Calculating sand wave-induced form roughness coefficients for a section of the Netherlands Continental Shelf.

Coastal environments exhibit various bedforms, with sand waves being of particular interest due to their influence on flow, sediment transport, and morphology (van der Meijden et al., 2023). While numerous models simulate tidal flow, none explicitly includes form roughness induced by these sand wave fields. For instance, the roughness coefficient in the Dutch Continental Shelf Model (DCSM) is calibrated solely to match observed water levels. Portos-Amill et al.'s (submitted) process-based modelling approach addresses this gap by quantifying form roughness induced by sand waves, based on water depth, tidal flow amplitude, grain size, and sand wave characteristics. This provides four criteria to compute form roughness value; either amplitude-based or phase-based, to match the M2 depth-averaged flow or sea surface elevation. The resulting roughness may vary depending on the criterion chosen, highlighting the complex interactions between sand waves and tidal currents.