GEOGRAPHY NOTES - COASTS 2020 AREAS TO LOOK AT 1 DEFINITION OF TERMS 2.PROCESSESES AND RESULTING LANDFORMS IN COASTS 3.WAVES 4.MANAGEMENT OF COASTS 5.OPPORTUNITIES AND HAZARDS IN COASTLINES 6.CASE STUDY ON COASTS The coast is also known as the coastline. The coast is the border between the land and the sea.It is the most varied and rapidly changing of all landforms and ecosystem.It includes sand dunes/seas, the shore and cliffs. It is imperative to note that coasts are one of the most important ecosystems in the world but also yet very fragile due to anthropogenic and anthropological factors (Environmental and human factors). THE IMPORTANCE OF COASTLINES(BENEFITS /OPPORTUNITIES OF) - For tourism -due to many resort areas at coastlines tourists often enjoy to visit these places bringinging in foreign currency(Sunbathing , swimming etc) -Beach sports can take place like ,beach volleyball , sailing ,surfing ,kite surfing ,cliff diving and many others thereby entertaining people and revenue collection. -Oil and gas reserves. Most of the worlds gas and oil is found under oceans and these are used for a variety of uses and are important energy sources for people -fishing -these coastlines are full of fish which a lot of people make a living out of this business (though under threat) including aquafarming aquaculture-seafood farming also take place at oceans -Varied ecosystem- A Variety of plants and animals exist in the coasts like mangroves ,sand dunes ,lagoons and estuaries all provide food and beauty to the ecosystem making it valuable. -These coasts provide employment to millions of people due to various activities taking place there. -Transport –coasts allow transportation of goods and services to take place thereby promoting trade and improve GDP and GNP amongst countries -Industries – many industries prefer to locate at the coasts because it’s easy to trade and for reducing transport costs. -Housing – peple prefer to live close to the coastline because of the beautiful scenic views and the luxurious life style together with a peaceful life presumed there. -Walkers –people enjoy riding , walking and cycling on the coast thereby giving value to the coasts. -Waves are used for generation of electricity HAZARDS OR DANGERS OF COASTLINES AND THREATS -Sea level rises due to global warming. Low lying areas such as Bangladesh will be affected by considerable flooding because water in the ocean will have increased due to icebergs melting due to climate change for example(influx of global temperatures) -Pollution –large industries discharge their effluent sewage in oceans thereby polluting it and putting aquatic life in danger, also accidents like the BP oil spill in the Gulf of Mexico could be tangible examples. - Litter thrown into oceans by people when they visit beaches or coastlines can also be very harmful to animals. Turtles for example often confuse plastics to jellyfish and the results are usually devastating to these innocent species. -Fishing. Many fish stocks are being overfished for business and this is resulting in some type of fish becoming extinct or getting to very low levels in the oceans. -Tropical storms. Due to rampant rising sea levels frequency and magnitude of storms are at a rise resulting in severe flooding ,storm surges and wind damage. -Erosion. Many coastlines are being eroded by stronger storms and also rising sea levels. -Privatisation . More stretches of the beach are now privately owned as houses , hotels etc making it difficult for locals for example to have access to them and the land there becoming very costly and difficult to acquire. -Beach sports cause noise pollution which would otherwise disturb aquatic life and swimming on the other hand can attract dangerous animals like deadly white sharks which can kill people. -The coastlines are the first to be affected by large seismic waves (tsunamis) if the plates are triggered. Making it deadly to build houses or Hotels. Many processes occur along coastlines , either on the land or in the sea and some unnatural features are constructed to cope with the effects of these processes , such as groynes or sea walls. WAVES Waves are formed because of the friction between the wind and the sea. Tsunamis in this case are exceptions. When waves near the coast , the bottom of the wave is slowed down by friction with the sea bed. Therefore the top of the waves will be experiencing less friction it travels faster and eventually topples over the bottom of the wave and it breaks.This is the point where the swash begins. The swash transfers energy forwards or up the beach. The backwash on the other hand returns energy down the beach. The size of the wave is affected by 3 factors: 1.Duration of wind 2. Strength of wind and the 3.Fetch (the maximum distance that the wave travels) Waves that result from local winds often travel only short distances areas are known as sea waves whereas those waves formed by distant storms and travelling large distances are referred to as swell waves. WAVE TERMINOLOGY The crest -highest point of the wave The trough - Lowest point of the wave Wave height (H) –Distance between the crest and trough –rarely exceeds 6m Wave length – distance between two crests and two troughs Wave frequency/wave period(T) - The number of waves per minute Wave velocity - the speed that a wave is travelling at a given time is usually influenced by the wind , fetch and depth of the water. Wave steepness(H/L) is the ratio of the wave height to the wave length cannot exceed 1:7 because at that point the