Scaling of Submerged Rubble-Mound Models

Submerged mound breakwaters are viable eco-friendly structures for shore protection, serving as an alternative to their emerged counterparts. Physical modelling is still extensively used to study coastal processes and provide calibration and verification data. The aim of this study is to present a methodology adapted exclusively to submerged structures to tackle the problem of scale effects when determining the size of the core material. Such effects have been adequately studied in emerging mounds, thus forming the rationale for the present work. Hydrodynamic pore pressures inside the underwater body were evaluated using experimental results; these were then input into the extended Forchheimer equation, including the nonlinear effects of velocity upon the drag force induced by the pressure gradient. The experimental results used were satisfactorily compared with other laboratory measurements and with results from two numerical models. The proposed calculation methodology combined with the corresponding hydraulic resistance can yield a correction factor K for model downscaling of the breakwater material. Numerical applications are given along with design nomographs providing the K value. The presented results on the required scale correction to be applied to determine the sizing of the core material in physical models of submerged mound breakwaters deviate significantly from those related to emerging breakwaters, thus justifying the undertaking of the present work.