Sediment transport patterns

Bedform patterns on a shallow inner shelf of the southern North Sea are examined in various hydrodynamic energy conditions. A sediment transport mechanism based on small-scale bedform dynamics is constructed from high-resolution swath bathymetric datasets. Dynamic response of bedforms on different spatial and time scales has been studied and rapid adjustment of the seabed to varying hydrodynamic energy conditions has been established. Small, megaripple-scale bedforms superimposed on the shoreface sand ridges suggest that the fair-weather tidal currents, enhanced by morphodynamic feedback mechanism, maintain the shoreface morphology. A storm event in January 2003, having generally erosional effect on the shoreface, amplified the small as well as large scale morphology. Recovery from the temporary erosion caused by the storm was rapid and in less than a month time the shoreface returned to its dynamic equilibrium height. The proposed sediment transport model implies a possibility of net westward sediment transport direction on the lower shoreface as opposed to the generally accepted net eastward sediment transport direction on the upper shoreface and in the surf zone along the East-Frisian coast.

Sediment transport directions deduced from the synthesis of the megaripple-scale bedforms, surficial sediment grain size patterns, and the tidal flow field. Continuous arrows mark the net sediment transport direction in the areas of dominating flood current and the dashed arrows in the areas of dominating ebb current, respectively. Overall net sediment transport appears to be westwards due to the 10-14° clockwise directional asymmetry of the flood vs. ebb currents. Isolines depict the depths below chart datum.


Publication (in review)
R. Noormets, V. Ernstsen, B. Flemming & D. Hebbeln. Sediment transport patterns on the inner shelf of the southern North Sea construed from small-scale morphodynamics.