Coasts (Autumn, second half)

Topic 6: Subaerial processes and mass movement

Key ideas

• Subaerial processes act on the cliff face and top. They include weathering and mass movement, as opposed to marine processes at the base.
• Weathering:
  • Mechanical:
    • Freeze–thaw: water expands about 9% on freezing and widens cracks.
    • Salt crystallisation: salt crystals grow in pores and exert pressure.
    • Wetting and drying: especially affects clays and shales.
  • Chemical:
    • Carbonation: CO₂ in rain forms weak carbonic acid, which dissolves limestone and chalk.
    • Hydrolysis: feldspar in granite is altered to clay.
    • Oxidation.
  • Biological:
    • Plant roots widen cracks.
    • Burrowing animals.
    • Rock-boring molluscs (e.g. piddocks).
    • Organic acids.
• Weathering produces sediment and weakens rock, which increases recession.
• Mass movement means the downslope movement of material under gravity:
  • Blockfall / rockfall: steep cliffs of jointed rock; blocks detach, often after freeze–thaw or undercutting.
  • Rotational slumping: weak clays and permeable-over-impermeable strata. Saturated material slides along a curved slip plane, leaving rotational scars and terraced (stepped) cliff profiles.
  • Landslides / translational slides: material slides along a planar surface, often a seaward-dipping bedding plane.
  • Mudflow: saturated fine material flows.
• Landforms produced:
  • Rotational scars.
  • Talus/scree slopes of debris at the cliff foot, which are then removed by the sea.
  • Terraced cliff profiles.
• Mass movement is important on coasts with weak and/or complex geology:
  • The Holderness boulder clay.
  • The Isle of Wight's Undercliff at Ventnor, which is a complex landslide.
  • Barton-on-Sea.
  • The Black Ven–Spittles landslide complex near Lyme Regis (Dorset).

Glossary

Term	Definition
Subaerial	Processes acting on the land surface (not under the sea).
Freeze–thaw	Repeated freezing of water in cracks that widens and breaks rock.
Carbonation	Dissolution of calcium carbonate rocks by weak carbonic acid.
Rotational slump	Mass movement along a curved slip surface.
Talus / scree	An accumulation of fallen rock fragments at the foot of a slope.
Pore-water pressure	The pressure of water within pore spaces; high values reduce rock strength.

Self-test

Q1: Explain how rotational slumping occurs. A: Rain percolates into permeable or weak material and saturates it, which raises pore-water pressure and weight while reducing friction. Where an impermeable layer below concentrates water, the mass fails along a curved slip plane and rotates backwards. Marine erosion at the toe removes support and encourages further failure.

Q2: Name three landforms produced by mass movement. A: Rotational scars, talus scree slopes and terraced cliff profiles.

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Topic 7: Sea-level change changes coasts

Key ideas

• Eustatic change is a global change in sea level caused by changes in the volume of water or in the shape of ocean basins:
  • Ice formation and melting: during the last glacial maximum, about 20,000 years ago, sea level was roughly 120 m lower than today.
  • Thermal expansion of warming water.
• Isostatic change is a local change in the level of the land:
  • Post-glacial adjustment (isostatic rebound): land that was depressed by ice sheets rises after melting.
    • Scotland is still rising.
    • South-east England is sinking slightly; the see-saw effect is linked to the British Isles' tilt.
  • Subsidence: e.g. sediment compaction in deltas, or groundwater and gas extraction.
  • Accretion: sediment build-up.
  • Tectonics: earthquakes can raise or drop coasts suddenly, e.g. the 2004 Indian Ocean earthquake changed land levels in Sumatra and the Andaman Islands.
• Emergent coastlines: relative sea level has fallen.
  • Raised beaches are former beaches now above the reach of waves, often backed by fossil (relict) cliffs, sometimes with old caves or stacks.
  • Examples: the raised beaches of western Scotland (e.g. on the Isle of Arran and Jura).
• Submergent coastlines: relative sea level has risen.
  • Rias are drowned river valleys, e.g. Kingsbridge Estuary, Fal Estuary and Salcombe in Devon and Cornwall.
  • Fjords are drowned glacial troughs: deep, steep-sided and with a shallow threshold at the mouth, e.g. Sognefjord (Norway) and Milford Sound (New Zealand).
  • Dalmatian coasts are drowned parallel ridges (Croatia).
• Contemporary sea-level rise is a risk to many coasts. The IPCC Sixth Assessment Report (2021) found that global mean sea level rose by about 0.20 m between 1901 and 2018, and that the rate is accelerating. Rise comes mainly from thermal expansion and melting land ice. Future rise is uncertain and depends on emissions and ice-sheet behaviour (an F theme).
• Most at risk:
  • Low-lying island states, e.g. the Maldives, where most land is only about 1–2 m above sea level.
  • Subsiding megadeltas, e.g. the Ganges–Brahmaputra and Mekong.
  • Coastal megacities.

