Costal systems and landscapes. Flashcards
Heysham and Morecambe- four defence options:
Hold the line- retain the existing coastline by maintaining current defences or building new ones where existing structures no longer provide sufficient protection.
Do nothing but monitor- on some stretches of coastline, it is not technically economically or environmentally viable to undertake defence works.
Retreat the line- actively manage the rate and process of the coast retreats.
Advance the line- build new defences seaward of the existing line.
Heysham and Morecambe- Background.
Current defences along the 8.5km stretch of coastline are the results of an improvement scheme of existing structures during a multi-phase programme between 1989-2018- costing £30m.
The mix of traditional hard engineering with more contemporary methods to improve the potential for sustainable management.
Heysham and Morecambe- Strategy 1.
Rock armour/rip rap to enhance and protect the existing sea wall.
Boulders of locally sourced limestone are placed along the existing promenade and sea walls from the west to 1km east of the town centre.
Heysham and Morecambe- Strategy 2.
Breakwaters or rock groynes.
Around ten breakwaters and rock groynes were built at intervals in front of the town.
Heysham and Morecambe- Strategy 3.
Repaired and replaced sea walls.
The traditional sea wall was repaired and reinforced. Cost £11m and protects 11,400 homes and 2,246 commercial properties.
Design to last 100 years.
Holderness- Case study:
- How long is the coastline?
61km long- Flamborough head to Spurn Head.
Holderness- Case study:
- What are the cliffs made of and what type of wave are there?
-Boulder clay ‘till’.
-Destructive waves.
Holderness- Case study:
-Coastal process operating in the area.
-Erosion: soft boulder is easily eroded, Great Cowden 10m/year.
-Mass Movement: boulder clay is prone to slumping when wet.
-Transportation: prevailing winds transport material southwards. Winds also create an ocean current that transports material south by longshore drift.
-Deposition: where ocean current meets the outflow of the Humber River, the flow becomes turbulent and sediment is deposited.
Holderness- Case study:
-Headland and wave-cut platforms.
To the north the boulder clay overlies chalk. Chalk is harder and less easily eroded so it forms a headland and wave-cut platforms. Flamborough head has features such as stacks, caves and arches.
Holderness- Case study:
-Slumping cliffs.
Frequent slumps give the boulder clay cliffs a distinctive shape. In some locations several slumps have occurred and have not yet been eroded, making the cliff tiered.
Holderness- Case study:
Beaches.
The area to the south of Flamborough Head is sheltered from wind and waves, and a wide sand and pebble beach has formed.
Holderness- Case study:
Sand dunes.
Around Spurn Head, material transported by the wind is deposited, forming dunes.
Holderness- Case study:
Spit.
Erosion and longshore drift have created a spit with a recurved end across the mouth of the Humber Estuary- this is called Spurn Head. On the landward side of the spit, estuarine mudflats and saltmarshes have formed.
Holderness- Case study:
How much has the coastline retreated in the past 2K years?
How many villages have been lost?
4km
30 villages.
Holderness- Case study:
Social, economic and environmental problems.
-Loss of settlements and livelihoods-farmland.
-Loss of infrastructure- gas terminal at Easington only 25m from the cliff edge.
-Loss sites of Special Scientific Interest (SSSIs)- the lagoons near Easington,
Holderness- Case study:
Hard engineering protection:
-Bridlington is protected by a 4.7km long sea wall as well as timber groynes.
-Hornsea- concrete sea wall, timber groynes, riprap.
-Mappleton- 2 rock groynes and a 500m long revetment were built (1991). Cost- £2million. Protects the village and B1242 coastal road.
-Skipsea used gabions to protect the caravan park.
-Withernsea- groynes and a sea wall with some rip rap in front of it.
-Easington Gas Terminal protected by revetment.
-Eastern side of Spurn Head- groynes and rip rap.
Holderness- Case study:
Negatives of the existing schemes.
-The groynes trap sediment- protects local area but increases cliff erosion down-drift. (Mappleton has caused increased erosion south of it).
