Physical and human challenges: issues, strategies, evaluation

Coastal Environments – Cambridge AS & A Level Geography (9696)

Learning objective

Explain the physical and human challenges affecting coastal environments, evaluate the range of management strategies used to address these challenges, and assess their effectiveness using appropriate criteria.

1. Physical processes that shape coasts

1.1 Wave generation

• Wind transfers energy to the sea surface.
• Key variables: fetch (distance wind blows), wind speed, duration of wind.

1.2 Wave characteristics

• Height, period, length, direction – determine the energy reaching the shore.
• Refraction – bending of waves as they enter shallower water; concentrates energy on headlands.
• Breaking type – depends on wave steepness:
  • Spilling (gentle slope, sandy beach)
  • Plunging (steeper slope, coarse beach)
  • Surging (very steep, cliffs)

1.3 Marine erosion

• Hydraulic action – water pressure in cracks.
• Abrasion (corrasion) – rock fragments act as tools.
• Solution – dissolution of soluble rocks (e.g., limestone).

1.4 Sub‑aerial weathering (above high‑water mark)

• Freeze‑thaw (frost shattering)
• Thermal expansion & contraction
• Chemical weathering (e.g., oxidation)
• Biological action (root wedging, burrowing animals)

1.5 Marine transport & deposition

• Swash (uprush) and backwash (downrush) move sediment up‑ and down‑the beach.
• Long‑shore drift – sediment transport parallel to the shoreline driven by oblique wave approach.
• Sediment load types:
  • Suspended load – fine particles carried in the water column.
  • Bed load – coarser material rolled or hopped along the seabed.

1.6 Sediment cells

• Geographically limited sections of coast with a relatively closed sediment budget.
• Boundaries are often set by headlands, groynes, or abrupt changes in wave direction.

1.7 Storm surges & extreme weather

• Low atmospheric pressure + strong on‑shore winds → temporary sea‑level rise.
• When coincident with high tide, can cause severe flooding.

1.8 Sea‑level rise (SLR)

• Long‑term rise caused by thermal expansion of seawater and melting of land ice.
• IPCC projections (RCP 4.5–8.5) for 2100: 0.3–1.0 m global mean rise.
• Implications: increased coastal erosion, higher flood risk, salt‑marsh inundation.

1.9 Classification of coastlines

• Concordant coast – rock layers run parallel to the shoreline; typically long, straight beaches with occasional headlands where harder rock outcrops.
• Discordant coast – alternating bands of hard and soft rock run perpendicular to the shoreline; produces headlands of resistant rock and bays of erodible rock.

2. Coastal landforms (erosional ↔ depositional)

Landform	Dominant process	Typical setting	Key features
Cliffs & wave‑cut platforms	Erosion (hydraulic action, abrasion, solution)	High‑energy coast, resistant rock	Steep face, flat platform at base, measurable retreat rate
Caves, arches, stacks	Erosion + differential weathering	Headlands with joints or faults	Progressive enlargement → collapse → isolated stack
Headlands & bays (discordant coast)	Erosion of soft rock, protection of hard rock	Alternating rock types perpendicular to shore	Hard‑rock protrusions (headlands) and eroded recesses (bays)
Beaches – dissipative vs. reflective	Deposition (balance of swash & backwash)	Energy & sediment supply dictate slope	Dissipative: fine sand, gentle slope, wide surf zone. Reflective: coarse pebbles, steep slope, narrow surf zone.
Spits & tombolos	Long‑shore drift & deposition	Low‑energy bays, estuaries, or sheltered inlets	Spit extends from coast; tombolo links island to mainland
Barrier islands & barrier beaches	Deposition within a sediment cell	Shelf with abundant sand, low gradient	Parallel ridges, lagoon behind, migrate landward with SLR
Dunes (fore‑ and hinter‑dunes)	Aeolian (wind) transport & deposition	Sand‑rich beach with on‑shore wind	Vegetation (e.g., marram grass) stabilises; important buffer
Salt‑marshes	Biogenic sediment trapping & accretion	Estuarine or sheltered low‑energy coasts	Vegetated, low‑lying; attenuates wave energy, provides habitat
Mangroves	Biogenic accretion, root‑matrix trapping	Tropical sheltered coasts, often behind a fringe of reefs	Complex root systems, high carbon sequestration, strong wave attenuation
Coral reefs (fringing, barrier, atoll)	Biogenic calcium‑carbonate accretion	Tropical, warm (23‑29 °C), clear, shallow water	Protect shorelines, high biodiversity, vulnerable to bleaching

