Coastal landscapes and change

  • Created by: remybray
  • Created on: 14-06-17 13:18

Enquiry question 1

WHY ARE COASTAL LANDSCAPES DIFFERENT AND WHAT PROCESSES CAUSE THESE DIFFERENCES?

  • Littoral zone - the wider coastal zone, including coastal land areas and shallow parts of the sea just offshore
  • The littoral zone can be divided into:
  • Coast - land adjacent to the sea and often heavily populated and urbanised
  • Backshore zone - the area between the high water mark (HWM) and the landward limit of marine activity. Above high tide level and only affected by waves during exceptionally high tides and major storms
  • Foreshore - the area where wave processes occur between the HWM and LWM
  • Nearshore - the area between the LWM and the point where waves cease to influence. Shallow water areas close to land and used extensively for fishing, coastal trade and leisure
  • Offshore - the area beyond the point where waves cease to impact upon the sea bed. The open sea
1 of 47

Enquiry question 1

There are a number of factors that determine the shape, form and appearance of a coastline:

  • Wave size, frequency, type, energy produced and direction
  • Local sea currents
  • Longshore drift
  • Tides
  • Depth of water offshore
  • Type and amount of sediments offshore
  • Rock type and structure
  • Sub-aerial processes (weathering, mass movement)
  • Land-based agents of erosion (rivers and glaciers)
  • Climate and weather
  • Fetch - the distance over open sea that a wind blows to generate waves
  • Long-term sea level change - eustatic (worldwide) and isostatic (local)
  • Coastal ecosystems (sand dunes, salt marshes and mangroves)
  • Human activity
2 of 47

Enquiry question 1

Coasts can be divided into 2 main types:

  • Rocky (or cliffed) coastlines with cliffs varying in height from a few metres to hundreds of metres
  • Coastal plains (with no cliffs) where the land gently slopes towards the sea across an area of deposited sediment, often in the form of sand dunes and mud flats

Rocky coasts

  • There are two main cliff profile types:
  • Marine erosion dominated: wave action domintates and the cliffs tend to be steep, unvegetated and there is little rock debris at the base of the cliff
  • Subaerial process dominated: not actively eroded at the base by waves; shallower, curved slope and lower relief; surface runoff erosion and mass movement are responsible for the cliff shape
3 of 47

Enquiry question 1

Coastal plains

  • Many contain estuary wetlands and marshes, being just above sea level and poorly drained because of the flatness of the landscape. Coastal plains form when:
  • Sea level falls, exposing the sea bed of what was once a shallow continental shelf sea, e.g. the Atlantic coastal plain in the USA
  • Sediment brought from the land by river systems is deposited at the coast causing coastal accretion (the deposition of sediment at a coast that expands the area of land) so coastlines gradually move seaward, such as a river delta
  • Sediment is moved from offshore sources (sand bars) towards the coast by ocean currents
  • Coastal plains are a low-energy environment usually lacking large and powerful waves except on rare occasions such as during hurricanes.
4 of 47

Enquiry question 1

Different coastal classifications:

Formation processes

  • Primary coasts - dominated by land-based processes, such as deposition at the coast from rivers or new coastal land formed from lava flows
  • Secondary coasts - are dominated by marine erosion or deposition processes

Relative sea level change

  • Emergent coasts - where the coast is rising relative to sea level, e.g. as a result of tectonic uplift
  • Submergent coasts - are being flooded by the sea either because of sea level rise and/or subsiding land

Wave energy

  • Low energy - sheltered coasts with limited fetch and low wind speeds resulting in small waves
  • High energy - exposed coasts, facing prevailing winds with long wave fetches resulting in powerful waves
5 of 47

Enquiry question 1

Tidal range

  • Microtidal (tidal range of 0-2m)
  • Mesotidal (tidal range of 2-4m)
  • Macrotidal (tidal range greater than 4m)
  • Geological structure - the arrangement of rocks in three dimensions. There are 3 elements:
  • 1. Strata - the different layers of rock exposed in a cliff
  • 2. Deformation - the degree to which the rock units have been deformed (tilted or folded) by tectonic activity. (Folding is often accompanied by joints and fissures)
  • 3. Faulting - the presence of major fractures that have moved rocks from their original positions 
  • Geological structure produces two main types of coast:
  • 1. Concordant - when rock strata run parallel to the coastline
  • 2. Discordant - when diffrent rock strata intersect the coast at an angle, so rock type varies along the coastline
6 of 47