Glossary

Term	Definition
Eustatic	A global change in sea level caused by changes in ocean water volume.
Isostatic	A local change in land level relative to the sea (e.g. rebound, subsidence).
Isostatic rebound	The uplift of land after the removal of ice-sheet weight.
Raised beach	A former beach left above the present sea level.
Fossil / relict cliff	A former sea cliff no longer attacked by waves.
Ria	A drowned river valley.
Fjord	A drowned glacial trough with a shallow threshold.
Thermal expansion	The increase in volume of seawater as it warms.

Self-test

Q1: Distinguish between eustatic and isostatic change. A: Eustatic change is a global change in the volume of sea water (e.g. ice melt, thermal expansion). Isostatic change is a local vertical movement of the land (e.g. rebound after glaciation, subsidence).

Q2: Give two landforms of a submergent coast and one of an emergent coast. A: Submergent: rias and fjords (also Dalmatian coasts). Emergent: a raised beach with a fossil cliff.

Q3: Why is south-east England at greater risk from sea-level rise than north-west Scotland? A: Scotland is still rising isostatically after the removal of ice, while south-east England is subsiding slightly. Combined with eustatic rise, the relative rise is larger in the south-east.

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Topic 8: Rapid coastal retreat causes threats to people

Key ideas

• Physical causes of rapid recession:
  • Geology: weak lithology, seaward dip, joints.
  • Marine factors: long fetch, storm waves, narrow beaches, high tidal range.
• Human actions can accelerate recession:
  • Dredging: offshore aggregate extraction removes sediment.
  • Coastal management that starves downdrift coasts (terminal groyne syndrome).
  • Dams that trap river sediment.
  • Sand mining.
• Subaerial processes and marine processes work together. Waves remove debris from the cliff foot, keeping the face steep and unstable. Weathering and mass movement then supply more debris.
• Rates of recession are not constant. They vary with:
  • Wind direction and fetch (e.g. north-easterly storms on Holderness).
  • Tides: spring high tides combined with storms.
  • Seasons: winter storms.
  • Weather systems: depressions; ENSO affects the Californian coast.
  • Individual storm events, e.g. the UK winter storms of 2013–14.

Case study: the Nile Delta, Egypt (human-accelerated recession)

• The Aswan High Dam (completed 1970) traps nearly all the Nile's sediment in Lake Nasser, so sediment no longer reaches the delta.
• The Rosetta promontory retreated very rapidly: published studies report rates of over 100 m per year from the 1960s to the 1980s.
• A seawall built in 1991 largely halted retreat at the tip, but erosion shifted to the ends of the protection.
• Delta subsidence, sea-level rise and irrigation diversion (which reduces flow) add to the threat.
• Threats: farmland, cities such as Alexandria and Rosetta, lagoons and fisheries.

