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The Danish and Swedish governments decided in 1991 to build a fixed link between Denmark and Sweden crossing the Øresund (the Sound). Two environmental concerns associated with the establishment of the link were identified:

  • The link itself could affect the water and salt flow through the Øresund and into and out of the Baltic Sea, leading to reduction of fish catches, and affecting other biological systems in the Baltic Sea.
  • Sediment spill during construction work could affect sensitive receivers such as mussels, sea grass and eiders.

An International Expert Panel, advising the Danish and Swedish governments, was formed to design mitigation strategies to avoid negative environmental impacts. The proponent was the Øresundskonsortiet, owned jointly by the Danish and Swedish Governments.

    General Project Description


    Title: Øresund Fixed Link
    Location: Øresund (Sweden - Denmark)
    Date: 1991 - 2000
    Companies: See figure under 'Governance context' for all companies involved
    Costs: 4 billion US$ / EUR 3 billion
    Abstract: A fixed link between Copenhagen (Denmark) and Malmö (Sweden) is built, consisting of a tunnel, an island and a bridge. During construction works an intensive environmental monitoring program was implemented, among which a so-called feedback monitoring system. Its aim was to ensure the earliest possible intervention whenever there was a risk of environmental norms being exceeded.
    Topics: Tunnel, Bridge, Artificial island, Environmental monitoring, Feedback monitoring, Design and construct

    The project aims at improving transport connections between Sweden and Denmark and thereby strengthening cultural and economic co-operation. The Fixed Link across the Øresund is expected to stimulate the development of a joint labour and housing market at each side of Øresund. In short the link is expected to further the integration of the Øresund Region, paving the way for successful competition with Europe's other regional centres.

    The Øresund link, which comprises a 4-lane motorway and a double-track railway, consists of three distinct elements:

    • A man-made peninsula adjacent to Copenhagen airport (Kastrup) and a 4 km long man-made island (called Peberholm) located south of Saltholm and roughly in the middle of the Øresund.
    • A 4,050 meters long immersed tunnel positioned between the peninsula and Peberholm.
    • A bridge of 7.8 km length between the artificial island and the Swedish coast south of Malmö.

    The realisation of these three elements were tendered in various contracts: a dredging, a tunnel and a bridge contract, respectively. In terms of environmental impact control, it was predicted that the dredging operations would have the most serious impact. Although some environmental requirements were also applicable on the operation of the tunnel and bridge contracts, the present chapter focuses on the dredging project.

    BwN dimension: The project development process followed a philosophy which agrees to a large extent with the Building with Nature principles. From the very beginning of the project thorough knowledge of the ambient biotic and abiotic ecosystem was the basis of the design and environmental effects were a point of concern. Throughout the project this environmental concern was addressed and communicated with stakeholders and the public at large. The environmental responsibilities of all actors were included in their respective contracts prior to project execution.

    Øresundskonsortiet was established on the 27th of January 1992 with the mission to plan, build, finance, own and operate the Fixed Link. The consortium is jointly owned by the states of Sweden and Denmark, on a 50-50 basis and through two companies: A/S Øresundsforbindelsen (Denmark) and Svenska-Danska Broförbindelsen SVEDAB AB (Sweden). The figure shows all parties and consortia involved.

    Right from the beginning of the planning process, Øresundskonsortiet adopted "Design & Construct" as a contract form for the realisation of the works. By doing so, they achieved a clear division of responsibilities between the owner (Øresundskonsortiet) and the contractor, an approach that proved to work well in practice..In terms of environmental effects, this meant that the contractors had to take full responsibility for the detailed design, construction methods and materials used in their part of the works, whereas the owner took full responsibility for the establishment of the Fixed Link, and for securing that the effects of the combination of works by different contractors would not exceed environmental norms. Thus the final responsibility for meeting the environmental goals (and not exceeding the prevailing norms) is held by the Contract Management. To that end, an Environment & Authorities staff was formed, which took responsibility for the daily administration of the Control & Monitoring Program. In order to make this scheme work in practice, Øresundskonsortiet took the following measures:

    • They created dredging instructions, aiming to reduce the dredging spill to overall 5% on average and to reduce the spill masses in duration, intensity and spatial extent. The dredging spill was defined as the mass of dredged material leaving through the boundaries of the work area as suspended material. These instructions served as quality documents for compliance monitoring and administration.
    • They implemented a feedback monitoring program, which provided input to planning and environmental impact control.
    • On top of this the authorities established an independent control program.

