually collapse to foaming water.

Swash is the forward movement of waves to the shore. It carries sediments to the shore.

Backwash is the flow back to the sea due to gravity. It carries sediments back to the sea.

Types of Waves: Constructive Waves

Waves that occur in calm weather on gently sloping coasts.

Have a strong swash but weak backwash.

Gentle gradient allows waves to surge a greater distance up the coast.

More sediment is thus carried up than cleared.

The coast is built up by the deposited sediment, hence its name.

Types of Waves: Destructive Waves

They occur on steeply-sloping coasts.

They break violently with high energy.

Weak swash but strong backwash as steep gradient causes waves to plunge directly down the coast.

The waves does not get to travel far to deposit sediments.

Its strong backwash allows it to erode the coast and transport costal rocks and beach materials away from it, hence the name.

Characteristics and differences of constructive and destructive waves:

Tides

Refers to the daily alternate rising and falling of sea level seen along coasts.

Mainly caused by gravity of the Moon.

The pull produces high tides on opposite sides of the Earth.

Each costal area receives 2 high tides and 2 low tides daily.

The difference in water level between the 2 tides is known as tidal range.

The rise and fall of sea level affects erosion and transportation.

Areas located between low and high tides will experience more weathering and erosion as it have continuous drying and wetting.

Currents

Refers to the large-scale and persistent movements of water in the ocean.

Driven mainly by winds.

Longshore currents is a ocean current that flow parallel to a coast and are formed by waves that approach the coast at an oblique angle.

Coastal Erosion:

Factors:

Type of waves: (Destructive waves as more materials are eroded than deposited),

Structure and composition of coastal rocks: Surface: Coastal rocks with numerous lines of weakness will break down more quickly. Texture: Soft rocks will also be eroded faster than harder rocks like granite. Composition: Rocks with mineral composition that can be easily dissolved in water or can chemically react with water to form new chemicals may be weakened gradually and broken down.

Position of Coast: Protected or sheltered from winds and wave action by obstacles will experience less erosion than open-air coasts.

Processes of Coast Erosion:

Hydraulic Action:

Refers to the direct impact of the waves against the coast.

Destructive waves are more effective in eroding the coast.

Air in cracks may be compressed by water entering it and pressure exerted can widen them, breaking the rocks eventually.

Abrasion:

Refers to the impact of materials carried by the waves scraping against the coast.

Destructive waves are better of lifting larger pieces of rocks from the sea bed and hurdle them towards the coast.

The powerful impact of the rocks being thrown against them will eventually erode the coast.

Solution:

Occurs when waves react chemically with soluble minerals contained in the rocks and dissolve them, forming a chemical solution.

Limestone is susceptible to this process.

Attrition:

Occurs when rocks carried by the waves rub or hit against each other, breaking down into smaller pieces.

They also become more round.

3476625123825Coastal Transportation:

The long shore drift is one way where waves transport sediment along the coast.

Where waves approach the coastline at an angle, the swash carries materials in the water up the beach at an oblique angle.

The backwash then drags the material down the beach perpendicular (at a 90º angle) to the shore by gravity.

This produces a zig-zag movement of sediment along the beach known as longshore drift.

The direction of the longshore drift is affected by the direction of the wind.

It is a powerful process that is capable of moving large amounts of sediments along the movement of direction.

Coastal Deposition:

Factors: Deposition of sediment along the coast is dependent on:

Supply of sediment: Most sediment is transported down to the coast by rivers, from coastal erosion or from coasts. When the waves cannot carry their load of sediment, deposition takes place.

Gradient of slope: On gentle slopes, the wave energy is spreaded out and reduced due to the friction with the shore and gravity, resulting in constructive waves as they deposit materials more than eroding them.

Position of the coast: Coasts that are sheltered from strong winds and the calm coastal condition allow deposition to take place.

Erosional Landforms:

Cliffs and Wave-Cut Platforms: A cliff refers to a steep rock face.

Cliffs are produced by the action of waves undercutting a steep rocky coast.

Hydraulic action and abrasion may erode a crack on the rock surface.

The crack can enlarge to form a notch, which is further deepened to produce a cave.

Further undercutting by the waves will cause the roof of the cave to collapse.

An overhanging cliff is formed, which will eventually collapse and its sediments deposited at the foot of the cliff.

Those sediments might be picked by crashing waves and thrown against the base of the cliff, causing further erosion.

