Approaches to managing risks associated with coastal recession and flooding

Hard Engineering

🔗A form of coastal management that involves the construction of man-made features

Soft Engineering

🔗A form of coastal management that involves working with natural features

Hard Engineering Strategies

Type	Construction & Materials	Purpose & Benefits	Negative Impacts on Physical Processes
Rip-rap	Large igneous or metamorphic rock boulders, weighing several tonnes	Often used at the base of sea walls to protect them from undercutting & scour • Break up & dissipate wave energy • Long-lasting & flexible in use • Causes sediment deposition between rocks • May become vegetated	• Expensive (£50 per m3) • Seawater can still move through ∴ some backshore erosion can occur • Relatively insightly
Offshore Breakwater	Large igneous or metamorphic rock boulders, weighing several tonnes	Forces waves to break offshore rather than at the coast ∴ ↓ in energy & erosive force • Allows LSD to continue behind them • Can create sheltered water areas behind them for water sports	• Cost £1-2 mil • May create ↑ deposition on the landward side, ↓ LSD • Other defences may be needed for the gaps between reefs
Sea wall	Concrete w/ steel reinforcement & deep piled foundations Tends to have a stepped and/or bullnose profile	• Can also act as flood barriers • Designed to dissipate rather than deflect (less secondary damage) • Provide a sense of security • Popular w/ tourists to sit on	• Destruction of the natural cliff face and foreshore environment • Very expensive (£5000 per m) • Greatly ↓ supply of sediment to sediment cell • Can be considered unsightly
Revetments	Stone, timber or interlocking concrete sloping structures which are permeable	• Absorb wave energy & trap sediment • LSD can continue • Cheaper than sea walls • ↓ erosion on dune faces & mud flats • Can encourage deposition & may become vegetated	• Cost £1500 per m • Need consistent maintenance • Reduce access from backshore to the beach
Groynes	Vertical stone or timber fences built at 90o to coast, spaced out along the beach	Prevent LSD and encourage deposition ∴ building a wider & higher beach • Encourage tourism as beach bigger & more visually appealing • Cheaper than sea walls	• Can cause Terminal groyne syndrome downdrift • Expensive (£1000 per m)

Soft Engineering Strategies

Type	Purpose & benefits	Negative impacts on physical processes
Beach nourishment	Replaces beach sediments eroded or transported by LSD • Uses natural sediments ∴ beach remains natural • Provides amenity for recreation & supports local tourist industry	• £10 per m3 • May have to be replaced frequently after winter storms • If sediment are dredged from offshore, alters sediment cell & removes habitats
Cliff regrading	Creates a new slope angle that is stable for the characteristics of the rock type • Creates a natural-looking slope • Will remain stable as long as the base of the slope is protected from marine erosion	• £1 million • Other defences needed to protect the cliff base • Cliff drainage may also be required
Cliff drainage	Help to drain the cliff using gravel when the cliff lithology has permeable above impermeable rock • Reduces the risk of mass movement after heavy rainfall • Looks natural once revegetated	• Only reduces risk of mass movement, does not prevent it • If implemented across the entire cliff, it can disturb the cohesion of the rock layers
Dune stabilisation	Provide a natural barrier to sea level rise & storm waves • Looks natural & good barrier to high tide/waves • Provides a natural ecosystem & recreation area • Can be used to restore dunes lost to storm surges	• Costs £1000 per 100m to replant dunes, dune fencing = £500 per 100m • May need to be fenced off while the plants grow ∴ ↓ in short-term amenity value • Powerful storms can undo stabilisation as relatively fragile

Sustainable Management

Provides ways to continue using coastal & marine resources in a way that will not ↓ the ability of future generations to use them in the same way

Examples of Sustainable Coastal Management

• Monitoring coastal change & adapting to unexpected trends
• Educating communities to understand why change is needed & how to adapt
• Adapting to rising sea levels by relocating, alternative building methods & water supplies
• Creating alternative livelihoods before existing ones are lost to sea
• Managing flood and erosion risk where possible, or relocating to safer areas
• Managing natural resources (fish, farmland) to ensure long-term productivity

Managed Retreat

🔗_An_ area is set aside for the sea to flood or erode

• Avoids the construction & maintenance costs of hard engineering

• Can extend valuable natural ecosystems

• Requires the agreement of affected land & property owners
• May only be a medium-term solution if sea levels continue to rise
• Defences often need to be constructed around the edge of the flooded area to protect property

Adaptation Strategy Examples

• Restoring mangroves
• Zoning areas of the coast Prevents further development there ∴ ↓ in risk
• Elevating critical infrastructure Prevents them from flooding