72
5 Challenges: Sectoral Descriptions
along the coasts of The Netherlands and the anticipation of possible consequences of an
accelerated sea level rise. Applying the baseline concept erosion can be allowed to take
place to a limited extent, but will be prevented on highly vulnerable coastal stretches.
The main technique deployed to implement this strategy was the application of sand nourishment and this has led to good results. The concept of the coastal defense strip was
introduced from the –20 m depth-line on the seaside to the polder on the landside (MVenW,
1990).
The Netherlands applied a scenario-driven approach for an accelerated sea level rise,
which was based on the IPCC scenarios and ranges from 20 cm/100 years (minimum
scenario) to 85 cm/100 years (maximum scenario) with a 10 % increase in wind speed
(MVenW, 2002). The safety level of the embankments will be reassessed every 6 years.
The Technical Advisory Committee has stimulated an investigation of the failure
mechanisms of coastal protection elements. Consequently, a large research project has
been launched called VNK (Veiligheid Nederland in Kaart, Flood Risks and Safety in The
Netherlands, Floris). The approach taken in this project was described as: “From probability of exceedance to probability of flooding” (TAW 2000, MVenW 2005a-c). This
means that the safety margins established by the Delta Commission are still valid, but
the design water level as criteria for the dike height will be substituted by an acceptable
risk.
The definitions are according to the Committee as follows (TAW, 2000, p. 8):
Exceedance frequency: The exceedance frequency of a water level is the probability
that the design water level is reached or exceeded. The design water level is used to design
a safe dike or hydraulic structure.
Flood probability: The flood probability is the probability, that an area might be inundated because the water defense around that area (i.e., a dike ring) fails at one or more
locations.The failure of a protective element can have different causes.
The background of the conceptual shifting in The Netherlands refers to the fact that
about 50 dike rings around polders have been installed to protect people against flooding
and at the rivers against inundation. The safety of the dike ring is provided by different
constructions such as dikes, sluices and locks. Every element has its own failure mechanism and its specific failure probability, especially, that of human error, as the experiences
of 1953 have shown (Slager, 1992). The aim of the Floris project was to determine as
exactly as possible the probability of failure of these components. This was done by assuming that a chain is as strong as its weakest link. Thus, the Floris project identified
Weak Spots. This approach and the paradigm shift has been integrated as early as possible
in a much wider approach to coastal development – see MVenW (2002). The final result
of the second phase of the Floris project was published in Vergouwe (2015) and will be
elaborated in Sect. 6.1.4.
5 Challenges: Sectoral Descriptions
along the coasts of The Netherlands and the anticipation of possible consequences of an
accelerated sea level rise. Applying the baseline concept erosion can be allowed to take
place to a limited extent, but will be prevented on highly vulnerable coastal stretches.
The main technique deployed to implement this strategy was the application of sand nourishment and this has led to good results. The concept of the coastal defense strip was
introduced from the –20 m depth-line on the seaside to the polder on the landside (MVenW,
1990).
The Netherlands applied a scenario-driven approach for an accelerated sea level rise,
which was based on the IPCC scenarios and ranges from 20 cm/100 years (minimum
scenario) to 85 cm/100 years (maximum scenario) with a 10 % increase in wind speed
(MVenW, 2002). The safety level of the embankments will be reassessed every 6 years.
The Technical Advisory Committee has stimulated an investigation of the failure
mechanisms of coastal protection elements. Consequently, a large research project has
been launched called VNK (Veiligheid Nederland in Kaart, Flood Risks and Safety in The
Netherlands, Floris). The approach taken in this project was described as: “From probability of exceedance to probability of flooding” (TAW 2000, MVenW 2005a-c). This
means that the safety margins established by the Delta Commission are still valid, but
the design water level as criteria for the dike height will be substituted by an acceptable
risk.
The definitions are according to the Committee as follows (TAW, 2000, p. 8):
Exceedance frequency: The exceedance frequency of a water level is the probability
that the design water level is reached or exceeded. The design water level is used to design
a safe dike or hydraulic structure.
Flood probability: The flood probability is the probability, that an area might be inundated because the water defense around that area (i.e., a dike ring) fails at one or more
locations.The failure of a protective element can have different causes.
The background of the conceptual shifting in The Netherlands refers to the fact that
about 50 dike rings around polders have been installed to protect people against flooding
and at the rivers against inundation. The safety of the dike ring is provided by different
constructions such as dikes, sluices and locks. Every element has its own failure mechanism and its specific failure probability, especially, that of human error, as the experiences
of 1953 have shown (Slager, 1992). The aim of the Floris project was to determine as
exactly as possible the probability of failure of these components. This was done by assuming that a chain is as strong as its weakest link. Thus, the Floris project identified
Weak Spots. This approach and the paradigm shift has been integrated as early as possible
in a much wider approach to coastal development – see MVenW (2002). The final result
of the second phase of the Floris project was published in Vergouwe (2015) and will be
elaborated in Sect. 6.1.4.