A_Level_Geography__Coastal_Systems_and_Landscapes.pdf

Coastal Systems and Landscapes Revision The Coastal System Coastal Processes Coastal Landforms Sea Level Changes Coastal Management Coastal Environments Humans at the Coast Coasts are Natural Systems They have: Inputs- such as...

Coastal Systems and Landscapes Revision The Coastal System Coastal Processes Coastal Landforms Sea Level Changes Coastal Management Coastal Environments Humans at the Coast Coasts are Natural Systems They have: Inputs- such as sediments and energy from wind, waves, tides and currents. Outputs- such as sediments deposited further along the coast or inland. Flows/transfers- erosion, weathering, transportation and deposition can move sediment within the system. Stores/components- landforms such as beaches, dunes and spits. Coasts are open systems and are generally in dynamic equilibrium because the inputs and outputs are balanced. A change in one causes negative feedback which restores the balance to the system. Negative feedback- a beach is eroded → the cliffs behind it are exposed to wave attack → sediment eroded from the cliffs is deposited on the beach → beach grows in size again. Positive feedback- as a beach starts to form, it slows down waves → more sediment is deposited → the beach grows in size. This will cause long term growth. The Coastline The coast officially extends 60 km inland and 320 km offshore. 40% of the world’s population live within 100 km of the coast and 10% are less than 10m above sea level. Backshore- An area of beach that extends from the limit of high water foam lines to dunes, or the extreme inland limit of the beach. It is only affected by waves in exceptional high tides or severe storms. Foreshore- An area between the high water mark and low water mark, Heavily influenced by marine activity. Tides will come in and out here. Inshore- An area between the low water mark and the point where the waves cease to have any influence on the land around them Offshore- The zone extending seaward from the point of low tide to the depth of wave-base level or outer edge of the continental shelf. Nearshore- where waves steepen and break and then reform in their passage to the beach, where they then break for the last time and surge up the foreshore. Much sediment is transported in this zone. Swash zone- The zone of water action on the beach which moves as water levels vary. Breaker zone- the zone within which waves approaching the coastline commence breaking (typically in depths of 5 and 10 metres). This moves throughout the day. Energy Sources There are lots of sources of energy in a coastal system: Wind Wind is caused by air moving from areas of high pressure to areas of low pressure. During storm events, the pressure gradient is high, so winds are strong. Strong winds can create powerful waves. Wind that blows consistently from the same direction, a prevailing wind, will cause higher-energy waves than those that change direction frequently. Waves Friction between wind blowing over the surface of the sea gives the water circular motion which causes a wave. As a wave approaches a shore, it breaks. Because of friction with the sea bed, the bottom of the wave slows down, and the top overtakes it which makes the motion more elliptical. The crest of the wave rises up and then collapses. The effect of a wave on a shore depends on its height and wave height can be determined by the wind speed, duration and fetch (the maximum distance of sea the wind has blown over to create the waves). A high wind speed, longer duration and longer fetch create more powerful waves. Water washing up the beach is called the swash and washing back towards the sea is called the backwash. Constructive waves have a low frequency (6-8 per minute) and are long and low. They have a more elliptical profile and a powerful swash which deposits material on the beach.  Destructive waves have a higher frequency (10-14 per minute) and are high and steep. They have a more circular profile and a strong backwash which removes material from the beach. They are most effective over steeply shelving seabeds which cause a rapid increase in friction and a steep wave front. In any area, waves usually predominate as either constructive or destructive. Wave refraction is the bending of waves due to varying water depths underneath. The part of the wave in shallower water slows down compared to the part in deep water, causing the wave to bend. For example, when a wave approaches a straight shoreline at an angle, the part of the wave crest closer to shore is in shallower water and moving slower than the part away from the shore in deeper water, so it bends in towards the beach. When a wave comes in, it has to go back out again, but if there are many waves behind it, it can’t just go straight back out. Instead, the waves find a divet in the seabed to go under the waves behind causing a rip current. Tides Tides are the periodic rise and fall of the ocean surface, caused by the gravitational pull of the moon and sun. Tides affect the position waves break on the beach at (high tide means waves will go further up the beach). Most landforms are created and destroyed in the area between maximum high and low tide- the foreshore. Talbot Bay in Australia West Coast, can rise by 36 feet, making it one of the largest tidal changes in the world A Spring tide is when the sun, moon and earth are aligned and a gravitational pull creates a large tidal range. A low spring tide occurs after a new moon and a high spring tide occurs after a full moon, so this occurs twice a month. A Neap tide is when the sun and moon are at a right angle to each other and there is a smaller gravitational pull on the tide. This creates a low tidal range A tidal bore is a phenomenon where the leading edge of the incoming tide forms a wave of water that travels up a river or narrow bay against the direction of the river or bay’s current. Currents Currents move material along the coast and is the general flow of water in one direction. It can be caused by wind or variations in water temperature or salinity. Estuaries are where a freshwater river and ocean meet. Water continuously circulates in and out of the estuary. Tides create the largest flow of saltwater whilst rivers create the largest flow of freshwater. When dense salty seawater flows into an estuary at high tide, it has an estuarine current which sinks and moves near the bottom of the estuary. When less-dense freshwater from a river flows into the estuary, it has an anti-estuarine current which is strongest near the surface of the water. Heated by the sun, anti-estuarine currents are much warmer than estuarine currents. The Earth tries to balance out all the heat the equator gets from the sun through currents running to the poles. The spin of the Earth causes this to change direction slightly. Warm water rises and cool water falls, creating a circular motion effect in the waves when forming current. At the end of the last ice age, fresh water from the Great Lakes of North America got into the Gulf Stream Pump, turning it off due to extreme temperature differences. This sent Europe into an ice age. Downwelling is when cold land causes cold currents to sink and warm water to rise further away, and be drawn back to the land- a conveyor system. Upwelling is when warm water by warm land is pushed away by surface winds and then deep, cold, nutrient rich water