Coastal Environments PDF

Coastal Erosion and Weathering - Onshore is when it is happening on land and offshore is when it is happening in the ocean or off land - Erosion is the wearing away of rock along the coastline, erosion removes material by a moving force such as running water/waves. There are fo...

Coastal Erosion and Weathering - Onshore is when it is happening on land and offshore is when it is happening in the ocean or off land - Erosion is the wearing away of rock along the coastline, erosion removes material by a moving force such as running water/waves. There are four types of erosion hydraulic action, abrasion (also known as corrasion), attrition and solution (also known as corrosion) Hydraulic action Abrasion Attrition Solution Powerful waves lash The sea hurls The knocking The dissolving of the cliffs, forcing air pebbles and sand together of pebbles, rocks such as into tiny cracks. The against the base of making them limestone and chalk pressure of the the cliff, chipping and gradually smaller and and the transport of compressed air grinding it down smoother dissolved chemicals weakens the rock and forces it to break up - Weathering: Weathering is the breakdown and decay of rocks by natural processes without any involvement of any moving force Biological Chemical Physical/mechanical The weakening and wearing The breakdown of rocks When rocks are broken down away of rock by plants, because of the interaction of by physical factors in the animals and microbes. air, water or acid with the environment, such as wind, chemical composition of the water, and temperature rock. change. Eg freeze thaw and onion skin weathering  - Freeze thaw weathering is when water enters the crack of a rock. The water freezes causing the rock to expand and the crack to widen. Through the repeat of this process, the crack expands until the whole rock breaks in half. Wave action, LSD, and deposition - Waves erode, transport and deposit materials. Waves are created by the winds as they blow over the surface of the sea. It is friction between the wind and the water that sets waves in motion. The strength of the wave depends on the strength of the wind. There are two types of waves – constructive and destructive. Characteristic Constructive wave Destructive wave Swash strong weak Backwash weak strong Frequency (breaking on 8-10 per minute 10-14 per minute coast) Height Low wave height (under Wave height over 1m 1m) Wave length (gaps long short between waves) Beach gradient flat/smooth steep Erosional or depositional Depositional Erosional - Longshore drift: the transport of sediment along a stretch of coastline caused by waves approaching the beach at an angle The transport of sand and pebbles along the coast is called longshore drift. The prevailing winds (the direction the wind usually blows from) causes waves to approach the coast at an angle. The swash carries sand and pebbles up the beach at the same angle. The backwash, however, carries the material back down the beach at right angles as this is the steepest gradient. If a pebble was placed in the water it would be carried along the coastline in a zig-zag motion and would eventually be deposited when the waves lose energy.  - When the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves. - Deposition is likely to occur when: - waves enter an area of shallow water - waves enter a sheltered area, e.g.: a cove or bay - there is little wind - there is a good supply of material Mass movement Mass movement: the downhill movement of material under the influence of gravity. There are four different types of mass movement: rockfall, mudflow, landslide and rotational slip. - The type of mass movement depends on lithology - unconsolidated material (like boulder clay) - slumping - consolidated rock (like carboniferous limestone and granite) - sliding Rockfall - Rockfall is a form of mass movement or mass wasting in which pieces of rock travel downward through some combination of falling, bouncing, and rolling after they are initially separated from the slope. - Typically occurs when mechanical weathering (freeze-thaw) occurs dislodging aspects of the cliff face or due to erosional processes Mudflow - Mudflows occur on very steep slopes, where there is limited vegetation to bind the soil together and the ground is saturated. Heavy rain can produce sheet flow  over the upper cliff surface. The soil continues to be lubricated and it eventually flows over the cliff face and down onto the shore at a fast speed. - Typically occurs when there has been heavy rainfall Landslide - A landslide is the downslope movement of discrete blocks of rock down a flat/linear slip plane, maintaining contact with the cliff surface throughout. Gravity pulls the discrete/loosened