Case study: California coast (e.g. Pacifica)

• Weak sedimentary cliffs (marine terraces of sandstone and mudstone).
• Severe erosion in strong El Niño winters (e.g. 1997–98 and 2015–16), with large waves and high sea levels.
• Damming of rivers and coastal armouring reduce sand supply to beaches.
• Cliff-top apartment buildings at Pacifica were evacuated and demolished after 2015–16 erosion.

Glossary

Term	Definition
Coastal recession	The landward retreat of the coastline.
Terminal groyne syndrome	Increased erosion just downdrift of the last groyne in a defended stretch.
ENSO	El Niño–Southern Oscillation; a periodic warming and cooling of the Pacific that alters storms and sea level.

Self-test

Q1: Give two human actions that accelerate coastal recession. A: Dams trapping river sediment (e.g. the Aswan High Dam starving the Nile Delta) and offshore dredging or coastal defences that starve downdrift beaches.

Q2: Why do recession rates vary from year to year? A: They depend on the frequency of storms, wind direction and fetch, tides (e.g. spring tides coinciding with storms), seasonal weather and the episodic nature of mass movement.

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Topic 9: Coastal flooding is a significant and increasing risk for some coastlines

Key ideas

• Local factors increase flood risk:
  • Land height: low-lying land.
  • Subsidence: e.g. of deltas, or from groundwater pumping.
  • Vegetation removal: e.g. the clearance of mangroves for shrimp farms removes a natural buffer.
• Global sea-level rise adds to these local factors.
• Storm surges are temporary rises in sea level caused by:
  • Low atmospheric pressure: each 1 hPa fall raises the sea about 1 cm.
  • Strong onshore winds piling water against the coast.
  • Funnelling into narrowing seas or bays (e.g. the southern North Sea, the Bay of Bengal).
  • Coinciding high (spring) tides.
• Causes of surges: mid-latitude depressions (e.g. in the North Sea) and tropical cyclones (e.g. in the Bay of Bengal).
• Climate change may increase flood risk through higher sea levels and possibly more intense storms. However, the pace and magnitude are uncertain, so both mitigation (cutting emissions) and adaptation (defences, retreat) are needed.

Case study: Bangladesh

• Most of the country lies on the low-lying Ganges–Brahmaputra–Meghna delta. The delta is subsiding in places and has a funnel-shaped bay (the Bay of Bengal) that amplifies surges.
• Major cyclone disasters:
  • The 1970 Bhola cyclone killed an estimated 300,000–500,000 people. This was mostly due to the storm surge, and it is the deadliest tropical cyclone on record (WMO).
  • Cyclone Sidr (2007) killed about 3,400 people (official reports about 3,363; some later studies give higher figures).
• The large fall in deaths came from cyclone shelters, early warning systems and volunteer networks (Cyclone Preparedness Programme). This shows adaptation working.
• Mangrove loss in the Sundarbans and shrimp farming increase the risk.

Case study: the Maldives

• Most islands are only about 1–2 m above sea level, so even modest sea-level rise threatens flooding, erosion and saltwater contamination of fresh groundwater.
• Responses:
  • Malé seawall.
  • The artificial raised island of Hulhumalé, built higher (about 2 m above sea level).
  • Debate about relocation.

Case study: the North Sea storm surges of 1953 and 2013 (UK and Netherlands)

• 31 January – 1 February 1953: a deep depression plus a spring tide and northerly gales.
  • 307 deaths in England and 1,836 in the Netherlands.
  • The disaster led to the UK's national surge warning service and the Thames Barrier (operational in 1982), and to the Dutch Delta Works.
• 5–6 December 2013 (Storm Xaver): the surge was comparable in height or higher in places, but there were no flood deaths in the UK. This was thanks to better defences, forecasting and warnings, although about 1,400 properties were flooded in England.
• Comparing the two events shows reduced vulnerability in a developed country.

Self-test

Q1: List four factors that combine to create a storm surge. A: Low air pressure (which raises the sea surface), strong onshore winds, funnelling by coastline shape or shallow seas, and a coincidence with high or spring tides.