rises to the surface to replace the water that was pushed away. Phytoplankton can breed here so it is a good fishing ground. The El Niño phenomenon is where easterly winds weaken and warm water moves eastward from Australia to South America, giving the USA a warmer winter. This is unusual given that in a normal year, cold water along the South American coast flows towards Australia by equatorial winds. La Niña is a similar phenomenon, but in the Northern Hemisphere between Japan and the USA. Energy High-energy coasts receive more inputs of energy from large, powerful waves, which can be caused by strong winds, long fetches and steeply shelving offshore zones. They tend to have sandy coves and rocky landforms such as cliffs, caves, stacks and arches. The erosion rate is higher than the deposition rate. Low-energy coasts receive low inputs of energy from small, gentle waves which can be caused by gentle winds (e.g. in sheltered areas), short fetches and gently sloping offshore zones. Some coastlines are low-energy because of coral reefs or islands that protect the coast from the full power of the waves. Low-energy coasts often have salt marshes and tidal mudflats. The deposition rate is higher than the erosion rate. Sediment Sources Inputs of sediment in a coastal system can include: Rivers carrying eroded sediment into the coastal system from inland. Sea level rise can flood river valleys, forming estuaries which then become a part of the coastal system. Erosion from cliffs by waves, weathering and landslides. From the crushed shells of marine organisms. Waves, tides and currents can transport sediment from offshore deposits. The sediment budget is the difference between the amount of sediment that enters the system and the amount that leaves. If more sediment enters than leaves, it has a positive sediment budget and the coastline builds outwards. If more sediment leaves than enters, the sediment budget is negative and the overall coastline retreats. The coast is divided into sediment cells, or littoral cells. These are sections of coastline where overall there is a balance between erosion and deposition within the cell. They are often split into sub-cells where there are specific inputs of materials whose transportation is then monitored. Clear boundaries define them such as headlands. They represent closed systems theoretically. Thus there is no transfer between the cells of material. There is a debate about the extent to which this is true. Coastal Processes Erosion There are six main ways waves erode the coastline: Abrasion Rock and sediment transported by waves smash and grind against other rocks and cliffs, breaking bits off and smoothing surfaces in sandpaper-like way, particularly if sand and shingle are present. Hydraulic Action Air in cracks in cliffs is compressed when waves crash in and the pressure exerted by this widens the crack, destabilises the cliff and compression breaks off pieces of rock. Cavitation As waves recede, the compressed air expands violently, again exerting pressure on the rock and breaking pieces off. Wave Quarrying The energy of the wave itself is sometimes enough to detach bits of rock from a cliff. Particularly, undercutting can cause material to collapse due to gravity. Corrosion Carbon dioxide in the atmosphere is dissolved into the ocean, turning the water into a weak carbonic acid which some rocks such as limestone are vulnerable to and will dissolve into it. Attrition Rocks in the water smash against each other and break into smaller bits. This often causes smoothing and rounding of material, eventually turning rocks into sand grains. Transportation Transport can be aeolian or fluvial but fluvial processes supply 95% of sediment entering the ocean. The energy from waves, tides and currents transports eroded material in four main ways: Solution Substances that can dissolve, such as calcium based limestone and chalk, are carried along in the water. This particularly happens when organisms form and decay. Suspension Very fine material, such as silt and clay particles, is whipped up by the turbulence and currents of the water and carried along. This is the way most eroded material is transported and the greater the energy of the water, the greater the size of material can be transported. Saltation Larger particles, such as pebbles or gravel, are too heavy to be carried by suspension, but the force of the water still causes them to bounce along the sea bed. Traction Very large particles like boulders are pushed along the sea bed by the force of the water through waves and currents. Often this is the only way to transport large material. Longshore Drift Longshore drift or littoral drift use all the processes above to transport sediment along the shore. Swash carries sediment up the beach parallel to the prevailing wind and backwash carries it back down the beach at a right angle to the shoreline. If there is an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash can move the sediment along the shore. Deposition Deposition is when the material being transported is dropped on the coast and it can be in the form of marine (carried by the seawater) or aeolian (carried by the wind). Both marine and aeolian deposition happen when the sediment load exceeds the ability of the water or wind either by the sediment load increasing (like be a landslide) or because the wind or water flow slows down and has less energy. Wind and water can slow down for similar reasons. Friction increases- when waves enter a shallow seabed or wind encounters land, friction between the ground surface increases which slows down the water or wind. Flow becomes turbulent- if water or wind encounters an obstacle, its flow can become rougher and decrease in overall speed. This could be a water current moving in the opposite direction or an area of vegetation. If the wind drops, the wave height, speed and energy will decrease as well. Weathering Sub-aerial weathering is the gradual breakdown of rock by agents such as ice, salt, plant roots and acids. Weathering weakens cliffs and makes them more vulnerable to erosion. Crystallisation The high salt content of sea water can lead to the growth of salt crystals in dryer conditions after high tide. These crystals expand as they form and can cause pressure within fissures and leaves to the rock fragmenting. Freeze-thaw Weathering Freeze-thaw weathering occurs in areas where temperatures fluctuate above and below freezing. When water enters cracks in the rock and freezes, it can expand by 10%. The pressure and other weather changes can cause rocks split and small  fragments to fall off. Wetting and Drying This only occurs in the intertidal zone where shale or clay rocks expand when they are wet and contract when dry, putting pressure on the rock and breaking fragments off. Chemical Weathering Chemical weathering is the breakdown of rock by changing its chemical composition. Carbon dioxide can dissolve in the rain or sea, forming a weak carbonic acid which reacts with rock that contains calcium carbonate, like limestone or chalk, and dissolves it. Rocks containing iron compounds oxidise when oxygen and water are present, leading to disintegration. Biological Weathering Plants and roots can grow into cracks in the rock, adding pressure, widening them and causing them to breakdown. Mass Movement Mass movement is the sudden downwards movement of sediment due to gravity. In