Investigation of Wave Attenuation by <i>Rhizophora apiculata</i> Mangroves: Coupled Laboratory Experiments and Boussinesq Modeling

Abstract Mangrove forests provide effective coastal protection by attenuating wave energy, yet quantifying wave‐vegetation interactions remains challenging due to vertically heterogeneous root structures and variable submergence conditions. This study advances phase‐resolving wave–vegetation modeling by integrating realistic, depth‐dependent Rhizophora apiculata root morphology into a fully nonlinear Boussinesq‐type model. A new vegetation module was developed and implemented in the model, allowing vertically varying projected area and submerged volume to dynamically respond to changing water levels. Unlike previous studies that typically represent vegetation using simplified cylinders, the present framework provides a physically consistent representation of how changing submergence modifies hydrodynamic resistance. Two parameterization approaches are examined: (a) laboratory‐derived constant drag and inertia coefficients (; ) obtained from direct force measurements, and (b) empirical relations (; ) expressed as functions of Reynolds and Keulegan‐Carpenter numbers, which introduce spatial and temporal variability. Model–data comparisons demonstrate that both schemes generally reproduce observed attenuation trends across different submergence conditions, but also reveal that transitional (near‐full) submergence constitutes a distinct hydrodynamic regime, where submergence‐independent empirical coefficients (; ) systematically underpredict wave damping by 5%–30%. Applying submergence‐dependent, depth‐specific parameterizations significantly improves agreement with laboratory measurements, particularly in the transitional regime. In this regime, only part of the root system is submerged, and flow blockage varies strongly with depth, limiting the applicability of submergence‐independent empirical formulations. These findings indicate the importance of accounting for realistic vertical root geometry and submergence‐sensitive resistance when modeling mangrove‐induced wave attenuation.