Modelling of the migration of tidal channels

With the advancement in the field of numerical models, the predictions of morphological developments in the tidal flats of the North Sea by the application of process based models are in our reach. In this study the predictive capability of a depth-averaged morphodynamic model in capturing the migration of a tidal channel on the German North Sea over a period of 10 years has been investigated.

Tidal channels in the Dithmarschen bight
Areal Photo of the oil rig Mittelplate. © Peter Rohde

Duration: 2009-2011

The investigations were carried out in the tidal flats of the Meldorf Bight on the German North Sea for the purpose of understanding the morphodynamic processes and the behavior of the tidal channel system. On the base of the Deft3D model system process based models for flow, wave, sediment transport and bed evolution were set up.

They were calibrated and validated with extended field measurements on currents (with ADCP), waves (with ADCP and SEAPACK), turbidity (transmission sensors) and sediments. The morphodynamic simulations were accelerated with a morphological factor 120 in conjunction with different representative periods selected with the cost function of Boone et al. (2002). The quality of the models was controlled according to international standards and showed good results.

The model results in the area of interest showed that the migration of channels was essentially driven by long-term sediment transport in the tidal flats. Sediments migrating from the one side into a channel narrowed its cross section so that the tidal current velocities increased and deepened the sandy channel’s bed by erosion.

If cohesive layers widely prevented the deepening of the bed, the channel’s cross section widened to the other side to maintain the rate of the tidal through-flow. It was found that the model results essentially meet the field observations.

Pic_text

Left: Tidal channels in the Dithmarschen bight © R. Mayerle; Right: Migration of a tidal channel © R. Mayerle, FTZ

References

  • Boon, J., Kerkamp, K., Dardengo, L. (2002): Alternative dumping sites in the Ems-Dollart Estuary. WL|Delft Hydraulics, Z 3822.
  • Van Rijn, L.C., Walstra, D.J.R., Grasmeijer, B., Sutherland, J., Pan,S., Sierra, J.P., (2003): The predictability of cross-shore bed evolution of sandy beaches at the time  cale of storms and seasons using process-based profile models. Coastal Engineering 47.

 

Research division:

Coordination:

  • Prof. Dr. R. Mayerle
  • M. von Borstel

Staff:

  • M.Sc. D. Nguyen
  • Dr. K.H. Runte
  • Dr. T. Etri   

Partners:

  • RWE Dea
  • WSA Lübeck