    The distribution of responsibility in the context of environmental impacts was:

    • The dredging contractor is responsible for his specific part of the works, i.e. the amount of dredged materials, the spill, the distribution of the spill in space and time
    • The owner takes responsibility for the overall management of the environmental impact of the works, as long as the contractors did not exceed the prevailing threshold values.
    • The authorities are responsible for the environmental conditions in Øresund in general, based on overall annual surveys.

    Planning and Design

    The decision to construct the Link was taken after lengthy discussions, mainly about the environmental aspects of the works and the predicted increase of road traffic. It was stated from the beginning of the project that the fixed link should be designed and constructed with due consideration of what is ecologically motivated, technically feasible and economically reasonable.

    During the years of discussion between the two governments on whether a fixed link should be built, many technical, economic and environmental investigations were carried out.

    In 1989 the final results were presented to the two governments, which concluded that there was a general political will in both countries to establish either a railway, or a combined rail- and road link between Copenhagen and Malmö. Further political negotiations in 1990 and 1991 finally led to a government agreement on a fixed link with a combined rail- and road connection should be constructed.

    During the first years of the project Øresundskonsortiet faced difficulties obtaining approval from both governments for the design and planning of the project. This was due to differences in administrative principles, rules and procedures between the two governments. Yet, the time-consuming process gave Øresundskonsortiet ample opportunity to develop the organization, contractual strategies, quality systems and to optimize the design and develop administrative and other procedures.

    One of the reasons why this authorities' approval process was so lengthy and complicated were the environmental requirements. One of the most important of these was the "Zero blocking effect”. This means that the flow of water, salt and oxygen through the Øresund had to remain unchanged. Through careful design and by optimizing the length of the tunnel, the size and shape of the artificial peninsula and the island, the flow blocking effect - as computed with sophisticated hydrodynamic models - was reduced from 2.3% of the water flow to 0.5%. During construction, compensation dredging in and around the project area was carried out in order to further reduce the blocking effect to zero. This compensation dredging was carried out in two phases, with the exact amounts and locations of the second phase determined by hydrodynamic modelling after all other marine construction activities had been fixed in the design. In this way the amount of compensation dredging could be kept as small as possible.

    Environmental regulations
    The Danish and Swedish authorities stipulated that the construction of the Fixed Link across the Øresund should not affect the marine environment in the Baltic Sea. Øresundskonsortiet developed new strategies and methods to limit environmental effects in the Øresund and the Baltic. Enquiry documents (dredging instructions) were made to translate the environmental regulations to the contractors. One of the main aspects of this document is that the total dredging volume may not exceed 7.5 million cubic meters and spillage must be limited to an average of 5% of the dredged quantities. Furthermore, the extent of spillage must be limited in accordance with seasonal and local conditions. The limit values for spillage of dredged material were described regarding several factors, such as:

    • The impact on flora and fauna in the Øresund
    • The impact on bathing water along the coast
    • The nature of the work and production methods
    • Nature and composition of the dredged material
    • The actual current conditions
    • Experience from projects of similar nature

    The limits were determined on the basis of preliminary examinations of the marine environment's sensitivity to sediment spillage. Although on average spillage from dredging operations may not exceed 5%, spillage may temporarily exceed this value during certain seasons. On the other hand, spillage must be lower during particularly sensitive seasons, i.e. the growth and breeding seasons. Dredging was planned to have a minimum effect on the Øresund environment. For instance, herring migration through the Øresund was carefully monitored in order to avoid barriers of spilt sediment across the Øresund during migration periods.

    Consultants tender
    In the spring of 1993 the Øresundskonsortiet tendered the engineering, monitoring and supervision services for the fixed link. Apart from the financial part of the tender, the consultant selection was based on a design contest. A number of combinations of consultants were invited to submit a design proposal for the project, based on the reference design of the Øresundskonsortiet derived from the feasibility study. This reference design had to be optimized environmentally and the consultants were invited to present an alternative design, as well. Based on these designs the consultants for the project were chosen.

    From the start of the project a Triple-P approach was adopted, with the statement that the fixed link should be designed and constructed with due consideration of what is ecologically sound, technically feasible and economically reasonable. From the very start of the project this principle, which is to a large extent in line with the BwN-principles, was adopted and communicated by the actors involved. In the design process many alternatives were created with the emphasis on environmental optimization.


    Contractors tender
    The design and construct concept adopted for the large construction contracts allowed the contractors' innovative freedom in the choice of design and construction methods while respecting the owner's wishes as laid down in the selected link design. In general terms this means that the contractors were allocated the responsibility for the detailed design and the construction of the different parts of the civil structures and installations of the link.