coastal areas, it is likely to happen due to undercut action of the waves as this causes an unsupported overhang which can collapse. Factors affecting mass movement Sediment cohesion Slope height & angle- the longer the cliff, the more speed can be picked up Sediment grain size Temperature and saturation level Rockfalls This is the rapid free-fall of rock from a steep cliff face, often caused by freeze-thaw weathering and gravity. Bare, well-jointed rocks are very vulnerable. A scree slope can often be found at the bottom. White Cliffs of Dover, Kent March 2012- thousands of tonnes of rock fell 300 ft to the shore and was blamed on February’s cold, wet weather which caused the chalk to absorb a lot of rain and expand as it froze. Landslide This is the downhill movement of large amounts of rock, soil and mud, caused when rain percolates down layers of rock and the heavier, saturated mass falls along a distinct slip plane. Cliffs of softer rock which are weakened by weathering are the most  vulnerable. Lyme Regis, Dorset May 2008- after a wet period in winter and early spring more than 400 m of cliff collapsed. Rotational Slump This happens where softer material overlies more resistant rock and heavy rain infiltrates and lubricates the joint at the resistant rock, creating a slide plain. A slump has a concave slip plane so material is rotated backwards into the cliff face. This is common on clay cliffs when hot summers bake the rock, causing cracks and then heavy rain infiltrates it. This happened in Port Mulgrave, 2018, a place where mass movement is common. Mudflow This occurs where topsoil overlies impermeable soil and heavy rain saturates the soil, causing it to become fluid and move downhill over the impermeable soil. The rate of movement depends on the angle and level of saturation and a mudflow ends with a delta or fan. Chamoson, Valais, Switzerland 2018- had received 18 mm of rain in just 10 minutes Material can also move gradually downwards over a prolonged period of time, known as soil creep. This is likely due to gravity, the angle of the cliff, moisture and layered bedrock bending down the slope and can cause tilted structures. Unconsolidated soils, such as clay, are prone to collapse as there is little friction between particles to hold them together. Heavy rain can saturate unconsolidated rock, further reducing the friction between particles and making it more likely for the structure to collapse. Runoff can erode fine particles and transport them downslope. Coastal Landforms Types of Coastline There are 2 types of coastline which both produce different landforms. Concordant Coastline- Where bands of hardrock and softrock are parallel to the coastline, with hardrock shielding the softrock from erosion e.g. South coast of the UK Discordant Coastline- Where bands of hardrock and softrock are perpendicular to the coastline, causing alternating strips of the 2 types of rock e.g. West coast of Ireland Coastal Landforms Caused by Erosion Cliffs and Wave-cut Platforms Cliffs form as the sea erodes the land as a result of the action of waves and weathering. They retreat over time. Weathering and wave erosion can form a notch at the high water mark which eventually develops into a cave. With nothing to support it, the rock above collapses leaving a flat wave-cut platform behind. Examples of this can be seen near Lannacombe Bay in South Devon. Headlands and Bays Headlands and bays form on discordant shorelines. The soft rock is eroded quickly, forming bays, and the hard rock is eroded less, sticking out as a headland. Bays are curved because the middle of the soft rock is available to wave attack from any direction. As the bay becomes deeper, it becomes more difficult for the waves to get in, so sediment can’t get out (making it a closed system) meaning the beach builds up from deposition. This will eventually prevent erosion and the bay won’t get bigger. An example of this can be seen on the Cape of Good Hope in South Africa Coves can be formed in bays by wave refraction, causing the bay to become very circular. This can happen on a concordant coastline when water finds a fault in the resistant hardrock and erodes it away to get to the soft rock behind. Through the small gap in the hardrock, the waves refract outwards to create the cove, which can be considered as a sediment cell e.g. Lulworth Cove Caves, Arches and Stacks Some landforms can be found in cliffs- these are called cliff profile features. Caves, arches and stacks can form there: 1. Cracks at the base of the headland within the intertidal zone become exposed through hydraulic action, which pressurises air, forcing the crack to widen. 2. Cracks are further widened by weathering processes such as salt crystallisation and wet and dry weathering that affects chalk.  3. Over time, the cracks widen and develop as wave-cut notches. Further processes of abrasion and hydraulic action will deepen the notch to form a cave. 4. As a result of wave refraction, which distorts the wave direction, destructive waves concentrate their energy on the sides. This deepens the cave. 5. Wave refraction affects all three sides of the headland. If 2 caves are aligned the waves may cut through to form an arch. Wave-cut notches widen the base of the arch. 6. Vertical joints are exposed by tall breakers associated with destructive waves. Joints can also be weathered from above such as through carbonation in limestone. Here blowholes may form. 7. Over time, the arch becomes unstable and collapses under its own weight to form a pillar of rock, called a stack. A good example of this is Old Harry along the Dorset coast. 8. The stack is further eroded at its base creating new wave-cut notches. Sub-aerial processes continue to weaken the stack form above 9. Eventually the exposed stack will collapse to form a stump. The broken material is further eroded through attrition and transported away to be deposited within the bay. An example of this can be found in Loch Bracadale, Scotland. Coastal Landforms Caused by Deposition Beaches Beaches are a store in the coastal system and form when constructive waves deposit sediment on the shore. Shingle beaches are steep and narrow and are made up of larger particles which pile at steep angles. Sand beaches are formed from smaller particles and are wide and flat. Beaches have distinctive features: Berms- ridges of sand and pebbles about 1-2 metres high which are found at the high-tide mark. Examples can be seen in Parque Tayrona, Colombia. Runnels- grooves in the sand running parallel to the shore, formed by backwash draining to the sea. Cusps- crescent-shaped indentations that form on beaches of mixed sand and shingle. Spits Spits form where there is a sudden change in direction of the coast, such as across river mouths. Longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea e.g. Spurn Head, Hull Simple spit- a straight spit that grows roughly parallel to the coast. Recurved end- changes to the dominant wind and wave direction, particularly wave refraction, can lead to a spit having a curved end.  