5.4 Estuaries in the Southern North Sea Region
103
and so on. Therefore, it is crucial to understand the natural dynamic and variability and
the influences of human interventions on these processes. In most cases it is difficult to
differentiate if these impacts are based on human interferences or natural variation or if
they are a mixture of both.
Nevertheless, tidal range is a proxy to show that changes have taken place in estuaries,
further parameters are also important such as current velocity, time of the tide capsizing
point and many more.
Dredging Activities
Anthropogenic morphological changes of river channels are generated by dredging and
other river conservancy works such as training walls along channels. The question is what
to do with the sediment? Two main strategies exist in sediment handling. One strategy is
to relocate the sediment from certain reaches or channel parts to another part where the
depth is insufficient for shipping and transport. This material is, for example, relocated on
spots where undesirable erosion occurs. The second strategy is the removal of sediment
from the river, mainly sand and gravel which can be used e.g. for infrastructure projects.
Prior to the use of this material on land it has to be tested for contamination with heavy
metals and other pollutants.
This section exemplifies the different strategies and the amount of dredging in two
estuaries. At the rivers Weser and Elbe the removal of sediment prevail either to be used
by third parties for infrastructure projects or by disposing the sediment on dumping sites
in the North Sea. At the Schelde the sediment is relocated to certain spots in side channels
(see Sect. 6.2.3).
Figure 5.33 displays the amount of dredged sediment in five distinct sections of the
Elbe river. At the mouth the amount of dredged material increased between 1999 and
2009. Unfavorable morphological changes (sediment accretion) demanded for higher efforts. The amount of dredging in the port of Hamburg showed reasonable amount as well.
Mainly fine grained sediment has to be dredged. A superficial explanation for increasing
dredging activities is that many estuaries have changed their tidal characteristics, that is,
tidal pumping is prevailing. For the Elbe river net sediment export has changed by different reasons but one of them is related to the changes due to river engineering works and
reduced fresh water discharge from upstream.
Figure 5.34 illustrates the increase of dredging between 2000 and 2009: from
15 Mio. m 3 in 2000 up to more than 25 Mio. m 3 in 2008. Efficacy of dredging plays an
important role. There is a distinction between maintenance and capital dredging. Capital dredging is applied to achieve a certain depth of a fairway, maintenance dredging is
necessary to keep the fairway or channel on a desired depth and shape.
In comparison at the Weser the amount of dredging is less (Fig. 5.35, mean
10 Mio. m 3 ). In 2006 the amount of dredged material was higher because a turning point
for big vessels was installed (total length of approximately 2 km and width of 600 m),
approximately 2 Mio. m 3 of sediment were relocated (Krämer et al., 2010). The reason
103
and so on. Therefore, it is crucial to understand the natural dynamic and variability and
the influences of human interventions on these processes. In most cases it is difficult to
differentiate if these impacts are based on human interferences or natural variation or if
they are a mixture of both.
Nevertheless, tidal range is a proxy to show that changes have taken place in estuaries,
further parameters are also important such as current velocity, time of the tide capsizing
point and many more.
Dredging Activities
Anthropogenic morphological changes of river channels are generated by dredging and
other river conservancy works such as training walls along channels. The question is what
to do with the sediment? Two main strategies exist in sediment handling. One strategy is
to relocate the sediment from certain reaches or channel parts to another part where the
depth is insufficient for shipping and transport. This material is, for example, relocated on
spots where undesirable erosion occurs. The second strategy is the removal of sediment
from the river, mainly sand and gravel which can be used e.g. for infrastructure projects.
Prior to the use of this material on land it has to be tested for contamination with heavy
metals and other pollutants.
This section exemplifies the different strategies and the amount of dredging in two
estuaries. At the rivers Weser and Elbe the removal of sediment prevail either to be used
by third parties for infrastructure projects or by disposing the sediment on dumping sites
in the North Sea. At the Schelde the sediment is relocated to certain spots in side channels
(see Sect. 6.2.3).
Figure 5.33 displays the amount of dredged sediment in five distinct sections of the
Elbe river. At the mouth the amount of dredged material increased between 1999 and
2009. Unfavorable morphological changes (sediment accretion) demanded for higher efforts. The amount of dredging in the port of Hamburg showed reasonable amount as well.
Mainly fine grained sediment has to be dredged. A superficial explanation for increasing
dredging activities is that many estuaries have changed their tidal characteristics, that is,
tidal pumping is prevailing. For the Elbe river net sediment export has changed by different reasons but one of them is related to the changes due to river engineering works and
reduced fresh water discharge from upstream.
Figure 5.34 illustrates the increase of dredging between 2000 and 2009: from
15 Mio. m 3 in 2000 up to more than 25 Mio. m 3 in 2008. Efficacy of dredging plays an
important role. There is a distinction between maintenance and capital dredging. Capital dredging is applied to achieve a certain depth of a fairway, maintenance dredging is
necessary to keep the fairway or channel on a desired depth and shape.
In comparison at the Weser the amount of dredging is less (Fig. 5.35, mean
10 Mio. m 3 ). In 2006 the amount of dredged material was higher because a turning point
for big vessels was installed (total length of approximately 2 km and width of 600 m),
approximately 2 Mio. m 3 of sediment were relocated (Krämer et al., 2010). The reason