coasts

• Coasts


  The sea forms coasts and winds working together in 3 essential tasks: erosion, transportation and deposition
• Components of a wave


  • Swash: when a wave breaks & washes up the beach
  • Backwash: when the water drains back into the sea
• Types of Waves


  • Constructive
  • Destructive
• Constructive waves

  • Low wave height
  • The beach gradient is gentle
  • Spill forward gently
  • Creates a strong swash
  • Water drains through beach material
  • Backwash is weak
  • Deposits material
  • Builds up beaches
• Destructive waves

  • High wave height
  • The beach gradient is steep
  • Plunge forward
  • Swash is weak
  • Rotation of water causes a strong backwash
  • Erodes beaches
• Erosion processes


  • Abrasion: larger rocks and sediments like boulders grind against the riverbed
  • Corrosion: salts and acids slowly dissolve a cliff
  • Attrition: smaller sediments collide with each other while moving in the flow, making them rounder and smaller
  • Hydraulic action: the force of waves compresses air in cliffs
• Longshore Drift

  1. Waves approach the coast at an angle

  2. Swash moves up the beach at an angle

  3. Backwash drains straight back down the beach

  4. Gradually moving material along the beach in a zig-zag motion
• Coastal Opportunities


  • Sports/recreation
  • Groundwater recharge
  • Habitat for fish
  • Transport (shipping goods)
  • Tourism
  • Job opportunities
• Coastal Threats


  • Hurricanes
  • Coastal storms
  • Tsunamis
  • Landslides
  • Flooding
  • Coastal erosion
• Hard Engineering Coastal Management Techniques


  • Sea wall
  • Groynes
  • Gabions
  • Revetments
  • Rip-raps
  • Breakwaters
  • Tidal barriers
• Sea wall


  Located at coastlines/foot of cliffs, reduces erosion and prevent flooding, curved structure breaks waves, very expensive and big, requires constant maintenance
• Groynes


  Located in front of the area facing coastal erosion, increases distance between waves and coasts → Waves lose energy → Reduces impacts of waves, certain sections of the coast may be more exposed to erosion
• Gabions


  Located at base of cliff, reduces the impact of waves on a cliff, prevents cliff from being undercut, and cheap, not as effective as other coastal defences
• Revetments


  Slanted barrier against waves at the base of the cliff, absorbs energy of waves, prevents cliffs from being eroded, rippled surfaces help dissipate wave energy, no need for much maintenance, expensive
• Rip-raps


  Rocks and stones put against the base of the cliff, absorbs wave energy, protects cliffs behind, visual pollution, susceptible to being moved by the sea
• Breakwaters


  Located near coasts, effective, breaks incoming water, visual pollution easily destroyed
• Tidal barriers


  Located at side of coasts, prevents storm surges, very effective, expensive
• Soft Engineering Coastal Management Techniques


  • Beach nourishment
  • Land management
  • Marshland
  • Beach stabilization
• Beach nourishment


  Sand/shingle added to the beach, increases distance between waves and cliffs → Waves lose energy → Less erosive power, effectiveness is uncertain
• Land management

  Protect and rebuild dunes, good barrier against coastal flooding and erosion, tourism is affected as dunes are marked out of bounds to the general public
• Marshland


  Break up waves and reduce speed and power of waves → Limits area which waves can reach → Prevents flooding, effectiveness is uncertain
• Beach stabilization


  Planting dead trees in sand to stabilize, widen beach and reduces wave energy, lowers the profile of the beach, effectiveness is uncertain
• Caves, Arches, and Stack

  1. A band of weaker rock extends through a headland

  2. Erosion produces caves on both sides of the headland

  3. More erosion produces an arch through the headland

  4. Eventually, the roof is weak & collapses, forming a stack
• Beaches


  • In bays, the waves diverge outwards
  • The wave energy is dissipated, creating a low-energy environment. Hence, deposition to form beaches
• Bays and Headland


  • Bays are formed due to softer rock getting eroded easily
  • Headlands are usually formed since they are made of resistant rock and are eroded more difficultly
• Spits


  1. Spits form when the coastline changes direction

  2. Longshore drift carries material in the same direction

  3. Sand & shingle is built up to form a spit

  4. End of spit curves due to wave refraction or wind
• Sand Dunes


  1. Dunes form behind wide sandy beaches

  2. Onshore winds pick up the dry sand from above the high-water mark & carry it landward by saltation

  3. If they encounter an obstacle, the wind loses energy & deposits sand in the lee of the obstacle

  4. Eventually, a dune is formed

  5. Plants grow on it, which stabilizes it & traps more sand
• Mangrove Swamps


  • Mangrove swamps are trees and shrubs that grow in saline coastal habitats in the tropics and subtropics
  • Provide habitat and protection for many fish & other sea animals, especially when young
  • They slow water flow, encouraging any sediment to be deposited, keeping sea water clear
  • Protect the coast from erosion, storm surges, hurricanes, and tsunamis
  • They are a source of food and material
• Coral Reefs


  • Coral reefs support a great diversity of life
  • Built from the limestone remains of coral skeletons & coralline algae
• Conditions required for the growth of coral reef


  • Warm water/seas; temperatures 20 - 30C
  • Shallow water; not more than 60 meters deep
  • Water free from sediment/clear/availability of light
  • A plentiful supply of oxygen in water/unpolluted
  • A plentiful supply of plankton
  • Lack of strong current
• Destructive waves


  Created in storm conditions, have high energy, short wavelength, steep, stronger backwash than swash, erode the coast
• Constructive waves


  Created in calm weather, less powerful, longer wavelength, lower height, stronger swash than backwash, deposit material and build up beaches
• Wave formation


  Wind blows over surface of sea, friction creates swell, water particles rotate and move wave forward
• Factors influencing wave size and energy


  • How long the wind has been blowing
  • Strength of the wind
  • Fetch (how far the wave has traveled)
• Swash and backwash


  Swash is water washed up the beach, backwash is water running back down the beach
• Destructive waves have a stronger backwash than swash, constructive waves have a stronger swash than backwash
• Coastal erosion


  The wearing away and breaking up of rock along the coast
• Processes of coastal erosion


  1. Hydraulic action

  2. Abrasion

  3. Attrition

  4. Solution
• Sources of material in the sea


  • Eroded from cliffs
  • Transported by longshore drift
  • Brought inland from offshore by constructive waves
  • Carried to coastline by rivers
• Longshore drift


  Swash carries material at an angle, backwash flows back to sea at 90 degrees, creating a zigzag movement of material along the coast