Evidence for a shore-normal energy gradient and its character in the speiekeroog back barrier tidal flats, german north sea coast

Authors

• N NYANDWI, Institute of Marine Sciences, University of Dar es Salaam, P.O. Box 668, Zanzibar, TanzaniaFollow

Section

Physical Sciences

Abstract

Sediment distribution in the Spiekeroog backbarrier tidal flats has been studied with the aim of identifying the factors controlling their deposition. Form the mainland coast northwards three physiographic units are recognizable namely, the tidal flats adjacent to the coast, the tidal channels with the intervening flats and the dunes and tidal flats adjoining Spiekeroog island. The areal distribution of the sand fraction (˂4.0 phi) shows a shore normal energy gradient with increasing energy towards the sea. Very fine sands are found very close to the mainland coast, fine to very fine in the central part and fine sand on the Spiekeroog Island, coarsening further towards the sea. Medium sand is found in the entrance areas of both the Otzum and Harle tidal inlets to the west and east of the island, respectively. Both the bivariate plot of the standard deviation against the mean grain size and the CM- diagram define the sediments into three groups each of which is characterized by a different energy gradient. The energy compartments coincide with the physiographic units identified. The energy level as represented by –log ₂/v_cmls, where V is the settling velocity of the sediment, varies linearly with the distance (R=0.83-0.9) across the tidal flats (N-S direction). Within the individual energy compartments however, better linear regressions (R˃0.9) predominate indicating a strong geomorphological control on the energy gradient. The linear regressions are thus an indication of strong exponential energy dissipation with distance away from the flow the flow channels, a feature underlying the grain size gradients.

Recommended Citation

NYANDWI, N (1997) "Evidence for a shore-normal energy gradient and its character in the speiekeroog back barrier tidal flats, german north sea coast," Tanzania Journal of Science: Vol. 23: Iss. 1, Article 1.
Available at:https://doi.org/10.65085/2507-7961.2404

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