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7.5 Signal from the north simultaneous with extreme storm surge
(including tide and external surge)
Severe storm surges are a familiar phenomenon to the population living on the North Sea
coast. That raises the question what would happen if a tsunami hit the German coast at the
same time as a storm surge. As the meteorological forcing had not been fitted to the new
version (North Sea 2 km) when the model computations discussed here were made, an older
two-dimensional barotropic model of the North Sea and western Baltic (Muller-Navarra et al.
2003), which has a horizontal resolution of about 10 km (North Sea 10 km), was used to
obtain a rough idea of the interactions between medium-length waves, tides, and a storm
surge event.
At first, the simulations using a realistic topography as described in section 7.4 were
repeated using the same input signal (Fig. 7.5.1), neglecting tidal and wind forcing. Although
the results differ with respect to the propagation velocity and signal height at Cuxhaven (cf.
section 6.1.5), they are similar enough to demonstrate the interactions between storm surge,
external surge, tide, and a hypothetical tsunami using the North Sea 10 km model.
Fig. 7.5.1: Water level distribution after 2, 8, 10, and 15 hours (input signal: 3 positive single
waves, T 1800 s, H 5 m, North Sea 10 km)
To carry out the simulation, the external surge of an extreme storm surge event (Jensen et
al. 2007) was superimposed with the pure tsunami signal at the northern boundary in such a
way that the second maximum of the simulation excluding the storm surge signal (Figs. 7.5.3
and 7.5.4, thin lower curve) arrives at Cuxhaven at the same time as the peak of the pure
storm surge signal (Figs. 7.5.3 and 7.5.4, thin upper curve). In addition, unlike the