Q2: Why were deaths in the UK from the 2013 surge so much lower than in 1953? A: Better defences (e.g. the Thames Barrier, raised sea walls), accurate surge forecasting and warnings, and coordinated evacuation and emergency planning.

Q3: Explain one local factor increasing flood risk in Bangladesh. A: Mangrove clearance for shrimp farms removes the vegetation that absorbs wave and surge energy, so surges penetrate further inland. Delta subsidence also lowers the land relative to the sea.

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Topic 10: Coastal erosion and flooding have serious consequences for communities

Key ideas

• Economic losses:
  • Housing and property values: coastal blight means homes become unsellable.
  • Businesses, e.g. tourism and caravan parks.
  • Agricultural land.
  • Infrastructure: roads, railways (e.g. the Dawlish railway, washed away in February 2014), utilities.
• Social losses:
  • Relocation.
  • Loss of livelihood.
  • Loss of community and amenity value.
  • Stress and health effects.
• Losses are greatest in densely developed coastal areas.
• Developed compared with developing countries:
  • Developed countries suffer higher absolute economic losses but fewer deaths, because of insurance, warnings and defences.
  • Developing countries suffer higher death tolls and larger losses relative to GDP, because of poverty and informal housing.
• Environmental (climate) refugees:
  • Climate change may force migration from coasts, e.g. from low-lying atolls such as Kiribati and Tuvalu, and from the Bangladesh delta.
  • The term "refugee" has no legal status for climate migrants under the 1951 Refugee Convention.

Case study: Happisburgh, North Norfolk (consequences and adaptation)

• Cliffs: about 6–10 m of soft sands, silts and clays.
• Management history:
  • Wooden revetments built in the 1950s failed in the 1990s.
  • Since then, dozens of properties along Beach Road have been lost to rapid erosion, often several metres in a single storm.
  • The Kelling to Lowestoft Shoreline Management Plan (draft 2004) concluded that continued defence was not sustainable. The policy moved away from Hold the Line towards managed realignment / no active intervention.
• Coastal Change Pathfinder: in 2009 Defra awarded North Norfolk District Council £3 million. Part of this funded a "rollback" scheme: the council bought nine at-risk Beach Road homes at market value, demolished them and permitted replacement homes inland.
• Temporary rock armour, part-funded by the community, was placed to "buy time" for adaptation.
• Consequences:
  • Residents could not sell homes or get insurance.
  • The community felt abandoned and campaigned through the Coastal Concern Action Group.
  • Heritage was lost, and the Grade I listed church and lighthouse are increasingly threatened.

Self-test

Q1: What is "coastal blight"? A: The loss of property value and saleability (and the dereliction that follows) because homes are threatened by erosion or flooding.

Q2: What did the Happisburgh Pathfinder project do? A: Using part of a £3 million Defra grant (2009), North Norfolk District Council bought and demolished nine at-risk homes on Beach Road at market value and allowed replacement homes inland (rollback). It also funded beach access, car park and toilet relocation and debris clearance.

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Topic 11: Different approaches to managing coastal recession and flooding

Key ideas

• Hard engineering consists of structures that alter physical processes. It is expensive and can have unforeseen consequences elsewhere.

Method	How it works	Advantages	Disadvantages
Sea wall (recurved)	A concrete wall reflects wave energy	Strong; protects towns; promenade	Very expensive; reflected waves scour the beach; visually intrusive
Groynes (timber/rock)	Trap LSD, widening the beach that absorbs energy	Builds a beach (tourism); relatively cheap	Starves downdrift beaches (terminal groyne syndrome)
Rip-rap / rock armour	Large boulders absorb and dissipate wave energy	Cheap compared with walls; quick to place	Can be outflanked; unattractive; access issues
Revetment	A sloping structure (timber/concrete/rock) absorbs energy	Cheaper than walls	Needs maintenance; may fail (e.g. Happisburgh)
Offshore breakwater	Breaks waves before they reach the shore	Reduces energy; encourages deposition	Costly; navigation hazard; alters sediment movement

