76
5 Challenges: Sectoral Descriptions
The aims of safety for coastal protection at the North and Baltic Sea are summarized
as follows:
The basic findings of the Advisory Committee for Coastal Protection – see EAK (2002) – are
as follows:
• The absolutely highest storm surge can not be determined,
• certain specific astronomical, meteorological and oceanographic circumstances coincide
may leading to higher storm surges as anticipated today,
• it is questionable whether dikes should be built which will hold back flooding water under
all perceivable conditions.
This led the Advisory Committee to the following recommendations for a main dike
(Kunz, 2004b, p. 256–257):
• The height of the dike is crucial for the safety of the protected marshes,
• the crest of the dike should be as high as the design water level, which is based on a defined
level of safety taking into account a certain probability of exceedance and the height of wave
run-up, which should prevent frequent and powerful over topping,
• the decision not to determine a “highest storm surge”, has to be considered by designing
dikes with a certain cross-section able to withstand strong and long-lasting over topping.
For the design of main dikes the Committee recommends
• For every stretch of the coast the “design water level” has to be determined – verified
by scientific research and clearly defined – which either will never or at least within a
manageable risk level – be exceeded within a certain time period. The currently applied
procedures (in Schleswig-Holstein with regard to the frequency of a certain water level,
and in Lower Saxony to the single value procedure) produce approximately the same
values, but are not verified by science and are more or less the result of empirical
studies,
• identification of a “design height for wave run-up”, which will only be over topped by
a certain wave level or only allow a defined amount of water to flow over the dike crest
(overflow).
These guidelines of the Advisory Committee are reflected in the current procedure to
determine the height of the dike crest and, thus, in the accepted safety standard, incorporated in the procedure applied in Lower Saxony as shown in Fig. 5.8. Since no absolute
safety against flooding can be guaranteed, the risks have to be limited and managed. There
are many uncertainties which have to be considered to determine the safety level of embankments. As mentioned above, for example, the highest storm surge cannot exactly
be determined, for example, because of uncertainties in projecting water levels into the
future. There is no doubt that the existing safety concept has to be enhanced; however,
step by step and not immediately by introducing new approaches before they are ready
5 Challenges: Sectoral Descriptions
The aims of safety for coastal protection at the North and Baltic Sea are summarized
as follows:
The basic findings of the Advisory Committee for Coastal Protection – see EAK (2002) – are
as follows:
• The absolutely highest storm surge can not be determined,
• certain specific astronomical, meteorological and oceanographic circumstances coincide
may leading to higher storm surges as anticipated today,
• it is questionable whether dikes should be built which will hold back flooding water under
all perceivable conditions.
This led the Advisory Committee to the following recommendations for a main dike
(Kunz, 2004b, p. 256–257):
• The height of the dike is crucial for the safety of the protected marshes,
• the crest of the dike should be as high as the design water level, which is based on a defined
level of safety taking into account a certain probability of exceedance and the height of wave
run-up, which should prevent frequent and powerful over topping,
• the decision not to determine a “highest storm surge”, has to be considered by designing
dikes with a certain cross-section able to withstand strong and long-lasting over topping.
For the design of main dikes the Committee recommends
• For every stretch of the coast the “design water level” has to be determined – verified
by scientific research and clearly defined – which either will never or at least within a
manageable risk level – be exceeded within a certain time period. The currently applied
procedures (in Schleswig-Holstein with regard to the frequency of a certain water level,
and in Lower Saxony to the single value procedure) produce approximately the same
values, but are not verified by science and are more or less the result of empirical
studies,
• identification of a “design height for wave run-up”, which will only be over topped by
a certain wave level or only allow a defined amount of water to flow over the dike crest
(overflow).
These guidelines of the Advisory Committee are reflected in the current procedure to
determine the height of the dike crest and, thus, in the accepted safety standard, incorporated in the procedure applied in Lower Saxony as shown in Fig. 5.8. Since no absolute
safety against flooding can be guaranteed, the risks have to be limited and managed. There
are many uncertainties which have to be considered to determine the safety level of embankments. As mentioned above, for example, the highest storm surge cannot exactly
be determined, for example, because of uncertainties in projecting water levels into the
future. There is no doubt that the existing safety concept has to be enhanced; however,
step by step and not immediately by introducing new approaches before they are ready