142
6 Prospects: Approaches of Integrated Management
• Depoldering: The dike on the riverside of a polder is relocated further away from the
river. This depolders the area and enables water from the river to flood this area at times
of high water levels.
• Riverbed excavation: The riverbed is made deeper by taking away the top layer of the
riverbed. Because the riverbed is lower, there is more capacity for river water.
• Water storage: As a result of the controlled combination of a closed flood gate and large
volumes of river water flowing to the sea, a specific retention polder serves as an area
of temporary water storage.
• High water channel: A high water channel is formed between two dikes. The channel
branches off from the river and transports some of the river water via another route at
times of high water levels.
• Lowering breakwater spurs: Breakwater spurs ensure that the river does not alter its
course or lose depth. However, at times of high water, spurs slow down the flow of the
water. By lowering them, the water has a better chance of being conveyed faster.
These measures will be implemented as tailor-made measures in about 30 projects along
the major rivers in The Netherlands.
The Floris research project (see Sect. 5.1.4) was launched to investigate the probability of flooding of the existing dike-rings in The Netherlands. This project developed
and applied a risk-based approach to flood safety which should offer the prioritization of
measures in flood protection. Until that time the Dutch strategy was mainly based on the
probability of exceedance and the consequences of over topping (see Sect. 5.1.4). Several
recommendations in the past already acknowledged that many more failure mechanisms
exist. The task was to analyze and assess the extend of the probability per dike-ring consisting of multiple and different protective elements. According to the slogan the chain is
as strong as the weakest link the dike-rings were further divided into dike sections.
In 2008 the Delta Commission published new recommendations for water management in The Netherlands which again recommended to apply a risk-based approach (Delta
Commission, 2008). The next step was the implementation of the Water Act in 2009 where
the safety standards per dike-ring were manifested again.
5 In §2 section 2.2(1) it is specified that “[ . . . ] for each dike ring as the average annual overtopping probability of the
highest high-water level that the primary flood defense structure erected as direct defense
against external waters, must be designed to withstand, also taking in to account other
factors that determine the flood defense capacity of such structures.” That means that in
the Water Act a shift slightly took place not to only rely on the probability of exceedance.
“The safety standard for each dike ring shall be further specified by ministerial order as
the average annual probability of flooding of the area protected by the dike ring as a result
of the breach of a primary flood defense structure” (§2 section 2.2(2)).
5 Here defined as: system of primary flood defense structures that, either alone or in combination
with high ground, provides protection against flooding, in particular by external water (§1, Section
1.1).
6 Prospects: Approaches of Integrated Management
• Depoldering: The dike on the riverside of a polder is relocated further away from the
river. This depolders the area and enables water from the river to flood this area at times
of high water levels.
• Riverbed excavation: The riverbed is made deeper by taking away the top layer of the
riverbed. Because the riverbed is lower, there is more capacity for river water.
• Water storage: As a result of the controlled combination of a closed flood gate and large
volumes of river water flowing to the sea, a specific retention polder serves as an area
of temporary water storage.
• High water channel: A high water channel is formed between two dikes. The channel
branches off from the river and transports some of the river water via another route at
times of high water levels.
• Lowering breakwater spurs: Breakwater spurs ensure that the river does not alter its
course or lose depth. However, at times of high water, spurs slow down the flow of the
water. By lowering them, the water has a better chance of being conveyed faster.
These measures will be implemented as tailor-made measures in about 30 projects along
the major rivers in The Netherlands.
The Floris research project (see Sect. 5.1.4) was launched to investigate the probability of flooding of the existing dike-rings in The Netherlands. This project developed
and applied a risk-based approach to flood safety which should offer the prioritization of
measures in flood protection. Until that time the Dutch strategy was mainly based on the
probability of exceedance and the consequences of over topping (see Sect. 5.1.4). Several
recommendations in the past already acknowledged that many more failure mechanisms
exist. The task was to analyze and assess the extend of the probability per dike-ring consisting of multiple and different protective elements. According to the slogan the chain is
as strong as the weakest link the dike-rings were further divided into dike sections.
In 2008 the Delta Commission published new recommendations for water management in The Netherlands which again recommended to apply a risk-based approach (Delta
Commission, 2008). The next step was the implementation of the Water Act in 2009 where
the safety standards per dike-ring were manifested again.
5 In §2 section 2.2(1) it is specified that “[ . . . ] for each dike ring as the average annual overtopping probability of the
highest high-water level that the primary flood defense structure erected as direct defense
against external waters, must be designed to withstand, also taking in to account other
factors that determine the flood defense capacity of such structures.” That means that in
the Water Act a shift slightly took place not to only rely on the probability of exceedance.
“The safety standard for each dike ring shall be further specified by ministerial order as
the average annual probability of flooding of the area protected by the dike ring as a result
of the breach of a primary flood defense structure” (§2 section 2.2(2)).
5 Here defined as: system of primary flood defense structures that, either alone or in combination
with high ground, provides protection against flooding, in particular by external water (§1, Section
1.1).