Enquiry question 1

  • Discordant coastlines are dominated by headlands and bays. 
  • Less resistant rocks are eroded to form bays.
  • More resistant geology remains as headlands protruding into the sea
  • Differential erosion - variation in the rates at which rocks wear away
  • E.g. East Coast of Dorset (Swanage Bay, Studland Bay, The Foreland, Durlston Head, Peveril Point)
  • Headlands and bays change over time because headlands are eroded more than bays. This happens because of the effect these coasts have on wave crests:
  • When waves approach a coastline that is not of regular shape, they are refracted and become increasingly parallel to the coastline
  • As each wave nears the coast, it tends to drag in the shallow water which meets the headland
  • This causes the wave to slow down, becoming higher and steeper with a shorter wavelength
  • That part of the wave in deeper water moves forward faster, causing the wave to bend
  • Wave energy becomes concentrated on the headland, causing greater erosion
  • The low-energy waves spill into the bay, resulting in beach deposition
  • Wave refraction - the process causing wave crests to become curved as they approach a coastline
7 of 47

Enquiry question 1

  • On concordant coastlines, the more resistant rocks form elongated islands, while the less resistant rocks form long inlets or coves, e.g. Lulworth Cove
  • Marine erosion has broken through the resistant beds, and then rapidly eroded a wide cove behind
  • There is resistant chalk at the back of these coves, preventing further erosion inland
  • The Dalmation Coast in the Adriatic Sea is another example of a concordant coastline, where:
  • The geology is limestone
  • The limestone has been folded by tectonic activity into a series of anticlines and synclines, that trend parallel to the modern coastline
  • This underlying structure of anticlines and synclines (which would have been eroded by rivers in the past) has been drowned by sea level rise to create a concordant coastline of long, narrow islands arranged in lines offshore.
  • Haff coastlines are also concordant
  • They are found on the southern edge of the Baltic Sea
  • Long sediment ridges topped by sand dunes run parallel to the coast just offshore, creating lagoons (the haffs) between the ridges and the shoreline
  • These coastlines form low energy environments where there is deposition of sands and muds
8 of 47

Enquiry question 1

  • Cliff profiles (the height and the angle of a cliff face, plus its features, such as wave-cut notches or changes in slope angle) are influenced by geology. Two characteristics are dominant:
  • The resistance to erosion of the rock
  • The dip of rock strata in relation to the coastline
  • Dip, meaning the angle of rock strata in relation to the horizontal, is important. Dip is a tectonic feature. Sedimentary rocks are formed in horizontal layers but can be tilted by tectonic forces. 
  • Horizontal dip - uniform strata produce steep cliffs. Vertical or near-vertical profile with notches reflecting strata that are more easily eroded
  • Seaward dip high angle - sloping, low-angle profile with one rock layer facing the sea; vulnerable to rock slides down the dip slope
  • Seaward dip low angle - profile may exceed 90 degrees producing areas of overhanging rock; very vulnerable to rock falls
  • Landward dip - steep profiles on 70-80 degrees and producing a very stable cliff with reduced rock falls
9 of 47

Enquiry question 1

  • Other geological features influence cliff profiles and rates of erosion. These include:
  • Faults - either side of a fault line, rocks are often heavily fractured and broken and these weaknesses are exploited by marine erosion
  • Joints - occur in most rocks, often in regular patterns, dividing rock strata up into blocks with a regular shape
  • Fissures - much smaller cracks in rocks, often only a few centimetres or millimetres long but they also represent weaknesses that erosion can exploit
  • Folded rocks - often heavily fissured and jointed, meaning they are more easily eroded
  • The location of micro-features (small-scale coastal features such as caves and wave-cut notches which form part of a cliff profile) found within cliffs, such as caves and wave-cut notches, are often controlled by the location of faults and/or strata which have a particularly high density of joints and fissures
  • Coastal recession refers to how fast a coastline is moving inalnd. The key factor is lithology or rock type.
10 of 47

Enquiry question 1

Igneous (e.g. Basalt, Granite, Dolerite)

  • Very slow erosion rate. Less than 0.1cm per year
  • Igneous rocks are crystalline, and the interlocking crystals mae for strong, hard erosion-resistant rock
  • Igneous rocks such as granite often have few joints, so there are limited weaknesses that erosion can exploit

Metamorphic (e.g. Slate, Schist, Marble)

  • Slow erosion rate. 0.1-0.3cm per year
  • Crystalline metamorphic rocks are resistant to erosion
  • Many metamorphic rocks exhibit a feature called foliation, where all the crystals are orientated in one direction, which produces weaknesses 
  • Metamorphic rocks are often folded and heavily fractured, forming weaknesses that erosion can exploit
11 of 47

Enquiry question 1

Sedimentary (e.g. Sandstone, Limestone, Shale)

  • Moderate to fast erosion rate. 0.5-10cm per year
  • Most sedimentary rocks are clastic and eroded faster than crystalline igneous and metamorphic rocks
  • The age of sedimentary rocks is important, as geologically younger rocks tend to be weaker
  • Rocks with many bedding planes and fractures, such as shale, are often most vulnerable to erosion
  • Where the rock forming the cliffs is unconsolidated material (such as sand or boulder clay) rates of recession can be much greater. Boulder clay on the Yorkshire Holderness coast erodes at 2-10m per year.
  • Erosion and weathering resistance are influenced by:
  • How reactive minerals in the rock are when exposed to chemical weathering
  • Whether rocks are clastic or crystalline - the latter are more erosion-resistant
  • The degree to which rocks have cracks, fractures and fissures, which are weaknesses exploited by weathering and erosion.
12 of 47

