ABSTRACTS 'Extreme Discharges' - CHR-KHR

For the measurement point Lobith, which is situated downstream of the Lower Rhine, the resulting peak discharges
for all hydrographs can be seen in figure 3. Also here all flood waves are damped due to the dike overflow
along the Upper Rhine and the Lower Rhine.
In NRW and Gelderland several flood reduction measures are planned. Some of them such as lowering of groynes,
lowering of the floodplains, removal of hydraulic obstacles from the riverbed or setting back of dikes will
cause an enlargement of the discharge capacity between the dikes. As the study showed, these measures cause a
lowering of the water level at the location of the measure and further upstream. By building retention basins
water will be extracted from the river and temporarily stored. As result of this reduction of the discharge, the
water level in the river at the location of the retention basin and downstream of the retention basin decreases.
The investigations showed, that the planned flood reduction measures in NRW are most effective at floods equal
to the flood of 1995, but have little effect under more extreme conditions. It could be shown, that these effects
can be enlarged by optimizing the control levels of the planned retention basins and by improving the combination
of measures (figure 4).
Measures in Germany affect the water levels in the Netherlands and the other way around (figure 5).
Effect planned flood reduction measures in NRW
Effect planned flood reduction measures in NRW
0,2
0,2
Difference in water level [m]
0,1
0
-0,1
-0,2
-0,3
-0,4
1995 HW1 HW2 HW3 HW4
HW5 HW6 HW7 HW8
Germany
NL
Difference in water level [m]
0,1
0
-0,1
-0,2
-0,3
-0,4
1995 HW1 HW2 HW3 HW4
HW5 HW6 HW7 HW8
Germany
NL
-0,5
620 640 660 680 700 720 740 760 780 800 820 840 860
Andernach Bonn Köln Düsseldorf Ruhror Emmerich Lobith
-0,5
620 640 660 680 700 720 740 760 780 800 820 840 860
Andernach Bonn Köln Düsseldorf Ruhror Emmerich Lobith
Figure 4. Effect of flood reduction measures
planned in NRW, improved version.
Figure 5. Combined effect flood reduction measures
planned in NRW (improved version) and The
Netherlands.
4. Conclusions and outlook
In the project “Effects of extreme floods along the Niederrhein (Lower Rhine)” the effects of flooding and flood
reducing measures were investigated in order to get insight in the occurrence and behavioure of extreme floods
along the Rhine. It was focused on the flooding pattern along the Lower Rhine and the Dutch Rhine branches, as
well as the development of the discharge and the effect of the flood reduction measures in this river reach.
It could be shown, that floods at the Lower Rhine can exceed the flood levels were dikes are designed for. This
causes inundations along the Lower Rhine, first in the southern part, later also in the middle part. Inundation of
the southern and middle part of the Lower Rhine reduces the peak discharge in the northern part of the Lower
Rhine and in The Netherlands. Nevertheless in present time (situation 2002) transboundary inundations can
occur. By building a flood wall, this will be prevented in future (situation 2020). The planned flood reduction
measures in NRW and in the Netherlands can reduce water levels in the river. These effects can be enlarged by
optimizing the control levels of the planned retention basins and by improving the combination of measures on
both sides of the border.
The flood design levels along the Rhine change along his course from Switzerland through Germany to The
Netherlands. The study made clear, that under such circumstances the effects of flood reduction measures must
be seen in combination with the effects of dike overflow upon the discharge and water level in the river. It also
became evident, that the impact of dike overflow, flooding and flood reduction measures upon extreme floods is
very large and should be taken into account in flood statistics. The techniques and tools, which are developed in
this project will make this possible.
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