Compound spit- over time several recurved ends may be abandoned as waves return to their original direction. This results in a spit with multiple recurved ends from several periods of growth. The area behind a spit often forms into mudflats or saltmarshes. Offshore Bars and Tombolos Bars form when spits join two headlands together- either across a bay or river mouth. A lagoon forms behind this e.g. Slapton Ley, South Devon Offshore bars form off the coast when material moves towards the coast as sea level rises. When waves approach a gently sloping coast, friction with the sea bed can cause the waves to break a distance away from the coast. Over time, materials build up parallel to the coast to form a ridge of sand called an offshore bar. If a body of water is completely cut off by the offshore bar, it is called a lagoon. These may remain partly submerged by the sea. A bar that connects the shore to an island, often a stack, is called a tombolo. For example, St Ninian’s Isle in the Shetland islands is joined to a larger island by a tombolo. Barrier Islands Barrier islands, or beaches, are long narrow islands of sand or gravel that run parallel to the shoreline, but are detached from it. They tend to form in areas where there is a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range. It is unclear how barrier islands actually form, but some scientists believe that they were formed when the last ice age ended, where rapid sea level rise flooded land behind beaches and transported sand offshore to be deposited in shallow water, forming islands. Others believe that the islands were originally bars attached to the coast which had sections eroded away, causing breaches and eventually becoming an island. Sand Dunes Sand dunes form in the intertidal zone when sand deposited by longshore drift is moved up the beach by wind. Sand is trapped by driftwood or berms and colonised by plants and grasses like marram grass. The vegetation stabilises the sand and encourages more sand to accumulate, forming embryo dunes which are about 1m high and 80% sand. Over time, the oldest dunes, which can get to 10 m high, migrate inland due to the beach extending outwards, as newer embryo dunes are formed. Estuarine Mudflats and Saltmarshes Haloseres are an ecological succession that develop highly saline environments like mudflats and saltmarshes. Mudflats are formed behind sheltered, low-energy environments like river estuaries and spits from a lot of deposition from rivers which build mud layers, but are still covered at high tide. Winding channels criss-cross through due to tidal action, but dry out at low tide. Eventually vegetation which can survive the highly saline environment and frequent periods of being under water, such as marram grass, colonise the land, forming salt marshes. This creates a positive feedback loop as the vegetation traps more sediment and reduces water velocity. Sea Level Changes Eustatic Sea Level Change Eustatic sea level change is caused by a change in the volume of water in the sea or alterations to the shape of the ocean basin, and is always on a global scale. Changes in climate can cause eustatic sea level change: Eustatic rise is caused by an increase in temperature as we come out of an ice age that causes the water itself to expand and increase the sea level. Higher temperatures will also mean more melting of the ice sheets which further raises the sea level as cryospheric stores decrease and hydrospheric stores increase and submerges land under water. Temperatures can increase due to the Milankovitch cycle, volcanoes and sunspots. Eustatic fall is caused by a decrease in temperature as an ice age approaches, sees more precipitation fall as snow and settle as glacial ice. The ice acts as a fluid store within the hydrological cycle and therefore sea levels start to fall and land begins to emerge. Tectonic movements of the Earth’s crust can alter the shape and volume of the ocean basins. For example, the sea floor spreading will increase the volume of the basin and so decrease the sea level. Isostatic Sea Level Change Isostatic sea level change is caused by vertical movements of the land relative to the sea. Any downwards movement of land will cause the sea level to rise and any upwards movement of land will cause sea level fall. This is always on a local scale and can cause isostatic fall or readjustment. It can be caused by: The uplift or depression of the Earth’s crust due to accumulation or melting of ice sheets. Isostatic fall can occur as the weight of the ice or sediment, particularly at the mouths of major rivers, can cause some coastlines to sink, whereas isostatic readjustment occurs after the weight of a retreating glacier is gone, land can slowly uplift for thousands of years and accumulation of sediment. e.g. the North of Britain had 1 km of ice during the ice age and as such, is seeing a see-saw motion where the North is “rebounding” up, forcing the South to sink. Iceland is “rebounding” as the 2 km of ice that was once on it is melting. Subsidence (vertical downward movement) of land due to shrinkage after abstraction of groundwater, like draining a marshland. Tectonic (crustal) processes, such as one plate being forced beneath another at a plate margin. This can only happen in certain places of the world and cause earthquakes e.g. Haiti 2010. It can be linked to volcanic caldera collapse where a volcano's magma chamber is used up and then collapses in on itself e.g. Kilauea, Hawaii 2018. Historic Sea Level Rise On a daily basis, the tidal cycle can alter sea level and temporarily, onshore winds and low atmospheric pressure systems can also cause sea surface rise. On a longer time scale, the sea level has risen in the last 10,000 years. During the last glacial period, which was between 110,000 and 12,000 years ago, water was stored in ice sheets, so the sea level was lower than the present, and it hit the last glacial maximum around 21,000 years ago where the sea level was about 130 m lower than present. As temperatures started to increase from 12,000 years ago, ice sheets melted and sea levels rose rapidly. It reached its present level around 4,000 years ago and has been fluctuating around it ever since. Since the 1930s, we have been seeing sea level rise. Climate Change Causing Sea Level Rise Over the last century, global temperatures have been rising rapidly with a sharp rise of 1.08 °C between 1900 and 2016. This very fast temperature increase has caused a consensus among scientists to say that the changes in the climate over the last century are down to human activities like deforestation and burning fossil fuels. These activities increase the concentration of greenhouse gases in the atmosphere which absorb outgoing long-wave radiation so less is lost to space. As their concentration increases, more energy is trapped and the planet warms up. Increases in temperature are likely to cause sea level rise through melting ice sheets, particularly in Greenland and Antarctica, and thermal expansion of water in oceans. We have seen a 6 cm increase during the 19th century and a 19 cm increase throughout the 20th century, averaging at 1.7 mm per year. Global sea level is currently rising at 3.2 mm each year, but if greenhouse gas emissions remain on the maximum predicted trajectory, by 2100 this may increase to 8 to 16 mm a year. If CO2 emissions were to reach zero by 2100, sea levels would hit a peak of 0.8 m rise by 2030, but in the high CO2 emissions scenario, sea levels would rise by 3.7 m by 2030. Impacts on Coastal Areas Storms will become more frequent and more intense due to changes in ocean circulation and wind patterns which would cause damage to coastal ecosystems and settlements. Sea level rise and increased storms will also increase coastal erosion, further putting ecosystems, homes and businesses at risk. Coastal flooding has become more severe and more frequent in low-lying areas with Kings Point in New York being flooded just 80 times between 1995 and 2004 to 160 times between 2005 and 2014. Many low-lying islands may become submerged. If the sea level rises by just 0.5 m, most of the Maldives will have disappeared. Coastlines can be changed because as sea levels rise, islands are created and the area of land is decreased. With just a 0.3m sea level rise, 8000 km² of land in Bangladesh will be lost which is 6% of the entire country’s land. An increase in sea level may lead to salt water entering bodies of fresh water near the coast, damaging the ecosystems and making the water unsuitable for many uses. Salt water entering soils may also damage crops and make land impossible to farm on.  