The body of evidence is quite clear that “hard” measures to mitigate erosion need to be carefully considered. The more we are learning, the clearer it becomes that once you start with the first groyne the others will continue to be needed.

The primary disadvantage of groynes is that interruption of longshore drift to promote beach widening on one section of coastline is likely to cause sediment starvation and erosion further downstream. This is because groynes do not add sediment to the shoreface but instead distribute the available materials differently. As such, groyne construction is perhaps most effective when complemented by beach nourishment as discussed above.

By promoting sediment build up on the updrift side of the groyne, there is a consequent sediment deficit on the downdrift side, requiring the construction of further groynes to maintain beach width. At the most downdrift extent of a groyne field, a symptom known as ‘terminal groyne syndrome’ often exists, whereby sediment starvation causes accelerated erosion of the unprotected coastline. This has obvious negative implications.

While groynes promote recreational beach use through beach widening, another problem with their use is related to the formation of rip currents adjacent to groynes. These can

present a hazard to bathers and furthermore, may also lead to sediment being transported to deep water and lost from the coastal system during storm events (Masselink and
Hughes 2003).

While beach widening is typically viewed positively, groynes affect the visual appearance of the coastline by introducing unnatural, shore perpendicular structures. Groynes may also reduce accessibility of the beach to those less mobile.