**5. Conclusions**

A comparison of the results obtained numerically in this research with experimental data from other authors, show that CFD REEF3D adequately models a hydrodynamic field in a combined domain of waves and currents, correctly depicting both the instantaneous water surface and velocities developed by the flow of a freestream and also the flow in the presence of a pile.

The average hydrodynamics determined for each of the simulated scenarios showed that in 6 (E01 to E06) out of 8 cases, currents were the main flow mechanism over the waves, despite the relative velocity of current ( *Ucw*) proposed by Sumer and Fredsøe [26], which indicate a combined flow regime. This was clearly reflected in the velocity profiles traced in points P1 to P8, where it could be verified that codirectional and opposite flow cases converge to the same vertical distributions of velocity.

The equilibrium scour estimated by the projection of the numerical data with the equation by Sheppard et al. [54], enabled us to estimate values close to those described in the literature and to use the numerical model e ffectively to solve a time scale lower than the equilibrium. From this projection, it was verified that the dimensionless scour would be less when waves and currents come from opposite directions.

The *Ucw* parameter is an indicator that adequately measures the interactions between of currents and waves under the condition of codirectional flow. However, it is recommended to modify this parameter for currents and waves from opposite directions, since it does not properly account for the interaction of both forcings. For such purposes, it is recommended to use the modified Froude number (*Fra*) proposed in this paper.

**Author Contributions:** The contributions from the author M.Q. corresponded to the numerical modeling, analysis of the results, discussion and conclusions of the document. A.T. and Y.N. contributed to the analysis of results, discussion and conclusions of the study. All authors contributed to the general development of the document through meetings and research sessions.

**Funding:** This publication has been partially-funded by CONICYT doctoral fellowship (21140091), CONICYT Project AFB180004, and the Department of Civil Engineering, Faculty of Physical and Mathematical Science, University of Chile.

**Acknowledgments:** Matías Quezada thanks the support received by Humberto Díaz and Ecotecnos S.A. Company for providing access to the company's computational resources.

**Conflicts of Interest:** The authors declare no conflict of interest
