Effects of Dredged Material Disposal in the Eems
The navigational channel between the harbour Eemshaven and the North Sea needs to be dredged regularly to remain accessible to seagoing vessels. The dredged sediment is disposed of at various disposal sites, which may have an impact on the local ecology. To assess these effects, flow conditions and sediment concentrations were measured at a disposal site during sediment disposal operations. Based on these measurements and a numerical modelling study, WaterProof assessed whether sediment disposal at location P0 could have significant adverse effects on the ecology.
- Client: Rijkswaterstaat Northern Netherlands
- Location: Monding Eems, west of Borkum
Analysis of Results
To keep the harbour ‘Eemshaven’ accessible to vessels with a draught of 14 metres (Panamax), the navigational channel between the North Sea and the Eemshaven needs to be dredged regularly. The dredged material from the channel is disposed of at several disposal sites in the Ems estuary, some of which are located within Natura 2000 areas. One of these disposal sites is P0, located in German waters west of the island of Borkum. Disposal of dredged material at this location is permitted on the condition that the ecological effects of sediment disposal are investigated and monitored.
As part of a measurement campaign in summer 2022, Rijkswaterstaat measured flow conditions and suspended sediment concentrations at disposal site P0 before, during and after sediment disposal. The characteristics of both the seabed sediment and the dredged material were also determined. WaterProof was subsequently commissioned to analyse the measurement data, model the turbidity plumes resulting from sediment disposal, and assess whether sediment disposal at P0 could have significant adverse effects on the ecology.
Analysis of the measured suspended sediment concentrations and the modelling results showed that the disposal of 2,000 m³ of sediment resulted in a maximum increase in depth-averaged suspended sediment concentrations of approximately 60–70 mg/L within the area of interest. As the disposed material consisted mainly of sand, with a silt fraction of less than 1%, the increase in suspended sediment concentrations was primarily localised, with sharp temporal boundaries observed in the measured concentration profiles.
The effects of sediment disposal on ecological parameters outside disposal site P0 were assessed as very limited. In particular, little effect was observed outside the disposal site on water-column turbidity or sediment deposition. Significant effects of the sediment disposal on visually hunting birds and benthic organisms outside the disposal site are therefore considered unlikely.
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Effects of Dredged Material Disposal in the Eems
The navigational channel between the Eemshaven and the North Sea needs to be dredged regularly to remain accessible to seagoing vessels. The dredged sediment is disposed of at various disposal sites, which may have an impact on the local ecology. To assess these effects, flow conditions and sediment concentrations were measured at a disposal site during sediment disposal operations. Based on these measurements and a numerical modelling study, WaterProof assessed whether sediment disposal at location P0 could have significant adverse effects on the ecology.
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