Economical Rock Groynes - Reducing Lifecycle Costs

Rock groynes (or groins) are regularly used in coastal engineering to control the morphological development of beaches and to provide protection against coastal erosion. Established design guidance provides a good degree of confidence in predictions of performance of many coastal structures, but it is widely perceived that simple design rules can be overly prescriptive, particularly for nearshore structures in shallow water depths. Strict adherence to design guidance has required many structures to be built using multiple rock sizes, imported rock and carefully prepared foundations. Some innovative groyne schemes within the UK have, however, used locally available rock with simplified cross-sections placed on unprepared foundations, apparently without significant reduction to the overall performance of the scheme. This paper presents findings from a short research project, relating to the design and assessment of low cost rock structures for beach control and coast protection. Practical experience from structures around the UK was reviewed, with particular emphasis on those that depart from conventional design rules. The paper demonstrates that lower cost rock groynes provide opportunities for reduced lifecycle costs and may be particularly appropriate in situations where conventional structures would be uneconomic.