Correction of coherent interference in wave-resolving nearshore models and validation with experimental data

Here we address the problem of coherent interference that arises in double-sum wavemakers of wave-resolving models. Identified as a key problem for experimental and numerical simulations since the late 1970s, this problem induces spurious persistent longshore variability and affects nearshore dynamics. To overcome this problem, we present the implementation of a single-sum wavemaker in the 3D wave-resolving model CROCO. The new wavemaker, which assigns only one pair of direction and frequency values to each component of the wave spectrum, definitively prevents coherent interference, unlike a conventional double-sum wavemaker that allows waves of different direction to share the same frequency. Each wave component must also strictly comply with the periodicity rules, to avoid any spurious boundary dynamics. We validate the single-sum wavemaker with experimental data collected in a wave basin with longshore-uniform bathymetry and compare results with the double-sum wavemaker simulations. We show that the new wavemaker produces transient rips devoid of any coherent interference effect and that, consequently, the model statistics closely match the experimental data. The new wavemaker therefore guarantees statistical integrity while reducing computational costs, a necessary step for realistic wave-resolving studies of nearshore dynamics.