Coastal Flood Defences: Groynes

Coastal Flood Defences: Groynes

• Coastal flood defences are crucial for protecting low-lying land from sea water.
• Groynes are a type of hard engineering, easy to construct and have long-term durability, requiring low maintenance.
• Groynes are designed at a 90-degree angle to the shore to trap sediment and prevent longshore drift.
• They are immediately effective but can be intrusive and cause problems elsewhere.

What are Groynes?

• Groynes are low-lying wooden or concrete structures placed offshore to trap sediment.
• They dissipate wave energy and restrict sediment transfer during longshore drift.
• Longshore drift is the movement of sediment along the shore due to waves at an angle.
• Groynes slow down erosion by preventing sediment from being transported further down the coast.
• Permeable groynes permit some sediment movement, while impermeable groynes prevent all sediment movement.

Advantages and Disadvantages

• Advantages:
  • Easy to construct and maintain
  • Long-term durability
  • Reduce need for beach nourishment
• Disadvantages:
  • Wooden groynes are less durable than rock
  • May visually impact the landscape
  • Can cause erosion downstream, necessitating further maintenance.

Case Study: Walney Island, Cumbria

• Walney Island is a narrow island in the west of England.
• The island has approximately 13,000 residents and is 11 miles long with 5 sq miles of area.
• Low-lying parts of West coast are vulnerable & exposed to high tides and storm surges.
• Groynes have been built to lessen the impact of flooding & coastal erosion.
• This coastal protection measure aims to prevent the island from splitting.