IB Geography B.3.1 Coastal Erosion and Flooding Management Strategies Notes

Coastal Management Changes Erosion and Flood Risk

1. Coastal managers first identify the source of a hazard, the path followed by waves or floodwater, and the people, property or ecosystems exposed to it.
2. A scheme that lowers risk at one frontage can increase it elsewhere because beaches, cliffs and sediment transport operate as a connected coastal system.
3. Management therefore combines physical effectiveness with cost, maintenance, environmental impact, public acceptance and the expected life of the scheme.
4. Sediment-cell scale: Managers should trace sediment sources, transfers and sinks before selecting a defence because intervention at one frontage can change beach volume and risk elsewhere.
5. Decision sequence: Hazard mapping identifies probability and process, exposure mapping locates assets, appraisal compares options, and consultation reveals whose costs and values are otherwise overlooked.
6. Adaptive pathway: Rather than committing permanently to one structure, managers can set evidence-based triggers for nourishment, stronger protection or relocation as sea level and maintenance costs change.

Hard Engineering Protects Selected Assets but Alters Sediment Movement

1. Seawalls: Concrete or stone barriers resist erosion and flooding, but reflected wave energy can scour the beach and maintenance costs rise as sea level and storm intensity increase.
2. Groynes: Barriers placed across the beach trap sediment moved by longshore drift, creating a wider beach on the updrift side while reducing sediment supply downdrift.
3. Rock armour and revetments: Sloping blocks or structures absorb wave energy more gradually than a vertical wall, although they occupy beach space and may require imported material.
4. Offshore breakwaters: Structures placed seaward of the coast reduce wave energy and encourage deposition, but they can change currents and transfer erosion around their ends.
5. Hard engineering is most defensible where the value of protected settlements and infrastructure exceeds the full economic, social and environmental cost over the scheme's lifetime.
6. Wave reflection: A vertical defence can prevent landward erosion while increasing turbulence and scour at its base, so structural survival does not necessarily mean the beach is being conserved.
7. Terminal effect: Where a defended frontage ends, the sudden loss of protection and sediment can focus erosion on the adjacent unprotected coast.
8. Whole-life cost: Construction cost is only the first expense because inspection, repair, raising and eventual replacement must be included over the design life.

Cliff-Line Stabilisation Reduces Slope Failure

1. Cliff drainage lowers pore water pressure because saturated material is heavier and more likely to slide along a weak layer.
2. Regrading reduces the slope angle, while retaining structures and rock armour support the cliff toe against wave attack.
3. Vegetation can bind surface sediment and reduce runoff, but roots cannot stabilize a cliff if waves continue to remove its base.
4. Cliff stabilization treats both marine erosion at the toe and subaerial processes on the slope, so it is more effective than protecting only one part of the system.

1. Pore-water mechanism: Rainfall raises water pressure between sediment grains, reducing friction along a slip plane, while toe erosion removes the support that helps hold the slope in place.
2. Regrading trade-off: Flattening a cliff lowers gravitational stress but consumes land at the crest and may require drainage and toe protection to prevent renewed failure.

Soft Engineering Works with Coastal Processes

1. Beach nourishment: Adding sand widens the beach so waves lose energy before reaching cliffs or buildings, but repeated replenishment is usually required.
2. Dune stabilization: Fencing, planting and controlled access help dunes trap sand and retain a flexible barrier against waves and wind.
3. Saltmarsh restoration: Intertidal vegetation slows water, traps sediment and stores floodwater, although it needs sufficient space and an appropriate tidal range.
4. Soft engineering often preserves amenity and habitat better than hard structures, but its performance depends on continuing sediment supply and space for natural adjustment.
5. Sediment compatibility: Nourishment lasts longer when added material matches local grain size and wave conditions, because sediment that is too fine is rapidly carried offshore or alongshore.
6. Coastal squeeze: Saltmarsh cannot migrate inland where fixed defences or development block its path, so habitat area may shrink as sea level rises.
7. Monitoring need: Beach profiles, dune condition and storm losses must be measured repeatedly so replenishment occurs before a protective buffer falls below its target width or volume.

Managed Retreat Exchanges Land for Long-Term Protection

1. Managed retreat can remove or realign defences so low-value land floods or erodes in a controlled way while more important assets are protected farther inland.
2. Breaching a sea wall may create mudflat or saltmarsh that attenuates waves and provides habitat, but landowners may lose farmland, property or access.
3. Compensation, consultation and a clear timetable influence whether affected communities regard retreat as a planned adaptation or an imposed abandonment.
4. Retreat is most practical where relocation is possible and the cost of repeatedly defending the existing shoreline would be greater than the value protected.
5. Realignment mechanism: Moving a defence inland creates space in which floodwater can spread and intertidal vegetation can develop, reducing wave energy before it reaches the new line.
6. Distributional justice: The wider coast may gain habitat and lower defence costs while a smaller group loses land, so compensation, tenure and participation are central to whether retreat is legitimate.

Holderness Shows How Protection Redistributes Risk

1. Spatial selectivity: The policy protects larger settlements and strategic infrastructure but accepts continued erosion along much rural frontage, making public value and political priority visible on the coastline.
2. Sediment consequence: Holding one cliff line reduces the erosion that would otherwise supply beaches farther south, so a local success can contribute to downdrift sediment deficit.
3. Power and evidence: Residents can document immediate losses, planners compare regional costs, and infrastructure operators emphasize continuity, but groups with fewer assets may struggle to justify expensive protection.

Evaluation Depends on Time, Scale and Equity

1. A strategy can be locally successful yet regionally damaging if it protects one place by interrupting sediment that would have replenished another.
2. Short-term protection may become unsustainable when maintenance costs, sea-level rise and more frequent extreme water levels are included.
3. Cost-benefit analysis favours high-value assets, so decision-makers must also consider cultural attachment, distributional fairness and the needs of people with less political influence.
4. An adaptive pathway sets trigger points for nourishment, stronger defences or relocation so that decisions can change as risk and evidence change.
5. Three tests: A defensible judgement should separate engineering effectiveness, environmental system effects and the fairness of how costs and residual risk are distributed.
6. Uncertainty: A strategy should remain workable across plausible sea-level and storm scenarios rather than relying on one forecast of future conditions.