-Reduction of sediment increases the risk of flooding along the Humber Estuary as the sediment produced in Holderness used to wash to Humber, this also increases erosion in the Lincolnshire coast.
-Protection of local areas is leading to a build-up of bays forming. this means wave pressure on headlands will increase eventually making the cost of sea defences too high.
-Existing schemes are unsustainable.
Sundarbans- Case study:
Where is it?
-Southwest Bangladesh and East India on the delta of the Ganges, Brahmaputra and Meghna rivers on the Bay of Bengal.
Sundarbans- Case study:
What is the land/area like?
-Part of the largest mangrove forest in the world.
-Very flat land and low-lying.
-Home to many rare species of plants and animals.
-In its natural state, the coastal system is in dynamic equilibrium.
Sundarbans- Case study:
Opportunities for economic benefit:
-Flat, fertile land is good for growing crops (rice).
-Rich ecosystem of the mangrove forest provides crabs, fish, honey and nipa palm leaves used for making roofing and baskets.
- Mangrove forests provide timber for construction, firewood and furniture.
Sundarbans- Case study:
Opportunities for services:
-Mangrove forest provides a natural defence against flooding, it acts as a barrier against the rough seas and absorbs excess water in the monsoon season- easier to live and grow crops.
-Mangroves protect the area against coastal erosion.
Sundarbans- Case study:
Opportunities for development:
-Tourism opportunities- attracted by wildlife.
-Since 2011, cargo ships transporting goods such as oil and food have been allowed to use some of the waterways.
-A power plant has been proposed just north of the national park, providing energy for people in the region.
Sundarbans- Case study:
Risks for occupation and development:
-Lack of fresh water for drinking/irrigation beause the water is diverted upstream for agriculture.
-Growing population leads to mangroves being cut down for more farmland and fuel- increases the risk of flooding and coastal erosion.
-Flooding can lead to salinisation- hard to grow crops.
-Home to dangerous animals.
-Lack of employment and income opportunities.
-Low-lying land at risk from rising sea levels.
-Relatively poor region- 1/5 of households have access to electricity, which makes communication for flood warnings difficult.
-Access is difficult- only a few roads which are poor quality - limits healthcare and education.
Backshore-
The area between the high water mark and the landward limit of marine activity. Changes normally only take place here in storm activity.
Foreshore-
The area lying between the HWM and the low water mark. The most important zone for marine processes in times that are not influenced by storm activity.
Inshore-
The area between the LWM and the point where waves cease to have any influence on the land beneath them.’
Offshore-
The area beyond the point where waves cease to impact upon the seabed and in which activity is limited to deposition of sediments.
Nearshore-
The area extending seaward from the HWM to the area where waves begin to break.
What 3 zones does the nearshore include?
-Swash zone
-Surf zone
-Breaker zone
Swash zone-
The area where a turbulent layer of water washes up the beach following the breaking of a wave.
Surf zone-
The area between the point where waves break, forming a foamy, bubbly surface, and where the waves then move up the beach as swash in the swash zone.
Breaker zone-
The area where waves approaching the coastline begin to break, usually where the water depth is 5 to 10m.
Inputs in a coastal system-
-Energy from waves, winds, tides and sea currents.
-Sediment
-Geology of the coastline
-Sea level change
Components in a coastal system-
-Characteristic erosional and depositional coastal landforms.
Outputs in a coastal system-
-Dissipation of wave energy
-Accumulation of sediment above the tidal limit
-Sediment removed beyond local sediment cells.
Erosion-
Wearing away of the earth’s surface by the mechanical action of processes of glaciers, wind, rivers, marine waves and wind.
Fetch-
Refers to the distance of open water over which a wind blows uninterrupted by major land obstacles. The length of fetch helps to determine the magnitude and energy of the waves reaching the coast.
Mass movement-
The movement of material downhill under the influence of gravity, but may also be assisted by rainfall.