block down the relatively flat slip plane of the joint or bedding plane, to the cliff foot - Typically occurs due to heavy rain, mechanical weathering, erosional processes Rotational Slip - Rotational slumping involves rock failure and movement along a curved rock plane. The slumping material usually moves intact as a single mass, without any internal deformation of material. It's slower than rockfall, often occurring in 'slow motion', and may take minutes, hours, days, or even years to occur. - Occurs when there are weak rocks (clays/shale), unconsolidated materials, complex geology  What factors can affect coastal environments? Geology and Rock type: Soft rock: sandstone, clay Hard rock: Granite - Difference: soft rock is much easier eroded than hard rock and valleys form more easily in softer rocks. Hard rocks would form cliffs - A bay is made where soft rock is found and a headland is made where hard rock is found Feature Hard rocks Soft rocks Shape of cliffs High and steep Lower and less steep Cliff face Bare rock and rugged Smoother; evidence of slumping Foot of cliff Boulders and rocks Few rocks; some sand and mud Vegetation: all plants and trees collectively, typically those in a specific region - The longer a coastline landform has existed, the greater the chances that it will be colonized with vegetation - Vegetation needs specific conditions in order to cope, such as high levels of salt in the air and soil. People:  - Settlement: coastal lowlands have attracted people and their settlements worldwide. Many of the most densely populated areas are located on the coast - Economic development: people have taken advantage of the economic opportunities that the coast offers, such as land for agriculture and industry, fishing and the chances to trade either along the coast or oversea have led to the building of ports and harbors and the coast is used for tourism - Coastal management: for many centuries, people have tried to control the coastline. For example, building seawalls and groins to help protect stretches of coastline from high rates or erosion or deposition. Because of human activity in the coast, coasts can be greatly changed and sometimes the actual shape of the coastline is altered. Sea level rise: - A rising sea level leads to a submerged coastline. The main features are rias (drowned river valleys) and fjords (drowned glacial valleys) - An emerging coastline is associated with a falling sea level, the most common landforms found in these areas are raised beaches. These areas of wave-cut platform and their beaches are now found higher than the present sea level. Erosional landforms Headland: a lump of hard rock that is sticking out because it erodes slower than its surroundings Bay: A low lying inlet of land on the coast. It is an inlet of the sea where the land curves inwards, usually with a beach Concordant: only one type of geology faces the sea so this is the only layer which gets eroded. This does not create bays or headlands Discordant: All types of geology are at right angles to the water. This means all the rock types are unable to be eroded at the same time (the rate of erosion for each type of geology may be different eg. clay eroded quicker than chalk). Creates bays and headlands How are bays and headlands formed 1) A coastline faces the wave attack with discordant beds of sediment 2) Wave attack causes hydraulic action and attrition which causes the cliff to retreat 3) Less resistant rocks are eroded at a faster rate to create bays, more resistant rocks stick out to sea as headlands 4) During calm periods the sheltered bays allow deposition of beaches Landforms created by erosion A - fault line B - cave C - arch D - stack E - stump 1) The sea will erode at weaknesses/faults/cracks in a headland using hydraulic action and abrasion. This is when air in cracks is trapped by breaking waves and where pebbles grind/are thrown at the headland. This pressure causes small pieces of rock in the crack to break off. 2) Over time, the faults become larger to form a cave. This will be happening on both sides of the headland. 3) Eventually the backs of the caves meet forming an arch. The bottom of the arch is undercut by erosion and weathering occurs on the bare cliff face. The arch grows wider and taller until it collapses under its own weight and the pull of gravity. This leaves behind a column of rock not attached to the cliff, known as a stack. 4) Continued wave erosion at the base of the stack makes it top heavy and eventually it topples over leaving a stump that is only visible at low tide. Wave cut notch and platforms - Wave cut notch: The point of maximum impact of destructive waves at the base of a cliff creating an indentation at the base of the cliff between the high and low tide mark - Wave cut platform: a gently sloping rock ledge that extends from the high-tide level at the steep-cliff base to below the low-tide level.  