groynegroyne

Groynegroyne is a term used in coastal engineering to describe a pair of groynes installed in close proximity along a shoreline, creating a twin-structure barrier that alters sediment transport and wave interaction. The name suggests a duplicated arrangement of the standard groyne, which is a structure built perpendicular to the coast to interrupt longshore drift.

Design and configuration commonly involve two groynes oriented parallel to each other with a narrow space or shared toe between them. This configuration aims to increase sediment capture and beach stability over a defined segment, while allowing some water circulation between the structures. Variations may include differing face slopes, materials, or offsets to adapt to local wave climate and tidal range.

Purpose and function center on beach protection and sediment management. By interrupting longshore transport, a groynegroyne can promote sand accumulation on the protected side and reduce nearshore erosion. It may also create a calmer zone behind the structures, which can be advantageous for small craft access or beach recreation. Planners must balance sediment benefits with potential downsides such as downdrift sand starvation or scour at the structure ends.

Construction considerations cover typical materials (timber, concrete, rock), durability under wave action, and maintenance needs. Spacing, height, and alignment are chosen based on coastal sediments, tides, and wave energy. Environmental and navigational impacts are routinely evaluated, along with long-term sediment budgets and potential need for future adjustments.

See also groyne.