Weathering-
The breakdown and/or decay of rock at or near the earth’s surface creating regolith that remains in situ until it is moved by later erosional processes. Can be mechanical, biological or chemical.
Features of wind as an input into the coastal system-
-Variations in energy result from variations in strength and duration of wind.
-Most coastline will have a prevailing wind direction (one direction)
-Length of fetch determines the size and energy of waves.
-Vital to wave formation, wave energy depends on strength of wind.
-Wind can pick up and remove sediment from the coast and use it to erode other features. (most common abrasion)
Wave characteristics:
-Wave height or amplitude: this is the height difference between a wave crest and the neighbouring trough.
-Wavelength: distance between successive crests
-Wave period: the time for one wave to travel the distance of one wavelength, or the time between one crest and the following crest passing a fixed point.
Backwash-
The action of water receding back down the beach towards the sea.
Constructive waves-
Waves with low wave height, but with a long wavelength and low frequency or around 6-8 min. Their swash tends to be more powerful than their backwash and as a consequence beach material is built up.
Destructive waves-
Waves with a high wave heigh with a steep form and high frequency (10-14 min). Their backwash is generally stronger than their swash, so more sediment is removed than added.
Swash
The rush of water up the beach after a wave breaks.
Wave refraction-
When waves approach a coastline that is not a regular shape, they are refracted and become increasingly parallel to the coastline. Wave energy become concentrated on the headland causing erosion.
Tides-
The periodic rise and fall of the level of the sea in response to the gravitational pull of the sun and moon.
Longshore current-
Known as littoral drift, occur as most waves do not hit the coastline head on but approach at an angle to the shoreline . Generates a flow of water running parallel to the shoreline. Not only moves water but transports sediment.
Rip currents-
Strong currents moving away from the shoreline. They develop when seawater is piled up along the coastline by incoming waves. Initially the current may run parallel to the coast before flowing out through the breaker zone, possibly at a headland or where the coast changes direction.
Upwelling-
The movement of cold water from deep in the ocean towards the surface. The more dense cold water replaces the warmer surface water and creates nutrient-rich cold ocean currents. These currents from part of the pattern of global ocean circulation currents.
How is a spring tide produced?
When the earth, moon and sun are in a straight line, the tide-raising force is the strongest. This produces the highest monthly tidal range, or SPRING TIDE.
How is a neap tide produced?
Twice a month, the Moon and Sun are positioned at 90 degrees to each other in relation the the earth. At this time the high and low tides are between 10 to 30 percent lower than the average.
Tidal range-
The difference in height of the sea water at high and low tide, This is not fixed due to the tide cycles. Tidal ranger determine the upper and lower limits of erosion and deposition and the amount of time each day that the littoral zone is exposed and open to sub-aerial weathering.
Tidal/ storm surges-
Occasions when meteorological conditions give rise to strong winds which can produce much higher water levels than those at high tide.
Coastal sediment budget-
The balance between sediment being added to and removed from the coastal system, that system being defined within each individual sediment cell.
High energy coast-
A coastline where strong, steady prevailing winds create high energy waves and the rate of erosion is greater than the rete of deposition.
Low energy coast-
A coastline where wave energy is low and the rate of deposition often exceeds the rate of erosion of sediment.
Sediment cell-
A distinct area of coastline separated from other areas by well-defined boundaries, such as headlands and stretches of deep water.
Sources of coastal sediment:
-Streams or rivers flowing into the sea.
-Estuaries
-Cliff erosion
-Offshore sand banks
-Material from a biological origin- shells, coral fragments, skeletons.
How many sediment cells are along the coastline of England and Wales?
11.
What is a sediment cell?
Within sediment cells inputs and outputs are balanced, it is the movement of sediment.
What defines sediment cells from the other?
Well-defined boundaries such as headlands and stretches of deep water.
What are large sediment cells divided into?
Sub-cells to allow closer study and management.
What is the coastal sediment budget?
Defined as the balance between sediment being added to and removed from the coastal system, that system being defined within each individual sediment cell.
