Seasonal variability in M₂ and M₄ tidal constituents and its implications for the coastal residual sediment transport

We use an observational data set of tidal gauges in the North Sea to investigate the annual cycle of the M 2 and M 4 amplitudes and phases. The sea surface elevation amplitude of the M 2 can vary by 8–10% and the M 4 amplitude by 12–30% over the course of the year, with larger amplitudes in summer. The annual phase variations are in the range of 3–15°. The reason for these variations is the thermal structure of the North Sea: a well‐developed thermocline in summer and well‐mixed water column during winter. The interaction of the M 2 and M 4 tides is one of the main drivers of the residual sediment transport. Using an analytical model, the seasonal variability in residual sediment transport is estimated. This transport can vary by 10–50% over the course of the year. These variations are mainly related to the seasonal variability of the M 2 and M 4 amplitudes.