More money will be needed for flood protection. The cities with the highest annual flood costs by 2050 are Guangzhou at $13.2 billion, Mumbai at $6.4 billion and New York at $2 billion. Coastlines of Emergence When sea levels fall relative to the coast, new coastlines emerge from the sea creating different landforms: Raised beaches- Formed over time these are areas of former wave-cut platforms and beaches which are at a higher level than current sea level and the beach sediment becomes vegetated and develops into soil e.g. Little Gruinard, Ullapool, Scotland Wave-cut Platforms- Sea level fall can expose wave-cut platforms, leaving them raised above their former level. Relict Cliffs- Cliffs above raised beaches are no longer affected by coastal erosion so start to slowly get covered by vegetation. Wave-cut notches, caves, arches and stacks can sometimes be seen within relict cliffs, although most raised features are gradually degraded by weathering over time. Coastlines of Submergence When sea levels rise relative to the coast, the sea submerges existing coastines, creating different landforms: Rias- These form where river valleys are partially submerged and have a gentle long and cross profile. They’re wide and deep at their mouth and become narrower and shallower the further inland they reach e.g. Solva Valley in Pembrokeshire was flooded when sea level rose between 12,000 and 6,000 years ago. Fjords- These are like rias but instead of formed from drowned river valleys, they are formed from drowned glacial valleys and are relatively straight and narrow, with very steep sides and over 500 m depth. They have a shallow mouth caused by raised ground known as a threshold, formed by deposition of the glacier. They’re very deep inland with places like Sognefjorden in Norway reaching over 1000 m depth in places. Dalmatian Coastlines- Where valleys are parallel to the coast, and increase in sea level can flood these places and leave islands parallel to the coastline. This is named after the Dalmatian coast in Croatia. Processes Individual landforms combine to form landscapes and coastal landscapes can be dominated by erosion or deposition, but most are formed by both. The processes acting at the coast can create new landforms or change existing ones meaning coastal landscapes change over time. A change in one factor can affect another, like a change in wave direction increasing deposition and eventually changing a landscape dominated by erosive landforms to be one dominated by depositional landforms. Relict landforms may also change over time as they can still be affected by coastal processes such as weathering. Coastal landscapes are therefore often made up of a mixture of active and relict landforms that reflect different time periods of change, such as a still forming beach may be backed by a relict cliff from an earlier time of higher sea level. Changes occur over a range of spatial and temporal scales, for example, changes can vary from short and episodic, like storms that last a few hours, to long and gradual, like tectonic uplift over thousands of years. Coastal Management The aim of coastal management is to protect homes, businesses and the environment from coastal erosion and flooding because they can have severe social, economic and environmental impacts. Unfortunately, due to limited availability of funding, not everywhere can be defended. Using a cost-benefit analysis, it is chosen which places are best to protect- this usually ends up being large settlements and important industrial sites, rather than isolated or small settlements. There are four options for coastal management: Hold the line- maintaining the existing coastal defences to stop erosion and keep the coast where it is at today. Advance the line- building new coastal defences to move the existing line of defence and the coast further out to sea, which is very expensive. Do nothing- build no coastal defences at all and deal with erosion and flooding as it happens. Managed realignment/Strategic Retreat- allow the shoreline to move, but manage retreat so it causes less damage, such as flooding farmland rather than towns. Hard Engineering This is done to protect coastal settlements and is generally used to deflect the power of waves. They are visible and reassure communities, but are expensive and not very long-term. Hard engineering solutions can have detrimental effects further along the coast. Sea Wall The wall reflects the hydraulic action of waves back to sea, preventing erosion and flooding at the coast. Using recurved sea walls are more expensive, but they can flick the waves back out to sea, preventing any water splashing over and the wall shaking from pressure. However, this can create a stronger backwash and reduce the size of the beach and make the base of the sea wall susceptible to erosion. This is expensive to build (£18,000 - £25,000) and maintain and people may end up getting stuck on the beach if there is only a sea wall. Revetment Revetments are slanted structures at the base of cliffs made of wood, concrete or rocks. When waves break against them, the revetments absorb the wave energy, preventing cliff erosion. These are relatively cheap and easy to install, but they prevent access to the beach so are often only temporary  solutions. Like the sea wall, they create a strong backwash which can encourage more erosion. Gabions These are rock filled cages usually placed at the foot of cliffs to absorb wave energy and reduce erosion. They are cheap to install and maintain and can be organised for other uses, such as becoming stairs. Vegetation can also be planted on top of gabions to provide extra protection. However, they are not very strong and can be quite ugly Riprap Boulders which are often made of gneiss or concrete piled up along the coast which are used to absorb wave energy and so reduce erosion. These are very portable, can look natural and are relatively cheap at £4,000 per metre. But they can shift in storms and restrict access to the beach. Groynes Groynes are fences built on beaches, perpendicular to the coast which trap material transported by longshore drift. This creates wider beaches, which slow the waves by reducing their energy and so giving the coast greater protections from flooding and erosion. Where the last groyne is placed is key as areas behind it will suffer rapid erosion- decision making for this is an example of strategic retreat. This is quite cheap at £200,000 for one. These only work on beaches with longshore drift and they can starve down-drift beaches of sediment, leading to thinner beaches which won’t protect the coast as well, and lead to greater erosion and flooding. Furthermore, they only have a lifespan of 50 years so won’t provide long-lasting protection. Breakwaters Breakwaters are lengths of concrete blocks or boulders deposited off the coast that cause waves to break offshore. They can be totally offshore or connected to land and reduce the energy and erosive power of the waves before they reach the beach. They can provide a protected harbour for ships to anchor and have walkways for pedestrians. These are expensive, can be damaged in storms and can cause sediment build up out to sea which can damage marine ecosystems and reduce longshore drift at the shore. Tidal Barrier Tidal barriers are built across river estuaries and have retractable floodgates which can be raised to prevent flooding during storm surges.  