Marine processes-
Operate upon a coastline and are connected with the sea, such as waves, tides and longshore drift.
Sub-aerial processes-
Processes that slowly breakdown the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen more easily. Material is broken down in situ, remaining in or near its original position. Affect the shape of the coastline and include weathering, mass movement and run-off.
Hydraulic action-
Refers to the impact on rocks of the sheer force of the water itself. This can exert enormous pressure upon a rock surface, thus weakening it. Such activity is sometimes referred to as wave pounding.
Wave quarrying-
A breaking wave traps air as it hits a cliff face. The force of water compresses this air into any gap in the rock face, creating enormous pressure within the fissure or joint. As the water pulls back their is explosive effect to the air under pressure being released. Weakens cliff overtime.
Abrasion/corrasion-
The material the sea has picked up also wears away rock faces. Sediment hurled against a cliff line does a lot of damage.
Attrition-
Rocks in the sea which carry out abrasion are slowly worn down into smaller and more rounded pieces.
Solution (corrosion)-
Dissolving calcium-based rocks.
Lithology-
Characteristics of rocks especially resistance to erosion and permeability.
Differential erosion-
Variation in the rates at which rocks wear away.
Concordant coastline-
A concordant coastline occurs where the bands of differing rock types run parallel to the coast.
Discordant coastline-
The rocks run at right angles to the coastline.
Traction-
Large stones and boulders are rolled and slid along the seabed and beach by moving seawater. This happens in high energy envionments.
Saltation-
Small stones bounce or leapfrog along the seabed and beach. This process is associated with relatively high energy conditions. Small particles may be thrust up and dropped to the seabed again. They dislodge other particles upwards when dropped causing more bouncing movements to take place.
Suspension-
Very small particles of sand and silt are carried along by moving water. Such material is not only carried but is also picked up, mainly through the turbulence that exists in the water.
Solution-
Dissolved materials are transported within the mass of moving water.
Situations when disposition occurs-
-When sand and shingle accumulate faster than they are removed.
-As waves slow following breaking.
As water pauses at the top of the swash before backwash begins.
-When water percolates into the beach material as backwash takes it back down the beach.
Aeolian processes-
The entrainment, transport and deposition of sediment by wind.
Surface creep-
A process similar to traction, where wind rolls or slides sand grains along the surface.
Saltation-
When the wind is strong enough to temporarily lift the grains into the airflow to heights of up to 1 meter for distances of 20 or 30 meters.
Sub-aerial weathering-
Processes that slowly break down the coastline, weaken the underlying rocks and allow sudden movements or erosion to happen easily.
The three types of weathering-
-Mechanical/physical weathering
-Biological weathering
-Chemical weathering
Mechanical weathering examples-
-Freeze-thaw
-Pressure release
Biological weathering examples-
-Some marine organisms are able to drill into rock with their shells.
-Seaweed attached to rocks can dislodge them in strong waves.
-Some organisms produce chemicals promoting solution.
-Animals can burrow into cliffs.
Chemical weathering examples-
-Solution
-Oxidation (disintegrates rocks)
-Hydration (expands the rocks)
-Hydrolysis (acidic water combines with rock minerals creating clay)
-Carbonation (dissolves limestone)
-Acid rain (weakens rocks)
What factors effects the nature of mass movement on coastlines-
-Level of cohesion within the sediment
-Height of the slope and angle
-Grain size within the sediment
-Temperature and level of saturation.
Mass movement: Landslides-
Occur on cliffs made from softer rocks or deposited material, which slip as a result of failure within it when lubricated, usually following heavy rainfall.
Mass movement: Rock falls-
These occur from cliffs undercut by the sea, or on sloped affected by mechanical weathering like frost action.
Mass movement: Mudfows-
Heavy rain causes large quantities or fine material to flow down hill. Soil is saturated and excess water makes surface layers fluid and flow downhill. Nature of flow is dependent on level of saturation, type of sediment and slope angle.
Mass movement: Rotational slip or slumping.
