Waterlogging is one of the issues addressed by the Delta Plan on Spatial Adaptation, along with heat, drought, and urban flooding. The KNMI’14 scenarios of the Royal Netherlands Meteorological Institute show that annual precipitation volumes are increasing, as is the intensity of downpours. This increases the risk of waterlogging. This page explains the issue of waterlogging and links to other relevant pages within and beyond the Knowledge Portal.
Three types of waterlogging can be distinguished:
- Waterlogging caused by short, severe precipitation (usually during summer)
- Waterlogging caused by prolonged precipitation (usually during winter)
- Excessive groundwater levels
The impact of these three types of waterlogging varies and depends on several factors, such as the location where the precipitation falls: in rural areas or built-up environments, in a sloping or flat area, in a (large) water system with a considerable storage capacity or a small system with limited storage.
How does waterlogging arise?
Waterlogging caused by short, severe precipitation
Waterlogging caused by short, severe precipitation often occurs during summer and especially in built-up environments and other paved areas, such as industrial estates and motorways. Paving prevents water from infiltrating the soil. In many cases, sewers drain the water to a water purification plant or to nearby surface water. In the event of a large volume of precipitation falling in a short period of time, the sewer system may be incapable of handling such volumes of water. In practice, sewer systems are designed to provide a maximum flow capacity of 20 to 30 mm/hour. Excessive downpours result in water in the streets.
In streets with insufficient local water storage capacity, rainwater may run off towards vulnerable objects or locations. Waterlogging results if, for example, rainwater flows into buildings or renders important through roads impassable. The animated film below shows how water in a building can cause problems.
In recent years, short, severe downpours have occasionally also caused waterlogging in rural areas. Across the board, compared to urban areas, rural areas feature more water storage capacity. Yet in some cases, the volume of rain falling within a short period of time is so large that the water cannot infiltrate, be stored, or be discharged sufficiently quickly. In these types of situations, sections of motorways and fields will be inundated, while the banks of roads and railroads will subside because the soil has become fully saturated.
Waterlogging caused by prolonged precipitation
In rural areas, prolonged precipitation poses more of a problem than severe, local downpours. Such large volumes of precipitation are not necessarily produced by a single downpour; in some cases, waterlogging is caused by the aggregate precipitation falling over several days. Prolonged large precipitation volumes can fill up the water system, causing rainwater to form puddles on the land, or water from overflowing ditches or streams to inundate the land. Waterlogging caused by prolonged precipitation predominantly occurs during the winter months. The district water boards have set down protection levels with the provinces that are geared to the purpose for which the land is used (meadows can be subjected to a higher frequency of waterlogging than high-grade crop fields or built-up areas).
Excessive groundwater levels caused by precipitation
It is normal for the groundwater level to rise during periods of heavy rain. Following a period of rain the level will slowly fall again, because the groundwater is further infiltrating the deep subsoil, flowing into ditches, or being absorbed and evaporated by plants and trees. Drainage facilities also contribute to draining and help to limit rising water levels. In the event of very long or severe precipitation, the subsoil and drainage facilities may not be capable of processing the water sufficiently quickly, thus raising the groundwater level. High groundwater levels may cause so-called wet damage to crops, and to nature. High groundwater levels may also cause problems in urban areas, for example, in buildings (wet basements and crawl spaces, rising damp), and gardens becoming saturated. Groundwater levels will generally be higher in winter and lower in summer. Consequently, precipitation is more likely to cause excessive groundwater levels in winter. High groundwater levels also foster the formation of surface-level puddles and thus increase the risk of other forms of waterlogging.
Excessive groundwater levels may also be caused by water welling up, or by higher water levels in nearby rivers. Climate change also impacts these causes of waterlogging. Especially in urban areas, waterlogging may be highly localised and caused by human intervention, such as the replacement of leaky drainpipes, by the construction of underground structures affecting groundwater flow, or by the termination of groundwater withdrawal.
The Climate Impact Atlas provides nationwide map information on waterlogging in the Netherlands. The Spatial Adaptation standardised stress test information leaflet indicates how the Atlas can be used to map out an area’s vulnerabilities.
Will the future be wetter?
The average annual precipitation in the Netherlands has risen by 18 percent since 1906. This rise can mainly be attributed to winters and autumns. Climate change is boosting average autumn, winter, and spring precipitation volumes. The risk of prolonged precipitation and ensuing waterlogging is continuing to grow. This is primarily due to the fact that a warming climate will increase the volume of water vapour in the air. In addition, winds blowing from the humid west occur more frequently, which also contributes to increasing precipitation.
Model calculations are not univocal in indicating whether average precipitation volumes in summer are increasing or decreasing. However, it is clear that the intensity of severe precipitation in summer is growing. Dutch summers feature increasingly frequent severe downpours with a high precipitation intensity. This can also be attributed to global warming. Over the past 130 years, the Earth has warmed by a worldwide average of 0.9 °C. Each degree of temperature rise will increase the maximum volume of water vapour contained in the air by 7 percent. The more water vapour in the atmosphere, the more severe the downpours. During a very heavy, short downpour, the Royal Netherlands Meteorological Institute KNMI even recorded an increase in precipitation intensity of 14 percent per degree Celsius.
An increase in average precipitation volumes can also increase the risk of excessive groundwater levels.
How can the impact of waterlogging be contained?
In order to contain the impact of waterlogging, it is imperative to adapt the environment to potential changes. The RIONED foundation [interest group for urban drainage concerns] has compiled a list of the measures that a municipality could take to prevent waterlogging as a result of severe precipitation. In addition, the Green-blue Grids design tool provides an inspiring overview of potential measures, including a filter to identify measures appropriate to specific locations.
Considering that property owners are responsible for the drainage of their premises, it is appropriate for them to take measures as well. The huisjeboompjebeter.nl and Rainproof websites provide tips for rain-proofing buildings, roofs, and gardens. Many green measures are multi-functional; for example, they prevent heat whilst fostering biodiversity. This article of the RIONED foundation provides more information regarding the effectiveness of a range of measures: what is working and what is not?
In collaboration with municipalities and farmers, district water boards and provinces can implement several measures to prevent waterlogging as a result of prolonged precipitation. For example, they can create water storage facilities in rural areas by allowing farmland to saturate or rest, or by converting fields into water storage areas. The WaterWindow website lists water and climate solutions that can contribute to rendering the environment climate-proof and water-resilient.
There is a range of constructional solutions to tackle groundwater issues. The RIONED website lists a number of relatively simple solutions. It also provides an overview of the roles and responsibilities of the various parties. The Bodem+ website features good examples and offers practical know-how for incorporating groundwater into municipal framework visions.