Wave-Driven Hydrodynamic Processes Over Fringing Reefs With Varying Slopes, Depths, and Roughness

Wave-Driven Hydrodynamic Processes Over Fringing Reefs With Varying Slopes, Depths, and Roughness: Implications for Coastal Protection

Buckley, Mark L. (North Central Climate Science Centre)
Lowe, Ryan J. (University of Western Australia)
Hansen, Jeff E. (University of Western Australia)
van Dongeren, Ap R. (Deltares; IHE Delft Institute for Water Education)
Pomeroy, Andrew (University of Melbourne)
Storlazzi, Curt D. (Pacific Coastal and Marine Science Center)
Rijnsdorp, D.P. (TU Delft Environmental Fluid Mechanics)
da Silva, Renan F. (University of Western Australia)
Contardo, Stephanie (University of Western Australia; CSIRO Oceans and Atmosphere)
Green, Rebecca H. (University of Western Australia)

2022

Wave breaking on the steep fore-reef slopes of shallow fringing reefs can be effective at dissipating incident sea-swell waves prior to reaching reef shorelines. However, wave setup and free infragravity waves generated during the sea-swell breaking process are often the largest contributors to wave-driven water levels (wave runup) at the shoreline. Laboratory flume experiments and a two-dimensional vertical phase-resolving nonhydrostatic wave-flow model, which includes a canopy model to predict drag forces generated by roughness elements, were used to investigate wave-driven water levels for along-shore uniform fringing reefs. In contrast to many previous studies, both the laboratory experiment and the numerical model account for the effects of large bottom roughness. The numerical model reproduced the observations of the wave transformation and runup over both smooth and rough reef profiles. The numerical model was then extended to quantify the influence of reef geometry and compared to simulations of plane beaches lacking a reef. For a fixed offshore forcing condition, the fore-reef slope controlled wave runup on reef-fronted beaches, whereas the beach slope controlled wave runup on plane beaches. As a result, the coastal protection utility of reefs is dependent on these slopes. For our examples, with a fore-reef slope of 1/5 and a 500 m prototype reef flat length, a beach slope of ∼1/30 marked the transition between the reef providing runup reduction for steeper beach slopes and enhancing wave runup for milder slopes. Roughness coverage, spacing, dimensions, and drag coefficient were investigated, with results indicating the greatest runup reductions were due to tall roughness elements on the reef flat.

canopy flow
coral reef
infragravity waves
numerical modeling
roughness
wave runup

http://resolver.tudelft.nl/uuid:11ea117c-1e5f-40a5-baf8-055d5bc75666

https://doi.org/10.1029/2022JC018857

2023-07-01

2169-9275

Journal Of Geophysical Research-Oceans, 127 (11)

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 Mark L. Buckley, Ryan J. Lowe, Jeff E. Hansen, Ap R. van Dongeren, Andrew Pomeroy, Curt D. Storlazzi, D.P. Rijnsdorp, Renan F. da Silva, Stephanie Contardo, Rebecca H. Green