Where softer material overlies much more resistant materials, cliffs are subject to slumping. Excessive lubrication make whole sections of cliffs move downwards with a slide plane that is concave, producing a rotation movement.
Mass movement: Soil creep-
This occurs where there is a very slow, almost imperceptible, but continuous movement of individual soil particles downslope. There is no confirmed cause but it is assumed it is the soil moisture working with weathering.
Run-off-
When there is more water than the land can absorb, creating small streams or just water that flows over the surface to reach the coastline.
Factors effecting coastal landscape-
Coastal geology and lithology
Climate
Nature of tides and waves.
Classifications of coastlines-
-Concordant or discordant, or
-A cliffed coast, flat coast or graded shoreline, or
-An emergent or submergent coast.
Characteristics of coastal landscapes depend on whether it is:
High or low energy coast
Dominated by processes of erosion or deposition
More or less intensely managed by people.
Main inputs of the coast-
-The geology and lithology of the coast
-The angle of the dip of the coastline in front of the headland.
-The nature of the waves approaching the coast.
-The direction and strength of the prevailing wind.
Components in systems operating at the coast-
-Wave refraction
-Differential rates of erosion of different rocks
-Erosion of the headland
-Deposition in the bay
Outputs in systems operating at the coast-
The characteristic features of the resulting landscape including:
-Headland and bays
-Erosional features of the headland
-Depositional features in the bay
How is a wave-cut notch formed?
High and steep waves break at the foot of a cliff with their energy and erosive action is concentrated into a small area of the rock face. With erosion concentrated at its base, the cliff begins to undercut.
Geo-
A crack in the cliff line will cut inland, widening the crack to form a narrow, steep sided inlet.
Ridges and runnels-
The small size of the sand means when its wet its compact and allows very little peroclation. Most swash returns as backwash, little energy is lost and material is carried down the beach. This leads to the development of ridges and runnels in the sand at the low-water mark. Run parallel to the shoreline and are broken by channels.
Storm beach-
Strong swash at spring high tide level creates a storm beach. This is a ridge composed of the biggest boulders thrown by the largest waves above the usual high tide mark.
Berms-
A series of ridges below a storm beach, marking the successively lower high tides as the cycle goes from spring to neap. Built by constructive waves.
Cusps-
Semi-circular shaped depressions which form when waves break directly on to the beach and swash and backwash are strong. They usually occur at the junction of the shingle and sandy beaches.
Swash-aligned beaches-
-Are generally oriented parallel to the incoming wave crests
-Experience minimal longshore drift
-Can be found on irregular coastlines where longshore drift is impeded and waves hit sections of the coast head-on.
Drift-aligned beaches-
-Are generally oriented parallel to the direction of dominant longshore drift.
-Can have considerable amounts of sediment transported long distances along them.
-Initially develop where a section of coastline is fairly regular or where the predominant wave direction is at an angle to the beach.
-Can extend out from the coastline if there is a sudden change in the direction of the coastline, upon reaching an estuary.
Characteristics of simple spits-
-Either straight or recurved
-Do not have minor spits, or recurved ridges along their landward edge.
Characteristics of compound spits-
-May have similar features to simple spits
-Have a number or recurved ridges, or minor spits, along their landward side, possibly marking the position where they terminated in the past.
How sand dunes develop-
As deposited sand dries out and is blown to their landward side of the spit, where it can accumulate and become stabilised by vegetation as species like marram grass get established.
Tombolo-
A spit that joins an island to the mainland is known as a Tombolo.
Barrier beach/ barrier island-
An elongated bank of deposited sand or shingle lying parallel to the coastline and not submerged by incoming tides.
Important in producing the present coastal landscape features-
-Local tectonic processes
-Sea level change- global and local
-Climate change- Natural an enhanced by human activity.
-Changing ocean currents and wave regimes
-Natural disasters or events- storms or tsunamis
-Changing sources, types and amounts of sediment
-The changing nature of human activity.