3598545421640The cliff may retreat further inland and over time, a wave-cut platform (a.k.a. shore tide) is formed, which is usually submerged during high tide.

Headlands and Bays

Coasts with alternate strips of resistant hard rock and less resistant soft rock will cause the soft rock to be eroded faster than the hard rock.

The result is the formation of indented coasts with headlands and bays.

Headlands (hard rock) and bays (soft rock) give rise to wave refraction which is caused by uneven depth of the sea floor.

As the waves bend, their energy is distributed unevenly throughout the shoreline, as the waves nearer to the shore touch the sea floor first and slow down due to friction.

As wave energy tends to concentrate and strike at their headlands rather than the bays, thus erosion takes place at the protruding headlands.

Therefore wave refraction determines where erosion, transportation and deposition take place.

Depositional Landforms

Beaches

Mainly consist of sandy materials.

Size and composition of the materials on the beach vary greatly and may change over time due to changes in weather conditions, wind direction and ocean currents.

2998470528955Finer materials are usually deposited nearer to the sea and the coarser materials are further inland if there are destructive waves. Likewise occurs for constructive waves.

Spits and Tombolos.

Spits are beaches joined to the coast at just one end.

Formed by longshore drift when the coastline turns but it continue to deposit materials which accumulate in the sea forming a spit.

If a spit continues to expand until it joins the island to the mainland, forming a tombolo.

Coastal Management is need as:

Coastal flooding caused by natural phenomena.

Erosion

Water Pollution

Protection of the coast is required to preserve the quality of the coastal environment.

Types of Approaches:

Hard engineering: Construction of physical structures to defend against the erosive power of waves.

Soft engineering: Focuses on planning, management and changing individual attitudes towards coastal protection.

342709518415Hard Engineering Measures:

Seawalls (e.g. Kallang River in Singapore)

They are built along the coast which absorbs the energy of waves before they can erode away loose materials.

However, they do not prevent the powerful backsplash of refracted waves from washing away the beach materials between the walls.

The backsplashes will eventually undermine the base of the seawall and eventually it collapses.

4538345667385They are costly to build and maintain as repairs have to be made to prevent their collapse.

Breakwaters

They help protect the coast and harbour by reducing the force of high energy waves before they reach the waves.

They create a zone of calm water behind them.

However materials deposited in the zones behind the breakwater are protected but the zones located away from the breakwater are not, and will be eroded away.

Groynes

They are built at right angles to the shore to prevent longshore drift.

They absorb/reduce the energy of the waves and cause materials to be deposited on the side of the groyne facing the longshore drift.

As no fresh materials are deposited on the downdrift side, that part will gradually be eroded.

To prevent this, the tips of groynes are sometimes angled about 5 to 10°, but if failed, erosion can still take place on unprotected areas.

Gabions

They are wire cages filled with crushed rocks that are piled up along the shore to reduce coastal erosion by weakening wave energy.

They need to be maintained as they are easily corroded.

If not properly maintained, the wire baskets become unsightly and pose a threat.

Soft Engineering Measures

Beach nourishment

Refers to the constant replenishment of large quantities of sand to the beach system, which leads to the improvement of beach quality and storm protection.

However it is expensive to constantly transport sand to fill up the beach as it is continuously eroded. Coral reefs may be in danger as the sand covers the corals. It can also led to muddy and polluted water.

Relocation of property

Coastal planners are trying to protect man-made structures by relocating them and let nature reclaim the beach slowly.

No building of new structures is allowed in coastal areas vulnerable to coastal erosion.

This approach is likely to be opposed by people who want to invest in the coastal areas.

Planting of mangroves

Mangroves can help to trap sediments and reduce coastal erosion.

However some areas with violent destructive waves may not support mangroves.

The depth of the coast may also become shallower, affecting coastal transportation and port activities.

Stabilising dunes

Coastal dunes can be found along the shore where lots of sand and strong winds exist. The winds carry and deposit the land on the coast further inland, forming coastal dunes gradually which help defend the coast from the sea.

However they are very fragile and thus access points to the beach are controlled and designated.

Shrubs and trees are planted to stabilise the dunes to anchor the sand.

Growth of coral reefs

They can weaken wave energy.

Artificial reefs are created along the coast to help enhance fishing opportunities, serve as undersea barriers and replace damaged coral reefs.