    The final report on the tender evaluation by Øresundskonsortiet’s consultants included recommendations for awarding the contract, and a list of matters which would have to be resolved with the preferred consortium before the award could be made. Øresundskonsortiet accepted these recommendations and a dialogue was opened with the preferred consortium. Øresundskonsortiet insisted that at the time of signing the contract there should be no known areas of doubt and no unresolved issues. The parties involved in the dialogue realized that price and scope were not negotiable; the dialogues were to clarify and resolve uncertainties.

    The requirements to ensure continuity between contracts were fixed by the owner. These were laid down in the reference design and functional specifications. Within these bounds, constructors had considerable scope to make the design compliant with all design requirements and at the same time suiting their preferred construction method.

    The rigorous environmental requirements concerned the environmental impacts both during construction and after completion of the link. To ensure compliance with these requirements during construction, the following measures were taken:

    • Each contractor had to provide an elaborate method statement with substantial environmental paragraphs. Construction works could not start before this statement had been approved. Strict adherence to this method statement gave the client, authorities and the public confidence that works were executed within agreed limits, to be confirmed directly by monitoring. Contractors had to monitor the environmental aspects (short-term monitoring) for which they were responsible, such as. the amount of dredged materials, the amount of spill, and the distribution of the spill in space and time.
      • The total dredged volume should not exceed 7.5 million m3 of seabed material. When the project was almost finished in 1998 the total dredged volume was 7.4 million m3, so this requirement was met.
      • The spill volume should not exceed 5% of the total dredged volume on average. Spillage was allowed to temporarily exceed this percentage during certain seasons, but it had to be less in the growth and breeding season. This requirement was also met, with an average spill percentage of 4.2
    • Øresundskonsortiet implemented an intensive environmental monitoring program (long-term monitoring), called feedback monitoring. Its aim was to ensure the earliest possible intervention whenever there was a risk of environmental norms being exceeded. The figure gives a flowchart of this feedback monitoring system. Monitoring was intensive and focused on factors with a rapid response to changes. In this case ‘feedback’ means immediate action whenever a breach of norms was observed or predicted. Such action may involve increased monitoring, adjustment of the construction work, or even temporary suspension of construction operations. One of the operation control options was to put a dredging vessel on maintenance, rather than dredging, as soon as the allowable mean sediment spillage rate threatened to be exceeded in a certain time interval. Because of the successful spillage control, none of the biological feedback loops resulted in a change of construction operations. The only time construction of the artificial island Peberholm was interrupted for a period of 10 days was due to severe ice conditions in the winter 1995-96.
    • Independent of Øresundskonsortiet, the Danish and Swedish authorities carried out their own monitoring and control program. The objective of this program was to assess whether the overall environmental effects of the construction were in line with the analyses and model predictions upon which the work has been planned, and whether the set environmental norms had been observed. The monitoring was therefore directed towards a broader section of the ecosystem, as opposed to the feedback monitoring which focused on the state of eelgrass and mussels, two particularly sensitive species. Samples showed that the impact on both these species remained within expected and acceptable bounds.
    • Guidelines for the handling of waste, wastewater from ships and work sites, oil spill emergency systems, etc. were drawn up in order to minimize the environmental impact of the dredging works.

    Before tendering, research was done to establish realistic environmental norms. These requirements were clearly communicated and each actor was clear on his responsibility regarding the environmental impact of his activities. The extensive monitoring program proved to work well and the construction was completed 6 month ahead of the original time schedule, within the agreed budget and with a minimal environmental impact.

    Operation and Maintenance

    The design and construct concept adopted for this project was an important factor contributing to the completion of the Øresund Link well within time and budget. Another factor that contributed to this achievement was the project management approach. The fact that all environmental requirements have been is due to the definition of clear guidelines and goals from the outset and the mutual trust between the owner, the contractors and the environmental authorities.

    Three years after the Øresund Link opened to rail and automobile traffic, an environmental survey of the biological systems in the sound did not show any negative effects and indicated that the ecosystem had returned to preconstruction conditions. The actual environmental effects are significantly less than was expected. Seals, for instance, were expected to disappear completely from Saltholm Island, just north of the link, as soon as building operations had started. Seals, however, are inquisitive by nature and have simply adapted to life on Saltholm during construction. In fact, environmental conditions may even have improved because of the extensive new area of hard substrata provided by the bridge pillars. Mussels and other organisms now occur in larger populations than before construction and serve as food for the large bird population in the Saltholm bird reserve.

