Coasts

• Fetch - how far the wind has been blowing over the water. The longer the fetch, the larger the wave
• Swash - waves rushes up the beach, depositing sediment
• Backwash - wave returns back to the sea, carrying sediment
• Constructive - low wave height

  Destructive - high wave height
• Constructive - waves far apart

  Destructive - waves close together
• Constructive - deposits sediment

  Destructive - erodes/takes sediment
• Constructive - forms a gently sloping beach

  Destructive - forms a steep beach
• Constructive - strong swash, weak backwash

  Destructive - weak swash, strong backwash
• Weathering:

  •Mechanical/physical - disintegration of rock

  •Chemical - caused by chemical changes

  •Biological - caused by flora and fauna
• Freeze-thaw weathering (mechanical) - water seeps into cracks in the rock, freezes and expands, breaking the rock apart
• Carbonation (chemical) - acidic rain (because of CO2 in the air) slowly dissolves alkaline rocks such as limestone
• Biological weathering examples - Plant roots grow in cracks, and animals burrow into them which breaks them apart
• Mass movement - downward movement of material and rock due to gravity
• Mass movement types:

  •Rockfall

  •Landslide

  •Mudflow

  •Rotational slip
• Rockfall - rocks break away from cliffs and fall down due to weathering, forming a pile of scree at the bottom
• Landslide - Large blocks of rock slide downhill
• Mudflow - saturated soil flows downhill
• Rotational slip - slump of saturated soil along a curved surface
• Solution (for erosion)- soluble chemicals dissolve soft rocks
• Corrosion - rocks carried by waves are thrown at a cliff face, eroding it back
• Abrasion - sandpaper effect of rocks grinding over a rock platform
• Attrition - rocks carried in the sea crash against eachother and become smaller, smoother, and more rounded
• Hydraulic action - waves hitting the cliff force air into cracks in the rock, which breaks it apart
• Solution (for transportation) - dissolved rocks are carried by the water
• Suspension - small particles of sediment are carried/suspended in the water
• Traction - large pebbles are rolled along the seabed
• Saltation - small rocks are bounced along the seabed by the water
• Longshore drift - the zig-zag movement of sediment along a beach due to a diagonal swash and straight backwash
• Concordant coastline - bands of different rock types run parallel to the coastline
• Discordant coastline - bands of different rock types run perpendicular to the coastline
• Hard engineering:

  •Sea walls

  •Groynes

  •Rock armour

  •Gabions
• Sea walls:

  •Concrete or rock barrier at foot of cliffs, curved to reflect waves back to sea

  •Effective, creates a walkway

  •Expensive, can look obtrusive
• Groynes:

  •Wooden posts built at right-angles to the sea to prevent longshore drift

  •Inexpensive, wider beach for tourism

  •Can lead to more erosion further down, can look unattractive
• Rock armour:

  •Piles of boulders at the foot of a cliff which absorb wave energy

  •Fairly cheap, easy to maintain

  •Expensive to transport rock, can be obtrusive
• Gabions:

  •Rock filled wire cages that support cliff and provide a buffer against waves

  •Cheap, eventually vegetate and merge into landscape

  •Initially unattractive, cages rust
• Soft engineering:

  •Beach nourishment

  •Dune regeneration
• Beach nourishment:

  •Sand and shingle is collected offshore and used to replenish the beach

  •Blends in with existing beach, creates wider beach for tourism

  •Needs maintenance, expensive
• Dune regeneration:

  •Planting marram grass to stabilise dunes

  •Good for wildlife habitats, fairly cheap

  •Time consuming, can be damaged by storms
• Managed retreat - allowing low value land to flood and relocating residents
• Headlands and bays are formed on a discordant coastline because hard rock is more resistant so erodes slower (headlands) and soft rock erodes faster (bays)