Innovative coastal defence using rock bag revetments: preliminary physical modelling

As climate change intensifies pressure on coastal areas and construction resources become increasingly scarce, innovation in coastal defense is essential. Traditionally, coastal revetments have primarily been constructed using rock or concrete armour units. However, these revetments are costly and have a high carbon footprint due to their large size and the long transport distances required. A viable alternative to large rock armour units is the use of rock bags (RB), where smaller locally sourced rocks are enclosed in polyester netting bags. This research examines the performance of a scaled rock bag revetment model in controlling wave runup and compares it with a scaled rock armour (RA) revetment through physical modelling. A total of 36 tests were conducted in a wave flume, revealing that the dimensionless wave runup in the RB tests was, on average, 53 % lower than in the RA tests, indicating superior runup control by the RB model. For the first time, we present a runup equation specifically developed for RB revetments, enabling more accurate design of these innovative systems in the future. Additionally, qualitative observations suggest that the RB model likely has lower wave reflection coefficients compared to the RA model.