Depositional landforms - Deposition: where sediment is put down Depositional Photograph Diagram Explanation of how this landform is Located feature created example of this feature Beach Tides and currents affect the way beaches are formed. They are created when waves deposit sand, gravel and other sediment along the shoreline and held in suspension and accumulate over time. Constructive waves are mandatory since they have a stronger wash than backwash. A relatively sheltered environment is also needed, such as a  bay or cove, as it promotes the formation of a beach Makena Beach, Maui - Hawaii Spit Spits occur when there is a change in the shape of the landscape or there is a river mouth or estuary. This is how spits are formed: Sediment is carried by longshore drift. When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit. Spurn head, The Holderness coast, Humberside Bar When a spit develops in a bay it may build across it and link the two headlands to form a bar. The water damned by the bar is called a lagoon- this will gradually be filled due to deposition. Slapton Sands, in Devon Tombolo Tombolos are spits that have continued to grow seawards until they reach and join an island. This is how a tombolo is created. Adams Bridge south india to sri lanka Sand dune Some of the sand is blown to the back of the beach by the onshore wind. The sand accumulates there often around an obstacle, often a piece of driftwood or dry seaweed. It keeps growing bigger and stable. Eventually more dunes start forming in front of the original dune seaward. This leads to a series of dunes being formed. Sahara desert When deposition occurs - Waves enter an area of shallow water (constructive waves) - Waves enter a sheltered area, e.g: a cove or bay - There is a little wind - There is a good supply of material - Beaches are there due to the deposition of rocks The formation of beaches - Beaches are made up from eroded material that has been transported from elsewhere and then deposited by the sea. For this to occur, waves must have limited energy, so beaches often form in sheltered areas like bays. Constructive waves build up beaches as they have a strong swash and a weak backwash. Exam practice 1) Identify one depositional landform Spit 2) Explain the formation of a spit It develops when there is a sudden change in the shape of a coastline like a headland. Longshore drift deposits material away from the coastline and continues depositing in the same direction, causing the spit to grow. 3) State one feature of a sand dune A range of vegetation 4) Explain the process of beach formation  Beaches are made up from eroded material that has been transported from elsewhere and then deposited by the sea. For this to occur, waves must have limited energy and are hence constructive waves which are suitable to build up beaches as they have a strong swash and a weak backwash which allows them to deposit a large amount of material. Coral Reefs Distribution - Wide spread - Many near the tropics of cancer and capricorn - A small amount are located outside the tropics - The highest concentration is found in the pacific ocean followed by the Caribbean sea - The rest lay within the center of the map Factors that influence distribution Temperature: coral growth needs a minimum water temperature of 18 degrees celsius, they grow best between 23 and 25 degrees celsius. This means they can only grow around the tropics due to the suitable temperatures there Light: needed for the coral to grow; because of this, corals only grow in shallow waters Water depth: because of the need for light, most reefs grow where the sea is less than 25m deep Wave action: corals need well oxygenated saltwater; this occurs in areas of strong wave action, like the tropics Salinity: since corals are marine creatures, they can only survive in salt water Exposure to air: corals need oxygenated water, but if they are exposed to air for too long they die Sediment: corals need clear, clean water; any sediment in the water blocks their normal ways of feeding and reduces the amount of light - Polip’s create a coral by creating an ex-skeleton around themselves to protect themselves  - Algae photosynthesis to create the color of the coral. If there is a change in pH, temperature, or someone touches it the algae gets stressed and expels its color - Global warming is the biggest threat towards coral reefs - Coral can also act as a coastal protection as they take out energy from waves Why are coral reefs important - Biodiversity: e.g the Great barrier reef has 700 species of coral and 1500 species of fish - Protection