These are very expensive Tidal Barrage These are dams built across river estuaries with their main purpose being to generate electricity. Water is trapped behind the dam at high tide and they control the release of water through turbines at low tide which generates electricity. These are very expensive, can be ugly and they stop shipping and disrupt ecosystems. They can disrupt sediment flow which may cause increased erosion elsewhere in the estuary. Cliff Fixing This is where large rods are inserted through the cliff to hold it together. Some have holes in the rods so water from the mud can dribble out. It can be quite expensive. Vegetation can be grown over it to make it look more natural e.g. Scarborough Soft Engineering Beach Nourishment This is where sand and shingle are added to beaches from elsewhere, such as dredged from offshore, creating wider beaches which reduce erosion of cliffs compared to thinner beaches. This is relatively cheap at £3,000 per km and a bigger beach can provide more financial opportunities, however where you take the sand from can suffer from erosion and, if taken from an offshore bar, it could cause greater wave power and erosion. Beach Stabilisation This involves stabilising the sand itself by reducing the slope angle, planting vegetation and sticking stakes and old tree trunks in the beach. This also creates wider beaches which will reduce erosion of cliffs. Dune Regeneration Dune regeneration is where dunes are created or restored by the nourishment or stabilisation of the sand by vegetating the dunes with marram grass and placing coconut matting. The dunes provide a barrier between the land and sea, absorbing wave energy and preventing flooding and erosion. Land use management is used to protect areas such as dune regeneration sites from being trampled and destroyed by walkers, cyclists and 4x4 drivers. Wooden walkways are provided and fragile areas are fenced off to reduce vegetation loss. Creating Marshland Creating a marshland from mudflats can be encouraged by planting the appropriate vegetation, such as glassworts and mangroves. The vegetation stabilises the sediment and the stems and leaves help reduce the speed of waves, which will reduce their erosive power and how far inland the waves can reach. All this will lead to less flooding of the areas surrounding the marsh. Coastal Realignment Also known as managed retreat, it involves breaching an existing defence, allowing the sea to flood the land behind and therefore causing vegetation to colonise the land and turn it into a marshland. Sustainability Coastal management needs to be sustainable, so strategies shouldn’t cause a lot of damage to the environment or people’s lives and shouldn’t cost too much. Hard engineering is often expensive and disrupts natural processes. Soft engineering tends to be cheaper and require less time to maintain than hard engineering schemes. It is also designed to integrate with the natural environment, like creating marshland and sand dunes, which are important habitats. Overall, soft engineering is a more sustainable management strategy because it has a lower environmental impact and cost. There are two different ways of considering how to manage coasts sustainably. Shoreline Management Plans- This is where the coastline is split into stretches of sediment cells and a plan is devised for each, with the aim of protecting important sites without causing problems elsewhere in the cell. For each area within a cell, authorities can choose to hold, advance or retreat the line, or do nothing. The overall plan for each sediment cell is called the Shoreline Management Plan (SMP) and all local authorities in a cell cooperate in coming up with it. There are 22 SMPs around the UK, roughly corresponding to the 12 sediment cells. They are designed to identify the most sustainable approach to managing flood risk and coastal erosion, whilst aiming to plan for the short, mid and long term. They assess risk in a sustainable way and so the plans comply with international and national nature conservation and biodiversity legislation e.g. Spurn Head. The large-scale assessment of coastal processes aims to reduce risk to people, developments and natural environments. The Humber SMP is from Flamborough head to Gibraltar point. Integrated Coastal Zone Management- This is a process created at the 1992 Rio summit which includes using SMPs to look at how the entire coastline is managed including land, water, people and the economy in the long-term, and resolving conflicts of interest. They recognise that it is important to protect the coast because they are some of the most productive areas of the world, offering valuable habitats and ecosystems that attract humans and their beauty and richness means more than 200 million Europeans live on the coastline. It aims to protect the coastal zone in a relatively natural state, whilst allowing people to use it and develop it in different ways. This is integrated in various ways: The environment is viewed as a whole- the land and water are interdependent. Different uses are considered, like fishing, industry and tourism. Local, regional and national levels of authority all have an input into the plan An example of this includes between 2001 and 2006 when the Humber Estuary turned 66 ha of farmland into saltmarsh because 22 ha were lost due to the expansion of the port. It is a dynamic strategy- decisions are reevaluated if the environment or demands on the area change.  