Application of Offshore Breakwaters to the UK: A Case Study at Elmer Beach

Abstract

The use of offshore breakwaters in the UK is relatively uncommon with only 6 schemes constructed to date (early 1998). The use of this technology in the UK is examined via a case study of the S-unit Elmer Beach offshorebreakwater scheme which fronts a shingle beach. Profile line surveying and aerial survey data are used to show the development of the planform during the first 38 months and the development is compared to empirical design guidelines. Also an intensive fieldwork program investigated shingle transport inshore of the breakwaters using sediment tracing techniques. The results show that the scheme exhibited rapid changes to planform during the first 6 months, with shingle salients and sand tombolos developing in the lee of the breakwaters. Changes to planform after this time were less marked, although areas of continued erosion/accretion were identified. The sediment transport experiments identified sediment pathways and rates of transport in the lee of the breakwaters. It is suggested that the breakwaters have reduced shingle transport by a factor of at least 2 compared to similar open beaches.