to low lying countries from tropical storms - Rich fish stocks: provides food for many LEDC’s - Tourism: snorkeling + scuba diving - attracts over 150 millions people each year Threats to coral reefs - Pollution - Coral bleaching - Coastal development - Fishing industries - Mining of coral reefs - Commercial farming - Tourism Coral bleaching: can kill coral or leave them vulnerable to other threats such as infectious disease Mangroves - Mangrove swamps: areas of sheltered vegetation found along sheltered coastlines and estuaries where there is a large area between high and low water mark  - Mangroves are made up of different species of evergreen mangrove trees and other plants - Halophytes: live in salty water and have adapted to learn to cope with salty conditions - Mangroves are found at coasts Location - Mainly by the coastline - Anomalies that some are located in between oceans by Australia - Most are located in the southern hemisphere, specifically South East Asia - The least amount are located in the northern hemisphere - They are found in warm areas as they need warm tropical oceans - Occur worldwide covering 60-65% of tropical and subtropical coastlines (globally they cover 138,000km in 118 countries - Between 32 degrees north and 38 degrees south of the equator - Found along sheltered tropical coastlines and estuaries (intertidal zones) - 5 countries with the largest quantity of mangroves: indonesia, brazil, australia, nigeria and mexico - The largest concentration are in southeast asia Factors that affect growth - They grow in the intertidal zone found along shallow coastlines They are regularly flooded by the sea. At low tide, especially during periods of high rainfall, there may be floods of fresh water. This quickly alters the sea levels as well as temperatures - Anaerobic (low oxygen) conditions Because it is regularly flooded, it needs to be able to deal with anaerobic conditions - Salty water  Mangroves are halophytes so they can cope in salty water - Temperature above 20 degrees Mangroves only survive in high temperature - Calm waters Waves or tides could wash them away Adaptations - Salt intake: filtering out as much as 90% of the salt found in seawater as it enters their roots using their complex salt filtration system and complex root structure that can cope with being immersed in salt-water. This allows mangrove trees to be halophytes - Anaerobic conditions: have specialized root structures that allow them to live in oxygen-poor sediments - Water loss: a waxy coating on the leaves of some mangrove species seals in water and minimizes evaporation - Survival of offspring/seeds: mangrove seeds begin growing while still attached to the parent plant Benefits - Can create a nursery for fish and protect biodiversity - Mangroves are an area of extreme biodiversity - They bring money from tourism - Areas of settlement - Is an economic resource: wood - They are a form of coastal protection - they can lower the energy of waves, protecting land from erosion Threats:  - 3% - herbicides: an insect killer - 5% - land reclamation: taking away lang e.g putting barriers and creating new land - 11% - diversion of fresh water: fish farming at mangroves - Deforestation - 38% - shrimp agriculture: demand for shrimp to eat Mangroves case study: UAE Biotic characteristics - Plants: there are forests containing shrubs and small trees. They are salt tolerant trees known as halophytes - Wildlife: 6 different families of crabs , 49 molluscs birds, Heron fish, shrimps, turtles, ea snakes Land: 155 square kilometers of the UAE’s coastline are covered with mangroves Benefits of mangroves to the UAE - Provides habitats for wildlife (marine and terrestrial species) - Encourages biodiversity - Part of the cultural identity of the UAE - Conserves fish stock - Provides recreation grounds for humans - Reduces the harmful greenhouse gasses which cause climate change (absorbs 41 million tonnes of carbon) - Protect coastal areas from erosion by creating a buffer zone, filtering and pacifying tidal flow, reduces the damage and loss of lives caused by tsunamis - Potentially could cure diseases  - Promotes to tourism, bringing in more money into the country Threats to the mangroves of the UAE: - Urban expansion - Limited freshwater resources - Pollution - Physical damage from humans - Climate change - Sea levels rising - Natural disasters - Shrimp aquaculture - Charcoal farming Sustainable projects - “National carbon sequestration project” will plant 100 million mangroves in the UAE by 2030 - The mangrove national park - mangrove forests in the UAE are very important for nesting birds. They help prevent erosion of the shoreline and are a rich source of food for many species of animals and insects Salt marshes - Salt marshes are coastal wetlands that are flooded and drained by salt water brought in by the tides - They are marshy because the soil may be decomposed of deep mud and peat - Peat is made up of decomposing plant matter that is often several feet thick - Peat is waterlogged, root-filled, and very spongy - Salt marshes are formed behind spits Where do we find them - Between mudflats that are permanently submerged by water and land (terrestrial) vegetation lying above the high tide mark - In the intertidal zone - Develop in locations sheltered from the open sea, eg. heads of bays and estuaries (the end of a river) What determines the type of animals and plants found here - Salinity - The frequency of flooding of the march - Water Depth - shallow water allows deposition which is needed to stabilize vegetation - Coastal position determines where we find salt marshes, salt marshes are found in sheltered areas of the coastline where there are large amounts of deposition of material due to low energy waves Sustainable management of the coastline - The blue line separates land and sea 1) We can view the coast as a system. The things that enter the system are called inputs such as sediment brought in by the waves or weathering. 2) They are then stored in the system as beaches/sand dunes etc. 3) Processes and transfers will happen within the system – such as the movement of sediment along the beach by longshore drift. 4) Eventually the sediment will leave the system as an output where it may be lost to the open sea. 5) When there is a balance between inputs and outputs, the system is said to be in equilibrium 6) Natural changes can sometimes upset this e.g. a storm could affect the sediment. 7) But more often it is human activity that changes and damages coastal ecosystems - A system is in equilibrium when its inputs match its outputs; this would be when sediment entering the system is the same as sediment leaving the system. - Sediment may be brought into the system by erosion or weathering, it may be transferred in the system by longshore drift, and it may leave the system as an output by being lost to the sea - Equilibriums can sometimes be upset by natural processes such as storms or activities by humans - People using the coastline are known as stakeholders  - Stakeholders of the coast: - Farmers - RTA (traffic management) - transport - Developers - Fisherman - Local residents Farmers: want land and shelter from prevailing winds RTA: want good road networks, well-connected ports and terminal Tourists: want beaches and hotels, entertainment Developers: want areas by the sea for tourists - hotels, duplexes, golf courses Fisherman: want harbor, unpolluted waters, ease of access to the sea Local residents: want jobs, clean beaches, affordable housing, schools UAE example Tourists vs local residents: local residents in Jumeirah may want to use the beach for leisure purposes like walking or swimming, whereas tourists occupy the space in which local residents use for leisure. Also development V conservation is a common issue in the UAE Offshore development Onshore development oil Tourism fishing Property development Artificial islands Management clearance Damage to coral reefs Coastal flooding Causes and prevention - Coastal flooding is a sudden and abrupt inundation of a coastal environment caused by a short-term increase in water level. Coastal flooding is generally a natural process and constitutes an important part of the natural coastal dynamics. Cause of coastal flooding How/why Storms surge The storms produce strong winds that push together the water into shore, leading to flooding Rising sea levels Sea level rise is increasing global temperatures, which heat seas and cause thermal expansion of water Tsunami A tsunamis long wavelength provides more momentum for flooding, so tsunamis travel far Low lying reclaimed land A small rise in sea level from a mild storm surge is enough to flood it and cause extensive damage - Prediction: forecasting future events or changes - Prevention: the action of stopping something from happening Prediction involves: This is achieved by: Historic records Looking back at historic records and identifying those areas that have been flooded most often and most seriously ie. defining the high risk areas Forecasting hazard events Forecasting hazard events should not only say when and where the event will occur, but also predict its scale and strength and the likelihood of damage and death Prevention involves: This is achieved by: Building flood defenses Building flood defenses along those stretches of the coast at most risk  Building emergency Building emergency centers where people can be safe from the flooding centers Restricting activity in high Removing housing