A new dataset of external surges in the German Bight and its application to potential high impact scenarios

External surges are a key component of extreme water levels in the North Sea. Caused by low pressure cells over the North Atlantic and amplified at the continental shelf, they can drive water level changes of more than one metre at the British, Dutch and German North Sea coast. To extend the knowledge on external surges, an automated approach to detect external surges was developed, using high resolution tide gauge data. The newly collected dataset of 101 external surges spanning from 1995 to 2020 revealed the phenomenon of series of external surges, whereat two or more external surges follow each other less than 72 h apart. This phenomenon accounts for 33% of the detected external surges. Serial events tend to occur more often during wind–induced storm surges. While the inclusion of external surges in design water levels is already applied in a few design level approaches, the effects of serial external surges on storm surges have not been studied. This presentation highlights past events of combined storm surges and serial external surges and analyses the corresponding storm tracks. Based on these events, modifications for further study are proposed, creating potential high impact events, which consist of storm surges combined with serial external surges.