• Soft engineering works with natural processes:
  • Beach nourishment: adding sand or shingle, e.g. on Bournemouth's beaches.
  • Cliff regrading and drainage: reducing the slope angle and removing water to cut slumping.
  • Dune stabilisation: marram planting and fencing.
  • Managed realignment: letting the sea flood low-value land to create salt marsh, which acts as a natural buffer.
  • Advantages: soft engineering is often cheaper and more natural.
  • Disadvantages: it needs repeating and can lose land.
• Sustainable management plans for future threats, such as more storms and higher seas. It combines mitigation and adaptation, but can cause local conflict, because some people "lose".

Case study: Mappleton, Holderness (hard engineering and its consequences)

• The scheme: in 1991 about £2 million was spent on two rock groynes and a rock revetment of large granite boulders imported from Scandinavia. The aim was to protect the village (about 50 properties) and the B1242 coast road.
• Success: the village and road are protected, and a beach builds up between the groynes.
• Consequences:
  • The defences trap LSD (which moves north to south), so the cliffs south of Mappleton were starved of sediment.
  • Erosion there increased from about 1.7 m/yr (1952–89) to about 3.3 m/yr (1989–2005).
  • This threatened farmland and farm buildings to the south (around Cowden).
  • It is a classic example of terminal groyne syndrome and of "unforeseen consequences".
• Other Holderness defences: Hornsea (sea wall and groynes) and Withernsea (sea wall and groynes); see Topic 3.

Case study: Medmerry managed realignment, West Sussex (soft engineering)

• Completed in 2013 by the Environment Agency at a cost of about £28 million (roughly £20 million construction plus £8 million land).
• The scheme breached the old shingle bank and built about 7 km of new embankments inland.
• This created about 183 ha of intertidal habitat (salt marsh and mudflat), forming part of an RSPB reserve.
• It protects about 350 homes, as well as the Selsey area, caravan parks and roads.
• It worked with nature, but farmland was lost.

Self-test

Q1: Why can groynes increase erosion elsewhere? A: They trap sediment moving by longshore drift, so less sediment reaches downdrift beaches. Those beaches narrow and the cliffs behind are attacked more (e.g. south of Mappleton, where erosion roughly doubled after 1991).

Q2: Give two advantages and one disadvantage of managed realignment. A: Advantages: it creates intertidal habitat that dissipates wave energy (a natural, self-maintaining defence) and is cheaper to maintain than walls. Disadvantage: farmland or property is lost, which can cause conflict.

Q3: How much did the Medmerry scheme cost and what did it create? A: About £28 million (2013). It created about 183 ha of intertidal habitat and new inland embankments.

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Topic 12: Holistic integrated coastal zone management (ICZM)

Key ideas

• ICZM is a holistic, long-term, sustainable approach. It manages the whole coastal zone (land and sea, natural and human systems) across administrative boundaries, involving all stakeholders. It often uses sediment cells as management units, so that action in one place does not harm another.
• The EU promoted ICZM (Recommendation, 2002). Many countries now develop sustainable, holistic schemes.
• Shoreline Management Plans (SMPs) in England and Wales:
  • 22 second-generation SMPs (SMP2) cover the coast, based on sediment cells and sub-cells.
  • Each policy unit is given a policy for three epochs: 0–20, 20–50 and 50–100 years.
• The four SMP policy options:
  • Hold the Line (HTL): maintain the current shoreline position (e.g. towns such as Hornsea).
  • Advance the Line (ATL): build new defences seaward (rare).
  • Managed (strategic) realignment (MR): allow the shoreline to move, with management (e.g. Medmerry).
  • No Active Intervention (NAI): no investment in defences (e.g. much of Holderness, Happisburgh in the long term).
• Decisions depend on complex judgements:
  • Engineering feasibility.
  • Environmental sensitivity, e.g. SSSIs and protected habitats.
  • Land value.
  • Political and social reasons, e.g. heritage and pressure from residents.
• Decisions are informed by Cost–Benefit Analysis (CBA), which in England broadly requires benefits to exceed costs for government funding, and by Environmental Impact Assessment (EIA).
• Conflicts and winners/losers:
  • Homeowners at Happisburgh (losers under NAI) versus taxpayers and environmental groups.
  • In developing or emerging countries, e.g. Chattogram (Chittagong), Bangladesh:
    • The coast and the area around the port city are exposed to erosion, cyclones and sea-level rise.
    • Embankments (e.g. the Patenga embankment) have repeatedly been damaged.
    • Priorities compete: port and industrial growth, informal settlements and fishing communities.
    • Responses include embankment repair, foreshore afforestation (mangroves) and international funding.
    • Poorer communities often have less say.