    Making the same organization responsible for building the Link and for its operation has led to an early focus on operational aspects. As a result, emphasis has been put on coordinating the different contracts with respect to functional requirements as well as requirements with respect to safety, availability and Life Support Costs. Øresundskonsortiet adopted an environmental policy for the operation and maintenance, which the following main goals:

    • to continually reduce the environmental impact by the link's daily operation;
    • to pay due attention to the environment while installing or maintaining technical facilities;
    • to comply with environmental legislation and to help protecting nature;
    • to contribute to reducing the environmental impact of traffic on the link;
    • to be open and informative about the environmental goals and the extent to which they are met.

    Examples of practical implementation of the above strategies are:

    • There must always be a well-functioning and operating rail system with sufficient capacity, in order to promote freight and passenger transport by rail.
    • The existing lighting in the tunnel was replaced in 2005 with a more energy-saving system. Together with other saving measures, this has led to overall energy savings of 15% in 2005.
    • The artificial island of Peberholm was kept inaccessible to the public, whence it has become an important habitat for endangered species. The Peberholm ecosystem is being monitored and an inventory of plants, breeding birds, insects and spiders is carried out.
    • The environmental authorities have defined norms for the noise level from the Link. A control program for vibration and noise affecting residential areas near the bridge zone is implemented. Surveys show that the risk of vibration disturbance is insignificant.

    The total project was executed within the environmental requirements. Three years after completion, the ecosystem has returned to preconstruction conditions.

    Lessons Learned

    • By considering various alternatives and by optimizing the design, the environmental impact of the project could be minimized. The blocking effect of the structure could be significantly reduced by optimizing the design. Thus less compensation dredging was needed.
    • Enough time should be allotted to developing organisation, contractual strategies and quality systems, to optimize the design and to develop administrative and other procedures.
    • If possible within the set project requirements, a flexible and adaptable design results in less environmental impact. By adapting the design of the compensation dredging in a late stage of the construction works, on the basis of model computations with the actual geometry, a zero blocking effect could be achieved with no more dredging than necessary.
    • Environmental research in the pre-construction stage can lead to realistic environmental norms. Estimates of the environmental impacts of construction works led to clear and strict environmental norms, e.g. limits to temporal and spatial extent of exposure to dredging spill.
    • Clear definition of responsibilities of all actors involved helps to reduce the environmental impact. The contractors, for instance, were quite clear about their responsibility regarding the dredging spill, as a result of which the mean spill limit was never exceeded during the works.
    • Extensive feedback monitoring during construction in combination with predefined limit values of relevant parameters proved to work well.
    • All environmental requirements have been met because clear guidelines and goals were set from the outset, and because mutual trust existed between the owner, the consultant and contractor consortia and the environmental authorities.

    To identify lessons learned on AMS we apply the Frame of Reference (Van Koningsveld, 2003) to the monitoring plan of the Øresund Fixed Link project. The Frame of Reference is a tool to support decision making, and it also sets a target for specialist involvement.

    Strategic Objective: The Oresund Fixed Link shall be designed and constructed with due consideration to what is ecologically motivated, technical feasible and economically reasonable in order to prevent detrimental impacts on the environment.

    Evaluation Procedure: two-fold in this case: 1) Are effects observed? 2) Is a stable situation achieved?

    Operational Objectives and other elements of the Frame of Reference: see below

    Authorities Independent Control & Monitoring


    Long term - Owners Feedback Monitoring


    Short term - Contractor's Spill Monitoring



    • Gray, J.S., 2005. Minimizing Environmental Impacts of a Major Construction: The Øresund Link, Integrated Environmental Assessment and Management, Vol 2, Number 2, pp. 196-199
    • Iversen, C., B. Mogensen, 1999. Proceedings - Øresund Link Dredging & Reclamation Conference: challenges, solutions and lessons on environmental control, project management, construction methodology, dredging & reclamation technology: 26-28 May 1999, Copenhagen, Denmark. Øresundkonsortiet.
    • Jensen A., J.E. Lyngby, 1999. Environmental Management and Monitoring at the Øresund Fixed Link. Terra et Aqua 74:pp. 10-20
    • Larsen, J., M. Puch, T. Niilonen, H. Karup, 1998. 6th semi-annual report on the environment and the Öresund fixed link's coast to coast installation: January - June 1998. ISBN 87-7909-070-2 (Original title: 6. halvårsrapport om miljöet og Öresundsforbindelsens kyst-til-kyst anlæg: 1. halvår 1998)
    • Russel, H., 2000. Partnership pays: Project management the Øresund way. Route One Publishing Ltd, UK
    • Immersed tunnel conference (5-7 April 2000), Proceedings, Copenhagen, Denmark
    • Øresundskonsortiet (1997), The environment and the Fixed Link across Øresund
    • Øresundskonsortiet (1997), The Øresund Fixed Link, Design and Construction

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