Enquiry question 1

  • Cliff profiles can also be influenced by the permeability of strata:
  • Permeable rocks will allow water to flow through them, and include many sandstones and limestones
  • Impermeable rocks do not allow groundwater flow and include clays, mudstones and most igneous rocks and metamorphic rocks
  • Permeability is important because groundwater flow through rock layers can weaken rocks by removing the cement that binds sediment in the rock together. It can also create high pore water pressure within cliffs, which affects their stability. Water emerging from below ground onto a cliff face at a spring can run down the cliff face and cause surface runoff erosion, weakening the cliff. 
  • Some coastlines including coastal sand dunes, salt marshes and mangrove swamps, are protected from erosion by the stabilising influence of plants. 
13 of 47

Enquiry question 1

  • Vegetation stabilises coastal sediment in a number of ways:
  • Roots bind sediment particles together making them harder to erode
  • When submerged, plants provide a protective layer so the sediment surface is not directly exposed to moving water and erosion
  • Plants protect sediment from erosion by wind, by reducing wind speed at the surface because of friction with the vegetation
  • Many plants that grow in coastal environments are specially adapted halophytes (salt tolerant) or xerophytes (drought tolerant)
  • On a coast where there is a supply of sediment and deposition takes place:
  • Pioneer plant species will begin to grow in the bare sand or mud
  • This forms the first stage of plant succession
  • The end result of plant succession is called a climatic climax community
  • Coastal climax communities include sand dune ecosystems (psammosere) and salt marsh ecosystems (halosere)
14 of 47

Enquiry question 1

  • Coastal sand dunes are accumulations of sand shaped into moulds by the wind. Sand is moved inland by a process known as saltation.
  • On coastal sand dunes the succession begins with the colonisation of embryo dunes by pioneer species. Embryo dune pioneer plants:
  • Stabilise the mobile sand by their root systems
  • Reduce wind speeds at the sand surface, allowing more sand to be deposited
  • Add dead organic matter to the sand, beginning the process of soil formation
  • The sequence of sand-dune development is as follows:
  • Sand may become trapped by obstacles at the back of the beach, possibly on the highest berm or storm beach. Few plants will begin to colonise here - pioneer plants
  • The first dunes to develop are known as embryo dunes. They are suitable for colonisation by grasses. These are able to grow upwards through accumulating wind-blown sand, stabilising the surface
  • Upward growth of embryo dunes raises the height to create dunes that are beyond the reach of all but the highest storm tides
15 of 47

Enquiry question 1

  • A similar process of successional development happens on bare mud deposited in estuaries at the mouths of rivers that are exposed at low tide but submerged at high tide. Estuarine areas are ideal for the development of salt marshes because:
  • They are sheltered from strong waves, so sediment (mud and silt) can be deposited
  • Rivers transport a supply of sediment to the river mouth, which may be added to by sediment flowing into the estuary at high tide
16 of 47

Enquiry question 2

HOW DO CHARACTERISTIC COASTAL LANDFORMS CONTRIBUTE TO COASTAL LANDSCAPES?

  • Waves are caused by the friction between wind and water transferring energy from the wind into the water. The force of wind blowing on the surface of water generates ripples, which grow into waves when the wind is sustained. In open sea:
  • Waves are simply energy moving through water
  • The water itself only moves up and down, not horizontally
  • There is some orbital water particle motion within the wave, but no net forward water particle motion
  • Wave size depends on a number of factors:
  • The strength of the wind
  • The duration the wind blows for
  • Water depth
  • Wave fetch (the uninterrupted distance across water over which a wind blows, and therefore the distance waves have to grow in size)
17 of 47

Enquiry question 2

  • As waves approach shallow water, friction with the sea bed increases and the base of the wave begins to slow down. This has the effect of increasing the height and steepness of the wave until the upper part plunges forward and the wave 'breaks' onto the beach.

