Coastal Management: Hard Engineering

Coastal Management: Hard Engineering

1. Involve constructing coastal defences to reduce the impact of natural processes on the coastline

2. Sea Walls

   • Concreate or stone barriers that either reflect or dissipate wave energy depending on their design
   • Effective but very expensive to build and maintain therefore are used to protect the highest valued land
   • Basic sea wall costs £2,000 per metre and can rise to over £6,000 for a sea wall and promenade featured in many seaside towns
   • 90%+ of Sea Walls need expensive maintenance within 10 years of being built and 96% suffer damage in a 30 year period
   • The older sea walls e.g. Porthcawl in South Wales in 1906, reflect the waves back resulting in the beach sediment being scoured and eventually the wall will be undermined and require expensive repairs. Newer sea walls are built with curved or stepped profiles

3. Revetments

   • The cheaper alternative to sea walls at £1,200-£2,000 per metre depending on the design and the materials used to make them
     • Steel, timber or concrete posts driven into the beach with timber or rock boulders connecting the posts
     • Timber Revetments are the cheapest to build but studies have shown that they do reflect wave energy leading to them being undermined. Also they have the shortest lifespan due to them being easily damaged in storms and the foundations undermined
   • Revetments are used at Barton On Sea, Dorset
   • Form a sloping, permeable barrier designed to dissipate wave energy

4. Rock Armour (Rip-Rap)

   • Sloping, permeable barrier of large interlocking boulders that absorb and dissipate wave energy
   • Costs approximately £3,500 per metre to construct but requires very little maintenance
   • While effective Rip-Rap is unsightly and can restrict access to the beach

5. Gabions

   • Wire mesh cages filled with rock aggregate and stacked together to form a permeable barrier which absorbs the wave energy
   • Cheapest protection measures £400 per metre but are the least permanent and require regular maintenance
   • Found at Bowleaze Cove and Hengistbury Head

6. Groynes

   • Wooden, concrete or rock barriers built perpendicular to the beach to reduce beach erosion due to longshore drift
     • By preventing Longshore drift the groynes deprive the beaches further along of sediment which can lead to increased coastal erosion in those areas due to the sediment not being naturally replenished
   • A single groyne can coast approximately £10,000 to construct
   • The length and spacing between each groyne has to be carefully planned to match the local conditions. the Groynes at Heacham , Norfolk had to be shortened after it was found that they were diverting sediment offshore
   • Sediment builds up on one side and is often scoured from the down drift side. Groynes refract incoming waves which could result in localised rip currents between the groynes which carry the beach material offshore.

7. Offshore Breakwater

   • Consist of a Rip-Rap barrier constructed parallel to the beach and just offshore. This causes the incoming waves to break off shore, reducing the wave energy. They create 'wave shadow' where sediment is dropped
   • By keeping the barrier below the sea level even at low tide , you can reduce the visual impact.
   • The barriers each the local conditions on the shoreline and affect the ecosystem. however it can create artificial reef habitats
   • costs around £6,000 per metre however cheaper versions are constructed by dumping quarry and mine waste
   • In Yorkshire an offshore breakwater made from used tyres anchored to the sea floor, has been proposed as part of the measures to reduce coastal erosion along Holderness Coastline