Overtopping Design Considerations for Non-conventional Revetments Under Bimodal Spectral Conditions

The Te Ara Tupua Alliance is currently supervising the upgrade of a 4.5 km long share path corridor along the western shore of Te Whanganui a Tara Harbour in New Zealand. The project site’s unique topography, bathymetry and consent constraints requires the upgrade solution to include the collocation of a numbers of different types of structures such as vertical concrete walls and a combination of revetments armoured with non-conventional concrete units. The present empirical guidance on overtopping performance of these structure configurations is not widely developed in literature, at least with sufficient reliability to inform design on this project. An additional complicating factor was a bimodal wave climate, the swell component of which was discovered to have a significant effect on anticipated overtopping flows through an extensive physical modelling program. Overtopping assessment was conducted through an extensive physical modelling program of over 100 individual tests undertaken in two different wave flumes at scales of 1:15 and 1:22.6. Testing clearly demonstrated that bimodal wave conditions had a critical influence on the measured overtopping, with a notable increase compared to equivalent unimodal spectral conditions. The results of the physical model tests were used to develop site-specific, data-driven formula based on relationships between relative overtopping and relative freeboard, as presented in EurOtop guidelines. These relationships were used to understand overtopping potential along the project site both now and in the future.