Constructive waves

  • Have a low wave height (less than 1m)
  • Long wavelength, often up to 100m
  • Low frequency (6-8 per minute)
  • As they approach the beach, the wave front steepens only slowly, giving a gentle spill onto the beach surface. 
  • Swash rapidly loses volume and energy as water percolates through the beach material. This tends to give a very weak backwash which has insufficient force to pull sediment off the beach.
  • As a consequence, material is slowly moved up the beach, leading to the formation of ridges
18 of 47

Enquiry question 2

Destructive waves

  • Have a wave height of over 1m and with a steep form
  • Short wavelength of around 20m
  • High frequency (10-14 per minute)
  • As they approach the beach, they rapidly steepen and, when breaking, they plunge down.
  • This creates a powerful backwash as there is little forward movement of water. It also inhibits the swash from the next wave.
  • Very little material is moved up the beach, leaving the backwash to pull material away. 
  • Destructive waves are commonly associated with steeper beach profiles. The force of each wave may project some shingle well towards the rear of the beach where it forms a large ridge known as the storm beach.
19 of 47

Enquiry question 2

  • Depending on the conditions, beaches experience both constructive and destructive waves over the course of time and this can mean significant changes to beach morphology on different timescales:
  • Over a day, as a storm passes and destructive waves change to constructive ones as the wind drops
  • Between summer and winter
  • When there are changes to climate, e.g. if global warming resulted in the UK climate becoming on average stormier, then destructive waves and 'winter' beach profules would become more common
  • Beaches have landforms that change constantly:
  • Storm beaches, high at the back of the beach, result from high energy deposition of very coarse sediment during the most severe storms
  • Berm ridges, typically of shingle/gravel result from summer swell wave deposition
  • Low channels and runnels between berms
  • Offshore ridges/bars formed by destructive wave erosion and subsequent deposition of sand and shingle offshore
20 of 47

Enquiry question 2

  • When waves approach the shore at an angle, material is pushed up the beach by the swash in the same direction as the wave approach.
  • As water runs back down the beach, the backwash drags material down at right angles to the beach line.
  • Over a period of time, sediment moves in this zig-zag fashion down the coast.
  • On most coastlines there is a dominant prevailing wind so over time there is a dominant direction of longshore drift.
  • Sediment is deposited when the force transporting sediment drops. Deposition can occur in two main ways:
  • Gravity settling occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first followed by smaller sediment. 
  • Flocculation is a depositional process that is important for very small particles, such as clay, which are so small they will remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink.
21 of 47

Enquiry question 2

  • Coastlines operate as sediment systems consisting of three interlinked components.
  • 1. Sources - places where sediment is generated
  • Erosion of cliffs
  • Eroding sand dunes
  • Onshore currents supplying sediment to the shore
  • Subaerial processes
  • Land sediments eroded by rivers
  • Offshore bars
  • WInd-blown sediments from land
  • 2. Transfers - places where sediment is moving alongshore
  • Longshore drift
  • Wave transport through swash and backwash
  • Tides moving sediment in and out
  • Currents (offshore)
  • Wind (alongshore, onshore of offshore)
22 of 47

Enquiry question 2

  • Coastlines operate as sediment systems consisting of three interlinked components.
  • 1. Sources - places where sediment is generated
  • Erosion of cliffs
  • Eroding sand dunes
  • Onshore currents supplying sediment to the shore
  • Subaerial processes
  • Land sediments eroded by rivers
  • Offshore bars
  • WInd-blown sediments from land
  • 2. Transfers - places where sediment is moving alongshore
  • Longshore drift
  • Wave transport through swash and backwash
  • Tides moving sediment in and out
  • Currents (offshore)
  • Wind (alongshore, onshore of offshore)
23 of 47

Enquiry question 2

  • 3. Sinks - locations where the dominant process is deposition and depositional landforms are created
  • Backshore depositional features (e.g. sand dunes)
  • Foreshore depositional features (e.g. beaches)
  • Nearshore depositional features (e.g. bars)
  • Under natural conditions the systems operate in a state of dynamic equilibrium, with sediment inputs balancing outputs to sinks.
  • For short periods of time, e.g. during a major storm that erodes a spit, the system's equilibrium may be disrupted but it will tend to return to balance over time. 
  • Negative feedback mechanisms help maintain the balance by pushing the system back towards balance:
  • During a major erosion event a large amount of cliff collapse may occur, but the rock debris at the base of the cliff will slow down erosion by protecting the cliff base from wave attack
  • Major erosion of sand dunes could lead to excessive deposition offshore, creating an offshore bar that reduces wave energy allowing the dunes time to recover
24 of 47

Enquiry question 3

HOW DO COASTAL EROSION AND SEA LEVEL CHANGE ALTER THE PHSYICAL CHARACTERISTICS OF COASTLINES AND INCREASE RISKS?

