Groyne

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Sea Bright Beach Jetty

Groyne at Mundesley, Norfolk

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groin

Groyne (also known as a groin in the United States) is a rigid hydraulic engineering structure built from an ocean shore (in coastal engineering) or from a bank (in rivers) that interrupts water flow and limits the movement of sediment. It is usually made out of wood, concrete, or stone. The primary purpose of a groyne is to prevent coastal erosion and to trap sediments that are moving down the beach due to the longshore drift. By doing so, groynes create wider beaches which can protect the coast from the effects of storms and high waves.

Design and Function

Groynes function by interrupting sediment transport by longshore currents and waves. They are placed perpendicular to the shoreline and extend from the upper beach or dune out into the water body. The design of a groyne takes into account local wave energy, beach slope, sediment size, and tidal range. The effectiveness of groynes can vary, with some causing more erosion downstream of the groyne due to interruption of sediment supply.

Types of Groynes

There are several types of groynes, depending on their construction material and design:

• Wooden Groynes: Often made from timber piles, they are less durable than stone or concrete but are cheaper and easier to construct.
• Stone Groynes: Constructed from large rocks or boulders, stone groynes are more durable but also more expensive.
• Concrete Groynes: These are the most durable but also the most expensive. They can be precast or cast in place.
• Rubble Mound Groynes: Made from loose stones or rubble, these groynes absorb wave energy effectively.

Impacts

While groynes are effective at beach nourishment and protecting coastlines, they can have negative impacts on the environment. By altering natural sediment transport, groynes can lead to erosion in areas down-drift of the structure. They can also affect local ecosystems by changing the habitat available for marine and beach species.

Management and Maintenance

The management of groynes involves regular monitoring and maintenance to ensure they are effective and do not cause undue harm to the surrounding environment. This can include replenishing lost sediment, repairing damage to the structures, and adjusting the placement or number of groynes as needed.

See Also

• Coastal engineering
• Coastal erosion
• Sediment transport
• Longshore drift

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