and restricting activity in high risk areas risk areas Planning new Planning new development that avoids high-risk areas and designing new developments buildings able to cope with low levels of flooding Installing advanced Installing advanced warning systems of possible flooding; clearly this depends warning systems on forecasting Educating local people Educating local people on what to do once warning systems have been activated Methods to protect the coastline - SMP - shoreline management plan - Strategies put into place are specific to that location e.g sediment cells around the U.K Hard engineering Soft engineering Aims to protect the coast from erosion and Aims to make use of elements of the coastal the risk of flooding by working against the systems such as beaches, sand dunes and power of the waves and altering/preventing salt marshes to work with natural processes natural processes. Hard engineering: Diagram / Describe Describe how it photo of what it Advantages Disadvantages works method consists of Recurved - Waves are Sea walls - Effective at still powerful protecting and can the base of break down Concrete walls the cliff. and erode that are placed They are curved to - Sea walls the sea wall. at the foot of a reflect the energy usually have cliff to prevent back into the sea. promenades erosion. - Expensive - so people approximatel can walk y £2,000 per along them. meter. Groynes - By trapping (wood or - Builds a sediment it steel) beach - starves which beaches encourages further down tourism. the Wooden or Wooden or rock coastline, rock structures structures built out - They trap increasing at 90 degree at right angles into angles the sea. sediment rates of being carried erosion by longshore elsewhere. drift. - They look unattractive. Rip-rap (also - They look called rock different to armor) the local - Cheaper geology, as Large boulders than a sea the rock has placed at the foot wall and been Large of a cliff. They easy to imported boulders break the waves maintain. from other placed at the and absorb their foot of a cliff. areas. energy. - Can be used for fishing. - The rocks are expensive to transport.  Revetments - reduces the (wooden) - Strong The height of the power of the waves can Concrete, revetments is waves, stone, or wood damage the designed to protect reducing the planks laid structure against erosion. It rate of against wooden absorbs wave erosion - Locals may frames energy to protect find it the land behind. - Low unattractive maintenance Gabions - Reduces erosion - Not very These rocks are Rocks that are strong placed in areas placed in - Cheap affected by erosion metal cages - Looks to prevent erosion - Also absorbs unnatural wave energy Offshore breakwaters - Very Breaks waves and effective at A structure reduces the wave protecting parallel to the - unattractive energy reaching the coastline shore the beach in the short run Soft engineering: Diagram / Describe what it Describe how it photo of Advantages Disadvantages consists of works method Beach - Can protect the - Long replenishment public and process (also known as Sand is pumped private meaning nourishment) Sand that is onto an existing structures constantly pumped onto a beach to build it up behind the disturbing beach in order to absorb beach the the wave energy ecosystem - It encourages vegetation - Ongoing  growth process so higher - A larger beach costs over encourages time more tourism Managed A coastal retreat management strategy that allows - Cheap the shoreline to - Land is lost move inland, - Creates a salt Structural as it is instead of marsh which engineering reclaimed attempting to hold can provide a by the sea the line with habitat for structural wildlife engineering Cliff regrading - local when the cliff is homes are - Cliff becomes being regarded, required to more stable part or the cliff has move so A cliff at a certain to be turned that they angle - Less prone to away in order for can reduce unexpected the angle of the din the movement to be reduced. gradient there Building bars - The high tensile strength Elongated, partially of the TMT submerged bed bards allow - Higher structures with a Elongated, partially them to absorb chance for length typically a submerged bed and distribute TMT bars few orders of structure stress to deter magnitude larger effectively corrosion than the water preventing depth structural damage Fencing, - Preserves hedging and beach by replanting reducing the - Sprinkler vegetation amount of sand Replanting Replanting systems being blown vegetation vegetation are inland expensive - Aesthetically pleasing/natura  l looking Coastal management in a developing country case study: Coastal management in an emerging country case study Sri Lanka: Sri Lanka Case Study Sheet