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Two Gas Pipelines Through the Baltic Sea to Meet the Future Gas Needs of the European Union
Figure 2: Pipe-laying Process for the Nord Stream Pipelines
Courtesy of Nord Stream AG.
The Nord Stream pipeline project extends through the exclusive concentration of suspended sediments and the sedimentation
economic zone (EEZ) of five countries (Russia, Finland, Sweden, to the seabed caused by the seabed intervention works have been
Denmark and Germany). These countries are considered ‘parties of simulated using the numerical model MIKE 3 PA developed by DHI. The
origin’ in the Espoo Convention, whereas the remaining Baltic Sea modelling simulates the transport and fate of both suspended and
coastal states (Estonia, Latvia, Lithuania and Poland) are considered dissolved substances in 3D. More than 1mm of sedimentation following
‘other affected parties’, as the project may affect these countries. As trenching of, in total, approximately 131km of pipeline will cover an
part of the Espoo process, a number of working group meetings area of approximately 3km
2
, depending on the weather conditions. The
with representatives from all nine Baltic Sea coastal states have been area where a sediment concentration greater than 10mg/l will occur
held, and comments from authorities and other stakeholders have (this is roughly the concentration that has an impact on the eyesight of
been received and included in the optimisation of the environmental diving birds and on the aesthetic quality of bathing water) is calculated
performance of the pipeline project. to be approximately 120km
2
, again depending on the weather
conditions. However, this impact is very short-term (hours), as the
Environmental Impact of the Project sediments eventually settle to the seabed within a few hundred metres
Most of the Nord Stream pipeline will be laid directly on the seabed. of the trenching and rock-dumping areas. Sediments that settle in
The presence of the pipelines, each with a diameter of 1.4m, will exposed shallow-water areas are re-suspended during rough weather
change the near-bottom current pattern near the pipelines. The conditions, finally ending up in net accumulation areas.
Swedish Meteorological and Hydrological Institute has carried out an
analysis of the impact on the hydrography and the water quality caused In general, marine benthic invertebrates are unlikely to be adversely
by the presence of the Nord Stream pipelines. Its analysis shows that affected by increased turbidity (light attenuation and scattering caused
the mixing of new deepwater flowing into the Baltic Sea might increase by suspended particles in the water column). Experience from other
by at most 2%. Increased mixing of new deepwater means lower pipeline projects shows that the impact on benthic invertebrate
salinity, increased flow rate and increased transport of oxygen, which communities and estuarine birds is limited in both time and space.
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would tend to improve the oxygen conditions in and below the
halocline and thereby increase the deposition of phosphorus in the Earth-intervention works in the deeper parts of the Baltic Sea will
deepwater. Although the effect is very small, the pipelines may thus have a considerably smaller impact on water quality in the photic
tend to decrease the effects of eutrophication in the Baltic Sea.
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zone than intervention works at shallower depths. In addition to the
larger dilution effects at greater depths, the presence of a pycnocline
As a consequence of dredging, trenching, backfilling, rock-dumping (a horizontal layer separating water masses of different densities
and pipeline layout in connection with the construction of the Nord because of different salinity and/or different temperature) effectively
Stream pipelines, sediments and associated substances will be prevents re-suspended sediments from reaching the surface layer.
mobilised. The sediment spreading from construction works will The release of nutrients as a consequence of the marine earthworks for
be most intense closest to the landfall sites in Russia and Germany. The installation of both pipelines has been estimated to be approximately
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EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 1
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