coasts

• Most waves form due to the wind blowing across the surface of the sea, creating ripples that increase in height as they travel towards the beach.
• There are two types of waves which have different characteristics: Constructive waves have a strong swash and weak backwash, low wave height and large wavelength, low frequency, and depositional.
• Destructive waves have a strong backwash and weak swash, high wave height and small wavelength, high frequency, and erosional.
• The size of a wave depends on various factors including the strength of the wind, how long the wind has been blowing for, water depth, the fetch, and the type of waves.
• Coastlines which are hit by constructive waves tend to have depositional landforms such as sandy beaches because the waves are less powerful and deposit material rather than taking it away from the beach.
• Coastlines that are hit by destructive waves typically have erosional landforms such as rocky headlands and landforms, such as tall cliffs and caves.
• Destructive waves tend to have a long fetch and are the most powerful waves.
• There are five coastal processes: erosion, weathering, transportation, mass movement and deposition.
• Erosion is the removal and destruction of rocks and sand along the coastline.
• There are five different types of erosion: corrasion, abrasion, attrition, hydraulic action, and bioerosion.
• Hard engineering methods include groynes and sea walls.
• Individual cases can often be ignored to save money, for example, a few houses may be lost in managed retreat instead of using engineering to save them.
• There are different types of sea defences, grouped into either soft engineering methods or hard engineering methods.
• Soft engineering methods include dune stabilisation and beach nourishment.
• Managed retreat is becoming more popular as the cost of hard and soft engineering is too much for local councils.
• The value of the land for the economy should be considered when choosing the most appropriate management strategy, including how many jobs depend on the coastal area, whether industry will be lost if erosion continues, and what the insurance cost will be of damaged properties.
• Hard engineering methods are cost effective and effective erosion prevention, but are visually unappealling and can deprive areas downwind of sediment, increasing erosion elsewhere.
• The cultural or social value should also be considered, including whether the coast is historic or a location of cultural/religious importance, the scale of events or festivals that affect lives, and whether the coast is home to a village or town.
• The environmental value should also be considered, including whether there are any rare or endangered species living along the coastline, whether nature reserves would become at risk if erosion and flooding continues, and if there are any farms at risk.
• Soft engineering methods are cost effective and create an important wildlife habitat, but can be easily damaged in a storm.
• Corrasion is the process where sand and pebbles are picked up by the sea and hurled against the cliffs at high tide, causing the cliffs to be eroded.
• Abrasion is the process where sediment scrapes and bangs against the base of a rockface, and so wears away the face gradually.
• Attrition is an erosive process within the coastal environment, but has little to no effect on erosion of the coastline itself.
• Hydraulic Action is a process where air is forced into cracks within a rock as a wave crashes onto the rock, causing the cracks to widen when the wave retreats and the air expands.
• Wave-cut notch and platform is a landform created by marine erosion, where the base of the cliff is eroded between high tide height and low tide height, leaving a platform of the unaffected cliff base beneath the wave-cut notch.
• Corrosion (Solution) is a process that can cause alkaline rock such as limestone to be eroded by mildly acidic seawater.
• The waves push sediment in the direction of the prevailing wind up the beach in the swash.
• This moves sediment along the beach over time.
• Waves hit the beach at an angle determined by the direction of the prevailing wind.
• Longshore Drift is a process where sediment is transported along the coast through the process of longshore drift.
• Old Harry Rocks in Studland, Poole is a chalk rock which is difficult to erode.
• Marine erosion widens cracks in the base of the headland, these get bigger over time and create a cave.
• The cave widens and deepens due to both marine erosion and sub-aerial processes, and eventually a large hole will form through to the other side of the headland.
• This is known as an arch.
• The Green Bridge of Wales, Castlemartin is a cliff made from sedimentary rock, which is made from layers of sediment that build up over time and are compacted.
• Caves, Arches, Stacks & Stumps is a sequence of erosional landforms that occurs on pinnacle headlands.
• Thornwick Bay, near Bridlington in Yorkshire is an example of a wave cut platform.
• This leaves a stack as one side of the arch becomes detached from the mainland.
• Due to gravity, the wave then carries sediment back down the beach in the backwash.
• With marine erosion attacking the base of the stack, eventually the stack will collapse into a stump.