CHAPTER 17
In Situ Settling Velocities and Concentrations
of Suspended Sediment in Spill Plumes,0resund,
Denmark
Karen Edelvang
17.1
Introduction
The fixed link between Denmark and Sweden, the 0resund Link, consists of a combination of a double-track railroad and a four-lane highway. Starting on the Danish side,
the link begins with a tunnel section, then crosses an artificial island and ends with a
high bridge crossing the Sound to Sweden (The Feedback Monitoring Programme for
the Fixed Link Across 0resund 1997). The link facilitates road and sea traffic between
the two countries, thereby promoting the social and economic growth of the 0resund
region. Strict environmental considerations accompany the construction of the 0resund
complex. In no manner whatsoever are the construction activities allowed to influence
and thereby modify the natural physical, chemical and biological environment of the
adjacent Baltic Sea. During the building phase, only short-term environmental damage
is allowed, provided it is restricted to areas close to the construction sites.
One of the ainIs of the environmental impact assessment is to evaluate the effectiveness of the so-called zero solution agreement concerning suspended matter fluxes
through the 0resund. As a consequence, sediment spills from dredging activities have
to be minimised. Monitoring and control programmes based on a co-operation agreement between Denmark and Sweden are designed for this specific purpose. All results
are gathered in the Feedback Monitoring Centre of the 0resundskonsortiet's monitoring and supervision unit. Computer models are an integral part of the monitoring prograntme. This chapter presents some of the results obtained from field surveys during
dredging activities dedicated to collecting information to validate the computed scenarios.
17.2
Study Area
The Sound between Denmark and Sweden is a strait connecting the Baltic Sea with the
North Sea (see Fig. 17.1). In the shallow parts of the Sound the seabed consists mostly of
lag deposits or till. Fine-grained material accumulates in the deeper areas (Kuijpers
et al. 1991). The concentration of naturally suspended sediment is generally very low in
the 0tesund «10 mg 1-1) showing systematic seasonal variations (Valeur et al. 1996).
Algae dominate in the summer, and in the winter stormy episodes resuspend sediment
deposited on the bed. During dredging operations large amounts of fine-grained material, mainly composed of chalky mud with no cohesive properties, are suspended in
sediment plumes with concentrations which are up to 100 times higher than the natural background concentration. As the settling velocities of the individual particles are
In Situ Settling Velocities and Concentrations
of Suspended Sediment in Spill Plumes,0resund,
Denmark
Karen Edelvang
17.1
Introduction
The fixed link between Denmark and Sweden, the 0resund Link, consists of a combination of a double-track railroad and a four-lane highway. Starting on the Danish side,
the link begins with a tunnel section, then crosses an artificial island and ends with a
high bridge crossing the Sound to Sweden (The Feedback Monitoring Programme for
the Fixed Link Across 0resund 1997). The link facilitates road and sea traffic between
the two countries, thereby promoting the social and economic growth of the 0resund
region. Strict environmental considerations accompany the construction of the 0resund
complex. In no manner whatsoever are the construction activities allowed to influence
and thereby modify the natural physical, chemical and biological environment of the
adjacent Baltic Sea. During the building phase, only short-term environmental damage
is allowed, provided it is restricted to areas close to the construction sites.
One of the ainIs of the environmental impact assessment is to evaluate the effectiveness of the so-called zero solution agreement concerning suspended matter fluxes
through the 0resund. As a consequence, sediment spills from dredging activities have
to be minimised. Monitoring and control programmes based on a co-operation agreement between Denmark and Sweden are designed for this specific purpose. All results
are gathered in the Feedback Monitoring Centre of the 0resundskonsortiet's monitoring and supervision unit. Computer models are an integral part of the monitoring prograntme. This chapter presents some of the results obtained from field surveys during
dredging activities dedicated to collecting information to validate the computed scenarios.
17.2
Study Area
The Sound between Denmark and Sweden is a strait connecting the Baltic Sea with the
North Sea (see Fig. 17.1). In the shallow parts of the Sound the seabed consists mostly of
lag deposits or till. Fine-grained material accumulates in the deeper areas (Kuijpers
et al. 1991). The concentration of naturally suspended sediment is generally very low in
the 0tesund «10 mg 1-1) showing systematic seasonal variations (Valeur et al. 1996).
Algae dominate in the summer, and in the winter stormy episodes resuspend sediment
deposited on the bed. During dredging operations large amounts of fine-grained material, mainly composed of chalky mud with no cohesive properties, are suspended in
sediment plumes with concentrations which are up to 100 times higher than the natural background concentration. As the settling velocities of the individual particles are