Geochemical characterisation and erosion stability of fine‐grained groyne field sediments of the Middle Elbe River

Because of the significant reduction of flow velocity relative to the main current there is an accumulation of sediment material in the centre of the groyne fields over time (years to decades) up to a maximum of 1.5 m. Based on the element‐ and compound‐specific depth functions of this fine‐grained material with high organic matter content the sedimentation history of the Elbe River sediments concerning the environmentally relevant nutrients and pollutants can be reconstructed. It could be shown that the fresh sediments are less polluted than the deeper older ones. During the extreme flood of the river Elbe in August 2002 the critical erosion shear stress in the groyne fields was high enough to remobilise a considerable portion of the sediment depot. The hazard to the environment is high due to the fact that a significant part of the remobilised polluted sediments was distributed over the recent floodplain which is normally used as pasture. Thus these groyne field sediments represent a temporary danger for the water quality of the river Elbe. But the hazard of the solids sedimented in the recent floodplain of the river can be viewed as long‐lasting.