wave will break. Energy (E) E is proportional to LH squared so this means even a slight increase in wave height can generate large increases in energy it is estimated that the average pressure of a wave in winter is 11 tonnes per square metre but this can be 3 times greater during a storm.This wave power is potential to sources of renewable power (wave power and tidal power) DIAGRAM WAVE FRACTION This occurs when a wave approaches the shore it behaves in a different manner. As waves reach shallower water the bottom of the waves experience greater friction with the sea bed causing the waves to slow down. This whole process helps disperse energy across the whole Bay. Distinguish headland from Bay. Types of Waves 1. Constructive waves - Constructive waves have a stronger swash and a much weaker backwash so they tend to deposit a lot of material and build beaches up. In other words the words are low and flat and cause sediments to build up on the Beach increasing length of beach. 2. Destructive waves - these have a fairly weak swash and the backwash is stronger. Due to this scenario destructive waves erode and transport material away from the beach. They remove sediments from beach and are more common when the fetch is short but beach angle steep. COASTAL EROSION Often known as marine erosion and mainly noticed on cliffs –generally the wearing away of material on cliffs. A cliff is generally any steep rock face adjoining the coast. Type of cliff depends on the nature of the rock and its resistance to erosion , there are vertical cliffs and gently sloping cliffs. The coastline in UK the Holderness coast is one good example of a coast suffering from erosion. The coastline is receding by an average of 2 metres per year under the relentless attack from the waves from the north and north – east. Cliffs will normally erode in the following ways : 1.Hydraulic action (pressure) – this takes place when seawater and air get trapped in cracks. The increasing pressure of the water and air cause the rocks to crack. 2.Abrasion(corrasion)- the most effective method of coastal erosion whereby cliffs are being worn away by boulders ,pebbles, and sand being hurled against them. More pronounced in stormy conditions. 3.Attrition – is where rocks and boulders already eroded from the cliffs are hurled against the shore and against each other by the breaking waves reducing them in size and transforming in shape. 4. Solution (corrosion) –the sea water dissolves the calcium carbonate in the rocks and weakens them especially in limestone and chalk coasts. 5.Wave pounding – This is the immense power of waves crashing into cliffs causing them to weaken and break off. 6. Sub aerial weathering –this is the top of the cliffs being attacked by the weather making the cliffs weaker and less stable. Agents like wind , rain, heat and cold weather can cause the cliffs to be weathered. RESULTANT EROSIONAL LANDFORMS WAVE- CUT NOTCH Continual wave attack at the foot of a cliff results in gradual undercutting of the cliff to create a wave - cut notch (basically an eroded hole at the base of the cliff). As the wave- cut notch gets bigger the weight of the rock above the notch gets greater , eventually the cliff cannot support its own weight and it eventually collapses. The process then starts again with the erosion of the sea making a new wave –cut notch. As the process continues the cliff starts to move backwards(retreat) In line with the Davisian cycle of erosion that of Parallel retreat. Due to the fact that the cliff is moving backwards a wave cut- platform (an expanse of bare rock) is created. Wave cut platforms are visible at low tides. Headlands and Bays The shape of the coastline results from erosion of different types of rock usually a band of hard and soft rock. A bay is an indented area of land normally found between two headlands. Bays have been formed where weaker , exposed rocks have been eroded at the coast. Headland is a piece of land that sticks out in the sea. More resistant rocks remain as outcrops. They experience a lot of erosion forming features like arches and stacks. NB. Coastlines with the rock structure running at right angles to the coast is known as discordant whereas those where the rock outcrops runs parallel are concordant coastlines, DIAGRAMS MORE EROSIONAL LANDFORMS CAVES ,ARCHES,STACKS AND STUMPS These landforms are usually found on Headland , where wave fraction is causing erosion on all 3 sides.The waves always look for weakneses in the headland like joints and cracks. Once they find a weakness they will start attacking that weakness.Hydraulic pressure is usually the main type of erosion taking place and overtime the crackmay turn into a large hole known as a cave. Slowly the cave will become bigger and bigger and cut all the way through the headland creating an arch.Waves will continue to erode the foot of the arch until its roof becomes too heavy to be supported leaving what is known as a stack (an isolated portion of a cliff).In time further wave action will result in the stack collapsing leaving a stump. DIAGRAMS TRANSPORTATION PROCESSES IN COASTAL REGIONS Although waves do carry materials through swash and backwash down a beach the major movement is along the coast by a process called Longshore drift – the movement of materials along a coastline through waves. The effect of longshore drift can be seen when wooden groynes have been built to prevent material from being moved along the beach. Material is slowly moved along the coast in a zig - zag course. Swash and Backwash