Parametric modelling of wave transformation across porous artificial reefs

Porous artificial reefs can provide nature-based coastal protection by reducing nearshore wave transmission. Existing approaches to predict wave transmission across porous artificial reefs have relied on empirical formulations to describe bulk wave transmission that aggregate the role of different hydrodynamic processes responsible for wave attenuation, including wave dissipation by both breaking and drag forces and wave reflection from the reef. The lack of an integrated predictive model capable of accurately parameterizing these different hydrodynamic processes adds uncertainty to predictions of wave attenuation by artificial reefs when applied to different reef designs and hydrodynamic conditions. To address this gap, this study develops a parametric phase-averaged modelling approach to predict wave transformation processes across porous artificial reefs by parameterizing the individual contributions of breaking, drag dissipation and wave reflection to the changes of wave energy fluxes across a reef. Observations of wave transformation over an impermeable reef (i.e., in the absence of interior-reef drag forces) were initially used to assess breaking dissipation formulations, while non-breaking wave cases across three different cubic-type porous reefs were used to assess formulations to describe drag-induced dissipation by the reef. The model was further shown to accurately predict wave transformation for porous reef cases where both breaking and drag dissipation simultaneously occurred, for conditions that spanned a wide range of water depths, regular and irregular wave conditions. The validated model was finally applied to investigate the influence of different design parameters, including water depths, wave conditions and reef geometry parameters, on wave transmission and energy balances across a broad range of reef application scenarios. The predictive framework developed in this study is designed to be applicable to other porous reefs when geometry-dependent parameters can be robustly defined, which can be incorporated into phase-averaged wave models to predict wave transformation processes across porous reef structures to aid the design of modular artificial reefs for nature-based coastal protection.