Holderness Case Study Holderness Coastline The Holderness coastline is 61 km long, stretching from Flamborough Head to Spurn Head and mostly made of till (‘boulder clay). The coast is exposed to powerful destructive waves from the North Sea during storms and has one of the highest coastal erosion rates in Europe at 2 m per year. There are a number of processes operating in the area: Erosion- the soft boulder clay is easily eroded by wave action and in places like Great Cowden, the rate of erosion is over 10 m/year. Mass movement- the boulder clay is also prone to slumping when wet as the water makes the clay heavier and acts as a lubricant between particles, making it unstable. Transportation- Prevailing winds from the northeast transport material southwards and create ocean currents which transport material through longshore drift. Rapid erosion means that there is always plenty of sediment to be transported. Deposition- where the ocean current meets the outflow of the Humber River, the flow becomes turbulent and sediment is deposited. Landscapes The coastal landscapes of Holderness coast vary, with the north having steep chalk cliffs, wave-cut platforms and sandy beaches, and the south having less-steep boulder clay cliffs and depositional features around Spurn Head. Headland and Wave-cut In the north, boulder clay overlies the chalk and, because the chalk is harder and less Platforms easily eroded, it has formed a headland, Flamborough Head, and wave-cut platforms near Sewerby. Flamborough head has features like stacks, caves and arches. Beaches The area south of Flamborough Head is sheltered from wind and waves, so a wide sand and pebble beach has formed near Bridlington. Sand Dunes Around Spurn Head, sediment transported by the wind is deposited, forming sand dunes. Slumping Cliffs Like in Atwick Sands, frequent slumps occur on the boulder clay cliffs, with some locations having experienced several slumps and previous movements not being eroded. This gives the cliff a tiered look. Spit Erosion and longshore drift have created a spit with a recurved end going across the mouth of the Humber Estuary called Spurn Head. Behind it, estuarine mudflats and saltmarshes have formed. Management The Holderness coast has retreated 4 km in the past 2000 years and around 30 villages have disappeared as a result. Ongoing erosion could cause social, economic and environmental problems: Settlements and livelihoods could be lost. For example, the village of Skipsea is at risk and 80,000 m ² of good quality farmland is lost each year, having a huge effect on the farmer’s livelihoods.  Infrastructure could be lost as the gas terminal at Easington is only 25 m from the cliff edge and the main coastal access road on the east coast is only 50 m from the cliff edge at Mappleton. Sites of Special Scientific Interest (SSSIs) could be lost, such as the Lagoons near Easington which provide habitats for birds. 11.4 km of the 61 km coastline is currently protected by a range of defences and strategies: Flamborough The strategy here is do nothing because the chalk headland is resistant to erosion and requires no protection. Bridlington Bridlington is protected by a 4.7 m sea wall which was recently strengthened by steel piling as well as timber groynes. The coastal town is home to 35,000 people and is largely supported by its summer tourism industry and sea-fish trade as it is the largest lobster port in Europe with over 300 tonnes of the crustaceans landed there each year. Hornsea With 8,000 residents Hornsea also has a tourism and small fishing industry to protect. It is protected by 1.86 km of concrete sea walls which have recently been upgraded to become recurved, timber groynes, rock armour, beach nourishment and gabions south of the town to protect a caravan park. Mappleton Mappleton’s 50 properties and the nearby B1242 coastal road which is only 50 m away from the cliff edge are protected by two rock groynes, a 500m long revetment and 61,500 tonnes of rock armour built in 1991 with £3.2 million of funding from the local council, UK government and EU after an economic case was made. This worked and brought the 2 m of erosion per year down to just 2 mm, but this has caused erosion rates to accelerate further south with some places losing 1 m a month to coastal erosion, farms being lost and 100 chalets being lost to erosion at Golden Sands Holiday Park. Furthermore the B1242 will eventually have to be moved anyway, especially with rising sea levels. Skipsea A landowner in Skipsea is using gabions to protect his caravan park. Withernsea There are 2.3 km of concrete seawalls costing £6 million which were recently upgraded to become recurved, timber groynes, rock armour and a small offshore rock armour reef built in the 1950s during the height of its tourism industry, but now this has gone into decline and the defences are only protecting the houses of the town’s 6,000 inhabitants. Easington Easington Gas Terminal is protected by a 1 km revetment and rock armour so as not to starve Spurn Head, an international wildlife site, and other Environmentally Sensitive Areas nearby of too much sediment. The defences were designed to hug the base of the cliff, preventing further erosion without attempting to build beach levels so sand continues to move past and damage to the SSSIs is minimal. These defences are also temporary because the gas fields are depleting and there is a general move towards renewable energy sources. Spurn Head This is a 5 km long spit stretching across the River Humber and provides a saltmarsh environment which is of international wildlife significance and lifeboat station. The eastern side of Spurn Head is protected by groynes and riprap, however, following increasing maintenance costs, the Holderness Borough Council decided in 1995 to not replace the now crumbling defences and let nature run its course, washing away the spit to leave an island, then gradually re-forming further west. This ‘do nothing’ strategy saves money and allows the spit to function naturally, but puts the marsh environments behind and a coastguard station at risk of overwashing. Challenges These existing schemes are not sustainable and create challenges: Sediment from the Holderness coast usually supplies the tidal mudflats of the Humber Estuary and the Lincolnshire coast, but schemes that reduce the down-drift movement of this sediment increases the risk of the Humber Estuary flooding, and increases erosion along the Lincolnshire coast. The protection of local areas is leading to the formation of bays which increase wave pressure on headlands and eventually the cost of maintaining the sea defences may become too high. The SMP for Holderness coast for the next 50 years is ‘holding the line’ at some settlements like Bridlington, Mappleton and Easington Gas Terminal and ‘doing nothing’ along less-populated stretches. This is unpopular among owners of land or property where there is nothing being done. Managed realignment is being suggested for certain areas, such as relocating caravan parks further inland and letting the previous location to erode. This would be more sustainable as it would allow the coast to erode naturally and not endanger businesses, but there are issues surrounding the compensation businesses will get for relocating and sometimes relocation may not be an option if there is no land for sale to relocate to. The SMP recommends to keep the Easington Gas Terminal protected by revetments for as long as it is operating, but the defence only spans 1 km in front of the terminal, so the 700 people in the village of Easington are not protected. Sundarbans Case Study Sundarbans Region The Sundarbans region is in southwest Bangladesh and east India, on the delta of the Ganges, Brahmaputra and Meghna rivers on the Bay of Bengal and covers 10,000 km². Large parts of the region are protected as a National Park or forest reserve. It is part of the largest mangrove forest in the world, a type of forest found in tropical areas where the trees are adapted to living in salt water and grow on mud flats. The land is very flat and low-lying and is intersected by thousands of channels, many containing small sandy or silty islands. It is home to many rare species of plants and animals including orchids, white-bellied sea eagles, Royal Bengal tigers and Irrawaddy dolphins. In its natural state, the coastal system is in dynamic equilibrium. Material is deposited by the