The influence of submerged coastal structures on nearshore flows and wave runup

The influence of submerged coastal structures on nearshore flows and wave runup

da Silva, Renan F. (University of Western Australia)
Hansen, Jeff E. (University of Western Australia)
Rijnsdorp, D.P. (TU Delft Environmental Fluid Mechanics)
Lowe, Ryan J. (School of Earth Sciences; University of Western Australia)
Buckley, Mark L. (North Central Climate Science Centre)

2022

Engineered and natural submerged coastal structures (e.g., submerged breakwaters and reefs) modify incident wave fields and thus can alter hydrodynamic processes adjacent to coastlines. Although submerged structures are generally assumed to promote beach protection by dissipating waves offshore and creating sheltered conditions in their lee, their interaction with waves can result in mean wave-driven circulation patterns that may either promote shoreline accretion or erosion. Here, we analyse the mean flow patterns and shoreline water levels (wave runup) in the lee of idealised impermeable submerged structures with a phase-resolved nonhydrostatic numerical model. Waves propagating over submerged structures can drive either a 2-cell mean (wave-averaged) circulation, which is characterised by diverging flows behind the structure and at the shoreline, or 4-cell circulation, with converging flows at the shoreline and diverging flows in the immediate lee of the structure. The numerical results show that the mode of circulation can be predicted with a set of relationships depending on the incoming wave heights, the structure crest level, and distance to the shoreline (or structure depth). Qualitative agreement between the mean flow and proxies for the sediment transport using an energetics approach suggest that the mean flow can be a robust proxy for inferring sediment transport patterns. For the cases considered, the submerged structures had a minimal influence on shoreline wave setup and wave runup despite the wave energy dissipation by the structures due to alongshore wave energy fluxes in the lee. Consequently, these results suggest that the coastal protection provided by the range of impermeable submerged structures we modelled is primarily due to their capacity to promote beach accretion.

Phase-resolved wave modelling
Reefs
Submerged breakwaters
Submerged coastal structures
Wave runup
Wave-driven flows

http://resolver.tudelft.nl/uuid:a8abafdf-c56c-426f-9320-4adcaa9a5402

https://doi.org/10.1016/j.coastaleng.2022.104194

2023-07-01

0378-3839

Coastal Engineering, 177

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2022 Renan F. da Silva, Jeff E. Hansen, D.P. Rijnsdorp, Ryan J. Lowe, Mark L. Buckley