OVERTOPPING HAZARD MITIGATION: EXPERIMENTAL INVESTIGATION OF LIVE SALTMARSH GRASS EXPOSED TO BORE FLOW

Extreme weather events and sea level rise will continue to increase the frequency and intensity of coastal hazards (Paulik et al. 2020). Hybrid solutions, which combine an engineered structure with a nature-based solution, offer the potential to manage risk and achieve greater socioeconomic and environmental benefits (Blakely et al., 2023, IPCC, 2022). However, implementation is hampered by a lack of robust and definitive design guidance (Burmeister and Pomeroy, 2021). Blakely et al. (2023) identified that native Aotearoa New Zealand saltmarsh grass, oioi (Apodasmia similis), when placed on the crest of coastal protection structures, may be a feasible hybrid solution for mitigating wave overtopping hazards. Given the difficulty to accurately represent vegetation at scale, Blakely et al. (2023) concluded that future physical model tests using live, full-scale vegetation under wave overtopping conditions are fundamental for understanding the true interaction between vegetation behaviour and overtopping flow. Therefore, in this study, experiments were conducted with live, prototype scale vegetation in a flume that replicates prototype scale green-water overtopping bore flow. The aim is to investigate the relationship between vegetation response and flow parameters. The experimental data set is proposed to be used for developing preliminary design guidance and numerical model validation.