How can we restrict waterlogging?

Many water systems in the Netherlands are designed to drain rainwater as quickly as possible. However, many of them are incapable of handling extremely prolonged precipitation and severe downpours, as a result of which problems or damage can occur. Waterlogging can best be prevented by allowing precipitation to seep into the soil, at the location at which it lands. This is called infiltration. If infiltration is not feasible or not sufficient, water can be stored temporarily. A final option is draining water at a slower pace.

Need for clear requirements for infiltration measures

For a long time, it was common practice in the Netherlands to drain rainwater as quickly as possible.  But rainwater infiltration and rainwater storage are increasingly becoming the trend. However, the requirements for infiltration measures are not always clear yet. Therefore, the Climate Adaptation Standards Consultation Committee (in Dutch abbreviated to OSKA) has made an inventory of what has and what has not been laid down in standards, and what should change in them.  You can read more about this on the page about OSKA (in Dutch).

How is rainwater infiltrated?

Rainwater can be infiltrated where it falls in several ways. This not only helps to prevent waterlogging, it also helps to combat drought.  The KAN brochure Infiltration of rainwater in urban areas contains up-to-date insights on how to infiltrate rainwater into the ground via bioswales, raingardens and pervious pavement. The Urban Infiltration Opportunities map narrative of the Climate Impact Atlas can help to determine whether an area qualifies for rainwater infiltration. In addition, the Green-blue Grids design tool features an inspiring overview of measures, including a filter to identify locally appropriate measures.

How can rainwater be stored?

Rainwater that cannot (sufficiently) infiltrate can be temporarily stored in, e.g., wadis or underground water storage facilities. In addition, street levels may be lowered vis-à-vis the houses, or kerbs can be raised in order for excess water to collect in the street. Other water storage methods are gravel coffers, green rooftops, and watery rooftops. Such measures all provide temporary water storage and ensure its slow drainage to groundwater and surface water.

How can rainwater be drained?

Excess water can also be drained. Care should be taken to prevent sewage system overloads during severe downpours, as these may result in dirty water ending up in the streets or in surface water. To this end, rainwater downspouts should be disconnected from the wastewater sewer. A separate sewer system will drain rainwater via separate pipes to surface water. Such a separation will also improve the efficiency of wastewater purification.

Who is responsible for restricting waterlogging?

Government authorities are assuming primary responsibility for preventing waterlogging, through sewer system investments, through spatial planning, and through relevant legislation. The specific government tasks are outlined below.

• The municipal duties mainly extend to rainwater and urban wastewater. This means that municipalities are responsible for collecting and processing rainwater run-off at public premises. They are also responsible for the collection and drainage of wastewater, including the construction and management of sewer systems.
• District water boards and the central government are responsible for water management. For example, the district water boards are responsible for the purification of rainwater and wastewater that is discharged by the sewer system. It is the duty of the central government and of Rijkswaterstaat [the executive branch of the Ministry of Infrastructure and Water Management] to protect our country against flooding from, e.g., the major bodies of water and rivers.
• The provinces are largely responsible for groundwater management.

Collaboration between government tiers is vitally important in this respect. The Waterlogging Case maps out how government bodies can harness the Environment Act instruments to this end. Very extreme precipitation may cause waterlogging nonetheless, even though the water system is functioning properly. In such cases, responsibility will largely shift to the owners of premises and other objects. Would you like to know more? Take a look at the report on who is responsible for the risks of extreme weather events.

How can damage be prevented?

In some cases, waterlogging can cause damage. Water can flow over building thresholds and enter houses via the basement, it can flood tunnels and cause pothole covers to float away. Some damage is relatively easily prevented. A threshold may be sufficient to direct water elsewhere or block it. The Rioned Foundation [interest group for urban drainage concerns] has compiled an overview of potential municipal-level measures to prevent waterlogging as a result of severe precipitation. The Wet Newspaper tool also lists several measures to prevent damage.

How can waterlogging be prevented in rural areas?

Rural areas have other options for combating waterlogging. District water boards and provincial authorities can take a range of measures, in concert with municipalities and farmers, to combat waterlogging ensuing from prolonged precipitation. For example, they can provide water storage in rural areas by saturating farmland and by switching to wet crops. Another option is converting farmland into nature or into water storage areas. The WaterWindow website features an overview of solutions to render an area climate proof and water resilient. The Deltafact Trees, Forests and Water Management from STOWA provides  information in Dutch on how natural forests, forest gardening and agroforestry in river basins can contribute to water storage, among other things

How can excessive groundwater levels be prevented?

Various constructional solutions are available to address groundwater issues. For example, cellars can be sealed in order to prevent groundwater from entering a basement or crawl space. Or groundwater levels can be lowered by constructing a drainage system. The Kenniscentrum InfoMil website provides more information on groundwater. It also outlines the responsibilities of municipalities, district water boards, and residents. The Bodem+ website features best practices and helpful know-how to incorporate groundwater in municipal framework visions.

What can residents do?

Residents are often unaware that they can restrict waterlogging on their own property. This can be done with various measures. For example, residents can green their garden so that rainwater can seep into the soil. Another solution is to disconnect the downspout from the sewer, so that rainwater can infiltrate locally into the soil. It can also be collected in a water storage tank. And if homes are prone to waterlogging, it might be a good idea to check whether the sewer is properly connected and the drainpipe has non-return valves.