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

August 25, 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.

    Publication Year 2022
    Title The influence of submerged coastal structures on nearshore flows and wave runup
    DOI 10.1016/j.coastaleng.2022.104194
    Authors Renan F. da Silva, Jeff Hansen, Dirk P. Rijnsdorp, Ryan Lowe, Mark L. Buckley
    Publication Type Article
    Publication Subtype Journal Article
    Series Title Coastal Engineering
    Index ID 70236759
    Record Source USGS Publications Warehouse
    USGS Organization St. Petersburg Coastal and Marine Science Center