Hard Engineering Flashcards
How do groynes work?
Barriers on a beach set at right angles to the coast to slow down longshore drift. They make a beach wider and higher so waves expend energy on it rather than on the backshore.
What are the benefits of groynes?
-Maintain the size of the beach, protecting coasts in the area.
-Enhance the beach as a recreational amenity.
-Less expensive than sea walls.
What are the disadvantages of groynes?
-Expensive (£1000 per linear metre).
-May hinder people crossing the beach.
-Reducing longshore drift will narrow beaches down drift = more erosion there.
How do sea walls work?
Recurved sea walls reduce wave energy by reflecting the waves back on themselves. Stepped sea walls dissipate wave energy with their edges.
What are the benefits of sea walls?
-Very effective at preventing erosion.
-Prevent high water levels from moving inland.
-Gives people a sense of security.
What are the disadvantages of sea walls?
-Very expensive (£5000 per linear metre).
-Greatly reduces supply of sediment to the sediment cell.
-May be considered unsightly.
How does rip rap work?
Boulders that are resistant to erosion and have a large surface area dissipate wave energy.
What are the benefits of rip rap?
-Long-lasting and flexible in use.
-Can be placed at susceptible points.
What are the disadvantages of rip rap?
-Cost about £50 per metre cubed.
-Seawater can still move through, permitting some backshore erosion.
-May look unsightly.
How do revetments work?
They are sloped walls, placed parallel in front of the backshore. They take the force of breaking waves, weakening erosion.
What are the benefits of revetments?
-Absorb wave energy and trap sediment.
-Longshore drift can still continue.
-Cheaper than sea walls.
What are the disadvantages of revetments?
-Costs £1500 per linear metre.
-Needs constant maintenance.
-Reduces access from backshore to beach.
How do offshore breakwaters work?
Boulders dropped in shallow nearshore waters and aligned parallel to the shore. These absorb wave energy and dissipate waves before they can damage the foreshore/backshore.
What are the benefits of offshore breakwaters?
-Allows longshore drift to continue behind them.
-Can create sheltered water areas behind them for water sports.
-Proven to protect vulnerable areas.
What are the disadvantages of offshore breakwaters?
-Costs £1-2 million.
-May create increase deposition on the landward side, reducing longshore drift.
-Other defences may be needed for the gaps between reefs.
What are the unforeseen consequences of hard engineering?
If it interrupts the sediment flow along a coast, places down drift can experience increased erosion.
