Design of Detached Emerged and Submerged Breakwaters for Coastal Protection: Development and Application of an Advanced Numerical Model

An advanced fully hydro- and morphodynamic two-dimensional horizontal (2DH) numerical model, describing the processes of nonlinear wave propagation, sediment transport, and morphological changes and being suitable for the design of structures for coastal protection against erosion, has been developed and tested here. The Boussinesq-type equations, including nonlinear higher-order terms, which can enhance a model's behavior regarding highly nonlinear wave propagation in the nearshore region, including the swash zone, are used. The bed load and sheet flow transport rate are estimated using a quasi-steady formulation for waves and currents. Both phase-lag and acceleration effects are included in the formula. The suspended sediment transport rate is estimated by solving the depth-integrated transport equation for suspended sediment. Model predictions are compared with laboratory data and field measurements (breaking wave-induced current field and morphological changes associated with emerged and submerged detached breakwaters). Numerical results and data are in satisfactory agreement. In the case of emerged detached breakwaters, the well-known criteria for tombolo or salient formation (based on empirical design guidelines) agree with the model predictions. The methodology is also applied to simulate the morphological changes behind submerged breakwaters, resulting in useful conclusions concerning the role of the transmission coefficient and the net mass influx over the breakwater. The developed model can be used for the design of emerged and submerged detached breakwaters.