3. Physical & human challenges

• Coastal development – high‑value land attracts dense settlement; increases exposure to erosion, flooding and storm surge.
• Tourism pressure – seasonal influx creates spatial variation in waste generation, water demand and infrastructure stress.
• Pollution – point sources (oil spills, sewage outfalls) and diffuse sources (plastic debris, agricultural runoff) degrade water quality and marine life.
• Resource extraction – sand and gravel mining disrupt sediment budgets, often accelerating erosion.
• Land‑use change – removal of dunes, mangroves, salt‑marshes reduces natural buffers and ecosystem services.
• Sea‑level rise & increased storm intensity – long‑term hazard that amplifies all of the above pressures.

4. Management strategies

4.1 Hard engineering

• Sea walls – vertical or sloping structures that reflect or absorb wave energy.
• Groynes – perpendicular barriers that trap long‑shore drift sediment.
• Breakwaters – offshore structures that reduce wave energy before it reaches the shore.
• Revetments – sloped armour of rock or concrete that dissipates energy.

4.2 Soft engineering & nature‑based solutions

• Beach nourishment – adding compatible sand to eroding beaches.
• Dune regeneration – planting marram grass, installing sand fences, re‑shaping dune profiles.
• Living shorelines – use of mangroves, salt‑marshes, oyster reefs, or vegetated buffers to attenuate waves while providing habitat.
• Managed realignment (retreat) – deliberately breaching or lowering defences to allow the sea to inundate low‑lying land, creating new intertidal habitats.

4.3 Policy, planning & institutional measures

• Coastal Zone Management Plans (CZMPs) – integrated assessment of hazards, land‑use, and stakeholder interests.
• Set‑back (buffer‑zone) regulations – minimum distance of new development from the high‑water mark.
• Insurance & risk‑based pricing – economic incentives for risk reduction and for adopting resilient building standards.
• International frameworks – UN Sustainable Development Goal 14 (Life Below Water), Convention on Biological Diversity, IPCC guidance on SLR.

5. Evaluation of strategies

Strategy	Advantages	Disadvantages	Effectiveness (hazard × scale)
Sea walls	Immediate, long‑term protection; predictable performance.	High construction & maintenance cost; can increase downdrift erosion; visual impact; limited against extreme surge + SLR.	Best on high‑energy, high‑value urban coasts (local scale). Less effective where sea‑level rise exceeds design height.
Groynes	Relatively cheap; widen beaches; boost local tourism.	Interrupt long‑shore drift → downdrift erosion; require periodic repair.	Effective on moderate‑energy, sediment‑rich coasts (site‑scale). Not suitable for large storm events.
Breakwaters	Protect harbours and extensive beach stretches; reduce wave energy over a wide area.	Can cause accretion on leeward side and erosion on windward side; may affect navigation.	Ideal for ports and low‑energy beaches (regional scale). Limited where deep‑water access is needed.
Beach nourishment	Preserves natural appearance; supports tourism & wildlife.	Requires repeated replenishment; source‑sand may be scarce; can disturb benthic habitats.	Works on low‑to‑moderate energy coasts with adequate sediment supply (site‑scale). Success depends on wave climate and sand compatibility.
Managed realignment	Creates space for natural processes; long‑term cost savings; enhances biodiversity and ecosystem services.	Social disruption; loss of land/value; political resistance.	Most viable on sparsely populated, low‑lying coasts with high erosion rates (regional scale). Requires strong governance and compensation schemes.
Living shorelines	Multiple ecosystem services (habitat, water‑quality improvement, carbon sequestration); aesthetically pleasing.	May be less effective against extreme storms; longer establishment period; limited to suitable substrate.	Ideal for low‑energy estuarine or lagoonal settings (site‑scale). Often used in combination with hard structures in high‑energy zones.

