2B.11A - Hard Engineering

Hard engineering (groynes, sea walls, rip rap, revetments, offshore breakwaters) are economically costly and deliberately alter physical processes and systems. 

This is the traditional management process for erosion/flooding, encasing the coastline in concrete, stone and steel. The aim is to directly stop physical processes altogether (such as erosion or mass movement) or alter them to protect the coast (such as encouraging deposition to build larger beaches)

Advantages

• It's obvious to at-risk people that something is being done to protect them, its reassuring
• A 'one-off' solution that could protect a coastline for decades

Disadvantages

• Costs are usually very high, and there are still ongoing maintenance costs
• Even very carefully designed engineering solutions are prone to failure
• Coastlines are made visually unattractive and the needs of a coastal ecosystem are usually overlooked
• Defences built in one place frequently have adverse consequences further along the coast

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Groynes	Sea Wall	Rip Rap (rock armour)	Revetments	Offshore rock breakwater
Vertical stone or timber 'fences' built perpendicular to the coast and spaced along the beach.	Concrete with steel reinforcement and deep-piled foundations; can have a stepped and/or 'bullnose' profile, to dissipate wave energy	Large igneous or metamorphic rock boulders, weighing several tonnes	Stone, timber or interlocking concrete sloping structures which are permeable	Large igneous or metamorphic rock boulders weighing several tonnes (offshore rip-rap)
Their purpose is to prevent longshore movement of sediment and encourage deposition, building a wider, higher beach.	A physical barrier against erosion. They often also act as flood barriers Modern sea walls are designed to dissipate, not reflect, wave energy	Their purpose is to break up and dissipate wave energy ​Often used at the base of sea walls to protect them from undercutting and scour	Purpose: To absorb wave energy and reduce swash distance by encouraging infiltration Reduce erosion on dune faces and mud banks	Forces waves to break offshore, rather than at the coast, reducing wave energy and erosive force
Impact on physical processes: Deposition and beach accretion Prevention of longshore drift, sediment starvation and increased erosion downdrift	Destruction of the natural cliff face and foreshore environment ​If reflective, it can reduce beach volume	Reduced wave energy  Sediment deposition between rocks May become vegetated over time	Reduced wave power ​Can encourage deposition and may become vegetated	Deposition encouraged between breakwater and beach  Can interfere with longshore drift
Cost £150-250 per metre	£3000-10,000	£1300-6000