Case study: the Netherlands – "Building with Nature" (ICZM in a developed country)

• In 2011 the Sand Motor (Zandmotor) placed about 21.5 million m³ of sand as a hook-shaped peninsula on the Delfland coast. Waves, currents and wind redistribute it naturally along the coast and into the dunes.
• This reduces repeated nourishment disturbance and adds recreation and habitat value. It is an integrated, adaptive approach.

Exam technique: the 20-mark "Evaluate" question

Example question: "Evaluate the view that holistic ICZM approaches are the most sustainable way to manage coasts" (20 marks).

Introduction:

• Define ICZM and sustainability (economic, social, environmental).
• State your line of argument, e.g. "ICZM is the most sustainable in principle, but its success depends on funding and on resolving conflicts between players."

Paragraph 1: ICZM's strengths. It is cell-based, avoids moving problems downdrift (contrast Mappleton) and takes a long-term view (SMP epochs). Use Medmerry or the Sand Motor as evidence.

Paragraph 2: Weaknesses. Losers and conflict (Happisburgh: NAI and blight), CBA undervalues poorer rural places, and ICZM needs money.

Paragraph 3: The developing-country context (Chattogram/Bangladesh). Priorities and capacity differ, so hard defences and shelters may be the only option.

Paragraph 4: Alternatives. Hard engineering protects high-value towns (Hornsea, the Thames Barrier) and may be more sustainable for those places.

Conclusion: Make a balanced judgement, e.g. "largely sustainable environmentally, less so socially", and bring in futures and uncertainty (sea-level rise).

Marks: each paragraph should evaluate (strengths and limitations) – that is where the 15 AO2 marks are.

Glossary

Term	Definition
ICZM	Integrated Coastal Zone Management: holistic, sustainable management of the whole coastal zone.
SMP	Shoreline Management Plan: a non-statutory plan setting policies for each stretch of coast in England and Wales.
Hold the Line / Advance the Line / Managed Realignment / No Active Intervention	The four SMP policy options.
Cost–Benefit Analysis	Comparing the monetary costs of a scheme with the value of the losses it prevents.
Environmental Impact Assessment	A formal study of a project's likely environmental effects.
Stakeholder / player	An individual or organisation with an interest in a decision.

Self-test

Q1: List the four SMP policy options. A: Hold the Line, Advance the Line, Managed Realignment and No Active Intervention.

Q2: Why do SMPs use sediment cells? A: Sediment moves within cells, so managing a whole cell together avoids defences in one place starving or harming another.

Q3: Give two factors that influence the choice of SMP policy. A: Any two of: engineering feasibility, environmental sensitivity (e.g. protected habitats), land/property value (CBA), and political and social factors such as public pressure or heritage.

Q4: Why might a developing country find ICZM harder to implement? A: Limited funding and technical capacity, competing priorities (port and economic growth versus protecting poor communities), weaker governance, many informal settlements and higher exposure to cyclones.

Assessment checkpoint (before Christmas): the Coasts end-of-unit assessment with a 20-marker. Revise all 12 topics. Make sure you can use Holderness/Mappleton, Happisburgh, Medmerry, the Nile Delta, Bangladesh and the Sand Motor flexibly.

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