  • Sea level change is complex because both land level (isostatic) and water level (eustatic) can change over time.
  • A rise or fall in water level causes a eustatic change, which is a global change in the volume of sea water in all the world's seas and oceans
  • Isostatic change is a local rise or fall in land level
  • On a coastline, isostatic and eustatic change can happen at the same time.
  • Since the end of the last ice age 12,000 years ago the UK has felt the impact of continuing sea level change:
  • Scotland is still rebounding upward, in some places by up to 1.5mm a year, because of post-glacial adjustment (the uplift experienced by land following the removal of the weight of ice sheets)
  • England and Wales are subsiding at up to 1mm per year
  • The UK is pivoting, with the south sinking and the north rising
  • Sea level rise caused by global warming (eustatic) compounds the effect in the south but reduces it in the north
25 of 47

Enquiry question 3

Emergent coastlines

  • The extent of isostatic and eustatic changes during and after the last ice age was large:
  • Global sea levels fell by 120m as ice sheets grew
  • An equal sea level rise happened over about 1000 years when the ice sheets melted
  • In North America and northern Europe the post-glacial isostatic adjustment was up to 300m
  • These two linked changes happened at very different rates:
  • Post-glacial sea level rise was very rapid, submerging coastlines
  • Isostatic adjustment was very slow, with land gradually rising out of the sea
  • The effect of these changes is to produce an emergent coast, with landforms reflecting previous sea levels

Submergent coastlines

  • Coastlines that were never affected by glacial ice cover do not experience post-glacial adjustment. Instead they were submerged (drowned) when post-glacial sea level rose. Submergent coasts are found in southern England and on the east coast of America. The most common coastal landform is a ria (drowned river valleys, caused by sea level rise flooding up the river valley, making it much wider than would be expected based on the river flowing through
26 of 47

Enquiry question 3

Emergent coastlines

  • The extent of isostatic and eustatic changes during and after the last ice age was large:
  • Global sea levels fell by 120m as ice sheets grew
  • An equal sea level rise happened over about 1000 years when the ice sheets melted
  • In North America and northern Europe the post-glacial isostatic adjustment was up to 300m
  • These two linked changes happened at very different rates:
  • Post-glacial sea level rise was very rapid, submerging coastlines
  • Isostatic adjustment was very slow, with land gradually rising out of the sea
  • The effect of these changes is to produce an emergent coast, with landforms reflecting previous sea levels

Submergent coastlines

  • Coastlines that were never affected by glacial ice cover do not experience post-glacial adjustment. Instead they were submerged (drowned) when post-glacial sea level rose. Submergent coasts are found in southern England and on the east coast of America. The most common coastal landform is a ria (drowned river valleys, caused by sea level rise flooding up the river valley, making it much wider than would be expected based on the river flowing through
27 of 47

Enquiry question 3

  • Fjords are submergent landforms found on the coasts of Norway and Canada. Fjords are drowned valleys, but they differ from rias in that:
  • The drowned valley is a U-shaped glacial valley
  • The fjord is often deeper than the adjacent sea, some over 1000m deep
  • At the seaward end of the fjord there is a submerged 'lip', representing the former extent of the glacier that filled the valley
  • The east coast of the USA has barrier island (offshore sediment bars, usually sand-dune covered but, unlike spits, they are not attached to the coast) landforms:
  • They may have formed as lines of coastal sand dunes attached to the shore
  • Latter sea level rise flooded the land behind the dunes forming a lagoon, but the dunes themselves were not eroded and so became islands
  • As sea level continued to rise, the dune systems slowly migrated landward
28 of 47

Enquiry question 3

  • Sea level is very difficult to predict because there are many factors involved:
  • Thermal expansion of the oceans depends on how high global temperatures climb
  • Melting of mountain glaciers in the Alps, Himalayas and other mountain ranges will increase ocean water volume
  • Melting of major ice sheets (Greenland, Antarctica) could dramatically increase global sea level
  • In addition, sea level can change locally because of tectonic forces. 
29 of 47

Enquiry question 3

  • Rapidly eroding coastlines have the following physical features in common:
  • Long wave fetch, large destructive ocean waves
  • Soft geology
  • Cliffs with structural weaknesses such as seaward rock dip and faults
  • Cliffs which are vulnerable to mass movement and weathering, as well as marine erosion
  • Strong longshore drift, so eroded debris is quickly removed exposing the cliff base to further erosion
  • Human actions can make the situation worse and usually involve interfering with the coastal sediment cell. E.g. the construction of major dams on rivers can trap river sediment behind the dam wall. This then starves the coast of a sediment source, leading to serious consequences.
  • The construction of the Aswan High Dam on the River Nile in 1964 reduced sediment volume from 130 million tonnes to about 15 million tonnes per year. Erosion rates jumped from 20-25 metres per year to over 200 metres per year as the delta was starved of sediment.
  • Dredging (scooping or sucking sediment up from the sea bed or a river bed) is another cause of problems. Sand and gravel are often dredged from the sea bed or rivers for use in construction. This removes a sediment source, which can have knock-on effects further along a coast by increasing erosion.
30 of 47

