Weser dredge disposal

The impact of dredge spoil disposal on seabed morphology
As modern ships require increased navigation depth, harbor authorities the world over are forced to dredge the shipping channels to their harbors, and subsequently dump the dredge spoil disposal off-shore. These activities cause substantial changes in local morphological and sedimentological patterns which may constitute in turn a major problem to sustainable, and hence, cost-effective waterway management.
Dredge spoil disposal can have a significant impact on bedforms, as has been documented for a field of asymmetrical large-scale dunes at a disposal in the outer Weser Estuary, German Bight. The artificial supply of sediment resulted in the in-fill of dune troughs and even the complete burial of individual dunes. However, even completely buried dunes began to regenerate within a few months.

In addition, slow migration of the dunes towards the open sea was observed, indicating a net seaward sediment transport of sediment in the survey area which also partly incorporates dumped sediments. And indeed, after a time period of 5 months, ~20% of the originally dumped material (3 mill. qm) had already removed from the site.

The impact of dredge spoil disposal on sediment distribution patterns

A new acoustic seabed classification system, QTC View/Impact, provided a sophisticated technique to discriminate seabed characteristics and to map their distribution at high spatial and temporal resolution.
At a study site in the outer Weser estuary, three acoustic classes could be identified. These represent the three main surface sediment types ranging from fine to coarse sand, and with varying contents of shell fragments (Wienberg and Bartholomä, in press). This information was used to interpret changes in the spatial distribution of the sediment types as reflected in a time series of successive QTC surveys. It was shown that small dunes in the shipping channel were destroyed by dredging, and that the sediment distribution changed from a very inhomogeneous mix of different sediment types to a dominance of medium sand with a moderate content of shell fragments. As a result of dredge-spoil dumping at the disposal site, the sediment distribution showed a change to coarser sand (Wienberg and Bartholomä, 2005).

Publications

Wienberg, C. & Bartholomä, A. (2005): Acoustic seabed classification in a coastal environment (outer Weser Estuary, German Bight) - a new approach to monitor dredging and dredge spoil disposal. Continental Shelf Research 25(9): 1143-1156.

Wienberg, C. & Hebbeln, D. (2005): Impact of dumped sediments on subaqueous dunes, outer Weser Estuary, German Bight, southeastern North Sea. Geo-Marine Letters 25(1): 43-53.

Wienberg, C., Dannenberg, J, & Hebbeln, D. (2004): The fate of dumped sediments monitored by a high-resolution multibeam echosounder system, Weser Estuary, German Bight. Geo-Marine Letters 24(1): 22-31.

Wienberg, C. (2003): The impact of dredge spoil dumping on coastal morphodynamics monitored by high-resolution acoustic measuring instruments (outer Weser Estuary, German Bight). PhD-Thesis, Department of Geosciences, University of Bremen, Bremen, 100p.

Wienberg, C. (2003): Korrigiert und ausgebaggert - Die Außenweser im Wandel der Zeit. In: Heidbrink, I., Konfliktfeld Küste: ein Lebensraum wird erforscht, Hanse-Studies, Vol. 3, Bilbliotheks- und Informationssystem der Universität Oldenburg, Germany, pp. 139-160.