Geography Coastal erosionThis lesson will cover:• coastal erosion• coastal transport• coastal deposition•Constructive and distractive waves• transportation (information)•Hard and soft engineering methods By Merina
Geography Coastal erosionDestructive waves erode the coastline in anumber of ways:• Corrosion C• Attrition To A remember• Solution S• Hydraulic action H
GeographyCorrosion:Bits of rock and sand in waves grind down cliff surfaces likesandpaper. This is also sometimes called abrasion.
Attrition GeographyWaves smash rocks and pebbles on the shore intoeach other, and they break and become smoother.
Geography SolutionAcids contained in sea waterwill dissolve some types of rocksuch as chalk or limestone.
GeographyHydraulic action Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.Waves have great energy which isreleased as they break against thecliff. Waves trap air in the cracks inthe rock. This air becomescompressed by the waves, eventuallycausing the rock to become more orcompletely cracked.
Solution GeographyMinerals are dissolved in sea water and carriedin solution. The load is not visible. Load cancome from cliffs made from chalk or limestone,and calcium carbonate is carried along insolution.
Suspension GeographySmall particles are carried in water, eg: silts and clays,which can make the water look cloudy. Currents pick uplarge amounts of sediment in suspension during a storm,when strong winds generate high energy waves.
Saltation Geography Load is bounced along the sea bed, eg small pieces of shingle or large sand grains. Currents cannot keep the larger and heavier sediment afloat for long periods.TractionPebbles and larger sediment are rolledalong the sea bed.
Geography DepositionWhen the sea loses energy, it drops the sand, rockparticles and pebbles it has been carrying. This is calleddeposition. Deposition happens when the swash isstronger than the backwash and is associated withconstructive waves. Deposition is likely to occur when: •waves enter an area of shallow water. •waves enter a sheltered area, eg a cove or bay. •there is little wind. •there is a good supply of material.
Constructive and distractive waves GeographyWaves can be destructive or constructive.When a wave breaks, water is washed up the beach - thisis called the swash. Then the water runs back down thebeach - this is called the backwash. With a constructivewave, the swash is stronger than the backwash. With adestructive wave, the backwash is stronger than theswash.
Distractive waves. GeographyDestructive waves are created in storm conditions.They are created from big, strong waves when the wind ispowerful and has been blowing for a long time.They occur when wave energy is high and the wave has travelledover a long fetch.They tend to erode the coast.They have a stronger backwash than swash.They have a short wave length and are high and steep.
GeographyThe power of waves is one of the most significant forces ofcoastal change. Waves are created by wind blowing overthe surface of the sea. As the wind blows over the sea,friction is created - producing a swell in the water. Theenergy of the wind causes water particles to rotate insidethe swell and this moves the wave forward.The size and energy of a wave is influenced by:how long the wind has been blowingthe strength of the windhow far the wave has travelled (the fetch)
Constructive waves GeographyThey are created in calm weather and are less powerful thandestructive waves.They break on the shore and deposit material, building upbeaches.They have a swash that is stronger than the backwash.They have a long wavelength, and are low in height
Transport GeographyThere are various sources of the material in the sea. Thematerial has been:eroded from cliffstransported by longshore drift along the coastlinebrought inland from offshore by constructive wavescarried to the coastline by riversWaves can approach the coast at an angle because of thedirection of the prevailing wind. The swash of the waves carriesmaterial up the beach at an angle. The backwash then flowsback to the sea in a straight line at 90°. This movement ofmaterial is called transportation.Continual swash and backwash transports material sidewaysalong the coast. This movement of material is called longshoredrift and occurs in a zigzag.
sea wall GeographyA wall built on the edge of the Advantagescoastline. •Protects the base of cliffs, land and buildings against erosion. Can prevent coastal flooding in some areas. Disadvantage Expensive to build. Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high.
Groynes GeographyA wooden barrier built at rightangles to the beach. Advantages Absorb the energy of waves. Allows the build up of a beach. Disadvantages Can be seen as unattractive and Costly to build and maintain.
Rock armour GeographyLarge boulders are piled up Advantageson the beach. Absorb the energy of waves. Allows the build up of a beach. DisadvantageCan be expensive to obtainand transport the boulders.
GeographyBeach management This replaces beach or cliff material that has been removed by erosion or longshore drift. The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches also attract tourists. It is a relatively inexpensive option but requires constant maintenance to replace the beach material as it is washed away.
GeographyManaged retreat Areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be of low value - eg places not being used for housing or farmland. The advantages are that it encourages the development of beaches (a natural defence) and salt marshes (important for the environment) and cost is low. Managed retreat is a cheap option, but people will need to be compensated for loss of buildings and farmland.
GeographyOld cliff line Original Land su rface stack stump Natural Wave-cut platform Arch
Sediment accumulation Geography Groynes due to Longshore DriftWaves approach beach at oblique angle
Geography Wave-cut platform Wave built terrace Ouch!large angular rocks rocks and pebbles soft sand
Geography The force of the waves pushes air into cracks in the rockThe compressed air exerts enormous pressure at the tip of the crack. As the water falls backthe air pressure is released and rock is pulled out from the crack further enlarging the hole.