Numerical sensitivity studies on the physics of storm tides in the German bight, North Sea

The most relevant processes contributing to significant water level variations at the German North Sea coast are the tides, external surges, generated on the Northeast Atlantic, and surges generated by storms over the North Sea. If these processes occur in adverse combinations their effects might accumulate to scenarios of extremely high water levels. The aim of this study is to provide new insights into the nonlinear interactions between the different processes and to determine adverse process combinations.

Influence of superimposed tide, sea level rise, storm surge and external surge on the water level in Cuxhaven, North Sea
High water level in Cuxhaven during storm wind conditions over the North Sea © G. Bruss, FTZ.

Duration: 2009-2010

The study focuses on Cuxhaven located at the mouth of the Elbe estuary. A procedure, based on a modified existing modeling system covering the entire North Sea and parts of the Northeast Atlantic is proposed to investigate the processes involved during conditions of extreme water levels within the outer Elbe estuary. Techniques for the isolated modeling of each of the contributing processes are developed and verified.

To investigate the mutual interactions, the processes are overlaid in various combinations. Various conditions in the astronomical tide, three major storm events over the North Sea, several external surges and an increase in the mean sea level are analyzed. The isolated processes are temporally shifted relative to each other and superimposed in various combinations. The most adverse superimpositions lead to new scenarios of extreme water levels.

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Superposition of water levels due to tide, sea level rise, storm winds over the North Sea and external wave. © G. Bruss, FTZ.

The results obtained from the method proposed provide new insights into the nonlinear interactions between the involved processes. Generally, the effects of the processes seem to be reduced in superpositions with high absolute water levels. However, due to the large scatter of the results no general relations are found. New extreme scenarios are determined by iterative maximizations of the peak water level of different superpositions around spring high tide. 

Research division:

Coordination:

  • Prof. Dr. R. Mayerle
  • G. Gönnert

Staff:

  • G. Bruss
  • R. Osinski

Partners:

  • Landesbetrieb Straßen, Brücken und Gewässer (LSBG) - Stadt Hamburg