5.1 Evaluation criteria (AO3)

• Cost‑benefit analysis (construction, maintenance, opportunity cost).
• Environmental impact (habitat loss/gain, water quality, biodiversity).
• Longevity & resilience to sea‑level rise and extreme events.
• Effect on the sediment budget (accretion vs. erosion).
• Social acceptance, equity and community involvement.
• Provision of ecosystem services (coastal protection, carbon storage, recreation).

5.2 Limitations of quantitative evaluation

Monetary valuation often fails to capture non‑market benefits such as cultural heritage, intrinsic biodiversity value and long‑term adaptive capacity. Discount rates can undervalue future benefits, and data gaps (e.g., precise sediment budgets, long‑term maintenance costs) introduce uncertainty into cost‑benefit calculations.

6. Illustrative case studies

6.1 “Room for the River” – Dutch coastal realignment

Location: Rhine–Meuse delta, southwestern Netherlands.

• Pressures: historic sea‑level rise (~3 mm yr⁻¹), land subsidence, increasing flood risk to densely populated polders.
• Response: breaching and lowering dikes, creating secondary flood‑plains, establishing wetland nature reserves, relocating villages and adapting agriculture.
• Evaluation:

  Criterion	Positive outcomes	Limitations
  Flood protection	Peak discharge reduced up to 30 %; lower long‑term dike‑raising costs.	Requires continuous monitoring; extreme events could still overtop new flood‑plains.
  Environment	30 km² of new wetland habitat; increased biodiversity and carbon sequestration.	Initial construction disturbance; succession trajectories uncertain.
  Economic & social	Long‑term savings on dike maintenance; new recreation/tourism opportunities.	Compensation for relocated residents; opposition from some agricultural interests.
  Scalability	Model adopted in other Dutch deltas and internationally (e.g., UK Thames Estuary).	High upfront land‑acquisition costs limit use on densely built‑up coasts.

6.2 Miami‑Dade County sea‑wall & beach‑renourishment programme (USA)

• Hard sea‑walls protect high‑rise beachfront; periodic beach nourishment maintains tourism‑driven economy.
• Evaluation shows high maintenance costs and increasing vulnerability to SLR‑induced “sunny day flooding”.

6.3 Managed retreat in the Sundarbans (Bangladesh & India)

• Accelerating erosion and SLR have prompted relocation of villages and conversion of former settlements to mangrove‑dominated buffer zones.
• Success depends on community participation and compensation mechanisms; challenges include loss of agricultural land and cultural ties.

7. Exam‑style discussion prompts (AO3)

1. Compare the short‑term economic benefits of hard engineering with the long‑term sustainability of soft engineering and managed retreat.
2. Under what geological (e.g., sediment supply, wave energy) and socio‑economic (population density, land value) conditions is managed retreat the most viable option?
3. How do community perceptions and cultural values influence the success of dune regeneration schemes?
4. Discuss how cost‑benefit analysis can incorporate ecosystem services and the methodological challenges involved.
5. Assess the effectiveness of policy tools (set‑back lines, CZMPs, insurance premiums) in reducing exposure to coastal hazards.

8. Suggested diagrams (for classroom or exam revision)

• Cross‑section of a coastline showing hard‑engineering structures (sea wall, groyne, breakwater) alongside soft‑engineering features (dune, vegetated marsh, living shoreline).
• Diagram of wave transformation from deep water to breaking on a beach (including refraction and breaking type).
• Sediment budget of a coastal cell illustrating sources, sinks and the effect of a groyne.
• Conceptual map of the “Room for the River” programme – original dike line, breach locations, new flood‑plain areas.