Enquiry question 3

  • Rates of recession are not constant and are influenced by different factors (wind direction and fetch, seasonal changes to weather systems and the occurence of storms). 
  • On the Holderness Coast in East Yorkshire average annual erosion is around 1.25m per year, but there are wide variations in this rate, from 0m per year to 6m per year. This is because:
  • Coastal defences at Hornsea, Mappleton and Withernsea have stopped erosion 
  • These defences have starved places further south of sediment as groynes have interrupted longshore drift
  • Erosion rate therefore generally increases from north to south
  • Some areas of boulder clay are more vulnerable to erosion than others
  • Some cliffs are more susceptible to mass movement
  • Erosion of Holderness varies over time:
  • During winter, 2-6m of erosion is common when storms, combined with spring tides, increase erosion rates
  • Summer erosion, during periods when constructive waves dominate, is much lower
  • Northeasterly storms cause most erosion, because of the long wave fetch of 1500km from the north Norwegian coast
31 of 47

Enquiry question 3

  • Coastal flooding risk is more widespread than rapid erosion risk. Low-lying coastal land is densely populated for several reasons:
  • Coastlines are popular with tourists, especially when access to beaches and the sea is easy
  • Deltas and estuaries are ideal locations for trade between up-river places and places along the coast or across the sea
  • Deltas and coastal plains are especially fertile and ideal for farming
  • Many of the world's major river deltas are home to some of the world's largest cities. Coastal flooding risk in these river delta locations is made worse by a complex set of processes that increase risk.
  • In addition to low-lying coastal plains and deltas being at risk from sea level rise, many islands are also at risk.
  • In the Indian Ocean the Maldives has a population of 340,000 people spread out across 1200 islands. The highest point in the country is 2.3m above sea level.
  • Sea level rise of 50cm by 2100 would see 77% of the Maldives disappear into the sea.
32 of 47

Enquiry question 3

  • The most common cause of coastal flooding is a storm surge (a localised, short-term rise in sea level caused by air pressure change) event caused by:
  • A depression (low pressure weather system) in the mid-latitudes, e.g. the UK
  • A tropical cyclone (hurricane, typhoon) in areas just north and south of the equator
  • Strong winds from these weather systems push waves onshore, increasing the effective height of the sea. If high tides occur at the same time as the storm surge and onshore winds, sea levels increase even more.
  • Coastal topography can also have an effect. In the North Sea the coastline narrows into a funnel shape for a storm approaching from the north. The storm surge can be funnelled into an increasingly narrow space between coastlines and, as the sea shallows towards the coast, the effect is severe coastal flooding.
33 of 47

Enquiry question 3

  • Bangladesh is especially vulnerable to the impacts of tropical cyclone storm surges for a number of reasons:
  • Much of the country is low-lying river delta, only 1-3m above sea level
  • Incoming storm surges meet out-flowing river discharge from the Ganges and Brahmaputra rivers, meaning river flooding and coastal flooding combine
  • Intense rainfall from tropical cyclones contributes to flooding
  • Much of the coastline consists of unconsolidated delta sediment, which is very susceptible to erosion
  • Deforestation of coastal mangrove forests has removed vegetation that once stabilised coastal swamps and dissipated wave energy during tropical cyclones
  • The triangular shape of the Bay of Bengal concentrates a cyclone storm surge as it moves north, increasing its height when it makes landfall
34 of 47

Enquiry question 4

HOW CAN COASTLINES BE MANAGED TO MEET THE NEEDS OF ALL PLAYERS?

  • Economic costs - loss of property in the form of homes, businesses and farmland. These are relatively easy to quantify
  • Social costs - costs of relocation and loss of livelihood/jobs (which can be quantified) but also include impact on health (such as stress and worry) which are much harder to quantify
  • Environmental costs - loss of coastal ecosystems and habitats. These are almost impossible to quantify financially but are likely to be small
  • Losses becase of erosion tend to be very localised and costs are specific to those locations. In 2015 farmland in the UK had an average value of about £20,000 per hectare, whereas residential land can vary from £500,000 to £2.5 million per hectare. If roads are lost to erosion they can cost between £150,000 and £250,000 per 100m to re-route and replace. There are also some losses in terms of amenity value (the value in cultural, human wellbeing and economic terms of an attractive environment that people enjoy using) and economic losses to businesses if coastlines become unattractive and depopulated.
35 of 47

Enquiry question 4

  • Economic losses because of erosion are small because:
  • Erosion happens slowly with a small number of properties affected over a long period of time
  • Property that is at risk loses its value long before it is destroyed by erosion, because potential buyers recognise the risk
  • Areas of high-density population, esepcially towns and villages, tend to be protected by coastal defences
  • For coastal people erosion means:
  • Falling property values, as the date of eventual loss approaches
  • An inability to sell their property because the possibility of loss by erosion is too great
  • The loss of their major asset, and facing the costs of getting a new home
  • An increasingly unattractive environment scarred by collapsing cliffs, failing sea defences and blocked roads and paths
  • In the UK there are 'Coastal Change Pathfinder' projects, which:
  • Cover the cost of property demolition and site restoration
  • Provide up to £1000 in relocation expenses such as removal vans and storage
  • Provide up to £200 in hardship expenses
  • Have 'rollback' policies, giving people fast-tracked planning approval to build a new home somewhere else
36 of 47