Sand dunes inputs-
-Plentiful supply of sand
-Strong onshore winds
-Large tidal range
-Obstacle to trap the sand
-Vegetation growth to encourage further growth of the dune.
Embryo dunes-
First dunes to develop. They are suitable for colonisation by grasses. These are able to grow upwards through wind blown sand.
Foredunes-
Initially yellow, because they contain little organic matter.
Dune slacks-
These are depressions within the dunes where the water table is on or near the surface and conditions are often damp.
Wasting dunes/ Dune heath-
Behind the yellow and grey dunes the supply of sand is gradually cut off giving smaller dune features.
Features of mudflats-
-In estuaries or landward side of spits
-Low-lying areas of shore, submerged at high tide
-Composed of silt and clay
-In estuaries, the saltwater brings large amount of fine sediments and meets the river which is also carrying its own fine silts and clays.
-In estuaries, when the two flows meet fine particles settle by process of flocculation, forming heavy particles together.
-Low tide- water is only left in permanent channels, smooth surface shows tidal action.
-Can be extensive covering 10s of squared km.
What makes mudflats not necessarily a permanent feature-
-Changes in sea level
-Wave action
-Changes in discharge levels to the river
-Changes to tidal flows
Eustatic change-
A global change in sea level resulting from an actual fall or rise in the level of the sea itself.
Fjord-
Former glacial valley drowned by rising sea levels.
Isostatic change-
Local changes in sea level resulting from the land rising or falling relative to sea level.
Raised beaches-
Areas of former wave cut platforms and their beaches which are at a higher level than the present sea level.
Ria-
Former river valley drowned by rising sea levels.
Tectonic change-
The rise or fall in sea level resulting from tectonic processes.
Coastal managements two main aims-
-To provide defence against and mitigate the impacts of flooding.
-To proving protection against and mitigate the impacts of coastal erosion.
Examples of hard engineering-
-Sea walls
-Rock armour (rip-rap)
-Gabions
-Groynes
Disadvantages of hard engineering:
-Structures can be expensive to build and to maintain (sea wall= £7,000/m)
-Defence in one place can have serious consequences for another area of the coast.
-Structures are sometimes an eyesore, spoiling landscape and disrupting natural habitats.
Heysham and Morecambe- Strategy 4: Gabions
Over 500 cages, measuring 2 X 1 X 1m, filled with small limestone boulders were used in various locations to reinforce the coast.
Heysham and Morecambe- Strategy 5: Concrete revetment and sea wall.
To the west of Heysham Head, extending to the port and power station, the existing sea wall and large concrete revetments were repaired and left in place.
Formby point- Where is ti?
Sefton coast north of Liverpool
Formby point- Largest dune area in England, how big?
Over 17km, and ranging from 200m to 4km in width
Formby point- Natural causes of erosion:
-Periodic storms combined with high tides
Formby point- Human causes of erosion:
-Dredging beach material for glass
-Building of hard sea defences in the north and south
-Activities developing ports in Liverpool and Preston
-Soil dumping in the north
-Human access
-Off-road vehicles
-Afforestation of a conifer plantation.
Formby point- If the sea levels rise what role will the sand dunes play?
A vital role in protection against flooding.
Formby point- Sefton Coast management scheme, includes:
-Planting used Christmas trees
-Fencing off areas to restrict human access
-Wooden posts to encourage dune regeneration
-Building boardwalks
-Signage to direct people around the dunes
-Educate local children
-Banning off-road vehicles
-Controlling commercial extraction of sand
Shoreline management plans (SMP) timelines:
-Short term (0-20 years)
-Medium term (20-50 years)
-Long term (50-100 years)
Key features of SMPs:
-Assess risks with evolution of coast.
-Provide framework to address risks to all
-Address risks sustainably
-Policy agenda for coastal defence planning
-Promote long-term management policies
-Technically sustainable, environmentally acceptable, economically viable.
-Ensure plans line up with national legislation
-Incorporate a route-map
-Provide foundation for future research
-Working documents continually reviewed and updated.
