Layer 1: Prevention in the water system
Layer 1 involves minimising the probability of waterlogging and flooding. For example, waterlogging can be prevented by using the soil as a sponge. The probability of flooding is minimised through robust flood defences, which constitute the basis of our flood protection system. This page explains what is already being done in terms of the prevention of flooding and waterlogging, and how we can minimise the probability of waterlogging.
What is already being done?
The paragraphs below outline the efforts that are being taken at the national, (supra-)regional and local levels to minimise the probability of waterlogging and flooding.
What is the national government doing to prevent waterlogging and flooding?
The national government and Rijkswaterstaat (the executive branch of the Dutch Ministry of Infrastructure and Water Management) are protecting our country against flooding and extreme waterlogging from the major waters and rivers. To that end, they are building and reinforcing dykes, sluices, dams and other flood defences. In addition, they are creating more room for rivers, in order to minimise flood risks.
What is happening at the supra-regional level?
With effect from 2025, supra-regional stress tests will be conducted, alongside the existing stress tests under the Delta Plan on Spatial Adaptation. For each catchment area, these stress tests identify locations prone to major disruption in the event of extreme precipitation volumes for a prolonged period of time, such as occurred in July 2021 in Limburg. Based on these outcomes, stakeholders can collectively decide on the most appropriate measures for each location, both to prevent waterlogging and to minimise problems, damage and societal disruption.
What are the provinces doing?
In the provinces, regional water standards apply to waterlogging. The standards are set down by the provincial authorities and are observed by the district water boards in their management of the water system.
What are municipalities doing?
Municipalities seek to maximise local rainwater retention. Their efforts largely involve the greening of public space wherever possible. The municipalities are responsible for the collection and processing of rainwater falling on public grounds. This is referred to as the rainwater duty of care. Furthermore, they are responsible for the collection and drainage of wastewater, and thus for the construction and management of the sewer system. This is referred to as the urban waste water duty of care.
What are residents and businesses doing?
More and more residents and businesses are taking measures to protect their houses or business premises against waterlogging, for example, by greening their gardens. Many municipalities are setting up campaigns to encourage residents to take greening measures. More information on ways to take municipal action is provided in the Toolkit for Basic Communication in the event of Waterlogging, Flooding, Heat and Drought.
Collaboration is important
At all these levels, it is important for different governments and stakeholders to collaborate. The waterlogging case maps out how governments can use the Environment Act instruments to that end.
How can we minimise the probability of waterlogging?
The paragraphs below explain how we can minimise the probability of waterlogging.
More protection in high-risk areas
The locations prone to the highest risks of waterlogging will have a higher protection level. The extent of the risk depends on the location and its land use. For that reason, water management standards have been drawn up that indicate the maximum limit for the probability of waterlogging in a particular area. Areas where potential damage exceeds such limits need a higher protection level. Consequently, the standards for built environments are much higher than those applying to, for example, meadows. More details can be found in the Integrated waterlogging risk analysis pilots study. For this study, the Foundation for Applied Water Research (STOWA) conducted several pilots among four different district water boards, with different characteristics.
Using the soil as a sponge
One way to maximise local rainwater collection and processing is using the soil as a sponge: the rainwater seeps into the soil, where it is retained. This sponge effect can be utilised in several ways. In any case, reducing soil coverage is helpful, for example, by replacing pavements with greenery. The brochure on Rainwater infiltration in urban areas published by the KAN platform contains up-to-date insights into the collection and retention of rainwater in the soil, via bioswales, raingardens and water-permeable pavements. However, the sponge effect of the soil may differ from one location to the next, for example, because some soil layers are less capable of absorbing water or because of high groundwater levels. More information is provided in the knowledge dossier on the Sponge effect. This knowledge dossier also features a guide to properly understand and improve the sponge effect of a landscape. The Urban infiltration opportunities map narrative in the Climate Impact Atlas can help to determine an area’s suitability for rainwater collection and retention in the soil. In addition, the Green-blue Grids design tool features an inspiring overview of measures, including a filter to identify locally appropriate measures.
Need for clear requirements
Collecting and retaining rainwater in the soil, rather than draining it as quickly as possible, is becoming a growing trend in the Netherlands. However, the requirements for measures to this end are not always clear yet. For that reason, the Climate Adaptation Standards Consultation Committee (OSKA) has mapped out what has and has not been set down in standards, and what would need to be changed in this respect. More information can be found on the OSKA page. Furthermore, a sponge effect assessment framework is being developed, and an ongoing study is exploring how waterlogging standards can be transformed into a more risk-based framework. The latter is intended to gain insight into the consequences and risks for each area, and thus to put stakeholders in a better position to identify the best ways to prevent waterlogging, including at a large scale.
How can rainwater be stored?
Rainwater that cannot, or not sufficiently, be retained in the soil can be stored temporarily, for example, in bioswales or underground water storage facilities. Other options are recessing streets vis-à-vis the houses or raising kerbs, in order to collect excess water in the streets. Other water storage measures include gravel trenches, green rooftops and water rooftops. All such measures provide temporary water storage and ensure its delayed drainage to groundwater and surface water. The Deltafact Underground Water Storage features information on options for underground water storage.
Are you unable to store all the rainwater?
Excess rainwater that cannot be stored can be drained right away. In such cases, it is imperative to prevent overloads of the sewer system, which would lead to wastewater ending up on streets or in surface water. To this end, rainwater needs to be disconnected from the wastewater sewer, and a separate sewer system has to be constructed. Thus, a separate pipe drains rainwater to surface water. Such a separation also enhances the efficiency of wastewater purification.