Enquiry question 4

  • By 2100, in some places sea level rise resulting from global warming will be very difficult to manage. The most at-risk places are low-lying islands including the Maldives, Tuvalu, the Seychelles and Barbados. These small islands have particular risk factors. 
  • Tuvalu's highest point is 4.5m above sea level, and most land is 1-2m above sea level
  • 80% of people in the Seychelles live and work at the coast
  • Coral reefs, which act as a natural costal defence against erosion, are being destroyed by global warming-induced coral bleaching
  • Water supply is limited and at risk from salt-water incursion as sea level rises and groundwater is over-used
  • They have small and narrow economies based on tourism and fishing, which are easily disrupted
  • They have high population densities and very limited space, so no opportunity for relocation
  • Environmental refugees - communities forced to abandon their homes because of natural processes, including sudden ones such as landslides or gradual ones such as erosion or rising sea levels 
37 of 47

Enquiry question 4

  • By 2100, in some places sea level rise resulting from global warming will be very difficult to manage. The most at-risk places are low-lying islands including the Maldives, Tuvalu, the Seychelles and Barbados. These small islands have particular risk factors. 
  • Tuvalu's highest point is 4.5m above sea level, and most land is 1-2m above sea level
  • 80% of people in the Seychelles live and work at the coast
  • Coral reefs, which act as a natural costal defence against erosion, are being destroyed by global warming-induced coral bleaching
  • Water supply is limited and at risk from salt-water incursion as sea level rises and groundwater is over-used
  • They have small and narrow economies based on tourism and fishing, which are easily disrupted
  • They have high population densities and very limited space, so no opportunity for relocation
  • Environmental refugees - communities forced to abandon their homes because of natural processes, including sudden ones such as landslides or gradual ones such as erosion or rising sea levels 
38 of 47

Enquiry question 4

Hard engineering

  • Advantages:
  • Obvious to at-risk people that 'something is being done' to protect them
  • A 'one-off' solution that could protect a stretch of coast for decades
  • Disadvantages:
  • Costs are usually very high, and there are ongoing maintenance costs
  • Even very carefully designed engineering solutions are prone to failure
  • Coastlines are made visually unattractive and the needs of coastal ecosystems are usually overlooked
  • Defences built in one place frequently have adverse effects further along the coast
39 of 47

Enquiry question 4

  • Coastal communities around the world face the dynamic nature of the coast's every-day environment. They increasingly face threat from:
  • Rising global sea levels, but there is uncertainty about the scale and timing of the rise
  • Increased frequency of storms and the possibility of increased erosion and flooding
  • To cope with these threats, communities need to adapt and employ sustainable coastal management (managing the wider coastal zone in terms of people and their economic livelihood, social and cultural wellbeing, safety from coastal hazards, as well as minimising environmental and ecological impacts).
  • Adopting sustainable coastal management may lead to conflict because:
  • Coastal natural resources may have to be used less in order to protect them - so some people may lose income
  • Relocation may be needed where engineering solutions are too costly or not technically feasible
  • Some erosion and/or flooding will always occur, as engineering schemes cannot protect against all threats
  • Future trends, such as sea level rise, may change, creating uncertainty and the need to change plan
40 of 47

Enquiry question 4

  • ICZM is coastal management planning over the long term, involving all stakeholders, working with natural processes and using 'adaptive management', .i.e changing plans as threats change. It has a number of key characteristics:
  • The entire coastal zone is managed, not just the narrow zone where breaking waves cause erosion or flooding. This includes all ecosystems, resources and human activity in the zone.
  • It recognises the importance of the coastal zone to people's livelihoods as, globally, very large numbers of people live and work at the coast - but their activities tend to degrade the coastal environment.
  • It recognises that management of the coast must be sustainable, meaning that economic development has to take place to improve the quality of life of people but that this needs to be environmentally appropriate and equitable (benefit everyone).
  • ICZM works with the concept of littoral cells (they contain sediment sources, transport paths and sinks. Each littoral cell is isolated from adjacent cells, and can be managed as a holistic unit) or sediment cells. The coastline can be divided up into littoral cells and each cell managed as an integrated unit.
41 of 47

Enquiry question 4

  • In England and Wales there are 11 sediment cells
  • Each cell is managed either as a whole unit or a sub-unit
  • In both cases a plan called a Shoreline Management Plan (SMP) is used.
  • The SMP area is further divided into sub-cells
  • SMPs extend across council boundaries, so many councils must work together on an agreed SMP to manage an extended stretch of coastline
  • In the UK coastal management is overseen by DEFRA. Since DEFRA introduced SMPs in 1995 there have been only four policies available for coastal management:
  • No active intervention - no investment in defending against flooding or erosion, whether or not coastal defenes have existed previously. The coast is allowed to erode landward and/or flood.
  • Hold the line - build or maintain coastal defences so that the position of the shoreline remains the same over time.
  • Strategic (managed) realignment - allow the coastline to move naturally (in most cases to recede) but managing the process to direct it in certain areas. 
  • Advance the line - build new coastal defences on the seaward side of the existing coastline. Usually this involves land reclamation.
42 of 47