are therefore part of transportation processes. Saltation- the wind can also transport sand and small pebbles and they bounce against each other across a beach. DEPOSITIONAL LANDFORMS IN COASTAL AREAS Deposition in coasts takes place when materials being transported by longshore drift will in time reach an area where the water is sheltered and the waves lack energy .The material may be temporarily deposited to form a beach .Beaches are not permanent features as their shape can be altered by waves every time the tide comes in and goes out. Spits ,bars and tombolos are all made by a combination of longshore drift and deposition. There are collectively known as depositional landforms. SPITS – this is a long , narrow accumulation of sand , with one end attached to the land and the other projecting at a narrow angle either into the sea or across a river estuary. Spits are formed in areas of calmer water where the sea has less energy. There are normally found near the mouths of rivers where coastline changes direction creating some protection. If the sea has less energy material is deposited instead of it being transported. If deposition is greater than erosion , then overtime a spit will build up. Its shape is usually considered by the wind movement. Spits become permanent when sand is blown up the beach , by the prevailing wind to form sand dunes. Salt marsh is likely to develop in the sheltered water behind the spit. The spit is unable to grow across the estuary as the river current carries the material out to sea. Should there be no river the spit may grow across the bay to form a bar. A bar is therefore , a spit that connects two headlands or runs across the face of a bay. Behind the bar is usually the Lagoon which is a salt water lake and overtime the lagoon will become smaller as deposition takes place. Behind the spit is also the Salt marsh – that is a low energy intertidal ecosystem usually characterised with some salt resistant vegetation. A tombolo on the other hand is a pit that joins the mainland with an island. An island is a small body of land found in oceans and seas. Mainland is the main land mass of an area which differs in size from one mainland to the other. Tides are the twice daily ,movement of the sea in and out. Tides are constant are caused by the gravitational pull of the moon. Tidal ranges often differ in length. Explain sea – level changes and their effects. DIAGRAMS ON DEPOSITIONAL LANDFORMS COASTAL MANAGEMENT Coastal management is the protection of the coastline and its wildlife , the improvement in the quality of life of local residents and the provision of recreational facilities for visitors. Coastlines as mentioned before are often experiencing changes through natural processes of climate , mass movement , waves and the tides also human intervention and activities. These threats therefore ,require sustainable national management plan. There is need to have contingence plan on rising global sea levels ,having sea defences and maintaining the existing ones and above all protect people and their property. CASE STUDY ON COASTAL MANAGEMENT CHESIL BEACH –PORTLAND –BRITAIN Chesil beach has flooded many times the first being in November 1824 where 26 people died and 8o houses were destroyed in a devastating storm. Coastal protection and sea defence works were first taken since 1969 and these have been constantly been improved. Human activities has excavated beach material for commercial activities .The beach is a feature of international significance where a lot of people in Britain and across the world come to visit. Other serious floods came in 1979 when Chesil was overwhelmed by constructive waves attacking the shore at 18 second intervals .Flooding allowed to break over the top of the beach and on to Chioswell settlement below.Portland was temporarily cut off from the mainland because of the overtopping waves EFFECTS -30 Chiswell properties were destroyed -water , gas and electricity supply were cut -emergency services were needed for ten days -also families were evacuated as they were left homeless This flood alerted all stakeholders that something significant had to be done. On 14 February 1979 a firm of consultant engineers were contracted to do the job of reducing thye flooding hazard at Chesil Beach .the engineers produced a flood control system known as The Chesil Defence Sea Scheme with a total cost of 3 million pounds.The system was built in 4 main stages Stage 1 – 1981 A Gabion matress 150m in length and 14.5 metres in height was constructed. The matress strenghthened the crest of the beach , reducing the effects of erosion from the constructive and destructive waves .This control was expected to last 20 yrs. Stage 2 – 1983 300m sea wall constructed 30 yrs back was modified -easy access was provided to pedestrians -ramps were created for disabled persons -access also took into account the needs of the local fisherman Stage 3 -1985-86 Was the most expensive part of the construction at 2.5 million pounds. -It was to reduce the amount of sea water percolating into Chiswell. A large drain with openings was built in times of floods water emerges from the drains and flows Northwards along an open ditch towards Portland Harbour. Stage 4 –June 1987 The A354 road was raised above the level of the December 1978 flood. Success of the Scheme There was a storm on 16 December 1989 The system proved the efficiency of the sea defence scheme as flooding was minimal and the interceptor drain flowed at its maximum. COMPILED BY MR MAKAWONESU 76029746
