24 Oct 2014

Assessing sediment spill risks of the Øresund Fixed Link

We helped Øresundsbro Konsortiet ensure that works carried out during construction of the Øresund Fixed Link did not block water exchange between the North Sea and the Baltic Sea. We also conducted a monitoring campaign of local flora and fauna to ensure sediment plumes would not negatively impact them.

The Øresund Fixed Link is a combined road and train connection that links Denmark with Sweden across the Øresund (the strait that separates the two countries). To help Øresundsbro Konsortiet comply with very stringent and legally binding environmental requirements, we set up advanced hydrodynamic models to assess and optimise the design of the different elements of the Fixed Link. This included:
  • calculating the blocking effect
  • assessing possibilities for compensation dredging to reduce these effects
We also deployed a number of monitoring stations to measure water levels, currents, salinity, temperature and other variables to provide data for the numerical models. In addition to modelling water quality, we conducted a wide range of field surveys on flora and fauna using remote equipment. Our monitoring focused on:
  • coverage and biomass of eelgrass
  • coverage of common mussel (which is a source of food for a number of species) 
This was done to ensure that the eelgrass could survive the increased blockage of light caused by sediment plumes. We provided Øresundsbro Konsortiet with a modelling tool that could predict the impact of the sediment plumes on the eelgrass biomass. 

This allowed them to manage dredging operations according to impact. As a result, contractors could increase dredging intensity throughout the project time, enabling the Fixed Link to open on budget six months ahead of schedule.