rivers, allowing the growth of the mangrove forests. It is also eroded by the sea, so the size of the sediment store remains roughly the same. Tidal action is the primary natural process that shapes this distinctive coastal landscape. A dense well-developed network of interconnecting river channels flows across the clay and silt deposits and remains relatively static due to the silts and clays being quite resistant to erosion. The larger channels are generally straight and up to 2 or more kilometres wide, flowing generally north to south due to the strong tidal currents. The extensive network of interconnecting smaller channels or khals drains the land with each powerful ebb tide. Sand is washed out of the delta and deposited on banks or chars at the river mouths where the strong south-westerly monsoon winds then blow them into large ranges of sand dunes. Further deposition from wave action eventually causes the dunes to vegetate and the natural succession proceeds into its climax, a mangrove forest. Opportunities The Sundarbans region is home to more than 4 million people. The area provides a range of natural products which can be used by the people who occupy the area or sold to bring economic benefits to the region: The flat, fertile land of the river deltas is ideal for growing crops, particularly rice. The rich ecosystem of the mangrove forest provides the local population with fish, crabs, honey and nipa palm leaves used for roofing and basket-making. The mangrove forests provide timber for construction, firewood and furniture. The Sundarbans also provides services for the people who live there: The mangrove forest provides a natural defence against flooding- it acts as a barrier against rough seas and absorbs excess water in the rainy monsoon season. They also protect the area against coastal erosion as their roots bind the soil together. This makes it easier to live and grow crops. They are a breeding, nursery and fishing ground and also provide local and global climate controls as a major carbon sink whilst also regulating processes in the ecosystem and providing soil fertility. The mangrove forest furthermore provides cultural, religious, scientific, tourism and heritage values to the region. There are also opportunities for development to increase the wealth of Bangladesh as a whole. 1 hectare of mangrove forest has an annual economic value of over $12,000 because: There are opportunities for tourism because visitors will be attracted by the mangroves and wildlife. Since 2011, cargo ships transporting goods such as oil and food inland have been allowed to use the waterways. Some channels have been dredged to make passage easier for the ships. A power plant has been proposed just north of the national park, providing energy for people in the region. Challenges The location and nature of the Sundarbans create numerous risks for occupation and development: There is a lack of fresh water for drinking and irrigation in much of the area. This is because fresh water is diverted from the rivers for irrigation of agricultural land further upstream. The growing population has led to an increase in the demand for fuel, agricultural land and areas for the development of infrastructure, so the mangrove forests are being removed, increasing the risk of flooding and coastal erosion.  Flooding and higher temperatures can lead to salinisation of soil, making it harder to grow crops. The Sundarbans is home to dangerous animals that attack humans including tigers, sharks and crocodiles. There is a lack of employment and income opportunities and the region is relatively poor. Only 1/5 of households have access to mains electricity, making communication by television and radio difficult, so residents often don’t receive flood warnings. The low-lying land is at risk from rising sea levels due to global warming. Access is difficult because there are few roads and those that exist are of poor quality. This limits opportunities for development, and makes it harder for residents to receive goods, healthcare and education. Management People can respond to risks through resilience, mitigation and adaptation. Resilience Resilience means being able to cope with the challenges the environment presents and there are attempts to increase the population’s resilience: The Public Health Engineering Department is increasing access to clean water and sanitation. This will improve health and quality of life. Better roads and bridges are being built in the region to increase access for residents and visitors, but this can lead to deforestation and other environmental damage. Mains electricity is being extended to more areas and subsidised solar panels are being made available to remote villages so they can generate their own power. This will make it easier for flood warnings to reach communities and could create employment opportunities. There are efforts to decrease poverty and increase food security in the region, for example by providing farming subsidies to increase food production and provide jobs. However there is a risk that some areas of land may be farmed too intensively, causing environmental damage. Mitigation Mitigation means reducing the severity of hazards and other problems, for example: 3,500 km of embankments were built to prevent flooding. However, the embankments are gradually being eroded, and around 800 km are vulnerable to being breached during storms and tsunamis. Coastal management projects aim to protect existing mangrove forests and replant areas that have been removed to protect against flooding and erosion. However, it is difficult to prevent illegal forest clearance throughout the whole region, and it is unclear whether the mangroves will withstand sea level rise. There are attempts to mitigate the impacts of extreme events e.g. cyclones. For example, the government and NGOs have provided funding for cyclone shelters and early warning systems, which should help people shelter or evacuate. However, many people may not have transport available to enable them to evacuate quickly. Grassroots NGOs run education programmes to encourage farmers to return to more traditional ecologically-friendly methods. Adaptation Adaptation means adjusting behaviour to fit the environment. As the environment in the Sundarbans changes due to climate change and sea level rise, people will need to adapt to it to reduce risks and increase benefits, for example: In some areas, salt-resistant varieties of rice are being grown which could help residents cope with flooding and sea level rise. However, relying on a smaller range of crops can reduce biodiversity and may increase vulnerability to pests and diseases. Projects are underway to increase tourism to the area, providing jobs and income. For example, lodges have been built and tour operators run boat trips on the rivers. However, if not properly  managed, tourism can cause environmental damage. People can adapt to sea level rise or flooding by building houses on stilts. However, infrastructure such as roads cannot be protected as easily. Sustainable adaptations such as using non-intensive farming practices and promoting ecotourism, will help ensure that the fragile environment remains relatively undamaged and usable for future generations. USAID trains communities to become resilient to future climate shocks. 30,000 people have received training on improving agricultural techniques.