Physical Landscapes

• The coast marks the point where the land meets the sea. Coastal areas are dynamic and are constantly changing due to geomorphic processes such as weathering, mass movement erosion, transport and deposition
• The main erosion processes attacking our coastlines are hydraulic action, abrasion and solution. Attrition also breaks rocks down into smaller pieces within the waves.
• Hydraulic action occurs as waves dislodge loose material and air trapped in cracks in rocks compressed by waves helps to force rocks apart
• Abrasion occurs at the coast as pebbles hurled by waves against cliffs, or grinding along wave-cut platforms gradually wear rock away like sandpaper
• Solution occurs at the coast where chemicals in the water react with minerals in rocks to dissolve them, common in rocks such as limestone and chalk.
• Attrition occurs as rocks carried by the waves hit against each other gradually becoming smaller / more rounded or broken into smaller pieces
• Material is moved along the coastline by the process of Longshore Drift - the direction of movement controlled by wind direction.
• Deposition occurs at the coast when waves lose their energy and drop the material they are carrying. This is common in shallower water and where waves enter shallow bays. Material is deposited where the swash is greater than the backwash (constructive waves).
• Waves are created where wind creates frictional drag as it passes over the surface of the water causing a transfer of energy and a disturbance which gradually builds into waves. Waves are energy passing through water causing it to move in a circular motion.
• As waves reach the coast, the base of the wave slows down due to friction with the sea bed and wave height increases until it reaches a critical height and breaks.
• When a wave breaks at the coast, water moves up the beach in the swash and back down the beach in what is called the backwash
• The distance the wind has travelled over open water forming waves is known as the FETCH. Along with the strength of the wind & the time it has blown for, the wave fetch influences the strength of the wave. The greater these variables, the stronger the wave.
• Constructive waves, are low energy waves, with a stronger swash than backwash, which means they deposit material and build up beaches. These waves have a low wave height, long wave length and low frequency.
• Coastal erosion results in the formation of a number of distinct landforms, including Cliffs and Wave-Cut Platforms; Headlands and Bays; Caves, Arches, Stacks and Stumps
• Cliffs are steep rock faces found at the coast. The diagram shows how coastal erosion, creates a wave cut notch, which gradually undercuts the rock above which eventually collapses. The cliff retreats gradually and leaves a wave-cut platform

  
• Concordant coastlines are those where the same rock type occurs along a stretch of coast, with rock strata parallel to the coastline. In Discordant coasts different types of rock are perpendicular to the coastline, resulting in differing rates of erosion.
• Rates of coastal erosion are affected by the wave fetch and in turn wave strength, additional factors such as weathering that can weaken rock, rock type and structure and the level of human interference.
• Headlands and Bays are formed along discordant coastlines. As more resistant rock erodes slowly, headlands remain protruding out into the sea, whilst the less resistant rock is eroded away leaving an inlet known as a bay.

  
• Once cliffs form, wave refraction causes energy to be concentrated on the headlands resulting in the erosion of a headland, whereas in bays the waves energy is dispersed resulting in the deposition of sand and the creation of beaches.
• As the wave energy is concentrated on a headland it gradually creates a sequence of landforms: crack, cave, arch, stack and stump through a combination of weathering and erosion as shown below

  
• Deposition occurs at the coast where there is a drop in energy and the waves can not longer transport the material they are carrying
• Sand dunes, beaches, spits and bars are all examples of coastal deposition features
• Beaches are made up of material lying between the high and low tide mark. Most are deposits of sand and shingle
• Sources of beach material include material deposited at the mouth, material from cliff erosion, material carried by longshore drift and material brought up the beach in the swash
• Sandy beaches have a shallow gradient, are wide, may have dunes towards the back in contrast pebble/ shingle beaches have a steep gradient are narrow and have storm berms
• Sand dunes are formed on large flat beaches where there is a large supply of sand, a large tidal range and a strong offshore wind to move sand up the beach
• Sand dunes form as wind picks up sand and obstacles such as drift wood blocks the wind causing sand grains to be deposited around them. Sand builds up forming a crest before the pile of sand collapses causing lighter grains to slip down the leeward side
• Spits are long narrow ridges of sand and shingle which project from the coastline into the sea. Their formation begins due longshore drift moving material along the coast and deposition occurs where there is change in the shape of the coastline.

  This continues building up a ridge of material projecting out into the sea. A change in wind direction may crest a curved end. Sand dunes often form on spits and salt marshes often form in the low energy zone behind the spit.

  
• A spit will sometimes grow across a bay, joining two headlands to create a bar. Behind the bar a lagoon is created where water is trapped and a salt marsh is created

  
• Coastal erosion can be managed through hard and soft engineering techniques to protect a coastline from erosion and flooding.
• Hard engineering involves the construction of man-made defenses to control natural processes - e.g. groynes; sea walls; rip rap (rock armour) and gabions
• Sea walls are long concrete barriers built at the base of a cliff, often with a recurved base to reflect wave energy. These are effective but expensive!
• Groynes are wooden structures built perpendicular to the beach to trap longshore drift and build up the beach so that waves break on the beach protecting the cliff line from erosion.
• Rip rap (rock armour) is large resistant rocks placed in front of cliffs to absorb wave energy. These can make the beach inaccessible and are not very attractive however they can be an effective way of protecting the cliff by forcing the waves to break

  
• Gabions are wire filled cages filled with stones, absorbing wave energy and protecting the cliff behind.
• Soft engineering works with natural processes and doesn’t involve major construction so is visually unobtrusive and more environmentally friendly than hard engineering
• Soft engineering including beach replenishment, beach reprofiling and sand dune regeneration
• Beach replenishment involves adding sand to a beach, often pumped from offshore. This maintains a wider beach to form a natural defence by causing the waves to break before they reach the cliff line
• Beach reprofiling involves reshaping a beach after winter storms, using bulldozers to move shingle back up the beach to restore the beach to reduce wave energy
• Sand dune regeneration involves restoring existing sand dunes, planting marram grass to hold dunes together or creating new ones to provide a natural barrier between land and sea