Enquiry question 4

  • In England and Wales there are 11 sediment cells
  • Each cell is managed either as a whole unit or a sub-unit
  • In both cases a plan called a Shoreline Management Plan (SMP) is used.
  • The SMP area is further divided into sub-cells
  • SMPs extend across council boundaries, so many councils must work together on an agreed SMP to manage an extended stretch of coastline
  • In the UK coastal management is overseen by DEFRA. Since DEFRA introduced SMPs in 1995 there have been only four policies available for coastal management:
  • No active intervention - no investment in defending against flooding or erosion, whether or not coastal defenes have existed previously. The coast is allowed to erode landward and/or flood.
  • Hold the line - build or maintain coastal defences so that the position of the shoreline remains the same over time.
  • Strategic (managed) realignment - allow the coastline to move naturally (in most cases to recede) but managing the process to direct it in certain areas. 
  • Advance the line - build new coastal defences on the seaward side of the existing coastline. Usually this involves land reclamation.
43 of 47

Enquiry question 4

  • Making decisions about which policy to apply to a particular location is complex. It depends on a number of factors including:
  • The economic value of the assets that could be protected, e.g. land
  • The technical feasibility of engineering solutions: it may not be possible to 'hold the line' for mobile depositional features such as spits, or very unstable cliffs
  • The cultural and ecological value of land: it may be desirable to protect historic sites ad areas of unusual biodiversity
  • Pressure from communities: vocal local political campaigning to get an area protected
  • The social value of communities that have existed for centuries
  • Cost-benefit analysis (CBA) is used to help decide if defending a coastline from erosion and/or flooding is economically justifiable.
  • E.g. Happisburgh in North Norfolk. The policy adopted in this area is 'no active intervention'. This is because to defend the village would have an impact on the wider coastal management plan. Happisburgh would end up as a promontory, blocking longshore drift and causing further erosion downdrift. Longer term, the plan is managed realignment, although this would still involve property being lost to the sea by erosion. 
44 of 47

Enquiry question 4

  • The cost of building coastal defences at Happisburgh is around £6 million. This is very close to the value of property that could be saved, and much higher than the compensation costs payable to local residents. Coastal managers argue that Happisburgh must be seen in the wider context of the whole SMP, further justifyinfg the decision not to defend the village.
  • Coastal management usually requires an Environmental Impact Assessment (EIA) to be carried out. EIA is a process that aims to identify:
  • The short-term impacts of construction on the coastal environment
  • The long-term impacts of building new sea defences or changing a policy from hold the line to no active intervention or managed realignment
  • EIA is wide-ranging and includes assessments of:
  • Impacts on water movement (hydrology) and sediment flow, which can affect marine ecosytems because of changes in sediment load
  • Impacts on water quality, which can affect sensitive marine species
  • Possible changes to flora and fauna, including marine plants, fish, shellfish and marine mammals
  • Wider environmental impacts such as air quality and noise pollution, mainly during construction
45 of 47

Enquiry question 4

  • Coastal management decisions directly affect people's lives. These effects can be positive or negative, producing perceived:
  • Winners: people who gain from a decision, either economically (their property is safe), environmentally (habitats are conserved) or socially (communities can remain in place)
  • Losers: people who are likely to lose property, their business or job, be forced to move, or see the coastline as 'concreted over' and view this as a environmental negative
  • In some ways this is inevitable because:
  • Coastal managers produce plans for entire SMP areas, so some areas are protected but others are not
  • Local councils and government (DEFRA) have limited resources, meaning all places cannot be protected
46 of 47

Enquiry question 4

  • In many parts of the developing world, such as the Maldives, parts of Vietnam and the West African coast, erosion is rapid, often because of a combination of:
  • Upstream dams reducing sediment supply to the coast and disrupting local sediment cells
  • Rapid unplanned coastal development, urbanisation and the development of tourist resorts with piecemeal defences and no overall plan
  • Widespread destruction of mangrove forests for fuelwood and shrimp-ponds, exposing soft sediments to rapid erosion
  • In many cases, the losers are the poorest people. Farmers and residents usually lack a formal land-title so cannot claim compensation. Coastlines become more vulnerable to sea level rise, the impact of tropical cyclone storm surges and even tsunami. When the disaster strikes it is the poorest that lose everything. In many cases it is the individual property owners that take responsibilty for coastald defences in the absence of local council or government plans. 
47 of 47

Comments

No comments have yet been made

Similar Geography resources:

See all Geography resources »See all Coastal environments resources »