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.

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 and entrepreneurs are responsible for processing rainwater that lands on their premises. A host of measures can be taken to combat waterlogging. Some examples:

• Green your garden to allow rainwater to infiltrate into the soil. Greenery in the garden is also conducive to insects and combats heat. So: out with pavement, in with plants! The Huisje Boompje Beter website features tips and measures for greening gardens. The Manual for Water-friendly Gardens contains practical tips and explanations to help you get started.
• Disconnect your downspout from the sewer system. This will retain rainwater locally before it is drained. Additionally installing a rain barrel will enable you to use the rainwater for watering your garden.
• Ensure that sewer pipes are properly connected and that the waste pipe is fitted with one-way valves. This will stop wastewater from flowing back into the toilet during severe rain and prevents waterlogging in your home. A Rioned video shows how to keep rainwater out. Are you still faced with waterlogging? Then the sewer pipes may be blocked.