Coasts

Waves dependency

Waves depend on the strength and the distance the wind has travelled (the fetch).

Swash

Waves go up the beach.

Backwash

Waves go back down the beach.

Constructive Waves

Build up the beach. Low energy waves = low rates of erosion. Strong swash and weak backwash. Low frequency and low wave height.

Destructive Waves

Destroys the beach. High energy waves = high rates of erosion. Weak swash and strong backwash. High frequency and high wave height.

Coastal Processes: Erosion definition

Wearing away of rock along a coastline

Erosion: Hydraulic action

Shear force of water compressing air into cracks, causing the cliff to break apart.

Erosion: Abrasion

Waves throw sediment against the cliff causing it to wear away.

Erosion: Attrition

Rocks / pebbles carried by waves collide with each other becoming smaller and rounder.

Erosion: Solution

Sea water dissolves rocks e.g lime stone or chalk.

Coastal Landforms: Wave-cut Platform

Waves erode the base of the cliff through hydraulic action + abrasion, creating a wave-cut notch. Cliff becomes unstable + collapses, so further cliff retreats leaving behind a flat rocky surface called a wave-cut platform.

Coastal Landforms: Headland and Bays

On a discordant coastline, the coastline erodes (by hydraulic action + abrasion + destructive waves) the soft rock fast (as its less resistant) causing bays to form. Then the hard rock (more resistant) resist the erosion, causing them to stick out further into the sea. Constructive waves would deposit sediment on bays to form beaches.

Coastal Landforms: Stack

Formed in headlands where waves attack weak points through hydraulic action + abrasion. Continuous erosion widens the crack forming a cave. Then erosion on both sides of the headland can cause two caves to meet forming an arch. Top of the arch collapses due to gravity and weathering, leaving a pillar of rock called a stack. It can eventually erode to a stump.

Coastal Processes: Transportation definition

Movement of eroded material (sediment) along the coastline by waves.

Transportation: Traction

Large, heavy pebbles/rocks rolled along the seabed.

Transportation: Saltation

Smaller stones / pebbles are bounced along the seabed.

Transportation: Suspension

Light materials (e.g silt and clay) are carried along within the water.

Transportation: Solution

Dissolved minerals are carried along within the water.

Transportation: Longshore drift

The movement of sediment along the coastline determined by the direction of the prevailing wind. Swash moves sediment up the beach (45°) and backwash moves sediment down the beach due to gravity (90°). This results in a zig zag movement along the coast.

Coastal Processes: Deposition definition

When sea loses energy, drops material it has been carrying.

Coastal Landforms: Estuaries

Partially enclosed body of water that is very wide and funnel-shaped, where fresh water from rivers mixes with salt water from the sea occurring at the mouth of the river. Deposition of fine sediment (silt and mud) form mudflats.

Coastal Landforms: Spit

A long narrow ridge of sand / shingle that extends into the sea. Formed by sediment carried across the coastline through longshore drift, when the coastline changes direction, waves lose energy + deposit sediment. A curved end (recurved tip) can form due to changes in wind/wave direction. In sheltered low energy water behind spit sediment builds up to form a salt marsh.

Coastal Processes: Weathering definition

Breaking down of rocks at or near the earths surface, without involving movement of the material. Weathering weakens cliffs making it more vulnerable to erosion.

Types of Weathering: Physical Weathering

The process of breaking down rocks through physical forces (e.g temperature changes) without changing their chemical composition. Example: Freeze-thaw as water enters cracks and freezes causing it to expand and widen.

Types of Weathering: Chemical Weathering

The process of breaking down rocks by chemical changes. Example: Acid rain.

Types of Weathering: Biological Weathering

The process of breaking down rocks by living organisms. Example: Plant / Animals.

Coastal Processes: Mass Movement definition

The large-scale downward movement of rocks and material caused by gravity.

Mass Movement: Rockfall

Bits of rock detach due to freeze-thaw weathering (intensifies cracks) in hard rock and falls straight down the cliff by gravity.

Mass Movement: Landslide

large blocks of material slide downhill along a straight slip plane due to gravity.

Mass Movement: Rotational Slip / Slumping

When the soft rock on top of hard rock becomes saturated after a period of rainfall due to infiltration. The bedding plane between them becomes lubricated (slippery) so soft rock slumps down.

Human Activity Impacts on Coastline

Coastal areas are honeypot sites so attract tourists so footpaths are worn down + plant/vegetation worn away to expose underlying rock vulnerable to weathering (e.g freeze thaw) causing rockfall mass movement, coastal management as can increase rate of erosion elsewhere.

Hard Engineering: Sea wall

Concrete wall that is placed at front of cliff and reflect the wave energy back into sea to prevent coast erosion.

Adv- protects local homes + businesses, attract tourists with promenade to boost local economy and lower insurance people pay as less risk of flooding.

Disadv- Expensive to build/ maintain (2,000-5,000 per m) could be spent on health/education, Increase local taxes and eyesore.

Hard Engineering: Rock armour

Large boulders placed at foot of cliff that break waves and absorb their energy to prevent coastal erosion.

Adv- can look natural and used for recreational.

Disadv- expensive to transport, look different to local geology and dangerous.

Hard Engineering: Gabions

Rocks held in mesh cages to stop coastal erosion in areas that are affected.

Adv- Cheaper than other hard engineering.

Disadv-not very strong, affect wildlife as may caught in wire and looks unnatural.

Hard Engineering: Groynes

Wooden structure built out at right angles into the sea to prevent removal of sediment through long shore drift so beaches are wider, deeper + steeper to prevent coastal erosion.

Adv-builds a beach to attract tourism.

Disadv- terminal groynes syndrome (increase rate of erosion further down coastline), eyesore as wood can rot, cost of maintenance.

Soft Engineering: Managed retreat

Allows the sea to flood the land by becoming a natural buffer zone (wetland e.g salt marsh) against future coastal erosion.

Adv- traps sediment (builds up over time in wetlands so more resistant to erosion), cheaper to maintain (sea level rise they grow + repair itself), habitats for wildlife (increase biodiversity), carbon sinks and agriculture diversification (livestock to graze + eat salty vegetation to make meat richer so farmer sell higher price).

Disadv- land is lost to sea so people + businesses relocate so unemployment, bad for economy as government pay compensation.

Soft Engineering: Beach nourishment

Sediment is transported/deposited on beach to make it wider, steeper + deeper to absorb wave energy and prevent coastal erosion.

Adv- builds a beach to attract tourism, look natural and used for recreation.

Disadv- transport/maintenance costs (constantly replaced due to destructive waves), damage habitats, inconvenient for locals with construction.

Soft Engineering: Beach stabilisation

vegetation is planted on sand dunes to stabile them/ trap sand to build up to prevent coastal erosion.

Adv- relatively cheap and look natural.

Disadv- damaged by worm waves and areas zoned off from visitors.

Shoreline Management Plan (SMP)

When the government divides Uk into 11 sediment cell where each cell has 2 SMPs (local authorities).

They do a cost benefit analysis on which out of the 4 strategies to implement (Hold the line, advance the line, managed retreat or do nothing).

This is sustainable as SMPs take into account further down the coast and social/economic/ environmental long-term plans.